POLITECNICO DI MILANO

School of Electronic, Information and BIO-Engineering

Master of Science in Electronic Engineering

Interface circuit for driving heating, ventilating, and air conditioning systems with a PLC

Under Supervision of

Professor Andrea Bonfanti

Sergio Vicentini CEO of K4TECH .srl

M.Sc. Thesis of

Sahar Valimohammadi

Academic Year2016-2017

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Abstract Nowadays, the Siemens POL687 controller is one of the most adopted Programmable Logic

Controllers (PLCs) to drive a HVAC (Heating, Cooling, and Air Conditioning) system because

easy to be programmed and for the great variety of applications they are intended for. Besides,

these controllers are universal, i.e., they are able to send data to output devices, such as pumps,

compressors and air conditioning systems, as well to receive data from the same devices. Aside

from all the advantages, they have two major limitations. The first is the limited number of

input/output pins, which entails that each POL687 controller can be used to manage just one

HVAC system; The second drawback is their relative high cost, which makes the use of more

controllers in parallel unaffordable.

Aim of this thesis is to create an interface for a Siemens POL687 controller so that a single

device can drive multiple HVAC systems in parallel (shown in figure below), with a great

reduction of cost and area with respect to the solution with more controllers. In particular, we

designed and assembled a Printed Circuit Board (PCB), connected to the Siemens POL687

controller, in order to manage the data exchange between the controller and the HVAC systems.

The design, assembly, and final test of this circuit have been carried out at the K4tech s.r.l

(www.K4tech.it), a software house company specialized in embedded system design.

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Acknowledgment I would like to express my deepest gratitude to my Academic supervisor, Prof. Andrea Bonfanti

and technical Supervisor, Sergio Vicentini for their excellent guidance, patience, an excellent

atmosphere that provided for me and also every needed resource which helped me to carry out my

research. I would like to thank my Family for supporting me for every moment in my life.

Contents

Abstract …………………………………………………………………………………………………………………II Acknowledgment ............................................................................................................ III Contents …………………………………………………………………………………………………………………V List of figures ................................................................................................................. VII Introduction. ..................................................................................................................... 1 Chapter1….........................................................................................................................3 Heating, Ventilating and Air conditioning system ........................................................... 3

1.1 HVAC introduction .......................................................................................... 3 1.1.1 Heating ..................................................................................................... 3 1.1.2 Ventilation ................................................................................................ 4 1.1.3 Air Conditioning ...................................................................................... 4

1.2 HVAC system functions .................................................................................. 4 1.2.1 Temperature ............................................................................................. 4 1.2.2 Humidity .................................................................................................. 5 1.2.3 Pressure .................................................................................................... 5 1.2.4 Ventilation ................................................................................................ 5

1.3 HVAC architecture .......................................................................................... 5 1.3.1 Mechanical Room .................................................................................... 6 1.3.2 Air Handling Units (AHUs) ..................................................................... 8 1.3.3 Room Control ......................................................................................... 11

1.4 HVAC control system .................................................................................... 12 1.4.1 Controller ............................................................................................... 13 1.4.1.1 Electric Control ...................................................................................... 13 1.4.2 Controller Action ................................................................................... 14 1.4.3 Control system examples ....................................................................... 16

Chapter2..…………………………………………………………………………………………………………….……20 The POL687 controller .................................................................................................. 20

2.1 Controller (POL687) structure ....................................................................... 21 2.1.1 Power supply .......................................................................................... 22 2.1.2 Output relay ........................................................................................... 23 2.1.3 Triac output (DO1, DO2 (T12)) ............................................................. 23 2.1.4 Current sensor B1…B3 (T1)......................................................................... 24 2.1.5 Universal Pins ............................................................................................... 25

2.2 The POL687 limitation .................................................................................. 28 Chapter 3……………………………………………………………………………………………………………………29 Interface circuit for the POL687 controller.................................................................... 29

3.1 Different POL687 connection for designing the circuit ................................. 29 3.2 Circuit design ................................................................................................. 30 3.3 Software Design ............................................................................................. 35

3.3.1 The Receiver POL687 design ....................................................................... 35 3.3.2 The sender POL687 design ........................................................................... 37

3.4 The circuit test................................................................................................ 40 3.4.1 Maximum difference and Alarm test ..................................................... 40 3.4.2 Two POL687 communication ................................................................ 41

3.4.2 Results ............................................................................................................ 42 3.5 PCB (Printed Circuit Board) Design .............................................................. 42 Conclusion .................................................................................................................. 44

References……………………………………………………………………………………………………………..….45

List of figures Figure 1.1 Simple stylized diagram of the refrigeration cycle ......................................... 4 Figure 1.2 Location of HVAC Equipment in a building .................................................. 6 Figure 1.3 Hot water gas-fired boiler ............................................................................... 6 Figure 1.4 Simple example of steam converter ................................................................ 7 Figure 1.5 Centrifugal chiller ........................................................................................... 7 Figure 1.6 Cooling tower function system ....................................................................... 8 Figure 1.7 Air Handling Unit ........................................................................................... 8 Figure 1.8 AHU Mixed Air section ................................................................................. 9 Figure 1.9 Filter for Mixed Air Sensor ............................................................................ 9 Figure 1.10 Supply Fan for Mixed Air .......................................................................... 10 Figure 1.11 Hot water system model ............................................................................. 10 Figure 1.12 Chilled water system operation .................................................................. 11 Figure 1.13 Steam Humidifier ....................................................................................... 11 Figure 1.14 Return Fan .................................................................................................. 11 Figure 1.15 Cooling VAV box ....................................................................................... 12 Figure 1.16 Air Diffuser ................................................................................................ 12 Figure 1.17 Basic control system ................................................................................... 13 Figure 1.18 Controller Models ....................................................................................... 14 Figure 1.19 An example of the controller operation ...................................................... 14 Figure 1.20 Direct controller .......................................................................................... 15 Figure 1.21 Direct controller action graph ..................................................................... 15 Figure 1.22 Reverse controller ....................................................................................... 16 Figure 1.23 Reverse controller action graph .................................................................. 16 Figure 1.24 A pilot duty relay ........................................................................................ 17 Figure 1.25 Two-position control diagram .................................................................... 17 Figure 1.26 Floating Control .......................................................................................... 18 Figure 1.27 Static pressure controlled diagram ............................................................. 18 Figure 2.1 POL687 scheme………………………………………………………………………………………..22 Figure 2.2 Power supply of the POL687 ....................................................................... 23 Figure 2.3 Output relay pins .......................................................................................... 23 Figure 2.4 Digital Output Block in SAPRO software .................................................... 23 Figure 2.5 Triac Output pins .......................................................................................... 24 Figure 2.6 NTC 10K graphs........................................................................................... 24 Figure 2.7 NTC 100 K graphs ........................................................................................ 24 Figure 2.8 Analog PIN configurations ........................................................................... 25 Figure 2.9 Analog Output Blocks in SAPRO ................................................................ 25 Figure 2.10 Analog Input connection ............................................................................ 26 Figure 2.11 Analog Input SAPRO Block....................................................................... 26 Figure 2.12 Digital input PINs connection .................................................................... 26

Figure 2.13 Digital Input SAPRO Block ....................................................................... 27 Figure 2.14 Analog Output PINs Connection ................................................................ 27 Figure 2.15 SARPO Analog Output Block .................................................................... 27 Figure 2.16 PINs Connection Configuration ................................................................. 28 Figure 2.17 SAPRO Digital Output Block..................................................................... 28

Figure 3.1 Total idea of using different POL687for designing the circuit………………..…29 Figure 3.2 Circuit total Idea ........................................................................................... 30 Figure 3.3 3bit FLASH-ADC ........................................................................................ 30 Figure 3.4 LM324 ......................................................................................................... 31 Figure 3.5 SN74HC148 ................................................................................................. 31 Figure 3.6 Analog MUX sync with Encoder ................................................................. 32 Figure 3.7 CD4051BE used as MUX. ........................................................................... 32 Figure 3.8 Buffer amplifier ............................................................................................ 33 Figure 3.9 schematic of the circuit designed by Pspice ................................................. 34 Figure 3.10 Analog Action Sensor Block ...................................................................... 36 Figure 3.11 Analog Input Reference Block ................................................................... 37 Figure 3.12 Analog Output Block .................................................................................. 37 Figure 3.13 Main Receiver layout ................................................................................ 38 Figure 3.14 Data and selector value logic ...................................................................... 39 Figure 3.15 Analog Output Reference Block ................................................................. 40 Figure 3.16 The test block ............................................................................................. 41 Figure 3.17 The POL687 Communication ..................................................................... 42 Figure 3.18 Front side overview of the PCB ................................................................. 43 Figure 3.19 Back side overview of the PC ..................................................................... 43

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Introduction A Heating, Ventilating, and Air Conditioning (HVAC) systems are usually exploited to perform

heating and/or cooling of residential, commercial or industrial buildings. They may also be responsible

for providing fresh outdoor air to dilute interior airborne contaminants such as odors from occupants,

volatile organic compounds (VOCs) emitted from interior furnishings, chemicals used for cleaning,

etc. These systems need a controller to regulate the operation of heating and cooling: It compares the

actual state (e.g., temperature) with a target state and draws a conclusion about what action has to be

taken (e.g., start the blower).

HVAC systems are typically managed through Programmable Logic Controllers (PLCs). These

controllers are programmable, meaning that the digital control program code may be customized for

the intended use. The program features include time schedules, setpoint, logic, timers, trend logs, and

alarms. The unit controllers typically have analog and digital inputs that allow measurement of the

variable of interest (temperature, humidity, or pressure) and analog and digital outputs for the control

of the transport medium (hot/cold water and/or steam). Digital inputs are typically contacts from a

control device, and analog inputs are typically a voltage or current measurement from a variable

(temperature, humidity, velocity, or pressure) sensing device. Digital outputs are typically relay

contacts used to start and stop equipment, and analog outputs are typically voltage or current signals

to control the movement of the medium (air/water/steam) control devices such as pumps, compressors,

etc.

One of the most adopted PLCs for such HVAC systems is manufactured by Siemens, named

“POL687”. This controller can be programmed to monitor the temperature and the moisture in the air,

so that it can eventually drive an output device such as a pump or a compressor, on the basis of a target

condition set by the user.

The intelligence of an HVAC system depends on the ability of the POL687 controller to read the

signals from various types of input field devices and convert these signals into commands to be sent

to the external operating units (pump, compressors, etc). However, the limited number of input/output

connections of the POL687 controller is a big issue. In fact, in the case of an increasing number of

input and output devices, the HVAC system has to feature more controllers that lead to a significant

increase in the overall cost.

In this thesis, the POL687 controller has been provided with an interface circuit built on a PCB in order

to allow the connection to more external input and output units this allows to minimize the amount of

errors on the PLC program, increase the quality of the manufacturing system and keeping at bay the

overall cost.

The thesis is structured as in the following. In Chapter 1 HVAC systems are reviewed. It explains how

a Heating, Ventilating, and Air-conditioning control system is used to operate a building’s mechanical

equipment in order to maintain the desired environmental conditions.

Chapter 2 describes the POL687 controller, its pin configurations and the SAPRO blocks have been

define. Pins have different operations, such as analog and digital. They can also model as input or

output. The operations are different for different configuration.

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Chapter3 describes the design of the interface circuit and the programming of the PLC. For what

concern the hardware design, we used Pspice software for simulating the circuit and Proteus 8.6 for

designing the PCB board. The POL687 programming has been done through SAPRO* (Siemens

software for programming the controller for HVAC systems). Furthermore, testing of the circuit in

different conditions such as variable temperature, pressure, flowing water, returning water and others

has been done.

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Chapter1

Heating, Ventilating and Air conditioning system This chapter serves as an introduction to how a Heating, Ventilating, and Air Conditioning

(HVAC) Control system operates in a building mechanical equipment by use of POL687

controller so as to maintain the desired environmental conditions.

1.1 HVAC introduction

The invention of the components of HVAC systems went hand-in-hand with the industrial

revolution, and new methods of modernization, higher efficiency, and system control. It was

introduced in 1851 by Dr. John Gorrie for a refrigeration machine. By the 1880s, refrigeration

became available for industrial purposes. Initially, the two main uses of refrigeration were

freezing meat for transport and making ice. However, in the early 1900s, there was a new initiative

to keep buildings cool for comfort. In 1902, it was one of the first comfort cooling systems for

buildings. Comfort cooling was called “air conditioning”. It thus used to develop the HVAC

industry which, encourage different companies such as Siemens, Heil, and inventors to start

manufacture and develop it.

HVAC is well known for using in technology of indoor and vehicular environmental comfort. Its

goal is to provide thermal comfort and acceptable indoor air quality. It is also an important part

of residential structures such as single family homes, apartment buildings, hotels and senior living

facilities, medium to large industrial and office buildings such as skyscrapers and hospitals. It can

also use in marine environments, where safe and healthy building conditions are regulated with

respect to temperature and humidity, in order to, use fresh air from outdoors.

The three central functions of heating, ventilation, and air-conditioning are interrelated, especially

with the need to provide thermal comfort and acceptable indoor air quality within reasonable

installation, operation, and maintenance costs. In the following, we had briefly introduced the

three central functions of HVAC system.

1.1.1 Heating

Heaters are appliances whose purpose is to generate heat (i.e., warmth) for the building. This can

be done via central heating. Such as a system contains a boiler, furnace, or heat pump to heat

water, steam, or air in a central location such as a furnace room in a home, or a mechanical room

in a large building. The heat can be transferred by convection, conduction, or radiation.

Heaters exist for various types of fuel, including solid fuels, liquids, and gasses. Another type of

heat source is electricity, normally heating ribbons composed of high-resistance wire. This

principle is also used for baseboard heaters and portable heaters. Electrical heaters are often used

as the backup or supplemental heat for heat pump systems.

The heat pump gained popularity in the 1950s in Japan and the United States. Heat pumps can

extract heat from various sources, such as environmental air, exhaust air from a building, or from

the ground. Initially, heat pump HVAC systems were only used in moderate climates, but with

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improvements in low-temperature operation and reduced loads due to more efficient homes, they

are increasing in popularity in cooler climates

1.1.2 Ventilation

Ventilation is the process of changing or replacing air in any space to control temperature or

remove any combination of moisture, odors, smoke, heat, dust, airborne bacteria, or carbon

dioxide, and to replenish oxygen. Ventilation includes both the exchange of air with the outside

as well as circulation of air within the building. It is one of the most important factors for

maintaining acceptable indoor air quality in buildings. Methods for ventilating a building may be

divided into mechanical/forced and natural types

1.1.3 Air Conditioning

An air conditioner is a system or a machine that treats the air in a defined, usually enclosed area

via a refrigeration cycle in which warm air is removed and replaced with cooler and/ or more

humid air. As shown in Fig1.1 the most operation of the system will be that pump transfer Heat

from lower temperature source into a higher temperature heat sink. Heat will naturally flow in the

opposite direction. This is the most common type of air-conditioning. A refrigerated air

conditioning system works in much the same way pumping heat out of the room in which stands.

In figure1.1, the coil “1” is well known as condensing coil which will be caused to have Heat

Exchange between solid objects and fluids, the “2” is an expansion valve which controls the

amount of refrigerant flow into the evaporator thereby controlling the superheat at the outlet of

the evaporator.”3” shows an evaporator coil, an evaporator is used in an air-conditioning system

to allow a compressed cooling chemical, such as R-22 (Freon) or R-410A, to evaporate from

liquid to gas while absorbing heat in the process. It can also be used to remove water or other

liquids from mixtures. “4” is a compressor, a mechanical device that increases the pressure of a

gas by reducing its volume

Figure 1.1 Simple stylized diagram of the refrigeration cycle

1.2 HVAC system functions

An HVAC Control system operates to manage the mechanical equipment (boilers, chillers,

pumps, fans, etc.) to maintain the proper environment in a cost-effective manner. A proper

environment is described with four variables: temperature, humidity, pressure, and ventilation.

1.2.1 Temperature

The comfort zone for temperature is between 68F (20°C) and 75F (25°C). Temperatures less than

68F (20°C) may cause some people to feel too cold while, temperatures greater than 78F (25°C)

may cause some people to feel too hot. Of course, these values vary between people, regions, and

countries.

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1.2.2 Humidity

The comfort zone for humidity is between 20% relative humidity (RH) and 60% RH. Humidity

less than 20% RH causes the room to be too dry, which has an adverse effect on health, computers,

printers, and many other areas. Humidity greater than 60% RH causes the room to be muggy and

increases the likelihood of mildew problems.

1.2.3 Pressure

The rooms and buildings typically have a slightly positive pressure to reduce air infiltration. This

helps in keeping the building clean.

1.2.4 Ventilation

Rooms typically have several complete air changes per hour. Indoor Air Quality (IAQ) is an

important issue. The distribution pattern of the air entering the room must keep people

comfortable without feeling any drafts, and this is important as well.

In order to create a reliable HVAC system, the designers must consider all the possible

requirements of the system to manage the comfortable temperature. In this case, an architecture

function must be considered for the HVAC system. In the next part, we will describe more about

HVAC system architecture.

1.3 HVAC architecture

Designing an efficient air conditioning system for a residential building or area has to be consider

as the most important feature of the HVAC system. In this case, we can present three different

areas in the buildings such as mechanical room, the Air Handling Unit (AHU) and the individual

room control. These three areas in the building must work together to maintain the proper

environment for living or working.

As we can see from Fig 1.2, boilers, chillers, pumps, heat exchangers, and other associated

equipment are found inside the mechanical room. This area is sometimes called the main

equipment room. While, AHUs may be found on the roof, in the main equipment room, or in their

own equipment room. AHUs may heat, cool, humidify, dehumidify, ventilate, or filter the air,

then distribute that air to a section of the building.

Finally, individual room controls regulate the air coming from the AHU to serve a room or a part

of a larger area called a zone. Devices such as wall thermostats and Variable Air Volume (VAV)

boxes provide local temperature control. There are also room controls which have not been

associated with an AHU. These may directly control a mechanical equipment that only serves one

room or zone (zone control). These room controls are installed on equipment such as unit

ventilators, fan coil units, and heat pumps.

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Figure 1.2 Location of HVAC Equipment in a building

1.3.1 Mechanical Room

The mechanical room may contain a boiler or a group of boilers to operate under a heating

condition. The boilers provide heat for the building. In cooler climates, boilers are large or

consist of a number of smaller modular boilers. In warmer climates, boilers are small or even

absent from the mechanical room. When enabled, boilers supply a source of hot water that is

used by coils throughout the building. The temperature of this hot water may be varied based on

the outside temperature. Most boilers produce hot water, but there are also boilers that produce

steam. Boilers develop their heat through gas, coal, oil burners, or electric coils. Figure 1.3 shows

a hot water gas-fired boiler. The hot water developed by the boiler is used by hot water coils,

which are similar in appearance to car radiators. These coils are found inside the air handling

units and, in cold climates, may also be located around the outside walls (perimeter fin-tubes) of

the building. In the preceding example, a pump forces water from the boiler to the coils, then

back to the boiler. In cold climates, a normally open (N.O.) valve is installed to control the volume

of water flow through the coil. The amount of flow is expressed in gallons per minute (GPM) or,

in metric units, in liters per second (L/s). The valve is described as normally open because when

no power or control signal is received, the valve goes to 100% open.

Figure 1.3 Hot water gas-fired boiler

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Where a steam boiler is used, a steam converter is commonly incorporated into the design. A

steam converter is a type of heat exchanger. Steam provided from the boiler is used to heat water

inside the converter. In turn, the hot water developed by the converter is used in the same way as

the hot water is used from a hot water boiler. In Fig 1.4, a normally closed (N.C.) valve is used

to control the amount of steam going to the heat steam converter. When no power or signal is

received at this type of valve, it closes. Different types of heat exchangers may be used for other

applications, including cooling.

Figure 1.4 Simple example of steam converter

The other important part of a mechanical room is the pump. Pumps are essential to move the water

in a system, whether it is from the boiler to the hot water coils, or from the chiller to the chilled

water coils, or from the chiller to the cooling tower. Some HVAC systems require at least two

pumps so that a standby pump is ready in case something happens to the operating pump. The

operating pump is referred to as the lead or primary pump, and the standby pump is the lag or

secondary pump. Finally, each HVAC system needs a cooling part in the case of warmer climates.

The chiller is the source of cooling for many buildings. There are a variety of chiller types. A

simple drawing of a centrifugal chiller is shown in Fig 1.5.

Figure 1.5 Centrifugal chiller

In the image above, a chiller produces cool water, which is pumped to the chilled water coils

inside the air handling units. In case of any increasing in the water temperature, the chiller is

providing three basic steps to transfer the heat and cool down the HVAC system which are

describing in the following:

1. The chilled water supply (CHWS) is pumped to the cooling coils in the AHUs, then the

cooled return water, is circulated back to the chiller (chilled water return, or CHWR). At the

cooling coil, the heat for space is transferred to the chilled water and the water carries the heat

back to the chiller.

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2. In the chiller, the heat is transferred to a refrigerant, which in turn transfers the heat to the

water going to a cooling tower.

3. The cooling tower expels the heat to the outside air. As we can see in Fig 1.6, the cooling

tower is a container that is open to the atmosphere (Open area System), through which water is

passed. When heated water comes from the chiller, it is forced upward to the top of the cooling

tower, then sprayed down into the container. Evaporation causes the water to lose some of its

heat. To increase the heat loss, fans may be turned on, causing more evaporation. Once the water

is cooled, it settles in the sump and is sent back to the chiller.

Figure 1.6 Cooling tower function system

1.3.2 Air Handling Units (AHUs)

An AHU supply conditioned air to a particular part of a building. AHUs can supply different

sized areas, whether it is a part of a room, a zone, or an entire group of rooms. The standard

AHU contains a mixed air chamber, a filter, a chilled water coil (commonly called a cooling

coil), a hot water coil (commonly called a heating coil), a fan, and a humidifier. Figure 1.7 shows

the Air Handling Unit. In this figure, we can see different equipment which they are described

more in detail in the following.

Figure 1.7 Air Handling Unit

1.3.2.1 Mixed Air sector

As shown in the Fig 1.7, an AHU is a complicated system that can be divided in different sections.

Further, for better description about the functionality of the A.H.U. system, we will start from

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mixed air section. As shown in the Fig 1.8, a mixed air refers to the mixing of outside air with the

air returning from inside the building. This is accomplished by dampers controlling airflow in a

way similar to venetian blinds controlling sunlight. In this figure, there are dampers for the

outside air and the return air. It is important that these dampers work together. As outside air

dampers open, the return air dampers must close. An actuator (sometimes referred to as a motor

or operator) and linkage are set up so that Mixing Air operation occurs.

Ventilation requirements determine the minimum position of the outside air dampers. In the

winter, when the chiller is shut down, the outside air dampers may open beyond the minimum

position to provide cooling. Using outside air for cooling rather than mechanical cooling is

referred to as an economizer mode. During the summer, when the outside air is too warm to use

for cooling, the outside air dampers are set to the ventilation requirement, which is the minimum

position. Exhaust air dampers allow air to leave the building in proportion to the amount of outside

air that enters.

Figure 1.8 AHU Mixed Air section

Then, filters shows in the Fig 1.9 remove dirt particles from the mixed air. It is essential that

these filters be replaced periodically. A mixed air sensor is typically located after the filter. This

sensor averages the mixed air temperature throughout the cross-section of the duct. This is

important because in mixed air, stratification, which is the layering of the warm and cold air inside

the duct, can occur, possibly resulting in control or comfort problems.

Figure 1.9 Filter for Mixed Air Sensor

Finally, The Supply Fan shows in Fig 1.10 moves the air through the air-handling unit and out

into the rooms. The amount of air going through the fan may be controlled by the use of inlet

vane dampers (blades that cover the inlet of the fan), or by the use of a variable frequency drive*

(VFD) that controls the speed of the fan motor by varying the cycles of electricity. The fan may

be positioned before the coils as shown below (blow-through fan) or after the coils (draw-through

fan).

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Figure 1.10 Supply Fan for Mixed Air

1.3.2.2 Hot water sector

The Hot Water Coil presents in Fig 1.11, heats the air as it passes over the coil. It may be

necessary to heat the air even when providing cooling to a building. This concept may be

confusing at first. To help understand this application, it is important to remember that the core

of a large building may require cooling year-round, regardless of the outside air temperature.

Typically, air used for cooling is delivered to the space at 55F (13°C). If the mixed air temperature

is below 55F (13°C), it may be necessary to heat the air to 55F (13°C) for a cooling application.

In figure 1.11, the discharge air sensor modulates a two-way normally open (N.O.) valve to

maintain the 55F (13°C) discharge air temperature. With the removal of the input signal, this

valve goes completely open, putting as much hot water into the coil as possible. This reduces the

chance of the water freezing, which may destroy a coil.

Figure 1.11 Hot water system model

1.3.2.3 Chilled water sector

The chilled water coil shows in Fig 1.12, operates during the summer to drop the discharge air

temperature to 55F (13°C). As shown in the preceding drawing, chilled water is modulated

through the coil by the use of a three-way mixing valve. The valve forces the chilled water

through the coil or bypasses the water around the coil. The Chilled Water coil may also be used

for dehumidification of the air, provided the temperature of the cooling coil surface is below the

dew point of the air passing over the coil. The humidity levels are controlled from a sensor in the

rooms being served by this AHU, or by a sensor in the return air duct.

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Figure 1.12 Chilled water system operation

1.3.2.4 Steam humidifier

A Steam humidifier, or some other form of humidifier, is placed inside an AHU to add moisture

to the air when needed. Humidity levels, sensed in the return air, are set at 35% RH (Relative

Humidity), for example. The two-way normally closed (N.C.) valve is modulated to maintain

35% RH, plus or minus an acceptable tolerance. Fig 1.13 shows a Steam Humidifier.

Figure 1.13 Steam Humidifier

1.3.2.5 Return Fan

The supply air fan distributes the air into the rooms or zones. After the air has gone through the

zones, it comes back to the Return Fan presents in Fig 1.14, which routes the return air back to

the return air dampers or the exhaust air dampers.

Figure 1.14 Return Fan

1.3.3 Room Control

One way to control the temperature in a room is with a wall thermostat that sends a signal to an

actuator that positions a damper to modulate the airflow in a variable air volume (VAV) box.

These VAV boxes are installed in the space between the ceiling tile and the structural ceiling.

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This space is sometimes used as a return air plenum, as part of the building air distribution system.

The VAV box has a Damper that modulates to maintain the space temperature by increasing or

decreasing the volume of air being delivered to the space. The airflow is measured in cubic feet

per minute (CFM) or liters per second (L/s). If the space is too warm, the damper is adjusted to

allow more 55F (13°C) air into the space. If the space is too cool, less air is delivered to the space.

It is also important that these boxes filter the noise that is developed by the AHU. The Fig 1.15

shows a cooling-only VAV box. There are numerous other types of boxes, including electric

heaters, separate fans, or hot water coils. The airflow regulated by the VAV box is distributed

into the space by Air Diffusers. The airflow patterns in a zone or space should not cause people

to feel a draft. Two types of diffusers are shown in figure 1.16, but there are numerous other

types of diffusers. Air leaving the room passes through return air grilles, to the return air fan in

the AHU.

Figure 1.15 Cooling VAV box

Room controllers can also control equipment independent from an AHU. This type of equipment

includes fan coil units, unit heaters, unit ventilators, and heat pumps. A unit ventilator serves as

the local air handling unit and has dampers for the outside and return air, a fan, and a hot water

coil. The hot water comes from the boiler. The diffusers are on the top of the unit. A space

thermostat controls the valve and dampers in this unit. A switch on the base of the thermostat

starts the fan inside the unit ventilator. The fan coil units differ from unit ventilators in that they

have no dampers. Fan coils are typically installed above ceilings or as console units in a room.

There are many different ways to control the environment of a building. In the following, we will

define one of the ways to control it.

1.4 HVAC control system

An important part of the HVAC system is the Control System which works as the brains of HVAC

equipment. Every control system, from the simplest room thermostat to the most complicated

computerized control, has four basic elements in figure 1.17, a basic control system has been

shown.in this figure, a Sensor monitors, and measures a variable. The variable can be temperature,

Figure 1.16 Air Diffuser

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pressure, and others. The sensor provides information to the controller. A Controller receives

information from a sensor, selects a portion of that input for control, and then produces an

intelligent output signal. While there may be several other functions performed by a controller,

all controllers provide setpoint, sensitivity (differential or throttling range) and action. Then, a

Controlled Device acts upon the signal from the controller. The valve can act as a controlled

device, modulating hot water to maintain the proper temperature in the room. Finally, A Source

of Energy is needed to power the control system. Control systems use either a pneumatic or

electric power supply. Pneumatic controls use a compressed gas as a source of energy, typically

compressed air. Care should be taken to ensure the air supply is clean, dry, and oil-free. Most

HVAC pneumatic controls are powered with 15 to 22 psi. Electric and electronic controls could

be powered by a variety of electrical power supplies of either Alternating Current (AC) or Direct

Current (DC). These four parts are needed in any control system, however, two of these parts may

be combined under the same cover, as in the case of some thermostats. While there are occasions

when the sensor and controller are combined into one physical device, their basic function remains

the same. The sensor, controller, and controlled device are needed for any control system,

however, an installed system may have additional parts beyond the basics.

In this thesis, the main focus is on the controller and its theory. In the next part, we will describe

the controller functionalities. Furthermore, related actions and two example of the controller will

be added to the document.

Figure 1.17 Basic control system

1.4.1 Controller The controller receives the signal from the sensor and produces an output signal with setpoint,

sensitivity (differential or throttling range), and action. Types of signals from these devices are

as follows:

1.4.1.1 Electric Control

The majority of electric control systems contain the sensor and controller as one piece. Electric

controls use ON / OFF signals.

1.4.1.2 Pneumatic Controls

Controller outputs are 3 to 15 psi (21 to 105 kPa).

14

1.4.1.3 Electronic Controls

There are basically two types of electronic signals. Voltage outputs may be 0 to 10 Vdc, 2 to 15

Vdc, or other ranges depending on the controller. Voltage outputs have the disadvantage when

compared to current signals, that voltage signals are more susceptible to distortion over long wire

distances. Current outputs modulate from 4 to 20 mA. They have the advantage of producing

little signal distortion over long wire distances. Figure 1.18, shows an example of controllers.

Figure 1.18 Controller Models

Many controllers are housed inside a control panel. In the case of the DDC (Direct Digital

Control) electronic controls, the controller itself may be the control panel. Figure 1.19 shows an

example of the controller operation. In this case, a signal from the sensor is sent to the controller.

In this example, 72.5°F (22.5°C) is the setpoint or desired temperature for a room. The electronic

controller has an output of 6 Vdc at 70°F (21°C), and an output of 9 Vdc at 75°F (24°C). This

throttling range of 3°F is used to identify the voltage change to temperature change. The output

is then sent to the controlled device.

Figure 1.19 An example of the controller operation

1.4.2 Controller Action All controllers, from pneumatic to DDC electronic, have an action. They are either Direct Acting

or Reverse Acting.

1.4.2.1 Direct Action

It means that the controller’s output increases as the sensor’s input increases. For example, as

room temperature (the variable) changes from 70°F (21°C) to 71°F (21.5°C), the controller

changes its output from 10 to 12 mA. Shown in Fig 1.20, as the sensor reads an increasing input

15

(temperature), the controller responds by increasing its output (pressure) to the valve, closing the

normally open valve and reducing the hot water flow. Also, the relationship between the input to

a controller (temperature) and its output (current) can be displayed on a graph as shown in figure

1.21.

Figure 1.20 Direct controller

Figure 1.21 Direct controller action graph

1.4.2.2 Reverse Action

It means that as the variable (for example, temperature) increases, the controller’s output

decreases. For example, as room temperature rises from 70 to 71°F, the controller output

decreases from 8.1 to 7.3 mA. In figure 1.22, as the sensor reads an increasing temperature, the

controller responds by decreasing its output (pressure) to the valve, closing the normally closed

valve and reducing the amount of heating. This relationship has been displayed in figure 1.23.

16

Figure 1.22 Reverse controller

Figure 1.23 Reverse controller action graph

1.4.3 Control system examples

There is four kinds of controlling functions in an HVAC system. They are well-known as ON/OFF

control, floating control, P.I. control (basic proportional and integral feedback control) and DDC

control (Direct Digital Controller). In the following, we will describe how ON/OFF and floating

controllers work in an HVAC system.

1.4.3.1 ON/OFF control

A type of control system where the output is either 0% or 100% is sometimes referred to a two-

position control or ON / OFF control. Mechanical equipment such as fans, pumps, chillers,

boilers, electric heaters and Direct Expansion (DX) cooling may be controlled by a two- position

control system. In the figure 1.24, a room sensor monitors the temperature. The controller uses

this sensor information to operate a relay output, by using an appropriate program, the correct

action, a setpoint, and a differential. Some controller outputs cannot be used directly to control

the large amperage of equipment. In that case, a pilot duty relay is used, as shown in figure 1.24.

In this figure, when the room temperature rises, the controller sends a signal to close the pilot

duty relay. The normally open contact is then made to common. This completes the circuit and

starts the DX cooling. When the temperature drops, the controller returns the relay output to its

open (normal) position, thereby turning OFF the DX cooling. A diagram of two-position control

as it relates to time and temperature appears in figure 1.25. When the temperature reaches 76°F

(24°C), the controller turns the DX cooling ON, causing the space to cool. When the temperature

17

has cooled to 72°F (22°C), the controller turns the DX Cooling OFF, causing the space

temperature to rise. This 4°F (2°C) swing in temperature is not noticeable to most people. The

difference between the temperatures at which the controller turns ON or OFF is called the

Differential. The differential is similar to throttling range except that the output is two-position,

not proportional. The differential must be wide enough to prevent short-cycling, which can cause

mechanical equipment to break down prematurely. The differential is the change in the measured

variable (i.e. temperature) required to cause the controlled device to go from ON to OFF. A 4°F

(2°C) differential exists between the temperatures at which DX Cooling comes ON and goes OFF.

There are actually two differentials. Mechanical Differential is the difference in the temperatures

at which the equipment is turned ON or OFF. The other type is the Thermal Differential, which

is the swing that occurs in the actual room temperature. The thermal differential is wider than the

mechanical differential because the cooling or rising of the actual room temperature always lags

behind the equipment turning ON or OFF.

Figure 1.24 A pilot duty relay

Figure 1.25 Two-position control diagram

1.4.3.2 Floating control

Another variation of ON / OFF Control is Floating Control. Figure 1.26 shown an example of

this application, in which an electric actuator is used to maintain static pressure inside a supply

air duct in a VAV air-handling unit. The DDC controller in this example is controlling an actuator

that positions normally closed inlet vane dampers on a supply fan. At start-up, the inlet vanes are

closed and the duct static pressure is low. Because the controller is set up to maintain the duct

static pressure at 2 in. W.C. (water column) (500 Pa), it completes the OPEN circuit. This in turn

drives the electric actuator clockwise, causing the dampers to open, thus allowing more air to

18

enter the duct. This does not necessarily mean the dampers are opened fully. Instead, the system

opens the dampers just enough to raise the static pressure to the setpoint, inside the differential.

Once this pressure is reached, the controller breaks the OPEN circuit. If the static pressure is too

great, the controller completes the CLOSE circuit. This causes the actuator to drive

counterclockwise (anti-clockwise), closing the dampers and reducing the airflow, thus lowering

the static pressure. Once the static pressure is within the differential, the controller breaks the

CLOSE circuit. At setpoint, neither the OPEN nor CLOSE circuits are made, and the actuator

"floats" at its last position.

The diagram of static pressure controlled with floating control is shown in figure1.27. At the left

of the graph, when duct pressure is 2 in. W.C. (500 Pa), the controller does not respond. As the

demand for cooling drops and several VAV boxes begin to close down, the static pressure inside

the supply duct rises. It is only the static pressure reaches 2.1 in. W.C. (525 Pa), that the controller

responds. At that point, the controller completes the CLOSE circuit and the actuator slowly drives

the inlet vane dampers further closed. If the CLOSE contacts stay closed for only 6 seconds, and

it takes 120 seconds for the actuator to travel from one end of its stroke to the other, this would

mean that the actuator closed the dampers 5%. When the demand for cooling increases, some

VAV boxes open, and static pressure begins to drop. When the pressure reaches 1.9 in. W.C.

(475 Pa), the OPEN contacts are made for 12 seconds, so that the dampers are opened by 10%.

Figure 1.26 Floating Control

Figure 1.27 Static pressure controlled diagram

19

Variety in a type of controllers, cause to control different model of HVAC system. There are

different companies such as ABB, Heil, Honeywell, and many others which design and/ or

manufacture the HVAC controllers. One of these controllers produced by Siemens which later on

has been named as POL687.in the next chapter, we will describe more in detail about this

controller, pin configurations and operations and its usage in the HVAC system. Later, we will

explain about limitations of POL687 and problem formulation.

20

Chapter 2

The POL687 controller POL687 is one of the HVAC system controller which is produced by Siemens Building

Technology department for OEMs *(Original Equipment Manufacturer System which describes

web of relations among IT Hardware, Software and channel partners). This controller operates in

the field of air conditioning and refrigeration systems.

The POL687 has been manufactured by Siemens for supporting integration trend of air

conditioning and refrigeration equipment on the OEM’s production line. As the result, a high

level of energy efficiency can be achieved primarily by using some devices such as pumps, valves,

and others. These devices can also ensure interoperability and required effort for installation and

commissioning. For this reason, POL687 supports all tested, proven and certified standard

communication protocols, such as BACnet*(a communications protocol for Building Automation

and Control network), Lon Works *(Local Operating Network is a networking platform

specifically created to address the needs of control applications), KNX*(Home and Building

Automation Standard) and Modbus*(serial communication protocol for working with PLCs),

enabling the controllers to be straightforwardly integrated into building automation and control

systems. Communication and integration capability also form the basis of services that enhance

energy efficiency, for preventive maintenance and performance contracting.

The POL687, covers all types of programmable inputs and outputs that offer a great measuring

accuracy and a high level of flexibility for a host of demanding applications. This includes basic

standard controllers, cost-optimized HVAC applications, such as fan coil units, and controllers

for more demanding applications featuring communication. It also will be able to program for

complex AHUs or chiller systems. As a result, it will provide the maximum flexibility in terms

of communication with different systems. On the other hand, POL687 controllers are equipped

with a USB connection facility or a built-in IP port to ensure the simplest communications via the

internet. Using the SD card, software or controllable parameters of the system can be easily and

directly loaded to the controller.

On the user side, the POL687 also included various types of communicating and network-

compatible operator units such as HMIs*(Human Machine Interface). The POL687 can be

programmed easily by the user through the manual or automatic applications produced by

Siemens. In this programming, the user will be able to consider different temperature zones from

-40 °C to 70 °C.

Apart from all advantages which has been mentioned, the POL687 has also some disadvantages.

The pin number limitations and high price are well-known as the most important disadvantages

of the POL687. This limitations will cause the HVAC system designers to use more than one

controller or external controllers connected to the local POL687 to control a HVAC system. As a

result, it will cause to increase the final cost of the whole system and also increase the occupied

area by HVAC system.

In this chapter, we will describe more in detail about the POL687 pins and their operations,

architecture and related blocks in the SAPRO (Siemens software for programming the HVAC

controllers). Then, we will discuss about limitations as the main problem of this controller.

21

2.1 Controller (POL687) structure

The POL687 controllers are designed for using in ventilation, air conditioning, and refrigeration

systems. It will give the user free and Object-orientated programming by a graphical editor

through SAPRO*(programming software for the POL687 introduced by Siemens) software. On

the other hand, there are some features which have to be considered by users for using the

controller in the HVAC systems such as:

Power supply (used to turn on the controller )as AC 24 V or DC 24 V

8 universal pins for making input and output connection

3 analog inputs with NTC(Thermistor)10k and/or 100k

On board active sensors with power supply range of DC 5 V and DC 24 V

2 digital inputs for potential-free contacts

2 digital inputs Galvanic isolated AC 24 V

2 digital inputs Galvanic isolated AC 115/230 V

8 relay outputs (6 NO contacts, 2 relays switching type)

2 Triac outputs (AC 24/115/230 V)

RS-485*(serial communications protocol ) in Modbus RTU*(Remote Terminal Unit)for third-

party bus

Operating temperature -40…70 °C

According to all these features, the POL687 will be use in different area zones and for different

HVAC systems. Fig 2.1 shows a scheme of the POL687 with input and output pin configurations.

These configurations will give user the ability to connect limited number of devices as an input

and / or output to the controller in order to make a specific HVAC system. The input pins can

read both digital and/ or analog values, as well as outputs which can be programmed by the user

to send both analog and digital values to the external devices such as pumps, valves and etc.

As we can see from table 1.1 there are different pin functions which give the controller the

possibility of having input and / or output for both analog and digital values. T9, T10, T11, T12,

and T13 are used only for digital outputs which means they will apply the digital values to each

connected devices, while T1 (consist of B1, B2, and B3) is an analog input pin which is able to

read analog values in different ranges. There also 8 pins (X1-X8) which are able to read /write

both analog and digital values from input and /or to the output. In the following we will describe

how each pin works and also how they can be defined in a project through the SAPRO application

for creating a good HVAC system?

22

Figure 2.1 POL687 scheme

Table 1.1 POL687 pin functions

2.1.1 Power supply Power supply pin is the most important part of each POL687. The operating voltage to turn on

this controller ON is 24 V DC ±10%. It will also able to work with AC voltage in the range of 24

V ±20% with the frequency range of 45…65 Hz. Figure 2.2 shows the power supply connection

model. In this connection, G0 pin uses as the ground connection while, the 24V pin will be use to

connect positive value. In the case of connecting the true values to each pin, the POL687 will turn

on and ready to work.

order PIN number Operations INPUT/OUTPUT Digital/Analog

1 T8 power supply output 24VAC

2 T9 RELAY output DIGITAL

3 T10 RELAY output DIGITAL

4 T11 RELAY output DIGITAL

5 T12 TRIAC output DIGITAL

6 T1 sensor current input ANALOG

7 T2 UNIVERSAL input/output ANALOG/DIGITAL

8 T3 UNIVERSAL input/output ANALOG/DIGITAL

9 T4 POTENTIAL FREE input DIGITAL

10 T5 24V input DIGITAL

11 T13 BINARY output DIGITAL

23

Figure 2.2 Power supply of the POL687

2.1.2 Output relay The pin numbers T9, T10, T11 are known as the output relays or output pins which they will work

with both NC (Normally Close) and NO (Normally Open) operations. They will provide a digital

output connection which is able to switch voltage in the range of 0 to 24VDC. In order to use

these pins, the HVAC system designers need to define them as a binary output block in the

SAPRO software. Binary output is a block which users can easily send NC/NO functions to

pumps, valves and other devices. Fig 2.3 shows the PIN connections for digital output, while,

Fig 2.4 shows the SAPRO block for defining digital outputs. In this block, we have to define the

number of the pin, the number of the POL687 which we are using and also there is a white area

which give user the ability to introduce a name for the block. The name must be specific and not

same as other block names.

Figure 2.3 Output relay pins

Figure 2.4 Digital Output Block in SAPRO software

2.1.3 Triac output (DO1, DO2 (T12)) There is a pin functionality for the Triac switches which is able to act as a Solenoid valve. The

solenoid valve is an electromechanically operated valve which controlled by an electric

current through a solenoid. In the case of a two-port valve, the current flow will cause switching

24

on or off. For a three-port valve, the outflow is switched between the two outlet ports. Multiple

solenoid valves can be placed together on a manifold.

Solenoid valves are the most frequently used control elements in fluidics. Their tasks are to shut

off, release, dose, distribute or mix fluids. They are found in many application areas. Solenoids

offer fast and safe switching, high reliability, long service life, good medium compatibility of the

materials used, low control power and compact design.

As we can see in Fig 2.5 there is a Triac switch which they will act with AC 24…230 V (-20%,

+10%) while they use external protection for an inductive load.

Figure 2.5 Triac Output pins

2.1.4 Current sensor B1…B3 (T1) These pins will act as analog input pins. These pins can be used for two different values of

thermistors (NTC 100K and NTC 10K). Thermistors are thermally sensitive resistors known for

exhibiting a large change in resistance with only a small change in temperature. It is important to

note that a thermistor’s change in resistance is non-linear. It follows a pre-defined curve which is

provided by the thermistor manufacturer. In Fig 2.6 and 2.7 we can see two different curves;

which the left ones show the accuracy value change according to the temperature, while the right

ones show the resolution change according to temperature values.

Figure 2.6 NTC 10K graphs

Figure 2.7 NTC 100 K graphs

25

In the case of using each of the analog pins, we have to know that they will deliver voltage in the

range of 0 to 10 VAC. Fig 2.8 shows the pin connection for the analog values while Fig 2.9 shows

the analog output blocks used by SAPRO application. In this block we can be able to define the

type of transition of the NTC. In this case, we can select the input value in the range from 0 % to

100%. This transition will be defined in different categorizes as:

AO to PWM – converts analog output signal (AO) to pulse width modulated signal (Q=PWM

(pulse width modulated)).

AO to STEP – converts analog output signal (AO) to different analog values as an output (Q).

Figure 2.8 Analog PIN configurations

Figure 2.9 Analog Output Blocks in SAPRO

2.1.5 Universal Pins

Universal pins can be used as both analog and/ or digital for input and/ or output functions. They

will have different functionalities according to the user request. The pin functions have been

described in the following:

2.1.5.1 Analog Inputs:

These PIN can be defined analog inputs with different current and resistivity values such as:

Ni1000*(HVAC temperature sensor) with current value equal to 1.4 mA

Pt1000*(thermos-resistance) with current value equal to 1.8 mA

NTC 10k with sensor current value equal to 140 uA

NTC 100k with sensor current value equal to 140 uA

Fig 1.10 shows the current connections. In this case, we are able to change the current values by

the software and control the input through a thermal resistor.

26

Figure 2.10 Analog Input connection

On the other hand, the analog input pins are used as voltage (0-10 volt DC) or current (0-20mA)

sensors. Figure 2.10 shows the analog input connection as voltage or current sensor. In this case,

we have to consider the best configuration to be used in the HVAC system by considering the

type of devices (pumps, valves and etc) which will be connected to these pins. On the other hand,

for controlling devices we need to choose the correct analog blocks in SAPRO software. Figure

2.11 shows the SAPRO block, which we need to define the type and number of the pin. In this

case, type refers to resistivity values.

Figure 2.11 Analog Input SAPRO Block

2.1.5.2 Digital inputs (X1…X8)

Universal pins can be defined as a digital inputs. They will be able to provide voltage between 0-

24 volt and current of 0-8 mA. In this case, the receiving data for each pin must be 0 or 1 (True/

False) and if we give them voltage or data out of 0 or 1 range they will not work. Fig 2.12 present

the digital input connection, while Fig 2.13 shows the related SAPRO block. As we can see in the

SAPRO block, “pos” shows the pin number and XI gives user the ability to control the pin.

Figure 2.12 Digital input PINs connection

27

Figure 2.13 Digital Input SAPRO Block

2.1.5.3 Analog outputs (X1…X4)

As mentioned before, all the universal pins used as analog and /or digital input, while they can

also use as analog or digital outputs. The pins X1-X4 can be defined as analog outputs for

controlling both current and voltage. The voltage range could be equal to 0-10 volt and current is

equal to 0-20mA.

Figure 2.14 Analog Output PINs Connection

Figure 2.15 SARPO Analog Output Block

2.1.5.4 Digital outputs (X5…X8)

Finally, the universal pins can be used as digital output. In this case, we can use pins X5-X8.

These pins will work in the range from 0 to 24 volt. If we select it as analog output so the pin will

work on Voltage range from 0 to 10 volt while, in the case of digital function it will have digital

value of 0 or 1(24VDC). Figure 2.16 shows the pin connections while Fig 2.17 shows the SAPRO

block for digital outputs.

28

Figure 2.16 PINs Connection Configuration

Figure 2.17 SAPRO Digital Output Block

2.2 The POL687 limitation

In reviewing a POL687 as a local control unit of an HVAC system, it is important to determine

how many connections (pins) can be made to manage sensors and controlled devices. Each

controller has a maximum number of pins. Some pins have a fixed configuration, while other pins

have universal, or adaptable arrangements. Fixed pins are those that are dedicated to a specific

type and cannot be changed. For example, a controller may have four AIs (Analog Input). These

AIs may not have to be used, but they are AIs only and cannot be changed to another pin type. To

address the problem of having fixed pins that go unused, some pins may be programmed as any

of the four different types that are, AI, AO, DI, or DO. As an example, if an additional temperature

sensor (an AI) is desired, and all that is available in a fixed configuration controller is a digital

input, another controller would be required to accommodate the sensor. This trend has

disadvantages such as increasing the cost of each HVAC system, increased complexity to solve

the problems, more area for mounting the system and finally will cause to reduce the number of

customers. Some customers prefer to have less area occupied by HVAC and external devices.

Some prefer to pay less for a reliable HVAC system while some don’t have any knowledge about

the HVAC systems so in case of any problem, they must pay to professional in order to solve the

system’s problem. As a result, the number of customers who ask for this system will decrease.

Therefore, we designed a small circuit which can connect to the local controller. This circuit will

be very cheap and good for solving the cost problem. It will also occupy very small area by

connecting to one or two universal pins of the local POL687. This is able to read an analog values

which user apply to one of the universal pins as an analog value and convert it to 8 different digital

values. These digital values will be send to the correct output pin by use of a selector. The total

operation of this circuit will be very simple which will solve the complexity of the HVAC system.

In the next chapter, we will describe the circuit, the design, schematic and its advantages more in

detail

29

Chapter 3

Interface circuit for the POL687 controller

As we mentioned in the second chapter, the POL687 has limited number of pins with different

functionalities. It will cause the HVAC system designers to use a different number of controllers

in order to create a reliable HVAC system. A system with less repair cost, easy to clean, easy to

mount, high energy efficiency, and cooling sufficiently known as a reliable HVAC system.

In this Part, we will design a circuit which can be connected to the local controller. The circuit

schematic are tailored by using the Pspice application. This circuit is able to control different

HVAC systems and one or more devices such as fan, valve, pump, and etc, simultaneously.

There are two tests, which have been designed and simulated by SAPRO application in order to adjust circuit to work properly. In the first test, the circuit operates in different conditions such

as different temperature, different input values which has been sent in order to find the

maximum fault values between actual sent value and actual received value. The second test has

been done for different POL687 communications directly and without any extra circuit

connection. Finally, we will see the actual implementations and printed circuit board (P.C.B.) of

the circuit.

3.1 Different POL687 connection for designing the circuit

Designing a circuit which will be connected to the local POL687 for supporting the customers to

have a reliable HVAC system is the goal of this thesis. As we can see from Fig 3.1, there are two

different POL687 which will be used for designing this circuit. In this case, the first POL687, can

work as a data sender, while the second one will act as a receiver.

In the first POL687, we will use 2 universal pins. Both will work as analog output, one has been

used as a data value, and the other as selector value. According to the datasheet of the POL687,

the analog value can be changed by a user in the range of 0-100% (0-10 Volt). This value will

be used as a ‘Data’ in our circuit. On the other hand, the selector is an analog value with the

range of 0-10 Volt. Both Data and Selector values are used as circuit input values.

The second POL687, will receive 8 different values from the circuit. The circuit will convert an

analog input data to 8 analog outputs. The received values must be in the range of 0 to 10 Volt.

Related to the input data, the received value will be read by the second POL687. In this case, the

value read by the POL687 must be equal to the data value which has been applied to the input.

POL687 Sender Designed circuit POL687 Reciever 2 Analog values 8 Analog values

Figure 3.1 Total idea of using different POL687for designing the circuit

30

3.2 Circuit design

As we can see from Fig 3.2, the goal of this thesis is to use one of the eight universal pins of first

POL687 as a selector for selecting the right channel (channel in this chapter refers to different

HVAC system or different connected device).In this case, the analog selector’s value which is

in the range of 0 to 10 Volt (0-100%) needed to be compared with the constant (+10 volt) value.

Then, we can apply an analog (0-100%) value to a FLASH ADC circuit which is also called the

parallel A/D Converter, the circuit is simple to understand. It is formed of a series comparators,

each one comparing the input signal (analog value in the range of 0 to 10 volt) to a unique

reference (constant + 10 volts) voltage. The comparator outputs connect to the inputs of a priority

encoder circuit, which then produces a binary output. Figure 3.3 shows a 3-bit FLASH ADC

circuit. In this figure, Vref is a stable reference voltage provided by a precision voltage divider as

part of the converter circuit. As the analog input voltage exceeds the reference voltage at each

comparator, the comparator outputs will sequentially saturate to a high state. Therefore, the

priority encoder generates a binary number based on the highest-order active input.

Flash

_ADC

8 to 3

En

code

r

Analo

g MUX

Buffe

r

POL6

87 Se

nder

POL6

87 Re

cieve

r

Figure 3.2 Circuit total Idea

Figure 3.3 3bit FLASH-ADC

In order to use FLASH ADC for designing the schematic, we will use two LM324 integrated

circuits. LM324 which has four independent operational amplifiers with high-gain internal

frequency to operate from a single power supply over a wide range of voltage .Figure 3.4 shows

31

the LM324 which can connect to the voltage supply with the range up to +32 Volt to pin 11 and

connect pin 4 to GND. Also, it works with the double power supply by connecting the +16 Volt

to pin 11 and -16 to pin 4. The output values will receive after comparing the input values of the

positive and negative pins. These Output values, will be connected to the 8 to 3 line priority

encoders.

Figure 3.4 LM324

Figure 3.5 shows the encoder SN74HC148 pin configuration. The SN74HC148 will encode the

inputs to ensure that only the highest-order data line is encoded. This device, encodes eight data

lines to 3-line (4-2-1) binary (Octal). Also, cascading circuitry (enable input EI and enable output

EO) has been provided to allow octal expansion without the need of external circuitry. The inputs

and outputs data are active at the low logic level. The VCC value must be in the range of the

2(Min) and 6 (Max) Volts. While, each output voltage will be 0-VCC.

Figure 3.5 SN74HC148

In the next step, the output of the priority Encoder will be connected to an analog multiplexer.

A multiplexer (also sometimes spelled as multiplexor) is a device that can select from several

different input signals and transmit either one or more output signals. There are different kinds of

analog multiplexers. At future electronics, we stock many of the most common types categorized

by signal type, configuration, ON-resistance, supply voltage, packaging type and No. of channels.

The most common values for No. of Channels are 2, 4 and 8 channels. We want to carry out the

32

8 channels multiplexer as an analog MUX. In this case, we will connect the 3-bit outputs of

priority encoder as the selector of the analog MUX. Figure 3.6 shows the analog MUX

connected with the 3bit encoder. In this figure, according to the output of the encoder, the data

will send to one of the eight output channels of the multiplexer. The Data value should be

changing from 0 to 10 volt by the user, through the SCOPE (Siemens application to monitor

and/or apply the changes to controller) application. On the other hand, we can use the

CD4051BE as digitally-controlled analog switches. It has a low ON impedances and very low

OFF leakage current. Control of analog signals up to 20 Vp.p can be achieved by digital signal

amplitudes of 4.5V to 20V (if VDD-VSS = 3V, a VDD-VEE of up to 13V can be controlled;

for VDD-VEE level differences above 13V, a VDD-VSS of at least 4.5V is required). For

example, if VDD = +4.5V, VSS = 0V, and VEE = -13.5V, analog signals from -13.5V to +4.5V

can be controlled by digital inputs of 0V to 5V. These multiplexer circuits dissipate extremely

low quiescent power over the full VDD-VSS and VDD-VEE supply voltage ranges.

Independent of the logic state of the control signals, all channels are OFF when a logic “1” is

present at the input terminal. Figure 3.7 shows the pinout configuration of the CD4051BE and

as shown it can have 3 selector pins as A, B, and C. Each can connect to the output of the

encoder and the voltage range of each must be 0-5 volt in order to select the output channel for

each address value.

LM324 comparators Multiplexer

8 Analog values 3 Analog values8 to 3 bit Encoder Buffer

8 Analog values

Figure 3.6 Analog MUX sync with Encoder

Figure 3.7 CD4051BE used as MUX.

In order to store the voltage values without any drop or changes, we need to use a buffer amplifier.

A buffer amplifier (sometimes simply called a buffer) is one that provides the electrical

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impedance transformation from one circuit to another, with the aim of the signal source being

unaffected by whatever currents (or voltages, for a current buffer) that the load may produce.

A voltage buffer amplifier is used to transfer a voltage from a first circuit, having a high output

impedance level, to a second circuit with a low input impedance level. The interposed buffer

amplifier prevents the second circuit from loading the first circuit and interfering with its desired

operation. In the ideal voltage buffer, the input resistance is infinite, the output resistance zero

(output impedance of an ideal voltage source is zero). Other properties of the ideal buffer are

perfect linearity, regardless of signal amplitudes, and instant output response, regardless of the

input signal speeds. If the transferred voltage unchanged (the voltage gain Av is 1), the amplifier

is a unity gain buffer also known as a voltage follower because the output voltage, follows or

tracks the input voltage. Although the voltage gain of a buffer amplifier may be (approximately)

unity, it usually provide considerable current gain and thus power gain. However, it has a gain of

1 (or the equivalent 0 dB), referring to the voltage gain. According to Fig 3.8, we will build a

buffer simply by using the LM324 amplifier and connecting it to the analog Mux outputs.

Figure 3.8 Buffer amplifier

The figure 3.9 shows a schematic of the circuit designed by Pspice. As we mentioned before, in

this circuit, LM324 used as a comparator for creating a FLASH ADC, while 74HC148 act as an

encoder and give the right value to the CD4051BE multiplexer. The output values will be stored

in 1nf capacitor. This capacitor will be work as a value register which will store the output value

of each MUX outputs. On the other hand, the buffer will help a user to connect the load to each

of the output pins without having any voltage drop.

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Figure 3.9 schematic of the circuit designed by Pspice

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3.3 Software Design

One of the important part of this thesis is related to the software designing. This software has

been designed for providing communication between POL687 and the circuit of this thesis. In

this case, we will use SAPRO. The SAPRO is an application made by Siemens S.P.A in order to

program the POL687. This software gave user the ability to program each input or output pins

and also will be able to see the result of each operation throw SCOPE software. In the following,

we will see how we used this application to program POL687 for communicating with the circuit.

3.3.1 The Receiver POL687 design

The receiver POL687, is our second controller which will monitor the circuit operation by use of

the SCOPE. First, we will see how the user can work with SAPRO in order to programming the

POL687. In this application, the user will create a new chiller and heat pump project. The CHHP

is a standard template for the HVAC system which made by Siemens. In the CHHP project, there

will be normally three different main blocks such as Common, Interface, and Dispatch.

The 'Common unit' contains blocks with various functionality for enabling blocks, general and

common settings, operating mode, HMI, alarms snapshots, archive and update handling, etc.

while The 'Dispatcher unit' manages cooling and heating requests, defines the operating mode,

control the supply pump and the various producers in the chiller heat pump machine. On the other

hand, all hardware, BACnet and related automation communication objects are located in the

‘interface unit’.

So for programming a receiver controller, we need to create a new CHHP template. This template

will give user the opportunity to design the software for reading values from the circuit. As a first

step, we need to select the proper analog input block as the main receiver blocks. For this, we

need to select the block type from different analog input blocks in the SAPRO application. There

are different type of analog input blocks such as temperature sensor blocks, Action sensor Blocks,

temperature sensor counter blocks, etc. On the assumption, we decide to select analog action

sensor blocks in order to receive the values from the circuit. The analog block as shown in Fig

3.10, act as a receiver voltage value in the scale of 0 to 10 Volt. In this block the ‘POS’ shows the

POL687 pin number which is used for this block while, the ‘Type’ shows set point model which

could be:

0 = 0-10V (Other ranges like 0-5V needs calculation from adapted curve)

1 = 4-20mA (Other ranges like 0-20mA needs calculation from adapted curve)

LoLmRlb set the Reliability Low Limit, this will detect a short Loop of this X

Input.

On the other hand, ‘ALMDIS’ will be shown as temporary alarm disable. In this case, FALSE

use for enabling alarm and TRUE for disabling alarm. Then, we have to set the pin numbers in

each block.

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Figure 3.10 Analog Action Sensor Block

After selecting the analog input block, we need also to select the reference for analog input action

sensor blocks. As a result, we can select the analog reference block from all reference block in

the SAPRO library. As shown in Fig 3.11, reference block is mostly used in HVAC part from

application to read and write values from input to the output. This block is using ‘Reference

system’ which has instance name and DB-access to input and output blocks. It also has different

options to create an understandable logic for users.

The block has different input and output pins. The ‘RefObj ‘shows the name of reference block.

The settled name must be contain only number and words. As long as "gSysEnbl" variable is

equal to true, this output variable will have different operations:

FALSE = Referencing object not found

TRUE = Related reference object found Finally, Commissioned state will define with "gSysEnbl" which means:

FALSE = Referencing object is disabled (ENO support = passive)

TRUE = Referencing object is enabled (ENO support = active)

The ‘Val’ shows the Present value from referenced main BACnet IO object, while ‘FLT’ is a

Fault from interface which has been placed in reference BACnet IO object. Fault means bad

reliability. After choosing the input and reference block, we need to consider one block for each

pin. In this case, we are using all the universal pins of the receiver POL687. Then, we need to

put 8 Analog Input Blocks for each outputs and also 8 reference Block for each Analog Block.

In this case, each changes in the outputs will be written in the related input pin and we could

be able to see their change in SCOPE software.

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Figure 3.11 Analog Input Reference Block

3.3.2 The sender POL687 design

Another POL687, needed for sending the data to the circuit. In this case, we used analog output

blocks for programming the POL687. There are different output blocks in the SAPRO. We used

‘FbAO’ block for creating data and selector blocks. As we can see in Fig 3.12, the ‘FbAO’ block

has different types for the output:

0 = Analog output Y

1 = Universal output configured as 0-10 Volt

2 = Universal output configured as 0-20 m

This Block can accept an ‘Invert Signal’ as an input value. This value has different operations

such as:

FALSE (0% = 0 Volt or 0 mA)

TRUE (0% = 10 Volt or 20/25 mA)

The ‘POS’ is one of the inputs. It shows the position of the output pin which will use in order to

send data value from the POL687 to the circuit.

Figure 3.12 Analog Output Block

For sending data, we decide to consider 8 values for the selector which will send by one of the

universal output pins and will be changed in the range of 0 to 100% (0-10Volt). This 8 values will

cause that user be able to apply any changes to the HVAC system simultaneously .On the other

hand, we will also consider 8 ‘Setpoint value’ Blocks in order to give the user the opportunely

to send 8 different float values to the selected output in this case user has more options to send

the values and control different output by different values at the same time. As we can see in the

Fig 3.13, the Sender POL687 contains 8 real ‘Setpoint value’. The set point’s initial value has

been defined zero. Zero cause the values start from very basic values. The setpoint blocks are

easy to use. Each set point can be defined between minimum (which in this case considered as 0)

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and maximum (in this case consider as 10 volt) values. The user can change the values easily by

use of SCOPE application.

Figure 3.13 Main Receiver layout

As a total feature of this program, we can see that the sender program will give user the possibility

to have:

8 real set point values

DT-SEL designed block

‘Enable all object’ set point block as main enabling object

‘Data’ present value

‘Selector’ p1resent value

Inside the Data-Selector block a special logics for data and selector values was considered which

shows in Fig 3.14. In this Block, there is also a delay block. The delay block could set for the

minimum 500ms delay value which means the data will be send to the output after each 500ms.

The delay value is value which user will decide and it will choose by the change of two maximum

setpoint values in the range of 0 to 32000ms. In order to have a proper delay value applied to both

date and selector we have to choose the right values from 0 to 32000ms. In this case, the circuit

will be able to changes each data or selector values after each 500ms.

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Figure 3.14 Data and selector value logic

On the other hand, this program has an automatic part which we had design. It would receive an

input value as ‘iCount’ by 0 initial value, whenever the cycle start after each 500ms the ‘iCount’

value will be sent to the ‘EnlSel_15UINT’ in order to Enable the block and send the ‘Val1’ to

the output. The output is an ‘iCount’ which after reaching to 9, the cycle will start again. In the

following of what has been mentioned, the counter will start to count from 1 to 8 and after reach

to value as 9, it will start the cycle again. In this case, user can give 8 different values to the circuit

by passing 8 different cycles and after 9 cycle it will restart. This help the sender POL687 to check

if the user change any value and send the updated value to the circuit. This trend will continue as

far as the controller is running and the delay between each value changes will be 500ms.

The ‘iCount’ value will change the selector value and send 8 values in each cycle from one of the

analog output universal pins to the main circuit. On the other hand, it will give one of the 8

selected data value by the user from other output pins to 8 different outputs that will be used as

the input of the second POL687. The ‘iCount’ may also use as the state of the MUX‘s input. The

block multiplexer is in principle of different inputs. Depending on the state of the input K one of

the value inputs is put through to the output. If K has the value 0, the first input is put through. In

the case of value1the second input is used, in the case of value 2 the third etc. If the K-input is

connected with a value too high (i.e. with value for which no input exists), an error is displayed

via ENO (i.e. FALSE is output at the ENO-output).Finally, the Output of the MUX will be applied

in the analog output reference block (‘fABO’ Reference).The Block as shown in the Fig 3.15 is

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mostly used in HVAC to read values and write them to BACnet compatible In- and Output blocks

placed in interface ‘Itf’. This block is using Referencing system there is connected over Instance

name and DB-access to in- and Output blocks. ‘

Figure 3.15 Analog Output Reference Block

3.4 The circuit test

After designing the circuit both in hardware and software part, we have to check if the circuit

result is exactly the goal of this thesis or not. The goal is that we can send an input data only by

one analog output pin of POL687 to the circuit and convert it to 8 different output values for

controlling 8 different analog HVAC system.

So, we start to test the circuit in different conditions. In the following, we will describe some tests

and their results.

3.4.1 Maximum difference and Alarm test

For this test, we will consider some blocks. This blocks will create an alarm test logics for

figuring out the total function of the circuit. So, we will put some more blocks in the receiver

program which already had been created in order to find out the alarm and maximum value of the

differences between the Data and the output values.

In more detail, we will consider a ‘Setpoint value’ for each analog input blocks equal to the

values that will set by user and this value will be compared with the receiving values of the Analog

Input Blocks. In the case that the differences will be less than the considered value (for example

0.5volt), it will show in the SCOPE that there is NO Alarm for the receiving value while the

difference is more than 0.5 it will show an Alarm

As can see in the Fig 3.16, there would be a ‘gPgm.SUF20s’ variable. This variable will show

that there is 20second delay by default to start sending the value to ‘Alarm display ‘block. In this

case, this variable will be activated after 20s. Then there would be a ‘rIN.Flt’ variable which is

the fault value of the reference blocks. In the case of receiving any fault value by the reference

block, it will activate the ‘NOT’ port and send the opposite value to the ‘AND’ gate. A bitwise

AND-operation of all values connected to the inputs is performed and the result is put in the

output. Then, the block RS-FLIP-FLOP is analogous to the block SR-FLIP-FLOP. The output

value Q1 is set by input S and the output is reset by input R1. The terms R1 indicates that the

reset-input is dominant. Illustration of block functionality has been shown a function block

diagram in Fig 3.16. As far as the RS Flip –Flop output is a BOOL (0/1) and the input of the

display multistate is a UINT value we need to use ‘Any to UINT’ operand which the value

connected to the input is converted to data type UINT. If a value that is connected to the input is

covered by the common value range of the input and output data type, the input value is taken

over by the output. Then any situation of the Test equal to ALARM or NO ALARM will be seen

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in the SCOPE through multistate display block. This block can be used to get a 16-bit unsigned

integer from the application into the object handler.

Figure 3.16 The test block

In a logical point of view, there must be a simple formula for the operation in the case of Alarm

or No Alarm situation same as the one that has been shown in Equations 1.1 and 1.2:

Equation 1.1:

𝑁𝑂 𝐴𝐿𝐴𝑅𝑀 = (𝐷𝐴𝑇𝐴 − 𝑅𝑒𝑐𝑒𝑖𝑣𝑒𝑑 𝐼𝑛𝑝𝑢𝑡) ≥ 0.5

Equation 1.2:

𝐴𝐿𝐴𝑅𝑀 = (𝑅𝑒𝑐𝑒𝑖𝑣𝑒𝑑 𝐼𝑛𝑝𝑢𝑡 − 𝐷𝐴𝑇𝐴) ≥ 0.5

The receiver POL687, receives the values by the considered fault interval. The range of recieved values must be equal to: Read value = Actual value ± (0.1- 0.2)(V) In the case of the data is out of the interval, the test shows an Alarm. It means that one of or more electronic component(s) have been dropped. In general, the received value shouldn't be

too far from the data which has been sent.

3.4.2 Two POL687 communication

In the second test, the goal is to realize the POL687 communication with each other. It means

that we want to check the response of POL687 when they connect directly to each other. So, we

decide to put 8 different analog output blocks for the first controller and it will send 8 values

equal to 10 Volts directly to the second controller. In the second controller, there would be 8

analog input blocks which they will read the voltage that has to send from the first POL.

According to the POL687 datasheet, the universal pins has output send in the range of 0-10

Volt, while they will also read the value as input in the same range from 0-10 Volt. The result

of the test shows that the input of the second POL687 will also read more value than 10 Volts

with some fault errors and they are not exactly working same as the values which has been

written in the controller’s datasheet.

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POL687 SENDER

POL687 RECIEVER

8 ana

log va

lue

Figure 3.17 The POL687 Communication

3.4.3 Results

After using different test on the circuit, we reach to the point that the circuit itself can give us the

voltage exactly same as the data. If we need to read it in the receiver controller, we need to

consider some value faults. In this case, it is much better to read the value not only by use of the

controller but also through the voltmeter. We can also use the SCOPE application to see the

received values graphs. In the SCOPE there is an online-trend option which will shows the

variables graphs. According to the graphs we can show the value changes in the system. Some

values are changing by change of the data while some will remain constant.

3.5 PCB (Printed Circuit Board) Design

After considering all tests and reach to the final version of the Circuit, the design the PCB board

by using a new application called ‘Proteus’ would be started.

For this step, we consider to have a double side P.C.B. board as a rigid fiberglass laminate and

will make with different materials in the manufacturing process determined by the PCB designers.

For this part, we decide to use the standard material which is Fiberglass and often referred to as

FR4. The FR4 material is already clad with copper when purchased by the PCB manufacturer. A

standard thickness would be .059″ of material clad with 1 oz. of copper (1.34 mils) thick. The

amount of copper weight that covers a square foot of area is what determines the 1 oz. The

total then would be closed to .062″ in final thickness. Solder Mask and Legend can be added

as well and adds a tiny bit to the overall thickness.

In the next step, we consider the maximum size of the board equal to 6×6 cm (6 Height and 6

weight) with top and bottom copper layers. There are both front and back sides view of the board

which shows in Fig 3.18 and 3.19.

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Figure 3.18 Front side overview of the PCB

Figure 3.19 Back side overview of the PC

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Conclusion

This study proves that an efficient HVAC system controller is one of the most cost-effective

options to improve the energy efficiency of a building. The effect of changing the control

strategy is usually difficult to predict, so every strategy shall be tested. In this thesis, an HVAC

system development has been done by designing a circuit which is connected to the main

controller of the HVAC system. The old HVAC system controller was able to control only one

HVAC system at the moment and also it occupied more area. In Compare, this circuit will be

able to control 8 different systems simultaneously with less area needed. This very tiny circuit

designed in 6*6 cm PCB. As a result, it features not only lower cost and smaller area

occupation but also is able to control more devices or HVAC systems at the same time.

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References

[1] Programmable Logic Controllers, W. Bolton , Fourth edition 2006

[2] Programmable Controllers Theory and Implementation, L.A Bryan Second edition 1997

[3] Fundamental of the HVAC system, Robert McDowall , First edition,2007

[4] www.buildingtechnologies.siemens.com/bt/global/en/buildingautomation-

hvac/hvac-products/oem/Documents/Brochure_product_segments_Z-

500381303-en.pdf

[5] www.buildingtechnologies.siemens.com/bt/global/en/buildingautomation-

hvac/hvac-products/oem/climatix-product-range/pages/chillers-and-heat-

pumps.aspx

[6] www.buildingtechnologies.siemens.com/bt/global/en/buildingautomation-

hvac/hvac-products/oem/Pages/oem.aspx

[7] www.downloads.siemens.com/download-

center/Download.aspx?pos=download&fct=getasset&id1=A6V10807585

[8] https://www.scribd.com/document/58550688/POL-687-70

[9] en.wikibooks.org/wiki/Analog_and_Digital_Conversion/ADC_Converters

[10] myclassbook.org/flash-adc-parallel-adc-working-principle/

[11] www.allaboutcircuits.com/textbook/digital/chpt-13/flash-adc/

[12] www.electronics-tutorials.ws/combination/comb_4.html

[13] Open book STMicroelectronics Printed in Italy ,All Rights Reserved

STMicroelectronics GROUP OF COMPANIES,2001

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