Energy Efficiency E-modules - Guidance

Steam and High Temperature Hot Water Boilers

Application of Steam and Pressurised Hot Water Boilers in the Public Sector | 2

Contents

1 Introduction 4

2 Learning Objectives and Outcomes 4

2.1 Learning Objectives 4

2.2 Learning Outcomes 4

3 Overview and Principles of Steam and Pressurised Hot Water 5

3.1 Theory of Water at Pressure 5

3.2 Why Use Steam? 5

3.3 Key Components - The Steam Boiler 5

3.4 Key Components - The Burner 6

3.5 Steam Traps 6

3.6 Key Components - The Hot Well 7

4 Opportunities for Energy Saving in the Public Sector 8

4.1 Opportunities for Energy Saving - The Boilerhouse 8

4.2 Opportunities for Energy Saving - Steam Distribution 8

5 Energy Saving Opportunities - Boiler Replacement and System Upgrades 9

5.1 Maximise Combustion Efficiency 9

5.2 Flue Gas Economisers 9

5.3 Flash Steam Recovery 9

5.4 Boiler Blowdown Heat Recovery 10

6 Energy Saving Opportunities - Monitoring Boiler Performance 11

7 Energy Saving Opportunities - Steam Distribution 12

7.1 Insulation 12

7.2 Plate Heat Exchangers - Heating 12

7.3 Plate Heat Exchangers – Domestic Hot Water (DHW) 12

8 Energy Saving Opportunities - Maintenance 13

8.1 Maximising Combustion Efficiency 13

8.2 Keep Boiler Surfaces Clean 13

8.3 Water Treatment and TDS Control 13

8.4 Steam Trap Monitoring 14

9 Building Business Case 15

9.1 Before considering a Major Steam System Improvement Project 15

9.2 Information Gathering 15

9.3 Business Case - Case Study 15

Steam and High Temperature Hot Water Boilers | 3

10 Useful Links and References 17

Steam and High Temperature Hot Water Boilers | 4

1 Introduction

This guidance follows the format of the associated e-module, “Steam and High Temperature

Hot Water Boilers”, to provide further details on the subjects covered in the module.

Please note that module users working in a healthcare environment should always refer to

the relevant Scottish Health Technical Memorandum (SHTM) prior to considering installation

of the measures suggested in the module. The advice given in the SHTM may conflict with

the advice given in this module, as it has been developed for the wider public sector. The

relevant SHTM can be found on the Health Facilities Scotland website.

2 Learning Objectives and Outcomes

2.1 Learning Objectives

The learning objectives from this module are:

Understand the principles of steam and pressurised hot water; and

Assess and prioritise the opportunities for energy saving in the public sector

2.2 Learning Outcomes

The learning outcomes from this module are:

Explain the principles of steam and pressurised hot water supply systems;

Identify where the opportunities for energy reduction exist in Scottish public sector sites

and buildings;

Understand the key components of an energy efficient boiler house;

Describe the main energy recovery technologies, including their typical efficiency range

and the advantages and disadvantages of each technology;

Undertake a simple monitoring exercise of a boiler house to understand operating

efficiency; and

Understand the key aspects in relation to steam and pressurised hot water projects

when building a business case.

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3 Overview and Principles of Steam and Pressurised Hot Water

3.1 Theory of Water at Pressure

Normally when water when it is heated above 100 degrees Celsius it boils and create steam.

This is only true however, when the water is at atmospheric pressure. If the water is being

heated in a sealed vessel, then the pressure in vessel will begin to rise as the contents

expands. This increase in pressure makes it more difficult for the water molecules to

separate to form steam, thus effectively raising the boiling point of the water.

This is a simplified example of how a steam or high temperature hot water system operates.

In a steam boiler the pressure is regulated to produce steam with the desired temperature

and pressure. For example, a steam boiler controlled to produce steam at 7 bar will have a

temperature of approximately 170°C.

3.2 Why Use Steam?

There are two main reasons why steam has been used for heating in the public sector.

The first application is when temperatures of over 90°C are required. This is more common

in manufacturing than in the public sector, though there are some healthcare applications

where steam is required for high temperature applications, such as for sterilisation.

The second application for steam is to transport heat over large distances. Steam is

advantageous in this situation as the higher temperatures mean smaller pipes can be used

to transport equivalent quantities of heat. The requirement for pumping power is therefore

substantially reduced.

3.3 Key Components - The Steam Boiler

There are several key components of a steam system that must be considered. At the heart

of the system is the steam boiler.

The most common type of steam boiler in use is the 3 pass, wet back shell boiler and so this

will form the basis for this e-module. There are numerous other less common types

including:

Lancashire Boilers - with twin internal flues/combustion chambers.

Two pass-dry back - where the burner and flue exit are on the same side of the boiler.

Reverse flame boilers - where combustion gases ‘bounce’ back of the furnace back wall

before passing though tubes around the side of the combustion chamber.

Details of these alternative designs can be found in some of the further reading outlined at

the end of this guidance document.

In the 3 pass, wet back shell boiler the fuel is burnt in the combustion chamber and the

combustion gasses pass along the combustion chamber, transferring heat to the ‘wet’ side

of the boiler through the ‘wet back’. This is a space behind the combustion chamber where

water flows. This increases heat transfer area and decreases the standing losses of the

boiler. Typically up to 65% of heat transfer occurs in this first pass.

Steam and High Temperature Hot Water Boilers | 6

The combustion gasses then turn at the back of the boiler and pass through a number of

tubes, which are surrounded by water. This forms the second pass. The process is then

repeated one final time giving the third pass before exiting the boiler through the flue. .

On the wet side of the boiler, the bulk of the space is filled with water, with a small space at

the top of the boiler where steam forms.

3.4 Key Components - The Burner

The burner is the part of the system that does the bulk of the work in a steam or high

temperature system. When the burner starts up, the first stage is the purge cycle, when

cold air is blown through the combustion chamber to purge it of any residual gases from the

previous cycle. The burner then burns burning oil or gas in the combustion chamber to

maintain steam pressure in the system.

How fluctuations in the demand for steam are matched depends on the type of burner.

Some old systems may have a single stage on/off, burner which simply switches on and off

as required. This is the least efficient type. More common are two stage burners, which

have high and low fire settings allowing a degree of modulation to meet demand. Most

modern boilers have fully modulating control. These are the most efficient type as they

allow the burner to ramp up and down to meet the varying demand. In an ideal scenario

this allows the burner to fire constantly without switching off at all, which reduces losses

from purge cycles and improves efficiency.

Another important aspect of the burner is the provision of combustion air. This is achieved

using a fan. Changes in air demand with varying firing rate are met either by using

mechanical dampers or by varying the speed of the fan. This and other aspects such as

digital combustion control are explored in more detail later.

A good way to ensure that the burner is efficient is to specify that it must meet the

requirements set out in the UK Government Enhanced Capital Allowance Scheme Energy

Technology List for burners.

3.5 Steam Traps

Once steam leaves the boiler it is distributed to the various users via the steam distribution

network. Usually, once the steam has delivered heat to the user via the heat exchanger or

coil, it condenses back into its liquid form. This is known as condensate.

This condensate is at high temperature and should be recovered and returned to the hot

well (see below). A key challenge in steam systems is how to remove the condensate

without also releasing some of the energy in the system. When hot condensate experiences

a pressure drop ‘flash steam’ can form and can be potentially lost from the system taking

thermal energy with it. This can be a particular issue when condensate first passes into the

condensate recovery side of the system.

In order to prevent this, steam traps are used. These devices allow condensate to pass

whilst ‘trapping’ steam (including flash steam) and keeping it within the steam side of the

system. Steam traps are typically installed on condensate lines immediately after the

heating coil and on long runs of steam pipe to remove any condensate which may have built

up. From these, condensate is piped away, usually to a condensate vessel before returning

to the hot well.

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Steam Traps can be either:

Thermostatic - operated by changes in fluid temperature, allowing fluid to pass when it

senses the lower temperature of condensate;

Mechanical - operated by changes in fluid density, allowing denser condensate to pass

whilst restricting the flow of steam; or

Thermodynamic - operated by changes in fluid dynamics, relying on the formation of

flash steam from the condensate.

3.6 Key Components - The Hot Well

Condensate, on its return to the boiler house, is collected in a tank known as a hot well.

This vessel is normally located at a high level within the boiler house. Cold water is also

added to the system to replace water lost through steam or condensate loss from any

steam used in the distribution system. In systems where there is high steam use, and thus

a high demand for cold water to top up the system, there may also be a steam supply to

the hot well direct from the boiler. This is known as steam sparge, where steam can be

injected into the hot well to raise its temperature.

Ideally, the hot well temperature will be as high as possible without reaching the point

where condensate starts to boil off, thus wasting energy. The higher the condensate

temperature, the less work required in the boiler to raise steam. Another issue is the

oxygen content of boiler water. Oxygen is a significant factor in boiler corrosion and

normally steps are taken to reduce oxygen levels such as adding oxygen scavengers. As

oxygen is less soluble in hot water, raising the temperature of the hot well reduces the

amount of these oxygen scavenging chemicals that are required.

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4 Opportunities for Energy Saving in the Public Sector

4.1 Opportunities for Energy Saving - The Boiler House

To consider where energy savings can be made, the location of losses in the system must

be explored.

The most significant energy loss is the flue gas losses which typically account for around

18% of all boiler losses. This can be reduced by deploying a flue gas economiser. This is an

additional heat exchanger that traps heat from the flue gasses.

To maximise efficiency, boiler feed water must be at as high a temperature as possible. This

is best achieved by maximising condensate return temperature, ideally through recovering

condensate in a fully insulated system. Although steam sparge can be used to boost

temperatures, this should not be used in preference to steps to maximise condensate return

temperatures.

Boiler blowdown accounts for losses of around 3% on average. This can be reduced by

ensuring good water treatment and by implementing boiler blowdown heat recovery, usually

to pre-heat boiler feed water.

Boiler radiative losses account for around 2% of total energy consumed and can be

minimised by ensuring good insulation of the boiler and scheduling of boiler operation where

a site has multiple steam boilers.

Finally, there are heat transfer losses which again account for around 2-3% of the energy

consumed by the boiler. This can be minimised by ensuring the water is well treated and by

frequent cleaning of the boiler.

4.2 Opportunities for Energy Saving - Steam Distribution

There are also opportunities for making savings in the distribution system, although it is

more difficult to quantify the savings available.

The most important area to focus on is to ensure that any steam leaks are repaired as soon

as possible. Steam is an expensive resource and steam leaks are often the cause of a

needless waste of energy, water and boiler chemicals. Particular attention should be given

to valves and flanges where leaks most commonly develop.

Even though condensate is less energy intensive than steam, nevertheless high levels of

heat, water and boiler chemical loss will result if condensate leaks are not quickly repaired.

As noted previously, steam traps are an important part of the steam distribution system and

these should be regularly maintained to ensure they are functioning properly.

Malfunctioning steam traps which are allowing steam to escape from the system along with

condensate can be a significant source of losses within the distribution system.

Finally, poor thermal insulation can lead to unnecessary losses within the system. This

should be addressed at the earliest opportunity, with priority given to high temperature

steam pipework and fittings. As well as the cost savings from insulating pipes, there can

also be an improvement in steam quality as there will be less cooling of the steam as it

travels through the pipe and therefore less build-up of condensate and wet steam.

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5 Energy Saving Opportunities - Boiler Replacement and System Upgrades

5.1 Maximise Combustion Efficiency

As combustion is the process with the highest losses within the system, it is worth

considering how this process may be improved. One of the most effective approaches is to

install a digital combustion control, sometimes referred to as a digital combustion and

management control (DCMC) or a direct digital combustion control (DDCC), on the burner of

a steam boiler.

The amount of fuel used by the burner is highly dependent on the air to fuel ratio. Modern

digital control systems offer precise adjustment and optimisation of air and fuel

characteristics, thus minimising energy consumption.

This approach is most cost effective if specified when installing a new steam boiler, although

it can be retrofitted to boilers with modulating burners, or when installing a new burner. It

can lead to savings of up to 5%.

Where the system can accept this modification, further savings are available from variable

speed control of the fan providing combustion air compared with a single speed fan linked to

mechanical dampers.

5.2 Flue Gas Economisers

A flue gas economiser recovers more heat from the flue gas (which can be at temperatures

of around 200°C) as it exits the boiler. Flue gas economisers can be fitted to the flue

immediately after the boiler. In practice, it is the boiler feed water that is passed through

the flue gas economiser. As a result, they require the boiler to have modulating water level

controls and a variable speed control of the boiler feed pump to ensure a constant flow of

water through the heat exchanger. These units are usually available off the shelf from

steam boiler manufacturers and, where space allows, can be retrofitted to existing boilers.

Economisers can reduce boiler consumption by up to 5% and are particularly effective

where condensate return temperature is low, as this offers the greatest potential for heat

recovery. In general, economisers are best applied to gas fired boilers, though economisers

for oil boilers are available.

5.3 Flash Steam Recovery

A major source of flash steam generation is in systems where the rate of condensate return

is high and where condensate is at a high temperature. Here, flash steam loss typically

occurs when the hot well temperature rises close to 100°C and water starts to boil off to

atmosphere (as the hot well is not pressurised). It is possible to recover some of the energy

in the steam by using the hot condensate to pre-heat the boiler feed water under

pressurised conditions. This often allows the boiler feed water to rise to temperatures of up

to 110°C.

This type of heat recovery works by first passing the returning hot condensate through a

flash steam separation vessel. This vessel separates the flash steam from the condensate,

sending each to a dedicated heat exchanger. In this way the boiler feed water from the hot

well is pumped through the first heat exchanger where some of the heat from the

condensate is recovered. This raises the boiler feed water temperature and reduces the

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condensate temperature. The condensate then returns to the hot well. The boiler feed water

then passes through the second heat exchanger. Here it is further heated at pressure by the

flash steam, which in turn is then condensed before joining the first condensate line and

returning to the hot well. The boiler feed water is then pumped in to the boiler at high

temperature, thus reducing the fuel required by the boiler to raise steam.

5.4 Boiler Blowdown Heat Recovery

The use of chemicals to dose the boiler feed water leads to the presence of suspended solids

in the boiler. These tend to collect as sludge at the bottom of the boiler, which is removed in

a process known as a blowdown. This can be done manually or using automatic total

dissolved solid (TDS) control.

As noted previously, up to 3% of the energy entering the boiler as fuel can be lost during

boiler blowdown. Automatic TDS control ensures that the boiler only blows down when this

is required and so reduces the energy lost in this process. It is possible to improve the

system efficiency further by implementing boiler blowdown heat recovery.

Blowdown heat recovery works by passing the hot blowdown fluid into a flash steam vessel,

which separates the steam from the condensate/sludge. The recovered steam is then

delivered to the hot well where it is mixed with the returning condensate and any mains

cold water being used to top up the supply (thus making up for any lost steam or

condensate) before being fed in to the hot well.

The condensate is passed through a strainer and then a plate heat exchanger, which is also

used to preheat the cold water top up supply to the hot well. This raises the temperature

and reduces the fuel required of the boiler to raise steam.

This process can recover up to 80% of the energy in the blowdown fluid, whilst also

reducing the requirement for treated make up water by recovering the flash steam.

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6 Energy Saving Opportunities - Monitoring Boiler Performance

Monitoring boiler performance requires data. This can include temperatures, pressures, flow

rates and timing boiler firing. To achieve continuing energy savings, it is recommended that

metering is installed to monitor boiler performance.

As a minimum, it is recommended that the boiler house is fitted with:

A dedicated fuel meter;

A cold water meter on the hot well top up; and

A steam meter on the main steam header.

The data from these meters can then be collected and a high level assessment of boiler

house performance can be undertaken. It is important that the meters are accurate. Some

types of steam meter in particular will require maintenance and recalibration at regular

intervals.

The steam meter reading can be converted to kW or kWh by noting the operating pressure

and using steam tables. The fuel meter reading can be converted to kW or kWh using

conversion factors for the calorific value of the fuel. Dividing the energy in the steam by the

energy in the fuel can provide an indicator, albeit simplistic, of boiler house efficiency

helping identify any deterioration in performance that may require investigation. The cold

water meter is used to track the volume of water being added to the system. Any increase

in the water supply may suggest an issue that is affecting energy performance, for example

excessive boiler blowdown or major steam and condensate leaks.

Other simple checks that can be made to monitor boiler house performance include:

Checking the TDS control settings against those recommended for the boiler type in

order to avoid excessive blowdown;

Checking the oxygen readings on any burner displays and comparing with past

combustion efficiency checks; and

Timing the burner on/off patterns to assess for excessive boiler cycling.

An infrared thermal imaging camera is a good tool to help assess the boiler performance.

Areas of poor insulation or refractory (the heat resistant lining in the boiler) can be quickly

identified, as can any uninsulated valves, fittings, pipework or other ancillary items. This

can be particularly important after annual strip downs to ensure that the insulation and

refractory have not been damaged, and sections removed have been replaced. Taking a

before and after infrared image is a good way to ensure that the boiler has returned to its

pre-maintenance state or better. This method can also be used for other items that require

annual strip downs, such as shell and tube heat exchangers.

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7 Energy Saving Opportunities - Steam Distribution

7.1 Insulation

Insulation is important with steam systems, both for the boiler and the distribution systems.

Heat loss from uninsulated or poorly insulated steam systems can be particularly high due

to the high temperatures involved. For more information on thermal insulation of boilers,

pipework and fittings see Module 6, How to Implement Thermal Insulation to HCVAC

Services.

7.2 Plate Heat Exchangers - Heating

Savings can be made by replacing large shell and tube heat exchangers or calorifiers with

more compact plate heat exchangers.

There are a number of benefits to this approach including reduced standing losses, since

plate heat exchangers are much more compact than shell and tube heat exchangers, so

there is less surface area for heat loss to atmosphere. It also results in improved

controllability as plate heat exchangers can respond much more quickly to fluctuations in

demand, improving overall efficiency and reducing maintenance costs. Unlike calorifiers,

plate heat exchangers do not require a full annual shutdown.

Packaged heat exchangers are available on the market and can be installed on existing

systems relatively easily.

7.3 Plate Heat Exchangers – Domestic Hot Water (DHW)

Plate heat exchangers can also be applied to domestic hot water applications, where similar

benefits apply. In addition, they eliminate the need for large water storage vessels thus

reducing the risk posed by legionella bacteria and further reducing ongoing maintenance

costs.

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8 Energy Saving Opportunities - Maintenance

8.1 Maximising Combustion Efficiency

There are some key maintenance activities which, when carried out properly, can help ensure

steam system efficiency is optimised. One method is monitoring boiler combustion efficiency.

Regular monitoring of combustion efficiency can help ensure that any deterioration in boiler

performance is identified early and that boiler efficiency is maximised. For combustion to be

carried out effectively, the mixture of fuel and air must be correct. Too little air will result in

incomplete combustion, too much will cause increased heat loss up the flue. Both cases will

mean that more fuel is required to deliver heat to the boiler than when air supply is

optimised.

The following conditions should be checked regularly:

Flue gas temperatures;

Flue gas constituents;

Flame shape; and

Fuel and air trim settings.

A combustion efficiency check will produce a printout which gives, among other things, a

reading of the net combustion efficiency. It is worth noting that typically, a 2% reduction in

oxygen levels in the flue gas will provide a fuel saving of 1.2%.

Regular monitoring of combustion conditions can help the user to address any minor issues

to ensure optimum conditions when they arise. This prevents the boiler from operating

inefficiently for long periods.

8.2 Keep Boiler Surfaces Clean

Keeping boiler surfaces clean can help maximise heat transfer efficiency and ensure energy

is not being wasted. Steam boilers are particularly susceptible to the build-up of debris on

the wet side of the boiler as dissolved solids and particles in the water can be deposited on

the boiler surfaces.

Build-up can be reduced by treating the boiler feedwater, however the boiler should be

cleaned at least once a year during the insurance inspection to ensure optimum heat

transfer.

8.3 Water Treatment and TDS Control

Water treatment is required in steam boilers to ensure effective operation. The water supply

for the wet side of the boiler will contain various particles and impurities, which can cause

issues with steam systems if not treated.

These issues include:

Reduced efficiency as surfaces are fouled and boiler blowdown is required more often;

Increased cleaning costs as the process of keeping the boiler clean becomes more

laborious; and

Carryover. This is where TDS particles are carried in the steam into the distribution

system can cause reduced heat transfer at points of use and potentially damaging

Steam and High Temperature Hot Water Boilers | 14

corrosion of plant and pipework. In extreme cases this can lead to catastrophic failure

of plant – clearly something to be avoided.

Good water treatment and control of TDS can help minimise the risk of these issues

occurring and ensure the boiler operates efficiently. For more information on water

treatment and TDS control, see the further reading section at the end of this module.

8.4 Steam Trap Monitoring

Steam traps are an integral part of a steam system and their effective operation is

imperative to the overall efficiency and efficacy of the steam system. One way to ensure

that steam trap failure is identified as soon as it occurs is to implement a steam trap

monitoring system to detect any failures and allow them to be addressed promptly.

This approach is particularly worth considering for large steam systems where keeping on

top of maintenance can be difficult. An automatic monitoring system can help the operator

target maintenance resource at problem areas and ensure energy is not being wasted due

to poor steam trap performance.

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9 Building the Business Case

9.1 Before Considering a Major Steam System Improvement Project

When thinking about replacing boilers, it is important to consider all other low cost

measures which could be implemented to save fuel consumption prior to proceeding. For

example, it may be prudent to ask the following questions of the project:

1. Have the controls been optimised? It is important to make sure that energy is not being

wasted through poor control as this can usually be rectified for relatively low cost.

2. Is insulation up to standard? Insulating hot pipework and valves is a low cost way to

save energy and money and this should be taken account of before considering new

boiler plant.

3. Is the best fuel being used? If the site uses oil, is there a natural gas connection

available? Could gas burners be retrofitted to the existing boilers?

4. Is the building appropriately zoned? Could improved zoning help with better control? If

so, this should be done before replacing boiler plant, or it could be included as part of

the same project.

Once all of the above have been considered, an effective business case can be made.

9.2 Information Gathering

To build an effective business case, one of the most important things is to gather accurate

information. In particular, collect the following data:

The building or boiler total fuel consumption;

The boiler combustion efficiency;

The building peak heating demand;

The age of the existing boilers; and

In addition, it is likely that any boiler replacement will require modification to the

existing pipework and flue. As a result consider any other site specific issues which may

influence the viability of the project, for example:

o Is the boiler house in the basement?

o Could flue or modified pipe routes be complicated?

o Is redundancy required anywhere in the system?

o How will hot water be provided?

9.3 Business Case - Case Study

Consider this example of a successful steam boiler replacement project. The site had been

operating with an ageing temporary boiler plant which had reached the end of its

serviceable life. As a result, a business case was developed for the installation of new steam

raising plant to service the site.

Under this project, two new boilers were installed in an existing boiler house.

This project was progressed as an energy and carbon saving project, with a focus on

making the new installation as energy efficient as possible. Therefore the new installation

included:

Flue gas economisers on both boilers;

Digital combustion control;

Variable speed control of the burner fan;

Steam and High Temperature Hot Water Boilers | 16

Controls interface with the site BMS;

Automatic TDS Control and boiler blowdown;

Oxygen trim control of the boiler house; and

Enhanced thermal insulation of pipework.

After installation the boiler performance was monitored and the following savings were

recorded:

27% reduction in gas consumption, or 6,745,000 kWh per year;

A cost saving of £141,000 per year;

CO2 savings of over 1,200 tonnes per year; and

A reduction in water consumption by 11,000 m3 or £17,000 per year.

Against a capital cost of £630,000 this is a payback of 4.5 years, giving an attractive return

on investment for the site. This example shows the kind of financial and energy savings that

can be made from replacing old, inefficient steam boilers with new systems.

Application of Steam and Pressurised Hot Water Boilers in the Public Sector | 17

10 Useful Links and References

Title Source Link

Steam Tutorials Spirax Sarco www.spiraxsarco.com/resources/steam-engineering-tutorials.asp

Steam & High Temperature hot water

boilers overview (CTV052) The Carbon Trust

www.carbontrust.com/media/13332/ctv052_steam_and_high_temperat

ure_hot_water_boilers.pdf

How to implement blow down heat

recovery (CTL020) The Carbon Trust

www.carbontrust.com/media/147111/j7940_ctl020_how_to_implement_

blowdown_heat_recovery_aw.pdf

How to implement oxygen trim control

(CTL147) The Carbon Trust

www.carbontrust.com/media/147167/j8054_ctl147_how_to_implement_

oxygen_trim_control_aw.pdf

How to implement advanced combustion

control (CTL058) The Carbon Trust

www.carbontrust.com/media/147147/j7971_ctl058_advanced_combusti

on_aw.pdf

Enhanced Capital Allowance Scheme DECC https://etl.decc.gov.uk/etl/site/etl.html

Application of Steam and Pressurised Hot Water Boilers in the Public Sector | 18