COMPONENTS OF AN ENERGY EFFICIENT BUILDING

8/7/2019 COMPONENTS OF AN ENERGY EFFICIENT BUILDING

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COMPONENTS OF ANENERGY EFFICIENT BUILDING

Green Buildings and Energy EfficientBuildings

Green building (also known as greenconstruction or sustainable building) is thepractice of creating structures and using processes

that are environmentally responsible and resource-efficient throughout a building's life-cycle: from sitingto design, construction, operation, maintenance,renovation, and demolition. This practice expandsand complements the classical building designconcerns of economy, utility, durability, and comfort.

Although new technologies are constantly being

developed to complement current practices increating greener structures, the common objective isthat green buildings are designed to reduce theoverall impact of the built environment on humanhealth and the natural environment by:

Efficiently using energy, water, and otherresources

Protecting occupant health and improving

employee productivity Reducing waste, pollution and environmental

degradation
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Some of the major components and devices used inan energy efficient building are as follows

Energy Recovery Ventilator

Heat Recovery Ventilation

Radiant Flooring - Under Floor Heating

Structural Insulated Panels

Photovoltaic Array

Heat Pumps

North Wall

Clerestory lightings and Skylight

Attached Greenhouses

Roof Ponds

Energy Recovery Ventilator (ERV)


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Introduction

An Energy Recovery Ventilator (ERV) is a mechanicaldevice that draws stale air from the house and

transfers the heat or coolness in that air, to the airbeing pulled into the house. This can help reduceenergy costs and dilute indoor pollutants. It is a typeof air-to-air heat exchanger that not only can transfersensible heat but also latent heat. Since bothtemperature and moisture is transferred, ERVs canbe considered total enthalpic devices

Energy Recovery VentilationIntroduction

Energy Recovery Ventilation (ERV) is the energyrecovery process of exchanging the energycontained in normally exhausted building or spaceair and using it to treat, precondition, the incomingoutdoor ventilation air in residential and commercial

HVAC systems.

During the warmer seasons the system will pre-cooland dehumidify while humidifying and pre-heating inthe cooler seasons. This system will allow for theindoor environment to maintain a relative humidityof an appealing 40% to 50% range. This range can bemaintained under essentially all conditions. The only

energy penalty is the power needed for the blower toovercome the pressure drop in the system.

Brief Description

ERVs are especially recommended in climates wherecooling loads place strong demands on HVAC
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(heating, ventilation and air-conditioning) systems.However, keep in mind that ERVs are notdehumidifiers. They transfer moisture from thehumid air stream (incoming outdoor air in the

summer) to the exhaust air stream. But, thedesiccant wheels used in many ERVs becomesaturated fairly quickly and the moisture transfermechanism becomes less effective with successivehot, humid periods. In some cases, ERVs may besuitable in climates with very cold winters. If indoorrelative humidity tends to be too low, what availablemoisture there is in the indoor exhaust air stream, is

transferred to incoming outdoor air.

ERVs also allow the exchange of moisture to controlhumidity. This can be especially valuable insituations where problems may be created byextreme differences in interior and exterior moisturelevels. For instance in cold, heating-dominated

climates, better air flow and the introduction ofhumidity to the indoor environment can help controlwintertime window condensation. In humid summerclimates which are cooling dominated, it can becritical to dry out incoming air so that mildew or molddoes not develop in ductwork.

Methods of Transfer

Throughout the cooling season, the system works tocool and dehumidify the incoming, outside air. This isaccomplished by the system simply taking therejected heat and sending it into the exhaustairstream. Sequentially, this air cools the condensercoil at a lower temperature than if the rejected heat


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had not entered the exhaust airstream. During theheating seasons, the system works in reverse.Instead of discharging the heat into the exhaustairstream, the system draws heat from the exhaust

airstream in order to pre-heat the incoming air. Atthis stage, the air passes through a primary unit andthen into a space. With this type of system, it isnormal, during the cooling seasons, for the exhaustair to be cooler than the ventilation air and, duringthe heating seasons, warmer than the ventilation air.It is this reason the system works very efficiently andeffectively. The Coefficient of Performance (COP) will

increase as the conditions become more extreme(i.e., more hot and humid for cooling and colder forheating).[4]

Efficiency

The efficiency of an ERV system is the ratio of energytransferred between the two air streams comparedwith the total energy transported through the heat

exchanger.[5][6]

Types of Energy Recovery Devices

EnergyRecoveryDevices

Type ofTransfer

Rotary Enthalpy

Wheel

Total &

SensibleFixed Plate

Total** &Sensible

Heat Pipe Sensible

Run AroundLoop

Sensible
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Thermo-siphon Sensible

Twin Towers Sensible

**Total Energy Exchange only available on

Hygroscopic units and Condensate Return units

Rotary Air-to-Air Enthalpy Wheel

The rotating wheel heat exchanger is composed of arotating cylinder filled with an air permeable materialresulting in a large surface area. The surface area isthe medium for the sensible energy transfer. As thewheel rotates between the ventilation and exhaustair streams it picks up heat energy and releases itinto the colder air stream. The driving force behindthe exchange is the difference in temperaturesbetween the opposing air streams which is alsocalled the thermal gradient. Typical media usedconsists of polymer, aluminum, and synthetic fiber.

The Enthalpy Exchange is accomplished through the

use ofdesiccants. Desiccants transfer moisturethrough the process ofadsorption which ispredominately driven by the difference in the partialpressure of vapor within the opposing air-streams.Typical desiccants consist ofSilica Gel, andmolecular sieves.

Though very effective in its energy recovery, rotaryenthalpy wheels have the common characteristic ofhigh static pressures and poor durability. Thereforethey are not as practical for energy savingspurposes, and should only be considered for acheaper alternative - in comparison to other ERVs -for situations where increased fresh outdoor
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ventilation is required. High static pressures result inincreased fan power lowering the net energy savingsof an installation. As for durability, rotary enthalpywheels are normally guaranteed for no longer than 1

year, and the characteristic lifetime is about 5 years.

Plate Heat Exchanger

Fixed plate heat exchangers have no moving parts.

Plates consist of alternating layers of plates that areseparated and sealed. Typical flow is cross currentand since the majority of plates are solid and nonpermeable, sensible only transfer is the result.

The tempering of incoming fresh air is done by aheat or energy recovery core. In this case, the core ismade of aluminum or plastic plates. Humidity levels

are adjusted through the transferring of water vapor.This is done with a rotating wheel either containing adesiccant material or permeable plates.[11]Thepercentage of the total energy saved will depend onthe efficiency of the device (up to 90%) and thelatitude of the building
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Heat Pipe Exchanger

A heat pipe is a passive energy recovery heatexchanger that has the appearance of a commonplate-finned water coil except the tubes are notinterconnected. Additionally it is divided into twosections by a sealed partition. Hot air passes throughone side (evaporator) and is cooled while cooler airpasses through the other side (condenser). Whileheat pipes are sensible heat transfer exchangers, ifthe air conditions are such that condensation formson the fins there can be some latent heat transferand improved efficiency.


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Heat pipes are tubes that have a capillary wick inside

running the length of the tube, are evacuated andthen filled with a refrigerant as the working fluid, andare permanently sealed. The working fluid is selectedto meet the desired temperature conditions and isusually a Class I refrigerant. Fins are similar toconventional coils - corrugated plate, plain plate,spiral design. Tube and fin spacing are selected forappropriate pressure drop at design face velocity.

HVAC systems typically use copper heat pipes withaluminum fins; other materials are available.


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Run-around Loop Systems

The run-around heat recovery system is a simplepiping loop, containing a circulator; the loop connects

a finned-tube coil in the exhaust plenum with afinned-tube coil in the make-up air plenum or AHU.The coils are connected in a closed loop viacounterflow piping through which an intermediateheat transfer fluid (typically water or a freeze-preventive solution) is pumped.

The warm exhaust air heats the circulating fluid; thisfluid then warms the cool make-up air. The heatrecovery system typically operates to preheatoutdoor make-up air but also to pre-cool the make-upair when the exhaust air stream is cooler than theoutdoor makeup air.

This system operates for sensible heat recovery only.In comfort-to-comfort applications, energy transfer isseasonally reversiblethe supply air is preheated

when the outdoor air is cooler than the exhaust airand precooled when the outdoor air is warmer.
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Thermo-Siphon

Thermosiphon refers to a method of passive heatexchange based on natural convection which

circulates liquid without the necessity of amechanical pump. This circulation can either beopen-loop, as when liquid in a holding tank is passedin one direction via a heated transfer tube mountedat the bottom of the tank to a distribution point -even one mounted above the originating tank - or itcan be a vertical closed-loop circuit with return to theoriginal vessel. Its intended purpose is to simplify thepumping of liquid and/or heat transfer, by avoidingthe cost and complexity of a conventional liquidpump.

Solar Energy
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Thermosiphons are used in some liquid-based solarheating systems to heat a liquid such as water. Thewater is heated passively by solar energy and relieson heat energy being transferred from the sun to a

solar collector. The heat from the collector can betransferred to water in two ways: directlywherewater circulates through the collector, or indirectlywhere an anti-freeze solution carries the heat fromthe collector and transfers it to water in the tank viaa heat exchanger. Convection allows for themovement of the heated liquid out of the solarcollector to be replaced by colder liquid which is in

turn heated. Due to this principle, it is necessary forthe water to be stored in a tank above the collector.

Heat Recovery Ventilation

Introduction
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Heat recovery ventilation, also known as HRV,Mechanical ventilation heat recovery, or MVHR,is an energy recoveryventilation system, usingequipment known as a heat recovery ventilator, Heat

exchanger, air exchanger or air-to-air exchanger,that employs a counter-flowheat exchanger(countercurrent heat exchange) between theinbound and outbound air flow. HRV provides freshair and improved climate control, while also savingenergy by reducing the heating (or cooling)requirements.

Incoming Air

The air coming into the heat exchanger should be atleast 0C. Otherwise humidity in the outgoing airmay condense, freeze and block the heat exchanger.

A high enough incoming air temperature can also beachieved by

recirculating some of the exhaust air (causingloss of air quality) when required,

by using a very small (1 kW) heat pump to warmthe inlet air above freezing before it enters theHRV. (The 'cold' side of this heatpump is situatedin the warm air outlet.)
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Air to Air Heat Exchanger

There are a number of heat exchangers used in Heatrecovery ventilation-HRV devices, as diagrammed to

the right :

cross flow heat exchanger up to 60% efficient

(passive) countercurrent heat exchanger up to 99%

efficient (passive) rotary heat exchanger (requires motor to turn

wheel) heat pipes thin multiple heat wires (Fine wire heat

exchanger)

Earth-to-Air Heat Exchanger
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This can be done by an earth warming pipe ("ground-coupled heat exchanger"), usually about 30 m to 40

m long and 20 cm in diameter, typically buried about1.5 m below ground level

In high humidity areas where internal condensationcould lead to fungal / mould growth in the tubeleading to contamination of the air, several measuresexist to prevent this.

Ensuring the tube drains of water. Regular cleaning Tubes with an imbedded bactericide coating

such as silver ions (non-toxic for humans) Air filters F7 / EU7 (>0,4 micrometres) to traps

mould (of a size between 2 & 20 micrometres). UV air purification Use a earth to "water" heat exchanger.The pipes

may be either corrugated/slotted to enhance

heat transfer and provide condensate drainageor smooth/solid to prevent gas/liquid transfer.

Earth-to-Water Heat Exchanger
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An alternative to the earth to air heat exchanger isthe earth to "water" heat exchanger. This is typicallysimilar to a geothermal heat pump tubing embeddedhorizontally in the soil (or could be a vertical

pipe/sonde) to a similar depth of the EAHX. It usesapproximately double the length of pipe 35 mm iearound 80 metres compared to an EAHX. A heatexchanger coil is placed before the air inlet of theHRV. Typically a brine liquid (heavily salted water) isused as the heat exchange fluid which is slightlymore efficient and environmentally friendly thanpolypropylene heat transfer liquids.

In temperate climates in an energy efficient building,this is more than sufficient for comfort cooling duringsummer without resorting to an airconditioningsystem. In more extreme hot climates a very smallair to air micro-heat pump in reverse (an airconditioner) with the evaporator (giving heat) on theair inlet after the HRV heat exchanger and the

condensor (taking heat) from the air outlet after theheat exchanger will suffice.

Radiant Heating

Introduction

Radiant heating is a technology for heating indoorand outdoor areas. Radiant heating consists of

radiant energy being emitted from a heat source.Radiant heating heats a building through radiantheat, rather than other conventional methodsincluding convection heating. The heat energy isemitted from a warm element, such as a floor, wall oroverhead panel, and warms people and other objects
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in rooms rather than directly heating the air. Theinternal air temperature for radiant heated buildingsmay be lower than for a conventionally heatedbuilding to achieve the same level of body comfort,

when adjusted so the perceived temperature isactually the same.

In the case of heating outdoor areas, the surroundingair is constantly moving, making conventional patioheaters, also known as "mushroom heaters", whichrely partly on convection heating, impractical. Thereason being, that once you heat the outside air, it

will blow away with air movement. Outdoor radiantheaters allow specific spaces within an outdoor areato be targeted, warming only the people and objectsin their path.

The radiant heating systems can be divided into:

Underfloor heating systemselectric or hydronic Wall heating systems Radiant ceiling (overhead) panels Trace heating - Gutter and Roof De-icing Snowmelt system - Electric or Hydronic Overhead natural gas-fired radiant heaters

Underfloor Heating

Underfloor heating and coolingis a form ofcentralheating and cooling which achieves indoorclimate control for thermal comfort usingconduction, radiation and convection.

Description
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Hydronic systems use water or a mix of water andanti-freeze such as propylene glycol as the heattransfer fluid in a "closed loop" that is recirculatedbetween the floor and the boiler.

Various types of pipes are available specifically forhydronic underfloor heating and cooling systems andare generally made from polyethylene including PEX,PEX-Al-PEX and PERT. Older materials such asPolybutylene (PB) and copper or steel pipe are stillused in some locales or for specialized applications.

Hydronic systems require skilled designers andtradespeople familiar with boilers, circulators,controls, fluid pressures and temperature. The use ofmodern factory assembled sub-stations, usedprimarily in district heating and cooling, can greatlysimplify design requirements and reduce theinstallation and commissioning time of hydronicsystems.

Hydronic systems can use a single source orcombination of energy sources to help manageenergy costs. Hydronic system energy sourceoptions are:

Boilers (heaters) including Combined heat andpower plants heated by:

Natural gas , coal, oil or waste oil Electricity Solar thermal wood or other biomass bio-fuels

Heat pumps and chillers powered by:
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Electricity Natural gas

Electric systems

Electric systems are used onlyfor heating and employ non-

corrosive, flexible heatingelements including cables,pre-formed cable mats, bronze

mesh, and carbon films. Due to their low profile theycan be installed in a thermal mass or directly underfloor finishes. Electric systems can also takeadvantage oftime-of-use electricity metering and arefrequently used as carpet heaters, portable under

area rug heaters, under laminate floor heaters, undertile heating, under wood floor heating, and floorwarming systems, including under shower floor andseat heating. Large electric systems also requireskilled designers and tradespeople but this is less sofor small floor warming systems. Electric systems use
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fewer components and are simpler to install andcommission than hydronic systems. Some electricsystems use line voltage technology while others uselow voltage technology. Power consumption of an

electric system is not based on voltage but ratherwattage output produced by the heating element.

Indoor Air Quality

Underfloor heating can have a positive effect on thequality of indoor air by facilitating the choice ofotherwise perceived cold flooring materials such astile, slate, terrazzo and concrete. These masonrysurfaces typically have very low VOC emissions(volatile organic compounds) in comparison to otherflooring options. In conjunction with moisture control,floor heating also establishes temperature conditionsthat are less favorable in supporting mold, bacteria,viruses and dust mites. By removing the sensibleheating load from the total HVAC (Heating,Ventilating, and Air Conditioning) load, ventilation,

filtration and dehumidification of incoming air can beaccomplished with dedicated outdoor air systemshaving less volumetric turnover to mitigatedistribution of airborne contaminates. There isrecognition from the medical community relating to
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the benefits of floor heating especially as it relates toallergens.

Typical Installation Details

General considerations for placing radiant heating

and cooling pipes in flooring assemblies where otherHVAC and plumbing components may be present.

Technical Design

The amount of heat exchanged from or to anunderfloor system is based on the combined radiantand convective heat transfer coefficients.
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Radiant heat transfer is constant based on theStefanBoltzmann constant.

Convective heat transfer changes over timedepending on

o the air's density and thus its buoyancy. Airbuoyancy changes according to surfacetemperatures and

o forced air movement due to fans and themotion of people and objects in the space.

Convective heat transfer with underfloor systems ismuch greater when the system is operating in a

heating rather than cooling mode. Typically withunderfloor heating the convective component isalmost 50% of the total heat transfer and inunderfloor cooling the convective component is lessthan 10%.

Sample - Mechanical Schematic Representation
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Illustrated is asimplifiedmechanicalschematic ofan underfloorheating andcooling systemfor thermalcomfort qualitywith a

separate airhandlingsystem forindoor airquality. In highperformanceresidentialhomes of

moderate size(e.g. under

3000 ft2 (278 m2) total conditioned floor area), thissystem using manufactured hydronic controlappliances would take up about the same space as athree or four piece bathroom.

Structural Insulated Panels

Structural insulated panels, SIPs, are a compositebuilding material. They consist of an insulating layerof rigid polymer foam sandwiched between twolayers of structural board. The board can be sheetmetal, plywood, cement or oriented strand board
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(OSB) and the foam either expanded polystyrenefoam (EPS), extruded polystyrene foam (XPS) orpolyurethane foam.

SIPs share the same structural properties as an I-beam or I-column. The rigid insulation core of the SIPacts as a web, while the OSB sheathing exhibits thesame properties as the flanges. SIPs combine severalcomponents of conventional building, such as studsand joists, insulation, vapor barrier and air barrier.They can be used for many different applications,such as exterior wall, roof, floor and foundation

systems.

Materials

SIPs are most commonly made of OSB panelssandwiched around a foam core made of expandedpolystyrene (EPS), extruded polystyrene (XPS) orrigid polyurethane foam, but other materials can be
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used, such as plywood, pressure-treated plywood forbelow-grade foundation walls, steel, aluminum,cement board such as Hardibacker, and even exoticmaterials like stainless steel, fiber-reinforced plastic,

and magnesium oxide. Some SIPs use fiber-cementor plywood sheets for the panels, and agriculturalfiber, such as wheat straw, for the core.

The third component in SIPs is the spline orconnector piece between SIP panels. Dimensional
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lumber is commonly used but creates thermalbridging and lowers insulation values. To maintainhigher insulation values through the splinemanufacturers use Insulated Lumber, Composite

Splines, Mechanical Locks, Overlapping OSB Panels,or other creative methods. Depending on the methodselected other advantages such as full nailingsurfaces or increased structural strength maybecome available.

Slab Energy Loss

Even if the foundation walls under the slab areinsulated, that will not helpmuch if the slab edge close tothe outside air isnt alsoinsulated.

Slab Insulation

Slab insulation uses a rigid insulation material:

typically foam boards. The installation is easy: justapply the right product with the right r-value underthe face of the slab.

As the figures show, a well done slab insulation alsocomprises perimeter insulation, that is, insulation ofthe slab edge closer to the outside air.

Slab Insulation Depth and R-values


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The depth and the R-value recommended wheninsulating a slab varies with climate zones. Moreexactly they vary with the Heating Degree Days(HDD) of your particular climate zone. The HDD is an

index reflecting the energy needs to heat or cool ahome.

If your climate zone has a HDD of zero that meansthat you do not need to insulate your slab. Thathappens whenever the difference between 65F/18Cand the average outside temperature is very close tozero during the whole year (outside 65F/18C - the

base temperature - is the temperature thattechnicians consider the ideal to get a comfortableindoor temperature; with that outside temperature,the occupants and the home appliances will addmore heat to indoor home temperatures, makingthem comfortable).

The higher the difference between the outsidetemperature and the 65F/18C, the higher the HDD

and the needs of insulation; the higher the number ofdays with a high HDD, the higher the needs ofinsulation.

The table below shows recommended R-values andslab insulation depth by the official EnergyConservation Code Council (IECC) .

Recommended R-Values andDepth for Slab InsulationHeatingDegreeDays(HDD)

Feet/cmInstalledVertically R-Value
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0 to 2,499nonerequired none required

2,499 to4,500

2 feet/6cm R-4

4,500 to6,000

4feet/12cm R-5

6,000 to7,200

4feet/12cm R-6

7,200 to

8,700

4feet/12

cm R-7

8,700 to10,000

4feet/12cm R-8

10,000 to12,400

4feet/12cm R-9

12,400 to14,000

4

feet/12cm R-10

Insulation of the Outside or the InsideFoundation Wall

The insulation may be applied outside or inside thefoundation wall. You should also apply a good finish

protection (metal flashing, is a common option) anda protective termite shield (also advisable in theinsulation involving the inside foundation wall).


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Insulation Slab Techniques

Slab insulation can be installed using foam boardrigid insulation directly against the footing and theexterior of the slab, as shown in the imagesabove.Alternatively, when building the slab you can

also build "contained/"floating" slab with interiorinsulation. The material is typically the same: boardrigid insulation.

Photovoltaic Array

A photovoltaic array (also called a solar array) isa linked collection ofphotovoltaic modules, which arein turn made of multiple interconnected solar cells.

The cells convert solar energy into direct currentelectricity via the photovoltaic effect. The power thatone module can produce is seldom enough to meetrequirements of a home or a business, so themodules are linked together to form an array. MostPV arrays use an inverter to convert the DC powerproduced by the modules into alternating currentthat can plug into the existing infrastructure to power

lights, motors, and other loads. The modules in a PVarray are usually first connected in series to obtainthe desired voltage; the individual strings are thenconnected in parallel to allow the system to producemore current. Solar arrays are typically measured by
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the peak electrical power they produce, in watts,kilowatts, or even megawatts.

A photovoltaic array is a linked system of

photovoltaic (PV) modules. The solar cells in the PVmodules convert sunlight into electricity by bouncingthe sun's photons off of silicon solar cells whichproduce current through the photoelectric effect.Most PV systems utilize an "inverter" to convert DCpower produced by the modules to alternatingcurrent (AC) that can be used to power appliances.

The solar cells are usually connected in series on thepanel to achieve the desired voltage. Each individualstring thereafter is connected in parallel to producemore current.

Tracking systems and sensors are also placed onmany solar arrays to increase the output. In somecases the increase in viable output has been up to100%. Large scale photovoltaic arrays producing

more than 1MW of electricity use solar trackers tooptimize the amount of sunlight it collects.

Solar collectors are another way to optimize thesunlight reaching the PV array. Solar collectorsconcentrate sunlight through the use of mirrors andreflective surfaces in a cost efficient way to increasethe output in PV arrays.

Uninsulated slabs are a cause of heating losses anduncomfortable floors and energy-inefficiency.
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Heat

Pumps

Air-source heat pumps (ASHP) can be thought of asreversible air conditioners. Like an air conditioner, anASHP can take heat from a relatively cool space (e.g.

a house at 70F) and dump it into a hot place (e.g.outside at 85F). However, unlike an air conditioner,the condenser and evaporator of an ASHP can switchroles and absorb heat from the cool outside air anddump it into a warm house.

Air-source heat pumps are inexpensive relative toother heat pump systems. However, the efficiency ofair-source heat pumps decline when the outdoor

temperature is very cold or very hot; therefore, theyare only really applicable in temperate climates.

For areas not located in temperate climates, ground-source (or geothermal) heat pumps provide anefficient alternative. The difference between the two


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heat pumps is that the ground-source has one of itsheat exchangers placed undergroundusually in ahorizontal or vertical arrangement. Ground-sourcetakes advantage of the relatively constant, mild

temperatures underground, which means theirefficiencies can be much greater than that of an air-source heat pump. The in-ground heat exchangergenerally needs a considerable amount of area.Designers have placed them in an open area next tothe building or underneath a parking lot.

In terms of initial cost, the ground-source heat pump

system costs about twice as much as a standard air-source heat pump to be installed. However, the up-front costs can be more than offset by the decreasein energy costs. The reduction in energy costs isespecially apparent in areas with typically hotsummers and cold winters.

Other types of heat pumps are water-source and air-earth. If the building is located near a body of water,

the pond or lake could be used as a heat source orsink. Air-earth heat pumps circulate the buildings airthrough underground ducts. With higher fan powerrequirements and inefficient heat transfer, Air-earthheat pumps are generally not practical for majorconstruction


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North Walls

In an east-west oriented building, a north facingexterior wall will receive little sunlight during thewinter and this will be a major source of heat losssince heat always moves toward cold. Additionally,building shading of north side open space usuallyrenders it unusable for outdoor use. To alleviatethese situations the building should be shaped sothat the roof slopes downward from the south to thenorth wall. This reduces the height of the north faceof the building and therefore the area through which


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heat is lost. This also allows sunlight to reach morearea of north side outdoor spaces. Variations ofreducing heat loss conditions manifest in north wallsinclude backing the building into a sloped hillside or

providing a berm, both of which reduce the exposednorth area.

South to north downward sloping roofreduces heat loss from the north wall andallows sunlight to reach north side openspace.

Clerestories and Skylights

Many conditions make south wall heat collection fordirect gain problematic, but it can be easily mitigatedby the use of clerestories or skylights. Both of thesefeatures admit sunlight at the roof structure of abuilding and can be used to direct sunlight to aspecific interior surface. They can also be used incombination with or as a supplement to a south

facing glazed wall. Additionally, they provide fornatural light applications, which can reduce the needand cost of artificial lighting.

Clerestories are vertical south facing windowslocated at roof level ,Their advantages are that they


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allow diffuse lighting into a room; they provideprivacy; and they can be placed almost anywhere ona roof. In a compartmentalized building layout, eachroom can have its own source of heat and light. They

should be located at a distance from a thermalstorage wall that allows direct sunlight to hit the wallthroughout the winter. This distance is roughly 1.5times the height of the wall. Ceilings in roomscontaining clerestories should be light in color toreflect or diffuse sunlight into the living space. Largeinterior spaces may have multiple clerestoriesarranged to allow maximum admission of sunlight.

Care must be taken that they do not shade eachother, so the clerestorey roof angle (from horizontal)of each clerestorey should be roughly the sameangle of the sun at its lowest winter point (noon onDecember 21). Skylights are simply openings in aroof, which admit sunlight -they are either horizontal(a flat roof) or pitched at the same angle as the roofslope. In most cases. horizontal skylights are used

with reflectors to increase the intensity of solarradiation (remember the angle of incidence). Largeskylights should be provided with shading devices toprevent heat loss at night and heat gain during thesummer months


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Clerestory -clerestories can beused to provide

sunshine onto interiorwalls which wouldnormally not have aclear view of wintersunlight.

. Skylights provide analternative for directsolar gain, shadingdevices must be

included as an integralpart of the skylight toprevent overheatingthe space during mildperiods.

Attached Green HousesAn indirect gain heating system, using a green housestructure as a heat collector, is multi-purpose,practical and efficient. It also requires the mostrigorous design because of its multiple nature, whichaffects sizing for space heating, creating idealconditions for greenhouse conditions, and accuratelypredicting performance for both. The attachment of agreenhouse to the south side of a building enablesthe structure to benefit from the normal, heatcollecting greenhouse operation. The greenhousecollects heat due to its solar exposure. This heat canbe conducted through a thermal storage wallseparating house and greenhouse, or can beconvected to the interior space of the building. In thisway the greenhouse serves both as a heat collector,

and a solarium for people and plants. Generally, incold climates, a greenhouse design would usebetween 0.65 and 1.5 square feet of south facingdouble glass greenhouse collecting surface for eachsquare foot of floor area in the adjacent living space.In more moderate climates this can be reduced to


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0.33 and 0.9 square feet. This should provide enoughheat to keep the average temperature in theadjacent space between 60F and 70F.

It is desirable for a solar greenhouse structure to berecessed into the south facade of the building,thereby minimizing east and west exposures, whichhave little effect on heat collection but can be a

great source of heat loss. Furthermore, heat transferthrough the common wall between the greenhouseand the living space is increased in this configurationGreenhouses for heating purposes can be added toframe buildings to provide for direct heat duringwinter days, but such buildings, without thermalstorage mass, do not have the ability nor capacity tostore heat for use at night. Some designs integrating

greenhouses, adjust for nighttime heating by transferof all greenhouse heat to main building storage mass(floors, walls, etc.) for deferred use at night. This onlyworks in moderately cold climates, because very coldclimates require the residual heat collected by the


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greenhouse to keep it, and its contents, fromfreezing at night.

The common wall between the greenhouse and the

building interior can be constructed of thermal massmaterials (masonry, water, etc.). The greenhouseside of common walls should be dark in color (betterabsorber) and should receive maximum sunlightthroughout the day. Wall vents and/or operablewindows can be used to allow heated air directly intothe interior space during the daytime.

Wall thickness should be same as that provided for inan indirect gain (Trombe) wall. If water is used, itsminimum thickness should be 8 inches (or 0.67 cubicfeet for each square foot of south-facing glass).

Masonry walls cannot absorb and transfer heat asfast as a greenhouse can collect it. As a result,temperatures in the greenhouse will fluctuate asmuch as 60F on a clear day. To dampen (level out)

these fluctuations, extra storage mass (such asmasonry units or containers filled with water) can beplaced in the greenhouse. These act as an interiorheat dampening water wall (1 cubic foot of water foreach square foot of south facing glass will reducetemperature fluctuations 25F to 29F).

If water is used as the common wall between the

greenhouse and the living space, temperaturefluctuations will be smaller, and if more than the 0.67cubic feet of water for each square foot of glass isused in the wall, temperature fluctuations will befurther reduced.


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In cold climates, it may be advantageous to utilize aheat storage, in the form of a rock bin, under thebuilding or living space, which would act as thermalstorage of heat collected during the day. Heat

transfer can occur by natural convection if thebuilding is terraced up a slope, or by use of a fan,which would transfer heat to a rock bed located in acrawl space under the floor of the structure The rockbed should spread across 75 to 100% of the floorarea of the structure in cold climates, and 50 to 75%of the floor area in moderate climates. Heat from thegreenhouse should be directed over the rock bed and

a means of returning cold airfrom the bottom of the rockbed to the greenhouseshould be provided. If aterraced design is used,colder air will naturally settledue to the convective loop cycle. About 1.5 to 3cubic feet of fist-sized rock is necessary in cold

climates and .5 to 1 cubic feet in temperate climates.Rock bin storage has also been used as a part of acooling system in warmer climes.


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By extending theend walls of anattachedgreenhouse, loss to

the outside isreduced while theheat gains to thespace are incresed.

Small fans (less than0.25 H.P.) can be usedto aid in the transfer of

heat from collectionspace to more remoteparts of the structure.

Roof Ponds

Roof ponds can be used both for heating during the

winter months and for cooling during the summermonths. For latitudes higher that 36 north, roofponds require greater solar gain exposure as well asgreater protection from loss of gained heat.

The system is simple in concept. The roof pondapproach brings the differing building aspects of abuilding - roof, ceiling, heating (and cooling) system,and heat distribution (does away with ducts) into one

system. The roof ponds of contained water are theheating (and cooling) unit. The roof/ceilings of thebuilding act as the structural support for the roofponds; the "radiator" device for evenly distributedheating of the spaces below; and as a waterproofroof system providing protection from the elements.


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The movable insulation above the ponds is theweather protection, heating/cooling system"manager" and additional protection from theelements. Wintertime heating is comprised of

daytime opening the insulating roof layer to allowsolar radiation to heat the water beds; water bedwarming heats the supporting structure which is alsothe ceiling for spaces below; heated supportstructure radiates heat to the space. At night theinsulated roof panels close to contain heat gatheredby the ponds to continue heating the spaces below.

The sun in northern latitudes is at a lower angle withsolar radiation traveling through a greater mass ofatmosphere, which reduces its energy content byscattering and reflection. In this situation, increasedarea of exposure or use of solar reflection can beused to increase roof pond effectiveness.Additionally, in colder climates, the roof pond systembenefits from insulating covers to prevent nighttime

losses. The most beneficial insulation system is onethat is multi-purpose and movable, operating onlytwice a day to 1) expose the ponds for heatcollection, and 2) to cover the ponds to prevent heatloss at night. This insulation system is also beneficialin the summer when the roof ponds must beinsulated to prevent summer heat gain. The movableinsulation structure can operate in a number of ways- rolling, hinged, etc.. In climates where snow islikely, ponds can be placed in a solar attic below thesloping roof with south facing glazing to allow solargain, and the attic ceiling can be painted o areflective color or sheathed with a reflective material.To increase system performance, glazing for cold


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climate solar ponds can be dual pane, or the pondscan contain an upper layer inflated air cell.

It is important to provide a waterproof layer

(membrane, etc.) at the pond support system surfaceto provide protections during draining of water formaintenance, and from water bed material failureand/or weather impacts. The capability to drain theponds in an easy and non-damaging manner isimportant. The water should be enclosed in ultra-violet light inhibiting (prevents degradation) plasticbags, waterproof structural metal or fiberglass tanks

which form the ceiling below. The top of the watercontainment system must be transparent and thesides/bottom a dark color. Insulation panels shouldbe constructed so that they can be tightly sealedwhen closed to prevent infiltration heat loss. In someapplications insulating panels can also serve asreflectors when open in order to direct more solar tothe ponds.


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uninsulated ceiling can result in condensation anddrippage, so effective water barriers and insulationare critical.

COMPONENTS OF AN ENERGY EFFICIENT BUILDING

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