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Abstract:

Solar Energy for Buildings presents basic information on solarbuilding design, which includes passive solar heating, ventilationair heating, solar domestic water heating and shading. The articlesuggests ways to incorporate solar design into multi-unit residentialbuildings, and provides calculations and examples to show howearly design decisions can increase the useable solar energy.

This Introduction to Solar Design Issues, presents basic notions ofsolar design and describes different passive, active and hybridsystems and the solar aspects of design elements, which includewindow design, cooling and control, and water heating.

Upon reading this article, the reader will understand:

1. The benefits of solar energy in building design.

2. The difference between passive, active and hybrid solar technologies.

3. The design opportunities available for multi-unit residentialbuildings (MURB).

THE PRINCIPLES OF

SOLAR DESIGN

Benefits of solar energy

For both new and retrofit projects,solar energy can substantiallyenhance building design.

Solar energy offers these advantagesover conventional energy:

� Free after recovering upfront

capital costs. Payback time can

be relatively short.

� Available everywhere and

inexhaustible.

� Clean, reducing demand for fossil

fuels and hydroelectricity, and

their environmental drawbacks.

� Can be building-integrated,

which can reduce energy

distribution needs.

Solar Energy forBuildingsIntroduction: Solar Design Issues

By Keith Robertson and Andreas Athienitis

Solar Energy for Bui ld ings

2 Canada Mortgage and Housing Corporation

The amount of energy that reaches earth’supper atmosphere is about 1,350 W/m2—the solar constant. The atmosphere reflects,scatters and absorbs some of the energy. InCanada, peak solar intensity varies fromabout 900 W/m2 to 1,050 W/m2,depending on sky conditions. Peak solarintensity is at solar noon, when the sun isdue south.

Energy from the sun reaches earth as direct,reflected and diffuse radiation.

Direct radiation is highest on a surfaceperpendicular to the sun’s rays (angle ofincidence equal to 0 degrees) and providesthe most usable heat.

Diffuse radiation is energy from the sunthat is scattered within the atmosphere byclouds, dust or pollution and becomesnon-directional. On a cloudy day, 100 percent of the energy may be diffuse radiation;on a sunny day, less than 20 per cent maybe diffuse.

The amount of the sun’s energy reachingthe surface of the earth also depends oncloud cover, air pollution, location and thetime of year. Figure 1 shows the solarenergy available in five Canadian cities atdifferent times of the year.

The amount of solar energy reaching atilted collector significantly changes theresult. Figure 2 shows the amount of solarenergy received by a horizontal collector,such as window, for a passive solar design.Note that even Yellowknife receives asignificant amount during part of theheating season.

Passive, active and hybrid solar

Solar buildings work on three principles:collection, storage and distribution of thesun’s energy.

A passive solar building makes the greatestuse possible of solar gains to reduce energyuse for heating and, possibly, cooling. Byusing natural energy flows through air andmaterials—radiation, conduction,absorptance and natural convection.

A passive building emphasizes passiveenergy flows in heating and cooling. It canoptimize solar heat gain in direct heat gainsystems, in which windows are thecollectors and interior materials are theheat storage media.

The principle can also be applied to wateror air solar heaters that use naturalconvection to thermosiphon for heatstorage without pumps or fans.

An active solar system uses mechanicalequipment to collect, store and distributethe sun's heat. Active systems consist ofsolar collectors, a storage medium and adistribution system. Active solar systemsare commonly used for:

� Water heating;

� Space conditioning;

� Producing electricity;

� Process heat; and

� Solar mechanical energy.

Hybrid power systems combine two or moreenergy systems or fuels that, when integrated,overcome limitations of the other, such asphotovoltaic panels to supplement grid-supplied or diesel-generated electricity.

Hybrid systems are the most common, exceptfor the direct gain system, which is passive.

S o la r E n e r g y o n a V e r t ic a l P la n e

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Source: RETScreen1

Figure 1 – kWh/m2/day on a ver tical surface, for selected Canadian cities

1 RETScreen is free energy assessment software that assesses renewable energy options against a base building model. Software modules are available at

http://www.retscreen.net/ang/menu.php

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Glossary

Absorptance—The ratio of absorbed toincident radiation.

Active solar—A solar heating or coolingsystem that operates by mechanical meanssuch as motors, pumps or valves to sortand distribute the sun's heat to a buidling.

Energy rating (ER)—A rating system thatcompares window products for theirheating season efficiency under averagewinter conditions.

Evacuated tube collectors—Solarcollectors that use individual, sealedvacuum tubes surrounding a metalabsorber plate.

Flat-plate collectors—The most commontype of solar collector. Can be glazed orunglazed.

Hybrid power systems—Combines activeand passive solar power systems or involvesmore than one fuel type for the same device.

Latent Heat—Also called heat oftransformation. Heat energy absorbed orreleased by a material that is changing state,such as ice to water or water to steam, atconstant temperature and pressure.

Low-emissivity (low-e)—Coatings appliedto window glass to reduce inside heat losswithout reducing outside solar gain.

Passive solar—A solar heating or coolingsystem that operates by using gravity, heatflow or evaporation to collect and transfersolar energy.

Photovoltaic (PV) system—System thatonverts sunlight into electricity. Can beautonomous or used with another energysource. (Can be connected to the mainpower grid, for example).

R-value (imperial), RSI-value (metric)—A measure of resistance to heat flowthrough a material or assembly—anumerical inverse of the U-value.

Solar balcony—An enclosed balcony thatacts as a solar collector.

Solar constant—1,350 W/m2 —Theaverage amount of solar energy reachingthe earth’s upper atmosphere.

Solar Domestic Hot Water (SDHW)—Asupplement to traditional domestic hotwater heating. The most common systemuses glazed, flat-plate collectors in a closedglycol loop.

Solar Heat Gain Coefficient (SHGC)—Equal to the amount of solar gain througha window, divided by the total amount ofsolar energy incident to its outside surface.

Solar south—180 degrees from true orgrid (not magnetic) north.

Solarwall®—A proprietary system thatuses perforated metal panels to pre-heatventilation air.

Switchable glazing—Glazing materialsthat can vary their optical or solarproperties according to light (photochromic),heat (thermochromic) or electric current(electrochromic).

Thermosiphon solar collector —A systemin which the circulation of hot water in theloop is based only on buoyancy.

U-value—A measure of heat flow througha material or assembly. Measured inWatts/m2/°C.

Warm-edge spacers—Separate a window'sglazing layers with thermal break or a low-conductivity material.


Canada Mortgage and Housing Corporation

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Figure 2 – kWh/m2/day on a south-facing horizontal surface, for five Canadian cities

Source: RETScreen

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Building design issues

Careful solar design can:

� Maximize possible solar transmission andabsorption in winter to minimize or reduceto zero the heating energy consumption,while preventing overheating.

� Use received solar gains forinstantaneous heating load and storethe remainder in embodied thermalmass or specially built storage devices.

� Reduce heat losses using insulation andwindows with high solar heat gain factors.

� Employ shading control devices orstrategically planted deciduous trees toexclude summer solar gains that createadditional cooling load.

� Employ natural ventilation to transferheat from hot zones to cool zones inwinter and for natural cooling in thesummer; use ground-source coolingand heating to transfer heat to andfrom the underground, which is moreor less at a constant temperature, andutilize evaporative cooling.

� Integrate building envelope devicessuch as windows, which includephotovoltaic panels as shading devices,or roofs with photovoltaic shingles;their dual role in producing electricityand excluding thermal gain increasestheir cost-effectiveness.

� Use solar radiation for daylighting,2

which requires effective distributioninto rooms or onto work planes, whileavoiding glare.

� Integrate passive solar systems withactive heating–cooling/air-conditioningsystems in both design and operation.

What is design

integration?

The most important factor for a successfulsolar building is “integration.” Thisconcept includes not only the integrationof design professionals at the project’s start,but also the integration of those who areresponsible for the systems operation. Thispotential for synergy is usually overlookedbecause architects and engineerstraditionally do not explore the conceptstogether closely enough to truly integratesystems, and they infrequently discuss newconcepts with property managers, exceptwhen auditing a building failure.

The architect may design the buildingenvelope to passive solar design principleswhile the engineer designs HVAC toextreme design conditions, ignoring thebenefits of solar gains and natural cooling.The result is an oversized system that does

not use the building enclosure as part of an integrated energy system in which the components fit together well.Collaboration between architects andengineers is increasing, but the traditionalworking relationships between architects,engineers, property managers and otherprofessionals do not foster an integrateddesign approach.3

A preferable approach is to consider thebuilding and its HVAC system as oneenergy system and to design them together,taking into account possible synergies suchas electricity generation, thermal storageand control strategies.

Passive solar heating systems (thermal) areseparated into two broad categories, directgain and indirect gain (see Figure 3). Anindirect passive system insulated from theheated space is an isolated system.

Solar Facade

DirectGain

Collector-storageWall



2 See Daylighting Guide for Buildings at: http://www.cmhc.ca/en/inpr/bude/himu/coedar/coedar_001.cfm3 See Integrated Design Process Guide at: http://www.cmhc.ca/en/inpr/bude/himu/coedar/coedar_002.cfm

Figure 3 – Two major options for thermal mass placement in passive solar

design: direct gain and Trombe wall, or collector-storage wall

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Depending on climate and buildingfunction, certain heating/cooling systemsare more compatible with passive systems.For example, the thermal mass in a floormay store passive solar gains and act as afloor-heating system. This is a controlchallenge that must be carefully planned ifit is to achieve acceptable thermal comfortfor the occupants.

The key aspects of passive solar design areinterlinked, dependent design parameters:

� Location and orientation of a building;

� Fenestration area, orientation and type;

� Thermal massing and envelopecaracteristics;

� Amount of insulation;

� Shading devices—type, location and area;

� Effective thermal storage insulated fromthe exterior environment, as well asamount and type;

� sensible—such as concrete in thebuilding envelope with exteriorinsulation, or

� latent such as phase-changematerials.

The ultimate objective of design integrationis to minimize energy costs whilemaintaining interior comfort. A largerthermal mass within a building can delayits response to heat sources such as solargains—the thermal lag effect. This thermallag can avoid comfort problems if takeninto account in selecting the thermal mass,choosing appropriate control strategies and sizing the heating–cooling system.



Figure 4 – Sixteen of the 42 units in this apar tment building in Amstelveen, the Nether lands, take advantage of solar

energy from the atrium as an air pre-heating system. Solar domestic hot water panels provide about half the building’s

domestic hot water energy.

Source: CMHC, at http://www.cmhc-schl.gc.ca/en/imquaf/himu/buin_018.cfm

Design procedure

The initial design steps in solar design are to:

1. Set performance targets for energysources and uses.

2. Minimize heating and cooling loadsthrough orientation, massing, envelopeand landscape design.

3. Maximize solar and other renewableenergy to meet the building load, thento design efficient HVAC systems that are integrated with the buildingenvelope performance characteristics.

4. Use simple energy simulation tools anddetailed simulations in evaluatingoptions at the early design stages andlater to assess alternatives.

Building orientation

Orientation is crucial since it can providefree savings from the concept stage. Thereis a difference between true north andmagnetic north. The deviation betweenmagnetic north and true north—magneticdeclination—varies between east and westcoasts. In Nova Scotia, the compass points west of true north; in B.C., east of true north.

The maximum difference (as a percentage)between south-facing and 30ºE (or W)orientations occurs when the sun is lowestand the days shortest (Dec. 21). When solarfacades or roofs generate photovoltaicelectricity that is sold to the grid at time-of-day rates, these rates may change theoptimal orientation if their peak value isnot at noon.

Further information about magneticdeviation and a calculation routine isavailable at

http://www.geolab.nrcan.gc.ca/geomag/magdec_e.shtml

Generally, buildings with long axes runningeast and west have greater solar-heatingpotential if their window characteristics arechosen accodingly. For MURBs with atypical double-loaded corridor, this meanshalf the units face south and half facenorth. A partial solution could be a south-facing central atrium or solar heaterthat pre-heats and delivers air for thenorth-facing units.

Buildings with east-and west-facingorientations have greater potential foroverheating in the non-heating season andget little solar gain in winter. In figure 5 theFoyer hongrois in Montréal angles thewindows to the south creating a sawtoothplan, to avoid east-and west-facingwindows.



Generally, deviations up to ±30ºfrom due south reduce solar gainsby up to about 12% and are thusacceptable in solar building design,providing significant freedom inchoice of form.

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Building Conditions

NRC’s EE4 software4 was used to modelthe energy use of a Halifax MURB, andshowed modest energy reductions fromorientation, window performance and

window size. The advantage of energyreductions due to orientation is that theyare free, and the savings continue for thelife-time of the building. Note also thatthese energy simulation results are specificto a particular location. The MURB hadthe following characteristics:

� Four-storey, double-loaded corridor,wood-frame.

� Window-to-wall ratio: 19 per cent onprimary facades.

� Double-glazed, low-e vinyl windows.

� High insulation levels.

Simulation Results

� Using a higher Solar Heat GainCoefficient (SHGC) glazing reducedthe total annual heating cost by threeto four per cent.

� Orienting the building along the longeast–west axis instead of north–southaxis reduced annual heating cost byabout one per cent.

� Increasing the window area on thesouth-facing suites reduced annualheating cost by less than one per cent.

� Increasing the interior mass reducedannual heating cost by about two percent.

Although differences in assumptions andinput data make comparisons difficult, astudy of a Toronto building produceddifferent results. RETScreen’s passive solarenergy module was used for the Torontobuilding. The RetScreen model of a 110 m2

(1,184 sq. ft.), south-facing suite inToronto with 7.2 m2 (75 sq. ft.) of windows(similar to the suites in Halifax) gave thefollowing results. (Increases in cooling loadwere not calculated, as this was assumed tobe an unconditioned building.):

� Increasing the glass Solar Heat GainCoefficient (SHGC) from .45 to .65saved 1,100 to 1,200 kWh annually.

� Doubling window area and increasingthe SHGC gave a slight annual energyloss in a low-mass (wood-frame)building and a slight saving in a high-mass (concrete-frame) building.

� Increasing the glass R-value andmaintaining a high SHGC saved about900 kWh annually.

� The best results came from increasingthe R-value, increasing the mass,increasing the window area, andmaintaining a high SHGC.

These results are expected from basic solardesign principles. Increasing the resistanceof windows to thermal loss (low-e glazing)while admitting high solar gains reducesheating energy consumption if the buildingis well insulated and there is enough thermalmass to store the solar gains and preventoverheating. Obviously, the thermalperformance of windows cannot beseparated from solar gains, which relate toform, orientation and solar transmittance.Optimizing requires rigorous energymodelling and project-specific analysis.



Figure 5 – Foyer hongrois in Montréal. South angled windows on a building with a

long nor th-south axis. Sunshades shadow these windows in the summer time.

4 EE4 is the software developed for NRCan’s Commercial Building Incentive Program to check for compliance to its program requirements.

More details on the design of windows andglazing selection are presented in Selectionand Commissioning of Window Installations5

The analytical tool selected depends on the detail required. For basic energy flows,an analysis based on solar heat gaincoefficients and thermal conductanceprovides an approximate estimate of thenet energy transfer across the buildingenvelope. The calculations can beperformed in MathCAD, Matlab or aspreadsheet-based program such asRETScreen.

To determine room-temperature swingsand associated thermal mass response,more detailed simulation tools are needed.However, even for the calculation oftemperature swings and the effectiveness of thermal mass, simplified models existwhich are based on thermal admittancecalculations.6 “Thermal admittance” isessentially a dynamic U-value and istypically calculated for a daily cycle. (It is

approximately equal to the amplitude of thecyclic heat flow into the mass divided by itssurface temperature amplitude or swing.)

A good design strategy for buildingorientation is to “tune” windows to admitor exclude solar energy based on theirorientation. Generally, south-facingwindows should admit winter solar gainand east- and west-facing windows shouldexclude low-angle solar gain. Windowdesign strategies are discussed in moredetail later.

Another approach is control of solar gainswith motorized blinds, which are widelyused in airports, atriums and somecommercial buildings in Europe. Alongwith other control technologies, such aselectrochromic coatings, motorized blindsmay soon become cost-effective. If activesolar control is taken into account in sizingcooling systems, there may be significantsavings from reduced energy consumptionand reduced equipment sizing.

Obstructions to sunlight

Obstructions can have a significant effecton solar potential. For low- to mid-risebuildings, obstructions are usuallybuildings, terrain or trees. For largerbuildings, obstructions are usually otherlarge buildings.

Obstructions can be identified on the sunpath chart in figure 8. East and westobstructions can reduce solar gain in thesummer and admit energy in the winter,when the sun rises in the southeast and setsin the southwest.



5 See http://www.cmhc.ca/en/inpr/bude/himu/coedav/upload/Article_Design_Aug31.pdf6 Athienitis A.K. and Santamouris M., 2002. Thermal analysis and design of passive solar buildings, James and James, London U.K..

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Direct-gain passive solartechniques

Pure passive solar design uses the sun’senergy directly, without mechanicalintervention. In its simplest form, the sunshining through a window directly heatsthe space. Thermal mass within thebuilding can absorb some of the heat and release it at night.

Internal thermal mass reduces temperatureswings within a space. In a properlydesigned passive solar system, thermal mass absorbs solar energy during the day,preventing the building from overheating,and releases the energy at night. Thermalmass is most effective when it can gainenergy directly from the sun. An idealthermal mass for passive solar heating hashigh heat capacity, moderate conductance,moderate density and high emissivity.Additional cost is negligible if the materialis also structural or decorative. Concreteand masonry are good thermal massmaterials. (Plaster, drywall, and tile are alsouseful in this respect, but calculations areneeded to determine if they have sufficientmass, as was done in the Halifax study.)

Passive solar design in single-familyresidences shows that operational energycan be reduced by 30 to 50 per centthrough window sizing and thermal massstorage. A recent study of MURBs inSweden reported that operational energyuse in a heavy structure is only slightlylower than in a similar, lightweightstructure.7 The additional energy used tobuild the heavy structure outweighed itsoperational advantage in a lifecycle analysisof costs.

Mass is known to be able to reduce peakcooling load when night temperatures arecooler than day temperatures. Exterior andinterior masses cool down at night andreduce peak cooling demand while alsodelaying the time of the peak solar gainduring the day. However, the effectivenessof thermal mass is proportional to theallowable room temperature variation overa day.

Windows

Window orientation, layout andperformance are important in passive solardesign. The goal is to provide anappropriate amount of window area in theright place. Where there is no fenestration,a conventional insulated wall is a solarbarrier, transmitting little energy to theinside.

Window sizing

There are two ways to quantify a building'ssouth-facing glass.

It can be calculated as a percentage of thetotal area of the south-facing exteriorwall—of limited use because it is notaffected by what goes on beyond thewall—or as a percentage of heated floorarea—which accounts for the volume ofthe building.

A typical passive solar-heated building mayhave south-facing glazing equal to 10 to 15per cent of the heated floor area. As thearea of south glass increases, the amount of mass inside must also increase. TheAdvanced Buildings Technologies andPractices website, athttp://www.advancedbuildings.org,recommends a window-to-exterior wallarea ratio (WWR) of 25 to 35 per cent,similar to a typical MURB.

WWR may increase with proper control ofsolar gains (for example, with motorizedshading) and transfer of excess energy tonorth-facing zones. This could possiblyapproach 50 per cent when a large atriumis included with adequate thermal storage



Figure 6 – Effect of internal mass on internal temperature swings

7 Stahl, Fredrik, The effect of thermal mass on the energy during the life cycle of a building, presented at Building Physics 2—6th Nordic Symposium

Outdoor temperature

Light timber-framed building

Heavy building with external insulation

Heavy building set into andpartially covered with earth

Time of dayA

ir t

emper

ature

capacity. Utilization of double facades withblinds in the cavity, or exterior controlledshading reduces cooling loads during summer.(Figure 4 – Urban Villa, Amstelveen)8

Glazing

This section describes some the mostimportant parameters of window andglazing design.

Solar heat gain coefficient (SHGC)

The Solar Heat Gain Coefficient (SHGC) isa useful measure of a window's ability toadmit solar energy. SHGC is the amountof solar gain a window allows, divided bythe amount of solar energy available at itsoutside surface, a number between zero(solid wall) and one (open window).

SHGC can be measured for the windowunit, including the frame, or the glazedarea. The higher the SHGC, the better thewindow will perform as a solar collector. Ifoverheating is a concern, low-SHGCwindows exclude solar energy to reducecooling loads.

A single pane of clear glass facing the sunwill admit most of the visible solar radiation,some of the infrared and very little ultravioletand have the highest heat loss from insideto outside. Ways to modify windows toenhance their performance include:

� Adding a second or third layer of glass,which can dramatically lower the U-value (increase the R-value), whilemaintaining a large SHGC. Additionallayers of glass also permit thin, low-emissivity (low-e) coatings to beapplied onto a protected glass surface.Low-e coatings still allow solar gain(short wavelength radiation) and they

help retain heat by reducing longwave(infrared) radiation losses. This is veryhelpful from a passive solar heatingpoint of view.

� There are reflective coatings that blockunwanted solar gain (reduce the SHGC)to reduce the cooling load. There are manytypes of spectrally selective glazings thatblock out selective wavelengths that canchange the SHGC and levels of visiblelight transmittance.

� Evacuating the space between thepanes, using an inert gas such as argonor krypton, or transparent insulation,can reduce heat loss by conduction andconvection. Because gas-fills performwell and are low cost, they should beused whenever a low-e coating is usedin a glazing unit.

High-performance windows may make itpossible to move heating outlets further fromwindows to eliminate ducting or piping.

A recent glazing development is switchableglazing. These can vary their optical or solarproperties according to light (photochromic),heat (thermochromic) or electric current(electrochromic). Initial computer simulationsshow that electro chromic glazing has themost promise for improving comfort. Theseare prototype systems. They will likely beable to reduce cooling loads and glare andimprove visual comfort if high solartransmittance is not needed. Switchableglazings may have poorer optical propertiesand not be suitable in residential buildings.

Visible light transmittance

Visible light transmittance (VT) measuresthe visible spectrum admitted by a window.Typical daylight strategies require windowswith a high VT. A low SGHC is also desirablewhere heat gain is a concern. Reflectiveglass is not recommended for daylighting.

Table 1 shows typical values for lighttransmittance and SHGC of commonglazing systems.



Figure 7 – Double-glazed, low-e window

8 See Innovative Buildings Case Studies — “Atrium, Solar shading and ventilation for residents’ confort”, Amstelveen :

http://www.cmhc.ca/en/inpr/bude/himu/inbu_001.cfm#CP_JUMP_58686

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Frames

Frames are often the weakest thermal partof a window. Although frames (sash andmullion assemblies) are only 10 to 25 per cent of window area in commercialbuildings, they can account for up to halfthe window heat loss and be the prime sitefor condensation.9

Thermal performance of frames is improvedeither by using a low-conductivity thermalbreak in metal frames or a frame of a low-conductivity material, such as wood, vinylor fibreglass. Low-conductivity windowframes reduce energy consumption in alltypes of buildings. For MURBs thedesigner should note that Canadian firecodes state that the area of windows withcombustible framing materials must be lessthan 40 per cent of the building wall areaand that non-combustible materials mustseparate windows.10

Spacers

Spacers separate panes of glass in a sealedwindow to prevent the transfer of air andmoisture in and out of the glass cavity.

Warm-edge spacers use low-conductivitymaterials, rather than aluminum, and areimportant in reducing heat loss throughthe window. By reducing the likelihood ofcondensation on the glass surfaces, theycan also influence daylighting performance.The low cost and good performance ofwarm-edge spacers make them suitable forall window systems and should beconsidered mandatory whenever low-ecoatings and inert gas fills are used.11

Window orientation

The greatest amount of solar energy isgenerated at noon on any given day in theyear. The greatest amount of energyreceived through a window is when the sunis perpendicular to the window and 30 to35 degrees above the horizon. South, eastand west windows receive about the sameannual maximum of solar radiation. Thetime and date that the maximum energy isreceived depends on the building’s latitudeand wall orientation. The earth rotates 15 degrees an hour; when a window isoriented 30 degrees east of south, themaximum heat gain will be about two

hours before solar noon. East and westfacades receive maximum solar gain in thesummer; a south-facing surface receives itsannual maximum in the late fall or winter.

Figure 8 shows a sun path chart for latitude44ºN. The sun’s path varies by a project’slatitude. The X-axis gives the direction ofthe sun; the Y-axis the sun’s angle above thehorizon. The curved lines show the arc ofthe sun across the sky on the 21st day ofeach month. The dashed lines show thetime of day. An accurate location of thesun can be determined by plotting the timeof day and month.

Obstructions are also plotted to show whena building will be shaded. Sun charts forany latitude can be generated through aUniversity of Oregon online program athttp://solardat.uoregon.edu/SunChartProgram.html

Figure 9 shows the intensity of solar energystriking a vertical surface facing the sun. Themaximum energy entering a window occurswhen the sun is 30 to 35 degrees above thehorizon and directly in front of the window.



Table 1 – Visible Light Transmission–solar heat gain coefficient (per cent)

Glazing system (6 mm glass) Clear Blue-green Grey Reflective

Single 89–81 75–62 43–56 20–29

Double 78–70 67–50 40–44 18–21

Double, hard low-e, argon 73–65 62–45 37–39 17–20

Double, soft low-e, argon 70–37 59–29 35–24 16–15

Triple, hard low-e, argon 64–56 55–38 32–36 15–17

Triple, soft low-e, argon 55–31 52–29 30–26 14–13

Source: ASHRAE Fundamentals 1997,Table 11, page 29

9 Website: Advanced Buildings: Technologies and Practices http://www.advancedbuildings.org/_frames/fr_t_building_low_conduct_window.htm10 Website: Advanced Buildings: Technologies and Practices http://www.advancedbuildings.org/_frames/fr_t_building_low_conduct_window.htm11 Website: Advanced Buildings: Technologies and Practices http://www.advancedbuildings.org/_frames/fr_t_building_warm_edge_windows.htm



Superimposing Figure 9—Solar energyintensity – over the sun path chart shows theeffect of window orientation on solar gain

Figure 10 aligns the solar intensity chart tosouth on the sun path chart. This showsthat the maximum solar gain occurs atnoon in October and February.

To indicate the solar gain on a westwindow, align the solar intensity chart withwest on the Sun path chart, as shown inFigure 11. This clearly shows how windoworientation affects the time of day and thetime of year of maximum solar gain.

North-facing windows provide consistentindirect light with minimal heat gains, butcan also create heat loss and comfort problemsduring the heating season. South-facingwindows provide strong direct and indirectsunlight that varies during the day. Controllingheat gain can be a problem during thecooling season. Shading is easily done withhorizontal shading devices in these windows.

East- and west-facing windows can createmore problems with glare and heat gainand are more difficult to shade because thesun is closer to the horizon. In Canada’s

North, the sun is at a low angle in the skyduring winter, when sunlight is mostneeded to contribute to heating. This iswhen south-facing clerestory windows havean advantage over horizontal roof glazing.However, the sun also creates glare.Overhangs over south windows may needto be large to prevent this. Also, when thesun is low, buildings and trees can createshade, which is desirable in some seasons.

Note that south-facing surfaces receivemore energy in the winter and less in thesummer than east- and west-facingsurfaces. A strategy to control overheating

Figure 8 – Sun path char t

Figure 9 – Solar energy intensity

Figure 10 – Energy striking a south window for latitude 44ºN

Figure 11 – Energy striking a west window for latitude 44ºN

Adapted from Edward Magria “The Passive Solar Energy Book”

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is to maximize window area on the southand use less on the east and west. Formainly cloudy regions, where overheatingis less of a problem, interior spaces benefitfrom larger windows (including the northfacade) that allow more light into abuilding. There can be a trade-off betweenallowing more daylight and increasing heatloss. In mainly clear regions, glare and heatgain are more problematic. In directsunlight, smaller windows can provideadequate daylight. Direct sunlight can alsobe reflected or diffused, or both, withwindow shading.

Window performance and tuning

Window orientation, size, layout andperformance are important in passive solardesign. Proper glazing and frame selectioncan enhance daylighting and energyperformance. General rules for tuningwindow orientation include:

� Determine the window size, height and glazing treatments separately foreach facade.

� Maximize southern exposure.

� Optimize northern exposure.

� Minimize western exposure when thesun is lowest and most likely to causeglare and overheating. Windowsthemselves can be oriented differentlyfrom the plane of the wall in a“sawtooth” arrangement.

Larger window areas increase the risk ofglare, overheating in summer and heat lossin winter. For areas with direct sun,shading needs to reduce transmittance to10 per cent or less to prevent glare.

Glare from windows can occur when theincoming light is too bright compared with the general brightness of the interior.Punched windows can create strongcontrasts from the interior betweenwindows and walls. Horizontal stripwindows provide more even daylightdistribution and, often, better views. Thisarticle discusses other interior designguidelines later.

Shading

Shading may be exterior, interior, fixed,motorized or between an exterior glazingand an interior facade in double-facadesystems. Figure 12 shows some examples of shading systems. A good shading systempermits lower levels of artificial illumination,because the eye can accommodate itselfwithout strain to function within a wideillumination range.

Exterior shading devices are the mosteffective at controlling solar gain. Interiorwindow shading allows much of the solarenergy into the building and allows moreheat, sometimes an unwanted partner of daylight, to enter the building. Light-coloured interior shading will reflect someof this energy back through the window.However, a minimum of about 20–30 percent of incident solar radiation will comeindoors as transmitted or be absorbed andre-emitted as heat when interior blinds are used. Exterior blinds collect dust andmay be difficult to maintain and clean.One solution is to place reflective blindsbetween the two glazings and possibly to have airflow within the cavity—adouble-facade.

Figure 12 – Common types of exterior shading

Overhang Louvred Overhang Lightshelf Vertical Fins



South-facing windows are the easiest toshade. Horizontal shading devices, whichblock summer sun and admit winter sun,are the most effective. East- and west-facing windows are best shaded withvertical devices, but these are usually harderto incorporate into a building and notlimit views from the window. On lowerbuildings, well-placed deciduous trees onthe east and west reduce summeroverheating and allow desirable wintersolar gains. Some practioners are testingvines hung on metal lattices to reduceoverheating. Interior shading is mosteffective at controlling glare and can becontrolled to suit the occupants.

Energy Rating—ER

Energy Rating (ER) is a rating systemdeveloped by the Canadian StandardsAssociation and the window industry. Itcompares window products for theirheating season efficiency under averagewinter conditions. The ER is the value ofenergy gained or lost in watts per squaremetre (W/m2). RSI value is a misleadingmeasure of energy efficiency because itoften only accounts for the heat lossthrough the centre of the glass. The ERconsiders all the energy flows through thewindow, the total glass R-value, the frameR-value, air infiltration and average solargain. The solar gain is an average of thefour orientations.

Because the ER relies on an average solargain, it cannot be used to compare actualperformance for a specific locationorientation and window size. Furthercalculations can determine the EnergyRating Specific (ERS). This determines aspecific ER value for a window based onthe climate of a particular location, thewindow-to-floor area ratio and the windoworientation on the building.

Both the ER and ERS are part of CSA-A440.2 Energy Performance of Windowsand Other Fenestration Systems standard.

Figure 13 – Double facade in a residential building,

Klosterenga, Oslo, Norway

Figure 14 – Glazed solar pacade from the outside of

Klosterenga

15



Solar cooling

Traditionally, passive solar cooling isassociated with much warmer climates thanCanada’s. In Canada, the most effectivemethod is to exclude solar gain throughfenestration design, window glazingselection and shading devices. Anothercommon strategy is to use the mass of thebuilding, which cools down at night tomitigate overheating by absorbing solarenergy during the day.

Harnessing the stack effect, that is theupward movement of warmer, more buoyantair, is possible if a building is designed tocapture solar heat and exhaust it at rooflevel. This warm air can be released to theoutside, drawing cooler ground-level airinto and up through the building. Anatrium can act as a solar chimney withmotorized windows to harness the stackeffect and help the natural ventilationprocess. Using thermal mass in an atriumhelps prolong the chimney effect well intothe night to draw cool air into thebuilding. In Europe, cool night air ispassed (using fans) through hollow corefloors to store coolness. During the day,room air is recirculated through the coolfloor to provide free cooling.

Absorption cooling involves high-temperature solar collectors connected toan absorption chiller operating at around100°C (212°F). The device uses a solarcollector to evaporate a pressurizedrefrigerant from an absorbent–refrigerantmixture. Absorption coolers require littleelectricity to pump the refrigerant

compared to that of a compressor in aconventional electric air conditioner orrefrigerator. This system is not yet efficientenough for conventional buildings andrequires a large, upfront investment.

Desiccant cooling uses a desiccant, achemical drying agent, in contact with theair to be cooled. The air becomes so drythat moisture can be injected into itwithout affecting comfort. The moisturedroplets evaporate and cool the air. Thedrying agent is regenerated by hot air thatis heated through solar air collectors or acoil connected to liquid-based collectors.12

The Rankine-cycle cooling process is avapour compression cycle similar to that ofa conventional air conditioner. Solarcollectors heat the working fluid, whichhas a very low vaporization point, whichthen drives a Rankine-cycle heat engine.This technology is mainly experimentaland not used often because it needs a largesystem size to do any meaningful amountof cooling.13

Overheating

Overheating tends to occur more fromunshaded west-facing windows and, to alesser extent, east windows. Late summer isoften the most crucial time of year. Designstrategies include minimizing the amountof east- and west-facing glass, selectingglazings with a low SHGC to exclude heat and provide shading. Thermal massinside the building can also have the effect of reducing the peak-cooling load in some climates.

Solar balconies

Glazed, stacked balconies can also work aspassive collectors. They passively re-radiateheat or actively ventilate to the rest of theunit or to the outside.

An effective method is to inset the balconyinto the building envelope. This simplifiesthe building envelope and eliminates theneed to separately support or cantilever thebalcony. It also reduces the amount ofthermal bridging across the envelope, butmay require additional shading devices ifthe room is to be occupied regularly or iftemperature fluctuations are not desirable.Of course, the balcony becomes lesseffective as a solar collector as it is orientedaway from south. An enclosed balconypartially or entirely projecting from theexterior allows solar gains in units withoutdirect southern exposure.

In the CMHC study of renewable energyat the building envelope, energy modellingof a six-storey MURB in Halifax predictedthat solar balconies would reduce energyconsumption by about four per cent.

A Dutch study14 looked at solar balconiesin renovating post-war, multi-familyresidential buildings with aged and failingenvelopes. The study showed that the newsolar elements were a cost-effective way toupgrade while reducing energyconsumption by about 35kWh per squaremetre. Optimizing thermal, glazing andventilation parameters and using simpleventing and solar shading enhancedoccupant comfort.

12 Natural Resources Canada website: http://www.canren.gc.ca/tech_appl/index.asp?CaID=5&PgID=164#desiccant13 U.S. Department of Energy website: http://www.eren.doe.gov/consumerinfo/refbriefs/ac2.html14 Advanced glazed balconies: Integration of solar energy in building renovation, W/E consultants, The Netherlands, EuroSun'96



Cour tyards, atriums andcommon spaces

A south-facing atrium can collect pre-heatingair to be circulated throughout the building.This requires airtight construction and ahigh level of insulation. Overheating in theatrium can be avoided with properly sizedand located motorized shades and a passiveventilation system. Architects mustrecognize the fire safety issues of atriumsand provide protection for their occupants.This is addressed in a separate article onthe CMHC website Fire Safety in High-riseApartment Buildings.15 The difficulty indealing with smoke control and using anatrium to pre-heat building air becomes a challenge.

In high-rise and mid-rise apartments, itmay be easier to consider common spaces,such as entry and elevator lobbies andstairwells, as solar space. This makesorientation of individual units moreflexible and may allow greater variations intemperature swings.

Solar water heating

Solar domestic hot water heating systems varyin complexity, efficiency and cost. Modern

solar water heaters are relatively easy tomaintain and can pay for themselves inenergy savings well within their lifetimes.In MURBs, they may pre-heat water forthe boiler in hot water heating systems.This works best in large projects that havesignificant system heat losses (when the returnwater is cooled sufficiently that solar can re-heat it). For boilers heating water for spaceheating and hot water, solar panels may allowthe boiler to be shut down in the summer andprovide hot water from solar energy alone.

An efficient flat-plate solar hot water heatercan collect approximately 2GJ of energyper m2 (550 kWh/m2) of collector area peryear in most of southern Canada. Othersystems available include thermosiphonsystems, common in southern Europe, thateliminate the need for pumps.

Several projects in Europe are working withprototypes of seasonal storage, the “HolyGrail” of the solar world. These projectsuse large solar arrays to collect heat in thesummer and store it in large, well-insulatedunderground water tanks. The heat isextracted from the water during the heatingseason. To illustrate the scope of suchsystems, they use approximately 10 m2 to20 m2 (107 sq. ft. to 215 sq. ft.) ofcollector and 20 m3 to 40 m3 (706 cu. ft.to 1,412 cu. ft.) of storage for every flat orhouse. Performance projections indicatethat they would provide from 30 to 60 percent of a buildings’ energy. Planning for a100-unit solar demonstration housingproject in Bavaria assessed systems capableof providing 60 to 90 per cent of heatingusing seasonal solar heat storage. The

project consists of 100 well-insulated units;each with 140 m2 (1,506 sq. ft.) heatedarea, and assessed configurations ofcollector area (900 m2 to 1,500 m2) andinsulated underground water storage 1,600m3 to 6,300 m3 (56,503 cu. ft. to 222,482cu. ft.).16

In Hamburg, 24 single-family, detachedhouses used 3,000 m2 of collector with4,500 m3 (158,916 cu. ft.) insulatedunderground water storage. A sister projectin Friedrichschafen used 5,600 m2 (60,277sq. ft.) of collector with 12,000 m3

(423,776 cu. ft.) of storage for 570 flats in eight buildings. Both projectsanticipate solar energy will cover 50 percent of heating and hot water needs.17

In much of Canada we have clear coldwinters and under these conditions asubstantial amount of solar energy isavailable when needed, so short-term (1-2 days) storage is more cost effective. An equivalent climate in Canada for theseEuropean examples would be the lowermainland of British Columbia.

Figure 15 – Glazed flat-plate collector

15 http://www.cmhc-schl.gc.ca/en/imquaf/himu/upload/Fire-Safety-in-High-Rise-Apartment-Buildings.pdf16 D. Lindenberger et al., Optimization of solar district heating systems: seasonal storage, heat pumps and cogeneration, May 199917 B. Mahler et al. Central solar heat plants with seasonal storage in Hamburg and Friedrichschafen

Outlet

InletHeader

Tube

Box

Glazing

Inlet

The design shown isan example of a typicalliquid-cooled collector.

Air-cooled collectordesign will vary

accordingly

Bottom Plate

Absorber Plate

Note: for further information oncollector design and performance,see manufacturers’ specifications

Insulation

17



Unglazed flat-plate collectors are the mostcommon North American collectors, asmeasured by area installed per year. Theyare used most for warming water up to30°C (86°F) for outdoor and indoorswimming pools.

They are inexpensive, simple systems thatcan provide all the heating needs forresidential outdoor swimming pools,eliminating both fossil fuel consumptionand the capital costs of conventionalheating equipment. They are simple toinstall and generally have a three- to six-year-year payback.18 In Canada, their use islimited to non-heating seasons.

Simple RETScreen calculations show thatunglazed collectors deliver about 2.0 to 2.4 kWh/m2/day during summer. Outdoorpools are usually seasonal and in warmermonths a solar blanket can be used, orsolar collectors and pumps can heat thepool directly. When indoor pools are at or below grade, rooftop collectors are

impractical on high-rise buildings. To avoidheat loss during transit, a glycol collectorwith a well-insulated circuit may be usedclose to the pool. Southern or overheadglazing can also provide direct solar energyand cut conventional lighting costs. Solarenergy can supply between 30 and 100 per cent of the required heat, depending on variables, including location, collectorangle and orientation, desired pooltemperature, size of pool and use of a pool cover.

Evacuated tube collectors are individuallysealed vacuum tubes surrounding a metalabsorber plate. The vacuum minimizesconductive heat loss, like a thermal jug.These collectors are commonly used in verycold climates. Evacuated tube collectors areable to provide higher water temperatures,but are also more expensive, with longerpayback periods. RETScreen calculationsshow that an evacuated tube collector candeliver about 1.2 kWh/m2/day in winterand up to 2.9 kWh/m2/day in June.

Natural Resources Canada

Figure 16 – Unglazed flat-plate collector

18 Sheltair Group et al, Healthy High-Rise: A guide to innovation in the design and construction of high-rise residential buildings, (Canada: CMHC, 1996) p. 49

Active solar space heating

SDHW—Solar domestic hotwater systems

Solar Domestic Hot Water (SDHW)systems supplement traditional hot waterheating. The most common system usesglazed, flat-plate collectors in a closedglycol loop. A heat exchanger transfers theenergy from the glycol to one or more solarstorage tanks. These are usually connectedin series to the hot water system. Thetraditional water heater comes on to keepthe water at the required temperature if thesolar heat is not enough.

There are seasonal variations in the energythey collect, depending on location, collectorefficiency, collector angle and orientation,ranging from about 0.6 to 1.0 kWh/m2/dayin winter up to about 2.4 kWh/m2/day insummer. It is easy to get 50 per cent of hotwater energy from the sun. A reasonabletarget for fossil fuel displacement is 30 to40 per cent. This allows the panels to operateat a more efficient temperature. Thesesystems are easily integrated into currenthot water systems and have a payback inthe range of 10 years. In Canada, thisvaries tremendously, depending on fundingincentives and fuel cost.



Figure 17c – Rooftop evacuated tube collector

Source: Architectural Graphic Standards

Figure 17a – Evacuated tube collectors

Source: Natural Resources Canada1

Figure 17b – Evacuated tube collectors

Source: Natural Resources Canada

Evacuated tube

Glazing

Outlet

Inlet

Cross section of

evacuated tube Outer Glass Tube

Inner Glass Tube

Fluid Tube

Copper Sheet

Evacuated Space

19



Table 2 – Cost and benefits of solar collectors

Collector Typical uses Advantages DisadvantagesCapital

cost $/m2

Energy delivered

annually kWh/m2

Unglazed Swimming poolsEconomical, efficient at low

temperature differentials.

Not for freezing

temperatures.150–350

210–250

(summer only)

Glazed DHW pre-heat Economical.Needs glycol protection

from freezing.450–750 500–600

Evacuated tube DHW pre-heat Provides hotter water.

Expensive; needs glycol

protection from

freezing.

1,100–1,500 800–840

Figure 18 – Solar domestic hot water system

Source: www.AdvanceBuilding.org

SolarCollectors

Gas orElectricWaterHeater

HotWater

to House

SolarHeatedWater

HeatExchanger

Solar StorageTank

Pump

ColdWater in

PumpController

Anti-Freeze Solution



Solar air heating

The following summary is based on SolarAir Systems: A Design Handbook, edited byS. Robert Hastings and Ove Mørck. Theauthors looked at European and NorthAmerican applications. Cost analyses are inCanadian dollars, unless otherwise noted.

Six principal solar air-heating systems aresummarized below. All systems consist of thefollowing common elements in one formor another: collector, distribution system(ducting), storage unit and control system.

A total system can consist of any combinationof the four different components.

The applications analyzed in the studywere for industry, dwellings (apartments,row and single-family houses), offices,schools, sports halls and swimming pools.

The factors affecting system performanceare type and mass of building, insulationlevel and climate.

Design procedure

The Solar Air Systems design handbookrecommends the following design steps.More technical details can be found in the guide.

� Define necessary basic data aboutbuilding and climate.

� Determine if it is possible to obtainenough collector area.

� Determine ventilation rate through thesolar air collector.

� Determine if there are restrictions oninlet temperature from ventilationsystem.

� Investigate if it is appropriate toinclude storage in system.

� Define the required control strategy.

� Choose a solar collector.

� Investigate if the system may serveother purposes.

� Determine the collector area.

� Size the ducting.

� Choose a fan.

� Choose diffusers.

Using an integrated design approach willenable the building design team to betterconsider any possible alternative purposesfor the various systems, which could helpreduce the payback time or provide otherbenefits to the occupants.

Table 3 – Common elements in solar air-heating systems

Collector systems Storage systems Control systems Distribution

� Flat-plate collector

� Window air

collector

� Perforated

unglazed collector

(Solarwall®)

� Double facades

and double-shell

collector

� Spatial collector

(atriums,

sunrooms,

greenhouses)

� Hypocaust

(ceiling or

floor slab)

� Murocaust

(wall)

� Rock beds

� Water

� Phase-change

material

� Continuous

performance

� Temperature

control

� Solar cell

control

� Timer control

� Usually

through

ducting.

21



System 1: Solar heating ofventilation air, such as Solarwall®

This system provides the simplest, andusually least costly way to bring solar-heated fresh ventilation air into a building.It uses mainly off-the-shelf components in its design. Its major disadvantage is that it will reduce cost-effectiveness of thebuilding’s ventilation heat recovery unit.

An example of this type of system developedin Canada is Solarwall®, in which a south-facing wall is clad with dark metal panels,typically steel or aluminum, perforated with

small holes. A gap is left between the claddingand the wall so that outside air passesthrough the holes in the collector panel.Air is aspirated into the airspace betweenthe collector and the wall, is heated, andrises as a result of the stack effect and thelower pressure zone above, which is createdby fans moving air through the system tothe interior. This pre-heated ventilation airis then incorporated into the building'snormal distribution system. A recirculationdamper controls the mix of air from thecollectors and from inside the building tomaintain a constant air temperature fordistribution. Using the sun to pre-heat airfor ventilation in this way is a fairly new

technology. In the last 10 years, about35,000 m2 (376,737 sq. ft.) of Solarwall®

collector systems have been installed inbuildings, including low-rise and high-riseresidential. Pre-heated ventilation airsystems can be integrated into newconstruction or as a retrofit (see figure 19).

In the early 1990s, Ouellette Manor, a 24-storey, 400-apartment seniors residencein Windsor, reclad part of its complex withSolarwall®. The new Solarwall® had anincremental cost of about $30,000 and theenergy savings provided a simple payback ofabout six years. There is more informationabout Ouellette on the CMHC website at http://www.cmhc-schl.gc.ca/en/imquaf/himu/buin_006.cfm

Solarwall® is ideally suited for applicationsthat require large quantities of ventilation airduring the day and has proven effective atpre-heating ventilation air in MURBs. Innew and retrofit situations, it has the benefitof offsetting the cost of traditional claddingmaterials. As a result, it can have very quick,and sometimes immediate, payback.

Table 4 – Solar heating of ventilation air

Benefits Limitations

Less cost to heat ventilation air

Recaptures heat loss through wall

May replace conventional cladding

(new construction)

Conceals old cladding (retrofit)

Requires large, south-facing wall area

Reduces opportunity for south facing

glazing

Reduces the cost-effectiveness of

ventilation heat recovery (because

owner pays less to heat incoming air)

Doesn't replace normal heating system

Conserval

Figure 19 – Ouellette Manor, Windsor,

uses Solarwall® to pre-heat corridor

ventilation air

SolarCollector

System 1

PreheatedVentilation Air

Figure 20 – System 1, solar air pre-heat system concept



System 2: Open collection loopwith radiant discharge storage

In this system, air circulates, eithernaturally or mechanically, through thecollector, distribution system, room spaceand back to the collector. It can be builtwith or without storage, and may require aseparate ventilation system.

System 3: Double envelope(facade) systems

In a double-envelope or double-facadesolar air system, solar heated air iscirculated through cavities in the buildingenvelope, surrounding the building with alayer of solar-heated air. This creates abuffer space that reduces the building’sheating and cooling load. Inner comfort isimproved because inner surfaces of theexternal walls are warmer. The outerenvelope can be made of opaque materials(traditional cladding materials with an airspace) or glass. The Klosterenga project inOslo, Norway uses the space betweendouble layers of south-facing windows topreheat the air. The figures in Table 5 arefor glass-enclosed systems. Questions ofcleaning and maintenance for this type ofsystem must be addressed.

This system is versatile and integrates intomost existing heating systems, but isusually much more expensive than othersystems. In North America, costs arereported to be four to five times that oftraditional, low-cost cladding systems,19 butthe effective cost may drop if the doublefacade reduces energy consumption.

Figure 21 – System 2, without storage

Figure 22 – System 3a, double-envelope system with storage

19 Meyer Boake, Terry et al. Canadian Architect, August 2003, p. 38

SolarCollector

System 2

Open Loop Air Circulation

SolarCollector

System 3a

Solar AirSurroundsEnvelope

CavityWall

RadiantHeat

23



There are numerous concepts for doublefacade. The following exampledemonstrates the heating effect of an air-heating solar collector with a motorizedblind as the surface absorbing the solarradiation. Major design parameters are thespacing between the two skins of thefacade, the air velocity and the propertiesof the blind, which is controlled by thebuilding automation system, with manualoverride and automatic refresh every houror so.

The blind, even when closed, must allowenough daylight into the space. Thisrequires a 20 per cent transmittancedepending on window area. The glazingmust be clear. The airflow-window type ofdouble facade was considered for theSeville adaptive reuse project in Montréal.20

Each floor may be separate (with boxwindow types) with individual inlets andoutlets or connected to form one large“chimney.” Figure 23 shows double glazingfor the outer skin with low-emissivitycoating facing the skin cavity to reduceheat losses in winter. However, this coating,which increases the outlet temperature by a couple of degrees, may possibly beexcluded as it can deteriorate in this case.The inner glazing may be operable. Theinlets and outlets of the airflow windowneed to be carefully designed.

Figure 23 – System 3b, double-facade design option

20 “Seville Theatre Redevelopment Project Integrated Design Process,” CMHC Technical Series (63175) Research Highlight 03-102

Open LoopAir

Circulation

System 3b

SolarFacade



The following results show an example ofthe air temperature rise of the solarcollector due to varying the distancebetween the two “facades” or skins.

v=air velocity: 0.1–0.2 m/sec

w=width of the space=3.6 m,

Outdoor air temperature of -5ºC

L= the distance between the two skins;

Outer glazing, clear double; innerglazing single

low-emissivity coating on inner side ofouter glazing (double)

blind solar absorbance: 60 per cent,transmittance 20 per cent.

Height of the space=4 m

Note that the larger the gap width betweenthe skins, the smaller the air velocityneeded to achieve the required fresh-airflow rates.

1. For L=20 cm: for v=0.1 m/sec, thecollector air temperature will rise toabout 15ºC (rise of 20ºC) when theblind is closed with incident solarradiation of 600 watts/m2.

2. For L=30 cm: for v=0.2 m/sec (L=30cm), the collector air temperature willrise to about 5ºC (rise of 10ºC) whenthe blind is closed with incident solarradiation of 600 watts/m2.

System 4: Closed-collection loopwith radiant discharge storage

In this system, an air collector is connectedto the building’s integrated heat storage. Theair is circulated in a closed loop, normallywith the aid of fan-forced convection, throughthe collector to the storage and back to thecollector. The room-facing surface of thestorage discharges heat by radiation andconvection to the room space. The collectorsystem can be used as part of the buildingenvelope, with lower extra costs.

Figure 24 – Fresh-air pre-heating in double facade (Klosterenga, Oslo, Norway)

Figure 25 – System 4, with storage

SolarCollector

System 4

RadiantHeat

SolarCollector

ClosedLoop

ChargeMass

System 5: Closed-collectionloop with open-discharge loop

This system provides comfort, even inrooms with high internal and solar gainsand small losses, because it allowscontrolled discharge of stored solar energyto the heated room. This increases the solarsystem’s efficiency and reduces the risk ofoverheating. It can use existing buildingcomponents and can be combined easilywith existing HVAC systems. It is moreexpensive than other systems.

System 6: Closed-collection loopwith heat exchange to water

The closed-loop solar-air system hasadvantages over liquid systems, as there isno risk of leaking, boiling or freezing. Itmight also be chosen for its economy orfor architectural reasons. Solar-air heatedwater can provide space heating, domestichot water heating or be used for industrialapplications. Apart from the collector, thesystem consists of standard HVACcomponents. This system can be used forheating hot water during the summer. Itrequires that the air temperature in thesystem be hotter than ventilation pre-heatsystems. It is usually bulkier than liquidsystems.

System design

For more technical details, see pp 103-104of Solar Air Systems: A Design Handbook

� Step 1-Profile the loads

� Step 2-Select collector type

� Step 3-Decide on air mass flows

� Step 4-Specify the heat exchanger

� Step 5-Size the storage and determineheat loss

25



Figure 26 – System 5, with storage

Figure 27 – System 6, with hot-water storage

SolarCollector

System 5

RadiantHeat

SolarCollector

System 6

Air to WaterHeat Exchanger

Solar PreheatedWater

SolarCollector

Mass

Open LoopDischarge


Tab

le 5

– C

om

pari

son

of

six s

ola

r-air

heati

ng s

yst

em

s

Saved

en

erg

y

110–550 k

Wh/m

2

(sunny–

cold

)

90–300 k

Wh/m

2

(clo

udy–

tem

per

ate)

80–200 k

Wh/m

2

(sunny–

cold

)

40–75 k

Wh/m

2

(clo

udy–

tem

per

ate)

150–400 k

Wh/m

2

(sunny–

cold

)

100–225 k

Wh/m

2

(clo

udy–

tem

per

ate)

100–425 k

Wh/m

2

(sunny–

cold

)

50–200 k

Wh/m

2

(clo

udy–

tem

per

ate)

30–150 k

Wh/m

2

(sunny–

cold

)

10–100 k

Wh/m

2

(clo

udy–

tem

per

ate)

300–400 k

Wh/m

2

(sunny–

cold

)

120–130 k

Wh/m

2

(clo

udy–

tem

per

ate)

Syst

em

perf

orm

an

ce

600–800 k

Wh/m

2

Pay

bac

k 25 y

ears

Pay

bac

k tim

e dep

ends

on inte

grat

ion

80–240 k

Wh/m

2

(Hea

ting

seas

on)

175–375 k

Wh/m

2

Co

st

Sola

rwal

l®

$194/m

2

$200/m

2

$90–$475/m

2

$250–$650/m

2

Dis

ad

van

tages

Dec

reas

ed p

erfo

rman

ce o

f hea

t re

cord

ing

unit

Colle

ctor

mat

eria

ls m

ust

be

non-t

oxic

May

req

uir

e se

par

ate

ventila

tion

Rel

ativ

ely

more

expen

sive

Win

dow

colle

ctors

may

ove

rhea

t ad

jace

nt

room

s;ro

cked

sto

rage

bulk

y

Furn

iture

can

't b

e pla

ced a

gain

st w

alls

Incr

ease

d inst

alla

tion c

ost

s bec

ause

of

faca

de

shel

l

Bulk

ier

than

liq

uid

sys

tem

s

Ris

k of fr

eezi

ng

in h

eat

exch

ange

r

Ove

rall

effic

iency

red

uce

d d

ue

to

tem

per

ature

dro

p o

ver

hea

t ex

chan

ger

Ad

van

tages

Sim

ple

,inex

pen

sive

Low

tem

per

ature

air

usa

ble

All

colle

ctors

usa

ble

Syst

em u

ses

stan

dar

d c

om

ponen

ts

Sim

ple

,can

be

use

d w

ith o

r w

ithout

stora

ge

Hig

h d

egre

e of in

tegr

atio

n p

oss

ible

,eve

n in

retr

ofit

s

Usi

ng

colle

ctor

as p

art

of build

ing

enve

lope

low

ers

extr

a co

sts

for

the

sola

r sy

stem

Exis

ting

build

ing

com

ponen

ts u

sed

Can

com

bin

e w

ith h

eat

and v

entila

tion

syst

em

No p

roble

m w

ith fre

ezin

g,boili

ng

and lea

king

in c

olle

ctor

Stan

dar

d v

entila

tion e

quip

men

t ca

n b

e use

d

Can

be

use

d t

o h

eat

hot

wat

er in s

um

mer

Syst

em

1 2 3 4 5 6

So

lar E

ne

rgy f

or B

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27



Photovoltaic (PV) systems

The photovoltaic effect converts solarenergy directly into electricity. Whensunlight strikes a photovoltaic cell,electrons in a semiconductor material arefreed from their atomic orbits and flow ina single direction. This creates directcurrent electricity, which can be usedimmediately, converted to alternatingcurrent or stored in a battery. Wheneversunlight arrives at its surface, the cellgenerates electricity. PV cells normally havea lifespan of at least 20-25 years; however,they usually last longer if frequentoverheating—temperatures in excess of70ºC (158ºF) is prevented.

PV systems can be used as a building's soleelectricity supply or with other sources,such as a generator or a grid connection.

Autonomous PV systems include an array ofPV cells and a power conditioner thatconnects to the building's electrical loads.To have electricity when there is no sun,this system must have storage batteries.Battery storage must be sized to theanticipated load and solar access. Aweakness of the system is that the supply ofsolar energy may be intermittent.

Hybrid PV systems have at least oneadditional electricity source, such as a fuel-fired generator or a wind turbine. Thesesystems can still be off the utility grid andcan minimize or eliminate the problem ofintermittent solar energy.

While autonomous systems can beimmediately cost-effective in remotelocations, they are not likely to be cost-beneficial for MURBs.

Grid-connected PV systems cancel out theneed for onsite generators and batteries andeliminate the problem of intermittent solarenergy. In many jurisdictions it is possibleto supply excess solar-generated electricityto the grid and receive credit from thepower company.

The cost of PV technology is now muchmore expensive than traditional electricityand has a very long payback period. In 2000,Natural Resources Canada assessed the break-even point for PV products in Canada usingmarket data from the past 25 years. Basedon annual growth rates of 20 per cent(growth has been closer to 30 per cent forthe past six years), the break-even point forcompeting with bulk electricity generationwas calculated to be between 2020 and2030.21 This was based on lowest productioncost but does not consider technologicaladvancements or the advantage of reducedgreenhouse gas production.

Building-Integrated PV systems(BIPVs)

A more recent trend is the development of Building—Integrated Photovoltaics(BIPVs). The PV cells are incorporatedinto a building element. Currently there ismuch development in PV roofing, PVshading elements (see figure 28) and PVcladding or semi-transparent curtain wallcomponents (see figure 29). With PVcladding it is best to have a vented cavitybehind the panels so as to operate at lowertemperatures. By following such aconstruction approach one may alsodevelop an effective rainscreen systemwhich hinders rain penetration. PV roofing is installed much the same way as

21 Ayoub, J., Dignard-Bailey, L. and Filion, A., Photovoltaics for Buildings: Opportunities for Canada: A Discussion Paper, Report # CEDRL-2000-72 (TR),

CANMET Energy Diversification Research Laboratory, Natural Resources Canada, Varennes, Que., November 2000.

Figure 28 – PV as window shading

elements (overhangs) at Queen’s

University, Kingston

Source Kawneer



conventional roofing and is available inshingles, tiles and metal standing-seamroofing (see Figure 30). PV shading can beeffective as a window shading element,entrance canopy or walkway shading. PVpanels can be opaque, used where no lighttransmission is needed, or semi-transparentfor areas where light is wanted, such asatriums or skylights, but some shading isneeded to reduce cooling loads.

Figure 29 – PV integrated in cur-

tain wall elements at the Mataró

Librar y, Mataró, Catalonia, Spain.

(The facade is also used for fresh

air pre-heating).

Sol Source Engineering

Figure 30 – BIPV metal-standing seam roof, Toronto

29



Until the use of BIPVs becomes morewidespread, there are barriers to overcome.Canadian utilities are often not familiarwith small, decentralized energyproduction. Consequently, utilityinterconnection for BIPVs is a majorbarrier to their use. Another barrier is theabsence of technical standards andinstallation codes. Non-technical barriersinclude the lack of experience amongbuilders and electrical inspectors; lack offinancing for systems with large capitalcosts; additional permit, insurance andinspection fees for net-metering systems;unawareness of potential and long-termbenefits to system integrators.22

Photovoltaic hybrid heatingsystem (PV-thermal system)

A typical crystalline silicon PV panel hasan efficiency of 10–15 per cent. PV solarpanels produce more than four times asmuch heat as electricity. This heat isnormally lost to the environment. A PVcell can have a stagnation temperature of50°C (122ºF) above the ambient if theheat is not removed. The cooler the PV cells,the higher the efficiency. A solar air collectorhas a typical thermal efficiency of 40–70per cent. Drawing outside air in across theback of panels pre-heats the HVAC supplyair and also increases the PV efficiency bykeeping them cooler.

Combining these two systems producesboth heat and electricity. (This isequivalent to a co-generation power plant.)Test results show that using PV panels togenerate both electricity and useful heatsubstantially improves the overall efficiency(electrical plus thermal). The payback for a

grid-connected PV electrical system wasdecades. By 2004, the cost of panels hadfallen to $4.5 per kW-peak (one kW-peakis electricity generated with 1,000 W/m2

incident solar radiation). Annual electricalproduction is generally in the 70-200kWh/m2 range, depending on climate.

Consider a simplified analysis of a PV-thermal system—a PV panel with airflowbehind it (see figure 10, page 12).

Assume that 1,000 W/m2 of solar radiationis incident on the solar panel, whichconverts 10 per cent to electricity toproduce 100 watts of electricity for onesquare metre of panel (a panel costs about$450 at mid-2004 prices).

About 5–10 per cent of incident solarradiation is reflected but the rest becomesheat. By bringing in fresh air through aninlet at the bottom and passing it behindthe panels the air is heated the same way asin a Solarwall® system. The faster the

airflow, the more heat is transferred to theflowing air and less is lost to the outside air.

Optimal cavity width and air velocity areselected by taking into account fan energy,required outlet temperature and fresh airrequirements. The PV can extend overmultiple stories, with multiple inlets. In anycase, if the inside heat transfer coefficient hiis equal to the exterior film coefficient ho(about 12 W/m2 for still air), then theflowing air may capture about 400 watts/m2

of thermal power. This gives the followingenergy balance on the PV panels:

This shows that four times more thermalenergy is generated than electricity. Theelectrical efficiency is 10 per cent, while thethermal efficiency is 40 per cent. This givesan overall efficiency of 50 per cent. Ifthermal energy is worth half as much aselectricity, then this system generates aboutthree times the revenue of a simple PVsystem on the facade.

This simplified analysis shows whyPV–thermal applications are the key toearly, cost-effective use of PV.

Integration into MURBs

For MURBs, facades have the highestpotential for cost-effective BIPVs. Infacades, they can easily generate thermalenergy. Semi-transparent panels can alsoprovide daylighting. There are two mainoptions for using the hot air. Like theSolarwall® system, the PV system can beapplied in vertical strips with a fan drawingthe air into the HVAC system. Analternative is installation into box-type,airflow windows. If they project from thefacade, they need a separate supportstructure, adding to installation costs.

The applications may range from smalloverhangs to large continuous facade areas.Figure 30 shows a double facade with PVoverhangs, in Freiburg, latitude 48o N.

Simplified Analysis

Incident solar

radiation=reflected+ electricity+

heat transfer

to air+

heat lost

to exterior

1,000 W= 100+ 100+ 400+ 400

22 Ayoub, J., Dignard-Bailey, L. and Filion, A., IBID.



Figure 31 – Double facade with PV overhangs in Freiburg,

Germany

Table 6 – Description of collector types

Collector type Advantages Disadvantages Capital cost $/kW Efficiency

Single crystal High efficiency High cost, fragile,

uniform look

5,000–10,000 11–15%

Polycrystalline High efficiency High cost, fragile,

non-uniform look

5,000–10,000 10–14%

Thin-film amorphous Flexible, can be applied to different

types of surfaces

Low efficiency,

degrades

5–8%

Spheral solar (crystalline

family)

Low cost, flexible, can be applied to

different types of surfaces.

Low efficiency 4,500 9–10%

Table 7 – BIPV manufacturers

BIPV product Manufacturer–country

Sloped roof Atlantis Solar Systeme AG, Switzerland

Ecofys,The Netherlands

BMC Solar Industrie GmbH, Germany

BP Solar, United Kingdom

Canon Inc., Japan

Lafarge Brass GmbH, Germany

MSK Corp., Japan

United Solar Corp, U.S.A.

Facades Atlantis Solar Systeme AG, Switzerland

Pilkington Solar Inter., Germany

Isophoton Inc., Spain

Saint-Gobain Glass Solar, Germany

Sanyo Solar Engineering Ltd., Japan

Schuco Int. KG, United Kingdom

Shading Ecofys, Netherlands

Colt Solar Technology AG, Switzerland

Kawneer, U.S.A.

Flat roof Powerguard, U.S.A.

31



Summary

Passive solar is best for buildings that havelow internal heat gains and in which directsolar gain is directed to absorbent thermalmass. The housing market today may objectto hard floor surfaces out of concern forcomfort and impact noise, but increaseddrywall thickness and concrete ceilings maycompensate for the lack of hard flooring.Mass is most effective if it receives directsolar gains, i.e. usually on the floor. However,if this is not possible, a concrete ceiling willabsorb much of the energy from air heatedby the floor; this air will rise throughbuoyancy. Generally, about 5-10 cm ofconcrete—or equivalent—on the floorprovides adequate mass.

� The cost of passive solar is minimal,but must be planned during the initialdesign stages.

� Orientation in most MURBs provideschallenges. An effective strategy is totune the selection of glazing based onthe orientation of each facade.

� Solar domestic hot water can have areasonable payback time and isrelatively easy to install in newbuildings and retrofits.

� Solar water heating is less likely to beeffective for space heating, except invery large heating systems.

� Solar water heating for swimming poolsis very effective for seasonally usedpools, with short payback times.

� Solar air-heating systems for pre-heating ventilation air can have veryshort—even immediate—payback.Their drawbacks are the need for primesouthern exposure and their industrialaesthetic. Such considerations need tobe part of the architectural design ofMURB installations.

� Presently, photovoltaics are anexpensive way to provide electricity andare more cost-effective combined withheat recovery as well. However, the costof building-integrated PV (BIPV)systems is coming down as competitionand market share increase.

Tools and resources

Canada Mor tgage and HousingCorporation

www.cmhc.ca key word: Innovative Buildings

NRCan and CMHC’s AdvancedBuildings Technologies

www.advancedbuildings.org

C2000 Commercial BuildingProgram

This is a Natural Resources Canadademonstration program for designassistance in energy-efficient commercialbuildings. The goal is 50 per cent lessenergy consumption than a buildingconstructed to the Model National EnergyCode of Canada for Buildings (MNECB).

Commercial Building IncentiveProgram (CBIP)

CBIP is probably the largest federalgovernment initiative to reduce energy usein commercial buildings. Building ownersare given a financial incentive of threetimes the annual energy savings if thepredicted building energy use is 25 percent below that required by the MNECB.Computer simulations are done withNRCan's EE4 software. This program hasno provision for analyzing PV systems.Energy from PV is a credit towardsmeeting the energy target and contributesto the eligibility of the incentive. The

program is being phased out in 2007.However the EE4 software and CBIP goalsare part of the LEED prerequisites.

Renewable Energy DeploymentInitiative (REDI)

REDI provides an incentive of 25 per centof the installed cost of renewable energysystems for space and water heating andcooling. Eligible systems include:

� active solar hot water systems

� active solar air heating systems

� highly efficient, low-emitting biomasscombustion systems.

PV systems are not eligible but receiveaccelerated depreciation under Class 43 ofthe Income Tax Act.

Natural Resources CanadaRETScreen

RETScreen is free energy-assessmentsoftware that assesses renewable energyoptions against a base model. RETScreenhas specific modules for passive solar, solar-air heating and solar domestic hot waterheat. Output includes financial analysis,payback periods and energy displaced.Modules are available athttp://www.retscreen.net/ang/menu.php


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33



References

Tap the Sun: Passive Solar Techniques andHome Designs (Canada: CMHC, 1998)Canada Mortgage and HousingCorporation (CMHC)

Ayoub, J., Dignard-Bailey, L. and Filion,A., Photovoltaics for Buildings: Opportunitiesfor Canada: A Discussion Paper, Report # CEDRL-2000-72 (TR), CANMETEnergy Diversification Research Laboratory,Natural Resources Canada, Varennes, Que.,November 2000, pp. 56 (plus appendices).

Sheltair Group, Healthy High-Rise: A Guide to Innovation in the Design andConstruction of High-Rise ResidentialBuildings, (Canada: CMHC, 1996)

Solar Air System: A Design HandbookEditors S. Robert Hastings, Ove Morck,James & James 2000

Edward Mazria, The Passive Solar EnergyBook, Innovative Building Case Studies,CMHC website.

Questions

1. Name three benefits of using

solar energy.

2. Why is passive solar a good

choice for new construction

MURBs?

3. What four window technologies

can improve a window’s

performance as a solar

collector?

4. What is the difference between

active and passive solar energy

systems?

5. What are the main elements of

a hybrid grid-connected

photovoltaic system ?

6. What are the main elements of

a typical solar domestic hot

water system?

7. Name three types of active solar

collectors.

8. What are three pros and three

cons of a Solarwall® type of

ventilation air preheat system?

9. Describe two ways of integrating

PV in MURBs and improving

their cost-effectiveness



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