design and build a solar house

Design and Build a Solar House

IntroductionThe goal of this engineering project is to construct and test the energy efficiency and solar heat gain of a model house. You will be working with a model rather than a full-sized house, but the principles are the same. This project uses a standard procedure for measuring the ther-mal performance of a house. For the house to lose heat, there must be a temperature difference. The interior must be warmer than the outside. Since you can’t cool down your classroom to 0 °C, you will warm up your house to 10 °C above room temperature. This is done with a heater light bulb inside the house.

As with a real house, what matters is how much of the time the furnace must be on to keep the house warm. The more it’s on, the more energy is used per day and the greater your heating bill. To imitate this situa-tion, you will record what percentage of time the heater light bulb must be on to keep the house at 10° C above room temperature.

Finally, you will perform the same test, but with a bright light shin-ing on the house, imitating sunshine. You can then tell how much your energy bill is reduced by “solar heating.”

The setting is the temperate climate of the northern United States: hot summers and cold winters, with moderate spring and fall seasons. There is a fair amount of sunshine all year, but of course the angle of the sun and the length of the day change significantly from season to season.

You have two basic strategies are to cut down on heat loss and to gain some heating from the sun during cold months. You are limited to pas-sive solar strategies. Designs that depend on collectors, pumps, and fans are called active solar collectors and they are not available in this project.

The initial materials will be cardstock, clear acetate, and tape. You must write down a design rationale before you start building and testing. Af-ter you test it, you can start trying other materials and modifications to make it perform better. (See “Modify Solar House.”)

Design a model house that uses as little energy as possible to keep it warm.

Note: This is one chapter of a longer engineering project which includes modifying and retesting this house as well as explorations of the various mechanisms of heat transfer—conduction, con-vection, radiation, and heat capacity—with hands-on or model-based experiments. See: http://concord.org/ engineering

United States License (CC BY-NC 3.0 US).

The design of the house is up to you, but there are specific goals that you should address:

• Thehousehasfeaturesthatyouthinkwillmakeitenergyefficient.• Theinteriorwouldbecomfortabletobeinonasunnydayora

coldnight.• Thehouseshouldbeattractiveandhave“curbappeal.”

Inadditiontherearegeometriclimitations:

• Thehouseshouldfitontoa28x36cmplatform.• Tomakeroomfortheheaterlightbulb,thewallsmustbeatleast

20cmhighandtheremustberoomtocuta12cmdiameterhole(thesizeofaCD)inthecenterofthefloor.

• Thehousemustbebuildable–thatis,nottoocomplexandnottoomanypieces.

• Theminimumwindowareais50cm2.

Note:Inyourinitialdesign,youarelimitedtocardstockandclearac-etateasbasicbuildingmaterials.

Design goals

1. Design the house using sketches to help you picture it. Make three different designs.

2. Review the three designs and choose the best one for building and testing.

3. Make the pieces for the chosen design and assemble the house.

4. Test the house for energy efficiency.

All of the tools and materials required for this project are described in the “Tools and Materials” Appendix.

Students design and build their

ownhouse,basedonwhat

theyhavelearnedaboutheat

transfer.Theyareaskedto

comeupwiththreedistinct

designs,makesketchesofeach,

and choose the best one for

constructionandtesting.

Learning goals:

• Explainmaterialanddesign

choices based on

constraintsorstatedgoals.

• Justify a design using

scientific content

knowledgeandprinciples.

• Justify results using

scientific content

knowledge.

Beforeyoubegindesigningyourhouseonthecomputer,brainstormwithyourteamaboutthegoalsandhowyouwilladdresseachone.Then answerthefollowingquestions.

Whatshapeandsizeofthebuildingwillcontributetothehouse’senergy efficiency?

Whatroofshapewillcontributetothehouse’senergyefficiency?

Howwillyouorientthebuildingtotakeadvantageofsunlight?What windowsizesandplacementwillbegoodforsolargain?

Design rationale

Besurestudentswriteouta

serious design rationale before

theystartdesigning.

Describetheotherfeaturesthatyouwouldlikeyourhousetohavein ordertomeetthedesigngoals.

Design procedure

Makesketchesorscaledrawings(whateverworksbestforyou),sothatyoucanpicturewhatyourhousewilllooklikeandcommunicateyourideastoyourteam.Ifyouuseextrapages,tuckthemintotheworkbook.

Design #1

NowstepbackandconsiderasateamhowwellDesign#1meetsyourgoals.Hereisachecklist,butaddothergoalsifyouhaveany.

• Energyefficiency• Ease of building• Attractiveness• Shape• Simplicity• Size• Comfort

DescribehowDesign#1successfullymetthesegoals.

DescribehowDesign#1wasnotsuccessful.

EvaluationofDesign#1

Askeachteammemberto

makeanindependentsketch,

sothateachstudenttakes

responsibility for at least one

design.Theteamasawhole

candiscussandevaluateeach

design.Encouragethemto

comeupwithavarietyof

designs.

Don’tbesatisfiedwithyourfirstattempt!Tryanaltogetherdifferent design.Again,makesketchestoworkoutyourdesign.

Design #2

StepbackandconsiderhowwellDesign#2meetsyourgoals.

StepbackandconsiderhowwellDesign#3meetsyourgoals.

Tryonemorealtogetherdifferentdesign.Again,makesketchestoworkoutyourdesign.

Design #3

Younowhavethreedesignstochoosefrom.Eachonemayhavefeaturesthatyoulikeordislike.Reviewthedesigngoalsandselectoneofthemforbuildingandtesting.Tohelpyouchoose,fillouttheratingchartbelow.3=excellent,2=good,1=fair,0=bad

Whichdesignwillyouselect?

Explainwhyyouselectedthedesignthatyoudid.

Select your best design

Results

Goal House #1 House #2 House #3

Energy efficiency

Ease of building

Attractiveness

Simplicity

Comfort

Aftereachteamselectstheir

preferreddesign,havethem

presentittothewholeclass

andexplainthevirtuesand

drawbacksoftheirdesign

choices.

Construction

1.Youhavedesignedabuildingwithacertainshapeandfeatures.Nowyouneedtomakeallofthepiecesandassembleit.The examplebelowshowshowyoucouldproceed.

2.Drawtheoutline(firstfloorplan)ofyourhouseoncardstock.To accommodatetheheaterlightbulb,itmustbelargeenoughtoplaceacircleonitwithadiameterof12cm.Itmustfitentirelyonthebase.

3.Cutacircleoutofthecenterofthefloorthatis12cmindiameter(thesizeofaCD)sothatthelightbulbheatercanfitin.

4.Makewallsforyourhousethatare20cmhighandgoallthewayaroundthefloorplan.Notethatifyouwantagableroof(seeexam-plebelow),someofthewallswillhavetriangulartops.Usethelay-outshownbelowtofindthewalllengthsfromthefloorplan.Drawoutthewallsoncardstock,allnexttoeachothertosavematerials.Cutoutthewalls.

Results

Goal House #1 House #2 House #3

Energy efficiency

Ease of building

Attractiveness

Simplicity

Comfort

Tools & materials

• Scissors

• Pencils

• Metalruler(cm)

• Protractor

• Safetyutilitycutter

• Cardstock(approximatelyone 20x30 in sheet)

• Acetatesheets(8.5x11in)for windows

• Maskingtapeand/orcleartape

• 28x36cmplatform

Here is one procedure for

makingahousefromasketch.

Thedesignshownisthesame

as the standard house used in

Chapter1.Studentscanuse

anotherprocedureiftheywish.

Encouragethemtogroupthe

piecestocutdownon

measuringandreducepaper

waste.

5.Decidewhatkindofroofwillwork.Trytouseadesignthatisnottoohardtobuild.Drawalloftheroofpiecesoncardstock.Youcanusethewalllengthstodetermineroofdimensions,asshowninthedrawingbelow.Ifyouareuncertainaboutsomedimensionsandangles,makethemoversizedandtrimthemdowntofit.

6.Drawandcutoutwindowsthatareinthewalls(androof,ifany)andtapepiecesofacetateoverthemontheinside.

7.Tapetheedgesofyourhousetogether.Hereisonesetofstepsthatyoucouldfollow:Itworkswelltofollowthesesteps:

a)tapethewallpiecestogether

b) tape the roof pieces together

c)tapetherooftowalls

d)tapethefloortowalls

Hereisanothermorecomplexexample–anL-shapedhouse.Notethatthedashedlinesonthefloorplan(AandB)givethelengthsoftheroofpiecesattheridge.

Hereistheassembledhouse.

Your house

Floor area (cm2)

Window area (cm2)

Window/floor ratio

South-facing window area (cm2)

South window/floor ratio

8.Makeaholeinonewallforthetemperaturesensor10cmabovethefloor.Pickthewallthatisfarthestfromtheheaterlightbulb.Thesensorwillgo3cmintothehouseanditmustbeatleast5cmfromtheheaterlightbulb.

9.Calculatethetotalfloorareaandwindowareaofyourhouse.Alsocalculatethewindowareathatfacessouth.Yourmeasurementscanberoundedtothenearestcentimeter.Filloutthetablebelow.

Yourgoalintestingyourhouseistomeasurehowmuchpowerittakestokeepyourhouse10°Cwarmerthantheairaroundit.

House heating test

Collect data

1. Connectonetemperaturesensortoyourcomputer.Setupdatacollectionforonereadingpersecondandatotaltimeof600sec-onds.

2. Measuretheroomtemperature.Wewillassumeitstaysreasonablyconstantthroughouttheexperiment.Recordtemperaturein thetablebelow.

3. Calculateyourtargettemperature:10°Caboveroomtemperature.Recordyourroomandtargettemperatureinthetablebelow.

4. Insertthetemperaturesensorintheholeyoumadeinthehouse.Itmustbepushedthroughthewall,sothatitis3cmfromthewall.

5. Turntheheateron.

6. Startcollectingdatawhenthesensorisafewdegreesbelowthetargettemperature.

7. Whenthesensorreaches0.2°Cabovethetargettemperature,switchtheheaterOFFandrecordthetimeinthetablebelow(A).

8. Whenthesensordropsto0.2°Cbelowthetargettemperature,switchtheheaterONandrecordthetimeinthetablebelow(B).

9. Whenthesensoragainreaches0.2°Cabovethetarget temperature,switchtheheaterOFFandrecordthetimeinthetablebelow(C).

10.Stopcollectingdata.

11.Clickthe“scale”icontofitthegraphtoyourdata.

12.Savethedatafile.

13.Calculatetheaveragepowerrequirementtokeepthehousewarmbyfillingouttherestofthetablebelow.

Tools & materials

• Onefast-responsetempera-ture sensor (for example, the Vernier surface tem-perature sensor STS-BTA)

• Computerorothergraph-ing interface for tempera-ture sensor

• One40Wlightbulbheaterin a socket with an inline switch, covered with foil (page 23)

NOTE:Ifyourhouseislargeor has lots of window area, you may need to change the 40Wheaterbulbto75W.Besuretouse75Winsteadof40Wwhenyoucalculatetheaverage power requirement on the next page.

This is the basic house heating

test.Pointoutthatthe

students are acting as a

“humanthermostat.”Review

howitisanalogoustoareal

housefurnace,whichturnson

andofftokeepthehouseat

aconstanttemperature.The

furnaceoutput(power)multi-

pliedbythepercentageoftime

itison(percent)istheaverage

powerrequirementtokeepthe

housewarm.

House heating test

Room temperature: _____°C

Target temperature: _____°C

Upper limit (target temperature + 0.2): _____°C

Lower limit (target temperature – 0.2): _____°C

Event Time (from data table)

A. Turn heater OFF at upper limit

B. Turn heater ON at lower limit

C. Turn heater OFF at upper limit

D. Total cycle time (C - A)

E. Total time ON (C - B)

F. proportion of time the heater is on(C - B) / (C - A)

G. Average power requirement(40 watts * the proportion of time the heater is on)

_______W

Note: the house does not need

tocooldownbetweenthisand

thenextexperiment(page18)

sostudentscansavetimeby

doingthembothtogether.

Makeatableofeveryone’s

results so that they can be

comparedanddiscussed.

Includethefloorandwindow

areas,whichmayhelpexplain

someofthedifferences.

Oncetheroomtemperature

hasbeenmeasured,

thewholeclasscanusethe

samevaluethroughoutthe

project unless a large change

(morethan2-3°C)isnoticed.

Thenstudentsdon’tneedto

waitfortheirhousetocool

downbetweenexperiments.

Thiswillsaveconsiderabletime.

Whatspecificfeaturesofyourdesigncontributedtoordetractedfromtheenergyperformanceofthehouse?

Results

Basedonyourresultswhatdesignchangeswouldyouproposeto improvetheperformanceofthesedesignfeatures?

Collect data

1. Connectthetemperaturesensortoyourcomputer.

2. Setupdatacollectionforonereadingpersecondandatotaltimeof600seconds.

3. Assumethatroomtemperaturehasnotchanged.Calculatethetargettemperature(roomtemperature+10°C)andenteritinthetablebelow.

4. Setupthegoosenecklampwitha300Wbulbinit,duesouthofthebuilding.Thetipofthebulbshouldbe20cmfromthehousewindowandaimeddownwardatabouta35°angle,asifitwerenooninwinterat40°NorthLatitude.Usethetemplatetopositionthesun.

5. Switchtheheaterlightbulbandthesunlightbulbon. NOTE: The bulb is very hot. Be careful not to touch it, and wait un-til it cools down to move or store it. Turn it off except while doing the experiment.

Solar heating test

Tools & materials

• Onefast-responsetempera-ture sensor (for example, the Vernier surface tem-perature sensor STS-BTA)

• Computerorothergraph-ing interface for tempera-ture sensor

• One40Wlightbulbheater

• One300Wsunlightbulbin a gooseneck desk lamp (page 23)

• Templateformeasuring“sun’s”angle(page25)

Insistthatstudentsbevery

carefulwiththelightbulbs,

turningthemoffwhennot

inuse.

6. Startcollectingdatawhenthesensorisafewdegreesbelowthetargettemperature.

7. Whentheuppersensorreaches0.2°Cabovethetargettempera-ture,switchtheheaterOFFandrecordthetimeinthetablebelow(A).Leavethesunon.

8. Whentheuppersensorreaches0.2°Cbelowthetargettempera-ture,turntheheaterON.Recordthetimeinthetablebelow(B).

9. Whenthesensoragainreaches0.2°Cabovethetargettempera-ture,switchtheheaterOFFandrecordthetimeinthetablebelow(C).

10.Stopcollectingdata.

11.Clickthe“scale”icontofitthegraphtoyourdata.

12.Savethedatafile.

13.Calculatetheaveragepowerrequirementtokeepthehousewarmbyfillingouttherestofthetable.

Solar heating test

Room temperature: _____°C

Target temperature: _____°C

Upper limit (target temperature + 0.2): _____°C

Lower limit (target temperature – 0.2): _____°C

Event Time (from data table)

A. Turn heater OFF at upper limit

B. Turn heater ON at lower limit

C. Turn heater OFF at upper limit

D. Total cycle time (C - A)

E. Total time ON (C - B)

F. Proportion of time the heater is on(C - B) / (C - A)

G. Average power requirement (40 watts * proportion of time heater is on) _______W

H. Power requirement without sun _______W

I. Solar contribution _______W

Add these results to the shared

tablefordiscussion.

Results

Howdidthissolar-heatedhouseperformcomparedtothehousewith-outsunlight?

Whatspecificfeaturesofyourdesigncontributedtoordetractedfromitsperformanceasapassivesolarhouse?Includetheevidencefromyourteststhatsupportyourclaims.

Basedonyourresultswhatdesignchangeswouldyoumaketoimproveitsperformance?

Whataretheadvantagesanddisadvantagesofhavinglargesouth-facingwindows?

Advantages:moresolargaininwinter,lessinsummer.Coldsurfaceinwinter.

Disadvantages:largeconductivelossinwinter,conductivegaininsummer.

Procedure

1. Cutofftheoutletendoftheextensioncord.Stripthewires.

2. Installtheinlineswitchintheextensioncord.Notethatthe common(ground)wirehasribsandthelive(hot)wireissmooth.Makesuretheswitchinterruptsthehotwire.

3. Drilla5/16”(8mm)holethroughthesideofthepancakeboxandinsertthecord.

Fabricating a light bulb heater

Tools & materials

The required parts, available at any hardware store, are:

• keylesssocket(plasticorceramic)

• 6’extensioncord

• inlineswitch

• metalpancakebox

• 40Wlightbulb

• aluminumfoil

4. Attachthewirestothekeylesssocket.Theribbed(ground)wireisattachedtoasilverscrewandthesmooth(hot)wireisattachedtoabrass-coloredscrew.

5. Screwthesockettothepancakebox.Coverthebulbwithalayeroffoiltocutdownonradiation.

design and build a solar house

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