OXFORD BROOKES UNIVERSITY

P30401 – Building Physics & Thermal Comfort. Professor M. G. Hutchins

Assignment 3 – Monday 8th December 2008

Andrea Luise Schrader

CalculationOfAnnualSpaceHeatingRequirement.Atwostoreydetatchedhouseis10mwide,8mdeepwiththelongfacadesfacingNorth/South. Theheight of each storey is 2.75mThe glazed areason theNorth, South, East&West facadesare10m2,15m2,4m2&4m2 respectively.Window framesoccupy15%ofthewindowarea,allwindowshavecleardoubleglazingandallwindowsareunshaded.Theheightoftheatticespaceis2.75mandtheridgeoftheroofarearunsEast/Westandis10mlong.Forallmonthsthereareanaverageof0.5airchangesperhour. Internalgainsamount to 15kWh/day, and the mean internal temperature is required to be 19 oC. A“medium”utilisationfactor(a=1.8)applies.TherespectiveU‐valuesoftheenvelopecomponentsare:WallU‐value=0.35W.m‐2oC‐1FloorU‐value=0.40W.m‐2oC‐1RoofU‐value=0.20W.m‐2oC‐1WindowU‐value=2.7W.m‐2oC‐1(frame&glazing)Windowtotalsolarenergytransmittance,g=0.76The monthly mean daily ambient temperatures and the monthly mean daily solarirradianceoneachverticalplanearegiveninTable1&Table2respectively:

Month JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DECMeanTemp0C

2.9

3.8

7.6

11.0

14.4

18.7

19.6

19.8

14.2

11.7

6.4

1.9

Table1.Monthlymeandailyambienttemperatures.

Month JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DECNorth 0.27 0.49 0.86 1.39 1.87 2.14 1.88 1.45 1.05 0.60 0.34 0.21South 1.24 1.87 1.69 2.23 2.77 2.73 2.78 2.98 2.59 2.33 1.57 1.10East 0.42 0.87 1.37 2.05 2.52 2.75 2.74 2.47 1.65 0.96 0.50 0.32West 0.47 0.87 1.42 2.37 3.03 3.04 3.01 2.78 1.99 1.36 0.72 0.40Table2.Estimatedmonthlymeansofdailyglobalradiationonverticalplanes(kWh/m2day)Additionaldata:No.ofsecondsinoneday=86400Specificheatcapacityofair=1050J/kg.oCDensityofair=1.25kgm‐2MeanDailyGroundTemperature=13oC

FINDTHERESPECTIVEDAILYANDMONTHLY1. HEATLOSSinkWh;SOLARGAINinkWh;TOTALGAINinkWh2. GAIN/LOSSRATIOANDUTILISATIONFACTOR3. USEFULGAINinkWh4. FABRIC/VENTILATIONLOSS5. MONTHLY/ANNUALSPACEHEATINGREQUIREMENT(inkWhandin£)Assumethecost

ofakWhtobe£0.096. INVESTIGATE THE SENSITIVITY OF THE ANNUAL SPACE HEATING REQUIREMENT TO

REPLACINGTHEGLAZINGWITHAWINDOWWITH:

(i) g=0.75,U=1.6W/(m2C);(ii)g=0.34,U=1.1W/m2C7. FOR CASE i) INVESTIGATE THE SENSITIVITY OF THE ANNUAL SPACE HEATING

REQUIREMENTTOTHEWINDOWWALLRATIO.8. FORCASEi)ANDTHEDEFAULTGLAZINGAREASINVESTIGATETHESENSITIVITYOFTHE

ANNUAL SPACE HEATING REQUIREMENT TO THE AIR TIGHTNESS OF THE BUILDING.ASSUMINGANAIDIABETICINTERFACECALCULATEANDCOMPARETHEANNUALSPACEHEATINGREQUIREMENTFORASEMI‐DETATCHEDANDMID‐TERRACEBUILDING.

TotalMonthlyHeatLosses(kWh)

MonthlyHeatLossesDividedBySource(kWh)

TotalMonthlySolarGain.(kWh)

MonthlySolarGainsDividedBySourcingFaçade.(kWh)

TotalMonthlyGain.(kWh)

TotalLosses/TotalUsefulGains/TotalLossesGraphsTobeaddedasoverlayedgraph.

TotalMonthlyGains&Losses.(kWh)

TheGainsToLossesRatio(GLR)&TheUtilisationFactor(UF)Compared.

MonthlyUsefulHeatGain(kWh)

MonthlyVentillationLosses(kWh)

MonthlySpaceHeatingRequirement.(kWh)

AnnualSHR(kWh) 10825.6825

AnnualCost(£0.09) 974.3114251

INVESTIGATE THE SENSITIVITY OF THE ANNUAL SPACE HEATING REQUIREMENT TOREPLACINGTHEGLAZINGWITHAWINDOWWITH:

(i) g=0.75,U=1.6W/(m2C);

AnnualSHR(kWh) 9597.516277

AnnualCost(£0.09) 863.7764649

(ii) g=0.34,U=1.1W/m2C

AnnualSHR(kWh) 9046.125425

AnnualCost(£0.09) 814.1512882

AComparisonOfTheMonthlySHROfOption(i),(ii)&Default.(kWh)

TheaffectofairchangeontheASHRinadetatched,semidetatchedandmidterracehouse.(kWh)

DataForOption(i)Detatched AirChanges/n

AnnualSHR(kWh) Cost(£)

0.1 8026.88 542.420.2 6887.26 619.850.3 7771.00 699.390.4 8675.23 780.770.5 9597.52 863.780.6 10535.81 948.220.7 11488.38 1033.950.8 12453.75 1120.840.9 13430.62 1208.761.0 14417.89 1297.61

DataForOption(i)SemiDetatchedAirChanges/n

AnnualSHR(kWh) Cost(£)

0.1 4384.5 394.610.2 5189.77 467.080.3 6026.12 542.350.4 6889.24 620.030.5 7775.61 699.80.6 8682.31 781.410.7 9606.92 864.62

0.80 10547.41 949.270.90 11502.04 1035.181.00 12469.33 1122.24

DataForOption(i)Mid‐TerraceHouseAirChanges/n

AnnualSHR(kWh) Cost(£)

0.1 2595.75 233.620.2 3305.88 297.530.3 4062.51 365.630.4 4858.13 437.230.5 5686.76 511.810.6 5643.67 588.930.7 7424.95 668.250.8 8327.49 749.470.9 9248.65 832.381 10182.26 916.76

g=0.85TOTALDAILYHEATLOSSES/GAINS/USEFULLGAINSinkWh

MONTHLYHEATLOSSES/GAINS/USEFULLGAINSinkWh

GAIN/LOSSRATIOANDUTILISATIONFACTOR

g=0.75TOTALDAILYHEATLOSSES/GAINS/USEFULLGAINSinkWh

MONTHLYHEATLOSSES/GAINS/USEFULLGAINSinkWh

GAIN/LOSSRATIOANDUTILISATIONFACTOR

g=0.34TOTALDAILYHEATLOSSES/GAINS/USEFULLGAINSinkWh

MONTHLYHEATLOSSES/GAINS/USEFULLGAINSinkWh

GAIN/LOSSRATIOANDUTILISATIONFACTOR

MONTHLYSPACEHEATINGREQUIREMENT(in£)costofakWh‐>£0.09