[Greenbuilding] An annotated St. Louis TMY2 simulation

Tue Jan 18 14:51:15 CST 2011

Although there are always a lot of assumptions of how heat transfers to the storage mass in the house and the tank of water (which in practise has been found to be one of the limitations of standard models) this is likely not far off of what would be needed to get a 100% solar house.
To accomplish this, 48' of the 60 ft long fully exposed south-facing house (no trees or neighbors please) would need to be covered with air collectors.  
Note that the house has about half the windows of a normal house of 2400 sf, and would likely need to have R60 roof (cause that is cheap) and maybe more R in walls and windows to make up for the heat loss of air leakage, ventilation, and slab, although indoor electrical use of 300-600 kWh/month should help make up for a lot of that.
Then there would need to be the 1075 gallon tank (more likely 2000 once all the additional losses have been added in).
Once such a well insulated airtight house has been built and all the space heating load avoided by using solar mass and indoor temperature swings, the energy bills from the domestic hotwater and electric use would still be pretty big.  Hence why many designs aiming for low energy use / low energy cost have ended up trying to combine a solar hotwater collection system with a space heating system: you get a major offset in what is often the largest energy consumer in the house (once you have low demand with passive solar assist) and can dump available heat into a large tank for space heating as needed.

On 2011-01-18, at 9:06 AM, nick pine wrote:

> Here's a basic simulation for a 40'x60' house with 96 ft^2 of U0.25
> windows and R30 walls and an R40 ceiling using NREL's TMY2 hourly
> weather data file for a Typical Meteorological Year in St. Louis.
> 
> The first few lines set up the screen to allow
> displaying hourly temperatures during the year.
> 
> 20 CLS:SCREEN 9:LINE (0,0)-(639,349),,B
> 30 TMIN=0:TMAX=140:V=350/(TMAX-TMIN)'vertical scaling
> 40 FOR TR=0 TO TMAX STEP 20'plot temp ref lines
> 50 LINE (0,349-V*(TR-TMIN))-(639,349-V*(TR-TMIN)):NEXT
> 60 DS=0:DE=365'start and end display days
> 70 HS=24*DS:HE=24*DE'start and end display hours
> 80 XSF=640/(HE-HS)'horizontal scaling factor
> 
> The next few lines describe the house, thermally-speaking.
> 
> 90 L=60'house length (ft)
> 100 W=40'house width (ft)
> 110 AWIND=96'window area (ft^2)
> 120 UWIND=.25'window U-value (Btu/h-F-ft^2)
> 130 GWIND=AWIND*UWIND'window conductance (Btu/h-F)
> 140 AWALL=8*2*(L+W)-AWIND'wall area (ft^2)
> 150 RWALL=30'wall R-value (h-F-ft^2/Btu)
> 160 GWALL=AWALL/RWALL'wall conductance (Btu/h-F)
> 170 RCEIL=40'ceiling R-value
> 180 GCEIL=L*W/RCEIL'ceiling conductance (Btu/h-F)
> 190 GH=GWIND+GWALL+GCEIL'house conductance (Btu/h-F)
> 200 CH=7000'inherent house capacitance (Btu/F)
> 
> An 8'x48' patch of solar siding and a 1075 gallon tank
> can provide 100% of the house heat in a typical year:
> 
> 210 AHA=384'air heater area (ft^2)
> 220 CW=1075*8.33'warm store capacitance (Btu/F)
> 230 CFM=1000'fan cfm
> 240 RAH=2/AHA+1/CFM'air heater equivalent resistance
> 250 TW=110'initial warm store temp (F)
> 260 TH=70'initial house temp
> 270 TAMIN=100'initialize min outdoor temp (F)
> 280 FOR YEAR=1 TO 2
> 290 AHMIN=1000'min house temp (F)
> 300 NCD=-1'initialize # Nov cloudy days
> 310 OPEN "stlyear" FOR INPUT AS #1:LINE INPUT#1,H$
> 320 FOR H=1 TO 8760'TMY2 hours
> 
> Here's a fundamental simulation step: read the hourly
> outdoor temp and find the house heat loss and adjust
> the house temperature, based on its heat loss and
> thermal mass: IdeltaT = CdeltaV, in electrical terms...
> 
> 330 INPUT#1,MONTH,DAY,HOUR,TA,WIND,TDP,SH,SS,SW,SN,SE
> 340 IH=(TH-TA)*GH'house heat loss (Btu/h)
> 350 TH=TH-IH/CH'new house temp
> 360 TTA=TA+2*.8*SS'Thevenin equivalent air heater temp (F)
> 
> A night setback allows the inherent house mass to store
> overnight heat from solar-warmed air. Without the setback
> the house could not store any heat, so the tank and its
> water heater would have to be larger.
> 
> 370 IF HOUR<6 OR HOUR>22 THEN TT=60 ELSE TT=70'target temp
> 380 QHEAT=(TT-TH)*CH'house heating need
> 390 IF QHEAT<0 THEN QHEAT=0:GOTO 510'house needs no heat. Charge store?
> 400 IF TTA<TH GOTO 460'no ss heat available. Warm house with store?
> 410 IF TTA-QHEAT*RAH-TH<0 GOTO 430'partial sunspace heating
> 420 TH=TT:GOTO 510'full sunspace heating
> 430 IA=(TTA-TH)/RAH'partial sunspace heating (Btu/h)
> 440 TH=TH+IA/CH'new house temp
> 450 QHEAT=(TT-TH)*CH'heat required to reach target temp
> 460 AWARM=(TW-TH)*CW'available warmstore heat
> 470 IF AWARM<0 THEN GOTO 510'no warmstore heat available
> 480 IF QHEAT<AWARM THEN TH=TT:SHEAT=QHEAT:GOTO 500'full target heating
> 490 TH=TH+AWARM/CH:SHEAT=AWARM'partial target heating
> 500 TW=TW-SHEAT/CW'new warmstore temp (F)
> 510 IF TTA-QHEAT*RAH<TW GOTO 560'no heat available for warmstore
> 520 QWARM=(140-TW)*CW'warmstore heating need (Btu)
> 530 IF QWARM<0 GOTO 560'warmstore needs no heat
> 540 IW=(TTA-QHEAT*RAH-TW)/RAH'warmstore charging (Btu/h)
> 550 IF IW<QWARM THEN TW=TW+IW/CW ELSE TW=140'new warmstore temp
> 560 IF TH<AHMIN THEN AHMIN=TH'min house temp (F)
> 570 IF H>HE OR YEAR=1 GOTO 690
> 
> Defining a cloudy day as "one with less than 50% of average sun,"
> ie less than 510 Btu/ft^2, this St. Louis TMY2 file contained
> 11 cloudy days in November of 1979...
> 
> 580 IF MONTH<>11 GOTO 620
> 590 IF DAY=LDAY THEN ST=ST+SS:GOTO 620'accumulate daily solar energy
> 600 LDAY=DAY:STT=ST:ST=0
> 610 IF STT<510 THEN NCD=NCD+1'count November cloudy days
> 620 X=(H-HS)*XSF'horizontal screen coordinate
> 630 PSET(X,349-V*(TA-TMIN))'plot ambient temp
> 640 IF TA<TAMIN THEN TAMIN=TA
> 650 'PSET(X,349-V*(SS/4-TMIN))'plot south sun
> 660 PSET(X,349-V*(TH-TMIN))'plot house temp
> 670 'PSET(X,349-V*(TW-TMIN))'plot warm temp
> 680 IF DAY=1 AND HOUR=.5 THEN LINE (X,349)-(X,345)'mark months
> 690 NEXT H
> 700 CLOSE #1
> 710 NEXT YEAR
> 720 PRINT "2000'";CH,AHA,GH,TAMIN
> 730 PRINT "2010'";CW,TW,AHMIN,NCD
> 
> 7000     384           134.1333     -4.000127E-02
> 8954.75                109.2637      60            11
> 
> This simple simulation can be refined further with heat gain
> from indoor electrical use, direct solar gain from windows,
> slab heat loss, ventilation heat loss, and DHW preheating
> with a pressurized plastic pipe coil in the tank.
> 
> Nick 
> 
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Dr John Straube, P.Eng.
Associate Professor
University of Waterloo
Dept of Civil Eng. & School of Architecture
www.buildingscience.com