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Church solar heating improvements

Discussion in 'Home Power and Microgeneration' started by [email protected], Jan 10, 2008.

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  1. Guest

    When the Pottstown PA UU church was built, one part of the plan
    was a sunspace on the south wall, which hasn't been built yet...

    The main room is 44'x48'x16' tall. The 48' east and west walls slope in 4'
    as they rise to 8'. The ceiling has a 4'x48' north-south horizontal strip.
    The south wall includes 4 sliding glass doors D, each about 6'x8', with
    no eyebrows for summer shading.

    Here's a flattened view from above, viewed in a fixed font like Courier:

    . ---------------------- . --
    | \ | 430 ft^2 | / | 4'
    ......| \ |----------------------| / | --
    . | |\ |d | /| |
    . | D | \ | 860 ft^2 | / | |
    D | | \ |d | / | |
    . f | | \| |/ | | |
    . u | D | |----------------------| | |
    <--S . t | | |4' 192 ft^2 |160 |320 | 36'
    . u | D | |----------------------|ft^2|ft^2|
    . r | | /| |\ | | |
    D e | | / |d 860 ft^2 | \ | |
    . | D | / | | \ | |
    . | |/ |d | \| |
    ......| / |----------------------| \ | --
    | / | 430 ft^2 | \ | 4'
    . ---------------------- . --

    | 12' | 8' | 8' | - 48' - | 8' | 8' |

    We could collect heat with a new 36'x8'x8'-tall sunspace on the south wall
    (left above) with 2 American Craftsman 6068-2 6'x80" U0.48 glass patio doors
    ($269 each at Home Depot) with 63% transmission and 12 4'x8' clear flat U0.5
    polycarbonate panels (about $100 each) with 80% solar transmission and a $300
    clear corrugated Dynaglas R1 polycarbonate roof with 90% transmission, with
    80% shadecloth under 50% of the roof to shade existing doors in summertime.
    Vents in the upper part of the sunspace and thermal mass in the crawlspace
    could naturally cool the church in summertime, as previously envisioned.

    R20 walls and ceiling with 3540ft^2/R20 = 177 Btu/h-F plus R2 doors with
    192ft^2/R2 = 96 make the room conductance to outdoors 273 Btu/h-F, including
    10 for the ceiling strip, made shiny to keep the room cooler. On an average
    January day at 50 F, the room needs (50F-30F)273 = 5460 Btu/h, or 131K Btu,
    eg 131K/6h = 21.8K Btu/h of 90 F sunspace air collected over 6 hours at
    1000 cfm, with a 70 F thermal mass C with lots of surface.

    Storing heat for 5 cloudy days, (70-50)C = 5x131K makes C = 32750 Btu/F,
    eg 525 ft^3 (5") of water in 8 4'x40' $20 greenhouse poly film ducts laid
    flat in the crawlspace... 131K Btu of room heat and a sunspace gain of
    0.8x448ft^2x1000 = 358K Btu and a 6h(90-30)448ft^2xU0.5 = 80.6K Btu loss to
    the outdoors leaves 147K Btu of surplus heat for the rest of the building.

    A car radiator near the top of the sunspace might store heat in a 140 F
    4'x8'x3'-tall plywood tank lined with a single folded piece of EPDM rubber,
    with a $60 300'x1" PE black pressurized plastic pipe coil to make hot water
    for sinks and a quick warmup when the room is occupied, with subsequent
    venting, since 50 people make about 15K Btu/h, if they are not asleep :)

    On an average day, sunspace air could flow north under the ceiling and down
    to the crawlspace and back south through the crawlspace into the sunspace.
    At night, the existing furnace blower could pull room air down through
    a vertical duct in the sunspace and north through the crawlspace and push
    it back into the room from existing registers near the top of the north wall.
    We could quickly warm the room to 70 F on Sunday mornings by pumping tank
    water up through the radiator and moving room air up through the vertical
    duct without heating the crawlspace mass.

    We could have 100% solar heat in December with 100' of 30" crawlspace duct,
    according to this simple simulation using NREL's Phila hourly weather data
    for a Typical Meteorological Year (TMY2):

    10 SCREEN 9:KEY OFF:CLS
    20 DAYSTART=10'display start time (days)
    30 DS=DAYSTART*24'display start time (hours)
    40 DAYEND=30'display end time (days)
    50 DE=DAYEND*24'display end time (hours)
    60 RANGE=DE-DS'display range (hours)
    70 TMIN=10:TMAX=100'temp display range (F)
    80 LINE (0,0)-(639,349),,B:XDF=640/RANGE:YDF=349/(TMAX-TMIN)
    90 FOR TR=TMIN TO TMAX STEP 10'temp ref lines
    100 LINE (0,349-YDF*(TR-10))-(639,349-YDF*(TR-10)):NEXT
    110 GC=273'church conductance (Btu/h-F)
    120 SSA=448'sunspace glazing area (ft^2)
    130 SSU=.5'glazing U-value (Btu/h-F-ft^2)
    140 SSG=SSA*SSU'sunspace conductance (Btu/h-F)
    150 SST=.8'glazing solar transmission (fraction)
    160 CFM=1000'sunspace fan cfm
    170 LD=100'crawlspace duct length (ft)
    180 WD=4'crawlspace duct width (ft)
    190 AD=LD*WD'duct heat transfer area (ft^2)
    200 GD=1.5*AD'duct conductance (Btu/h-F)
    210 DW=6'water depth (inches)
    220 VD=LD*WD*DW/12'crawlspace water volume (ft^3)
    230 CC=VD*62.33'crawlspace capacitance (Btu/F)
    240 SER=1/SSG+1/CFM+1/GD'sunspace equivalent resistance (F-h/Btu)
    250 TR=50'constant church temp (F)
    260 TC=95'initialize crawlspace temp (F)
    270 TCMIN=200'initialize min crawlspace temp (F)
    280 OPEN "ecayear" FOR INPUT AS #1:LINE INPUT#1,H$
    290 FOR H=1 TO 8760'hours of typical (TMY2) year
    300 INPUT#1,MONTH,DAY,HOUR,TDB,WIND,TDP,IGLOH,SS,WS,NS,ES
    310 Q=-(TR-TDB)*GC'church heat loss (Btu)
    320 SSGAIN=SST*SSA*SS'sunspace solar gain (Btu)
    330 TSE=TDB+SSGAIN/SSG'Thevenin equivalent SS temp (F)
    340 IF TSE>TC THEN Q=Q+(TSE-TC)/SER'add sunspace gain (Btu)
    350 TC=TC+Q/CC'new crawlspace temp (F)
    360 IF TC>100 THEN TC=100'limit upper crawlspace temp (F)
    370 IF TC<TCMIN THEN TCMIN=TC:HMIN=H
    380 PSET(XDF*(H-DS),349-YDF*(TDB-10))'plot outdoor temp (F)
    390 PSET(XDF*(H-DS),349-YDF*(TC-10))'plot crawlspace temp (F)
    400 IF DAY=1 AND HOUR=.5 THEN LINE (XDF*(H-DS),349)-(XDF*(H-DS),345)'months
    410 NEXT H
    420 TCL=TC'end of year crawlspace temp (F)
    430 CLOSE #1
    440 PRINT CC;HMIN;TCMIN,TCL
    450 LINE (XDF*(HMIN-DS),100)-(XDF*(HMIN-DS),0)'mark hmin

    crawlspace yearly min year end
    capacitance time temp temp

    12466 Btu/F 848 h 61.9 F 93.60823 F

    The crawlspace water temp drops to about 62 F at 8 AM on 2/4.

    Nick
     
  2. Guest


    I don't think so.
    I suspect that the thin wall thickness and material conductances are much
    higher than the still water film conductances, with a layer of crud on
    the outside, and the pipe holds 13 gallons of water which can heat well
    between hot water usage bursts of 13 gallons or less.

    Nick
     
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