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

The main room is about 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, in a fixed font like Courier:

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

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

R20 walls and ceiling with 3540ft^2/R20 = 177 Btu/h-F plus R2 doors with
192ft^2/R2 = 96 would make G = 273 Btu/h-F of conductance, including
10 Btu/h-F for the ceiling strip.

On an average January day, we might keep the room 50 F for 6 hours with
sun shining through the doors and room air thermosyphoning through a new
air heater on the upper part of the south wall. When the room is warm
enough, we might push room air from the north part of the ceiling south
through a horizontal plastic film duct under the ceiling into the lower
part of the air heater and stop thermosyponing with one-way plastic film
dampers in vents from the room to the air heater just above the doors,
using Grainger's $62.90 4WT44 10" diameter 26 watt 665 cfm fan (which
has a 176 F max temperature rating.) The existing slow ceiling fans and
a thermostat could warm the room at night and on cloudy days.

With 160 ft^2 of U0.58 Thermaglas twinwall polycarbonate glazing with 80%
solar transmission over the upper south wall and 3520 pounds of water under
the ceiling strip (eg 64 10'x4" thinwall PVC pipes or a 4'x48'x3.5" tray
with water in a 4' layflat poly film duct), we could have 100% solar heat
in December, according to a simple simulation with Phila TMY2 weather data:

20 DAYSTART=344'display start time (days)
30 DS=DAYSTART*24'display start time (hours)
40 RANGE=8760-DS'display range (hours)
50 TMIN=10:TMAX=160'temp display range (F)
60 LINE (0,0)-(639,349),,B:XDF=640/RANGE:YDF=349/(TMAX-TMIN)
70 FOR TR=TMIN TO TMAX STEP 10'temp ref lines
80 LINE (0,349-YDF*(TR-10))-(639,349-YDF*(TR-10)):NEXT
90 GL=263'lower church conductance (Btu/h-F)
100 GU=10'upper church conductance (Btu/h-F)
110 PL=640'length of 4" ceiling pipe (feet)
120 CHU=5.5*PL'upper church capacitance (Btu/F)
130 GP=2*PL'pipe conductance (Btu/h-F)
140 TH=50'constant church temp (F)
150 TU=155'initialize upper church temp (F)
160 TUMIN=200'initialize min upper church temp (F)
170 OPEN "ecayear" FOR INPUT AS #1:LINE INPUT#1,H$
180 FOR H=1 TO 8760'hours of typical (TMY2) year
190 INPUT#1,MONTH,DAY,HOUR,TDB,WIND,TDP,IGLOH,SS,WS,NS ,ES
200 Q=-(TH-TDB)*GL'lower heat loss (Btu)
210 Q=Q+.6*192*SS'add solar gain from existing doors (Btu)
220 Q=Q-(TU-TDB)*GU'add upper heat loss (Btu)
230 QUW=.8*SS*160-(TU-TDB)*160*.58'solar gain from upper wall (Btu)
240 IF QUW0 THEN Q=Q+QUW'add solar gain from upper wall (Btu)
250 TU=TU+Q/CHU'new upper church temp (F)
260 IF TU180 THEN TU=180'limit upper church temp (F)
270 IF TUTUMIN THEN TUMIN=TU:HMIN=H:CLOSS=(TH-TDB)*GL
280 PSET(XDF*(H-DS),349-YDF*(TDB-10))'plot outdoor temp (F)
290 PSET(XDF*(H-DS),349-YDF*(TU-10))'plot upper church temp (F)
300 IF DAY=1 AND HOUR=.5 THEN LINE (XDF*(H-DS),349)-(XDF*(H-DS),345)'months
310 NEXT H
320 TUL=TU'end of year upper church temp (F)
330 CLOSE #1
340 PRINT CHU;HMIN;TUMIN,TH+CLOSS/GP,TUL
350 LINE (XDF*(HMIN-DS),100)-(XDF*(HMIN-DS),0)'mark Hmin

Chu min min water min water end of year
(Btu/F) hour temp temp need water temp

3520 8674 52.96889 F 53.92035 F 152.5393 F

The ceiling pipe water temp drops to about 53 F at 10 AM on 12/27...
The mass of the room itself (about 2K Btu/F, with 1/2" drywall) isn't
important in the simulation, since the room temp is constant. We can't
store useful heat in a thermal mass that doesn't change temperature.

Fin-tube vs PVC pipe would weigh less and might double the system cost,
counting 2 pumps and a stratified tank on the ground and controls, but we
could heat more of the church, and warm it up on Sunday mornings. We could
collect more heat with a new 36'x8'x8'-tall sunroom on the south wall with
8 American Craftsman 6068-2 6'x80" U0.48 sliding glass doors ($269 each at
Home Depot) with 63% transmission and a $300 layer of corrugated Dynaglas
R1 polycarbonate greenhouse roofing with 90% transmission, with 80% black
horizontal shadecloth under 50% of the roof to shade the existing doors
in summertime. (The fin tubes could also naturally cool the church.)

In wintertime, we could pump cool water up from the stratified tank in
the crawlspace through the fin tubes to store solar heat and pump or
thermosyphon hot water up to warm the room, with a thermostat on the cold
end of the fin tube to run the hot pump when the cold end is less than
80 F and a differential thermostat on the hot end to run the cold pump
when the hot end is warmer than the higher tank temp.

The stratified tank might be a 2'-tall plywood box lined with a single
folded piece of EPDM rubber, with a 2'-tall vertical wall to separate
warm and cool sections and a pipe in the upper part of the warm section
that goes to a lower pipe in the cool section.

If the room needs (70-30)273 = 11K Btu/h at 70 F (50 people make about
15K Btu/h) and 100 F ceiling mass with a low-e surface (e = 0.3) below
the ceiling strip radiates 192ft^2se((100+460)^4-(460+70)^4) = 1.9K Btu/h,
where s = 0.1714x10^-8, the ceiling fans with a room temp thermostat and
an occupancy sensor could supply the rest with about (11K-1.9K)/(100-70)
= 300 cfm of airflow.

Nick