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Posted by nicksanspam on June 26, 2006, 12:30 pm
 

Oops. I added instead of subtracted in line 240, so now it looks like
the savings would be larger, about $9K per year, or 44% with no roof cover.
The low RH indoor air required to avoid condensation on windows in wintertime
makes the room and the pool lose lots of heat. We might collect condensation
instead, or avoid it in other ways, eg a pool cover or local heaters below
windows and doors and ceiling to raise their surface temps, or a large
dehumidifier or air conditioner that puts heat back into the pool.

A single cover (eg a $00 50'x100' piece of polyethylene greenhouse film
with a 4-year guarantee attached to the roof at the edges) might save about
$4K per year, or a little more in July, if it preheats water for showers.

20 SLOPE=ATN(28*8/12/(19*2.34))'roof slope (radians)
30 DATA 30.4,37.9,620,1000,0.0025
40 DATA 33.0,41.0,870,1080,.0027,42.4,51.6,1200,1070,.0036
50 DATA 52.4,62.6,1520,950,.0050,62.9,73.1,1760,830,.0080
60 DATA 71.8,81.7,1940,790,.0111,76.7,86.1,1890,820,.0133
70 DATA 75.5,84.6,1710,940,.0130,68.2,77.6,1380,1070,.0104
80 DATA 56.4,66.3,1020,1150,.0070,46.4,55.1,680,900,.0048
90 DATA 35.8,43.4,530,900,0.0032
100 P87=EXP(17.863-9621/(460+87))'87 F sat vapor pressure ("Hg)
110 P85=EXP(17.863-9621/(460+85))'85 F vapor pressure near pool ("Hg)
120 APd00'indoor pool area (ft^2)
130 AR0*51.5/COS(SLOPE)'main roof area (ft^2)
140 TR0'roof water temp (F)
150 P100=EXP(17.863-9621/(460+100))'100 F sat vapor pressure ("Hg)
160 GG=7'glazing conductance to outdoor air (Btu/h-F-ft^2)
170 K10/GG'constant
180 GP=1.58'gas price ($/therm)
190 FOR MONTH = 1 TO 12
200 READ TA,TM,HSUN,SSUN,W
210 TN=TA-(TM-TA)'average daily min temp (F)
220 TD=TA+(TM-TA)/2'average daytime temp (F)
230 TW=TN+.7*(87-TN)/2'indoor window surface temp (F)
240 TDP=TW-5'max indoor dew point to avoid night condensation (F)
250 PA=EXP(17.863-9621/(460+TDP))'indoor vapor pressure ("Hg)
260 PLOSS$*100*AP*(P85-PA)/100000!'daily pool heat loss (therms/day)
270 RH0*PA/P87'max indoor RH to avoid night condensation (%)
280 RRH=INT(RH+.5)'round RH
290 SUN=HSUN*COS(SLOPE)+SSUN*SIN(SLOPE)'roof solar gain (Btu/ft^2-day)
300 PO).921/(1+.62198/W)'outdoor vapor pressure ("Hg)
310 RGAINNC=AR*(SUN-6*100*(P100-PO))/100000!'roof gain, no cover (therms/day)
320 IF RGAINNC<0 THEN RGAINNC=0'roof loss vs gain
330 IF RGAINNC>PLOSS THEN RGAINNC=PLOSS'more gain than loss
340 K2=K1*P100+460+TD'constant
350 TGQ0'initial Tg est (R)
360 TG=K2-K1*EXP(17.863-9621/TG)'glazing temp (R)
370 IF ABS(TGL-TG)>.01 THEN TGL=TG:GOTO 360'iterate
380 RGAINW=AR*(.9*SUN-6*(TG-460-TD)*GG)/100000!'roof gain (therms/day)
390 IF RGAINW<0 THEN RGAINW=0'roof loss vs gain
400 IF RGAINW>PLOSS THEN RGAIN=PLOSS ELSE RGAIN=RGAINW'more gain than loss
410 PRINT 500+MONTH;"'";TAB(8);RRH,PLOSS,RGAINNC,RGAIN,RGAINW
420 TGAINNC=TGAINNC+RGAINNC'roof gain with no cover
430 TGAIN=TGAIN+RGAIN'roof gain with cover
440 TGAINW=TGAINW+RGAINW'roof gain with cover and DWW
450 NEXT
460 SAVINGSNC0*GP*TGAINNC'yearly savings with no cover ($)
470 SAVINGS0*GP*TGAIN'yearly savings ($)
480 SAVINGSW0*GP*TGAINW'yearly savings with DHW ($)
490 PRINT SAVINGSNC,SAVINGS,SAVINGSW

Month  RH max   pool use          --- roofgain (therms/day) ---
       (%)      (therms/day)  no cover      cover         cover+DHW

1      19       150.2703      0             0             0
2      20       148.1657      6.165614      11.61019      11.61019
3      25       138.9444      24.38077      31.94458      31.94458
4      31       126.7394      40.49223      51.02791      51.02791
5      40       109.2206      54.99459      67.52151      67.52151
6      49       90.41354      68.24747      82.37038      82.37038
7      55       77.63085      69.73278      77.63085      84.81842
8      54       79.8583       62.59364      77.58797      77.58797
9      46       97.14828      44.37123      58.5638       58.5638
10     34       120.0277      22.22977      34.43198      34.43198
11     28       133.1368      0             6.749671      6.749671
12     22       144.7639      0             0             0

Yearly savings:              $8,638.07    $3,673.4     $4,014.09

This calculation only considers the pool heat loss, vs the energy loss
from cold dry outdoor winter makeup air or mechanical dehumidification
needed to keep the room RH low.

Nick


Posted by nicksanspam on June 27, 2006, 12:14 pm
 

If we consider the energy cost of dehumidification (and fix the bug in
line 230 below), the solar savings is about the same, but the heating
cost goes up...

20 SLOPE=ATN(28*8/12/(19*2.34))'roof slope (radians)
30 DATA 30.4,37.9,620,1000,0.0025,33.0,41.0,870,1080,0.0027
40 DATA 42.4,51.6,1200,1070,.0036,52.4,62.6,1520,950,0.0050
50 DATA 62.9,73.1,1760,830,.0080,71.8,81.7,1940,790,0.0111
60 DATA 76.7,86.1,1890,820,.0133,75.5,84.6,1710,940,0.0130
70 DATA 68.2,77.6,1380,1070,.0104,56.4,66.3,1020,1150,0.0070
80 DATA 46.4,55.1,680,900,.0048,35.8,43.4,530,900,0.0032
90 P87=EXP(17.863-9621/(460+87))'87 F sat vapor pressure ("Hg)
100 P85=EXP(17.863-9621/(460+85))'85 F vapor pressure near pool ("Hg)
110 APd00'indoor pool area (ft^2)
120 AR0*51.5/COS(SLOPE)'main roof area (ft^2)
130 TR0'roof water temp (F)
140 P100=EXP(17.863-9621/(460+100))'100 F sat vapor pressure ("Hg)
150 GG=7'roof glazing conductance to outdoor air (Btu/h-F-ft^2)
160 RW=2'window R-value (h-F-ft^2/Btu)
170 K10/GG'constant
180 GP=1.58'gas price ($/therm)
190 FOR MONTH = 1 TO 12
200 READ TA,TM,HSUN,SSUN,W
210 TN=TA-(TM-TA)'average daily min temp (F)
220 TD=TA+(TM-TA)/2'average daytime temp (F)
230 TW=TN+(87-TN)/RW*(RW-.7)'indoor window surface temp (F)
240 TDP=TW-5'max indoor dew point to avoid night condensation (F)
250 PI=EXP(17.863-9621/(460+TDP))'indoor vapor pressure ("Hg)
260 PLOSS$*100*AP*(P85-PI)/100000!'daily pool heat loss (therms/day)
270 WI=.62198/(29.921/PI-1)'indoor humidity ratio
280 WLOSS0000!*PLOSS/1000/24'pool water loss (lb/h)
290 CFM=WLOSS/(.075*60*(WI-W))'makeup airflow (cfm)
300 AIRLOSS$*1.06*CFM*(87-TA)/100000!'sensible heat loss (therms/day)
310 PLOSS=PLOSS+AIRLOSS
320 TPLOSS=TPLOSS+PLOSS'total pool loss
330 RH0*PI/P87'max indoor RH to avoid night condensation (%)
340 RRH=INT(RH+.5)'round RH
350 SUN=HSUN*COS(SLOPE)+SSUN*SIN(SLOPE)'roof solar gain (Btu/ft^2-day)
360 PO).921/(1+.62198/W)'outdoor vapor pressure ("Hg)
370 RGAINNC=AR*(SUN-6*100*(P100-PO))/100000!'roof gain, no cover (therms/day)
380 IF RGAINNC<0 THEN RGAINNC=0'roof loss vs gain
390 IF RGAINNC>PLOSS THEN RGAINNC=PLOSS'more gain than loss
400 K2=K1*P100+460+TD'constant
410 TGQ0'initial Tg est (R)
420 TG=K2-K1*EXP(17.863-9621/TG)'glazing temp (R)
430 IF ABS(TGL-TG)>.01 THEN TGL=TG:GOTO 420'iterate
440 RGAINW=AR*(.9*SUN-6*(TG-460-TD)*GG)/100000!'roof gain (therms/day)
450 IF RGAINW<0 THEN RGAINW=0'roof loss vs gain
460 IF RGAINW>PLOSS THEN RGAIN=PLOSS ELSE RGAIN=RGAINW'more gain than loss
470 PRINT MONTH;TAB(8);RRH;CFM;TAB(22);PLOSS;TAB(32);RGAINNC,RGAIN,RGAINW
480 TGAINNC=TGAINNC+RGAINNC'roof gain with no cover
490 TGAIN=TGAIN+RGAIN'roof gain with cover
500 TGAINW=TGAINW+RGAINW'roof gain with cover and DWW
510 NEXT
520 POOLOSS0*GP*TPLOSS'yearly pool loss ($)
530 SAVINGSNC0*GP*TGAINNC'yearly savings with no cover ($)
540 PSAVINGSNC0*TGAINNC/TPLOSS'% savings
550 SAVINGS0*GP*TGAIN'yearly savings ($)
560 PSAVINGS0*TGAIN/TPLOSS
570 SAVINGSW0*GP*TGAINW'yearly savings with DHW ($)
580 PSAVINGSW0*TGAINW/TPLOSS
590 PRINT TPLOSS,TGAINNC,TGAIN,TGAINW
600 PRINT PSAVINGSNC,PSAVINGS,PSAVINGSW
610 PRINT POOLOSS,SAVINGSNC,SAVINGS,SAVINGSW

Month  RH  cfm    total heat     --- roofgain (therms/day) ---
       (%)        (therms/day)  no cover   cover      cover+DHW

1      40  11948  282           0          0          0
2      41  11585  267           6.165614   11.61019   11.61019
3      45  10249  215           24.38077   31.94458   31.94458
4      50   9063  168           40.49223   51.02791   51.02791
5      57   8676  128           54.99459   67.52151   67.52151
6      63   8390   94           68.24747   82.37038   82.37038
7      68   8474   75           69.73278   74.96797   84.81842
8      67   8567   79           62.59364   77.58797   77.58797
9      61   8975  110           44.37123   58.5638    58.5638
10     53   9854  159           22.22977   34.43198   34.43198
11     47  10260  200           0          6.749671   6.749671
12     42  11272  251           0          0          0

                 2028           393.208    496.776    506.626
                                 19.410%    24.523%    25.009%

Cost/savings   $6,021.62  /   $8,638.07 $3,547.18 $4,014.09  per year

Changing line 160 above from R2 to R3 windows and doors (or collecting
condensation) would raise the max RH and lower the outdoor makeup air
required for dehumidification from about 8,000 cfm (twice the 275x15 cfm
= 4125 ASHRAE recommendation for 275 people) to about 5,000 cfm...

160 RW=3'window R-value (h-F-ft^2/Btu)

1      51   6676  182           0          0          0
2      52   6510  173           6.165614   11.61019   11.61019
3      56   5891  144           24.38077   31.94458   31.94458
4      60   5336  115           40.49223   51.02791   51.02791
5      65   5170   89           54.99459   67.52151   67.52151
6      70   5122   68           67.7277    67.7277    82.37038
7      73   5278   56           55.66928   55.66928   84.81842
8      73   5298   58           58.36979   58.36979   77.58797
9      68   5353   77           44.37123   58.5638    58.5638
10     62   5678  108           22.22977   34.43198   34.43198
11     58   5872  133           0          6.749671   6.749671
12     54   6354  164           0          0          0

                 1367           374.401    443.616    506.626
                                 27.383%    32.446%    37.055%

Cost/savings   $4,807.16  /   $7,746.61 $1,027.42 $4,014.09  per year

So we might save $6K-$5K = $1K/year by merely collecting condensation
from windows and doors, and save more by with a higher RH based on wall
and roof insulation, and save more by trickling water over the roof.

This would also reduce the yearly water bill.

Nick


Posted by nicksanspam on June 28, 2006, 1:30 pm
 
And changing it to

160 RW'wall and ceiling R-value (h-F-ft^2/Btu)...

Month  RH  cfm     total heat     --- roofgain (therms/day) ---
       (%)         (therms/day)  no cover   cover      cover+DHW

1      73   2099    73           0          0          0
2      74   2073    69           6.165614   11.61019   11.61019
3      75   1979    60           24.38077   31.94458   31.94458
4      77   1913    51           40.49223   51.02791   51.02791
5      79   1993    43           42.90388   42.90388   67.52151
6      80   2167    36           35.65553   35.65553   82.37038
7      81   2398    32           31.52559   31.52559   84.81842
8      81   2369    33           32.5141    32.5141    77.58797
9      80   2161    39           38.76485   38.76485   58.5638
0      77   2044    49           22.22977   34.43198   34.43198
11     76   2006    57           0          6.749671   6.749671
12     74   2054    66           0          0          0

                   608           274.632    317.128   506.626
                                  45.369     52.389    83.694%

Cost/savings    $8,692.67  /   $3,017.57 $5,031.88 $4,014.09 per year

So we might save $6K-$9K = $7K/year by collecting condensation from
windows and doors, with a higher RH based on wall and roof insulation,
and save more by trickling water over the roof.

The next step might be to maintain equal comfort by lowering the room air
temperature, based on the higher relative humidities...

Nick


Posted by Redigoogle on May 20, 2006, 4:10 pm
 Pardon my ingnoragnce but, what is DMH?
Thanks
Cliff


Posted by Duane C. Johnson on May 20, 2006, 5:58 pm
 Hi Cliff;



DWH = "Domestic Water Heating".


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