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Posted by on June 7, 2007, 1:37 pm
Bob G. <rg327_remove_comcast.net> wrote:
>... The slower the water travels thru the panel itself the more heat
>it will absorb
Hey, the pool might get really warm with zero flow through the panel :-)
Nick
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Posted by on June 7, 2007, 8:49 pm
On 7 Jun 2007 13:37:49 -0400, nicksanspam@ece.villanova.edu wrote:
>Bob G. <rg327_remove_comcast.net> wrote:
>
>>... The slower the water travels thru the panel itself the more heat
>>it will absorb
>
>Hey, the pool might get really warm with zero flow through the panel :-)
>
>Nick
Nice catch, thre fact is the faster the water moves the more efficient
the transfer process is. If for no other reason, you lose virtually no
heat to air if the water is cooler than ambient air temp. When you let
it linger and try to get real hot the air is fighting you. Pool
collectors are unglazed and work best with a small temperature rise in
a lot of water. The trick is optimizing between pumping cost and heat
rise.
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Posted by on June 8, 2007, 8:36 am
>... the faster the water moves the more efficient the transfer process is.
>... The trick is optimizing between pumping cost and heat rise.
OK. If it's 60 F outdoors and the pool is 70 F and 250 Btu/h-ft^2 of sun
is hitting 80 ft^2 of unglazed pool heaters 2' above the water surface,
how much water should we pump through the heaters to maximize the COP?
It looks like the answer is zero, with zero heat gain for the pool :-)
If 250x80 = 20K Btu/h = poolgain + airloss, and poolgain = 500gpm(Tf-70)
and airloss = (T-60)80ft^2x2Btu/h-F-ft^2, with final and average heater
temps Tf and T = (70+Tf)/2, Tf = (24K+35Kgpm)/(80+500gpm), which makes
COP = 89.5K/(gpm+6.25gpm^2), with a min COP = 0 at infinite gpm.
20 HEAD=2'pool heater head (feet)
30 FOR GPM=1 TO 5'heater flow
40 HP=HEAD*8.33*GPM/60/550'pump horsepower
50 PE=746*HP*3.412'pump power (Btu/h)
60 TF=(24000+35000!*GPM)/(80+500*GPM)'final heater water temp (F)
70 PS=60*8.33*GPM*(TF-70)'pool solar gain (Btu/h)
80 COP=PS/PE'coefficient of performance
90 PRINT GPM,TF,PS,COP
100 NEXT GPM
1 101.7241 15855.72 12338.92
2 87.03704 17030.23 6626.459
3 81.64557 17461.37 4529.477
4 78.84616 17685.23 3440.661
5 77.13178 17822.32 2773.866
Why pump more than 2 gpm? Going to 4 increases the pool heat gain by 4%
while halving the COP (to a thousand times more than an AC COP of 3 :-)
Nick
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Posted by on June 8, 2007, 1:16 pm
On 8 Jun 2007 08:36:36 -0400, nicksanspam@ece.villanova.edu wrote:
>OK. If it's 60 F outdoors and the pool is 70 F and 250 Btu/h-ft^2 of sun
>is hitting 80 ft^2 of unglazed pool heaters 2' above the water surface,
>how much water should we pump through the heaters to maximize the COP?
If it is 60f outside and you have unglazed collectors you are wasting
your money pumping water up there in the first place.
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Posted by on June 8, 2007, 1:53 pm
>>... If it's 60 F outdoors and the pool is 70 F and 250 Btu/h-ft^2 of sun
>>is hitting 80 ft^2 of unglazed pool heaters 2' above the water surface,
>>how much water should we pump through the heaters to maximize the COP?
>
>If it is 60f outside and you have unglazed collectors you are wasting
>your money pumping water up there in the first place.
No, in full sun. This is a Small Matter Of Physics.
Nick
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