re: water heat circulator SOLAR.KnowledgePublications.com

re: water heat circulator
23 apr 2005
pjm@see_my_sig_for_address.com wrote:

[re a $98 window ac in the middle of an apartment with an unpressurized tank
around the hot fins and a heat exchanger that warms pressurized water from
a cold tap (with 1/3 the usual electrical energy) and pushes it back into
the apartment's hot water supply tap...]

>> >> >you might just keep pumping hot water back into the pipe.
>> >>
>> >> yes, that's possible, but... the cold water is going to start
>> >> getting heated,like that).
>> >
>> >not if you use less ac energy than the water heating energy used
>> >by you and your neighbors, which seems likely.

>for instance, if you use 50k btu/h of ac, you put 0.2gpmx60minx5h = 120
>gallons of hot water into the system. if you and your 11 neighbors use
>12x50k = 600k btu/day of hot water, you remove about 600k/(110-60)/8 =
>1500 gallons/day from the system, at different times.

if your apartment needs ac from 4 pm till 2 am and the 12 apartments
use most of their hot water from 6-8 am and 5-9 pm, you might push
0.2gpmx60x(2am-9pm) = 60 gallons of 110 f water back into the water
heater when nobody's using hot water...

>with a very large hot water tank, the cold water would never get warm.
>as the tank size shrinks, this would happen more often. we could do
>simulations with various tank sizes and random hot water bursts to
>compare the value of the energy savings with the cost of the occasional
>hot water [that needs to be dumped when the cold water pipes begin
>warming up...]

>> >in the _unlikely event_ that that happens, you either dump some hot
>> >water into the drain in your apartment or you and your neighbors let
>> >the cold water run a bit more until it gets colder.

>the dump could happen automatically, with a thermostat on the incoming
>cold water line to the op's apartment and a solenoid valve to let some
>hot water flow into the drain...

an adaptive controller might learn from history by noticing that dumps
were often required from 9 pm to 2 am and overcooling the apartment
(below the setpoint, but still within the comfort zone) from 5-9 pm...

nick