Using water at 57 degrees to cool house

[dcaster]

The standard chilled water systems use water cooled to about 45 degrees going into the heat exchanger and a 10 degree rise in water temperature in the heat exchanger. I am not sure what the temperature of the air leaving the heat exchanger, but expect it would be about 58 to 60 degrees.

What I am contemplating doing is using water circulated through geothermal lines instead of the chilled water. This water would be about 57 to 60 degrees. If it rises 10 degrees , it would require about 285 gallons of water per hour for 2 tons of cooling. The air coming out of the heat exchanger would be about 73 to 75 degrees. There would not be much, if any dehumidifying. And the house would likely be about 80 to 85.

I see this as something to do when one was not home. It should reduce the time for the air conditioner to get the house comfortable. It would require the addition of a heat exchanger and probably some way to duct the air either through the regular evaporator or the added heat exchanger. Maybe the smarter thing would be to have the air conditioner / heat pump chill or heat water. And not have both an evaporator and heat exchanger to deal with.

Has anyone seen such a lashup? And are my numbers reasonable? Does anyone think it would save money over just using a standard geothermal heat pump with a timer to turn on the air conditioning before one expects to arrive home?

Note I am not asking for a design. Just wanting the opinions of practical people with experience. There is likely to be some thing obvious to you all, that I do not see.

Dan

[Noon-Air]

Actually it will be a little cooler than that

Won't be any dehumidifying without the coil temp being below dew point.

If your trying to save money on the utility bills, your going about it the wrong way as the jury rigged set-up your talking about will far ofset any savings.

Just use a quality, programmable, setback thermostat.

[Mark]

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Dan

set up your heat ex to feed the water cooled air to the condensor of your AC... that would be more effective...

Mark

[Stormin Mormon]

They make water cooled condensors.

[KJPRO]

Yeah, like the point that you don't understand anything about how a GEO system works and operates.

[geothermaljones]

ROT says 4 gpm per ton, 15dF delta T on water in & out of geounit & ground. Your running 4.75 gpm. Calcs show 2 tons of cooling, but reallife will prove you wrong.

Unless your water entering the coil is 40-45dF your not going to dehumidify... also, the size of the coil & flow through it will need to be controlled & may not match the flow to your loop field. The key to heat exchange is a difference in the temps of the water & the ground. Unfortunately, the ground won't recover as fast as you think, & over the course of the cooling season, your return water temps will climb & your cooling system will decrease accordingly. It'll probably flat line mid June...

I've seen Geo loop field returning water temps well over 85dF at the end of the summer, & well below 32dF in the late winter, these are well designed & sized fields (poor fields can run from 100dF)

I have to agree with the decent programmable stat idea, it's much cheaper. Better yet, put the ground issue away, if you intend to keep an existing system & replace your conventional A/C with an air source heat pump. That too will be cheaper that excavating a 2 ton loop field. If your sold on a ground loop then go all the way with a groundsource heat pump.

goodluck geothermaljones

[Bipolar Bear]

Put one of those "hot water heat pumps" onto it....recover what you can for domestic use then dump the rest into the ground...(or disconnect, rejecting into the air if the ground loop if so happens the ground loop saturates.

[dcaster]

Thanks. Easy to do the calculations and come up with the wrong answer. I appreciate having the rule of thumb.

I am pretty sold on putting in a ground source heat pump. But will probably wait until the existing air conditioner dies. My enthusiasm may wane when I get an idea of the cost of putting in a field.

Dan

b

[Jon Elson]

I saw such a system at "Fort Ritchie Site B", the former home of the Executive Communication System to keep in touch with the president of the US when he was traveling. This must have been used up to 1963 or something like that. Basically, they had a large well pump in a pit and a big air handler/heat exchanger, feeding air under a raised floor like a computer room. Obviously tons of vacuum-tube radio gear was in there when the site was in use. Unfortunately, I wasn't there when the whole system was running, so I have no idea what temperature they were able to maintain.

I've been thinking of trying out such a system, too. I think with a counterflow heat exchanger with several layers of heat exchanger core, it ought to give nearly as low a temperature as a normal residential AC operating under rated load, assuming the geothermal loop was big enough to not start warming up. That might require a larger than normal, vertical ground loop, unless you have a lot of moving ground water on your lot. Or, a pair of true wells rather than a sealed loop. That's what the Ft. Ritchie system used, although it looked to me like it might have been a single large-bore well, just returning the warm water down the same hole.

Jon

[dcaster]

There is a website

that has a fair amount of information on geothermal heat pumps including a map that shows earth temperatures. It looks to me that Fort Richie has earth temperature about 52 degrees. Much better for cooling than the 57 degrees I asked about.

Dan