Any HVAC Guys Here?

[BHarrison]

I have some technical questions about the operations of Geothermal Heat Pumps.

Is there anyone here that has experience working with these type of units?

Thanks

 

[kcbarnes]

We have one in our house does that count. I could also ask the hvac tech. that we us at work.

 

[Lane]

Ben, I owned a 2.5 ton water source residential system heat pump for about 12 years and when it’s compressor motor failed, replaced it with a 4 ton high SEER air source heat pump. I too am near Baton Rouge. Although different rated tonnage, both units run about the same amount of time to control to set point and remove moisture equally well.

The house is approximately 3000 sq. ft. and is super insulated. The water system was designed as an open loop. Well water of approximately 72 deg. F. was pumped through the exchanger/condenser one time for both heating and cooling. A 1/2hp pump was utilized on a 480 ft. well. The compressors hot exhaust gas heated a 50 gallon water heater before hitting the exchanger. It was extremely quiet and more efficient than HVAC units available at the time, made plenty of hot bath water but had a couple of drawbacks; 1) high volume of waste water to dispose of, 2) excessive buildup of mineral deposits in control valves, piping and exchangers. A semi-annual and later quarterly cleaning of all water lines and exchanger core with acid was needed to maintain water flow rate and keep deposits from acting as an insulator. A softener was out of the question for this amount of water.

An open system was selected for this climate as opposed to a re-circulating design as we have far to many cooling days compared to heating and would “stuff” more Btu’s in the ground in summer than we could ever remove in winter and the deep ground is a highly efficient insulator. A friend of mine earlier put down a series of 500 ft. deep wells with “U” shaped piping down them for a closed loop exchanger in a commercial building application. The system worked great for about a year and then got so hot the compressors would trip on high discharge pressure. It was all scrapped an a closed loop cooling tower put in it’s place.

Newer technologies exist like shallow earth coil placement and placing coils in ponds/lakes. Just wanted you to know I did not go back with a water source system. The new air source system electrical operating costs are the same as the water source system plus it’s ½ hp pump and, is a lot cheaper to install and maintain. I do however have to pay to heat my bath water now! /w3tcompact/icons/hmm.gif

Good luck, I’d be interested to learn what you wind up with. Maybe you can post some updates?

 

[brad_oatley]

I've owned an HVAC business for 29 years. We've installed hundreds of geothermal systems. I'd be happy to help, either here on the forum, or on the phone.

 

[frank_f15]

what exactly can i try to help u with? have been in ac&r, hvac for 30 years, had about 90 water source heat pumps that i took care of, closed loop system, but ask away. i am sure someone can help u.

 

[Chuck52]

Can I jump in here and ride along? I bought a house last year on 10 acres. There are two unused wells on the property. One was problably dug in 1958 when the house was built. The other is more recent and still has the pump in it. The house is now on county water. It was suggested to me by the seller that I could use the two wells for a geothermal heat pump system. Local laws in mid Missouri allow me to pump from one well and dump in the other. The seller said both wells were producing water when last used. The quality of the water from the first well wasn't so hot, so the second well was dug. Then county water came along, with better water quality than the second well gave, so they switched. Assuming the second and newer well produces water of sufficient quality and quantity to serve as the source for a heat pump, and that the older well will serve to accept the used water, would I save much money on a geo system as compared to having to bury the heat exchanger for a close system? The house is all electric and I am stocking up on pain killers for when my next bill comes. Been kinda cold around here for the last month.

Chuck

 

[BHarrison]

Wow, thanks for all the responses. A little background:

(I am a broadcast engineer, and automotive a/c tech)
I have a new ClimateMaster 42,000 BTU water source on a closed loop system in my house. I love it. No complaints. ...although I have wondered about how often I should flush & recharge the loop. Anyhow, that's not the issue at at hand.

In my shop, I have a CommandAire SCPH511EA (51,000 btu?) water source with hot water recirculator. I got this unit from a friend who removed it out of his house. It was set up on an open well configuration. He removed it because his electricity bill was too high. Come to find out that the shut off valve was faulty, and was not closing fully. He owned the well, and was paying to run the pump almost constantly because of this valve. (at the time, we did not know it was the valve) Anyhow, that's how I got this unit. Functionally it was fine.
This unit is fed with tap water. (the 1" PVC in the picture) I chose not to use a closed loop on this unit because of cost. I have the hot water recirculator loop on the 30 gallon tank, and the 30 gallon tank feeds the 40 gallon tank. (Yeah, I know, that's alot of hot water for a shop.) As far as the wasted water is concerned, I am temporarily dumping it into shop sewer system. I have'nt decided yet how I will get rid of the waste water. It kind of depends on how much water were talking about.
My problem is I dont think the unit is functioning correctly. i.e. I dont get a great temperature difference across the evaporator coil.
In cooling mode, it makes VERY hot water, but only makes cool air. (5-10 degree split.) My best readings were done by running about 10 gpm of water through it. The people that installed my home unit say I should be running about 2.5 gpm on a tap water system, but at 2.5 gpm I am making insanely hot water, and my evap coil does not cool as well.
in heating mode, it makes COLD water, but the coil barely comes off of room temp. Basically, the unit doesnt work very well.

My pressures are: Low=60psi, and High=150psi, although one time in heat I had a low of 25psi which caused me to ask my 1st question.

Should the gas pressures be the same in cool & heat?

What pressures should I expect to see? (150psi high side sounds low to me)

How much air temp split should I expect? I would think 20ish.

How much water temp split should I expect?

Feel free to ask more questions if I have not covered all of my bases. Thanks.

 

[frank_f15]

WHEW! LOT of questions. but to start. in cooling mode u should expect a max of 15 deg. rise in water temp and a 20 to 25 deg. drop across the coil. u give the gpm that u think is going trough it, but how are u setting it? is there a filter in the inlet side that coud be plugging off? usually if the screen is plugged, u will get high temp(water) and not so good cooling.insufficient water flow thro condenser will increace head pressure and thus increase suction pressure, which as u know will give u a higher temp and reduce cooling, this will result in just the oppisite when u are in the heating mode. also what is temp of entering water?stay with it it ain't that hard.

 

[BHarrison]

"stay with it it ain't that hard. "

I know. I keep telling myself "This aint brain surgery."

"u give the gpm that u think is going trough it, but how are u setting it?"

On the output of the primary loop there is a 24v soleniod valve, then a ball valve. I'm regulating my flow with this ball valve.
I asked my vender of my home unit about water split. If I recall correctly he said a 10 degree split. In order to get that I had to flow 14 gpm. I thought this to be an enormous amount of water. Even @ 14 gpm, my coil temp still sucked. (cool, not cold, semi dri air)

"is there a filter in the inlet side that coud be plugging off? "

No filters. I'm on city water. (it's filtered somewhere/w3tcompact/icons/smile.gif) There is a 1" line from a junction at the water meter that goes directly into the unit.

"also what is temp of entering water?"

In the summer, I want to say 65-70. I tried to make it heat yesterday, and the incoming water was too cold. The unit was throwing itself off on water temp fault. I had to mix hot water to the input side in order for the unit to stay running.

The one thing my local people said do, that I have not done, is to weigh in a new charge. (R22)

I don't think I'm fighting water issues. Water I have control over. I think it's something internal to the unit. Low charge? Over charge? Restricted drier? That sort of thing. Should I not bother continuing until I know the correct amount of gas is in place?

 

[RickM]

Ben,
I can't answer all of your questions, but I can provide some rules of thumb. First, your flow should be between 2 - 3 gpm per ton. That makes a 5 ton nominal needing 10 - 15 gpm. Second, you say it was on an open loop (pump and dump) and is now. Open loops are extremely prone to scale and fouling. Don't know the age of your unit, but it might be worth cleaning the water side of your heat exchanger now. Does this unit have a sightglass? Most do. Bubbles indicate lack of charge. You mentioned domestic hot water. I take it that it has a de-superheater? If so can you disable it to isolate it as a problem? With proper flow and a clean exchanger, then measuring superheat and subcooling will help in diagnosis. Don't give up, someone will nail this thing soon /w3tcompact/icons/wink.gif.