A way to temper geotherm loop

zepfan · January 2016

We have a job that has five geothermal heat pumps.The units currently have no supplemental electric heaters.The issue is when the temperature gets cold outside the loop temperature goes down as well.I was there today, and the water entering the units was 47 degrees.With this low of water temperature we get supply air temperatures in the mid to high 80's.My question is does anyone know the best way to temper the loop temperature so there would be higher water temperatures entering the units.Either with a supplemental boiler, and heat exchanger or other means.The entire system is about ten years old,Our company did not install it so I do not know if it is a vertical,or horizontal loop.The house does have natural gas, and the homeowner would rather not install electric heaters in the units.Thanks to all.

GW · January 2016

Where are you? If you're north, that seems pretty darn good. What number are you looking for?

zepfan · January 2016

This job is in Maryland, I would like to see it up around 60 degrees,that would result in a lot better heat transfer

njtommy · January 2016

LP condensing boiler would work. You could either run the boiler to heat up the geo loop. Or you could install the boiler to feed hot water coils in the duct work and run them when the temp is below cop or balance point.

njtommy · January 2016

Or you could get crazy with it and add hot water solar panels to temper the geo loop.

JUGHNE · January 2016

A single house that has 5 Geothermal heat pumps?

I have at least 2 houses with 2 WA HP's. Both owners say they have never used the supplemental heaters. If they get turned on accidently they might call because they smell the dust burning off and think something is wrong. Both of these are pump and dump well water @ 50-55 degrees. That 3 to 8 degrees must make the difference.

More houses with only a single zone WWHP might need supplemental heaters on occasion. The 2 zone houses have oversized capacity with the logic applied that in AC season one unit may cover the requirements.

Would slowing down the blower deliver air temps that are more tolerable?

NG preheat of inlet water would really make that ModCon condense, max efficiency and give you some really hot air. IMHO

GW · January 2016

So we can all agree increasing water temp will add to efficiency and cop. But it seems rather " Rob from Peter to pay Paul" like.

Is this house tight and well insulated, or is it kinda tight and sort of insulated?

Seems odd you can't heat with 47 degree water, you're sure the hp units are ok?

I can heat my home with my geothermal system with 40 degree water. I'm in Massachusetts. Of course I use my radiant heating instead.

JUGHNE · January 2016

Does the loop flow thru the 5 HP's in a series connection? Out of the first and then into the 2nd etc.

zepfan · January 2016

no they are piped in parrell, there is a piping package at each unit with one pump,pumping the water into the unit, and one pump pumping the water out of the unit.

SWEI · January 2016

In and out meaning source and sink loops, or in and out of the same HX circuit?

zepfan · January 2016

in and out of the same hx circuit

SWEI · January 2016

So the pumps are in series with the HX between them? Where does the expansion tank connect?

GW · January 2016

Maybe scratch a drawing out on a napkin?

So it's basically two pipe....two pumps on each hp?

Harvey Ramer · January 2016

47 degree entering water temp is not bad during heating season. I would look at the manual to see what air temps are expected under those conditions. May be, all you have to do is slow down the fan slightly. Throw your gauges on the units and make sure the refrigeration cycle is sound.

I certainly would not add a boiler to the ground loop if you have 47 deg entering water temp. Also, at the end of the day, a Geo unit is not a furnace. The air will be cooler. Actually, the cooler the supply air is, the more efficiently the compressor will run due to decreased head pressure and increased mass flow rate. The desired supply air temp is always a balance between comfort, efficiency and of course, it has to be high enough to effectively meet the heat load at desired indoor temp.

JohnWayne · January 2016

Is your loop a glycol loop? We have some here, also in Maryland. The glycol in the system is useless at this point. When we hit this teen and single digit days and nights the units run constantly. Ours have no "defrost" mode, and the water temp will drop enough that the loop basically begins to slush in the coil.

Before you add refrigerant, if you think that may cause it, run it in the cooling mode for 10 to 15 minutes to warm up the water loop for a bit. The units we have are usually pushing 90 to 95 degree air.

Your 47 degree loop temp doesn't sound all that bad at all. I would leak check those units. Also are you measuring discharge air directly at the unit? If you are taking the measurement at a vent in the space, compare it with one directly at the unit connection. You may need to consider duct insulation. Just a few ideas.

JUGHNE · January 2016

It seems odd that with 47 ODT an air to air HP will deliver comfortable TEMPERATURE rise across the coil. The 47 temp is of the air/water from which the heat is extracted. Assuming the IDT is at 70 in either case, both machines have this 47 degree heat source. No, I realize if the ODT is 10 then the air/air HP is needing help. But the geothermal still has this 47 to work with.

Are you moving enough fluid thru the coil, outlet temp drop should show some drop. Or a refrigerant issue? Air flow too high?

If I am missing something please tell me, thanks.

Rich_49 · February 2016

what heat pumps are these and what are the circs on each side ?

zepfan · February 2016

They are all Florida heat pumps with grundfos 1/6 hp circulators

Bryan_16 · February 2016

Flow rates and temp drop thru the heat exchanger will tell you if the Heat pumps are performing properly. We run a lot of 30- 35 degree loops and very seldom use back-up .

Chuck_17 · May 2016

I'd like to piggyback on the discussion. 47 deg is high. I would expect the design temperature for heating to be more like 32 deg. But for sake of the discussion let's say the heat pumps were sized based on say 50 deg loop for heating (so it is not heating sufficiently on a design day). So you can 1. replace the heat pumps (not practical), 2. Add a well or two (very expensive), 3. Install a boiler to "temper" the loop temperature.
Now thinking out loud - Using boiler you would have to heat the water from the below design temperature to the design temperature. Otherwise the heat would start going to the ground. Right? Otherwise pick up the entire heat add load on the boiler and shut off the flow to the wells. Please correct anything that I wrote that doesn't make sense.

I wonder if adding a well is the best answer.

I can't imagine that turning down the air flow would do anything but make the situation worse.

I know of a similar situation further north where the heat pumps are just not heating sufficiently on design days (<10 deg). Common piping, one pump, I would assume the loop design was more like 32 deg.

A.J. · October 2016

Start at the beginning with a heat of extraction, you will need your GPM through each unit and your delta T.
BTU = GPM x Delta T x 500 if your using water with methanol.
Closed loop units should get about 3 GPM per ton and open loop should see about 1.5 GPM per ton.
We design our loops to run down to 35 deg so there is no reason that 47 deg shouldn't work for you. This must be one big house to get five units.

zepfan · October 2016

Thank you so much, this is very useful. When you mention "heat of extraction" what exactly do you mean? Redoing the heat loss calc? or adding another piece of equipment. Yes this is a very large house about 10,000 ft. 2

A way to temper geotherm loop

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