Horizontal Loop Field - Advice Requested - Southeastern MA

A 2 ton dedicated W2W unit, recommended to me by a smart guy on the GE forum

I must admit, I have been wondering if I could/should make that unit dual-purpose for DHW and for cooling the theater. But maybe I'm over-complicating things again

 

Alright, ran through the pressure drop spreadsheet and the Geo-Flo pump sizing calculator...

7S NV060 and NSW025, 15% methanol, 10 circuits of 3/4" of 700-800' results in a max flow rate from a single 25-124 of 17.9-18.1 gpm.

Increasing to 12 circuits only increases the max flow rate from 18.0 to 18.5 gpm, so I can see why you recommended 10.

 

Yep...you don't gain much, you get to the point of no returns.

You can get a NSW, but the one designed for portable water (with a double walled and vented load heat exchanger) are not reversible, so they do not have chilling capacity.

You could get a NSW with a single wall heat exchanger which is reversible, but you would now need a DHW tank which has a large heat exchanger built in, like a stiebel eltron, or another means to put an additional separation between the refrigerant and the potable water.
Then you would need a second tank as a buffer tank for the chilled water to feed a hydronic fan coil for the theater room.

 

I read through all the previous discussions on turbulent vs. laminar flow that I could find on here, and also searched and did not find any reference to this paper:

"Effects of Ground Heat Exchanger Design Flow Velocities on System Performance of Ground Source Heat Pump Systems in Cold Climates"
https://www.semanticscholar.org/pap...tler/13f9e5ac5e03461f14e70d66e2f6279f1721195c

I found it very interesting in this context of an over-sized loop field and resulting "too low" flow per loop.

@docjenser I thought you would also find it interesting after reading your previous discussions of turbulence and your observations in your own testing. I realize it's from 2015 so it's possible it was previously discussed and I just missed it.

 

I've been told that methanol is not allowed in Massachusetts. I've done some research and this is what I could find...

From "Guidelines for Ground Source Heat Pump Wells" on mass dot gov:

"Propylene glycol (CAS No. 57-55-6) and ethanol (CAS No. 64-17-5) are the only acceptable antifreeze additives for closed-loop GSHP wells. MassDEP has also determined that denatonium benzoate (CAS No. 3734-33-6), ethyl acetate (CAS No. 141-78-6), isopropanol (CAS No. 67-63-0), pine oil (CAS No. 8002-09- 3), and tertiary butyl alcohol (CAS No. 75-65-0) are acceptable denaturants for ethanol additives. All other antifreeze chemicals and denaturants must be approved by MassDEP prior to use. The property owner, operator, and all parties involved in the design and installation of the GSHP system should be aware that the release of 10 pounds of ethanol to the ground surface or groundwater is considered a reportable release of a hazardous material per the Massachusetts Contingency Plan (310 CMR 40.0000). Therefore, if a closed-loop consists of 20 percent ethanol by volume, then a release of as little as 7.6 gallons of water/ethanol solution would meet the reportable release threshold of 10 pound of ethanol."

I hoped that this would only apply to wells and not much shallower horizontal loops, but I found this under Definitions within the same document:

"Ground Source Heat Pump (GSHP) Well - Any excavation by any method for the purpose of transferring heat to or from the earth for heating and cooling purposes in which the ambient ground temperature (prior to GSHP operations) is 90 degrees Fahrenheit or less."

So if this is in fact the case, and I have to use either Ethanol or PG, what would you guys recommend?

 

"The results suggest that keeping design pressure loss relatively low, as
suggested by Mescher (2011) is more important than keeping the flow turbulent for any specific portion of the year. In
fact, our simulations showed increased system performance as measured by seasonal system coefficient of performance as
the number of hours with turbulent flow decreased. The systems that performed best had significant numbers of hours
during the heating season with laminar flow."

That is their conclusion. Keep in mind that this is a computer simulation. But some aspects the software they used does not consider. The full effect of pausing the loops when the heat pump, or the higher thermal mass of the water in the pipes. They used a 2 ton heat pump sized for A/C, and supplemented the rest with electric strip heat. These are more academic exercises. They are pushing 5-6 gpm through a pipe. I am monitoring about 800 systems in real time online, all in 10 second intervals, with different configurations, pushing loop performance more to the limit. So we are gradually evolving, trying something out, and then gradually pushing further.

In real life, I would put a 4-5 ton variable speed 7 series in (17 gpm of the 5 ton), add to that a 2 ton water-water for DHW, so I am at a total of 24 gpm of specified flow. The 4-5 ton makes sure that I do not use any strip heat. Then I choose a Grundfos 32-140 and push all that water though as single borehole 500ft deep. I get about 17 gpm out of it with methanol and that single pump and 1.5" pipe, and have a Reynolds number of 11,000 in the borehole.
If I have room for a horizontal system with 7 circuits of 0.75" pipe each 600ft long, which spreads out the flowing I get around 17 gpm at a Reynolds of 2800. With Glycol I would be at a Reynolds of 1,100, and 16 gpm flow. But I use slinkies, so there is some turbulence to force the water going around in corners all the time. How much, I don't know.

My heat pump gets fed with water above 30F everyday during heating season. That is really all what matters.

Pumping power is about 83 watts on average when the system is running, the w-w heat pump kick in the variable speed hot water when either one or both pumps are running (190 watts), the rest of the time when only the space conditioning is working it throttles back to about 35-55 watts pumping power most of the time.

So we figured out a way to standardize loop and geo design, which work all the time. Everything else is truly academic.

 

There is some silliness here behind Massachusetts and methanol. they want you to report when 2 gallons of ethanol get spilled, and they banned methanol.

However, there are about 2.3 million cars in MA using about 1.8 million gallons of methanol in windshield washer fluid per year. Where do they (the gallons) end up?
The EPA considers Methanol environmentally friendly, it is very quickly bio degraded.

You can use ethanol, which is not as good as methanol, or use glycol.
Reynolds number of ethanol will be about twice as glycol is, but as discussed, it might not matter much.

 

I agree, it is extremely silly.

I am getting different results when running the calculators (your pressure drop spreadsheet, Geo-Flo Pump Sizing calculator, Geo-Flo Reynolds Number calculator) for methanol vs ethanol vs PG. All of these examples are 10 circuits of 3/4" 600', single UPM-XL 25-124.

15% Methanol: 18.3 gpm, 1,975 Reynolds
20% Ethanol: 18.0 gpm, 1,203 Reynolds
20% PG: 17.7 gpm, 1,564 Reynolds

So it shows more pressure drop with PG vs ethanol, as expected, but higher Reynolds numbers for PG vs ethanol.