Geothermal open loop solenoid control

In cooling mode control the discharge water. The manufacture will have the ideal temp.

In heating much the same but limit the low end.

There are variable speed pumps that operate off a temperature sensor.

You want adjustable current sensing relay on the power terminals of the heat pump. Set them to kick on at the power level you want the solenoids to turn on for each stage.

Open loop geo pumping gets pretty expensive. Depending on how deep you are pumping up from that might be a 3/4 or 1HP pump. So about 500w to 750w continuously. That is about the draw of my air source heat pump to heat the house in the shoulder season.

Not sure if this is possible, but might be better to at least look at using the well as closed loop setup for low load and switch to open only when it gets cold. This would save a lot of runtime on the well pump as now you can use a circulator for some of your heat and most of your cooling season.

Sorry to jump in, but I have to ask: why aren't you going with a closed loop? It eliminates so many problems

Very true, but as a well-driller, the original poster might not be too worried about that.

My well-driller in CT that I used was all set up to do the permit, drilling, sinking the pipe, grout, connect, and test the closed loop. He was really great.

Sounds good, Live Free or Die!

so you’re saying you have glycol circulating in the unit that gets it heat or gets rid of the heat from a plate frame heat exchanger?

a PICV is a pressure independent control valve. A dynamic balancing valve. You order them by the required gpm. You could put them downstream of the solenoid

They do have a pressure range they need to work within 2-32 psid for example. A Y strainer is a good idea also to protect them

Missing form there is power use. If you can't get this from the manufacturer, try to cross match to Groundfos. Their site has a great tool for figuring out flow/pressure/power ie:

https://product-selection.grundfos.com/ca/products/sq-north-america/10-sqc/10-sq15-370-92996053?pumpsystemid=2513128060&tab=variant-curves

Next step. Do you really need a 5 ton heat pump? Modulation allows for only so much turndown and oversized units cost more, have short cycling issues and create comfort problems. I'm in the north edge of zone 5 here and reasonably airtight code min construction is about 10-14 BTU/sqft.

The turndown on the unit is not that great. Looks like 3:1.

If you will be running it as water to water, you'll be fine as long as there is either high mass emitters or a buffer tank.

If you will only use fan coils, the unit will have cycling issues if you real house load is around 2.5tons. This means most of the heating season, it will be simply on/off, at that point might as well use a cheaper two speed unit.

Generally indirect water heater is not worth the cost or complexity. The bits needed to make it up are much more than a stand alone heat pump water heater and the overall efficiency is the same.

R410 based heat pumps also does not like to heat to 150F which you need to get a tank up to 140F needed to kill everything since you are not on chlorinated water.

For your water use, if you get the right setup, your domestic flow rate should not be in addition to your GSHP use. So if your heat pump is running at 5gpm and your house needs 3GPM, the only thing should happen is you dump now only 2GPM back to the well, you would not need 8GPM of flow.

Not to put words in Kaos' mouth, but I think when he says the "real house load" he means the design load, which by definition only happens 1% off the time. So if the design load is 2.5 tons, 99% of the time it's going to less than that and the average load might be half. So if the minimum is 2 tons, the design load is 2.5 tons, it's going to be short cycling a lot of the time.

This post is just too interesting to pass over. Enertech obvioulsy does not want you to use well water in their brazed plate heat exchangers due to the high potential for fouling with raw water which could be via sand, iron, mineral or bacterial means. How long have you been using this incredibly deep well and what experience do you have with its water filter/strainers? I ask this as a hydrogeologist and one who has looked after and applied open loop geothermal units as well as closed loop systems since the mid 1970's. I've seen the best of the best and the worst of the worst on open as well as closed systems so I might be able to assist with some suggestions.

First is the water quality history on this well. Deep water is under incredible hydrostatic pressure and will often contain carbon dioxide which will come out of solution as the water is released to atmospheric pressure and can be seen as bubbles on the wall of a glass of water. As carbon dioxide leaves the eH pH potential of the water changes and with some water supplies minerals will begin to deposit. If you have a 1 gallon glass jug of fresh well water and let it set for a week do you find sediment on the bottom or is it still clear? Does the color or tint change with time as it is exposed to oxygen? Any noticeable odor or sign of Radon in this deep water that might be a sign of future issues?

I looked at the wiring diagram for your unit and see that it is set up to manage a variable speed pump that will synchronize with the compressor speed and loop temperature. Enertech may have a modulating valve suggestion that could control water flow as though the system were installed in a public building and operated off a closed hydronic loop instead of well water. If such a valve can be used and your water supply is suitable it may be possible to operate directly from the well.

I am most familiar with WaterFurnace units and their modulating valves for open applications, but did not notice if such a connection exists on the Enertech control board.

Plate heat exchangers are difficult to clean. I will often pipe them with shut-off fittings and ports to blow out and back flush with compressed air. Once purged with compressed air I will allow the geo unit to freeze the heat exchanger and find that the frost created will dislodge iron and mineral deposits allowing them to be flushed from the exhangers when the water is turned back on. So far I've had a 100% success rate using this process but must be certain that all water has been removed from the exhangers both brazed plate and the same for the co-axial exchangers that your older system likely had. If one of my techs fails to completly purge a heat exchanger prior to the freeze process; it's a simple matter of switching the system to the AC mode to defrost and re-establish water flow.

I agree totally with Kaos and others on the negative side of VS constant pressure pumping. Constant pressure pumps set for a domestic pressure waste enough energy to make your new geo perform at a lower COP than your old one. If you must work with a VS pump set the pressure as low as possible for the geo unit and use the lowest HP motor the flow will require. Add a booster pump and small tank for your domestic load so you can have the 70 psi you wish for shower and appliances. It's that simple and you will save enough kW in your first year to pay for the booster pump.

If you well water temperature runs close to 55-50 degrees, your system will likely operate using only 1.5 gpm/ton but as it drops closer to 40 degrees or below the flow rate for heating should increase closer to 3 gpm which is the design flow for closed loop systems that are operating at the freezing temperature. In the AC mode there is more latitude with flow rate and 1.5 gpm / ton is appropriate at temperatures below 60 degrees and incerases toward 3 gpm as the entering fluid temperature approaches 90 degrees. Depending on your location in NH AC may not be a big factor or a significant load. If your well temp is 50 degrees or colder a simple water coil with fan will likely provide all the AC needed at an EER exceeding 30 BTU/Watt.