Geothermal open loop solenoid control

H2OBandit603 · November 8

I’m a well driller and pump installer and installed my own water to air geothermal wells and heat pump over 10 years ago. The open loop control was achieved with 2 solenoids and two flow limiters on the discharge side that allowed ~6 gpm when one was open for first stage and ~10 gpm when both solenoids were open for second stage. This worked great.

I’m now building a new house and looking at the new Enertech variable speed water to water units, specifically the Hydron Module Cruise WV.

https://hydronmodule.com/residential-products/item/cruise-wv

This unit is 2-5 ton, variable speed so no clearly defined stages and their rep told me it needs a plate heat exchanger between the well water and the unit, which is fine. He said the unit won’t control the well water side, but I assume I could connect a solenoid on the discharge side to the compressor circuit so the flow starts every time the compressor is energized.

Water flow is provided by a variable speed submersible pump system that will be more than adequate for 15 gpm plus domestic water usage simultaneously.

my question is directed at anyone who’s installed these units and at people with a finely tuned understanding of flow control.

I know they recommend 3 gpm/ton so that’s what I’m using for reference but I’ve had great luck at 2 gpm, whatever.

I don’t see any reason for the variable speed system to get 15 gpm of flow through the plate exchanger all the time when it only needs 6 gpm at its lowest speed and when it ramps up to 5 ton for domestic water heating it will need 15 gpm. Is there a good way to control the flow with a variable solenoid that can go from 6 gpm to 15 gpm as needed? I don’t know how this would work or if it could be tied into the exiting temp or what. When it was a 2 stage system it was simple and there were provisions for this built right into the hydron module vertical packaged heat pump.

I’m looking for clarification, this could be a very simple thing to achieve and I just don’t understand what technology is available to me. Looking for a peak behind the curtain from you HVAC gurus. Thanks in advance for taking the time to read this.

pecmsg · November 8

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

In heating much the same but limit the low end.

H2OBandit603 · November 8

I 100% agree with you that this is what needs to happen in an ideal set up, do you have a piece of hardware in mind that would let me set a minimum/maximum exit temp and ramp up to keep it there? The pump wants to push as much water as possible so i figured a variable solenoid would be logical but that’s not my area of expertise.

pecmsg · November 8

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

H2OBandit603 · November 8

would there need to be a solenoid as well or is the pump capable of stopping all flow when it’s not needed? I have little to no experience with in line pumps and this will already have plenty of pressure pushing it through the system. I could accomplish what I’m looking to do with a ball valve and stand there and adjust it as needed…I just want to automate that.

Kaos · November 8

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.

pecmsg · November 8

https://forum.heatinghelp.com/discussion/comment/1818696#Comment_1818696

It should be a submersible pump. TACO has variable speed in line pumps.

H2OBandit603 · November 8

I’m not terribly concerned with the pumping cost. I’m using a permanent magnet mag force high efficiency 1.5 hp variable speed submersible pump and the static level is 9”. I’ll end up putting an overflow on the well.

the pump will do 22 gpm at 100’ at 70 psi and 30 gpm at 0’ at 70psi

The only water leaving the well is residential use

pecmsg · November 8

Is that a submersible pump?

H2OBandit603 · November 8

yes, it’s going down 200’ but I don’t think there will be much of any draw down

pecmsg · November 8

so all you need is a speed drive to control your GPM’s

ethicalpaul · November 8

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

pecmsg · November 8

Many Jurisdictions do not allow open loops due to the contamination issues.

ethicalpaul · November 8

https://forum.heatinghelp.com/discussion/comment/1818735#Comment_1818735

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.

H2OBandit603 · November 8

ok back to the top. The variable speed pump is already controlled by a variable frequency drive, it will match whatever the house is asking for plus whatever is allowed through the plate heat exchanger after the 30 psi pressure reducing valve. I’m very familiar with the benefits and trade offs with open vs closed loop. This one well achieves residential use as well as geothermal, the water quality is perfect and the flow is fantastic. It’s an 8” well down to 420’ then 6.5” down to 1105’. The static is at less than a foot right now. With a 4” porter shroud to the bottom with holes drilled near the bottom and the pump in the porter shroud and return line on the outside both at either 100 or 200’ that’s 900-1000’ of transfer. This is the system I’m going to employ so I’m just trying to get a handle on my control philosophy. I like the idea of multiple solenoids, each with maybe a 4 gpm flow limiter so it can do 4, 8 or 12 depending on how hard it’s running but that’s outside my wheel house.

Keep in mind I’m planning to use passive house principles and this is way overkill but having 5 ton on tap for domestic hot water is really nice even if it only runs 2 tons any other time.

I considered putting in closed loops but we sold the well rig and drilled this one last well for my future house. It’s wasted as just a residential well. You couldn’t ask for a better standing column.

This is New Hampshire and I followed all best practices and regulations on open loop geothermal.

keep in mind this is a high efficiency permanent magnet pump that can move 30 gpm at 70 psi with 1.5 hp, and spinning even at Its lowest speed can move a bunch of water, plus the house will be so insulated run times are unlikely to be substantial. The hardest it may ever run will be doing domestic hot water.

ethicalpaul · November 8

Sounds good, Live Free or Die!

pecmsg · November 8

https://forum.heatinghelp.com/discussion/comment/1818742#Comment_1818742

My biggest issue with open loop is WHEN the heat exchanger fails, begins leaking refrigerant oil INTO the water supply.

H2OBandit603 · November 8

the company rep definitely told me I needed a plate heat exchanger between the water side and the heat pump. The variable speed pump in the unit circulates the fluid between the plate heat exchanger and the heat pump so I think the worst case would be glycol in the water if the exchanger failed. My last system was directly through the cuper nickel heat exchanger there was nothing between.

Kaos · November 8

I think for you setup, the simplest is your original suggestion. A couple of solenoids set to fixed flow rate activated based on load.

Don't underestimate pumping power. Househould water use is around 100gallons per day. 2GPM is 2880 gallon. This would still need to be pumped up to 50psi before being discharged back into the well, so it will take real pump power to do so.

Quick google shows about 500W for 4GPM, but all over the place. Make sure to check the manufacturer data and get the right sized pump. Even a variable speed pump, running a high flow rate unit at very low flow rates kills efficiency.

A better option might be to use the deep well pump to deliver water at say 5psi to 10psi water for house and GSHP and 2nd booster pump for house water. Significantly lower power use.

pecmsg · November 8

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?

DCContrarian · November 8

"The variable speed pump is already controlled by a variable frequency drive, it will match whatever the house is asking for plus whatever is allowed through the plate heat exchanger after the 30 psi pressure reducing valve. "

How does the pump know what the house is asking for?

Following that logic, what if you had a mixing valve that provided to the heat exchanger as much water as was needed to keep the output temperature constant. So rather than trying to adjust the pump speed, just use the same logic as the house water to provide as much as is being asked for.

I don't have a specific piece of hardware in mind, but I'm thinking something analogous to a thermostatic radiator valve, where the sensor is in the outlet water and it controls a valve on the inlet to the heat exchanger.

H2OBandit603 · November 8

the pumping system is set for 70 psi, when water is being used in the house or the geothermal it pumps whatever flow is required to maintain the steady 70 psi, it varies its frequency from 30 to 80 hertz which adjusts the rpm from 1800 to 4800 to match the demand. Whether you are running your sink or pumping 25 gpm off the bottom of the tank it maintains the same pressure in the captive air tank.

The pressure is dropped to 30 psi to the heat exchanger. The circuit is constantly pressurized so all you need is solenoids on the discharge side, they open, water flows. As much as it will allow, which is why you need the flow limiter in conjunction with the solenoid, without it, the pump would try to squeeze 30 gpm through any time the solenoid opens.

yes the glycol is the go between, the plate heat exchanger has well water on the well side and glycol between the unit and the heat exchanger.

H2OBandit603 · November 8

I’ve done other systems with two pumps, one pump was a 1/2 hp 10 gpm constant pressure pump doing about 12 psi through the heat pump and a second pump, 1.5/2 hp doing the house at 70 psi. This is a very efficient set up but costs a lot more by requiring two pumping systems which are not cheap. One pump isn’t ideal but it will work well in this application. If I had more time with the well rig I could have tried to drill another well just for residential use but I already have about $40,000(I drilled it so it’s “free”) into this 1105’ 8” well and the larger pump is 3 phase and permanent magnet, gets about 17% better efficiency than the single phase pumps.

H2OBandit603 · November 9

I like the idea of triggering multiple solenoids for different levels of demand but unless I have somebody walk me through that just having one solenoid that opens when the compressor is energized passing about 12 gpm might be the sweet spot for covering the 2-5 ton load while letting the pump spin free at its lowest rpm level. Keep the ideas coming! I’m waiting for somebody to explain how to get a variable solenoid to regulate flow based on discharge well water temp. Like I said if I was standing there with my hand on a ball valve I would set the flow to give me a discharge temp of 40 in heating, 60 in cooling or whatever is ideal and if the temp is lower or higher it increases flow. Someone must have thought of this already. A bleed line is often controlled by something like this…if the temp gets too cold or hot it opens a valve that allows water to be discharged to ground rather than back down the well, typically 10% of the flow and there must be some overlap there in application

Kaos · November 9

The automatic way is a thermostatic valve.

Set a small bleed that opens any time the heat pump runs so there is some small flow through the plate HX.

Say want the plate HX to always have above 40F water. You set the valve to open at 40F. So as the heat pump ramps up, the delta T across the HX increases until the outlet hits 40F. At that point the valves starts opening which increases the flow. Eventually the system stabilizes where the flow through the thermostatic valve is enough to meet the demand of the heat pump.

I think pumping 70PSI water at 2-5 GMP on continuous basis is going to get spendy. A tankless jetpump as booster is not that expensive.

hot_rod · November 9

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

IMG_8929.png

IMG_8930.png

H2OBandit603 · November 9

I would say the minimum flow would be about 6 gpm and max would be 15 gpm when it’s ramped up to 5 ton for making hot water. Any house water usage is added on. 6 gpm is like running several sprinklers. I’ve done several standing column geothermal wells that required large pumps, 3 HP, with low static levels, around 300’ and it’s feeding 3 heat pumps. Sometimes it’s only feeding 1 unit, systems run fine and the customers aren’t complaining about high electric bills. A 3 hp pump moving that kind of water at that depth is pulling about 2200 watts and they are seem very happy with the systems performance.

H2OBandit603 · November 9

alternatively I can run the same pump no higher than 30 psi through the heat pump and boost in line with this up to 70 psi for residential use, but now I’m running two pumps simultaneously for residential use.

That would drop the head from 160’ at 70 psi to 70’ at 30 psi given the static level is basically ground level.

The minimum output on the 1.5 hp constant pressure submersible is 2 amps, 1/2 hp

https://www.franklinwater.com/products/water-pressure-booster-pumps--packages/booster-pump-packages/inline-1100-constant-pressure-system/inline-1100-constant-pressure-system-sku-collection/90401101/

Kaos · November 9

If your static level is at ground, the head on the pump is 0, doesn't matter how deep it is. You are only pumping to the PSI you need for the water. The 1.5hp unit you picked is overkill unless the level will drop over time. You could even go with a regular jet pump with a deep intake except you'll use up the heat quickly in the upper column and there won't be much mixing from deep down.

You won't need to run at 5ton to heat house water. Most heat pump water heaters have a 1/2ton heat pump and they work. As long as you have a decent sized indirect and don't need to fill a hot tub, you'll be fine with much less.

Don't gets at PSI and flows. Get the curves for your pump and check where you need to run. Pumping costs kill efficiency of GSHP. That 2200W pump power you pointed to is power of a 1.5 ton AHSP that is delivering almost 2 tons of heat at 17F.

H2OBandit603 · November 9

the variable speed heat pump is 2-5 ton, 5 ton would be full power when heating the load water to 135 in a turbomax indirect/instantaneous water heating tank. The domestic hot water is going to have great recovery time for a heat pump.

DHW is built into the unit so it’s not like I’m going out of my way to heat water with 5 tons, it’s not a bug it’s a feature.

The 1.5 hp 20 gpm Franklin electric 3-phase Magforce permanent magnet motor can run as low as 2 amps at a 1/2 hp rating and still move a healthy amount of water and it could move over 30 gpm at 20 psi into the house. 15 gpm of that goes back down the well at max load leaving atleast 15 gpm for the house which can be boosted to 70 psi with the inline booster.

H2OBandit603 · November 9

At minimum speed with no head you are still moving 12 gpm with 2 amps draw. 460 watts seems very reasonable to me.

If I need 12 for a smooth running pump I can just set the flow to be 12 and run one solenoid, my instincts tell me running 6 gpm won’t bother the pump and will result in less energy used because these constant pressure systems are very adaptive and are designed to constantly ramp up and down but I’m not saying I can’t be convinced.

the static level took a while to come up to ground level and any water drawn from the well for residential use will result in draw down. I will be test pumping the well at various depths to get a comprehensive idea of the flow at 100’ and 200’

Kaos · November 9

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.

H2OBandit603 · November 9

I mean if I insulated enough I might only need 1-2 ton but let’s assume 2-5 ton variable speed heat pump fits the bill.

“Hydron Module WV variable-speed water-to-water system is the first geothermal heat pump to provide radiant heating, forced air heating and cooling, and 100% of the home's domestic hot water in one compact, efficient package. The variable-speed water-to-water can cut your heating and cooling bill by over 30% when compared to a standard geothermal system, which means up to 80% savings over a traditional HVAC unit. This unit can heat, cool, and provide hot water for any size home, building, net-zero structure, and more. The WV has been designated as one of the Most Efficient ENERGY STAR certified products in 2022.”

Available sizes: One unit covers 2 - 5 tons
Efficiencies: Up to 25.4 EER / 3.9 COP
Hot water provider

https://hydronmodule.com/residential-products/item/cruise-wv#features

Kaos · November 10

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.

H2OBandit603 · November 12

why would the 2-5 ton unit short cycle with 2.5 tons of load? It can modulate 1% at a time to exactly match the load, with a minimum of 2 ton.

The Turbomax tank has load water inside it, that load water is heated to 130 and copper tubing inside delivers water through the load water and exits close to the load temp. It’s not storing any water so there’s no concern over bacterial growth.

I don’t understand your last paragraph. The geothermal water goes back down the well, the house water goes elsewhere, they have no effect on each other. Whatever the geothermal unit requires, 6-15 depending on where it is in its 2-5 ton operating range, plus the domestic water use is what the pump needs to provide.

DCContrarian · November 12

https://forum.heatinghelp.com/discussion/comment/1819641#Comment_1819641

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.

Kaos · November 13

https://forum.heatinghelp.com/discussion/comment/1819641#Comment_1819641

If you take the house feed off after the HX for the heat pump, any house water flow will be part of the heat pump flow rate. About the only drawback is the cold water will be a bit colder to the house when the heat is running.

Geosman · November 19

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.

H2OBandit603 · December 1

thanks this is some great info give me a bit to digest it

Geothermal open loop solenoid control

Comments

Categories