GSHP on order...can this system work?

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rkamphui

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Hi all. I am ashamed to say that the excitement of cheap heating and cooling overcame my better judgement as an engineer and I after some research on this forum I am afraid I may be overestimating the capabilities of my well.

To make a long story short: I just purchased a house with no working heat. With a well, a pond/creek to dump into, and a blank slate to start from an open loop GSHP (dual fuel with NG for the coldest days) seemed like a nice option for the house. I had an anlysis done by the HVAC firm selling me the geo system and after measuring my flow they said I would have no problems. After reading some threads here on GSHP I see that sizing the well, pump, tanks, etc. can be a very complicated ordeal. Now I am extremely nervous that I may have made a bad mistake!

So here I am...looking to size a new pressure tank for the domestic supply and heat pump, I am hoping someone may be kind enough to provide me with some advice.

Here are the details of what I know today:

1) I will soon have a 3 ton 2 stage heat pump (climatemaster tranquility 27: model 038)
2) 4" case well down to 116 ft
3) Static water level of 14 ft. with drawdown to 42 ft after 3 hrs pumping at 22 GPM (measured almost 30 years ago...)
4) Current flow of 10.4 gal/min through a 50 ft. hose connected to an outside spigot
5) 1976 Submersible Red Jacket R75N1-12BC Pump (3/4 HP, 13 GPM capacity?)
6) Length of drop pipe 42 ft.

I essentially have a blank slate on the water side also and I am redoing this system from the well head out. My objectives are to:

1) supply the geo with adequate flow
2) recapture the geo water for my domestic supply
3) increase house pressure to normal levels with a booster pump (~60 psi)
4) maintain the life of the well pump as best I can...

Any advice you guys can provide on how to layout my system will be VERY appreciated. Thanks for contributing your free time to help out newbies like myself...


PS: the spent water from the open loop geo will be dumping in the back yard, down a fairly steep 30 ft. slope (30' drop), if I size my discharge pipes correctly could this help reduce the overall head on my pump??
 

Alternety

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I know this is not one of your questions, but some areas prohibit use of ground water this way. Have you checked?

The issues really are a bit more complicated. I will let the well guys talk about how everything needs to be plumbed and controlled. There are a few ways to do it.

Generally speaking, the larger the pipes the lower the pump power for the same lifting height. There are diminishing returns as diameter increases for the same volume. Dumping it in the yard or running a properly sized pipe down hill to the stream or wherever you are dumping will be essentially the same pumping load.

A closed loop in the well would reduce pumping power significantly, but that is a whole different issue with diameter and depth of well and transfer rate to surrounding earth/rock. This is also illegal in some areas.

If the pond is the right size it could be used with a closed loop. Or bury a closed loop. You don't say where you are or what "cold" means there. If the creek is year round and has the volume, and you have a nice non-freezing pool in it or can make a small dam, there is another possibility for a closed loop system. Living, and having lived, on wells it pains me to see this sort of use of the aquifer.

I don't know if you have figured required water volume for required heat load. This is arithmetic from manufacturers spec on what volume of water it needs at a given source temp, head loss across the heat exchanger, required temp of the air or water output you need, and BTUs per hour needed. If you are doing water to air, be aware that heat pumps tend to produce uncomfortable air temps in forced air systems. They match real well with in-floor radiant. You also need to know the chemistry of the well awater and the material characteristics of the heat exchanger. Agressive water = eaten heat exchanger.
 

rkamphui

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Thanks for the quick reply Alternety. I should have pointed out that I am in Southern Michigan. We generally don't have issues with lack of water or depleted aquifers but nonetheless I am concerned about displacing millions of gallons of water every year. I asked the question to the HVAC company and they said it has never been an issue - but I am doing my own investigation with the DNR. I would imagine at the very least I'll need to get a permit.

You bring up an interesting point with the radiant heat. My new system will be forced air, but the 53 year old house had a radiant system with copper pipes in the slab. In fact just today I removed the boiler and cut the pipes off at ground level. The previous owner told me that at least two zones leaked, and at this age I'm sure the rest would have shortly followed. At first I liked the idea of repairing the system, but I don't think that would have been a sound decision in the long term.

The geo unit can handle a flow of 1.5 - 3 gal/min per ton, or 4.5 to 9 gal/min overall. You raised the point of water chemistry...this is a certainly also a concern, but I didn't want to address too many issues at once. If anyone has any experience in this area I'll happily listen...
 
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Alternety

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You were right in not trying to reuse the copper. Copper and concrete were never a good idea. If you have an exposed concrete floor you could run 1/2" PEX and pour some gypcrete over it. You would then have to put something for a wear resistant layer over that (tile, wood if you do it right, etc.). You can carpet but it not is the best idea because of the insulation characteristics. You can also do it other ways with a different floor build-up. This obviously raises the floor - this can be a significant issue. You can also put radiant in the ceiling. A bit harder to put up but it is in my opinion the best way to install. You are always exposed to the radiation. Not blocked by furniture, rugs, etc.. This really is the best match for heat pumps. If you don't have to install ductwork for air conditioning, it may not be a whole lot less trouble to pipe.

Regarding well water; if I just moved into a house with a well I would have the water tested. You seemed to indicate this would be your domestic water source as well as the heat pump. It is not too expensive depending on how many things you want to test for. Talk to a local water testing lab or use the Internet. You can ask a well driller where to go. They will have any new wells tested. While you are talking to DNR ask if you have to do a periodic testing for bacteria. You want to know about biologicals, and things that are bad for you (lead, arsenic, etc.). I tested for pretty much everything including man made chemicals likely to be in ground water. They can tell you the pH and the mineral content that you need to know about from the standpoint of corrosion, deposits, hardness, and nuisance content (low levels of iron or manganese stains things).

Nearby well owners can give you an idea; but each well can be different. This is particularly true of surface contaminants. Cow field up hill, fertilizer, buried EPA super fund site, pesticides and so on.

And of course you know that sealing openings to the outside and insulating are cheaper than BTUs.
 

Valveman

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OK, first stage needs 4.5 GPM, second stage needs 9 GPM, the house needs about 5 GPM, and you have a 13 GPM pump. I would continue to use the pump you have as long as it works. You can't buy a pump that is made as good as they were in 1976. You do need to keep the pump from cycling itself to death. A 13 GPM pump always puts out 13 GPM. If you are only using 4.5 GPM or 9 GPM, the excess water produced by the pump will fill the pressure tank and the pump will shut off. Then because you are still using 4.5 or 9 GPM, the tank will quickly be empty and the pump will be restarted. Larger tanks will reduce the number of cycles but, the pump will still cycle.

This is a good application for a Cycle Stop Valve. Attached to the line before the heat pump and pressure tank, the CSV will vary the amount produced by the pump to exactly match the usage. When you are using 4.5 GPM, the CSV makes the pump produce exactly 4.5 GPM. When using 9 GPM, the CSV will give you 9 GPM, and so on. This keeps the pump from cycling itself to death and reduces the power consumed when the flow is restricted.

If you attach the house to the line after the heat pump but, before the discharge line, the water used by the house is not just wasted down the hill. The incoming water to the house will be somewhat colder in the winter and warmer in the summer. This does not really cause a problem anywhere in the house except the showers. The temperature to the cold water supply in the shower will change when the heat pump goes on or off. If the heat pump cycles on and off enough that you have to adjust the shower temperature several times, the heat pump is cycling to much or you are taking to long of a shower. (Ha Ha) Sometimes I have to readjust the shower temperature one extra time during a shower.

Now that the water going through the heat pump also goes to the house when needed, you really only need a 9 GPM pump. When your pump goes out, you can replace it with a smaller, more efficient pump. Probably still need a 10 GPM ½ HP pump though. With this type set up, a discharge pipe dropping down 30' is not going to reduce the power consumed. You still need to hold back about 50 PSI, so that the house has adequate pressure.

The 30' drop in the discharge pipe will only help if you have a pump strictly dedicated to the heat pump. Even then, a 1/3 HP submersible is the smallest pump you can get, so it would not help much. Especially because you would then need to store water in a cistern and use another booster pump to supply the house.

I would set it up like this; Pump, CSV, pressure tank, tee. One side of this tee would feed the house, the other side of the tee would feed the discharge line. The discharge line needs to split to two electric valves and ball valves. Only one valve comes on for stage one. The ball valve needs to be set to 4.5 GPM. Both electric valves are energized for stage two, and together they let out 9 GPM. The ball valves will regulate the flow to the discharge, and the CSV will keep the pressure at 50 PSI constant for the house.

I have a single stage heat pump and my well will barely make 4.5 GPM. I wish I had as good of a well as you do. Anyway this link has a picture and an explanation of my system.

www.terrylove.com/forums/showthread.php?t
 

Speedbump

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I lived in Southern Michigan and most of the water I was familiar with was not aggressive. The PH was usually in the 7.2 area.

I'm not keen on GWHP's as I had one and it was not all that efficient and was a lot of maintenance compared with a standard heat/air unit.

bob...
 

Valveman

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Only had my heat pump installed for two months. This time of year the AC loads are fairly light but, first month was $21.00, second month was $25.00 for the entire house. Which also includes all the normal house stuff like lights, refrigerator, dish and cloths washers, etc.. Of course this does not include the pumping cost from another meter which averages about $65.00 per month, of which $17.00 is the standard meter charge. This pump has to run all the time anyway to fill a livestock tank / fish pond. I just piped it through the heat pump then back to the livestock tank.

I consider the heat exchange from the water as a freebie, since the pump is actually there to fill the stock pond anyway. I am not sure how much the pumping cost would be if it were only used for the heat pump and house. I have calculated that the AC is running about 4 hours a day. If the pump was only running 4 hours a day instead of 24 hours, I assume the power bill would be about 1/6th of the $65.00, or about $10.00 per month.

The mobile home I replaced had three window AC units, and the monthly bill during the summer was usually around $250.00 per month. I think I am saving about $150.00 per month which still includes pumping water to the stock tank 24/7. The added cost of the heat pump and the additional piping I did cost an extra $5,000.00 over a standard AC unit. Even so, the pay out should only take about three years. As long as everything last at least 4 years without additional cost, I should be saving considerable bucks. The longer the heat pump and pump system last, the more it should save me.

I should also mention that I spent an extra $1,600.00 on insulation for the new house. I am sure this is making a big difference all by itself, as the mobile home I replaced had very little insulation. I also had the HWG feature added to my heat pump, which gives me free hot water so the electric water heater rarely comes on.
 

rkamphui

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Alright - thanks valveman, speedbump, and alternety. I really like the sound of those utility bills valveman, plus I'll have the added benefit of filling/circulating my semi-natural pond (aka my stagnant puddle). I'll also be using the HWG feature, but I'm still not settled on whether I'll be using one storage tank or two.

So maybe I'm not so bad off...I'll definitely pickup a CSV. Now I was imagining that I would need a huge tank to account for the huge demands of the geo, but it seems like with a CSV that won't be nessary. I currently have 2.5 bath (possibly expanding to 3.5 sometime down the road) and all the water hogging appliances. With this many demands should I still be looking at 100 gal + pressure tanks?

I have also been investigating booster pumps. I'm just thinking - would I be wise to turn the CSV to a lower pressure and use an auxillary pump to supply high pressure for the domestic water (maybe even do away with the pressure tank and just get a holding tank)? I would imagine it is better to put wear and tear on a $500 above ground pump than my $x,*** submersible pump?
 

rkamphui

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One more thought/question - my heat pump discharge water will be about 38 deg F in the winter. Will I be negating any energy savings by having to rewarm this water (directly or indirectly) for household use?

Thanks again, Ryan.
 

Alternety

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Good point. It is real brisk cold water. For hot water I would probably try to pull it off before the heat pump. You will indeed replace all the BTUs extracted for heating in order to make hot water. Running something like a shower it is a mix of hot and cold. Again replacing all the BTUs extracted. So maybe all your domestic water should be before/bypass the HP.

If the flow capability of the water supply is not enough to satisify both demands concurrently, it would be useful to have water controls that fed domestic water at a higher priority than the HP. You would need to avoid short cycling the HP. Reducing flow to the HP would certainly reduce effeciency for a bit, and may annoy the heat pump.

A comparable situation is DHW override on a boiler. When there is DHW demand, the controls stop heating the house until DHW demand is met.

Perhaps a pressure tank isolated from the HP to buffer domestic water demand. You would probably need some clever control electronics and a powered valve or two to make that work. How do you plan to use the HP outlet water to pressurize domestic water? You said a pressure boosting pump; but how will you implement. Perhaps an intermediate storage tank after the HP. But if water demand occurs when no heat is called for you need to pump water just to satisify domestic demand.

Another thought. If you can run gray water from showers and things through the HP system (isolated, of course) you could recover the heat from the hot water used. There are heat exchangers available that allow drain water to preheat a hot water ttank. Just food for thought. The manufacturers of the exchangers claim pretty decent cost recovery.

Probably want to draw some pictures and define states of all the parts for each load condition.
 

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With the CSV a 100 gallon pressure tank is OK but, you really only need a 20 gallon size tank. Your pump is plenty large enough to supply the house before the heat pump. Then you won't have to worry about the temp of the house water. My well is not large enough to do this. If you change to a smaller pump, you won't be able to do it either. Might want to stay with the size pump you have.

Reducing the pressure from the pump won't help anything as long as you still have the same size pump. Going to a smaller pump and reducing the pressure will lower the power consumption but, not by much and would complicated the system.

It would take a long time to save enough energy to pay for a booster pump and storage tank. You would also then have to worry about the quality of the stored water and even add chlorine. You would also then have wear and tear on two pumps instead of one. The sub can easily take the load without damage as long as it does not cycle excessively.

The heat exchanger for the grey water is a cool idea. However, it might be hard for me to get it in the right place since the pipes are under a slab.
 

rkamphui

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I also like the "reheater" option using my house grey water but I have the same difficulty as valveman: pipes in the slab. So rather than wasting all sorts of energy reheating water some other way I think I'll take your advice and put the pressure tank in pre-heat exchanger.

I read up a bit more on the Tranquility heat pump last night and the minimum recommended flow rates are 4 gpm in stage one and 6 gpm in stage two, and the HVAC company says that they run all their systems at these minimum rates. They are supplying a dual solenoid valve system with a split discharge and 4/6 gpm restrictors (as valveman suggested). So my flow demand for the HE will be less than the 9 gpm I discussed earlier...

I'll draw up a schematic of what I'm picturing to make sure I'm on the same page as you guys... Before I do that I want to ask one other thing. I like the idea of making the DW the priority in the system. What if I put one higher pressure CSV, say 55 psi, on the heat exchanger side of the tee and one slightly lower pressure CSV on the pressure tank line (i.e. 50 psi)? I'll then put pressure switch shutoffs in both lines (one NO, one NC) so that the pump only shuts off when both systems are not demanding water. I think this would accomplish the goal and keep things (fairly) simple...
 

Valveman

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You only need one CSV before the pressure tank, and one pressure switch on the pressure tank. Then you can tee off to the heat pump and the house or anything else you want. I plumbed mine where I could open a ball valve and supply the house before the Heat Pump, or close that valve and open another and supply the House after the Heat Pump. My well and pump produce so little water that if I supply the house before the Heat Pump, I starve the Heat Pump for flow and the temperature differential is to great. So I have to supply the house after the Heat Pump, which changes the temperature of my cold water supply to the house depending on the output temp of the Heat Pump water. Your pump and well is strong enough that you do not have to do this. However, when the house uses water after the Heat Pump, at least that much water is not wasted to the drain.
 

Bob NH

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At 3 Tons (36,000 BTUs per hour) with 10 deg F temp difference in the water, you need about 8 GPM. I haven't looked at the specs for the heat pump but they are probably somewhere in that range.

The existing pump is apparently adequate for domestic use. It appears that you want to keep the existing pump for both uses.

The simplest system is to put in a decent size tank for domestic use, with a back pressure regulator on the discharge of the heat pump evaporator to maintain pressure for domestic use. When the heat pump isn't running, or you need more water for domestic use, you can shut off that valve and all of the water will be available for domestic use.

The end of the discharge pipe doesn't matter much unless you are running the well pump at low pressure, which is probably not going to work for you.

You will need to have controls to make sure the heat pump doesn't freeze up if it doesn't have enough water when you are using a lot of water for domestic uses. That may already be in the heat pump control system.

I would have to look at the pump curve and heat pump specs to see what the settings would be for the water controls, but it looks like all would work with your existing pump only if that is no adequate for domestic uses.
 
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