Well modifications for Geothermal

I am installing a geothermal open loop system in my home. The system is 2 stage and will use ~5 gpm of well water on first stage and ~8 gpm on second stage. The system is sized so that it may run nearly continuously second stage in the dead of winter (i.e. 10,000 gallons/day). In the summer, it will never run second stage, but may run first stage for long spurts.

In any event, I know that my current well setup is not appropriate, and I am deciding what changes to make. I currently have a Myers 1 HP pump rated for 20 GPM. I compute my total dynamic head to be about 220 feet at 20 GPM. The well is pretty shallow at 50' with 18' static water level. We have an abundance of water, and the well can provide at least 30 gpm indefinitely. The well is less than 75' from the house and connected with 1" PVC. I am contemplating the following choices:

(1) Grundfos SQE constant pressure pump system (~$1400)
(2) Keeping current pump and replacing the pressure tank with a much larger tank (~$1000)
(3) Keeping current pump and existing tank size and adding a cycle stop valve (not sure of cost)

Note: my existing pressure tank recently failed and I've manually added air to keep it going so I will have to replace this even for option (3). Also, pump is 15 years old and may have experienced some short cycling before I discovered the pressure tank failure.

My question is what solution will work best for my current needs. Our existing system met our needs without the geothermal with the exception that the second floor water pressure was slightly low (system was set to 35/55). I think 20 gpm is reasonable for our needs.

As an aside, can anyone explain, how the Grundfos system works in the presence of two large water heaters. We will have two 85 gallon water heaters. One is a preheat tank for the geothermal desuperheater. Anyway, it does not seem like a little Amtrol ST-5 could overcome any heating expansion from the water heaters. Am I missing something or can their system work with a larger expansion tank too?

Sorry for the long post, but I appreciate any suggestions.

With a geothermal system that is going to run almost continuously you want to save energy. That is what gives you high Coefficient of Performance. You don't want to invest a lot of money in a geothermal system and fritter away much of the saving with inefficient pumping.

I say all of that because using a 20 GPM pump with 220 ft of head to pump 5 or 8 GPM through the evaporator which has low head requirement wastes a lot of electricity.

Before I make specific comments, please describe what is meant by two stages. Do you have two evaporators with two compressors operating at different temperatures? Can you describe each of the components of the system?

I like to approach system design by conceiving two or more designs and analyzing the hardware and operating cost. You can compare the operating cost and investment cost for the systems and pick the one that best suits your needs.

You have a nearly continuous flow requirement for the geothermal system which has limited head requirements since you are operating open-loop; combined with much more modest domestic water requirements but higher head for other uses.

A system that might work well is a variable speed pump that adjusts speed, and therefore pump head, in response to control demands. The system would consist of the following; to work as described.

1. A variable speed pump in the well with the capability to deliver the pressure for domestic uses

2. When the the pressure tank has enough pressure the pump will operate at a lower speed to supply the needs of the geothermal system. It will be operating at somewhat lower speed. Since the pump characteristic is that head (pressure) varies as the square of speed and flow varies directly with speed, the pump may be operating near half speed when only the geothermal system is demanding water.

3. When the water tank requires water as determined by a pressure switch or pressure transducer, the speed of the pump is adjusted to provide the required pressure. The tank should be selected so the high speed cycles will be of moderate length as they are for the usual pump/tank systems. If there are sustained high-pressure uses such as for irrigation the variable speed system can be used to prevent cycling of the pump.

I know that Goulds, and I'm sure others, have variable speed drive systems for standard 4" pumps. They should be competitive with Grundfos which has been a fairly expensive provider.

I don't believe a constant pressure system is the way to go because it will waste a lot of energy when the only demand is the geothermal system. With a check valve at the tank inlet it will hold pressure when the pump slows down to the pressure requirements of the geothermal system.

I'm have an engineering interest in such a system. If you can give us more details on the geothermal system, especially the details of the two-stage aspects, I will take a look at what kind of pumping system would do it.

Thanks for the reply. The geothermal system is a ClimateMaster Tranquility 27 (actually Carrier branded version) which uses a two stage scroll compressor. There will be a single 1" line running to the the inlet of the heat pump and then on the outlet the line is split into two 3/4" lines. Each of these lines has a motorized valve which is slow closing (Taco EBV valve or Taco 500 series geothermal valve) followed by a flow regulator (Watts CSM-61 for instance) which sets the flow rate through the system. When the unit is calling for first stage heat, the first motorized valves opens and the flow regulator will have been preset for 5 gpm of flow. When the unit can't meet demand and the compressor kicks into second stage, the second motorized valve opens and its flow regulator will be set to 3 gpm for a total usage of 8 gpm. The valves are controlled by thermostat.

In summary, there is one compressor with two stages and one condenser/evaporator depending on whether in cooling or heating mode. You are correct that this will form a nearly continuos component of 5 gpm in the summer when entirely first stage since it's not that hot in Michigan and 8 gpm in the middle of winter when the compressor is running second stage. Added to this will be the highly variable demands of a standard 2 1/2 bath house. I do also have a sprinkler system which is sized to my current pump. It only runs in the early morning in the summer when there is little to no additional water demand.

In the interest of completeness, my well is 4" with a submersible Myers pump (1 hp, 20 gpm). The model number is partially rubbed off. The pressure tank is a Clayton Mark CM10050 which I believe is 45 gallons.

Thanks in advance to Bob and any one else who has any suggestions!

The 1 HP 20 GPM Myers pump curves that I have seen (Predator 2ST102-20, Rustler 2NFL102-20 http://www.femyers.com/pdf/pdf.ws/ws brochure/k3153-20.pdf) show that the pumps deliver 14 GPM at 220 ft of head and 20 GPM at about 170 ft of head. If the same pump head is fitted with a 3-phase motor with variable speed drive system, operating from 30 to 60 Hz, it will deliver the same top end and can be modulated to deliver the lower flow requirements for the geothermal system at a saving of power compared to the fixed speed system.

The variable speed controller uses single-phase 240 Volt power to produce 3-phase power for the motor.

It could operate with the existing flow regulators, but could save some more power with speed control instead of the suffering the pressure loss of the regulators.

When operating only the geothermal system the variable speed system will probably use about 1/3 of the power it uses now with the motor operating at full speed. The power for delivering the high-pressure flow will be a bit more because of losses in the power conversion but the net kWhr increase for that condition will be small and that part of the pumping is a small part of the total pumping.

Otherwise, the system is just what you have.

OK, this has already gone too far. The biggest misconception in the world right now is that variable speed pumps save energy. This is NOT TRUE! It seems to make sense that slowing the motor down compared to choking back the pump, should save energy. Choking back the pump with a valve saves just as much energy, which makes it "counter intuitive".

The CSV and a small tank will save as much energy as the expensive and troublesome variable speed pumps. Many owners of heat pump systems have told me that it doesn't do any good to save a few hundred on energy by using a variable speed pump, if you have to replace a $1,100.00 controller, or even the pump every couple of years or less.

The CSV will save just as much energy, cost much less up front, and triple the average life of the pump system.

The Variable Speed Pump is expensive to purchase, doesn't save any more energy than the CSV, shortens the life of the pump and motor, and has an $800 to $1100 dollar computer that needs to be replaced on a regular basis.

I am sorry I didn't see this thread before it got confusing about head, flow, and variable speed, which doesn't make any difference when it cost an extra 1000 bucks a year just to keep a variable speed pump working.

Bob,

Thanks again for the reply. You have definitely stretched my thinking which is a good thing. Can you recommend a variable speed controller so I can research this a little further? Also, how does this impact the pressure tank requirements? Is my 45 gallon tank adequate? Thanks again.

Valveman,

Thanks for your reply. I am receptive to a CSV - one of the geothermal installers even suggested this. However, I am having trouble understanding how this saves energy? I even reviewed the patent (5,988,984) through Google, but I am missing the power savings part thought I would like to understand it. Also, does a CSV put the pump in a position of operating outside of the manufacturer's specs, for instance, without adequate flow?

It is "counter intuitive". Most pump installers and many engineers do not understand it but, it is a simple concept. Horse Power for a pump is determined by how much weight a pump must lift. When it is pumping 20 GPM, it has to lift more weight than when only pumping 5 GPM. So it takes more energy to pump 20 GPM than 5 GPM. The centrifugal impeller saves energy naturally, without needing to change the speed of the pump.

Some pumps are better at reducing energy naturally than others. I like the Hydroflo or other pumps that have stainless steel impellers instead of plastic. Not that plastic or stainless steel has anything to do with it. It is the way the impellers are attached to the shaft. The stainless impellers are locked to the shaft and do not drag on the diffuser. This causes them to reduce power consumption more than plastic impellers that "float" on the shaft. These plastic impellers have more drag at low flow rates and do not drop as good in power consumption.

I have a 2 HP stainless pump that draws 12 amps when pumping 25 GPM. Then the CSV makes the amps drop from 12 to 5.8 when my 3 GPM drip system is running. Other brands of pumps may only drop from 12 amps to 9 amps at low flow. Doesn't make that much difference but, if you want to get efficient, then lets get efficient, and not just variable speed extra money away.

Here is a link to some technical stuff that better explains it.

http://www.cyclestopvalves.com/comparisons.html

1HP 20 GPM pump and motor $463.00
PC 66 tank 147.00
CSV1Z Cycle Stop Valve 171.00
Total $781.00


Grundfos SQE, Goulds, or any other brand of
Variable Speed Pump
$1,400.00 or more

Less 781.00
Difference $619.00

You can't save energy with a variable speed pump. The original $619.00 difference, and the regular repairs and replacements for a variable speed pump and controls, will cost you more than the heat pump itself could ever save.

Just a quick note. When I lived in Michigan many years ago, the Ground Water Heat Pump as it was called back then was all the Rage. Everyone was pushing it because it could make us Well Drillers twice the work if people went with the two Well system. It came and went just about as fast as people began to realize that the savings was practically not existant and the initial costs were phenomenal.

Now they are starting to make a comeback as we are seeing more homeowners here asking questions about them. I believe you will see that this comeback will be short lived as the technology has not improved enough to make any difference in actual savings. Especially with a constant pressure Pump.

I bought a house years ago here in Florida that had a GWHP. All I did was work on it and I didn't see any difference from the home before it with a standard Air Conditioner in a home the same size.

bob...

valveman: I appreciate your thoughts on the CSV. I am intrigued. However, as I look at your numbers about reducing the draw from 12 to 5.3 or from 12 to 9, I am left to wonder if it might just be better to let the pump cycle. I know this is a killer for the lifetime, but is this possibly better than leaving the pump running continuously at 75% power for a 5-8 gpm flow. In other words, the wasted energy of running the pump at low volumes versus just replacing the pump every few years. Obviously, the size of the pressure tank factors in as it will determine how often it cycles, but I'm concerned about running the pump continuously at small flows if it only cuts power consumption to 75%. I'll need to run some numbers for my 1hp pump to see whether there is any savings here.

valveman and speedbump: the geothermal heat pump savings are substantial. My neighbor has had one for 20 years and can attest first hand. Given current rates, I am looking at $2.50/gallon for propane this winter. For me, that is $4500 for the upcoming year. Given our current electric rates, I can save ~$3000 this year switching to geothermal. That is by my calculation - the geothermal guys don't always capture the full cost of electricity delivery in their estimates and give even higher savings.

Yes, the systems are expensive to install, but the payback period can be very quick. For me, it is about three years since I'm doing it myself and it is open loop. I can understand where geothermal was difficult to introduce many years ago since fossil fuels were so cheap that it made the payback period difficult to justify. Also, if you are doing vertical loops with well drilling equipment, you just added another 8-10K to the job versus open loop. Horizontal loops can be done for an added 6K since they only require a backhoe and trenching equipment. Anyway, even at 15-18K for the total job, you can still see paybacks that are less than 10 years. The closed loop systems enjoy a reputation for being virtually maintenance free. The open loops do require periodic maintenance; however, they are even more efficient. I respectfully disagree that these are some sort of fad - unless our current gas prices are also a fad and we go back to $2 gas in the near future. In that case, the payback issues return although the systems will still dramatically outperform any 95% furnace. My $0.02.

valveman and speedbump: the geothermal heat pump savings are substantial. My neighbor has had one for 20 years and can attest first hand. Given current rates, I am looking at $2.50/gallon for propane this winter. For me, that is $4500 for the upcoming year. Given our curren

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I would need a lot more proof than that, since I can first hand tell you that mine didn't save me a Nickel. It really doesn't matter a lot what the price of Propane or Gas is these days, if the system doesn't save money, what's the difference?

bob...

I have a single stage open loop heat pump myself. I love it. My water is basically free as I just tapped into a 3 GPM line from my well, that was already running all the time to fill a livestock tank. So far my highest electric bill has been $71.00, when the window unit AC's I used in the past were using about $250.00 per month. The system ended up costing me less than $4,000.00 more than a standard unit, so the payoff should be a little over 2 years.

The cost of running the 1/3 HP pump 24 hours a day is about $70.00 per month. Even if I add this to the cost of energy for the heat pump, I am still saving money.

It cost very little extra to keep the pump running at low load, all the time the heat pump is running, compared to letting it cycle on and off into a BIG tank. Multiple starts also use up more electricity. As a matter of fact, cycling the pump won't even save enough to pay the extra for the big tank. Not to mention, that cycling is the worse thing you can do to a pump. Figure a normal house pump cycling will only last an average of 7 years, and cycling with a heat pump will make it last even less time than that. Using a Cycle Stop Valve should triple the life of the pump.

Cycling causes other problems as well but, would be better than a variable speed pump. Lots of Cycle Stop Valves have been installed with heat pumps, to efficiently solve the problems of cycling and variable speed.

PS;Since my 1/3 HP pump uses $70.00 per month and runs 24 hours a day, a ½ HP running 12 hours a day, or a 1 HP running 6 hours per day, should be about the same. Power for the pump depends on how many hours a day the heat pump has to run.

speedbump said:

I would need a lot more proof than that, since I can first hand tell you that mine didn't save me a Nickel. It really doesn't matter a lot what the price of Propane or Gas is these days, if the system doesn't save money, what's the difference?

bob...

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I can only offer my own estimates, but if you want more proof I would suggest looking at the specs from ClimateMaster or Waterfurnace. They publish all the specs you need to calculate savings for whatever application. However, the cost of propane is by definition a part of the savings calculation for me since a propane furnace is being replaced. Obviously, the cost of electricity is important too.

valveman: Thanks again for your thoughts. Is there any difference between the CSV valves and say the Cycleguard valves manufactured by Flomatic?

The idea is the same but, there is a big difference in the way they work. Those kind of valves have been around for decades and have not been accepted in the industry. The principle was sound but, a tiny drilled hole or small tube, bypasses a little water for the valve to function with a pump. The little holes and tubes would stop up with debris, the pump motors would burn up, and the idea would be scrapped. Even when there is perfectly clean water, the little holes will grow closed with mineral deposits, the same as holes in a shower head. There are also a lot of problems with the main valve having to close and open off of a valve seat at low flow.

We tried building valves this way 15 years ago. We realized very soon that keeping the little hole from clogging was the key. With considerable trial and error, we were lucky enough to stumble on the idea of a half moon notch instead of a hole. Two half moons come together when the valve closes to create a hole or orifice. Nothing can clog this hole, as a decrease in downstream pressure, causes the valve to open and again splits the hole in half. The location of this notch also keeps the valve from ever completely closing, which eliminates the problems associated with the old style fully closing valves. This simple difference is patented, at least for several more years. At which time you can bet their will be even more copies.

The several so called "copies" of Cycle Stop Valves that are available today, do not work like a Cycle Stop Valve. The names sound very close. The valve itself looks the same. The advertisements are surprisingly similar. The instructions are almost verbatim. Even our trade marked name is being used on search engines with very slight modifications such as "Cycle Stop (Control) Valves" and "Stop Valves". Even the companies manufacturing variable speed pumps use the same advertisements and try to make their product function as much like a CSV as possible They say imitation is flattery. Let me just say that we are so flattered, we can barely walk.

Having so much competition does prove that the idea is sound and accepted. It wasn't long ago when big pressure tanks were considered the best means of pump control. Now they are usually considered as a last option. "Constant Pressure" systems have now made it to the main stream. Cycle Stop Valves will have to make room for a little competition. However, do not get discouraged with problems and give up on the "Constant Pressure" concept, until you have tried a real Cycle Stop Valve. We first went through a lot of variable speeds, then hundreds of different kinds of valves, before we came up with what really works.

As I see it you need to separate house water supply from the heat pump water so that you can use a low pressure pump.

The lower the maximum head pressure, the more flow you can get for a given HP.

I would also recommend a CSV in this type of application, but you should start by looking for a pump that maxes out around 40 psi, since the heat pump really should not need much pressure to get the needed flow rate.

FYI: I'm planing to install a open loop system with a driven well for the heat pump and leaving my deep drilled well as it is.

Note: Study's have also shown that you are also better off using shallow water for the heat pump since it generally has less minerals and also reduces the risk of drawing contaminants in to the deep water.

Note: Study's have also shown that you are also better off using shallow water for the heat pump since it generally has less minerals and also reduces the risk of drawing contaminants in to the deep water.

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Bill,

Here in Florida (my area anyway) there are some fairly decent shallow wells as far as Mineral content is concerned and there are some less than 20 feet deep that are disgusting. Full of Iron, Tannin and Sulphur. So you have to be careful what water you put through a GWHP. My old one used to plug up all the time to where it would just quit cooling altogether because the heat exchange unit was so full of iron, the heat wouldn't exchange and the flow rate was reduced.

I know Engineer types and Survivors like to play with these concepts, but in my opinion, the numbers are not always what one should be looking at.

bob...

speedbump said:

Bill,
Here in Florida (my area anyway) there are some fairly decent shallow wells as far as Mineral content is concerned and there are some less than 20 feet deep that are disgusting.

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Yes, the results you get will vary greatly. I should have mentioned that the shallow well study was for MN.

My main point was that you should not be pressurizing the water up to such a high pressure when the system should only need 30 or so PSI to get the flow rate that is needed.

Then by getting a pump designed to produce less head pressure, you can use less energy to get the same flow rate.

This could also be done using one well and two pumps.