I got word back from Pahlen. Their recomendation is to use a plate hx model TTMP4-20. They tell me that they spec the plate type hx for geo units due to the lower dT, The plate exchangers have a larger surface area and can be sized for higher flow rates. They state "In fact high flow rates / high velocities will maintain the channels and prevent potential fouling." The model they quoted was for the following info:
Geothermal heat pump:
120*F supply temp
110*F return temp
Pool Water – Chlorinated
78*F supply temp (ewt)
105*F return temp (lwt)
Load
48,000 BTUH
Heat exchanger Model
TTMP4-20

I have to find the flow rates for my pool pump to see if it would work as I did not supply those rates with the initial information. But I am also looking at different pumps to see if operating one at a lower speed would work and also save some energy as my pump is a single speed 1hp unit. I asked further about using the Maxiflow tube/shell hx and they said it would have to be oversized to handle the lower dT and typically only use them for higher temperature applications.

Posted By gregs on 13 Jun 2012 10:39 AM
I got word back from Pahlen. Their recomendation is to use a plate hx model TTMP4-20. They tell me that they spec the plate type hx for geo units due to the lower dT, The plate exchangers have a larger surface area and can be sized for higher flow rates. They state "In fact high flow rates / high velocities will maintain the channels and prevent potential fouling." The model they quoted was for the following info:
Geothermal heat pump:
120*F supply temp
110*F return temp
Pool Water – Chlorinated
78*F supply temp (ewt)
105*F return temp (lwt)
Load
48,000 BTUH
Heat exchanger Model
TTMP4-20

I have to find the flow rates for my pool pump to see if it would work as I did not supply those rates with the initial information. But I am also looking at different pumps to see if operating one at a lower speed would work and also save some energy as my pump is a single speed 1hp unit. I asked further about using the Maxiflow tube/shell hx and they said it would have to be oversized to handle the lower dT and typically only use them for higher temperature applications.

Good to know their thoughts on this. I do use the Maxiflow for these applications and i oversize it because the pool pumps are high flow/ low head pumps and the biggest head loss is the filter. Plus the plate spacing is a bit of a risk in an open system but it may not be a huge risk (according to them)

I would strongly recommend a two speed pump. Our 2HP in low speed is significantly more quiet and uses just under 400w. It moves roughly 20 gpm in low and 70 gpm in high. I have heard it filters better in low speed as well. I did look in to variable speed, but what I read was most people ran them in a high or full and then a low or slow speed. The time a variable speed makes sense is when you have water features or things that actually need variable speed water flows.

I also found similiar information regarding the variable speed pumps. My current pump is a single speed pump rated for 70gpm but I could see how the 2 speed pump would work as well. Would there be much difference in the heat transfer between 20gpm and 70gpm?

Do the math -

Transferring 48kBtuh while reducing geo side water from 120 to 110 requires 9.6 GPM

Transferring 48k Btuh while raising pool water from 78 to 105 requires just 3.6 GPM.

I guess it could work as a side stream (only a fraction of the pool pump's flow) heat exchanger, but greater heat exchange is likely with greater flow through the heat exchanger. Most heat pump pool water heaters are designed to accept the full flow of the pump with low head loss. They only warm the water by a few degrees - this maximizes COP and minimizes compressor power.

I agree that a two speed pool pump offers excellent economy; however the ability of a true variable speed pool pump to be tuned to the application is head and shoulders above a two speed. I've deployed 4 Pentair Intelliflos in the past year or so. One pumps 15 GPM at 115 Watts, another 30 GPM at 200 Watts, and another 30-40 GPM at around 300 Watts.

I can see some heat pump high pressure issues with greatly reduced flow rates. It will have to be monitored very carefully and most HPs will have a 3 or 4 high pressure lockouts before a manual reset is needed.

Curt, Are the lower flow pumps used on systems with HPs that were previously set up for higher flow rates or designed from scratch?

I would be interested in how older pool systems with heaters perform when retrofitted with the new vs pumps. I wonder if its a situation where the pump goes to higher speed/flow when the pool heater comes on?

I am trying to determine the best balance for equipment. In the spring/fall the a/c side of the heat pump would be operating in a more limited capacity so I would want to extract as much heat out of the loop as possible. But in the summer when the a/c is running at the max and the pool is already warm I would want to run a higher flow thru the hx to minimize pool heating and lower compressor load. Could I oversize the hx and throttle it back in the fall and run it wide open in the summer? I plumbed a loop in the pool equipment when I built it with a 3 way valve after the filter that could operate it this way.

I think like Curt said even in low speed, approx 20gpm, you are moving way more water than what is needed for the heat pump transfer anyway. Honestly I would just let it run to the pool until the pool is as warm as you want it then switch back to the ground source for a bit. If you leave the hp running 24 hours you might gain 1 to maybe 2 F in the pool a day (depending on outside temps) so you can just watch it as you go.

We also have a 3 way with the bypass, I just leave the bypass cracked a bit even in low speed, but our hx only has 1 inch in and out where all the rest of the pool lines are 2 inch.

I think your heading in the right direction and I think in the end it will be easier than you think. And you will have a warm pool for free to boot. For me to sit in the water and know it is warm from the heat that was taken out of the house to keep it cool is a neat thought

Posted By MikeSolar on 14 Jun 2012 06:54 AM
I can see some heat pump high pressure issues with greatly reduced flow rates. It will have to be monitored very carefully and most HPs will have a 3 or 4 high pressure lockouts before a manual reset is needed.

Curt, Are the lower flow pumps used on systems with HPs that were previously set up for higher flow rates or designed from scratch?

I haven't interconnected a variable speed pool pump with a pool heat pump water heater, but it should be fairly simple to either ensure the minimum flow meets HPWH flow requirement all the time or increase flow rate during calls for heating

I agree Brock, that will be neat and if it saves water and wear and tear on my well its even better.

I have been running an hour meter on the hp to see how many hours it operates in a 24hr period and its been around 6hrs a day during these 90+ degree days. My pool is currently set to operate 5hrs a day for cleaning and the chlorine generator so its very close and should work well.

I now have 2 more items to research: how to design and what to use for the short closed loop to the hx, and if there is some type of timer I can integrate that will track the run time of the hp and be able to operate the pool pump if it doesnt meet the minimum run time for the pool.

I just bought some hour meters on ebay and connected them to on of the circ pump line on the geo so I know how much it runs. Does the chlorine generator run when ever the pump is on, or if the pump were on say 12 hours would it just shut off after the 5 hours it needs?

Currently the chlorine generator is wired with the pump so that it can only come on when the pump is running. Then on the chlorine generator there is a knob that controls the "percentage" of chlorine being made (0-100%). But in reality it is a timer because the cell is either on or off. I dont remember what the time factor is but lets say its 10 minutes, so if you have it set at 50% it is on for 5 minutes then off for 5 minutes.

So when I set up the pool timer I adjusted the run time for 2 cycles (1 in the morning and 1 in the evening) that would "turn" the pool one time a day and operate the cleaner long enough to keep it clean. Then I adjusted the chlorine generator to maintain 2-3 ppm of chlorine. In the winter I turn the percentage down since the water is colder and less things can grow in it.

Ahhh, makes sense. I wondered how they work.

I have looked at some different timers and will probably have to seperate the pump and chlorine generator. It would be nice to find something that is programable with varying set points that I can automate it with. For instance, when we go out of town for a few days I usually bump the a/c up a few degrees which would cause the pool not to run long enough. For the most efficent energy use I would want something that counts how long the pump ran for a certain period of time and then turns it on if it needs more run time. The other option is to leave the set-up I have now alone and let it continue to operate the pool as is. But be able to seperate the pool pump so that when the heat pump comes on after the pool cycle is over it would only operate the pool pump and not the chlorine generator.

Do you have any other lines to the pool? By far the simplest thing would be to use a separate in and out line with it's own small pump, that pump could be driven by the heat pump. But if you don't have the lines... In our last house I actually did just that using a 3/4 hose and a regular circ pump, which is what got me to where we are now, but we had the two hoses going in and out of the pool and running over to where the heat exchanger was, luckily my wife was fine with it, but I had to pull it when guest's came over.

I just have the typical in and outs for the pool water. I think it would be a hassle to plumb a seperate pump into the system for the hx. Sometimes simplier is better, especially when I am not home to manage the system. I am thinking about having the pump on one timer and the chlorine generator on another and have them syncronized maybe with the chlorine generator starting 5 minutes after the pump comes on and ending 5 minutes before the pump shuts off. And the chlorine generator does have a flow switch to make sure it doesnt operate without water flow. This would allow me to also operate the pump seperately from the chlorine generator for the heat pump. It may use more electrcity but it would be less complicated.

My current pump is a single speed unit and I think it would be beneficial to switch to a 2 speed pump and only have it run on high to operate the pool cleaner.

There you go, so it would run enough to make sure the chlorine generator gets it's time in and then what ever else the hp call for is just extra. I like that idea and you don't have to adjust anything daily.

Thats the great thing about forums like this. You can bounce ideas back and forth and come up with a better solution. Now I need to figure out what I need to make the short loop from the heat pump to the hx. My well water open loop in and out are close to the pool equipmet so it wont take much to get it there. But I will need to add a circulating pump, some way to bleed the air out and figure out what antifreeze to use in it. Then I will also plumb the well into the hx to be able to switch between it and the pool if it gets to hot.

The pumps in our system, one going out and one coming back in, are both before the manual valves between the field and furnace coil, so I don't have the pump issue and the same mix goes through both as well. I am not as familiar with the well system, does it use a secondary hx or just pump the well water past the hp? I would think as long as you drain it you wouldn't need antifreeze, but then again if it's in there you wouldn't have to worry about it.

My unit is a water to air heatpump with a open loop. Basically I have well water that goes in one side of the internal hx and comes out the other side to a electric solenoid valve and a butterfly throttle valve. So when the unit comes on, the valve opens and water flows thru the internal hx and dumps into the woods. My well water is typically in the mid 70's and I can adjust the throttle valve to achieve my dT.