desuperheater

SolarLurkerSolarLurker Solar Expert Posts: 122 ✭✭
Anyone have any experience with a central air desuperheater? I found this unit when looking for something else, Aquefier R6K-HP-V-F-410 seem like it might be a way to heat water during the summer (maybe I can use it for the pool).

Comments

  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: desuperheater

    They work well with low efficiency AC units, like SEER 10 or lower, with the new high efficiency they are not worth the installation costs, not enough high temperature energy to harvest from the compressed gas to heat water.
  • russruss Solar Expert Posts: 593 ✭✭
    Re: desuperheater

    The heat pump type of water heaters achieve a COP of about 2.1 - better than anything else including solar thermal but nothing like a normal heat pump.

    The loss of efficiency is due to the higher water temperatures they produce.

    The de-superheater option is offered in many new heat pumps but for me - İ didn't operate the heat pump in the AC mode last summer so it would have been one big waste.
  • LucManLucMan Solar Expert Posts: 223 ✭✭✭
    Re: desuperheater
    Anyone have any experience with a central air desuperheater? I found this unit when looking for something else, Aquefier R6K-HP-V-F-410 seem like it might be a way to heat water during the summer (maybe I can use it for the pool).

    If you live in a hot climate that requires daily a/c operation a desuper heater may be economical for you for generating domestic hot water.
    Connecting to a pool will require a stainless steel heat exchanger if you are using chlorine.
    titanium HX if using salt type disinfection.
    The installation costs may exceed your savings potential.
    But I assume that if you lived in a hot climate you wouldn't need to heat the pool.
    Check into a solar HW system.
  • russruss Solar Expert Posts: 593 ✭✭
    Re: desuperheater

    You never - never want to run open source water (such as a pool or the incoming water line) through a heat pump. The internal heat exchangers are not meant to be removed and cleaned (so İ am told). (added) Additional and external heat exchangers are added when heating an 'open source' water - by that İ mean a water where quality might not be so good or might be variable.

    Check into solar hot water all you want (İ have such a system) but it sure looks like a dedicated hot water heat pump (meant only for the sink, shower) is far more cost effective.

    The suppliers have jacked up the system cost for panels etc that it doesn't make sense.

    According to ACEEE they spell out a 'all in cost' for a dedicated heat pump type water heater of 4125 USD for 13 years and for a comparable solar system 7,072 USD.
    That is equipment plus elec plus. The COP is in the 2.1 range
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: desuperheater

    Are you trying to heat the pool or cool the house? Geothermal heat pumps often have desuperheaters on them and they will heat water in heat mode and cool mode. Obviously you get the most energy out of the system cooling the house and heating water, but even when heating the house it is typically cheaper to heat water via geothermal than other methods since you’re in the 2.5+ COP range. There are also air to air heat exchangers with desuperheater, likely what your looking at.

    The advantage of heating a pool is you’re not getting to the higher temps like you would be looking at with a pre water heater, so it tends to be more efficient that way. The down side is you’re typically looking at 10 to 25 percent of the capacity of the heat pump going in to the desuperheater. So if you have a 4 ton unit you’re looking at about a half to 1 ton (6000 btu to 12,000 btu) of heating, not much on a pool which might have a 200,000 btu heater running 4 hours a day.

    There are also heat pumps intended for just heating pools and work best to be run during the hottest part of the day. As Russ said for pool heating solar hot water is the way to go if you have the space, you can’t beat it cost wise, as a matter of fact it rarely counts for an energy rebates because it’s payback is so fast.
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • SolarLurkerSolarLurker Solar Expert Posts: 122 ✭✭
    Re: desuperheater

    I don't have a geothermal heat. This unit looks like it will works with a conventional air source central air unit. I know it wont run all the time, however if it can produce some hot water during the summer and make the ac more efficient, seems like it could pay for itself.
  • solarvicsolarvic Solar Expert Posts: 1,052 ✭✭✭✭
    Re: desuperheater

    My daughter has the geothermal heat pump that gets heat out of the ground and froze the first 2 years. It has the superheater and is not good to use in the heating season, only for the airconditiong season. I think the problem is that the heating contractor didn,t put wnough pipe in the ground and didn,t bury it deep enough. Finally after the 2nd season they had a factory rep come and he disconnected the superheater for the winter and they got enough heat this year.
    After winter is over desuperheater can be used till next fall. Solar Vic
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: desuperheater

    Solar Vic that is called "short looping" where the field isn't large enough to handle the load. If the field is big enough it can handle the de-superheater, but if not, it is best to shut it off. Once the entering water gets below about 25F you typically in the COP of 2 and below 20F you closer to 1. With everything running on ours, heating our house, pool and hot water in Green Bay, WI, we currently have a field temp of 36F so our COP is over3

    Solar Lurker, how much extra is the option on the setup your looking at? If it were me I would say go for it, why not stick that heat back in the pool rather than let it vent to the atmosphere. But it might not have a financial payoff. The further south you are the better the "payback" would be.
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • russruss Solar Expert Posts: 593 ✭✭
    Re: desuperheater

    @Brock - Pumping 20 degree F water around a loop? Maybe it is time to buy a new thermometer. Even 36 deg F is some very cold ground water!

    İ guess you are referring to the antifreeze mix? But that would still freeze the area around the well/ground loop rather quickly.
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: desuperheater

    Why would I need a new thermometer? I actually have 4 of them on our system and they are all within .2F of each other. Oh I think I see what you’re saying, yes water below 32F is ice :) Yes systems up here and further north typically run antifreeze to 10F, probably even less further north. Modern heat pumps cross the magic line where they are the same as resistant heat between 15F and 25F. My unit crosses about 18F. The lowest incoming water temp we have seen on ours was 33F and that was when it ran 3 weeks straight to warm the pool up initially.

    And yes if your incoming water gets below 32F you are starting to freeze the ground around the field. That is why most systems will hover around 33F for a long time before falling below 32F as it starts to freeze the field. It is amazing though how the ground or earth bounces back when you stop extracting heat. When were gone I had our system shut off for 3 days and the ground warmed up 3 degrees, probably to what the real ground temperature is, which is the reason it works so well.

    It is not uncommon for fields up here to dip below freezing in late winter, obviously the warmer the better. From what I have heard from others with geo systems around here our field is actually a bit warmer than most, but our field is oversized by about a ton. I should add in summer I have never had the field above 65F either and typically I run the field water through the coil to cool the house :)
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • solarvicsolarvic Solar Expert Posts: 1,052 ✭✭✭✭
    Re: desuperheater

    Brock I figure my daughters system is shortlooped. This last summer I used a 3500 pound tractor to mow with and probably got the ground packed tighter. My son inlaw is going to try and get the homebuildrt that built thier home to add more pipe in the ground. The circulating system didn,t freeze as they have antifreeze in it. I meant they couldn,t keep the house warm even with the heat strips also operating. They use lots of hot water and I think the superheater took all the heat out of the ground. I think thier loop water temperature got to 24 degrees. They also had to run a kerosene heater and a couple electric heaters. This winter they havn,t needed the kerosene heater and thier suplimental heat only come on a couple times. I think the weather and ground temperature should be similar to yours. The ground temp. is suposed to be about 51 degree f. Do you know if another loop can be added to thier system without tearing out the 3 loops they already have? If I didn,t already have free heat from a gaswell I would go for one of these systems. Vic
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: desuperheater

    Yes they should be able to add more to the loop field without removing the old install. I have heard of bad purges that left air in one of the loops which basically made that loop non-existent, it might be worth re-purging the field with at least a 2hp purge setup.

    You might also try watering above the loop field, often that will help settle the ground back down and increase conductivity once it's all packed back in.

    And yes a water heater does use quite a bit of that heat. Right now our city water is coming in at 39F, so I am guessing the ground is around that same temp.
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • russruss Solar Expert Posts: 593 ✭✭
    Re: desuperheater

    As Brock pointed out - you actually want the ground to be compacted around the coils - better heat transfer. Water would also improve heat transfer. This is the opposite of a septic system drain field in that regard.

    Using the desuperheater to make hot water in the winter is using the wrong tool. İt may be beneficial in the summer when using the AC but in the winter it is simply working the system harder with a mismatch in temperatures.

    İ operate our ASHP with a 90 degree F water temp - the lower the outlet water temp the better the COP (efficiency). İf İ had it set for 120 the power cost would go way up - same applies for a GSHP.

    İt should be easy enough to determine if water flow to the three loops is similar by checking the tube temp - might have to dig to get to the tube. İf one is not carrying it's share of the load that would not be good!
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: desuperheater

    While I agree that heating water in winter with a geo system isn't as efficient as it is in summer, it is still less expensive in most cases. Take ours for example.

    We have incoming loop temp of 36F, at 30F my heat pump is rated at a COP of 2.94. Our natural gas $1 per therm, our water heater is .94 percent efficient so to heat roughly 100,000 BTU I spend $1.06. Now using electric (.06/kw) to do that same heating in resistant mode (regular electric hot water heater) would be $1.82 Assuming only a COP of only 2.0 it would cost me $.91 to heat that same water. If I am really at a COP of 3.0 it would be $.61

    heating 100,000 BTU's for me
    $1.82 straight electric resistant
    $1.06 natural gas
    $0.91 geo with COP of 2.0
    $0.60 geo with COP of 3.0

    Depending on your energy rates geothermal might not be the least expensive way to heat water, for example if you didn't have tiered rates at paid the national average of $.12 for you electricity you would be better off heating the water with natural gas. But in my case geothermal is the least expensive way to heat water.
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • russruss Solar Expert Posts: 593 ✭✭
    Re: desuperheater

    What temperature are you heating the water to?
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: desuperheater

    We keep the pool at 88F. The system pulls water from the main pool and filters and heats it (if necessary) and dumps it in to the hot tub. Then if we want the hot tub to heat up the intake switches from the pool to the hot tub. So the hot tub is normally about 90F, but when we use it (at least every other day) we warm it up to about 100F. Then when we are done it mixes the two again so the heat is dumped back in to the main pool. This also helps a lot with maintaining chlorine levels and keeping everything clean.
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
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