desuperheater

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.

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

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.

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

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.

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.

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.