De-superheater Q

[jerryd_2008]

...

Some customers wanted a switch to turn the hot water pump off in cold weather. as in it was cold enough that some auxiliary heat was being called for. I looked at it as six of one or half a dozen of another.

They paid to run the water heater element some more or they paid to run the auxiliary heaters some more.

Under milder weather when auxilairy was not needed, I figured the desuperheater saved them money even if it stole from the heat that went to the house. ...

Carnak, sounds like you are saying that it doesn't matter if the resistance heat strips in the geo provide the hot water or an auxiliary electric HWH. Sounds reasonable but doesn't it assume that the HO has sufficient "spare" capacity in the geo system to be able to do this even in the coldest weather. I believe RoBo pointed out and I verified that this can be a very expensive choice if the HO buys "extra" geo capacity to do this. An extra half or full ton of geo is a very expensive HWH. I can't speak to the cost or even feasibility of adding enough heat strip capacity to handle this.

[Carnak]

I am saying when it is cold enough to need auxilairy heat to keep the house warm, it does not make any difference if you stop running the desuperheater or not.

I can't see anyone over sizing a geo to provide domestic hot water when it works from desuperheating, maybe you get 4000 Btu/hr desuperheating a 5 ton.

There were products out there that could put full heat output into water (be it potable or hydronic heat) or into air on demand.

I sold a lot of geos on the North Shore of Superior, sized anywhere from 65% of the heat load to 100%. You use bin weather data to make the decision. Do we put in a 3.5 ton system and 90% of our heat is from the geo and 10% of our heat for the heating season is from auxiliary. Do we buy a 4 ton, that costs more than a 3.5 ton, put more pipe in the ground, use more antifreeze and now 94% of the heat comes from the geo unit and 6% comes from auxiliary or do we put in the 5 ton, even a more expensive unit, more pipe in the ground and we get 97% of our heat economoically from the geo and 3 % of our heat from a duct heater at 8 cents a kWh?

Most common was size them for 80% or more of the demand heat loss. Probably gave them 95% of the heat they needed. During the extreme weather they either ran the duct heater or wore a sweater

[RoBoTeq]

What brought the subject of the domestic water heating up was the assumption made that "free" domestic water heating capability was available during the heating mode.

[Carnak]

This is correct, if the system is sized properly and there is adequate well length for the type of ground as well as proper well grouting.

In the winter operation though, the water heating is not really operating as a desuperheater, but rather as a water heating heat pump. You are getting your heat from the condenser side of the system, not the evaporator side.

It's always the condenser side

all that changes is the function of the air coil and water coil-- this is less anal than arguing free hot water

[RoBoTeq]

It's always the condenser side

all that changes is the function of the air coil and water coil-- this is less anal than arguing free hot water

I said it was the condensing side. Someone else here mentioned getting free heat from the evaporator in the heating mode.

[jerryd_2008]

...

I sold a lot of geos on the North Shore of Superior, sized anywhere from 65% of the heat load to 100%. ...l

Where might that be, Carnak? I know that on the South Shore of Lake Superior in the portion of the UP of Michigan that I am familiar with, I'm not sure that a HO would even know what geo is. Are we talking the same rocky and sandy soil mix? How did geo make inroads into Ontario?

[Carnak]

Across the Lake from the UP can be sand, clay , rocks or a mixture

but the typical common thing was 'wet'

I put them in from Pigeon River to Schreiber going back to the late 80s

[RoBoTeq]

Across the Lake from the UP can be sand, clay , rocks or a mixture

but the typical common thing was 'wet'

I put them in from Pigeon River to Schreiber going back to the late 80s

The wetter, the better. A closed loop system in soil with water moving through it can be just as efficient as an open loop system.

[Carnak]

liquid sunshine

144 btu a pound making frost

[drsmith012]

What brought the subject of the domestic water heating up was the assumption made that "free" domestic water heating capability was available during the heating mode.

I agree it is not free but at a COP of 5 it is a lot cheaper than the electric elements in the WH. But it still produces far more hot water in the winter than the summer. According to my contractor this is normal for the 410 systems. I do have a kick ass loop burried in the ground with springs all over the place(almost a swamp).

[RoBoTeq]

I agree it is not free but at a COP of 5 it is a lot cheaper than the electric elements in the WH. But it still produces far more hot water in the winter than the summer. According to my contractor this is normal for the 410 systems. I do have a kick ass loop burried in the ground with springs all over the place(almost a swamp).

I get that the wet loop system is a big benefit, but I see no reason why R410a would make any difference then a R22 system of the same capacity.

[jerryd_2008]

I agree it is not free but at a COP of 5 it is a lot cheaper than the electric elements in the WH. ...

DRS, I think that several are making the point that a COP of 5 is useless for HW unless you either have enough surplus geo capacity to heat your house and make HW too or if you don't you revert to electric stripes that are at about COP = 1 just like an electric HWH. If you do have this "surplus" you most likely paid a very high cost for your new "HWH". That said, I assume that you could shut down the geo HW generation when the an undersized (but cheaper) system gets strained but then again how long would somebody keep that up.

[dwaynew612]

I've got an FHP aquarius II installed this summer. I've had good results with controlling it with an outdoor stat ( shuts down DSH ) at 25 degrees F. This is also the point where the system would load for 2nd stage compressor. I'm still experimenting with the best temp, but so far It's heated most of the hot water unless there's high water demand

[thenuke]

I understand the DHW produced in the heating season is not free, but my question is it more efficient than a gas water heater?

I have an Envision 049 with buffer tank and gas HWH. In Northeast Wisconsin (long heating season) I'm wondering if I should flip the envision's DHW switch to OFF and let my gas HWH do the work, or just let the geo do the work. Any ideas?

[beenthere]

Your geo should have safeties that if the hot gas is being cooled too much. It shuts the desuperheater off.

If its not bringing on the aux heat. let it run.

[iaknown]

I have the same question that thenuke asks.....Since its been established that you are using your geo compressor to produce the heat in the winter and it is not a free by-product, is it cheaper to have the geo heat the domestic water or something like a tankless high-efficiency gas water heater? I know the answer for the summer is obvious but isn't using the geo to heat the water in the winter pretty much an electric water heater?

What's more efficient in the winter, a desuperheater or an efficient gas water heater?

[beenthere]

Still heats the water for less then what an electric water would cost to do the same job.

[dwaynew612]

It depends on what your cost per MCF of gas is and cost per KW of electric. Keep in mind most gas water heaters are only about 58-65% efficient. Electric is 100%, but the HP is 300-400%. I've successfully heated a lot of hot water this winter, but shut it down when it's below 20 outside ( that's just an arbitrary temp I picked and am still playing with it) I live in KY Electric is about 7 cents a KW here, gas is around $8-12 per MCF. The one thing for sure is both are going to go up. Last year we paid around $16 MCF so I decided to go Geo. This year, perhaps the gas would have been a little cheaper to heat with. All the calcs and info I've read show it would have been about the same with gas or geo.

My plans for this year are to keep my electric tank, set it at about 90degrees and let the desuperheater heat that tank to whatever it can. I plan to install a tankless on demand gas heater to raise the temp for use. If my calcs are right, I shouldn't need to run the gas much in the summer.

I've finally decided there really isn't a right or wrong way to do it, only more complicated ways that may or may not ever pay back. If you have a big house you have big utilities, no matter how efficient your heat, air or water heating is.

Hope that helps or if anyone has better thoughts please let me know

[jerryd_2008]

...

I've finally decided there really isn't a right or wrong way to do it, only more complicated ways that may or may not ever pay back. If you have a big house you have big utilities, no matter how efficient your heat, air or water heating is.

...

Interesting. Are you talking about HWH only or geo in general? If it doesn't pay back in some reasonable time, with your guesses on the trends of utility costs, why would you do it?

I was hot to do geo, but given our energy lifestyle it would never payback here in my lifetime. Swallowed my pride and desires and went with high end DFHP. Much time on this site has also raised the demon about whether I was sophisticated (or lucky) enough to get a good install. For an ole NG furnace and split AC guy that can still remember coal bins, the DFHP seemed like a maze at times.