What's a PI?
I think we'd all like to hear about the new installation on your unit and how it performs once that happens. Good for you for asking them.

I'm curious now on how! I'm guessing the custom module will monitor the temp of the preheat tank somehow and switch the geo unit on without the blower fan running so that just the desuperheater exchanger and pump are running until the preheat tank temp reaches a certain point? I wonder if it will run in Stage 1 only unless the water isn't heating fast enough, then kick to stage 2?

Very interested and curious! Hope you post more as this develops!

Wow, lots of discussion...

You should have emailed me, as geodean suggested. Anyway....

An EarthLinked system only allows the desuperheater to operate in the COOLING MODE ONLY. An internal controls change can be made to override that, and allow the desuperheater to operate in any compressor ON cycle. However, if one were to do that, they would need to also install an outdoor sensor control. The outdoor sensor control would allow the desuperheater to operate at outdoor temps well above balance point.

Balance point is the outdoor temperature at which supplemental heat is allowed to operate with the heat pump unit to cover the total load of the home. If the desuperheater is going to operate in the heating mode, it will use/take/steal 5%-15% of the compressor's output from heating the home. The desuperheater would then need to be taken out of service if the outdoor temp drops closer to balance point. Or, the balance point will need to be raised to allow the heat pump to have enough off time for the ground to recover...

As for the heat pump heating water without the air handler, EarthLinked has that option, as do many, many other manufacturers. It is done with an added HWHX. Typically, too, this might add the need for another ton of installed heat pump, as heating the water as priority adds to the total load of the heat pump. Each situation has to be evaluated and decided on.

Usually, adding the HWHX option for priority water PRE-heating (pre-heating water without it being just a by-product of compressor operation) will add $5,000-$8,000 to the installed price. As Joe has pointed out, it's not typically worth the extra investment. Unless it's a house with high hot water usage, and you're comparing to $3.00+ per gallon propane...Even then, straight electric water heating will cost less than propane.

As far as the 40 amps vs. 20 amps for the heat pump vs. the electric water heater... just because something is rated at so many amps, doesn't mean that's what it is using. My 3 ton heat pump pulls about 9 Amps. But I have a 20 amp circuit to it. To do a real comparison, you have to look at the BTUh output along with how many amps it takes to get those BTUhs. Typically, a priority water heating module with geothermal will have a COP of about 3. This means that it will be 3 times more efficient than straight electric resistance. Or rather, it will use 1/3 the energy of an electric water heater.

I hope all that is coherent, as I'm pretty tired from trying to follow all of the arguments in this thread...

Sorry, I don't check this site all that often, either.

Earlier I wrote that a desuperheater, by design, cannot accept / transfer the full output of a compressor. Despite subsequent sniping, I stand by that statement. If a HX is sized to transfer more than just the superheat from compressed refrigerant, then it is no longer a desuperheater...it becomes a condenser.

I have no problem with the idea of a separate, full sized condenser dedicated to potable water and able to accept the full output of a heat pump compressor. Modifications could be made to the controls so as to respond to water heating calls only. Unfortunately this option isn't yet offered by a majority of geo brands.

Posted By stuart.wyss on 29 Nov 2010 10:58 AM
What's a PI?
I think we'd all like to hear about the new installation on your unit and how it performs once that happens. Good for you for asking them.

I'm curious now on how! I'm guessing the custom module will monitor the temp of the preheat tank somehow and switch the geo unit on without the blower fan running so that just the desuperheater exchanger and pump are running until the preheat tank temp reaches a certain point? I wonder if it will run in Stage 1 only unless the water isn't heating fast enough, then kick to stage 2?

Very interested and curious! Hope you post more as this develops!

Product Improvement (PI)

I am waiting on a new controller to arrive from Florida and the contractor to install it. I don't know what cycling strategy they have in mind. Would they use a thermostat in the preheat tank, or maybe run it x number of times a day, or for a couple hours at night? I'll have to wait and see.

I suspect they would use the same arrangement used for a thermostat with the HWHX box.

They have to mod the controller. It could not have been too hard. They did it in a week. I think once they worked it out, they really liked the idea and embraced it.

Could be good for marketing and perhaps a bit of retrofit business for likely eager customers, such as yourself, if the energy savings are significant. They said I would be able to preheat hot water all year around economically, whatever economically means.

It would be good for contractors for sales and retrofits. It's good for the environment.

Everybody wins.

I wonder if it could work on other types of geo systems from other vendors?

I guess the HWHX box is really only for high demand like pool heating, commercial, and radiant flooring. It is limited to that now, because of price. So really this new arrangement could be the only cost effective viable geo alternative for year around hot water preheating, for low demand domestic use.

This is a whole new world of energy savings not yet tapped, using existing installed equipment, normally idle.

Earthlinked handles refrigerant differently than other systems, and while compressor is not variable speed, system more or less permits variable flow of refrigerant which is why it may be the one system that can run exclusively to provide heat to DSH. Other systems could not run long without fan adding or removing heat.

That said, I find it counterintuitive to fire up a compressor and put extra operating hours on it (as well as take heat from the ground) to "pre heat" water for a buffer tank that may or may not be used before it re cools. In a home with 2 people I like it less (as stand by loss is more likely). The big push for DSH in the first place was that you are taking "waste heat" and putting it to use. Cycling system intentionally to create "waste heat"?
I've stated my position on system sizing many times pointing out examples where the larger compressors of larger heat pumps draw enough amps that they can nix the savings of avoiding auxiliary coil usage. In this case we are suggesting running a large compressor to harness maybe 10% of it's capacity.......? So in this scenario the real "waste heat" is now that which is left in the fan coil or loop field.
Suffice it to say I'm skeptical but interested in measured results.

I wish Earthlinked would focus on PI's such as; getting their product recognized by the IMC or answering the refrigerant detector question.
That would be good for contractors and sales.

Just my humble opinion.
Joe

Here is a stock system that provides both all hot water and building heat.

http://www.ourcoolhouse.com/monitor/monitor.htm

I have no problem with the idea of a separate, full sized condenser dedicated to potable water and able to accept the full output of a heat pump compressor.

Given that ~50Kbtu heat exchangers are inexpensive, it's not clear why this isn't common. Using resistance heat (inefficient) and/or buying another efficient device (expensive) to heat water doesn't make sense, at least during most periods when the existing geo system has excess capacity.

There are many systems that can heat/cool and provide all the hot water you want...... whether or not it makes economic sense is another thing entirely.
Heat exchangers are relatively inexpensive, true, but that combined with larger compressor and loop field (to accomodate greater requirements) and more frequent failures (more operating hours on a system with more controls = more repairs) becomes expensive.
I know I look at things from the contractor perspective of "keep it simple, stupid" (kiss), but I'm not afraid of technology. I simply tell folks there is no free lunch, so pick what you want to eat.....In this case: higher water heating cost or higher maintenance and initial installation cost for your heat pump.
J

Posted By tuffluckdriller on 29 Nov 2010 02:31 PM

An EarthLinked system only allows the desuperheater to operate in the COOLING MODE ONLY. An internal controls change can be made to override that, and allow the desuperheater to operate in any compressor ON cycle. However, if one were to do that, they would need to also install an outdoor sensor control. The outdoor sensor control would allow the desuperheater to operate at outdoor temps well above balance point.

Balance point is the outdoor temperature at which supplemental heat is allowed to operate with the heat pump unit to cover the total load of the home. If the desuperheater is going to operate in the heating mode, it will use/take/steal 5%-15% of the compressor's output from heating the home. The desuperheater would then need to be taken out of service if the outdoor temp drops closer to balance point. Or, the balance point will need to be raised to allow the heat pump to have enough off time for the ground to recover...

Really? I wasn't aware of that. While I was aware that the desuperheater steals some of the heat from the system when it's in heating mode, just thought it was on all the time, since even when it's pre-heating hot water using the desuperheater it's still at least three times more efficient then using electric. When you say internal control change, do you just mean a dip switch change? I wouldn't think I would need an "outdoor sensor control" since my system is an open loop system the the heat sink I'm drawing from is thousand times bigger than any close loop system.

TG, good to see you.
The DX system Clark is speaking of requires more or less a defrost cycle. This would not be true of any open loop system or water to air closed loop.
j