Power Consumption of heat pump and general question on DHW

[micahgallant]

Hi all, I'm new to the forums and hopefully in the coming months will be a new owner of a geothermal system!

Couple questions that I didn't see answered in forum otherwise, at least not answered specific enough for what i'm looking for, so your help is appreciated!

1) What is the average power consumption of a heat pump? I hear your electricity bill doubles, wondering if its easy to run it off solar / wind or at least supplement it so that electricity doesn't double - in effect receive a completely free source or heating.

2) I've been reading a lot about DHW, this 'desuper' thing etc. sounds like geothermal uses waste heat from the pump to make hot water. question is, why use waste heat? If you're not using the ground heat itself for home heating, why not use THAT heat instead for hot water rather then JUST using excess heat created by the pump when its heating the house? This is confusing to me, seems that if the house is warm enough, then you can use the pump to transfer the ground source heat to water PLUS the excess heat created by the pump. If my thoughts are correct, then you can have the system creating hot water in the summer WITHOUT first having to heat or cool the house - ie, its sole job would be to create hot water. I don't understand why I don't read anything about this?

Micah, Canada

[gabby]

1. What size unit? The larger the tonnage the higher the run current for that compressor.

2. <<sounds like geothermal uses waste heat from the pump >> Correct...waste heat is a byproduct of the change of state from liquid to gas in all compressors, not just geo. Geo uses another coax to capture this heat so you can use it to assist or take over DHW production. The cooling cycle has the compressor running more than most heating cycles so the summer is the best output of DHW. This takes approximately 6-10 hours of running to generate the capacity for average use of DHW. A buffer tank in series with your HWT is the recommended way to use this option.

The ground heat in a GEO is used for the water to air exchange to warm or cool the home. A boiler, or water to water unit heats by radiant heating coils in the floor. The geo heats the home, the desuperheater reduces hot water costs.

[micahgallant]

1) say a 3ton system, I think thats what a local company suggested as being adequate. What is the kWh's for those ballpark?

2) Seems odd, I should be able to use the water to heat the DHW, in conjunction with the excess waste heat. Ohwell, I assume those who design this know why you can't do it I'll leave it up to them.

[gabby]

ClimateMaster Tranquility 27 3 ton has a total unit FLA of 25.4 amps with a LRA of 82 amps. The LRA would be similar to starting current prior to the run winding taking over. Typical breaker is 30-40 amp size.

You can find out about FLA, WF, or Geox units from their spec sheets.

I don't understand the oddity you refer to in your statement. You can preheat the DHW with a desuperheater rather than let the heat escape as a byproduct that does nothing for you.

You can also do a radiant heat system with a boiler, and a loop for DHW. You can do a combined system for radiant and water to air for AC.
The electric is reduced with a geo system, not increased unless you run resistance heating as a primary heat source.
I think you have been fed misinformation and to clarify what you need versus this guessing game you should state what you think you need (no manual J results), and what you wish to accomplish. If this theoretical system is a 3 Ton then start there with your desires and what you are trying to accomplish. That should include an emergency generator to keep the geo running, or what fuels are available for optional back-up heat. Most all electric homes have no generator, those that do usually use it for preserving food. Not only is a whole house generator expensive but the running cost is extremely high. There are alternatives, but you must produce a starting point and goal.

[micahgallant]

Ok thanks for all the info there. Ya, I'll need to get deeper in and I'm sure I'll learn a lot once I start getting quotes and such.

Thanks again!

[AMI Contracting]

Yes elecctric bill goes up, but gas, propane or oil heating bills are bigger and go away completely.
DHW = domestic hot water
DSH = de-superheater or hot water generator (HWG)
Have the bidders explain to you why there is waste heat.
Check bidders' references and put those above brand.
Do not shop by efficiency, most 2 stage systems run at about 3 C.O.P. winter average once removed from ideal test conditions (loop size will affect this number more than brand).
Make sure they perform a manual J load calculation and explain that to you along with % of load satisfied by heat pump and balance point. All should be able to give you average op cost.
Good luck,
Joe

[moondawg]

Hi all, I'm new to the forums and hopefully in the coming months will be a new owner of a geothermal system!

Couple questions that I didn't see answered in forum otherwise, at least not answered specific enough for what i'm looking for, so your help is appreciated!

1) What is the average power consumption of a heat pump? I hear your electricity bill doubles, wondering if its easy to run it off solar / wind or at least supplement it so that electricity doesn't double - in effect receive a completely free source or heating.

Nothing is "completely free." The additional cost of solar required to power a GSHP would be significant.(current installations run $5/Watt, minimum) It would be nearly impossible to do with residential wind power.

Looking at grid power: If you're currently using an air-source heat pump, your energy bill would most likely go down. If you're using gas/propane/oil, then of course, THAT bill will go down, and your electricity bill will go UP. Depending on how much electricity you already use, it may or may not double.

2) I've been reading a lot about DHW, this 'desuper' thing etc. sounds like geothermal uses waste heat from the pump to make hot water. question is, why use waste heat? If you're not using the ground heat itself for home heating, why not use THAT heat instead for hot water rather then JUST using excess heat created by the pump when its heating the house? This is confusing to me, seems that if the house is warm enough, then you can use the pump to transfer the ground source heat to water PLUS the excess heat created by the pump. If my thoughts are correct, then you can have the system creating hot water in the summer WITHOUT first having to heat or cool the house - ie, its sole job would be to create hot water. I don't understand why I don't read anything about this?

Micah, Canada

In a forced-air geothermal unit, the groundwater is used to participate in the phase-change of the refrigerant. There is then a heat exchanger that transfers heat between the house air and the refrigerant system. "Waste Heat" that is generated by the motor/compressor is carried off via separate heat exchanger to add some heat to your Domestic Hot Water.

In the system you describe, you would have to have a THIRD heat exchanger, to exchange heat between the refrigerant system and the DHW system. This would add much cost and complexity of control to the system, which would have a long payback. The system would provide marginal benefit and mucho cost over the relatively cheap DSH system already available.

I take it your PE is in civil engineering? (sorry, just a good-natured ribbing from an EE. :^)

[Mark Custis]

was self-taught and did not have an engineering degree.

Look what he did.

I can not remember but I think Edison was a businessman first.

[flynmoose]

I'm not really a geothermal installer (but I play one on TV).



Another engineer wanders into the "dark arts" of Geo. . .

[micahgallant]

Ah, thanks for the other replies there, thats great info!

Sorry the PE stands for Prince Edward Island (where I live). So I'm no engineer, just a curious future customer