A Heat Pump a good choice? 1

[daiosama]

I'm in the Detroit area and considering a heat pump as suplimental heat.

The gov rates the heat pump I'm looking at at 8.5 HSPF with the AC side at 13 SEER. The point at which the system switches from heat pump to gas is 38 deg. outside temp.

The cost of electricity is about $.09/kw. The price of gas is $1.33/ccf. The furnace is a 94.5% effecient furnace dual stage 30/60k btu output. The heat pump would be a 3 ton unit.

The house is usually 72 deg. during the day and 65 deg at night.

The added cost would be $600 plus added maintanence that comes with the heat pump.

Is there a way to calculate the efficiency of the heat pump at 38 deg given the above parameters? Is there a spread sheet or some other program out there that I can plug in average daily temps for a region that would give a comparitive analysis?

Thanks,

Brian

 

[Skogsgurra]

A very late answer for Welchita (Mechanical),

Your question: 'When you state: "We had less than half the total cost with the heat pumps". That could be understood as a figure of SEER bigger than 2. Is it?. If you payed 4000 USD for your heat pumps, then I suppose the energy consumption reached well above 8000 USD or something between 5000 and 6000 liters in a year, before the heat pumps. Is this corrected ?'

Yes. That is correct. We used close to 6000 litres the year before we installed the heat pumps. And, yes. We saved more than 50 percent on energy costs after having installed them. And that energy cost includes all fuel and electric cost - not only what we need for heating. So I guess that we save a lot more than 50 percent on the heating alone. It is a large house - 360 m2 plus an attic with 180 m2 floor area. We do not use the attic. It is just a storage space and also an extra "insulation layer".



Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Bubbleheadski]

We had a promo from "Water Furnace" in our wharehouse. It was a cardboard copy of a selfcontained Water Furnace unit. It was maybe 6 inches long and 4 inches square, It had the blower assembly and compressing section printed on it.
Anyways.... on the out side it makes the claim....
"The worlds first 30 EER and 20 COP heat pump". I was asking my Boss... and he said 30 EER is like 20 - 22 SEER
I know water to air units are more efficient. And I have yet to hear of a typical air/air heat pump at 20 SEER. ( I have heard 19) but yes 185 ft down/ton for a well and a 3 or 4 ton system does get pricey. Not to mention new units start around 10,000 Dollars installed. ( approx 2 ton system)
Bubz

 

[Bubbleheadski]

OOPs..... saw that "box" again today and it was a 5 COP not 20 as I posted above. Sorry.

 

[lilliput1]

What are the dimensions of your house. Give me approximate rectangle dimensions, number of floors, height per floor & % glass. Would you say it is a tight construction, average or loose (infiltratiowize)? What I don't like about using heat pump is that it's compressor will run summer and winter. Also to get more heating capacity, it is oversized therby degrading its dehumidification performance during summer. Detroit is a cold area. I am not sure because I am not at work. I may be able to use the Trane System Analyser to make a comparison energy simulation.

 

[GHGguerilla]

This website contains some very well developed information on alternative energy system design. It also includes free, well-supported applications for feasibility studies that have been widely adopted as reliable.

http://www.retscreen.net

For newbies, this is a great place to start.

 

[AbbyNormal]

My gut feeling is north of the mason dixon line all heat pumps should be ground/water source

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[zekeman]

The gov rates the heat pump I'm looking at at 8.5 HSPF with the AC side at 13 SEER. The point at which the system switches from heat pump to gas is 38 deg. outside temp.

The cost of electricity is about $.09/kw. The price of gas is $1.33/ccf. The furnace is a 94.5% effecient furnace dual stage 30/60k btu output. The heat pump would be a 3 ton unit.

The house is usually 72 deg. during the day and 65 deg at night.
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From data I have seen, you can expect a COP between 2 and 3. Taking 2.5, the cost of heating with the heat pump alone would be $.09/(3.413*2.5)=$.01/1000BTU.
For your fuel @ 94.5% efficiency, I get
1.33/100=.0133. So the difference is
$.0033 per 1000BTU. Now you have to get an estimate of the amount of heating you need above 38 deg in the Detroit area
I got some data for Detroit and came up with 2455 degree days during which you could use your heatpump Oct,Nov, few days in Dec,Mar,April,May. Now I also have data that has the annual number of heating deg days of 6442. I would take my annual heating bill and divide by cost of fuel (and efficiency) last year to get the number of therms used(100000 BTUs). For example if your heating bill was $3000 and gas was $1.33/therm, then x=$3000/$1.33/.945=2386 therms. The amount of this that could be used for heat pump would be in proportion to the heat pump usage or
2455/6442*2386=909 therms. For each therm, according to my earlier forecast of $.008/1000 would be $0.80/therm and the potentialannual savings$.8*909=$720 for my case.

 

[zekeman]

Correction,
Cost of gas heating should have been $.01407 to include efficiency. So the savings/therm should have been .00407 and the overall annual savings for the case I chose
$.407*909=$369
still, not bad.