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

 

[Welchita]

If I'allowed, just let me add a few more points for discussion:

1.So I ask to the Forum about the so-called solar heat-pumps I mean those which has the condensing module in form of black metalic surfaces in the role of solar pannels. My main doubts is that this device is trying to pretend to be a solar system, but it is mainly a heat pump.

2.That condensing module is depending greatly on the outside air hygrometic conditions, and that's all! You could have placed that module inside of the garage.

3. So when we calculate a solar system, we should simulate its performance all around-year as well. I wonder (because I ask before and I didn't receive any consistent reply so far from any manufacturer) which is the COP (or the SEER) profiles all-around year, I mean how much electric energy I have to spend every month during one year?

 

[daiosama]

I found an interesting study done by Florida Solar Energy Center.

http://www.fsec.ucf.edu/BLDG/pubs/hspf/

Although it doesn't specifically answer my question, it does shed some light on HSPF. Apparently HSPF is based on climate zone IV. As you go to colder climes, the actual HSPF drops. Conversely going to warmer areas the actual HSPF increases.

It still doesn't really tell me if investing the additional $600 is going to pay off in X number of years.

 

[MintJulep]

Off-hand, I doubt that a heat pump makes sense in Detroit.

In thread403-158370 I posted a link to a calculator.

 

[willard3]

A heat pump is a carnot cycle.

As the delta-t between inside and outside temps increases, the cycle efficiency decreases dramatically, at 38F with the unit proposed.

I'll bet there's a lot of days in Detroit below 38F in winter.......

 

[daiosama]

Yes, there are a lot of days where the temperature is less than 38 deg. And it probably doesn't make sense to buy one, but that is the real question. How does one go about doing the cost analysis?

Detroit has about 3 months where A/C is really nice to have. About 3 months where A/C and heat aren't required. About 3 months where a heat pump could certainly be used and about 3 months where gas would be the primary heat source.

Of course during the 3 months where a heat pump would be quite viable, the heating cost is not that high. It is during the 3 months where the average temp is less than 30 that the heating bill is the biggest.

So the question is whether or not operating a heat pump for three months out of the year instead of natural gas going to pay for the additional cost of installing the heat pump.

 

[Yorkman]

Another problem/consideratioin with that set up is the wet bulb temperatures, which will help you intially because of their latent heat content you gain in heating mode, will come back to bite you at lower OSA temps, as frost/ice starts to form on the outside coil. The heating cycle will need to stop and go into defrost to clear the coil. Depending on the method you will be heating the outside coil while trying to suppliment heat to the space at the same time, that gets pricey. A geo-thermal or air to water heat pump makes more sense in your climate zone.

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI

 

[Skogsgurra]

An empirical observation:

We used to pay around USD 8000/year for heating (big house, middle Sweden). After installing three air/air inverter technology heat pumps, we reduced total heating cost to USD 3500. We have had a quite cold winter with between -15 and -20 C for a couple of monts. The heat pumps worked well down to -15 C, but we had to burn oil when it was colder. In spite of that, we reduced heating cost with more than 50 percent. We are very happy with the heat pumps.

Gunnar Englund

http://www.gke.org

 

[MintJulep]

And what are fuel costs in Sweden compared to those noted by the OP?

 

[willard3]

And what did you replace with the heat pumps in Sweeden? An old 50% boiler or furnace?

Where I live (6000-6500 heating degree days/yr), the delta-t is frequently greater than 70 deg F in winter and I consider that air-to-air heat pumps are not economical with a delta t much above 30F.

Remember that the maximum efficiency of a Carnot cycle is in the 30% range with low delta t.

 

[daiosama]

I did look into using a geothermal system, but I don't have much land around my house (.2 acre). A geothermal system needs nearly an acre for horizontal loops. Vertical loops are a possibility, but the price of vertical loop installation would have been and extra $3000-4000. The pay off would have been 20-25 years with my size of house.

 

[Skogsgurra]

"And what are fuel costs in Sweden": We pay 1500 USD for 1 m3.

"And what did you replace with the heat pumps in Sweeden?": A furnace with a measured efficiency (Eta) = 93.8 percent.

The total cost for the tree heat-pumps was around 4000 USD, including installation. The pay-back time is less than a year.

Gunnar Englund

http://www.gke.org

 

[Welchita]

Hi Gunnar Englund!

Can you show us, how do you arrive at a "pay-back time is less than a year". Specifically, how is the SEER profile all the year-around ?
welch

 

[Skogsgurra]

That is very simple. I compared oil consumption cost and electricity cost from the year before we installed the heat pumps with same costs after having installed the heat pumps. We had less than half the total cost with the heat pumps. The sums can be read in earlier postings. Do not know what SEER profile is.

Gunnar Englund

http://www.gke.org

 

[MintJulep]

Gunnar,

Sorry, I'm having a hard time figuring out US$1500 for 1 m3.

Cubic meter of what? 1500? One-thousand, five-hundered?

The original poster's cost for gas is about US$0.40/cubic meter.

I know you guys have higher energy prices, but 5 orders of magnitude?

 

[walkes]

MintJulep,

It appears to be fuel oil from his post. North American oil burning appliances can't get to the condensing range that European units can, due to the high sulfur content in our oil supplies.

 

[Skogsgurra]

Yes. 1000 litres of oil for the furnace costs around 1500 USD in Sweden.

Gunnar Englund

http://www.gke.org

 

[Welchita]

To Gunnar Englund:
I wonder how the (COP) SEER varies all along the year and all along the day tipically?

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 ?

A basic question: can somebody define SEER?
Thanks.
Welch

 

[daiosama]

SEER = Seasonal Energy Efficiency Ratio

see wikipedia for the basics

http://en.wikipedia.org/wiki/Seasonal_energy_efficiency_ratio

see this artical for a little better understanding of really what SEER is

http://www.fsec.ucf.edu/BLDG/pubs/hspf/

SEER is not COP. It is very losely realated, but that is all.

 

[DickRussell]

For a heat pump type of system to handle the winter as well, check out the "Cold Climate Heat Pump" (CCHP), by Nyle Specialty, Bangor ME. Someone else does the marketing currently. I have been following this for a few years, am thinking of using it for a new house in a couple of years. They have operating data on one place where it still worked will down to -30 F one morning. It is a two-stage system, where one stage pumps up from air down to the 30s, below which the second stage kicks in. It has auto defrost, of course. I'd be interested in hearing of any actual experiences with this.