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HP vs std cooling

Posted by cavell (My Page) on
Wed, Jun 6, 12 at 10:22

How will an air source heat pump compare to a standard central air system for power consumption. Have 100k NG forced air heat with 3Ton central air. 2500 sq/ft house. Vendor says I need to combine HP with gas furnace for supplemental heat since its cold here. So he does not recommend a air HP. But I am wondering how the cooling side would compare.


Follow-Up Postings:

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RE: HP vs std cooling

Cavell

Not real clear on what you are asking.

But if you mean the electric operating cost of an AC condenser versus the HP version of same condenser, then yes they should be basically identical on same run time basis.

Of course, it would not be the same for strip heat or for defrost calls.

IMO


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RE: HP vs std cooling

The cooling side will be identical, unit to unit. That is, a 15 SEER 3ton HP will use the same power in AC as a 15 SEER 3ton AC unit. (Close enough, anyway.)

If you're looking to save money then the comparison is on the heating side. And this will depend on how much your NG and electricity costs, the efficiency of your furnace and your climate (location).

For example, there are some locations where doing a 80% eff furnace with a HP is good and others where doing a 95% furnace with AC is better.


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RE: HP vs std cooling

I don't mean to highjack this thread but I am also debating between HP with suplemental furnace heat vs AC with furnace and would love to hear how one can decide between the two. We do have natural gas service. Most all the companies I spoke with are suggesting AC with 80 AFUE furnace which is what we have already. This is for a 2nd story unit that will heat/cool aprox 2000 sq feet and will be located in an unconditioned attic space.

cavell not sure how utility rates are in your area but electricity rates here have been going up from 8.7 cents per kwh 2 years ago to 10.1 cents per kwh this month. Natural gas is going down from 99.5 cents per therm 2 years ago (3.4 cents per kwh) to 89 cents this spring (3.04 cents per kwh) to 81.7 cents this month (2.79 cents per kwh)

We are in NC and average temperatures are: Average high in the peak of the summer 87 degrees (record high 105), average low in Jan 27 degrees and average high 48. Record low 2 degrees.

Anyone have any thoughts? Thanks.


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RE: HP vs std cooling

I went thru the same thought process two years ago. Replace an A/C unit and oil furnace with a HP or A/C plus oil furnace???

It turned out the difference in price between the A/C and the HP was just a couple of hundred dollars. While the furnace and the HP in heating mode have numerous common equipments, the piece of mind of having the OPTION of heating with electricity versus heating with oil was worth the money.

Also, by going with the HP it gives me the FLEXIBILITY of heating with electricity much of the time and it turns out that it is frequently cheaper (in my case) to heat with electricity.

While some do not like the cooler heating air from a heat pump compared to a furnace, my wife and I actually prefer it.

YMMV


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RE: HP vs std cooling

mw

Unless operating costs are a driving factor, I would stay with the 80% eff two stg var speed furnace paired with straight AC condenser.

Electric rate prices are regulated usually by a state commission while NG prices are more marketplace driven. When is the last time you saw your KWH/cost from your electric company reduced? Ain't going to happen
unless electric is totally deregulated.

If you like I can run some numbers for you to compare.

I have a DF system purchased about 7 yrs ago. My savings using HP down to balance point was about 35+%. That difference has nearly evaporated because of the rise in electric rates and the decrease of NG
rates.

Keep in mind, you normally size HVAC with average temps not shortlasting extremes both cooling and heating.

How well is your home insulated and how good are your doors/windows plus have you ever had HP heat?

IMO


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RE: HP vs std cooling

One other thing to consider is the wear and tear of the heat pump operating in the summer and winter. The life expectancy of a heat pump will be shorter than an AC condenser.


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RE: HP vs std cooling

Tigerdunes thanks for chiming in again. No I have never had HP heat before (I am from Europe -we had oil fueled hot water radiator and then in floor heat growing up and in the US our last home was in northern NJ) . It's interesting that you are recommending the Ac condencer with 80% AFUE furnace. I see from your posts that you typically are a big advocate of heat pumps and 90+ AFUE furnaces. If you don't mind running some numbers I would definitely be interested in seeing what you come up with.

To answer your question our windows are not bad we had an energy audit done and while they are not low e, argon etc. they are double paned and we decided not to replace them (we have 40 of them !!!). We are planning to soon replace the 3 doors to the backyard as they are letting air in, plus the frames are rotting. So windows and doors are ok but not the latest and greatest in terms of energy efficiency.

The rest of the house is insulated per 1992 standards. We are planning to reside the back of the house (rest is brick) and adding housewrap. Our crawl space was sealed/ conditioned a few years ago and we have a much better time heating/cooling the 1st level of the house. We might add spray foam in the attic when we finish that space in the next couple of years.

Saltidawg thanks so much for sharing your experience. I would be interested in how your energy rates compare with ours. I think I might like the slightly cooler heat coming from a heat pump (I always find that our furnace blows too hot). I like the idea of a HP and how it uses the ambient heat from the air but it sounds like it might not make sense given our energy costs. Mike also makes a good point about the wear and tear from working a lot more throughout the year. I wonder if that is taken into account though when designing a HP . I am sure in some mild climates that all they use so it would have to handle year round use. I do intend on getting the extended labor warranty (10 year) in addition to the 10+ year parts warranty for whichever brand/type of equipment we go with.


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RE: HP vs std cooling

NC here with almost your exact same rates.

I went with DF with a seer 16 and 90% NG furnace. I have my balance point at 40 now since NG is so cheap. What you have to try and guess is the cost of NG for the life of the equipment. Good luck with that.

It is entirely possible that a good exporting NG system will get in place and drive domestic prices up. Excluding taxes, Europe pays 4 times what we do and Asia 9 times what we do. When you can get the NG out of the country, it will get done and sold to the much higher bidders. We could see NG prices double when this happens. There could also be a fracking disaster and the NG price could double over night. Do you feel like gambling?

Now - I personally wouldn't buy an NG ETF because the likelihood is that we will have relatively cheap NG prices for a decade. But you never know.

The price comparisons are changed significantly by the equipment you are installing. If you do Seer 13 and compare to 95% NG, NG will win for a long time. If you are going to Seer 15/16 and can only install an 80% NG, that favors DF far more.


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RE: HP vs std cooling

mwrede,

You asked, "I would be interested in how your energy rates compare with ours."

I live in the MD suburbs of DC. You said your electric rate was going to about 10.2 cents per Kwh. I'm paying north of 15 cents. I still am glad I got the HP!!! I also have oil, not gas, so no help there.

I had planned to post a detailed analysis of my energy costs before and after getting my new Carrier equipment and also a GE Electric hot water Heat Pump. The problem is that we had a VERY mild winter.

I heated almost exclusively with the heat pump and even with that my electric usage was down significantly from my usage of two years ago.

I have not had an oil delivery since March of 2011 and still have nearly 3/4 tank left.

(No matter how expensive oil is, if you don't use much you don't spend much. lol

I still would suggest that if the difference in cost of an A/C unit vs a HP unit is a couple hundred bucks, I'd go for it - if for no other reason than to provide flexibility. If you find you don't use it very much, if at all, for heating, then there will not be any extra wear and tear. If you do end up using it, well that two hundred bucks will look like a wise investment.


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RE: HP vs std cooling

Thank you saltidawg and David. You make some great points. So am I right in assuming that if electricity prices went up someone could set the economic balance point higher and have the gas furnace kick in at higher outside temperatures?

I was planning on at least 15/16 Seer equipment and pretty much all the local dealers are saying we should stick with 80% AFUE furnace due to the fact that there is water produced by the 90% and higher units and that could lead to freezing (equipment would be in unconditioned attic), also there is the cost of venting the unit. We don't HAVE to replace our furnace although I know that what's recommended. It's 80% 100k btu and is working fine but it's 20 years old and does not have 2 stage heat.

saltidawg, David and others I would love to hear which equipment you picked and why? Could you post over at my "Advice needed on new HVAC system in NC" thread? I really don't want to completely highjack this thread.
Thanks again.


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RE: HP vs std cooling

Elec usage for HP and std sys seem to be similar for cooling. Question answered.


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RE: HP vs std cooling

mwrede,

In order to select my equipment, I came to this forum and asked questions - I also spent a lot of time reading back threads and finally focused on finding three or more dealers that I felt were reputable and lacking formal complaints.

I solicited proposals and it turns out that all of these dealers were either Carrier or Trane dealers. Two years ago there was a nice Federal Tax Credit available for systems that were "matched" or appropriately sized and designed to produce the most efficient cooling (and heating?) At the Time, Trane did not have units that qualified so that put Trane at about a $1500 handicap.

After two winters of use and much support from members of this forum, I did the math - considering oil cost, electic cost, Coefficient of Performance (COP) of the HP as a heat source at different outdoors temperatures.

IN MY SITUATION, I use oil to heat my house when the outside temperature is below 30 degrees. When that temperature is at or above 30 degrees, I use the HP.

The house is comfortable, I feel I am minimizing my heating costs overall, and with the newer equipment the features available and greater efficiencies than older gear, I have seen a reduction in A/C electric usage and a huge increase in comfort.

with the advice you receive here, I wish you the same degree of satisfaction that I enjoy.


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RE: HP vs std cooling

I like the flexibility the HP provides. Atleast you have an option to heat with another source if you need it. Its true right now gas is very cheap. It might not always be that way. Even with cheap gas my heatpump is still very comparable or cheaper than using the furnace when above 35 degrees. Ofcourse the efficiency of your HP and the price of your electricity and gas will determine this. I like the heat pump heat over gas heat for the mild weather. Its not very hot and it evenly heats rooms. The actual price of the HP in many situations isn't to much more than a regular A/C. Some contractors want to make extra money and charge considerably more for the HP though.


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RE: HP vs std cooling

Thanks. I guess I need to do more research and get more estimates for Heat pumps and then compare the cost. It's a shame there are no more federal rebates. We just have a $200 and a $100 rebate from the local utility companies.


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RE: HP vs std cooling

The manufacturers may have rebates.


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