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  1. #1
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    With all the natural gas price increases has anyone worked out a breakeven analysis on heat pumps versus gas furnaces? I live in California where, in the past, electricity prices have kept almost all heating natural gas furnaces. I don't even know of a local contractor who would recommend a heat pump.

    Irascible, you must have looked into this.

    Thanks

  2. #2
    Join Date
    Sep 2004
    Posts
    3,157
    California is a big state and depending on where you live Gas vs Electric prices will be difficult to compair.

    we are all stuck with PG&E as far as I know for gas, and if you have been here for any length of time you should remember the scam they pulled a few years ago to raise our rates when the electric rates went as high as they did.

    Keep in mind that all of the Power plants that PG&E sold then operate on natural gas, so the gas rates are going to be just as high as their electricity.


    Also if you recall ,even after the electricity scam was exposed and pg&e filed for bankruptcy, our rates have continued to rise . They are blaming the increased price of gas this year on the hurricane , yet In california, we produce our own gas at our own refineries.....and the hurricanes didnt hit here

  3. #3
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    Take the best air source heat pump you can buy; design and install the system perfectly; and you might get a COP of about 3. In other words you'll get 3 BTUs of heat for every BTU of electricity that goes into the heat pump. My last utility bill shows me paying $1.25 a therm. A therm is 100,000 BTUs. Having an 80% efficient furnace would mean that I'd have to buy 1.25 therms to get 100,000 BTUs of heat. So that's $1.56 worth of gas per 100,000 BTUs. That same bill shows me paying 11.4 cents per kWh. A kWh is equivalent to 3413 BTUs. A COP of 3 means I'd get 10,239 BTUs per kWh. Therefore 9.8 kilo-watt hours of electricity would get me 100,000 BTUs. That's $1.12 per 100,000 BTUs. Hmmm.

    That was the heat pump shill's version. The reality is that the delivered COP of an average heat pump is more likely to be 2.5 or less. Personally I think it's often much less. But I'll use 2.5 since one study I looked at showed as much. The other problem with the above is that I used baseline charges. Averaged across all tier levels I was charged 16.8 cents per kWh on my last bill. My current baseline charge for gas is $1.25 per therm. By looking at how much I went over my baseline on last year's gas and how much extra they charged me, I estimate that my average cost per therm would be $1.39 if this were a cold month.

    Using those more realistic numbers gas costs me $1.74 per 100,000 BTU's and a heat pump would cost me $1.97. Get a 90+ furnace and that drops to $1.54 for gas vs. $1.97 for a heat pump. Currently gas is cheaper for me. What you're paying on your bill and how much you go over baseline may be different. But I doubt that it’s so different as to make up the gap and cause a heat pump to become cheaper. In parts of the country where they pay 5 cents a kWh and over a dollar per therm for natural gas it's a no-brainer. Get a heat pump. But out here gas still rules for the most part.

    That's not likely to change anytime soon for us. Most of our power plants are natural gas fired. If natural gas prices do spike by 70% as some are predicting, then for us at least our electric rates will spike as well. Given that reality and given the fact that most customers prefer gas over the more tepid heat pump, there's not much debate over which is better for my area.

  4. #4
    Join Date
    Sep 2004
    Posts
    3,157
    Irascible
    If you are EVER looking for an assistant-I will drive from my town to yours and be there on time every day that I can

    you should teach an hvac program

  5. #5
    Join Date
    Oct 2005
    Posts
    9
    Nice breakdown on relative costs above. This is my first post here; I'm a homeowner, in case that doesn't become obvious below.

    Got to thinking about this issue a few months ago when we wanted to add A/C to our house, and started looking at a heat pump and new furnace technology (we currently have an 80% gas furnace, 1992 model). We were hoping we could come out with no net increase in our energy usage.

    In our area (Portland, Oregon), electricity comes from a mixture of hydro and gas-fired turbines. It seems that the operating cost advantage goes to heat pumps quite handily, but since we want to be as green as possible (hate killing what few wild salmon are left), the necessary high-COP/SEER equipment is beyond our reach for the moment.

    As an aside, for the short term we bought a portable 13kBTU A/C unit that kept the upper floor of our house comfortable on the hottest days (the basement isn't a problem). Next will be to upgrade our attic insulation from R-19 to R-30 or R-38, maybe some duct-sealing in the garage, and other inexpensive tightening-up fixes. Shoulda done that long ago, I know....

    Anyway, back to the gas-vs-heat pump question. I got to thinking that a dual-fuel system would be ideal, in that you could switch to all-gas (for heat) at some time in the future, if electricity gets too high; Otherwise you only use gas as backup when it's too cold outside for the air-source heat pump.

    But then, what about optimizing for up-front costs of the systems as well as the fuel costs? E.g., to get the most efficient heat pump you want the variable speed air-handler, and with a typical dual-fuel system you'd end up with a $3-5k two-stage gas furnace to provide that feature, the gas-burner of which would only kick in for backup maybe 10-20 days out of the year in our climate. Seems a waste to me to have all that cash collecting dust, needing maintance, etc., let alone paying interest on the loan to purchase it.

    In our climate, I've been thinking that a great system would be to get a good air-source heat pump with a variable-speed fan-coil unit. Then instead of electric resistance coils for backup, have a water-to-air exchanger connected to an oversized gas water heater.

    The heat/cool load calc for our house came out such that we were recommended a 3-ton heat pump with 40,000 BTU/hr gas furnace for backup. Our existing gas water heater is 40,000 BTU/hr, also 1992 model, and there are certainly water heaters with 80k, 100k, and up. It would seem to be pretty cost-effective to invest in just one 80-90% gas burner in the form of a water heater, especially if it could do double-duty in a system like this.

    Of course, I suppose if we take this idea to its extreme, we might want to get hot water from a heat-pump too, in case gas prices get ultra-high in comparison to electric, but now we're getting into geothermal heat-pumps with de-superheaters, and way more up-front cost than we're likely to afford in the next decade or so. Plus our hot water usage isn't so high....

    I've so far not found any system like this (air-source heat pump with hot-water backup) available. Am I nuts for thinking this would be a good idea? What are the down sides? And if it is a good idea, where do I find one?

    Of course, I suppose if we take this idea to its extreme, we might want to get hot water from a heat-pump too, in case gas prices get ultra-high in comparison to electric, but now we're getting into systems like geothermal heat-pumps with de-superheaters, heat-pump water heaters, and way more up-front cost than we're likely to afford in the next decade or so.

    Great forum, by the way. Thanks.

  6. #6
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    I think the reason why you don't see a heat pump water heater chironian is the complexity and cost. An electric or gas water heater is an incredibly simple and relatively cheap device. Our house spends $20 per month on heating water for 4 people. Even if we had 5 cent/kWh electricity the cost and complexity of a heat pump system just isn't worth saving $5 or $10 a month.

  7. #7
    Join Date
    Oct 2005
    Posts
    9
    Originally posted by Irascible
    I think the reason why you don't see a heat pump water heater chironian is the complexity and cost. An electric or gas water heater is an incredibly simple and relatively cheap device. Our house spends $20 per month on heating water for 4 people. Even if we had 5 cent/kWh electricity the cost and complexity of a heat pump system just isn't worth saving $5 or $10 a month.
    Agreed, I wasn't really looking for a heat-pump water-heater; They're more geared for warm/humid climates, and for folks with high hot-water uses. Here's an article:

    http://www.ornl.gov/sci/btc/apps/hotwater.html

    But yeah, I've already got gas in the house, and a tiny 45-gal 40kBTU/hr water heater has proved adequate for our family of four. It'd never pay to get too fancy there.

    What I was wondering about, i.e. where can I find one, and am I nuts for thinking it's a good idea, was an air-source heat pump with variable-speed air handler, but with gas-fired hot-water heater as backup instead of the usual electric resistance strips for backup. Those 90+% gas burners are so expensive, it doesn't seem to make sense (in our Portland, OR climate) to buy one for heat-pump backup, or even for just our small hot-water load. But you might be able to justify one such burner if it could do both, and especially if electric prices go so high that you would shift over to gas for primary heating.

    Make sense? Maybe there's a new-product opportunity here.


  8. #8
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    You're talking about a duel fuel setup. It's very common in some parts of the country. There are quite a few guys well versed in such things on this board. Do a search for duel fuel or post a thread and you'll get more information than you know what to do with.

  9. #9
    Join Date
    May 2005
    Location
    Seabeck, WA
    Posts
    1,870

    Wink

    Go dual fuel and you're covered!
    Live for yourself and ask no one to live for you.

  10. #10
    Join Date
    Apr 2004
    Posts
    7,680
    Irascible,

    What formula or experience or calculation do you have that COP is only 2.5? That my be acurate at 17 degrees but not at 47. Also, while we are talking electric the HSPF for a system also includes the indoor blower which your gas furnace cost does not. Would it not be fair to include the electric costs of running a gas furnace blower if you were to compare apples to apples?

    I'll be the first to admit, I am not well versed in how to calculate costs. Maybe someone who does it for a living can.

    Nathan can you provide your electic costs, gas costs and your heating requirements? Also what are your cooling requirements? so we can size the imaginary heat pump.

    I ask because I have dual fuel. If I were to run the gas furnace all the time, my bills would be huge compaired to the way they operate. I cannot comment on electric heat because I dont use it. But I think my gas came on all of 10 times last year on its own (I turned it on when we had my grandmother here other times).

    Looking at a 12 SEER 4 ton heat pump with vs indoor blower included. I see 3.598 kw to produce 41,500 btuhs at 47 degrees. to even things out, thats 35.98kw to produce 415,000 btuhs. For gas thats 4.15 therms.

    4.15 * 1.25 = $5.18 for 415,000 btuhs ($1.25 = therm)
    35.98 * .13 = $4.68 for 415,000 btuhs ($0.13 per kw)

    Dont forget you still have to pay for the indoor fan on the gas furnace to run.

    At 17...

    The heat pump system requires 3,481 watts to produce 27,800
    or 3.481kw. Times 10 again thats 34.81kw to get 278,000. For the gas thats 2.78 therms.

    2.78 * 1.25 = $3.47 (gas) + indoor blower costs
    34.51 * .13 = $4.49 (HP).

    I guess now we need his weather data and load information. We also need his utility costs.

    Now I dont honestly know, is the cost per therm for the gas only or does that include the transmission costs and other things that make up a gas bill? Anyone know? Same goes for Electric, I dont know.






    [Edited by docholiday on 10-09-2005 at 10:32 AM]

  11. #11
    Join Date
    Apr 2004
    Posts
    7,680
    BTW, the actual matched SEER on that system was 13.4 the HSPF was 8.0 region IV.

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,233
    Originally posted by docholiday
    At 17...

    The heat pump system requires 3,481 watts to produce 27,800
    or 3.481kw. Times 10 again thats 34.81kw to get 278,000. For the gas thats 2.78 therms.

    2.78 * 1.25 = $3.47 (gas) + indoor blower costs
    34.51 * .13 = $4.49 (HP).

    I guess now we need his weather data and load information. We also need his utility costs.
    [Edited by docholiday on 10-09-2005 at 10:32 AM]
    One needs to perform H.A.P. cost-benefit analysis and comparisons based on Annual Energy use to determine which equipment is beneficial in what area.

    http://www.commercial.carrier.com/co...hvac/general/0,,CLI1_DIV12_ETI496_MID4355,00.html
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  13. #13
    Join Date
    Sep 2004
    Posts
    3,157

    Hydronic question

    I have seen coils at work (aprilair) i think, that are made to circulate hot water through. Since most of us are heating a tank of hot water, wouldnt this be a good source of additionl heat or instead of heat strips?

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