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The cold hard numbers of my Heat Pump + part II

Post in 'The Green Room' started by Amaralluis, Jan 27, 2011.

  1. Amaralluis

    Amaralluis Member

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    I got my december hydro bill and heres the cold hard numbers about my heat pump vs pellet stove since it was installed on November 1st.

    My electric bill runs from around the 17th of every month. For Nov/Dec period in 2009 I've used 572KWH for a period of 28 days (I know it was awesome) with the pellet stove. In 2010 the total was 1298Kw for a period of 29 days with the heat pump.
    For dec/jan then the usage was 786KWH for 2009 and 1739KWH for 2010.

    The difference between 2009 and 2010 besides the pellet stove we had a teen that moved in August, which increased the electric usage for quite a bit. It was not a constant difference so what I did is that I took the difference between 2009 and 2010 for august, september and October and calculated the average of the difference for those months. With it Im assuming that approx 390Kwh over 30days are because of the extra person in the Household. I know that its not super accurate but Its the only way I thought to get an idea of how much the person costs. If someone has a better idea please let me know.

    This means that for nov/dec period the heat pump used approx 336Kwh and for dec/jan 563Kwh.
    The hydro price is $0.11, 336*0.11=$36.96 and 563*0.11=$61.93.
    Pellets used for the same period of time in 2010 = 0

    Unfortunately I didnt record the bags usage in 2009 so I dont know exactly how many bags were used, but I can safely say that it would averaged one bag per day so 29+33=62 bags. Cost of Bags $6.20 (with the taxes).
    62*$6.20=$372.22

    There you have it, $372.22-$98.89=$273.33 difference.
    Are this numbers accurate?
    No.
    Do they tell me something?
    Yes, the heat pump is saving me money from pellets, It might not be saving me $273 up until now, but it is undoubtedly saving me money.

    PS - I know that the pellet stove also used electricity but I cant put a KWH value to it but from the readings in 2009 it was not considerable.

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  2. begreen

    begreen Mooderator Staff Member

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    It doesn't surprise me, was the temperature of the house identical? One thing for sure, you are paying too much for pellets. At $6.20/bag they are much too pricey.
  3. Amaralluis

    Amaralluis Member

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    I agree that the price of pellets is too high. I bought it at that price when they were on sale @ $5.49+tax (13%). Otherwise the price of pellets for the longest of time was $6.99+tax, but later last year it was $5.99-$5.49 + Tax of course.
    As for the temperatures the answer is no. With the pellet stove I had a programmable thermostate to have the temp @ 20 when we were home and 17 at night or when we were at work. With the heat pump I leave at 21c all the time.
  4. phatfarmerbob

    phatfarmerbob New Member

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    Tax on pellets ? are they not a fuel for home heating .... home heating fuel is tax exempt
  5. Amaralluis

    Amaralluis Member

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    I wish.... :)
  6. phatfarmerbob

    phatfarmerbob New Member

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    Really it seems to me there aught not to be tax on them
  7. PastTense

    PastTense Member

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    There is another difference between the two years: the weather. You might try to find the heating degree days for those years and compensate.
  8. midwestcoast

    midwestcoast Minister of Fire

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    Since he used metric temps I assume he's in Canada. Different tax rules.
  9. Amaralluis

    Amaralluis Member

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    Hello,

    Yes I am in the Maritimes Canada.
    I will have to look at the degree temps but I have a feeling that this year has been colder than last year.
  10. henkmeuzelaar

    henkmeuzelaar New Member

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    Thanks very much for reporting your pellet stove and heat pump numbers. I am trying to figure out whether the cost of installing a heat pump makes any sense for our new loghome in the Idaho Rocky Mountains in view of the low electric rates (less than $ .05/kWh) here and the purported loss of COP in really cold weather. So I tried to rewrite your cost comparison numbers into energy budget data.

    Your estimated 62 bags (40 lb each, I assume) of pellets should have generated roughly 20 million BTUs. Even at a low pellet stove efficiency of 75% (including the power cost of running the pellet stove auger) , this corresponds to no less than .75 x 20,000,000 / 3412 = 4396 kWh.

    When running the heat pump in 2010 your electric power usage over the two months increased by a little over 1600 kWh. So even if you do not subtract the teenager's extra power usage, this would already correspond to a heat pump COP in the 2.5 to 3.0 range (4396/1600) which is very good for these cold winter months.

    I know there are many other variables (weather differences, pellet stove operation, etc.) not fully accounted for, but the suggested heat pump performance got my full attention!!

    Please tell us more about the type (ductless?), brand and model of heat pump and how it was installed.

    Henk
  11. henkmeuzelaar

    henkmeuzelaar New Member

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    Sorry Amalluis, I just noticed the parallel thread where you described your heat pump as a Daikin 15,000 BTU unit.
    I have found some US dealers but am still looking for any attractive discounts/sales by one of the large national a/c suppliers.

    Henk
  12. Amaralluis

    Amaralluis Member

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    Hey PyMs.
    You are correct it is a Daikin FTXS15 model.
    At -18 outside the unit was still able to maintain the temp, this is really impressive technology.

    The idea of this thread was to give out real meaningful numbers that everybody can relate to.
    Everybody understands KWH and 40lbs bags.
    Everybody understands that my heat pump used 500kwh in one month against using 30 pellet bags instead of saying the it has COP of 3 or that the output of BTUS was X based on X degree Days.
  13. henkmeuzelaar

    henkmeuzelaar New Member

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    Well, yes it is of course always better to provide easy-to-understand information if that will do the job.

    In my particular case, however, it is not enough to know that electric heat sources can save money over wood pellet stoves. At our very low electric power rates even simple resistive heaters save quite a bit of money in fuel costs alone when compared to pellet stoves.

    Therefore, what people in my situation need to know is whether more complex and expensive electricity-driven systems such as heat pumps can save enough money -- compared to inexpensive resistive heating -- to pay for themselves in a limited number of years.

    Calculating the COP provides a relatively straightforward mechanism to make that decision. In short, if the COP would be much closer to 1.0 in winter, an expensive heat pump install would be a waste of money (unless one lives in a warm climate where it could pay for itself in summer, of course).

    Henk
  14. begreen

    begreen Mooderator Staff Member

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    That is correct if the electricity is cheap enough. The decision needs to be based on what you have, what you need, and how reliable current rates will be into the foreseeable future.
  15. woodsmaster

    woodsmaster Minister of Fire

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    Here in Ohio there is tax on kerosene. I think that it's wrong, but... Not sure about pellets.
  16. woodgeek

    woodgeek Minister of Fire

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    At <$0.05/kWh, I would think that COP=1, electric heat might be cheaper than pellets!
  17. Amaralluis

    Amaralluis Member

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    I wish it was that cheap too. :)
  18. henkmeuzelaar

    henkmeuzelaar New Member

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    Yep, at $0.05/kWh it should only cost a little over $200 to generate a similar amount of usable heat with electrical resistance heaters as generated from 60 bags of wood pellets. Even at 4 dollars per bag that would still be a losing game, let alone at the 6 dollars the OP was paying.

    At the same time, however, the calculated heat pump COP of 2.5 or better suggests that I might be able to save approx. $ 600 to 750 per heating season in my own home by a DIY install of a $3,000 or so ductless, minisplit heat pump system. If so, the system would pay for itself in 4-5 years.

    Just in case the OP's numbers might have been jinxed by weather differences, etc., I plan to keep an eye out for more heat pump cold climate performance data on this site before definitively committing to such an install.

    Henk
  19. woodgeek

    woodgeek Minister of Fire

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    PyMS-- It is amazing how much everyone's situation differs. At your low electric rate, the savings from a HP (relative to elec resistance) is so low, I can see how it might be hard to justify the cost of the unit. Now I am a big fan of ASHPs, and they make a lot of sense in mild climates like Maritime Canada (Amaralluis), the PNW (Begreen) or the MidAtlantic (Me), not to mention points south, BUT it seems that your climate is a bit more, well, extreme. Between the cheap elec and the climate it isn't clear what your ROI would look like.

    I would assume that it would shut down at some reasonable temp like 15-20°F, and estimate how many BTUs it would deliver seasonally when temps were above that. That is, if you know your demand you can figure at what outdoor temp the unit can carry you to without backup (say 25F), and what fraction of your seasonal heating demand are above that temp. Add to this the number of hours you spend below that point down to some set shutdown temp (say 15F) times the average BTU output running full cycle. I would then assume a worst case SCOP for those BTUs of ~2.0, and compute your savings and ROI on that basis.

    If you get like 10 feet of snow on a regular basis, I guess you know to mount it on the side of your house.
  20. henkmeuzelaar

    henkmeuzelaar New Member

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    Thanks for the valuable input, WoodGeek.

    One option that I have been thinking about is to try a ductless heat pump with outside (or garage-based) air intake and see what the COP turns out to be for 1 or 2 winters. If the results are disappointing we could then perhaps use our well water plus a suitable water/air heat exchanger (e.g. a big old car radiator?) to preheat the intake air a bit. I have noticed that water-to-air systems tend to have much better COPs.

    I know one can directly buy water-to-air HPs but am assuming that one cannot simply have an air-to-air heat pump modified to water-to-air operation at reasonable cost unless one is willing to do it oneself.

    Either way, this would require that we have a shallow re-injection well drilled and I am not sure how difficult it might be to get a permit for that since we do live in a pretty fussy county, alas.

    Henk
  21. begreen

    begreen Mooderator Staff Member

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    A ductless system recycles interior heat, it doesn't have an outside air intake. Just the compressor sits outside. The heat transfer is done with the freon coolant.
  22. henkmeuzelaar

    henkmeuzelaar New Member

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    Sorry for my confusing terminology. What I referred to as the "air intake" is the forced airflow past the compressor's freon-to-air heat exchanger. I understand that this is normally a wide open fan box, but know that it is usually fairly easy to attach some ducting to the intake (suction) side of the fan in order to move the actual "air intake" (sorry for using that term again) to a more advantageous nearby location.

    So, in my simple-mindedness, I assume that it must also be possible to cap off that inlet air flow with a water-to-air heat exchanger that would slightly preheat the intake air using well water.

    Looking forward to any further corrections or suggestions;

    Henk




  23. begreen

    begreen Mooderator Staff Member

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    I would suspect that the net gain of this type of mod would be short lived. These units move a fair amount of air which should not be restricted. To assure free flow I would think that would require a lot of air exchange from the garage which would very quickly cool it down to ambient. Maybe it would work if you had a barn full of animals to draw the heat from?

    The issue I would have with using water is how do you stop it from freezing? Above freezing these units are already amazingly efficient. My thought is for all the work, it's not worth it. The really good units are quite well fine tuned for performance already. If there was an easy way to make it better they would do it.
  24. henkmeuzelaar

    henkmeuzelaar New Member

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    Yeah, you are right. After reading up on heat pump compressor fans a bit more I realize that they are much too finely balanced to mess around with.

    I think our well water has a high enough temperature, though, to yield up to 7 degF without freezing. If so, I might be able to produce ~1 kW at a flow rate of 1 gal/min. Of course, a single stage water-to-freon heat exchanger (such as available in geothermal heat pumps, if I understand well) would be preferable by far.

    The only reason I briefly played with the idea of a DIY mod is that I am not ready for the cost of a complete ground-based (geothermal) HP system -- even with the big tax rebates-- and therefore was looking for a way to start first with a standard air-based HP.

    All in all, I think I'm gonna stick with resistive heating, plus passive energy conservation measures, for now and see where the power and technology markets are headed.

    Henk


  25. Mr. Heat Miser

    Mr. Heat Miser New Member

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    I have measured the electricity consumption of several pellet stoves with a P3 Kill A Watt meter and they average between about 125 Watts to 150 Watts instantaneous power draw depending on the auger and blower settings.

    Here's some actual numbers from a 20+ year old Whitfield Advantage II T Insert. During the monitoring period of approximately 2 weeks the stove was running 24 hours a day, only being shutdown for routine cleanings, with the auger and blower speeds being adjusted as usual by the user.

    Instantaneous Measurements:
    Stove Settings: Auger = 2, Blower = 3

    Auger Off Auger Feeding

    76 Watts 100 Watts
    1.33 Amps 1.71 Amps
    159 Volt Amps 197 Volt Amps
    .48 Power Factor .48 Power Factor

    Electric Rate: 19.1 cents/kWh (Townsend, MA)

    Elapsed Time 353 hours (14 days, 17 hours)
    kWh's used: 29.81
    Total Cost: $ 5.69 (29.81 kWh x .191 = $5.69)

    Projected Costs to run stove

    6 Months $70.00
    1 Month $11.55
    1 Week $ 2.69
    1 Day $ 0.38

    Based on the measurements above I could estimate that this stove uses approximately 2 kWh per day or 60 kWh per month the way the user runs it. Many articles I have read estimate about 100 kWh per month for pellet stoves, which is an acceptible number, but probably a little high.

    Surprisingly, my 2010 Harman P35i uses slightly more electricity than the Whitfield (125 Watts - Auger Off, 150 Watts Auger On), and most notably consumes a significantly higher amount (395 Watts) when using the electric heating element for the auto igniter, but only for about 6.5 minutes when starting the fire. This does not really add a significant cost to the electricity consumption however. Here's an example:

    395 W x 1 hr = 395 Watt Hours (That's about .4 kWh for roughly 10 fires - 1 hr / 6.5 minutes)

    So for every 20 fires, (about 20 days at 1 fire a day) the stove uses about 1kWh if you added up the consumption for the first 6.5 minutes of operation while the igniter is on, which for me costs 19.1 cents - fairly insignificant.

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