Heat Pump Revisited
Topic: Indianapolis Living
Posted: Sun, Apr 24, 2005 
Last month, the heat pump system in our house went out (see previous article for details). Since that time I have been waiting to get some proof of how efficient this new-and-improved system is. Sick fascination with the numbers? Yes, and I'm fine with that. Earlier this week, I got my electricity bill and the number crunching began...
Since we haven't been in our new house a full year, I wasn't able to make an apples-to-apples comparison of last month's bill against last year's bill for the same time period. I do have the bill for two months ago, plus some old data from our previous house which was on a gas heat system. With that, I can make some apples-to-oranges comparisons.
The first month's electricity bill using the new system was $131.81. This is a difference of $16.48 over the previous month's bill of $148.29. The weather.com site tells me that February's average temp of 30°F of Indy is a bit colder than March's average temp of 40 °F. Time will tell if the month-to-month difference in our electricity bill is purely seasonal, or if the difference is partially coming from the efficiency of the system as well.
A little historical data, our old house used a gas furnace; all other appliances were electric. Total energy costs for Feb and March the past three years :
Year March Feb 2002 - $196.90 $268.01 2003 - $290.88 $314.83 2004 - $213.96 $300.23
Average February energy cost for old house: 294.36
Average March energy costs for old house: $233.91
Since our new house is "all electric", our total energy costs are completely contained within the electricity bill. Looking at our historical monthly numbers above, it is clear that our new house's total energy cost is radically less than our old house. Great news.
Although a heat pump system is pricey to install, its operating costs are much less expensive than a gas furnace. More data is needed to determine if the new heat pump is that much more efficient than the old one.
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Comments
1. Apr 25, 05 04:15 PM | bilerico said:
If you contact the electric company, they'll be able to give you the history of electric usage for your new house. They'll give you up to the last 5 years, I think. Then you'll be able to compare apples and apples. :)
2. Apr 26, 05 11:10 AM | Norm Stephens said:
It would be interesting to look at the years where the temperatures dipped below 0 degrees. Typically that's where a heat pump has to use the supplemental heating coils ... and thus more electricity. We've been fortunate for quite a few years now that we haven't seen any sub-zero temperatures for any extended period of time.
3. Apr 26, 05 04:45 PM | Brent Mundy said:
bilerico - good points about the historical data. I didn't know that someone could just request this information. I'll follow up and see what I can get from IPL.
Norm - when I get the historical IPL data, we could plot it against historical weather data. It would be interesting to see how much the price curve bends when the heating coils are used.
Our current system is set to trigger the heat coils (2 or 4, depending on the need) starting at 30 degrees. From what the installer said, we can move this trigger point lower, but that 30 degrees is more efficient somehow. I don't remember if it is because the coils can be phased in rather than 'all-on'? Or maybe there is an efficiency point where it is cheaper to turn on the coils for a short period than it is to run the heat pump constantly?
4. Apr 28, 05 10:29 AM | Norm Stephens said:
I don't know very much about the efficiency of the heat pump below 30 degrees, but I know it's not enough to heat the house when the heating coils fail to work. I've had that experience before. It's been a few years ago now, but I seem to remember 50-55 degrees was the best it could do without the heating coils.
5. Oct 2, 06 11:39 PM | david tucker said:
A bit of info on heat pumps in our area -- they can save you a ton of cash but MUST be sized and installed correctly. Central indiana has a typical low winter temp of 15oF & we are predominately heating; if your resistive (usu called supplemental) kicks in anywhere above 20oF your system is too small. ACCA manual S authorizes a 25% oversize to deal with our cold winters, I recommend 50% cause we pay the bills. All modern heat pumps i have seen provide 2.3 COP down to 15oF. Hope this helps as my sister has purchased a new home and I now know more about this stuff than I care to.
p.s. buy Bryant they are on Morris St.
6. Oct 2, 06 11:39 PM | david tucker said:
A bit of info on heat pumps in our area -- they can save you a ton of cash but MUST be sized and installed correctly. Central indiana has a typical low winter temp of 15oF & we are predominately heating; if your resistive (usu called supplemental) kicks in anywhere above 20oF your system is too small. ACCA manual S authorizes a 25% oversize to deal with our cold winters, I recommend 50% cause we pay the bills. All modern heat pumps i have seen provide 2.3 COP down to 15oF. Hope this helps as my sister has purchased a new home and I now know more about this stuff than I care to.
p.s. buy Bryant they are on Morris St.
7. Aug 20, 12 06:08 PM | Heating Oil in PricesScotland said:
hello!,I like your writing so a lot! share we be in contact more about your post on AOL? I require a specialist in this house to unravel my problem. May be that is you! Having a look forward to peer you.
8. Jun 21, 13 06:37 AM | desert iguana health care manual said:
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