Huge Heat Pump Bills (Need Advice)

[Traderfjp]

I bought a 4300 sq. ft. house almost exactly a year ago in Asheville NC. We plan to move in full time in a few months. We have two heat pumps. One large unit that does the 1st level and downstairs. Then there is a smaller unit that does the two bedrooms upstairs on the 2nd level. On top of all that there is a propane furnace for when temps get to low for the heat pump to work efficiently.

I'm wondering if there might be something wrong with my HVAC system. The system keeps the heat at 72 and cools the house well in the summer when we are in the house. I called Duke energy and found out the old owners were paying 280 a month for the coldest months of the year. That was with them living in the house with 3 hot water heaters, tv's, electric stove, electronics, etc. We don't live in the house and have set the thermostat to 50 for the winter and 75 for the summer. Our last bill was 388.00. That is with the heat pump running, a dehumidifier at 60% setting, a small air pump in our pond, two fans and everything else is shut off including the hot water heaters. 388.00 seems outrageous since the house is closed up and well insulated by the way. We were not at the house at all during this billing cycle. Could it be a setting or maybe the thermostats are not wired properly. In July, August and September the AC was running at 75 with a dehumidifier, the pond pump, and two fans and bills were just under 150.00. We were there a week or so too. Then in December and January we are averaging 380.00 a month. Any advice or insight is appreciated.
BILL DATE BILL AMOUNT DUE DATE BILLING DAYS AMOUNT PAID BILLS

01/11/2019 $372.82 02/05/2019 31 $372.44 VIEW BILL

12/11/2018 $247.32 01/07/2019 32 $144.62 VIEW BILL

11/09/2018 $118.63 12/04/2018 29 $144.62 VIEW BILL

10/11/2018 $128.75 11/05/2018 28 $144.62 VIEW BILL

09/13/2018 $163.83 10/08/2018 34 $144.62 VIEW BILL

08/10/2018 $144.62 09/04/2018 29 $144.62 VIEW BILL

07/13/2018 $143.08 08/07/2018 29 $145.00 VIEW BILL

 

[Reach4]

We can't see the bills; we would have to have a login for that.

If we looked we would see how much is kWh, and how much was the price per kWh.

There could be an extra load turned on somewhere. When you are there, turn off breakers to the heat pumps, and watch the meter. Then turn off other breakers until you see a big change.

 

[Sponsor]

 

[Dana]

If a relay for strip-heat auxilliary backup could be stuck on running the strip heaters for most of the heating. If the refrigerant is low enough it could be that all the heat is coming from auxiliary resistant heaters, but still not getting cold enough to cross over to the fossil burner.

If it's on a well and the well pump is shortcycling like crazy or failing that could pull a lot of electricity too.

Electricity is sold in kilowatt hours, not dollars. Dollars is how you pay for that power. The rates do not stay the same year on year, so comparisons of billing based on the dollar amount has large errors built-in. The amount of kwh $380 buys this year can easily be less than what $280 bought a few years ago, though regulated electricity markets are only rarely that volatile.

 

[Traderfjp]

I will check those things. I only have the HVAC running. The water if off. Bill went up dramatically once the heat kicked in. As u can see our bill was way lower when the AC was running. 140 for AC vs almost 400 for heat. My rate is 11 cents a kw. The 260.00 bill from the previous owner was 2016. Prices may have gone up a few points from there but not too much.. Can't even imagine our bill once we move in and turn on everything. I probably need to call in a pro. What questions do I ask to make sure I get a qualified service person. Thanks again

We can't see the bills; we would have to have a login for that.

If we looked we would see how much is kWh, and how much was the price per kWh.

There could be an extra load turned on somewhere. When you are there, turn off breakers to the heat pumps, and watch the meter. Then turn off other breakers until you see a big change.

 

[WorthFlorida]

Do you know when and how the propane heat turns on for the auxiliary heat? It may have been turned off during by the previous owner and your using 100% electric. It is also controlled by the thermostat. The previous owners may have lowered the temp during the day while out to school and work with a programmable thermostat.

You probably have a smart meter and from your account via on line, you should be able to view your energy usage, sometimes down to the hour of a particular day. You show two dollar amounts per line, one is perhaps the actual bill and the second is an average bill amount of $144. You have a bill that is an average per month for an annual usage that gets adjusted once a year(?). In December the total wattage used for the last 12 months was perhaps more than the previous 12 month. Call Duke back and ask what type of bill program you are on.

This is a preferred way for many so the bill amount is about the same every month that makes it very easy for budgeting but there has to be an annual adjustment if you exceed the expected usage. Sometimes the amount used is less and your bill could drop.

 

[Traderfjp]

The first amount is the actual bill. The 2nd amount is what was paid My wife had auto pay on or something. There is a graph that shows a relationship between the outside temp and usage. Obviously the colder it is the more electricity we used. I did just put us on budget billing util I figure out what is happening. That should help until we move in. I had the propane tank (500 gal) filled last year and it was supposedly filled. At Christmas I checked the gauge and it showed 70% so I think the backup is working but am not 100% sure since I never checked the propane gauge once it was filled.

 

[Dana]

Have a pro do a service call to verify that the HVAC is running to spec.

Running an analysis to correlate energy use to the weather history requires the meter reading dates, not the billing dates. It's curious that you have logged a billing date of 02/05/2019, a date that is still in the future.

 

[Traderfjp]

Found this:
BILL DATE BILLING DAYS READ TYPE ELECTRICITY USED (KWH) AVG. KWH/DAY
01/11/2019 31 Actual 2577 83
12/11/2018 32 Actual 2626 82
11/09/2018 29 Actual 1216 42
10/11/2018 28 Actual 960 34
09/13/2018 34 Actual 1523 45
08/10/2018 29 Actual 1350 47

 

[Reach4]

Found this:
BILL DATE BILLING DAYS READ TYPE ELECTRICITY USED (KWH) AVG. KWH/DAY
01/11/2019 31 Actual 2577 83
12/11/2018 32 Actual 2626 82
11/09/2018 29 Actual 1216 42
10/11/2018 28 Actual 960 34
09/13/2018 34 Actual 1523 45
08/10/2018 29 Actual 1350 47

Do you have the prior December, January, February?

 

[Dana]

Found this:
BILL DATE BILLING DAYS READ TYPE ELECTRICITY USED (KWH) AVG. KWH/DAY
01/11/2019 31 Actual 2577 83
12/11/2018 32 Actual 2626 82
11/09/2018 29 Actual 1216 42
10/11/2018 28 Actual 960 34
09/13/2018 34 Actual 1523 45
08/10/2018 29 Actual 1350 47

Between 11/09 and 1/10 the KAVL weather station at the Asheville Regional Airport logged 557 heading degree days (base +50F) and between 11/10 and 1/11 it logged 570 HDD50, so averaging get rid of the time-of-day meter reading error let's call it 564 HDD50

During that period the house used 2577 + 2616 +1216= 6409 kwh, which would be 6409/564= 11.36 kwh/HDD50, or (/24=) 0.473 kwh/degree-hour. Converting that to BTUs (x 3142=) 1616 BTU per degree-hour.

Even for a 4300' house that's on the high side as a degree-hour heat loss constant even without the electricity being leveraged by a heat pump. If a presumptive COP of 2.5 for the heat pump was used (HSPF 8.5, which is pretty typical) it would be an insanely high 2.5 x 1616= 4040 BTU per degree-hour.

That constant is the amount of heat loss per hour per every degree of indoor to outdoor temperature difference to maintain something like 50F in an unoccupied house.

Putting it in some perspective, I have a sub-code antique house with 2400' above grade, 1600' of insulated basement, that has a constant of about 570 BTU/degree-hour. If my house were doubled to 4800' with similar exterior surface types & surface/floor ratio it would be about 1140 BTU/degree-hour. I may have less window/floor area ratio and higher air tightness than your NC house, but there's a range of "normal"- 1616 BTU/degree-hour would be in that range.

But while 1616 BTU/degree-hour isn't an insane load constant for a 4300' house, 4040 BTU/degree-hour is insane, only possible if a few windows or doors were propped open. Which is may be possible- perhaps a Canada goose crash through a sliding door, or somebody vandalized the place. But if it turns out the house is intact it's pretty clear that at least one of the heat pumps is delivering an extremely low efficiency.

 

[Traderfjp]

I tried to follow your post. In general you are saying that my usage is insane. I do have a dehumidifier running but it was also running when the heat was off and the AC was on and we were getting reasonable bills. Insanely high is the correct term for what I'm experiencing. I just made an appointment with a HVAC company that is local and has great reviews. I'm going to tell him about the high bills and see what he finds. I have two units so I'm getting charged 99.00 a unit which I guess is fair. I was told that the technician will explain how the unit works, settings, etc. Hopefully they can find the problem. Thanks again.

Between 11/09 and 1/10 the KAVL weather station at the Asheville Regional Airport logged 557 heading degree days (base +50F) and between 11/10 and 1/11 it logged 570 HDD50, so averaging get rid of the time-of-day meter reading error let's call it 564 HDD50

During that period the house used 2577 + 2616 +1216= 6409 kwh, which would be 6409/564= 11.36 kwh/HDD50, or (/24=) 0.473 kwh/degree-hour. Converting that to BTUs (x 3142=) 1616 BTU per degree-hour.

Even for a 4300' house that's on the high side as a degree-hour heat loss constant even without the electricity being leveraged by a heat pump. If a presumptive COP of 2.5 for the heat pump was used (HSPF 8.5, which is pretty typical) it would be an insanely high 2.5 x 1616= 4040 BTU per degree-hour.

That constant is the amount of heat loss per hour per every degree of indoor to outdoor temperature difference to maintain something like 50F in an unoccupied house.

Putting it in some perspective, I have a sub-code antique house with 2400' above grade, 1600' of insulated basement, that has a constant of about 570 BTU/degree-hour. If my house were doubled to 4800' with similar exterior surface types & surface/floor ratio it would be about 1140 BTU/degree-hour. I may have less window/floor area ratio and higher air tightness than your NC house, but there's a range of "normal"- 1616 BTU/degree-hour would be in that range.

But while 1616 BTU/degree-hour isn't an insane load constant for a 4300' house, 4040 BTU/degree-hour is insane, only possible if a few windows or doors were propped open. Which is may be possible- perhaps a Canada goose crash through a sliding door, or somebody vandalized the place. But if it turns out the house is intact it's pretty clear that at least one of the heat pumps is delivering an extremely low efficiency.

 

[Reach4]

I tried to follow your post. In general you are saying that my usage is insane. I do have a dehumidifier running

With the humistat at 60%, it is unlikely to kick on in the winter.

It could even be something silly like a clogged air filter contributing to inefficiency.

 

[Traderfjp]

I cleaned out most of the filters. Maybe I missed one. I'll update the thread when I have a diagnosis.

Thanks

 

[WorthFlorida]

Tomorrow maybe the worse day of the year, with gauges, to check the compressors. One unit could be low on refrigerant but with near zero temps it be nearly impossible even using a chart attached to the unit. However, a good tech looking at tell tale signs will know if something is wrong.

Don’t be surprised if he doesn’t show up. Furnaces break down in the coldest weather, just like AC units on the hottest days of the year. A dead furnace call may have priority since this polar vortex can freeze pipes. Hope it works out.

 

[Traderfjp]

I made an appointment for February 18th. If it's too cold should I cancel.? What is a good temp to get the units looked at? I don't want to waste two hundred dollars. Thanks!

Tomorrow maybe the worse day of the year, with gauges, to check the compressors. One unit could be low on refrigerant but with near zero temps it be nearly impossible even using a chart attached to the unit. However, a good tech looking at tell tale signs will know if something is wrong.

Don’t be surprised if he doesn’t show up. Furnaces break down in the coldest weather, just like AC units on the hottest days of the year. A dead furnace call may have priority since this polar vortex can freeze pipes. Hope it works out.

 

[Dana]

I tried to follow your post. In general you are saying that my usage is insane. I do have a dehumidifier running but it was also running when the heat was off and the AC was on and we were getting reasonable bills. Insanely high is the correct term for what I'm experiencing. I just made an appointment with a HVAC company that is local and has great reviews. I'm going to tell him about the high bills and see what he finds. I have two units so I'm getting charged 99.00 a unit which I guess is fair. I was told that the technician will explain how the unit works, settings, etc. Hopefully they can find the problem. Thanks again.

With heating degree day data compared against power use the number indicate the amount of electricity is only slightly on the high side (not insane) for a house that size if being maintained at 50F with electric baseboards.

But electricity use that high would be truly insane on a house that size if the heat pumps were actually delivering their nameplate efficiency, an efficiency level it should be beating somewhat at the lower indoor temperature.

AHRI efficiency & capacity testing is done at 70F indoors, and both +47F and +17F outdoors. That's at temperature differences of 23F (=70F - 47F) and 53F. They use a model to figure in the cycling losses etc, but the primary driver is the difference in temperature between the coil in the air handler and the coil in the outdoor unit (often refered to "condenser", but incorrectly so when in heating mode). The smaller the temperature difference the higher the steady-state efficiency, so by lowering the indoor temp to 50F it should deliver higher efficiency than at 70F.

From the power use against heating degree-day data numbers the efficiency it appears to be actually delivering is no better than an electric baseboard, and may even be lower, since it's burning power outdoors in the compressor & fan.

Any temperature that has a heating load is a good temperature to be testing it. If it's -10F outdoors (below the recommended operating temperature of many heat pumps) maybe it's not so good, but anywhere between +10F and 40F is fine if you're keeping the place at 50F, up to 60F it keeping it at 70F. It's probably good to test how well it's working at the lower 50F indoor temperature, since that can affect a number of operating parameters.

It occurs to me that if the outdoor coil is not defrosting properly during extended cooler weather the efficiency performance can be pretty atrocious, yet it might still have enough capacity to maintain 50F indoors.

 

[WorthFlorida]

Good techs will not overfill the system if they feel it is too cold, usually below 60 degrees. Some will recommend another visit in warm weather but with a heat pump, the tech should know if it is working correctly just but the temperatures coming off the coils. When my ac/ heat pump failed I could tell by the sound of the compressor. It was my air handler fan wasn’t working at times or running too slow. It’s all from the experience. You have a propane heater that needs to be check, electric strips are used or not. He’ll have a clamp meter to check current draw, etc. It won’t be a waste. Feb 18th in NC may be warm enough. On this visit and he finds a fault the savings on the electric bill will satisfy your concerns.

 

[Jadnashua]

Did you turn the furnace off while you were away? If so, the resistance heaters will possibly use a lot of energy.