Electric Heat Pump Usage

[djlew]

Hey everybody, I recently did some testing and was curious if anybody had any insight into the science/practicality of what I have been realizing with my electric heat pump. Just a bit of context:

My area does not get any natural gas service. You either get propane, oil, wood heat, or electric. I got a wood stove to cut down on the use of the electric heat pump. Made sense to me. During the times I have not had a fire going and relied on the electric heat pump (keeping thermostat at around 65F), and the outside temp was on the colder end (sub 35F), the heat pump would freeze over and kick on a defrost cycle. To me, this seemed like normal behavior, even though uncomfortable when the blower still keeps on going when the heat pump is trying to defrost and basically kicking AC in the house!

So a few weeks ago, I started keeping the temp on the thermostat at around 68F. We've had a few sub 30F nights, and before when trying to keep up to 65F I would wake up and the house would be 58F due to so many defrost cycles, but now keeping it at 68F I barely hear any defrost cycles and wake up to a nice and comfy 67-68F and everything runs great! Keep in mind, I purposely have the "emergency heat" heat strip off at a breaker to avoid confusion with that.

Does this make sense to anyone else? Is the warmer temperature I am trying to keep at keep things warm enough in the house (where the pipes run to the blower, etc) and outside on the equipment to where the heat pump isn't freezing over? I almost feel like I cracked a code or something, and maybe this was in a manual that I missed but I would love to get some expertise on this. From what I'm told, electric heat pumps aren't a great heating option but working with that I have.

Thanks again everybody, and I hope everyone had a wonderful start to the New Year!

 

[peakbagger]

Conventional single or two speed whole house heat pumps are not great for heating as they were not designed for it plus the ductwork rarely is well insulated and leak free. New cold climate heat pumps use different technology and working fluids and can be quite efficient down to the teens. They can go lower but the efficiency starts to drop down to roughly equal to strip heat usually at below zero temps.
As for your discovery, I have no idea what it going on. If I had to guess is the unit was not cycling enough at lower temps but does with the higher setpoint ?

 

[Highbeam]

Your system probably thought the resistance coils were working. Isn’t there a better way to lock those out so the system doesn’t blow cold?

Heat pumps are excellent at heating. Like anything, you just need to properly size your equipment.

 

[gthomas785]

For sure, warmer return air from the house will give you less subcooling at the indoor coil and could make a difference in the outdoor coil temperature. If your ambient temp is near freezing that would impact the amount of defrosting it has to do but it's highly dependent on the conditions.

I'd be more suspicious that a subtle shift in the outdoor temperature or humidity is responsible for the change you saw, but if you've controlled for that then it's possible that the indoor temperature could do this.

Keep in mind that your heat pump is not necessarily running more efficiently in this case, just warmer. There's no getting away from the laws of thermodynamics and the compressor will run longer and draw more power to maintain the higher setpoint. If you avoid a defrost then that does help with the efficiency to some extent.

 

[djlew]

Thank you all for your input! It's true, when considering outside temp, it's never a consistent control but seems like I am at least more comfortable which is a win for me.

I did do a tiny bit of research on why the blower continues to run even when the heat pump is on a defrost... I know next to nothing about the inner mechanics of this system (trying to learn more) but it seems like it doesn't make much sense to basically cool the heated air and net 0 or even lose heat because it's blowing cold. Something I've been thinking about for a while.

Thanks again everyone!

 

[peakbagger]

Mini split heat pumps do blow some cooler air during a defrost cycle. They need to take warm air from the room and melt off the frost from the coil. Its not a big issue when the system i not working hard but quite noticable when its running hard.

 

[gthomas785]

Yes the defrost needs to get heat from somewhere. If you turned off the blower completely, the coil inside would probably ice up. That's why they often run the aux heat during defrost. Depending where the heat strips are placed in the air stream they can also help boost the system pressure and speed up the defrost cycle a bit.

 

[djlew]

Gotcha, makes sense. Over these past few weeks of testing, I only had one day of the defrost cycles actually cooling the house more than it was heating it. Really interesting experiment, and curious about my electric bill for the month. I'm extremely hesitant to get the heat strip on because last time I did, I ran a 700 dollar electric bill. Granted, I have ecobee thermostats all over the house so it's kind of a pain in the neck to configure it to work in the most efficient way.

 

[djlew]

Hey, so out of curiosity those who have a air source heat pump how much are you finding you are paying a day to run your electricity we have now hit £11 in the last week as temperatures have dropped to single figures and this is scary as it is only going to get colder and therefore higher bills. We have only had the ashp a year but originally had a fault last year but of course since then rates have grown considerably too so I just don't know what is a normal cost to expect or wether I have a fault again. Every time I feel like I am doing the right thing whether it's a fixing a mortgage or now going green I make the wrong decision and it seems to go the other way 😩 I read that ashp even now should be like £1200 a year I'm going to be looking at that in 3/4 months... in summer my electricity was £150 a month in a 4 bed semi with just 2 adults... and I am due a baby February so definitely want a warm home. We keep at 18degrees as it says keep at constant temperature we have even knocked one thermostat to 16 that runs the whole except our open plan living area which is underfloor. I'm absolutely mortified at the cost and I just don't know what's normal I hear people saying their electric and gas right now is like £5 and I'm at £11... something just doesn't feel right... is this what others are seeing with a ashp? Thanks

Hey there, really sorry to hear you are stressed about the cost of this. I can totally relate. Last year, I refinanced my mortgage to buy out a previous occupant and took on a hefty mortgage payment solo. Truthfully, it's so hard to compare costs because there are so many factors... how insulated the home is, temp you are keeping everything at, type of system and whether or not it is sized properly, all that jazz.

What I can say is that on average, with electricity being my only utility (no gas service, every appliance is electric including water heater, dryer, stove, heat pump, etc), my monthly electric adds up to about 235 British Pounds (300 USD) according to Google's currency exchange rate. I'm in a 2 story 3 bed house. This can fluctuate, like last month my bill was 313 GBP (400 USD). As I noted above, I didn't actually see a change in electricity usage when switching from keeping the temp at 20C instead of 18C like you said you are doing.

Relying on wood heat has been a game changer when it comes to conserving electricity. I'm lucky, my property has basically limitless fuel for my wood stove, but I do find in the coldest months using wood saves my behind. I've had 550 GBP (700 USD) electric bills before with trying to supplement heat with a heat strip in the air handler when the heat pump freezes over.

Investing in another heat source is really starting to pay for itself in the coldest months. My bill is extremely consistent in the warm months. I actually just visited Hull over the Summer, our Airbnb had no AC but those nights were nice and cool! I know AC is a different story over there.

Seriously, good luck, and if I can provide any info or help in the meantime I will be happy to do so. Take care!

 

[shoot-straight]

So I have an all electric heat pump along with my stove. My stove will keep up until it gets pretty cold, and pretty windy. Like now. At these times I skip the heat pump altogether and put on the emergency heat. When the house needs a little help, it quickly does that without trying to squeeze heat out of the heat pump. It's also nice to distribute some heat to the areas of the house far from the stove.

 

[fbelec]

i install ecoer heatpumps. they tell me in class that the heatpump is running 100% efficient at 15 degrees outside. also we usually are running gas burners but i know you don't have service where you live. the gas usually kicks in when defrosting the coil outside. im told that the inverter compressor runs a loop inside itself and does not involve the air that is blowing inside. the inverter compessor has 40 speeds on it's own. i have a app on my phone that tells me how the unit is running if there is a code run from the compressor if bad enough will shut down the unit and let the company and me and the plumber that installs the unit that there is a problem with itself before the owner knows. i can see just how many amps that the unit is drawing also. and it's not much. when it is looking to heat from a cold outside temperature sometimes the amperage goes down and compressor speed goes up. so if your unit fails look into the ecoer unit
just my 2 cents

 

[djlew]

Welp, took a look at my usage for the December-January period and we cooked up an almost 700 dollar bill again (672 USD). Did have the emergency heat strip going for about 2 days of the billing period. I purposely turned the strip on because we had some sub 15 degree days here in NJ.

The only thing I can think of is I do have a dehumidifier going to help dry out some wood in a "makeshift kiln" along with LED Christmas lights still going well into this month. I don't know, it's extremely discouraging, because I felt like we still wouldn't have hit a super high bill this month, but I guess that's how the tides turn. Reality check for sure.

I guess for context a bit of background on the system. We have a York system kicking right now, but other than that I don't know much about it. I may have to dig deeper and see if this system is even sized properly for the house.

Thanks everybody for your input. This has been extremely helpful!

 

[fbelec]

that type of bill will happen with the electric strips. we install york they are very good for not failing compared to other types. york is our unit of choice.

 

[EbS-P]

Welp, took a look at my usage for the December-January period and we cooked up an almost 700 dollar bill again (672 USD). Did have the emergency heat strip going for about 2 days of the billing period. I purposely turned the strip on because we had some sub 15 degree days here in NJ.

The only thing I can think of is I do have a dehumidifier going to help dry out some wood in a "makeshift kiln" along with LED Christmas lights still going well into this month. I don't know, it's extremely discouraging, because I felt like we still wouldn't have hit a super high bill this month, but I guess that's how the tides turn. Reality check for sure.

I guess for context a bit of background on the system. We have a York system kicking right now, but other than that I don't know much about it. I may have to dig deeper and see if this system is even sized properly for the house.

Thanks everybody for your input. This has been extremely helpful!

How many kWh for the bill cycle? How does that compare to April and then July/August? All electric house here too. No heat/AC, no EV charging (5 kids though) I can do 750 kWh a month. Double that for hottest/coldest months.

When is the last time your hvac was serviced and all your filters replaced? How old is the duct work and where is it located?

 

[djlew]

How many kWh for the bill cycle? How does that compare to April and then July/August? All electric house here too. No heat/AC, no EV charging (5 kids though) I can do 750 kWh a month. Double that for hottest/coldest months.

When is the last time your hvac was serviced and all your filters replaced? How old is the duct work and where is it located?

Great questions. Almost embarrassingly, this bill reported 2970 kWh of use. Interestingly, this same billing cycle last year was my highest as well for that year, but with 2200 kWh of use for the cycle. I don't even hit 1500 most other months with the shoulder months more like what you are reporting. Filter was just changed, the system admittedly has not been serviced in ~2 years. Pretty old ductwork in the basement, but I did do a bit of sealing it over the past couple years. Getting some maintenance done on the system is definitely on the list.

Even when the unit was new, I was running up similar bills this cycle so it was easy for me to blame the heat strip. I only used the heat strip for 2 days this cycle and kept the thermostat at 63F. If it's the cost of being comfortable, that's fine I guess, but seems a bit excessive to me. I did run some space heaters, dehumidifier, Christmas lights and all that jazz which adds up, but sheesh just seems crazy to me. I figured there had to be a more viable solution.

Thanks again all for your input!

EDIT: Just thought of something else to mention... this is a 3 zone thermostat system. Seemed weird to me the setup which maybe causes the system to run more but the living room, kitchen, and upstairs rooms (vaulted ceilings too) are all on one zone, primary bedroom is its own zone, and the basement is a zone. Basement thermostat I keep off, the other 2 I keep the same mostly. When I mentioned keeping the thermostat at 63F during the heat strip days, both were set to that.

My electric bill app does say I am generally using above average electric. Windows also need to be replaced. Probably just a case of needing to make the home more efficient but definitely an intimidating task.

 

[EbS-P]

Great questions. Almost embarrassingly, this bill reported 2970 kWh of use. Interestingly, this same billing cycle last year was my highest as well for that year, but with 2200 kWh of use for the cycle. I don't even hit 1500 most other months with the shoulder months more like what you are reporting. Filter was just changed, the system admittedly has not been serviced in ~2 years. Pretty old ductwork in the basement, but I did do a bit of sealing it over the past couple years. Getting some maintenance done on the system is definitely on the list.

Even when the unit was new, I was running up similar bills this cycle so it was easy for me to blame the heat strip. I only used the heat strip for 2 days this cycle and kept the thermostat at 63F. If it's the cost of being comfortable, that's fine I guess, but seems a bit excessive to me. I did run some space heaters, dehumidifier, Christmas lights and all that jazz which adds up, but sheesh just seems crazy to me. I figured there had to be a more viable solution.

Thanks again all for your input!

EDIT: Just thought of something else to mention... this is a 3 zone thermostat system. Seemed weird to me the setup which maybe causes the system to run more but the living room, kitchen, and upstairs rooms (vaulted ceilings too) are all on one zone, primary bedroom is its own zone, and the basement is a zone. Basement thermostat I keep off, the other 2 I keep the same mostly. When I mentioned keeping the thermostat at 63F during the heat strip days, both were set to that.

My electric bill app does say I am generally using above average electric. Windows also need to be replaced. Probably just a case of needing to make the home more efficient but definitely an intimidating task.

Window replacements rarely save any money. Get a killawatt meter and figure out how much the space heaters and dehumidifier are using.

Single speed compressor multi zone systems are difficult to balance correctly.

Get a service appointment and get the coils cleaned. Ask them to explain how the different zones operate if you don’t already know.

 

[djlew]

Window replacements rarely save any money. Get a killawatt meter and figure out how much the space heaters and dehumidifier are using.

Single speed compressor multi zone systems are difficult to balance correctly.

Get a service appointment and get the coils cleaned. Ask them to explain how the different zones operate if you don’t already know.

Good advice, thanks for that. Going to take this and run with it.

 

[gthomas785]

I recently invested $165 in an Emporia Vue energy monitor. Self installed. Honestly, it was the best investment I've made in a while. Tells exactly what is using the power and when. It already saved my butt once because after 1 week I noticed a weird power draw pattern from my sump pump and yep, it was locked up. I was able to swap it out before the basement flooded. I bet this would help you at least verify exactly what is using so much power in your house.

For your case... 2970 kWh in a month represents an average of 4100 watts continuous power draw! Or, 10kW heat strips on a 41% duty cycle for the whole month. That does seem like a lot, even with heat pumps running continuously.

 

[stoveliker]

Windows are double pane? If not replacing them does make a large difference.

Get a candle and go around to find where air is leaking in (flickering flame). Caulk and foam (great stuff, not near electric if not fire resistant) cost very little.

 

[djlew]

I recently invested $165 in an Emporia Vue energy monitor. Self installed. Honestly, it was the best investment I've made in a while. Tells exactly what is using the power and when. It already saved my butt once because after 1 week I noticed a weird power draw pattern from my sump pump and yep, it was locked up. I was able to swap it out before the basement flooded. I bet this would help you at least verify exactly what is using so much power in your house.

For your case... 2970 kWh in a month represents an average of 4100 watts continuous power draw! Or, 10kW heat strips on a 41% duty cycle for the whole month. That does seem like a lot, even with heat pumps running continuously.

That's funny, these came up in my search! I was really interested, now to convince the fiance to be on board. I figured it seemed like a lot of usage too. They aren't terribly expensive, but I had a hard time finding out truly how invasive it is for self installation.

 

[gthomas785]

That's funny, these came up in my search! I was really interested, now to convince the fiance to be on board. I figured it seemed like a lot of usage too. They aren't terribly expensive, but I had a hard time finding out truly how invasive it is for self installation.

If you've ever worked in your electrical panel before (e.g. adding a circuit) and you've got some space inside, then installing it should be easy. There are also some DIY guides on the internet. The kit comes with everything you need, including some pigtails and wire nuts to tie in the monitor's power supply.

Basically, you clip a sensor around the hot side of each circuit you're interested in monitoring, then plug the sensors into the box. The box sits inside the panel. You need to remove 1 knockout so the wifi antenna can stick outside, otherwise the signal will be blocked. The only other thing is hooking up the power leads to L1 and L2 (which can go either on a dedicated double-pole breaker or any 2 existing breakers that are on opposite legs), and the neutral.

If you're not comfortable working in the electric panel then I would recommend finding an electrician to do the install but this can add significantly to the cost. Or perhaps you know a handy friend who can help.

 

[mellow]

Same type of install for Sense. I installed it myself 5 years ago and it is still working great.

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[djlew]

Thanks for the insight on that. I do have a few friends who know what they're doing so might consult with them and make a party out of it. My only concern for my case is a lack of space. I'm pretty sure my panel is pretty booked up. I'm thinking a system like these is exactly what I need to really get to the bottom of my usage. I'm glad an affordable solution exists. Well, troubleshooting solution anyway, lol. Thanks again all!

 

[gthomas785]

I have not used a Sense, but the big difference from Emporia is that it does not collect circuit-level data and instead relies on an algorithm to guess at what is consuming power. Could be useful if all your appliances consistently draw the same power profile, but would not be helpful for tracking down fluctuating power usage spikes. Just my 2 cents.

 

[mellow]

I went from a house with a wood stove for heat to a house with heat pump and after some crazy high electric bills like you got I installed Sense and tracked down all the energy hogs. It paid for itself within 3 months.