LG Red HeatPump (ducted) energy consumption

MattT

Comparing last winter (jan/feb) to November this year... my 11 month old heat pump is using almost double the amount of KWH/day compared to last heating season (in MA close to Boston).  No issues this summer using pump as AC... outdoor unit Luu420hhv and inside unit (in attic) LVN420HV.  I thought maybe the app for heat pump was wrong, but this was confirmed by a high electric bill this month. 4 month old merc 5 inch filter (air bear) still looks brand new.  November was mild, and january/feb was the middle of the winter last year. Any suggestions?

Hot_water_fan

What’s the energy data source?

MattT

Good question.  It's just in the LG thinkq app.  At first I thought maybe the app was wrong, so I waited the month and the electric bill confirmed my suspicion, so it seems accurate however it's reading it

bburd

Is it stuck in "emergency heat", running electric resistance strips and not the compressor in mild weather?

MattT

I was just going to say, there is no heat strip, this is strictly condenser (inverter) outside and air handler in the attic.  I have a back up gas boiler with forced hot water baseboards as back up... this system (ac and heat) runs independently from my gas boiler.

Hot_water_fan

I’d get last 30 days of kWh from last winter and find the corresponding 30 days of heating degree days (from online) and compare to November. 

MattT

I did.  Temperature was considerable lower on those days in jan/feb that I posted.  It was much warmer on the days in November I posted, and it used significantly more energy.

Hot_water_fan

Can you show it for 30 days?

30 days of both time periods and the HDDs for each. I think that’ll help with the installer. 

I’ve had a cold climate since 2021 and the kWh/HDD ratio has been constant.

Once we had a guy post that his new modcon was a scam, his contractor was a crook, etc and doing that exercise showed that he was saving 30% year over year, his rates had just changed. Not saying that’s you, but when you call someone local for help evidence will help. 

MattT

So for comparison January 22, 2023 it was high of 34 low of 30 and I used 35kwh for the day..... on November 29 2023 the high was 37 with a low of 28 and I used 54.5 kwh for for the day.  I compared multiple heating days amd temps for jan, feb and March, and similar Temps in November and December have been significantly higher.

Hot_water_fan

I am hearing you. Can you just do it for a 30 day stretch? 11/1-11/30 and a period in Jan too. Also, use heating degree days, not highs and lows. 

MattT

I'll have to figure out how to find the Hdd's for Boston but here is the month of Mar and November

Hot_water_fan

https://www.degreedays.net/ 

ethicalpaul

Why are there whole sections of time from last winter showing zero electrical usage? Maybe the logging was offline for periods of time then? And I'm sure others commented that you are trying to compare a single day from then vs a whole month now? Something may be up, but these are apples and oranges it seems to me

MattT

I'm comparing days of similar temperature to days of similar temperature (first post is individual days)... also here is the hdd's I think? Looks like gibberish to me, not sure it it helps... 

MattT

Also, the times of no electrical use is hours on that picture your looking at. The screen shots of the months show every day electrical usage.

ethicalpaul

Right but it just seems unlikely that in a day in January there would be 6 hours with no usage for a heat pump.

Does the heat pump stop when the temp goes to a certain low, and then the gas takes over, meaning that on the coldest days you will see less electrical usage because...it's not being used?

Hot_water_fan

HDD just measure how cold a period was. They’re more useful than an average temp because there’s a point where heat isn’t needed. HDD only count periods you need heat. 

Anyway thank you. Looks like the rate is substantially higher. What was Jan and Feb kWh? 

What turns the gas boiler on and off? Is it used frequently?

And why is the heat pump that size? 

MattT

@ethicalpaul I turn the gas boiler off completely and turn on manually as needed.  Double checked, it was a high of 41 (unseasonably warm) on January 19.  And I schedule to drop from 68 degrees during the day to 64 at night so it may have just been the difference.

MattT

@Hot_water_fan gas boiler I think I used 2 days in February (dropped down to like -8 degrees a few days straight) February was 739kwh for the month (turned heat pump off completely for 2 days when gas was running) January, I don't have calculated because I was still experimenting with the new system.

I manually turn boiler on with a separate thermostat.  Heatpump has its own thermostat, they don't know each other exist.  And my main living area is about 2500 sqft.

ethicalpaul

OK, that's why the degree days will be better, I'll bow out here as @Hot_water_fan is already explaining the usefulness of that metric. But you will have a lot of trouble comparing these with manual switchovers that are going to be very difficult to calculate I think.

I will say that there are thermostats that will automatically switch over from HP to gas at a certain threshold that you might consider so you can not have to worry about manually switching over to gas.

MattT

Calculating shouldn't be too hard... my gas boiler only ran for 2 days in 2023 when I turned in my other thermostats (February 9 and 10)

MattT

It has been all heat pump... my concern is all last year, only a handful of times the system used 3kwh when it kicked on (its usually 1.5-2).... now every single time it kicks on its 3 or above

MattT

@ethicalpaul manually turning on my has boiler isn't much of a bother (boiler thermostat is a Nest so its all done on my phone), it doesn't happen often at all.  My heatpump is advertising as going down to -13 air temp.  I only switch to gas when it gets extremely cold like those 2 days in February.

Hot_water_fan

@MattT and what was the utility bill kWh and therms from January - march? Also, can you provide the gas usage for a winter month prior to the install?

The part that doesn’t add up here:

using <1kwh/degree day is extremely impressive for a 2500 sqft house with a heat loss at least at one time expected around 36,000 Btu/hr. 

Let’s look at March. 724 kWh and 755 HDD. That’s about 25HDD daily, averaged. I’d expect a design of 60HDD, so 25/60 = 42% of that. If your heat loss was 34,120 Btu/hr, thats conveniently 10kw. So for a 25HDD day, I’d expect you’d need an output of 10 kWh * 24 * .42 = 100kwh. But you’re using a heat pump, so the COP is then used to divide that: a COP= 3 is a fine guesstimate, so you’d need input of 33kwh/average March day. That puts you well over 1000kwh for March. 

So a few things could be happening: you could have a pretty oversized system, you could have an especially efficient system (even more so than LG thinks), more gas was being used than you think, or the app was reporting wrong last spring. Could be a combination of these. 

MattT

I appreciate you taking the time to assist me with this btw....

The past few years (even though it's 2400-2500 sqft) I've replaced 18 windows and 4 exterior doors with all energy efficient (low-e) doors and windows.  This past year I stripped the old clapboard off the house and replaced it with vinyl siding.  I also had the foam board insulation to the house (under the vinyl) and had cellulose blown into the attic trying to get it as tight/energy efficient as possible.  

Here is my gas and electric bills (both should show previous months too).  Keep in mind that I decided to go with a heat pump instead of replacing my old (from the late 80's boiler, so its pretty inefficient).

Pretty much as of January 1 2023 I started using the heat pump.  First few weeks in Jan I was experimenting with using the gas boiler and heat pump at the same time before switching over exclusively to heat pump (except a few extra cold days in Feb).  Gas in the house is also used for hot water and stove/oven.

Also note that because or the Columbia gas/eversource change over, the earlier bill I have is for dec 2022.

Hope this helps...

MattT

This may also be helpful... 

ethicalpaul

Try a heat pump water heater, especially if your gas water heater is atmospheric and is acting like a heat ejection/cold injection device 24/7

MattT

The hot water heater was replaced in 2019, but if/when it goes I'd probably go heatpump.... typically in the summer, with showers, cooking ect the gas bill is usually only around $40-50/month.  Unless I run the 266,000 BTU pool heater.... but that's a different story lol

pedmec

i haven't read every comment and maybe you already answered this but are you lowering the thermostat on the heat pumps to try and save? Because that would be counter intuitive to what happens. The heat pump in an effort to recover the lost heat is going draw the max electricity for how long in can until it gets close to the set point and modulates. if it takes hours to recover you are getting charged at the peak demand for that whole hour and subsequent hours at the max rate. although there is no resistance heat in mini splits you still do not want to shut them off. As it get colder outside the discharge air temperature coming from the inside unit is going to drop which makes it harder to recover. you need to keep them running so they run on a low power draw

MattT

I do drop it down about 4 degrees for about 12 hours overnight but that's most for sleeping comfort.... but I also did the same schedule heat drop and times last winter, and I'm comparing like days to like days.  Even doing that last winter everytime the pump kicked on the draw was 1.5-2kwh, now when it kicks on its 3kwh or more.

MattT

This is right now... thermostat set to 68 @730am this morning... maintaining temp is still over 3kwh.

GGross

Are you sure its not using an electric resistance heat strip for some reason? it is almost maxing out, looking at the spec the electric usage for heating mode is 3.69 Kw.

maybe duct not insulated in the attic or something else up there causing you to use so much heat?

MattT

There is no resistance strips installed in this system... and nothing has been touched in the attic since it was installed.  I went up there the other day to check the filter and all returns/outlets looked fine... it's still putting out heat, but there is definitely something wrong.

ethicalpaul

I don't think anyone mentioned this, and I was hesitant to say it since I'm only an HVAC hobbyist, but is it possible that your system has lost refrigerant due to a slow leak (perhaps at a flare joint for example) and now is far less efficient than it was at installation?

MattT

That is very possible, I talked to the guy that installed it earlier and he is waiting for a call back from LG tech support to see if it may be something else.  He did mention a refrigerant leak could make it run harder and if it's a leak it will eventually stop blowing warm air, but it sounds like if he doesn't hear back from them in the coming days, he's going to stop by and check the levels.  

What are the tell tale signs of a leak? Will I notice wet spots? Actually dripping at unions? Is there a UV dye in the new refrigerant?

GGross

@ethicalpaul Could be on to something, there was a pretty rare, but still existent issue with the fusible plug in some models leaking. If you talk to your service tech ask them to check the fusible plug located in the outdoor unit for a leak (should still check other joints for leaks just to be sure). 9/10 times you would not be able to tell by looking at it that it is leaking, it would also be a very slight leak and could go about a year or two without being caught.

the fusible plug looks like this (without the black rubber cap of course)

Jamie Hall

Something doesn't add up. In one post, it is stated that the estimated heat loss is around 36,000 BTUh. If we assume a COP for the heat pump at that outside temperature of 3 --which is probably generous -- that's going to take just about 3 KW power input to the heat pump. If the heat pump runs an hour, that will be 3 KWh of energy.

Which it seems to me is what you are showing?

MattT

Trying to compare similar days from last heating season.... on February 18 2023 it was a hi 37 lo 21 36.8kwh used.  On November 13 2023 there was a hi 43 lo 21 with 58.9kwh used for the day.  Confirmed no gas boiler activation those days... the difference is significant and my electric bill is confirming my suspicions.  I'm hoping this guy finds a leak or something.... it's kinda driving me crazy and  becoming extremely expensive to run like this.

Hot_water_fan

@Jamie Hall that was my initial thought too but look at march 2023! 724 kWh and 755 HDD. 

So .95kwh/HDD65. 

For the 12 months pre heat pump, I’m getting a gas usage coefficient of .2therms/HDD. 

Which, assuming 80% efficient, gets a heat pump COP = .2 x 100,000 x .8 / (.95 x 3412)= 4.9! 

If the boiler is actually only 60% at this point, COP of 3.7. 

Either way, for a month with 755HDD this is really strong. 

Now I suspected more gas was being used in march, but no doesn’t seem like it (gas bills look to be on a different cycle so March ‘23 is more like “March-ish”. Either the heat pump is performing much different than it was in march or the app is reporting much different usage. 

MattT

@Hot_water_fan remember that term "there's an app for that".... here is my Nest thermostat for March that runs my gas boiler... haha gotta love technology... 

I also thought the app may have been wrong, but when I got that electric bill it pretty much jumped out at me that there was something wrong.

Hot_water_fan

@MattT if the boiler is heating the house, it’s doing it despite the thermostat being off. That’s possible! I wonder if it’s being kept warm and flow is getting out.