Heatpump Standby Load

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fastbike

212 posts

Master Geek

#319543 5-May-2025 15:57

I normally switch the heatpump off at the isolator when we're outside of heating season. I turned it back on in April when the cold weather arrived.

The heatpump circuit has a power meter - the single outdoor unit is connected to a 8kW and a 5kw indoor unit. The maximum power I've seen it pull is a little over 4.4kW so around 19A.

However this post is really related to the load that it draws when switched off in the house, but still connected to the power. Here's a graph of the load today - we ran it over night on low so it was drawing around 650-700W until we switched it off at 7am. However you can see that it constantly draws around 15W but then goes up to around 70W every 30 mins, and sits there for 30 mins before going back to the lower level.

What do you think it is doing when drawing that power ? Also why was this not happening between switch off at 7am and 9:30am ?

Otautahi Christchurch

rscole86

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#3370633 5-May-2025 16:10

(not an expert) but your indoor units won't switch off. They will go into standby when you use the remote. The only time they're off is when you use the isolation switch.

As to what the need power for?

At a minimum they'll be monitoring the temperature of the room as well as possibly the temperature of the outdoor unit. But I doubt it would correlate to what you're seeing.

tweake

2391 posts

Uber Geek

#3370634 5-May-2025 16:15

what part of the country are you in? wondering what the weather was like a the time.

fastbike

212 posts

Master Geek

#3370636 5-May-2025 16:23

tweake:

what part of the country are you in? wondering what the weather was like a the time.

In Christchurch, a frosty start but nice by around 8:30am. Very sunny today (solar panels have charged the house battery, topped up the car, heated the water and exported 30kWh). Outdoor unit (installed 2017, Misti Electric) is on a south facing wall.

I also noticed this consumption pattern back in Nov '23 when I had the meter installed, but had turned the unit off for the summer so never really thought about again.

I wonder how many people realise they could be having a ghost load of around 40W 24x7 from their heatpump. That's significant if you are paying high TOU tariffs.

Otautahi Christchurch

tweake

2391 posts

Uber Geek

#3370637 5-May-2025 16:26

my guess here is its cold enough that the compressor cooled down and the crankcase heater turned on. the wattage seams roughly right.

if you have the model number for the outdoor unit we can look up the manual for it and check. also knowing the weather temps in the aera would help.

geek3001

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#3370640 5-May-2025 16:32

I was told probably at least ten years ago by an aircon tech that the outdoor unit usually includes a sump heater fitted on or inside the compressor to keep the compressor and its lubricant warm. I recall him saying that if the heater fails and the compressor is very cold due to low outdoor ambient temperature bad things would happen to the compressor if it started when very cold.

That heater will draw around 20 watts but that may vary depending upon the size of the compressor.

gajan

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#3370641 5-May-2025 16:34

Some heatpumps have some sort of compressor outsideside heater (resistive element) to keep the refrigerant/oil in the right state in the loop. Google your specific manufacturer if they have this.

My comments and remarks are not necessarily of my employer.

tweake

2391 posts

Uber Geek

#3370642 5-May-2025 16:34

also check if the indoor unit has "Plasma Quad" which is on ionizer. manufactures tend to run them when its not running to "clean" the filter. no idea on what they draw tho doubt its much.

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fastbike

212 posts

Master Geek

#3370643 5-May-2025 16:46

tweake:

my guess here is its cold enough that the compressor cooled down and the crankcase heater turned on. the wattage seams roughly right.

if you have the model number for the outdoor unit we can look up the manual for it and check. also knowing the weather temps in the aera would help.

Thanks

This is what we had installed:

a SEZ-KD71VAQ bulkhead unit in the dining alcove
a MFZ-KJ50VE floor standing unit on the first floor landing.
a MXZ-6E120VAD outdoor unit.

Today's temps in screen shot below, but I also saw this is summer 18 months ago. At least I understand what it is now.

Otautahi Christchurch

richms

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#3371223 7-May-2025 14:17

I was also told about them having a heater in them which is why they should be switched on for a while before you start to use them.

Additionally I was told to blast them on cooling mode for a while if they have been unused for some time as that does something to the lubricant that will help them last, rather than powering them up and going straight to heating mode.

Richard rich.ms