Heat Pump Running Costs

It's absolutely Baltic out there and blowing a gale to boot. The heat pump is on course to consume 21kWh today. Fortunately the solar produced 13kWh to offset it somewhat before the crap weather rolled in.

a glorious day, currently 8 degrees celsius outside according to the screen on the internal unit. the 8kW HP is on course to use circa 10kWh of energy today (4.8kWh used from midnight to noon so i pro rata to get ~10kWh).

on the face of it i'm pleased as that's just €3 per day (ignoring the solar contribution) however i'm unsure its running as it should. the data from shelly is showing the heat pump coming on for 20 minutes, run for 20 or so minutes and then turn off. rinse and repeat for the 24 hour period apart for a single one hour session in the early hours when it heats up the tank.

does this sort of schedule sound right or would it be considered short cycling? the stats are dumb and UFH is one single big loop. the call for heat is controlled by the indoor unit which has the 'ROOM' temperature set to 19 although the stats are saying anything from 21.5 to 22.5.

It seems to keep the same routine no matter the temperature which I find odd but obviously works harder when it does come on as the temperature drops.

Something to keep an eye on, thanks for the feedback.

This is just a personal anecdote but thought it useful to share.

All week the heat pump was ticking along at 0.6kWh or lower with the dumb stats reading a steady 21 degrees. the mother in law arrives yesterday for a short break and says to the Mrs she's a bit chilly. So I cranked up 'ROOM' temperature setting on the indoor unit from 19 to 21 degrees (the house temperature is usually a couple of degrees above the 'ROOM' setting which would bring the house up to 23 degrees).

Last night I had a look at what shelly was recording in terms of consumption for the day. Lo and behold as soon as I made the change the HP went into overdrive. Consumption has doubled from 0.6 to 1.2kWh. It has been like that since 6pm yesterday and I presume will stay like that until the set temperature is reached.

Moral of the story, even modest adjustments can significantly affect the performance of a heat pump ...so if you're heat pump is running like crazy then by dialing down the settings a tad may have a significant impact on the HP's performance.

She's here till Tuesday 🥵

Yes, it makes a huge difference, if adjust the desired room as it offsets the heating curve.

If your desired room temp is not lower than your actual, you could probably lower your flow temp a bit and get them to match up. It made quite a big difference in efficiency for me. See below from my manual , line 1 is 21c desired room temp, 4 is 24 and 5 is 18. As you can see it makes an enormous difference to the curve if it is changed. It is best to have temp matched up to reduce compressor cycles and have the optimum heating curve slope. I'm using weather compensation.

The indoor unit has a built in stat. You set it to your preferred temperature and the HP does the rest.

I have 2.8m wide south facing window yet the temperature remains constant so all I can say is excessive solar gain isn't an issue.

flogas bwg smart electricity

day 24 cents

night 18 cents

peak 28 cents

standing charge works out at 65 cents / day.

i'm probably one of the few boardsies who signed up to the bwg deal who actually works with a bwg affiliate 🤣

It's the preferred room temperature.

I find whatever I set it to on the indoor unit the house stats report two degrees higher so in the photo below it's set to 19 degrees in order for the house to reach 21 degrees. I don't know why this is the case but it's something the plumber said would happen when he installed it and sure enough it has.

Other photos showing current temperatures of flow etc.

The house has been built to passive standards hence why I have a really low flow (supply line) temperature.

i would personally install everything…although i'm not sure how you would install UFH without manifolds. the actuators come with them.

i might try an experiment for a couple of weeks next winter with the zones to see how it affects the efficiency of the heat pump and comfort of the home.

the ufh usually comes as a kit. i along quite a few boardsies will tell you it'll take awhile for the end-user to get a handle on the set-up. i'm only in the house since christmas and am still learning the ins and outs.