Heat Pump Running Costs

I would be very careful choosing the correct sized unit, most manufacturers specify the output based on air to water temperatures of 7C/35C, but may not tell you that the performance then falls off at reducing air temps and/or with increasing water temperatures, Grant seem to sell a Aerona unit?, I looked at their site but it only gives the performance at this 7C/35C, Kingspan published figures below for Aero-Max units as well which gives some idea of the fall off in performance. I think the Aeronas have variable speed operation down to 50% whatever this means in minimum output at the various air/water temperatures.

You have a estimated heat loss of 4.8kw, don't know if this is based on a standard OT temperature of say -5C or what but you may require a 8KW unit to give this output at -5C/45C.

Daikin have an 8kw split unit

Given the current cold spell, I thought I'd resurrect this thread to get an idea of how HPs are performing. Just checked mine and consumed 25 kWh yesterday. House is 245m2 and rooms set to 21.5, with bedrooms at 19. All in all, probably not too bad.

I removed the zones also, averaging 10kwh daily in December. To be fair it was mild. House fairly constant 20'. Avg 2kwh for hot water (Dec total Heating 283.6, hot water 53.9) House size 2800sft. (House is in use all day every day with young kids) A1 rating officially thanks to solar (Realistically perhaps A3/A2). Windows are not triple glazed and theres lots of them.

Just to add that all of the heating is on night rate @12c. my 6th year doing this and find results really good in terms of efficiency/cost. All done via timer logic on the Heat Pump app. eg if the temp is below 20/21 @ 1am heating kicks in. if by 4/5am it hasn't reached desired temp it keeps going until 7/8am.

Slight adjustment needed in very cold weather but again all v easy by the app (On minus nights the daily figure could go up tp 20KWH). I do push the hot water to be fully heated by the time day rate kicks in. and after that it calls for it as it needs. Because hot water is so little of overall this probably makes very little difference.

For the year 2024 (Heating = 1669KWH / Hot water = 649.5KWH). Obviously heating is off from April to Oct as the house would exceed 20' by itself.

Above figures are very consistent yearly eg 2023 (Heating 1672KWH / Hot water =731KWH)

All in all the yearly bill for hot water and heating is circa Eur 300.

Consumed 21.4kWh yesterday for both heating and hot water. Total for December was 345kWh.

165m2 retrofit, single storey, radiators throughout and runs purely on weather compensation. We maintain a set temp of 19°

The solar pv these last couples of days is great so running costs are low, I expect if we get the snow forecast the costs are going to increase some what.

Moved to Bord Gais EV rate in October so my new strategy is to move as much as possible my HP consumption to the EV rate between 2-5am where the unit rate is 6.33cent. I can move the the DHW easy enough so set a schedule on the HP to only heat at 2am but I do boost it in the middle of the day for an hour where hopfully I would have excess PV and at least it will be warmer so efficeincy will be at its best.

My heating strategy is to pump as much heat into the house between 3-5am by artifially setting the stat temps high (22-23degs) over all the house so all the loops are open. I am lucky in that I do have a very well insulated house with underfloor upstairs and downstairs so I can get great thermal mass. This thermal mass lasts me well into the evening on most days. I then have the heating coming back on at 7pm (after peak rates) but this time I split the zones into two, upstairs and downstairs. Heat downstairs first then upstairs later. I only have it coming on for about 2.5 hours at most and I have the temps set to thier ideal temp of 20degs so it might not come on at all if it mild.

My aim is cost reduction which probably will not mean energy reduction as I am artifically pumping more heat at night to get thermal mass up, but at 6.33cent per kWh its for nothing practially so why not.

Is it working…I think so, these graphs show my daily cost is not as volitile or as high compared to last winter and my cost per kWh for my heatpump has drastically reduced (second graph below) but the next week will tell a lot as to be honest we have not have an decent cold spell yet this winter

Finally I did some regression analyis on my heating consumption based on Heating Degree days only (65% confidance so not great corelation) and comparing to 2023 and I am well below 2023 (but mostly this due to mild weather) and below predicted based on moving 28 day (long average but smooths out the curves)

will post more data after the cold spell😎

All those graphs are the auld excel…I download the data from Grafana on HA and just update one or two spreadsheets to do more complex graphing and analyis.

I do have energy trend graphs on Grafana on HA but unfortunetly back in November my SD card in my Pi4 failed resulting in me loosing about 12 days consumption data 😫😪😪 as also my daily backup to onedrive failed 12 days before my SD card failed and I didnt notice until too late. So as a result 3 years of flawless data is messed up a bit. My totals are ok just shows a **** spike where it caught back up in the consumption data. Still I use excel for any thing complex

its frustrating that HA cant recover info thats in the shelly DB for sure !

Essentially you are heating 105sqm? I doubt upstairs set at 19 comes on much?

The joys of 2 stories. Yeah I run 11pm to 1pm in this cold spell, mostly nigh rate like yourself but heating 242 sqm bungalow more or less double amount of your usage. Still had no bill for December with govt credit so I'm happy with the heating these days compared to first winter in house with less then optimal setup of heating system.

193m2 A1 rated bungalow. We averaged 10kWh per day in December.

Currently averaging 20kWh over the full 5 days of January.

On my current tariff heating and hot water would have cost circa. €400 in 2024. The solar FIT credit from the summer wipes that completely out.

Who are they?

What flow temperature are you running?

Open/closed loop etc?

I've an Ecodan and you can get some info. such as electricity consumption, heat delivered (space vs. DWH), etc. from the control panel on the inside unit. I'd imagine it's similar with other types of HP

I experimented with all sorts of technics at the start because our heat pump was consuming huge amounts of electricity.

We have a Mitsubishi Ecodan.

The installer had set it on auto adapt which really is meant for radiators, we have underfloor heating. The flow temps to the underfloor were in mid 40s and was running like an oil boiler, on for an hour then off, rinse and repeat, insanity really for a heat pump. I suspect this is the case for most heat pump homes in Ireland without fine tuning.

Once we embraced the idea of low and slow, meaning leave on for long long periods of time on a low flow temp, for the entire house, our usage plummeted.

In the end I found that using as few zones as possible, so for us zone 1 downstairs, zone 2 upstairs.

Heat all rooms even if not used.

Use a fixed flow temp of 26-30C.

All underfloor loops in house are open.

Obviously all houses, will have different levels of insulation and airtightness and many will not get away with such a low flow temp, but the concept will be the same for all heatpumps, low and slow with as little zones as possible, leave heat pump on even when not home. Some will find this impossible to grasp, but it works.

100kwh/day is absolutely insane, even eventually. Are you sure you measured it correctly?

Do you charge an EV with big batteries by any chance?