Heat Pump Running Costs

I thought I would add my 2nd thoughts on heat pump costs. Originally posted some data in Nov/Dec 2023. After the install the kWh usage was meh, ok, not great. A1 rated house, built 2000, with radiators. Oil boiler was replaced by heat pump in Nov 2023. We've done all the upgrades we could, but we couldn't do the floor lift-up to put in underfloor as that was a bridge too far. So we'll never get the "storage heater" that underfloor heating gives, nor can we use the cheap night rate for it. I guess my longer term plan is to size a battery for the average kWh used by the HP per day during the Nov-Feb period, and store night rate energy and use that for powering the heat pump during the day… In the future I can probably do this with my EV using V2G/V2H technology but that's 5-10years away; for now it would require a separate battery. In the meantime, here's my monthly and yearly kWh and cost. Over 700Kwh in Jan. Not great. At all. Stats are 22 downstairs and 18 upstairs, hot water tank set to 44 for showers etc.

I've been tweaking here and there but I don't think there's any way to substantially improve the cost. I tried leaving the unit off overnight, one view is that you'll save money as you're not heating when no one needs it, the other says heat to a temp and keep it ticking over as that's when the HP is most efficient. Tried both, nothing really changed in my figures. House is well insulated but no point being cold, just to say I've saved a few bob. I originally thought to myself - if it costs around the same as oil and we've moved away from fossil fuels then good. I think we've managed that, at least. Also the PV panels will offset some of the cost. But let's be realistic also- heat pumps cost a minimum 3 times that of an oil boiler. It's very unlikely we'll get that back over the lifetime of the product. For underfloor they seem perfect. But for rads…Mmmm

What size house are you heating ?

180sqm standalone house, rural location.

I was going to wait another couple of weeks to get a full year's worth of data before analysing the results, but since this thread is getting some interest, I will post my findings from changing my Heat Pump strategy.

In summary, early last October I switched to a smart tariff and, as a result, changed how I use my heat pump. Previously, I just let it do its thing, heating water and the house whenever required. For example, if a thermostat in just one room called for heat, the heat pump would switch on, and after every shower, it would immediately boost the hot water back up to the set temperature. After doing some research (with sources like Heat Geek and lads on Boards.ie), I decided to switch to a new approach to build up the house's thermal mass. I now force all my heating zones to open at the same time to heat the entire house in one go. This is primarily done during the super-low EV rate at night (6.5 cent/kWh). I also scheduled the domestic hot water (DHW) to reheat only during this time, with an additional one-hour slot at midday to hopefully take advantage of any solar PV generation and the warmest part of the day.

I've found it to be a great success. I have reduced my actual heat pump consumption by 25% and reduced my heat pump costs by 33%.

The graph shows the moving 365-day average daily cost for my heating and DHW over the past four years. You can see my daily average starting to drop from early October last year, and I expect it will begin to flatten out now.

I do think there are more savings to be had. My strategy isn't very "smart" yet. When the heating season comes on, I have to manually set the timer on each room thermostat (I have 12 zones), so making any changes requires going around to each one. I bought little Shelly relays that I was going to replace the stats with, but the missus wasn't keen on me blanking over the walls where the stats are. I reckon I could reduce my heating costs even more by using a system that predicts the next day's weather, so maybe I will look into it again.

Here is my 365 days moving average of my daily HP consumption, I have reduced this by 25% approx

@championc regarding SCOP for my HP here are pictures of the energy consumed and energy produced from the HP, for 2024 I think its saying maybe a SCOP of 4.5…thats very good if thats the case

I assume you've underfloor heating is that right?

yeah with underfloor i would expect some significant savings if e.g. someone was heating at night rate and then just needing a small top up in the evening as the thermal mass becomes exhausted. But with rads I don't think there's any magic bullet or strategy to get, e.g. a 15% improvement. Unless I'm missing something. I'm willing to experiment.

Yep it's why smart meters can be useful. I turn on heating during night rate and in real.cold weather I will leave run til noon maybe so most of the hard work done by the heat pump will be night rate.

same as discussed running HP at night for bones of 8 years. other than v cold periods the HP would run very little to nothing on day rate. (I do let the hot water do its own thing as it uses very little electricity anyway, just force it to top up before day rate comes on) Didn't move to a smart rate of cheaper windows as I didn't think the windows were long enough and had a higher 'peak times' I did the maths last year and my total heating and hot water costs were sub 500 euro for the year. that's before you even look at the offsetting my solar is doing.

I use the ecodan app for any changes in setup so very very handy. or even running reports. hopefully we'll be a bit into October before I change it to winter settings. Since April any heating has been off.

Sorry if I'm being a little slow,, but how come your 2025 analysis chart has data points in December when we haven't reached that point yet?

Also I assume you are 0 kWh for the spring and summer because the battery is covering the daily usage is that right?

How are people's HP's running?

How many kWh's this month for example?

@andyd12 So far this month 62 kWh..

only put on the heating yesterday for an hour at 4-5am. Didnt really need to put in on but at 6cent a kWh it was only 2.5kWh in total so cost me only 15cent so why not put it on!!. This is to start building up the thermal mass in the slabs and take the small bit of chill in the moring

31.5kWh so far this month, 2006 165m2 bungalow.

22.1kWh heating, 9.4kWh hot water

I'm 105kwh for October so far, much the same as you... Keep the house between 20 and 21 downstairs and 18-19 upstairs. Rads, no underfloor.

As I've no thermal mass there's not much else to be done, already A1.

Thanks. Any tips/videos on how to do that?

just get some home assistant compatible stats and compare their readings to the ones in the wall (also have a gun type thermometer for sense check)