Heat Pump Running Costs

The theory is that you reduce the number of heating zones in your house down to one if not two…the problem is if you have too many zones your HP could be coming on an off a lot and HPs work best in a low and steady state. Also what will happen if a heat stat comes on in your living room and its only calling for heat in your living room, then naturally the heat will transfer out of the living room to other rooms (unless its sealed very well!), thus that living room in effect is trying to heat all the house and might not get up to the set temp. There is a technical issue here also if you are heating one room as well, in that the flow temp and the return temp will become less and less and HPs need the return flow temp to be a good few degres less in order for the HP to work efficently.

With an open loop you keep all the zones open so when the HP comes on its heating the entire house (not just one room) so the whole house comes up to the set temp. The HP should work as efficent as possible because its getting the required flow rates and return flow temp differential will be optimal.

To do this there are a number of ways, some are technical in that you remove all the acuators that control the heating valves so they are all open or install a fancy heating control system that will alow this or you do what I did and trick it into doing it…

In my case I have 12 zones😯 (220m2 A1 (A2 without PV!)) house and what I have done is artfically set the room temps to a high value and set the heating to come on at set times so when the heating comes on it comes on for all the house. My aim is cost reduction so I have it coming on at my EV rate which is 6.33c kWh between 3-5am but its heating the entire house to build thermal mass. This then lasts me well into the evening, at 7pm then after peak rates it comes back on again for a couple of hours, again all zones on. It seems to be working well enough, Im not doing much more than 20 kWh/day and is a lot better than last winter where I had the 12 zones working independantly.

With this cold weather I think I will have to turn on the heating earlier in evening for another hour or two as I did feel in one or two rooms it was getting below what I would like (20deg). BUT if I am doing this I will mannually turn on the stats in as many rooms as possible. If the HP is on then its heating the entire house…my method requires a bit of attention but it interests me

I will post more data after this week is over to see how I did

(forget about that spike in the graph thats a data error 😪)

Removing the actuator heads i find was easy way to create the open loop. You can use the flow meters on manifold then to direct more heat to different parts. I have my kitchen and sitting room where we are most at 23/22 ish respectively. Master Bedroom at 20/21 and other rooms we don't use i have less flow going to them so they sitting at 18 approx. Ye are lucky who have partners that like the house at 20, herself likes 22/23, much less the hoody is on. 1 programmable stat runs the house, set at these outside temps 11pm - 1pm @ 31deg flow temp. Mostly night rate when heat pump working hardest initially after starting up.

Its costing in these temps approx 28kwh for 242sqm bungalow and mostly nightrate so im happy enough even if it costs bit more. Sitting room may drop to 21.5 and kitchen to 22.5 at times, when running for set period it doesn't maintain exact temp. But kitchen was 22 this morning when i got up and sitting room 21. By 1pm both will be up another degree and will maintain that more or less until it comes on again at 11pm. I do think 20deg is bit chilly to watch tv, i go around in shorts and t shirt in house.

How on earth did you get your underfloor to get to 40 degrees?I have an ecodan with underfloor and a large slab. I actually want to yo get it to 50 degree to avail of cheap night but it simply will not do it unless it's on for days.

There seems to be something inbuilt that only allows the flow temp to it to be approx 5 degrees higher than return temp. This means my return temp would have to be 35 degrees if I wanted 40 degrees flow temp. And my slab would have to be 35 degrees then and the house would be unbearable hot. It would take a few days to do this too.

If my floor is say 21 degrees the highest flow temp I can get would be approx 26 degrees even if I have it set to 40 degrees.

Somehow your ecodan will put in flow temps more than delta t of 5?? Would love to see your old settings.

These were the readings a few months into winter for our new build, the tile floors would be absolutely roasting.

I turned off auto adapt by a dip switch as the more I read about auto adapt the more it seemed like it was designed for a radiator built system and not for underfloor heating. I then experimented with fixed flow temps and weather compensation, but in the end went with fixed flow.

I believe it was the auto adapt that was letting the flow temp so high.

Our first Dec we used 363kWh, this Dec we used 185 kW just about half of that first year that the installer set up.

COP that Dec was 2.60(with auto adapt), COP this Dec was 4.69

Yes all valves are open on manifold and no trv's. I want the whole slab to heat up and and use it as a thermal store thru out the day. I dont want any cold rooms stealing heat from the rest of the building fabric.

I turned off both heaters for underfloor and hot water in settings, so that wasn't my issue. My system came with auto adaptation mode set to on. I'm not sure if this defaults to on or off but I subsequently found out it should only be used for rads and not underfloor heating.

I had to manually turn to off dip switch SW5-2 to turn off auto adaptation mode. This solved my sky high energy usage. Then it was just a matter of tweaking the system.

Yesterday was probably as bad a day for running a heat pump in the midlands as any, freezing fog and temp not above 0° all day.

Consumed 32.35kWh, producing 108.6kWh for both heating and hot water so giving a COP of 3.37.

Total cost for all electricity was €11.88 which includes EV charging on the 4 hour EV rate. Produced about 2.8kWh from the PV.

First things first I am no expert in heat pumps just a grumpy dad messing with the heating trying to save money.... 😋

Anyway on a typical winters day mid to high single digits and above the heating (not including DHW) alone runs for 2 hours at night (3-5am) and then for 2.5 hours from 19:00 to 21:30 so that's 5.5 hours in total. Up until this week where we had the artic vortex this was working great for my house. I am sure on warmer winters days I could cut back on this but I just leave it alone for now. I would really like to automate it more in Home Assistant like predicting the next days weather etc and I had plans for this but her indoors put a stop to it😪

I am not running fixed flow temps there is weather compensation on the HP so it goes higher for colder weather and lower for the milder weather. For example this evening the flow temp is 35 -36 degs and its about 0 degs outside.

Like you in the evening I do spilt the heating and concentrate on downstairs for the first 1.5 hours, then overlap for a half hour then only upstairs….I initially had all the zones on but I thought it wasn't heating up as fast downstairs when we needed it. At night its all on!! I count the EV rate at 6.5cent as almost free heating.

What I would say every house is different with different layouts so at the end of the day it what works best for you and its trial and error. Given that you have rads upstairs in the bedroom I would think leaving these this last in the evening is a good strategy.

I do think though that if the HP is on then you need to be heating as much area as possible so one room is not stealing heat from another room. I think you can have systems that outputs really low flow temps and are literally on all day long but just tip away on the background and I might be able to trick my HP into that but I don't think there is any need for my house.

There is a poster on here @championc and he posts his live data from his heat pump and you can see his flow temps and all the data here is a link to the thread its in the plumbing forum, so you might get some more insights.

My DIY installed Vaillant AroTherm Plus is now LIVE — boards.ie - Now Ye're Talkin'

and a link to his live HP data

https://emoncms.org/app/view?name=championc&readkey=5e5a2bd11d69740be46a55e1793e551d

Would be interesting to know how high your consumption went to keep house at 23' in minus conditions this week? 23' for most might be a bit uncomfortable heat wise. each to their own but I would say 20'c is probably the sweet spot. I know I generally have a daily usage of about 10kwh to maintain 19.5'/20' In normal winter conditions. That went top to about 30kwh daily this week. if I wanted 23' id be doubling that I would think.

Kitchen area 22/23 and sitting room 21/22 this week.I don't keep them at that,it's what they get to from running all night. Yesterday approx 34 mostly night rate, not bad as it's bungalow so heating whole house 242sqm. Bedrooms generally 20. I'd find 20 bit chilly watching tv in shorts, 22 I'd consider sweet spot.

Is that 120kWh for the day!!

Tbh, sounds like your install sizing was just about perfect. It was exceptionally cold yesterday, the country hits -10C maybe only once in a decade. Sizing your system for an outlier cold day would make it less efficient the rest of the time.

19.5C is still comfortable enough imho. If that is not enough, buy a couple of €10 fan heaters in power city for the next time it gets this cold, maybe sometime between 2030 and 2040 😂