Most efficient way to run underfloor heating

matelodave

Can you put up a piccy of your "hand held" thermostat. I cant quite understand what you've got or exactly what you are doing with it

BTW my heating chewed its way through 42kwh on Monday this week compared to an average of around 20kwh/day last week.

Don't get too hung up on short term measurements try to see what its averaging over a day, week or even a month. daily measurements help when you are making minor tweaks but don't give you the whole picture and as I said previously give adjustments enough time to take effect taking account of outside influences such as the weather. The power consumption of heatpumps are particularly sensitive to weather and temperature variations even though the heating response time might be quite slow.

My average household consumption is around 20kwh/day over the whole year but that includes really cold days when it's been as high as 60kwh (it was -14 outside then) and in the summer when we are on holiday and it drops to around 3kwh/day

dllive

This is what I mean by the  "hand held" thermostat. 

This is the one thing I have worked-out! Ive got it programmed to change the temp at different points in the day. 5am I have it come on at 20 degrees; then at 12pm it reduces to 17 degrees; then at 6pm it increases to 20 degrees; then at 10pm it reduces to 16.
I use the TRVs to fine tune it. I usually go no lower than 2 and no higher than 4.

I noticed when I reduced the flow temp by -5 that upstairs was really cold. (my office is upstairs so Im here all the time). But yesterday/today its been ok. So perhaps Ill increase it by a few degrees.

You say "...when the sterilisation function is activated, but only to get it from 55 to 60 so it's only on for 30 minutes a week. I can decide when I want it to sterilise and the temperature but it does it every week, I cant extend." By what you said in an earlier post I thought you had your legionella set to come on once every 14 days. Thats why I reduced mine to only come on every 14 days. (The videos Ive seen all say to do it 60 degrees for 1 hour each week. But perhaps thats overkill?). Like you say, I want to reduce as much as possible the immersion coming on!

matelodave

The so called handheld remote control is a room thermostat and really should be on a wall or somewhere it can sense sense the temperature of the place that you are trying to heat.

It turns the heatpump on and off and enables the flow through the radiators- it wont work stuffed in a drawer or cupboard.or even downstairs if its supposed to be controlling the upstairs zone.
You can put it on a shelf or on top of summat (ours are on shelves rather than on the wall but in a place where they can sense the room temperature and have air circulate around them)
. 
Dont put it on a windowsill, too close to a doorway or where the sun can shine on it either.

Put it in your office if that's the room you are most concerned about and, if you want your office to be warmer than 17 degrees during the afternoon, then dont turn it down. Make sure that the TRV in the room where you put the thermostat is fully wide open otherwise they'll fight each other for control and affect the other rooms on the same zone.

Set it up so the temperature doesn't drop below about 17 and bear in mind that the rads are still going to be slow to heat the room but possibly not as slow as the underfloor so give it adequate time to try and recover the room temps.
See how that goes and if it's not enough then you can tweak your compensation off-set from 5 to 4 and see how it affects things. Recognising that every increase by 1 degree will increase your consumption by about 2.5%.so small adjustments can make a big difference to your consumption  

You are trying to get a happy balance between the lowest flow temp you can get away with commensurate with adequate comfort and it can take a few weeks to get it just right.
It's not made easier when there are 10-15 degree variations in the outside temperature between one day and the next and the heat pump is trying to compensate for them whilst you are attempting to set up your controls..

Although my heatpump can only run the sterilisation function once a week there's no need to do it that often, once a fortnight is enough and some even stretch it to once a month. You do what ever you feel is appropriate

TBH I'm not convinced that it even needs it with a direct water tank where the tank is constantly replenished direct from the mains and the water isn't really stored for more than a couple of days but as the water is stored at less than 60c it's probably a good idea to do it occasionally.

dllive

Yes, I couldnt have picked a worse year to tweak the settings! Mon/Tues was really cold with ice on the roads. Yesterday and today has been quite pleasant! But Ill continue to take meters readings.

Ill bore/update you in due course! 

matelodave

Glad to hear how you get on and possibly others might get a better insight on how people set up their systems

It took my my first winter to get mine somewhere about right but I did have the advantage of borrowing a multichannel data logger so I could monitor about five different temperatures all at the same time and plot item all on a graph.
The second winter had a few minor tweaks so I could remember what I'd adjusted and what the result was (I've still got my tweaking spreadsheets - how sad is that?) but it does help you go back to where you started just in case you do foul it up.
I haven't adjusted any setting for about eight years although we might occasionally give ourselves an extra hour if we stay up late 
I now set the holiday function on the stats if we go away to turn the heating back on at least 24 hours before we get home. The first year I turned it down too far and it took 48 hours to reheat the place (but it was 2010 and exceptionally cold).

I've also disabled the 6kw back-up heater so it cant use it to supplement the heating - that kicked in a few times when it got cold but TBH it's only necessary if the heatpump is undersized or you are trying to achieve high heating flow temperatures.

The hot water tank immersion is still used for sterilisation.

dllive

By way of update:
Im keeping a log of meter readings and will check each monday (checking daily is overkill at the moment, and leaving 7 days between readings smooths any extremes in weather or other factors). My first 2 readings there is only 4 days between because, but from now on it will be 7.

10 Dec

Immersion: 220.64

Heat pump: 8105.48
Consumed: 243 (DHW 27; Heating: 215)
Delivered: 479 (DHW 73; Heating: 406);

COP = 1.97

14 Dec

Immersion: 220.64

Heat pump: 8171.05
Consumed: 320 (DHW 35; Heating: 284)
Delivered: 641 (DHW 95; Heating: 545);

COP = 2

Am I calculating those COPs correctly? If so, reducing frequency of sterilisation, reducing curve by 5 degrees, putting UFH on at a constant 17 degrees in one zone - has increased my COP by 0.4. (obviously, very roughly!)

matelodave

Yes - COP = energy out/energy in.

Dont forget that you are also using heating upstairs as well so a bit of a tweak of timing and temperatures up there will also affect your COP.
You do have the advantage that you unit gives you heat output info which makes it much easier to see what is going on - I have to try and guess mine based on my EPC and the electricity consumption of the heatpump. My RHI is based on a deemed COP of 2.5. It will also be a worse at this time of the year than it is in the spring to autumn months.

You may be interested on this performance graph based on predicted consumption compared with actual consumption (base on whats called degree days) It's collects meter readings and takes into account a base load of about 7kwh a day and works out how much energy I need to heat our place. It's not 100% accurate because it can't take into account the weeks when my wife goes mad with the washing machine and tumble dryer but it does give an idea how well the consumption tracks the weather. The extreme peaks are usually when we've got the family staying and we are using significantly more energy. (the green blob is the last seven days, which although ever so cold shows that we were slightly below target even though we used 240kwh) Note the dots are degree days v consumption so the left side corresponds to warmer days (ie the summer) moving towards cold days.

dllive

"Dont forget that you are also using heating upstairs as well so a bit of a tweak of timing and temperatures up there will also affect your COP."
I should do this via my handheld stat? (Im sure this is the case). Perhaps I can reduce by a degree or 2, or restrict the times a bit. I could probably have the timer stop early because there not much point having the heating on when Im in bed.

"You do have the advantage that you unit gives you heat output info which makes it much easier to see what is going on"
Its quite an impressive piece of kit. The installers said it was the latest model from Mitsubishi. The fact that its taken me 2 years before starting to understand how it works is quite shameful! 

Thanks for the chart. I think I can see what its illustrating. I shall digest it fully later. 

matelodave

I know it sounds a bit difficult to understand, but running the heatpump for longer at a lower flow temperature is better than just turning the stats on and off. Turn them down a degree or two but run them longer so the heatpump doesn't have to work so hard. You want it cruising gently rather than trying to heat the place rapidly after its cooled down overnight or during the day.(
200miles up the M1 at 90mph could cost you nearly twice as much as cruising up at 40-50 - you'll still get there at a slower speed, it's just take a bit longer and save you money)

If you can get you temps about right, try taking just one degree off the flow temp and see how that affects the temperatures in the house. It really is a case of minor tweak downwards until you are cold and then just adding a degree at a time until you are comfortable. My lounge drops to 17 overnight but is back up to 19 by late afternoon and then maintains it until bedtime. If I shut it down below 17 it wont get back up to temp by the time we are sitting down in the evening unless I wind the flow temperature up and that has a really adverse effect on the COP

dllive

Yes, it really is a paradigm shift in thinking isnt it? Even though I know the theory, I find myself turning the radiators down thinking it saves money, whereas Im probably using up more energy by doing so!! It is counter-intutive!

I find a constant 17 degrees downstairs is adequate. (Perhaps Im naturally cold-blooded. It has been mentioned! )

My next tweak will be to increase the temps upstairs by a degree or 2. Ive found that - since reducing the curve by 5 degrees - its been a bit chilly (even for me!).

Since reducing the curve, Ive also found that the water is slightly too tepid to do washing-up. Although - oddly - Ive noticed no difference during showers/baths.