Most efficient way to run underfloor heating

dllive

Ive just taken my weekly meter readings.

We have had very cold weather recently so - as you say - Im not getting too hung up on COP. My COP for the past week has been 1.93 (2.26 for DHW and 1.91 for heating).

Interesting to see the immersion heater figure has crept up by 2.18kwh . I doubt this is to do with the legionaire purge. More likely - becuase its been so cold - the boost/backup heater has kicked-in at some point.

Ive just taken it off Weather Compensation and set the flor to 40 degrees (as you suggest). Do I keep that on continuously or set it on a scheduler?

What energy company are you with? 12.5p/kwh is very reasonable. Im with Igloo and currently pay 15.54p/kWh (plus 22.6p per day standing charge). I compared Igloo to other companies using the Cheap Energy Club comparison, and even OutFoxTheMarket cant beat that. The only companies that can beat Igloo are ones which have no reviews.

vacheron

As you have discovered underfloor heating is a  and each one is different. The primary leaning curve is tuning the slow thermal response of the system so that you have heat when you need it and not when you don't.

The time for the temperature to rise and fall depends on many factors including the mass of the floor, the initial temperature of the floor, the amount of energy delved into the system, the insulation below and to the sides of the floor and the amount of insulation offered by the flooring you have fitted. 

Ours is a wet system in an extension and is ran as a second zone but from a gas system boiler rather than a heat pump, with the first zone being the rest of the house which is on radiators.

Our method now is to blast the UFH from about 6am-8am along with the central heating and that charges it up the temperature in the screed floor making it effectively a 7 ton storage heater. This stored heat will then see us through the day at 20-20.5 degrees.

Using very crude assumptions, we have a 19kw boiler and run it for 2 hours, so with say 75% efficiency factor, we are probably putting about 30KWh of heat into the floor in the mornings which sees us through the day (our UFH floor area is about 55m2), at a cost of around £1 for the gas @ 2.6p per KWh.

matelodave

vacheron said:

As you have discovered underfloor heating is a  and each one is different. The primary leaning curve is tuning the slow thermal response of the system so that you have heat when you need it and not when you don't.

The time for the temperature to rise and fall depends on many factors including the mass of the floor, the initial temperature of the floor, the amount of energy delved into the system, the insulation below and to the sides of the floor and the amount of insulation offered by the flooring you have fitted. 

Ours is a wet system in an extension and is ran as a second zone but from a gas system boiler rather than a heat pump, with the first zone being the rest of the house which is on radiators.

Our method now is to blast the UFH from about 6am-8am along with the central heating and that charges it up the temperature in the screed floor making it effectively a 7 ton storage heater. This stored heat will then see us through the day at 20-20.5 degrees.

Using very crude assumptions, we have a 19kw boiler and run it for 2 hours, so with say 75% efficiency factor, we are probably putting about 30KWh of heat into the floor in the mornings which sees us through the day (our UFH floor area is about 55m2), at a cost of around £1 for the gas @ 2.6p per KWh.

You cant do that with a heatpump, they don't run at the same temperature as your boiler and generally aren't sized anywhere near 19kw either. If you wind up the flow temperature then the efficiency drops off very rapidly increasing the energy cost dramatically.

matelodave

dllive said:

Ive just taken my weekly meter readings.

We have had very cold weather recently so - as you say - Im not getting too hung up on COP. My COP for the past week has been 1.93 (2.26 for DHW and 1.91 for heating).

Interesting to see the immersion heater figure has crept up by 2.18kwh . I doubt this is to do with the legionaire purge. More likely - becuase its been so cold - the boost/backup heater has kicked-in at some point.

Ive just taken it off Weather Compensation and set the flor to 40 degrees (as you suggest). Do I keep that on continuously or set it on a scheduler?

What energy company are you with? 12.5p/kwh is very reasonable. Im with Igloo and currently pay 15.54p/kWh (plus 22.6p per day standing charge). I compared Igloo to other companies using the Cheap Energy Club comparison, and even OutFoxTheMarket cant beat that. The only companies that can beat Igloo are ones which have no reviews.

If you've got a schedule timer than you could try reducing the flow temp overnight by a few degrees and then see how that affects both your reheat times and power consumption. I've got an Efergy Engage energy monitor clamped onto the main feed to my heatpump which allows me to see whats happening to my power consumption in a graphical format.

Last night the heatpump idled away overnight (temperature compensated) and averaged about 08kw (but that keeping the whole place above 18 degrees)
I'll put up a couple of graphs in a few minutes which should hopefully show the power consumption since midnight and the heatpump flow temp and the temp in my wife's study which I fixed at a permanent 20 degrees to see what happens.

I'm presently with Neon Reef on their Aqua One tariff, which is presently 12.25/kwh 7 13p/day standing charge - I dont know it that is still available. I was with Symbio and before that Eversmart and before that IRESA (both Eversmart and IRESA have gone bust).
I just go with the cheapest I can get and put up with any aggro when they go bust - which, TBH isn't really a problem if you keep a close eye on your bills and make sure you download and save all you bills and stataes

matelodave

Have a look at these graphs to see how the energy consumption tracks the temperatures and how the flow temp moves up and down depending on the load and what is happening outside (unfortunately I dont have an outside sensor - it packed up several months ago). They wont help you much except that you'll see how the heatpump tries to maintain as low a flow  temp as possible based on on outside influences.

The top graph shows the flow temp from midnight. the peak between 04:30 and around 06:00 is the hot water tank heating. Although the tank temp is set to 45, the heatpump overshoots that to ensure that the tank gets up to temperature. Everything in the house is set to 18 degrees and come up to 19-20 round about 7am except the study (see the lower trace) which I've experimentally fixed at 20 although you can see that because of the fairly low flow temp ovenight it's not actually attaining 20, but is slowly recovering during the day (it a difficult room to heat as its on the north side of the house)

The second graph shows the energy consumption during the same period and indicates when the pump is working much harder.

Gerry1

dllive said:

Im with Igloo and currently pay 15.54p/kWh (plus 22.6p per day standing charge). I compared Igloo to other companies using the Cheap Energy Club comparison

Try using Citizens Advice and 'Switch with Which?'.

dllive

Its been a week since I took the system off the Comp. Curve and have a constant Flow Temp of 40 degrees. I know we're talking very short timescales, so these figures arent accurate, but its interesting to see the COP go from 1.93 to 2.07.

Next Im going to try and setup a scheduler on the Ecodan so that the system is always on, but during the night when the upstairs stat is set to 14.5 degrees, Ill reduce from 40 degrees to 30 degrees. Theres no need for the flow temp to be at a constant 40 degrees 24/7.

As a slight aside, should I cover the exposed brass/metal bit on the system:

As Ive said in earlier posts, the garage is always warm, which is quite nice, but surely it shows the heat is 'leaking' from the system. The installer did lag most of the pipework (as you can see) but left the other bits. I dont know if he did that for a reason, or whether he just didnt bother. I thought about wrapping a few old tshirts or something around the brass bits just to help the system retain a bit more heat. (?)

matelodave

It's worth insulating any pipework that gets warm or hot - just buy proper pipe insulation rather than faffing around with T shirts, it's not everso expensive and much more effective (and it looks tidier)

Try all sorts of different settings and timer settings to see which works best, both with improving your COP but making sure that you keep reasonable reheat times especially if you let the place get quite cold overnight.

Dont forget to keep notes so you can see what effect different settings an timing have (ensure you record the outside temp as well)
Hopefully you are now a lot more comfortable with how it performs and more confident in tweaking it to get it operating to suite you rather than just leaving it on default. You shouldn't need to adjust much if at all after you've got it  set up.

We have our controller inside the house, so if it gets too cold (-5 outside on Saturday) I just tweak up the flow temp by a couple of degrees - the schedule timer sets it back to normal when the next sequence comes around, so don't  be afraid to use it as well. Mine is still on weather comp so today its about 6 degrees outside and the flow is down to 32 degrees whereas Saturday it was -5 with a flow of about 42)

dllive

Thanks @matelodave . Yes, Im certainly more comfortable tweaking settings and understanding how it all works together. (mostly thanks to you!). I just need to find a way to increase the COP so its getting closer to 3 or - preferably - more!

I thought it worth asking the question about lagging the exposed brass bits because I wasnt sure whether they were left exposed for a reason. But it doesnt sound like thats the case.

Ill give another update in a couple of weeks. (Something for you to look forward to!  ) 

matelodave

I think you'll struggle to achieve a COP of three at this time of the year, especially when the outside temperature is below 7-8 degrees. You also need to take into account the other stuff that's consuming power when the heatpump is running, pumps etc. and there might be a crankcase heater which will also use power.

Mine was also doing a fair bit of defrosting on Saturday - it was really damp, cold and foggy and there was ice build up on the evaporator coils so it reverses for a few minutes to warm it up and disperse the ice which I'm sure doesnt enhance the COP much