Electric Heating

[JohnMo]

As a follow on from my previous topic on our summer room, which the wife uses as healing space.

We installed UFH, which was to be run from the house heating system, but unfortunately the heat output of the system is pretty rubbish (due to the low flow temps for the house. Only getting the summer house to 15 degs.  So purchased an electric radiator. Thought buy a decent one, so opted for a Dimplex. It has a built in timer and thermostat.

 

One basic issue is the thermostat is built into the unit, so is measuring the temperature local to the radiator, not the room temperature. Room heat up time seemed very long, temp variable in the room.

 

So solution was it install a wireless thermostat (has 16A switching capacity) - I had left over from the house build. A Salus WQ610RF, which comes with a self learning algorithm for electric heating and has predicted stop and start, so room learns when to start and stop heating.

 

So thermostat on radiator is set to maximum, and timer is disabled. All programs are run from the thermostat.

 

Screenshot of the heater activity (smart plug) prior to modification, lots of starts and stops of the heater, as a result heat up time was very long and room temperature varied quite a bit.

 

After modifications, nice long heater run to get room up to temp quickly. Very short on off periods to keep room temp stable. Also note the power input seems to be modulated as same power setting is used on the heater.

Edited October 18, 2023 by JohnMo

[JohnMo]

The thermostat

 

 

[Iceverge]

1 hour ago, JohnMo said:

due to the low flow temps for the house

 

What are you using as a flow temp? 

 

Is the floating floor of OSB to insulative for UFH do you think?

 

 

[JohnMo]

4 minutes ago, Iceverge said:

 

What are you using as a flow temp? 

 

Is the floating floor of OSB to insulative for UFH do you think?

 

 

Tried up to 32 flow temp, but house was getting way to hot, and that was about 3-4 degs outside, think the summer house got to 14 deg after 24 hrs. Think the two layers of OSB and the laminate floor (and its underlay) are just to much for the low flow temps to break through.  Would need a min flow temp of about 35 and above to make a dent in the heating. That's too hot for the house.

 

The other issue is the house heating needs are so low and we are not needing the heating on for long. Did try to run the heat pump 24/7, running at the lowest flow temp (25), but the ASHP was below min output modulation, so ran for 20 mins and 40 mins off - so wasn't much use, could run the house like that, but didn't seem the most effective, as each start/stop cycle dents the efficiency. Found the happy temp for the heat pump is 28 or higher and it would run almost non stop over many hours, so have a WC curve set to 28 deg when it's 10 degs (OAT) and above, and at -8 to run at 36 degs and I am going back to batch charging the floor of the house overnight. Found this worked well at the end of the last heating season with the gas boiler.

 

Have set the inside thermostat to force floor charging overnight if at midnight the house is below 19.4 Degs and at 7am the thermostat reverts to 18.5 deg to effectively force the heating cycle to stop.  If the OAT well below zero and the house hasn't exceeded 18.5 deg, the heating would just stay on as long as required. - basically getting ready for E7 in a week or so.

 

The other night the OAT dropped to 1 deg and the heat pump charged the floor, running continuously for 5.5 hrs, then not starting again for 24hrs and only ran for a 1-1/4 hours.  Good thing so far is no defrosts have been needed, when it was 1 deg OAT, I went to have a look for frost on the evaporator and it was completely frost free.

[Iceverge]

You seem to have the house dialled in nicely. 

 

Shame about the summer house. I like the idea of the OSB over foam from a low carbon, dry install and soft floor perspective. Perhaps coupled to a super large radiator it may be a runner rather than UFH?

 

What COP do you reckon you'll average for the ASHP and how thick is your screed/slab?

 

 

[JohnMo]

1 hour ago, Iceverge said:

You seem to have the house dialled in nicely. 

 

Shame about the summer house. I like the idea of the OSB over foam from a low carbon, dry install and soft floor perspective. Perhaps coupled to a super large radiator it may be a runner rather than UFH?

 

What COP do you reckon you'll average for the ASHP and how thick is your screed/slab?

 

 

 

Concrete screed is 100mm thick.

 

Have an electric meter dedicated to the heat pump and all its associated controls etc. All the discussion below relates to house heating not DHW.

 

Had a couple of days at a very steady 7 degs, so ran steady state for 26 hrs (but that included heating around 50T of concrete floor up from about 18 degs to 23 degs, a check on CoP that was about 4.2, when comparing calculated heat loss compared to electric consumption. So straight electric consumption for 26hrs running was 13.1kWh - Heat pump heating cycle was basically one on/off cycle per hour. Theoretical CoP should have a little over 5.

 

The batch heating is a bit of a funny one, because on the face value the CoP is not as good as running for 24/7. But the run hours are way less, less than 7hr compared to 24hrs per day and during batch charging each run cycle was continuous, with no stop starts. But if it's cold the crankcase heater is on when you are standing idle, so is using electric.

 

On the 15th at 5pm the heat pump stopped house heating. The meter read was 625.21kWh. Made some changes to force it to batch charge only including changing the WC curve.

 

A reread of the meter just now and its on 638.2kWh, so 13kWh used over a period of 3 days and 4 hrs.  ASHP run time was only 6.75 hrs of that, the crankcase heater on for remainder.

 

If the heat pump was delivering it's full rated capacity for 6.75 hrs, that's 40.5 kWh, so CoP 3.1 including running the crankcase heater. But running for only 6.75 hrs, compared to running 24/7 over those 3 days if I ran normal WC, about 70 stop/start cycles instead of 2.

 

Or comparing average consumption per hour, 24/7 running is 0.5kWh. Batch heating is equivalent of 0.17kWh per hour. Not sure how accurate that is, due to different temperatures and solar gain, but will monitor.

 

[JohnMo]

Tested the intelligent startup this morning, setting the start time early this morning. The overnight garden room temp set to 16 degs, the day time temp at 21 degs.  The thick solid band is where the heater started to heat to 21, which was about 1.5hrs prior to its program to increase from 16 to 21 degrees. This should self learn and get closer to starting just in time to have the room temperature when we need it.

 

Interesting is the amount of stop starts the heater does to keep the room temperature stable.

 

 

A bigger view, based on the 1/2 hr usage in kWh. The calculation for heat loss, says I should have been using 430W and the electric input seems to back that up quite closely.

[JohnMo]

22 hours ago, Iceverge said:

Perhaps coupled to a super large radiator it may be a runner rather than UFH?

Had a look at this early today and worked out I would need two very large radiators at dT5, and not enough space for that. If I go to dT10 I assume the UFH would be ok.

 

22 hours ago, Iceverge said:

What COP do you reckon you'll average for the ASHP and how thick is your screed/slab?

Using reasonable heating kWh required and 3 days electric usage, the CoP looks to be averaging a little over 5.1, that's including all the electrical equipment used to heat the house (pumps, thermostats and valves) and all standby losses and the crankcase heater.

[Iceverge]

That's an excellent COP. 

 

For a small project if one wanted a heat pump without a heated slab or DHW an A2A HP would be a simpler proposal I guess. 

[JohnMo]

8 minutes ago, Iceverge said:

A2A HP would be a simpler proposal I guess. 

It certainly would. 

[JohnMo]

So back to square one. Realised I am actually putting more electric into the garden room than the house, with direct heating. Garden room direct electric and house via heat pump.  So have decided to sacrifice a little CoP and increase flow temp. To make this achievable, the house output needs to be reduced quite a bit, so flow rates have been set with a much bigger dT to compensate.

 

Have programmed a different WC curve into ASHP and will monitor and adjust as required. Tonight we are getting down to zero degrees, so a decent test.

[JohnMo]

Well have given up on that idea, had a flow temp of 37 overnight and dT across the floor loops of 3 to maximise the heat output.  Heat pump ran for 12 hours straight slowing only to defrost every hour, as it was zero overnight here.  Floor in garden room got to a massive 18 degs and the room only managed to stay at 16 deg room temp, because I set the thermostat for the electric heater at 16 deg. Think I would need a flow temp of 40+ to keep the garden room floor happy, and that's not going to happen.

 

The house UFH flow rates were reduced to prevent overheating managed to keep house down to around 21. So about to wind everything back again and reset the WC curve.

 

 

[Iceverge]

The nub of the issue here seems to be the limited power transfer capacity of the UFH at low flow temps. I imagine due to the dry install with a very thin insulating layer of air around the pipes and the insulative effect of the OSB and timber floor. 

 

The system would probably work pukka with a gas boiler. 

 

It's a done deal now as I guess you're not going to bother pulling up the floor an a simple resistive rad is so reliable and cheap to buy. 

 

However from a design perspective to maximize the heat transfer power of any UFH system my thoughts would be. 

 

1. Maximise the surface area of the pipes. Longer pipe runs with lower diameter. 

2. Higher conductivity pipes. 

3. Attaching the pipes to mesh as @TerryE did. Perhaps even using an extra roll of chicken mesh or similar to distribute the heat as quickly as possible. 

4. Using a very low viscosity screed to maximise contact area with the pipes when pouring.

5. A dark covered a rougher textured surface to loose heat to the room as quickly as possible. EG slate tiles. 

6. A screed with maximum thermal conductivity like anhydrous screed rather than concrete. 

 

This is of course separate to the energy storage side of a heated slab. 

 

 

 

[JohnMo]

 

31 minutes ago, Iceverge said:

the issue here seems to be the limited power transfer capacity of the UFH at low flow temps

 

Doing it again, I think a screed finish above the pipes, with pipes in full contact with the screed and a bonded down floor covering not floating. Think that would fix the transfer issue.

 

Certainly the sales model with the moulded polystyrene with aluminium spreader plated and 125mm pipe centres sound convincing, but in reality a bag of .....

 

But I think my electric heater and its modified thermostat, will do for now.  Wife is happy!  Basically now set on 16 degs 24/7, if the wife needs to use the room, she just turns up the thermostat an hour before, she needs to be in there.

 

It was 4 to 5 degrees overnight and is currently 11 degrees. Have used about 3kWh in the last 14 hrs. Below is the 30min output from the smart plug. Once I get E7 tariff sorted, all the electric will be cheap rate either from the battery or in the E7 window. So today would have about 50p so far.

 

Since my experiment with running higher flow temps for 24 hrs, the house heating hasn't needed to come on yet. So quite a big mismatch in demand rates.

 

[TerryE]

@JohnMo, sorry but I don't know the details of your house.  I can't recall any topic where you've given an overview of your house characteristics, but I suspect from your general posts that it is a well insulated low-energy build with a decent high thermal capacity slab.  The summer house is well insulated but everything has extremely low thermal capacity so it going to be very different in terms of its response curves.  By way of an example with our Warmslab, the UFH really heats up the concrete in the slab over say 5-7 hour heating period, then the warm floor transfers this heat into the house over the next 18 hours or so.   

 

If not identical then at least your main house UFH at least has 50 mm of concrete to act as a thermal buffer and spread the heat across the floor. However it sounds like you don't have any equivalent high-thermal capacity buffer in your summer house so its heating characteristics will be different in terms of ability to absorb and retransmit heat from the UFH loops to the room environment so hence the different in Δt for the two UFH setups.  It's going to be hard to match the two systems and drive them from the same ASHP without adding a low loss header extra pump and using the manifold TRV on the main house to drop the circulating water temperature.  @Nickfromwales  you have a better idea of this sort of stuff.

[JohnMo]

1 hour ago, TerryE said:

sorry but I don't know the details of your house. 

Hi, house floor 192m2 has 200mm PIR with 100mm concrete floor, with 7 loops at 300mm centres stapled to the insulation. Walls are Durisol, with 50mm service space and plasterboard. Roof is 350mm of spray foam, behind vapour barrier, 50mm service void and plasterboard. All room have high ceilings, so quite a big volume. As you say high thermal inertia house, low inertia summer house. But even running the summer house UFH at 35 for 24+ hrs did very little in the way of heating.

[TerryE]

If you think about the heat flow in the house UFH, you have the UFH loops conducting with roughly semi-radial heat-flow so each metre of pipe warms 0.03m³ concrete which then reradiates from the surface into the living space.  The rebar mesh improves the conductive spread, so this is a very effective store and radiate system.  Your loops are quite long, say around 80m on average and you have 7 in parallel increasing the effective flow cross-section accordingly.  If you get the effective power O/P of the ASHP and the average Δt out : return at the main manifold, then you can estimate your average flow rate.  Ditto for the Summerhouse.  I suspect that with 7 loops your flow vs head is with the tolerances to use a single circulating (?ASHP?) pump and no buffer. 

 

Does the SH only have 1 loop?  Here it is relying on conductive transfer from the UFH runs to the wood flooring without mechanisms for lateral heat dispersion.  Wood isn't a good insulator but it's a lot more of a one than concrete.  It's just not going transer the heat from the UFH floor effectively.  Without separate pumps, mixers and a LLH the main and SH circuits will see the same pump head and so the flow rate in the SH could  also be a lot less than the main house.  

 

Given that the SH has an intrinsically low thermal mass, you could realistically heat it "when occupied", shifted maybe 30-60 min say to take out heating lags, so let's say 5×8 hours per week for maybe 6 months a year.  I suspect that this is going to be a lot less than the amortised cost of trying to complicate the UFH systems.  Though it is probably worth leaving it as-as for basic anti-frost / chill protection and using the heater to lift the temp that extra 8°C or so.

[JohnMo]

8 hours ago, TerryE said:

suspect that with 7 loops your flow vs head is with the tolerances to use a single circulating (?ASHP?) pump and no buffer. 

Yes running everything from the ASHP circulation pump, no buffer. During the test flow temp was around 35, the house flow rate was 12.4L/min and average dT 4.7.

 

The summer house has 2x 50m loops, again driven by the same circulation pump within the ASHP. During the test, I had the flow date quite high in the summer house each loop getting 2.5L/min. The dT in the SH was 2

 

Interesting looking at my house power flows this morning, the ASHP was online from about 1am to 4am, and the there is a corresponding reduction in the start stops of SH heater. With an approximate lag of 1.5 hrs. The heater input dropping from an average of 300W/h to about 160W/h.

 

After I stopped the test, I also reduced the SH UFH loop flow rate to about 1L/min and increased the house flow rates back to around pretest levels, while at the same time reduced the temperature output from the ASHP.

 

[JohnMo]

So since the above, I have now switched to run the heat pump 24/7 under weather compensation (no longer doing batch charging), fairly simple WC starting at +8 OAT and down to -8. Starting flow temp is 29.4 end flow temp at -8 is currently 34.4. Had to make a few changes to the running parameters to get it running right, ASHP now cycling on and off much more at low loads (like it should). So currently about 8 degrees outside and the ASHP cycles to heating mode, running for 15 mins and then, 45 mins off, the circulation pump stays on throughout.

 

The battery and economy 7 able to provide nearly all the electric for the house and heating at the moment, yesterday we imported 2kWh of full price electric. Morning temperature was about 1 deg outside, the highest temp was 8 deg.

 

The starting flow temp of ASHP is higher than I expected but this is due to heat pump running about 15 minutes per hour when it's 8 degs outside and 20 inside. So most the time the water flowing through the UFH is around 23 to 24 degs.

 

Upside of this, is the summer house UFH is able to keep the temp at around 12 degrees, so electric heating only required for those hours the wife is actually using it. Saving 6 to 7kWh of electric per day.

 

Running the ASHP all the time is actually slightly cheaper than batch heating also. So win win.

 

 

[JohnMo]

Mods I made to the electric heater worked well, until the thermostat failed.

 

Had to heat the summer house twice over the last couple of days and used around 14kWh. It is only going to get worse as temperature drop, becuase the the summer house is being used most days.

 

So issues are, I need two very different flow temperatures, one for summer house and a much lower one for the house, the heating season for the summer house is much longer also. So need to make two zones.

 

Since decommissioning the gas boiler, I have an Alpha Flowsmart 50L cylinder, so will repurpose as a buffer, plumbed as a parallel, 2 port across the supply and returns. Will follow the recommendation of Kensa heat pumps complete with PRV (by-pass valve) to engage the buffer only when needed.

 

 

Also in my parts store is an ESBE CUA100 (cheap off eBay a fair while ago). This is an electronic mixer valve, that can be operated in either of two modes, fixed flow temperature or a modulating flow temperature based on house temperature. It incorporates a timer which works in both modes and allows a second temperature to be set. So in theory you can increase the temperature (either house temperature or flow temp) during E7 and lower at other times. So will install this and a pump on the house UFH. The summer house will be run on weather compensation, direct from the ASHP.

 

CUA100_en_F_LR.pdf

 

Just waiting for a new mixer valve to arrive. Controller is installed and everything seems to work, as it should. Have put the controller in the lounge using now defunct thermostat wiring and will use this room as a reference temperature. Will run on house temp mode first to see how it goes. If it not stable, its just a setting change to switch mode.

 

[JohnMo]

Have continued this on a new thread