Posted by: @tufty

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Hi all!

 

Ill quickly explain my situation: The property is 4 bed end of terrace house, 200 years old. Full renovation was carried out 4 years ago. Put loads of insulation in the loft, new double glazed windows, downstairs floor has 240mm insulation and new screed over the top (and UFH). Not much I could do regards the cob walls (I obviously couldnt have cavity wall insulation etc...). As part of the renovation, all new plumbing/wiring. Ecodan 11.2 kW ASHP, a Salus handheld thermostat, new Stelrad radiators with TRVs upstairs and UFH downstairs. The new EPC has a rating of D. 

 

Im 'cold tolerant' and live in the 4 bed house by myself, so I only use 2 bedrooms (1 is my office), sometimes the kitchen and the lounge. I use weather comp with flow temp set at 40c @ 0 outside levelling down to flow temp 25c @ 15 outside.

 

The installers were very attentive on the install and seemed to do a great job. When they finished I was given a (literally!) 5 minute handover talk. The footnotes being "dont touch anything, just let it do its thing".

 

That was 4 years ago. Since then each winter I turn on the heating; and in the summer I turn it off (apart from the DHW obviously). As I say, Im 'cold tolerant'. If theres a cold snap in spring I just put a jumper on.

 

This year I thought I should educate myself better on how to optimise the system. I have a few questions:

 

1. DHW: I currently schedule the water to be heated to 45c for 1 hour every 48 hours. I find this is adequate for shower and daily washing up. Is it better to keep this constantly on and keep the water at a steady 45c? After 48 hours of being off, I find the DHW cylinder temp drops to about 35c. So I suppose the question is: is it more efficient to heat water from 35c to 45c once every 48 hours; or keep the water at a constant 45c?

It's probably better as you have it.  Having it heating every time you use any HW will be less efficient.  Each time it heats water the heating will stop and then have to start up again.  Try and time the HW for the warmest time of the day or when you have the cheaper electricity.

1. How does my handheld Salus thermostat and TRVs work together? Should I just use my TRVs to control the temp? Or just use the Salus? Do the rads even work without the Salus? (ie: is it the Salus that requests the heat from the Ecodan!?)

It's likely that your ASHP is set up to start when it gets a demand for heat from the thermostat.  You should try and use the weather compensation to control the heat in the main part of the house but use TRVs to lower the temp in one or two rooms if you want to.

1. Ive realised that the objective is to get the flow temp as low as possible and the heat pump running 24/7 to prevent the heatpump turning on/off. So the heat pump fan should be running 24/7? At the moment, when I go away for a weekend, I turn the system off. Is 'cycling' when the fan turns off? If so, should I always try to have the fan on by having a low flow temp (via the comp curve as it currently is) and turning up the temperature on my handheld thermostat?

In general it's better to have the ASHP running for longer at lower levels.  This is likely to be more efficient.  It might not use the least energy though. Setting temperature back at night or if you are out often saves energy. When I go away I use holiday mode; it runs at a very low level to keep things moving.  I wouldn't turn off as in power down; maybe turn the thermostats down to 15 deg or so would be a good compromise. 

Cycling is the ASHP turning on and off because its minimum output is more than what is being demanded.  What happens is it overshoots the target flow and has to switch off for a bit then repeats.  It's unavoidable when it's warmer outside; it just needs to be controlled.   A low flow temp and high thermostat setting might cause more cycling because the demand will be low with a low flow temp and the minimum output is more likely to be too high for that low demand.  I found cycling reduced by having flow a little hotter at higher outside temps.  If that makes the house too hot I can limit it with the thermostats.    

1. I feel like these past few winters Ive been very inefficient: Ive been trying to control the costs via the TRVs by having them as low as possible. Have I potentially been generating much more energy than I actually consume by doing this?!

As above, try and control with weather compensation and use the TRVs to make small tweaks

1. When in weather comp mode, is it only my handheld thermostat that tells the Ecodan what temp it is inside? Or is the technology more clever than that somehow?

Unless your handheld is a Mitsubishi one or you have done some clever programming, the Ecodan doesn't know the house temperature.  All it does is switches on and off depending whether there is a demand for heat. While there is a demand it will try to achieve and maintain the target flow.  

Any advice/guidance gratefully received!

 

Cheers

 

It sounds like you are there or thereabouts.  I assume you are running in weather compensation mode and not fixed flow or room temperature.  You might want to try and tinker with the weather compensation so that it gets the house to the temperature you want without relying on the thermostats.  To do this start by turning all the TRVs and thermostats up and see what happens. Then change the curve so that your house temperature is where you want it at a range of outside temperatures. Then use the TRVs to tweak the rooms you want to be cooler.  It takes a bit of trial and error to get this right but it can be worth it. The downside of doing this is that it will take a long time for the house to warm up if it gets cold, especially with your old house and ufh. 

Thanks so much Kev. Very useful!

You say "A low flow temp and high thermostat setting might cause more cycling because the demand will be low with a low flow temp and the minimum output is more likely to be too high for that low demand." . I dont understand (perhaps I need my strong morning coffee!!). Do you mean "... A high flow temp and low thermostat setting..." ?

Yesterday I put my handheld thermostat on at 18 degrees and left it on my desk in the spare room (my office). The TRVs on both radiators are on 2. This morning the house feels comfortable, but the handheld thermostat is showing 17.5, which means the heating has been on all night because the thermostat never reached its target temp of 18c. Is that more efficient than if the stat had reached 18 and the heat pump turned off? Or should I place the handheld thermostat somewhere warmer so the target temp is reached and the pump turns off?

"...To do this start by turning all the TRVs and thermostats up and see what happens. Then change the curve so that your house temperature is where you want it at a range of outside temperatures..." Im certainly going to try this! We've got a few -3c days coming up, so a good time to test.

Last night I put the UFH on for the first time in 2 years. I set the stats at 15c. This morning when I went downstairs - although the floor wasnt warm to the touch - there was a nice ambient warmth. Tonight - when it will have been on for 24 hours - Im going to see what kwh the Ecodan has consumed. Im hoping that because the UFH target temp is only 15c it wont have consumed much. Watch this space!!! 🙂

Posted by: @tufty

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Thanks so much Kev. Very useful!

You say "A low flow temp and high thermostat setting might cause more cycling because the demand will be low with a low flow temp and the minimum output is more likely to be too high for that low demand." . I dont understand (perhaps I need my strong morning coffee!!). Do you mean "... A high flow temp and low thermostat setting..." ?

Yesterday I put my handheld thermostat on at 18 degrees and left it on my desk in the spare room (my office). The TRVs on both radiators are on 2. This morning the house feels comfortable, but the handheld thermostat is showing 17.5, which means the heating has been on all night because the thermostat never reached its target temp of 18c. Is that more efficient than if the stat had reached 18 and the heat pump turned off? Or should I place the handheld thermostat somewhere warmer so the target temp is reached and the pump turns off?

"...To do this start by turning all the TRVs and thermostats up and see what happens. Then change the curve so that your house temperature is where you want it at a range of outside temperatures..." Im certainly going to try this! We've got a few -3c days coming up, so a good time to test.

Last night I put the UFH on for the first time in 2 years. I set the stats at 15c. This morning when I went downstairs - although the floor wasnt warm to the touch - there was a nice ambient warmth. Tonight - when it will have been on for 24 hours - Im going to see what kwh the Ecodan has consumed. Im hoping that because the UFH target temp is only 15c it wont have consumed much. Watch this space!!! 🙂

Most ASHPs can modulate down to about 30-40% of their nominal rating.  So for a 10kW ASHP, 3kW.  If the target flow is 35 deg and the ASHP only needs 2kW to maintain that then it has to cycle.  If you increase the target flow to 40 deg you might find it needs 3kW to maintain that so the ASHP can now run without cycling. Your house will be warmer but you can limit this with the thermostat.  When the thermostat temp is reached, the ASHP switches off.  The theory is that this causes less on and offs than letting the ASHP cycle at lower flow temps.  It's not straightforward though and needs a bit of trial and error.     

You shouldn't put your thermostat somewhere cold and definitely not in a room you have the TRV turned down.  Like you say, this will mean the heating is on all the time and the rest of the house might be too hot. I would put it in the main living area.  Having the ASHP running all the time may be more efficient but it also may use more energy than you need if you're heating the house when you don't need to.  

I took a meter reading today. Ecodan has consumed 32kwh (and delivered 209kwh) in 24 hours to produce 18c on 2 radiators upstairs and UFH downstairs at 15c. The COP is 2.

I dont know if thats good or not, but I suspect not. Ecodan was reporting an outside temp of -3c this morning (which means a flow temp of 40c) so perhaps a COP of 2 is to be expected.

Posted by: @tufty

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I took a meter reading today. Ecodan has consumed 32kwh (and delivered 209kwh) in 24 hours to produce 18c on 2 radiators upstairs and UFH downstairs at 15c. The COP is 2.

I dont know if thats good or not, but I suspect not. Ecodan was reporting an outside temp of -3c this morning (which means a flow temp of 40c) so perhaps a COP of 2 is to be expected.

 

 

 

I suggest that you recheck your figures and/or repeat the test, since something is definitely wrong.

If your heat pump used 32kWh of electricity to produce 209kWh of heat energy, then the COP would be:-

209/32 = 6.53

This is not possible at an outside air temperature of -3C.

Posted by: @derek-m

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Posted by: @tufty

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I took a meter reading today. Ecodan has consumed 32kwh (and delivered 209kwh) in 24 hours to produce 18c on 2 radiators upstairs and UFH downstairs at 15c. The COP is 2.

I dont know if thats good or not, but I suspect not. Ecodan was reporting an outside temp of -3c this morning (which means a flow temp of 40c) so perhaps a COP of 2 is to be expected.

I suggest that you recheck your figures and/or repeat the test, since something is definitely wrong.

If your heat pump used 32kWh of electricity to produce 209kWh of heat energy, then the COP would be:-

209/32 = 6.53

This is not possible at an outside air temperature of -3C.

Ugh, apologies, I mis-spoke.

Since this post Ive kept a daily log:

8 December
Consumed: 76kwh (this was the starting figure showing consumption so far for the month. I hadnt had UFH heating turned on yet, hence why its only 76kwh for 8 days)
Delivered: 136kwh

9 December
Consumed: 108kwh
Delivered: 225kwh
CONSUMED 32Kwh

10 December
Consumed: 150kwh
Delivered: 322kwh
CONSUMED 42Kwh

11 December
Consumed: 188kwh
Delivered: 401kwh
CONSUMED 38Kwh

So for the past 4 days Ive been getting a daily COP of ~2.1.

Its been about zero degrees outside (so the flow temp has been 40c) so perhaps I shoudlnt expect more than a COP of 2.1.

@tufty 

It's an expensive time for ASHPs (and other heating systems).  My COP has been 2.8 for the last 4 days. Lower today I think.

Posted by: @kev-m

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@tufty 

It's an expensive time for ASHPs (and other heating systems).  My COP has been 2.8 for the last 4 days. Lower today I think.

Thanks. Other than lower the flow temp (again) is there anything else I can try on the Ecodan side of things? 

This week I will certainly try to lower the flow temp and turn-up TRVs and thermostats as you suggested above. 👍 I will keep a weekly log between each change I make.

I had a look on the Ecodan to see what the flow temp is when I put it in Holiday Mode. (which is flow temp: 35c; Heating Room temp: 15c). Im away next week so I will put it in Holiday Mode (rather than turning it off like I usually do!) and take a meter reading when Im back so see what energy its used.

Posted by: @tufty

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Posted by: @derek-m

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Posted by: @tufty

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I took a meter reading today. Ecodan has consumed 32kwh (and delivered 209kwh) in 24 hours to produce 18c on 2 radiators upstairs and UFH downstairs at 15c. The COP is 2.

I dont know if thats good or not, but I suspect not. Ecodan was reporting an outside temp of -3c this morning (which means a flow temp of 40c) so perhaps a COP of 2 is to be expected.

I suggest that you recheck your figures and/or repeat the test, since something is definitely wrong.

If your heat pump used 32kWh of electricity to produce 209kWh of heat energy, then the COP would be:-

209/32 = 6.53

This is not possible at an outside air temperature of -3C.

 

Ugh, apologies, I mis-spoke.

Since this post Ive kept a daily log:

8 December
Consumed: 76kwh (this was the starting figure showing consumption so far for the month. I hadnt had UFH heating turned on yet, hence why its only 76kwh for 8 days)
Delivered: 136kwh

9 December
Consumed: 108kwh
Delivered: 225kwh
CONSUMED 32Kwh

10 December
Consumed: 150kwh
Delivered: 322kwh
CONSUMED 42Kwh

11 December
Consumed: 188kwh
Delivered: 401kwh
CONSUMED 38Kwh

So for the past 4 days Ive been getting a daily COP of ~2.1.

Its been about zero degrees outside (so the flow temp has been 40c) so perhaps I shoudlnt expect more than a COP of 2.1.

 

I would have expected a higher COP than 2.1 if your system is operating at maximum efficiency.

Do you have heat loss calculations for your home? What is the size of your home? Do you have a buffer tank or low loss header in your system?

Open all the TRV's fully and set your Salus thermostat to 2C above your desired temperature. Monitor the room and radiator temperatures and see if they start to increase.

Turn the controls up for your UFH.

If the indoor temperatures start to increase then this would indicate that the weather compensation curve is set too high, though if it is truly operate over the range 25C to 40C, I would not expect this to be the case. Monitor the temperatures over quite a number of hours until they stabilise.

Great - thanks Derek - I will do exactly that.

I must say, the installers were really good and knowledgeable. I kept all email correspondence I had with them 4 years ago, so when I get time Ill trawl back through them and see what they say about heat loss calculations etc... I remember they did the heat loss calculations which then dictated what rad sizes I needed in each room.

The floor size (both floors) is 160sq metres. I remember a 'low loss header' was mentioned at some point in the many emails that bounced back n forth. I will investigate further! Thanks!

Hi @Derek M . Ive been keeping daily logs, so thought Id give an update:

Having both the upstairs rads (with TRVs open fully and stat set to 21c) and UFH downstairs set to 15c has been using ~35kwh each day.

I turned off the UFH downstairs as I really dont use downstairs much. This has reduced consumption to ~24kwh.

The stat has never quite reached the target temp of 21c. (perhaps it has and I havnt noticed, but if it has its probably only reached the target temp a couple of times).

I do find that - although its been very nice and toasty these past few days - sometimes its been too hot!! (a nice problem to have!)

Does the following sound sensible: Reduce the whole curve down by 5c (which gives the max flow temp of 35c) and keep the TRVs fully open and leave the stat at 21c? Then reaccess after a few days and see if Im cold (in which case Ill increase the curve up by 3c).

I went into the Holiday Mode settings yesterday and noticed that Holiday Mode sets at Flow temp: 35c. So perhaps Id be better off using it in Holiday Mode!! 🙂

Also, the daily COP has been ~2.1. Im hoping this will increase when the outside temps get above, say, 5c.