Ecodan: clarification needed on flow temp and radiators TRVs

Reed_Richards

chris_n said:

matelodave said: 

I've been experimenting with setting the room stats a degree or two above what we want and allowing the heatpump to control the room temps by the flow temp. It does mean that the pump runs on for a lot longer buts the average power consumption is definitely lower because the heatpump isn't being stopped and started as often (probably saves a lot of wear and tear on the compressor as well).

That is the holy grail of running a heat pump efficiently (assuming it is sized correctly) if you get your compensation curve right you can just let it run and maintain temperature with the lowest flow temperature possible. Having the stat a couple of degrees higher allows a bit for solar gain on sunny days or cooking without causing the heat pump to cycle needlessly. 

With what I call "hard core" weather compensation you completely abandon the use of room thermostats and TRVs and get everything so finely balanced that your house maintains your desired constant temperature irrespective of the temperature outside.  The downside to this is that if you want to increase the temperature it may take quite a long time - and of course you may have to spend a lot of time getting the fine tuning right.  But the upside is that you should be running heat pump at its maximum efficiency.    

Mstty

And this is why heatpumps are not just for Christmas!!

We are currently recording data on experiment number 38. With the plan being to keep the average daily usage in December for everything electrical under 25kwh a day.(tough benchmark)

dllive

Thanks for your comments, very helpful.

Im going to reduce the comp curve to 42 degrees and assess the situation. I feel at the moment the comp curve is set too high because the radiators very quickly heat up on TRV 3.

A few questions:

1) TRV: if the theremostat is in the TRV near the floor, surely thats the coldest part of the room. So it makes sense having it on a 1 or a 2, becuase all th eair above it will be a lot warmer?

2) What is 'heatpump cyling'? (as per @matelodave 's post). Is that where the pump shuts off becuase my handheld thermostat and/or TRVs have detected the room is up to temp? If so, is the objective to have the heat pump on constantly at a low flow temp? Becuase its efficient when its running whereas if its stopping/starting all the time its using more electricty? (a bit like starting a car frequently rather than leaving it idle?)

3) Should I lower the comp curve as much as possible; then open TVRs to full?

4) I have 4 bedrooms (1 ensuite) upstairs and 1 bathroom. I only use the ensuite bedroom and a second bedroom. The bathroom and other 2 bedrooms I never go in. Should I set the TRVs in the rooms I dont use to * or 1? (theres no point heating unused rooms). Ive reduced the bathroom towel rail lockshield valve right down so theres just a little bit of heat emitting from it.

5) At the moment I feel the heat pump is producing more heat/energy than I require. (Im very 'cold tolerant'). Is this even possible?

Thanks

matelodave

Mstty said:

And this is why heatpumps are not just for Christmas!!

We are currently recording data on experiment number 38. With the plan being to keep the average daily usage in December for everything electrical under 25kwh a day.(tough benchmark)

I'll be impressed if you can.

Our daily average consumption over the year works out at 19kwh*, however in the summer goes as low as 3 when we go on holiday, but generally around 8-10kwh/day but between December and Feb it increases to about 35kwh a day with some days peaking at more than 50kwh (I think the record was 60kwh when it was around -12 outside)

This week it's been very cold, damp and foggy since Monday and we've been using around 25-30kwh a day already (it's just 3 degrees outside at the moment and our flow temp is 38 degrees)

Our average annual consumption over 12 years has been around 7200kwh, but in a couple of very cold years that's gone up to 8500 and down to just under 6000kwh when we went on holiday for most of December one year and saved around 1000kwh (it did take several days to get the house warm again when we got home though).

Mstty

@matelodave

I think we stand a good chance going on last December which was our first winter with an ASHP and I was manually adjusting the flow temp depending on the weather daily and driving my Mrs nuts keep going to the cupboard lol. We managed less than 30kwh all in per day average for Dec 2021 and we have made changes to the ASHP as in weather compensation and a general reduction in our electricity use. (Ignore June 2021 and before as that was the previous owners)



Currently December looks like 24-25kwh a day and again that's everything hot water heating and all electrical use.

So for our 4/5 bedroom house estimating 6150kwh at best for the year and that works out at 4000kwh roughly for all heating and hot water so average 11kwh a day(have to do this roughly as no seperate meter on our ASHP as it was installed with the house build)

Flow temp set to 35oC

EDIT...Sometimes I wonder why I bother responding, someone says not sure you will achieve (x) you go to all the bother of explaining...historical use....changes made and they never reply 😂😂😂

Alnat1

Don't forgot, we had that crazy warm couple of weeks over Christmas and New year last time. Daytime temps were 16-18C over most of the country.

Mstty

Alnat1 said:

Don't forgot, we had that crazy warm couple of weeks over Christmas and New year last time. Daytime temps were 16-18C over most of the country.

Indeed not forgotten but factored in based on December 2021 no care in the world on electricity usage, hot water bubbling away frivolously and oven on twice a day and the ASHP setups mentioned above. 100kwh of the month will be reduced just on general days to day savings we started in the summer. 50kwh saved on the way we now heat our hot water.

Hoping for 800kwh use but won't mind if it matches last year's December given the expected temperature differences.

chris_n

dllive said:

Thanks for your comments, very helpful.

Im going to reduce the comp curve to 42 degrees and assess the situation. I feel at the moment the comp curve is set too high because the radiators very quickly heat up on TRV 3.

A few questions:

1) TRV: if the theremostat is in the TRV near the floor, surely thats the coldest part of the room. So it makes sense having it on a 1 or a 2, becuase all th eair above it will be a lot warmer?

2) What is 'heatpump cyling'? (as per @matelodave 's post). Is that where the pump shuts off becuase my handheld thermostat and/or TRVs have detected the room is up to temp? If so, is the objective to have the heat pump on constantly at a low flow temp? Becuase its efficient when its running whereas if its stopping/starting all the time its using more electricty? (a bit like starting a car frequently rather than leaving it idle?)

That is exactly what it is but with the car analogy it's like switching it off then sticking your foot on the floor when you start it up. When your heat pump starts it will get a load of cold water that has to be heated from 20 ish degrees to your 45 or whatever it is setting, then it switches off then repeats. When you have the curve right your return template is higher so you don't have to add as much heat. The lower the target temp the more efficient the heat pump runs. If you can get your top temp down by 5 degrees it will make a huge difference to the amount of heat you need to add with your pump.

3) Should I lower the comp curve as much as possible; then open TVRs to full?
The TRVs may be your only control for different areas unless you balance the radiators to better suit your needs.

4) I have 4 bedrooms (1 ensuite) upstairs and 1 bathroom. I only use the ensuite bedroom and a second bedroom. The bathroom and other 2 bedrooms I never go in. Should I set the TRVs in the rooms I dont use to * or 1? (theres no point heating unused rooms). Ive reduced the bathroom towel rail lockshield valve right down so theres just a little bit of heat emitting from it.

Yes turn the unused rooms down, not so sure about closing the lockshield on the towel rail though. It is probably meant to be the bypass the protect the pump when the other valves are closed. If you leave a towel on it you can reduce the heat it gives out anyway. 

5) At the moment I feel the heat pump is producing more heat/energy than I require. (Im very 'cold tolerant'). Is this even possible?

That is possible and says you need to lower your curve top value or shift the same top value to a colder temperature (I don't know if your controller allows this).

Thanks

          

dllive

The car analogy really resonates with me!! I wish I had grasped this concept a couple of years ago. So the goal is to have the lowest flow temp as possible (without the heating being ineffective) and the Heat Pump running for as long as possible.

But surely the heat pump turns off when my handheld thermostat has reached its target temp?

Im still confused whether I should be using my handheld thermostat, or the TRV's, or both!?

I dug-out an old fridge thermometer I had and Ive put that outside near the heat pump (I presume the heat pump has a thermometer inside too) so that I can easily see what the outside temp is, which will help fine tune the comp curv over the next few months.

This is the controller I have: https://www.youtube.com/watch?v=RX31v4NoQf4 , so it does have Auto Adaptive mode, but perhaps Ill continue with the comp curve for now.