Ecodan: clarification needed on flow temp and radiators TRVs

dllive

Hi all,

I currently have the Ecodan set at a flow temp of 45 degrees (and on compensation curve). Is that too low? I assume the lower the flow temp the more economic it is to run? Im happy with the warmth the radiators are giving off. (Ive only got the TVRs on 3!). I dont want the Ecodan generating more heat that I need. I could probably reduce it even further to 40 degrees and be happy.

Also, does turning the TRV down on a radiator from 3 to 1 save money? I dont need all the radiators to be pumping heat out on 3 or 4 all day. But if its costing no more then I happily will. Afterall, the TRVs controls the waterflow rather than the temperature(?)

Any clarifcation greatly appreciated! Thanks

[Deleted User]

You misunderstand how TRVs work.

They shut off the water flow to the radiator when the room temperature hits a certain point, just like your thermostat does for the whole system.

Turning it down from 3 to 1 will save money, but that's because that radiator will be turned off at a lower temperature.

It won't "pump out heat at 3 or 4 all day" any more than a normal thermostat in an old fashioned system would "pump out heat at 20C all day".

chris_n

Surely you can't have your heat pump flow set at 45 AND compensation curve unless you mean a maximumof 45. If you are using the compensation curve the flow temperature will vary depending on outside temperature. For best efficiency you should set the points you have control of as low as you can in order to keep your house warm. It can take some time to do this properly but it is worth taking the time to do it.

Mstty

As a comparison the coldest end of our weather compensation curve is set to 35oC

We have our heating on 24/7. Currently 3oC outside and inside varies from heavily glazed rooms (no solar gain today sitting at 18.6oC to the room we spend most time in in winter 20.5oC. EPC high B and underfloor wet system downstairs not a retrofit so that does appear to make a difference on efficiency having seen others high energy usage. Using 14-16kwh a day on just heating depending on outside temperature.

Upstairs single hall thermostat set to 19oC and the radiators never kick in due to the heat rising from downstairs.

I would only set ours to 45oC at the coldest end of the compensation curve if we were turning the system on and off trying to run it like a gas central heating system.

We have individual room thermostats downstairs rather than TRV's but effectively they do the same when they reach temp the hot water drops flowing through the pipes to that room. 

dllive

chris_n said:

Surely you can't have your heat pump flow set at 45 AND compensation curve unless you mean a maximumof 45. If you are using the compensation curve the flow temperature will vary depending on outside temperature. For best efficiency you should set the points you have control of as low as you can in order to keep your house warm. It can take some time to do this properly but it is worth taking the time to do it.

Hmm, yes, perhaps I have the comp curve on with a max of 45. Ill take a photo if it later so you can see.

dllive

Hi guys

Ive taken some photos. Hopefully this gives context:

So it seems I have the max flow temp at 45 ?:




The heating is on comp curve:




Is the comp curve right or should I reduce? At zero degrees it has a flow temp of 47. (although on the first screen it says 44 !?)




If I click the minus button will it bring the whole comp curve down? Should I do this or edit the comp curve itself?



Thanks

BUFF

dllive said:

Also, does turning the TRV down on a radiator from 3 to 1 save money? I dont need all the radiators to be pumping heat out on 3 or 4 all day. But if its costing no more then I happily will. Afterall, the TRVs controls the waterflow rather than the temperature(?)

Any clarifcation greatly appreciated! Thanks

It varies by manufacturer but as a very rough guide the settings on a TRV equate to:
1=10C
2=15C
3=20C 
4=25C
5/Max=28-30C
* or Frost=7C

Ceol

dllive said:

Is the comp curve right or should I reduce? At zero degrees it has a flow temp of 47. (although on the first screen it says 44 !?)

If I click the minus button will it bring the whole comp curve down? Should I do this or edit the comp curve itself?

Thanks

We can't tell you if your curve is right. Your installer will probably have had a good guess, but the only way to really nail the curve in correctly is trial and error.

Yes the plus and minus will change the flow temp for the whole curve. It's not the best way to change it really because there are other factors, but it's OK if you need a bit extra or less heat. Personally I would adjust both points on the curve, but you could use the auto adaptive mode and let your system learn it for you. I can't be 100% sure that your Ecodan has this, but assuming your controller is in a living space (ie not an airing cupboard or a garage), then you should have a third mode which will display the room temperature, and that's the auto adaptive mode.

With regards to TRVs, generally with heat pumps you're best having a constant or near constant room temperatures because that requires low flow temperatures. The problem with having complex timings like you would with a gas boiler is that you need the heat pump to run hotter to get rooms up to temperature quickly, and that significantly reduces the efficiency.

Importantly, you should always wait one or two days between making a change and seeing if it's worked.

matelodave

You comp curve is similar to mine although we have our max temp at 42 degrees when it's zero outside and 25 degrees when its 15 outside but that's with underfloor heating all over (no radiators except the bathroom towel rail) and we run it 24/7.

We dont have a buffer tank and so if the room stats cut down the flow (much like TRV's do with radiators) it does cause the heatpump to cycle a bit more because the water flow gets redirected through a bypass valve (or in our case through the towel rail) straight back to the heatpump

I'm not sure if that happens as much with a buffer tank where the water flow is not subject to flow restrictions in the heating pipe loops or radiators due to them shutting down. It's very noticeable when you look at a graph of the energy consumption which can get a bit spikey rather than nice and smooth. Potentially our heatpump is a bit oversized compared with the output capability of the underfloor loops especially if several of them shut down when the rooms get up to temp. The ideal situation is to balance the system so that the room temperature are maintained whilst under the control of the heatpump flow temp/weather compensation rather shutting down the flows

You are correct that pressing the +/- buttons shift the whole heat curve up and down by 1 degree which can be useful if you want the place to warm up a bit quicker but bear in mind for every degree you increase it, your energy consumption is likely to increase by around 2.5%

As Ceol says, only make small adjustments to one thing at a time and leave it a day or two to settle otherwise you wont kow what works and what doesn't but ultimately you need to get the flow temp as low as possible commensurate with adequate room temps and reheat times.

matelodave

As an addenum to the above, you really need to understand how all the controls interact with each other and the heatpump

Mine is relatively simple insofar as the heating loops have a stat in each room which not only control the flow in each room but they turn the heatpump circulation on as well (ie just the bathroom calling for heat will get it all going). The heatpump then controls the flow temp according to the weather compenstion but only shuts off when all rooms have been satisfied. 

Whereas you might find that the controls only operate on the floor loops and or a floor pump, and the upstairs stat might just open and close a motorised valve shutting of the flow the whole upstairs leaving the heatpump to maintain the buffer tank temp at whatever the weather compensation decides.

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).

I'm sure that a whole book could (and possibly should) be written on the various ways to optimise and control heatpump systems especially as they really should be optimised for the building, lifestyle and requirements of the user and as we are all different there really isn't a one size fits all, like there is with a gas or oil boiler.

My Daikin Altherma heatpump was installed over 12 years ago and has very different controls and characteristics to a modern one and is different again to Mitsubishi or any other unit, so in the end its all trial and error till you get it set up for you.

chris_n

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.