Optimise my ASHP

[ASHP-user]

I'm a new ASHP convert. Have recently installed the Daikin Altherma 3 H HT with the compact indoor unit and a separate pressurised water tank.

 

I requested a Honeywell Evohome to control all my rads with TR92 heads. Only few were installed in rooms outside of the main zone Daikin hallway thermostat.

 

If the main zone switches off as warm enough, the bedrooms stay cold.

 

Would it be OK to upgrade the main zone with TR92s so the whole house is controlled by Evohome?

 

Would I need to disconnect the Daikin thermostat? I would lose the ability to change hot water temperature and booster function, but a can do that on the boiler control panel also (or main install Daikin WiFi module)

 

Does creating these multiple zones have an adverse impact on the ASHP efficiency/ performance?

 

[TW9]

I'm not an expert, just someone with a heat pump, but I'm happy to give my 2p worth.

 

Creating multiple zones can adversely affect the efficiency of your heat pump. There are some people, such as Heat Geek on YouTube, who can explain better than me but in summary... when you switch off heat in a room, the rooms next to it will start losing heat into that room. That changes the heat loss characteristics of the heated rooms which can result in your heat pump working harder to heat those rooms. That can affect the efficiency of the heat pump so you could end up paying more to heat less of your house.

 

But there are lots of variables and it depends how your system was designed, how it is set up and how it's controlled.

[ReedRichards]

I have always thought that a hallway is a crazy place for a thermostat; hallways tend to be draughty and you don't need them to be particularly warm.  So the alternative to what you propose is to throttle back the flow to the radiator(s) in the hallway so that it heats more slowly

 

I too have a third party controller, it's a Drayton Wiser in my case.  It is wired so that when there is no thermostat or radiator calling for heat then the heat pump turns off its room heating.  This works perfectly well.  If you do this then you may lose any load compensation ability that the Daikin may have.  This could reduce the efficiency but it's more likely to be significant if your thermostat was not in the hall.  

 

Control of my heat pump is set to water temperature only (so it does not care what the room temperature is).  Hot water functions are unaffected by this.

 

There is an argument that you should disable all thermostatic controls and just set your weather compensation to give you the temperature you want in the house 24/7.  If you buy into this argument then room thermostats, TRVs and zones are all bad for efficiency/performance.  I don't entirely believe this myself.    

[ASHP-user]

Thank you TW9 and ReedRichards. Clearly not a simple black-white subject. I had previously configured a schedule that would turn off the system at night. That resulted in a big increase in electricity use as, I assume, the system had to work hard in the morning to bring tank and rads back to its desired temperature. Keeping it on constantly has been better. I agree that the hall is a poor location for the thermostat. Basically the hall, landing and living room are all controlled by the one thermostat. I do believe that keeping hall and landing a couple of degrees below the living room, and keeping living room door closed, will better control the spaces. But overall keep within a hysteresis that avoids the heat pump having to work too hard.

 

I'll also check out Heat Geek. May also have to review the design assumptions and see if anything else can be adjusted. I'm still mindful to get the extra TR92s (or manual TRV heads) in my hall, landing and living room. Will post back an update with any conclusions.

[Christiano]

When we had gas boilers I put a Hive TRV on each radiator, it was a nightmare especially when allowing individual radiators to call for heat. I took them all off.

 

We changed to a heat pump last year (Samsung), the thermostat is in the main living room. It struggles a bit to get this up to temperature unless we’re in the room so I put TRVs back in the bedrooms to cap the heat at comfy bedroom temperatures.

 

This worked fine except for when we had family staying at Christmas when we were all in the living room with the door shut so the heating hardly ran at all, the rest of the house got quite chilly. Luckily our thermostat is wireless and I moved it into one of the bedrooms on the second evening.

 

Since then I have reduced the weather compensation so it has been running around 38c for heating, seems to work nicely, electricity usage seems better and CoP is too although that may be because it’s not been so cold outside. I may remove weather compensation completely in favour of a fixed 38c.

[m0deller]

We installed an ASHP in October. Previously had gas with Drayton Wiser TRVs in all rooms .. all quite complicated. 

A heat pump , to maximise CoP and reduce starts (consume more power) should be run long and low. Mine is now 24x7 with setback of 2C at 10pm. So far we seem to be using less energy heating the whole house vs switching rooms on and off using the TRVs. 

The other thing to note is that by using the heat pumps thermostats it's able to work out the optimal flow temperate .. external binary controls won't do this. 

Also, unless it's changed, Drayton said not to use wiser with heat pumps as it causes too many starts. 

 

Evohome is expensive .. I'm sceptical that you'd ever get your money back vs using heat pump's controls

Edited March 10, 2022 by m0deller

[Marvin]

This is very close to what we are doing and our results.

 

We are 24/7 set back 2C at 10.30pm until 6am. ASHP using (altered to our particular site and use requirements) the weather compensation mode.

 

Difficult to split the heat/hotwater energy use so: All ASHP energy use approx 10kWh a day from 5th Jan until today for 100m2 floor.  

Presently 14C outside with heating automatic setup at 35C

 

 

Top one heating, bottom one cooling.

 

Edited March 10, 2022 by Marvin
The word ASHP added for clarity after "All"

[JohnMo]

I assume your heat pump is loaded with a heat curve based on outside temperature.

 

So basically it should work the same as weather compensation system on a gas boiler.

 

Where the heating is designed to run 24/7.  Each room has a TRV, to manage the room temp, but not call for heat.  The system will operate a setback of a couple degrees during night, so the pump has an easy time of it during the next morning.  Running this way your circulation temp can be reduced.

 

Don't try to operate as normal gas boiler, with lots of on/off, as you will wasting large amounts of energy.  Long, low and slow should be the way to think of it.  Run for long periods, to allow a slow build up in temperature at a low circulation temp.  Then let the system maintain it.

 

Set the hall thermostat higher and let the room stat/trvs manage the room temps.

[ASHP-user]

Thank you all. Slowly with a 2 degree variation does it. With or without TRVs, also set to small variations. My system is high temp, so rads are about 60 degr. not 35-38 degr.

 

@JohnMo if the hall main stat is set to, say, 20 degrees and the nearby TRVs to 18 degrees, does that not mean that the ASHP will keep on pushing to get to 20 but never gets there? Hence, better to disconnect the main hall thermo if possible and let TRVs control the ASHP? I'll reach out to Daikin also.

[JohnMo]

Your going to have to play with setting, including flow temperature.  Change one thing at a time.  See what happens for the next 24 hrs. Write down what you did and energy consumption and things felt.  This will make the whole process reversible and see what works and what doesn't.

 

But you should be able to reduce flow temperature, by setting the runs times longer.  Lower flow temps equal higher COP.

 

Was your ASHP a retrofit, did you increase the radiator size?

 

Read your manual to see if you can set to weather and/or load compensation.

[Marvin]

Hi @ASHP-user

 

There are many ways to set up the controls....

 

Main hall stat: In my opinion @JohnMo is right, that setting the stat higher is the way to go but only if every other emitter has its own temperature controller. ( you have experienced colder rooms already but if you turn it up without radiator TVRs those rooms could get too hot.)

 

Definetly do not disconnect the stat.

 

All my other questions @JohnMo just asked... 

[J1mbo]

On 10/03/2022 at 22:01, ASHP-user said:

My system is high temp, so rads are about 60 degr. not 35-38 degr

Do yourself a favour and get bigger rads.

[Marvin]

54 minutes ago, J1mbo said:

Do yourself a favour and get bigger rads.

+1

[ASHP-user]

Thank you all. Some more great advice. Will monitor and record setting and track energy use also. Now also understand the combination of the central hall controller together with the smart per-room controls. Thank you @Marvin and @JohnMo.

 

My ASHP was a retrofit of a gas boiler with gravity hot water to a pressurised indoor unit with a separate 210l cylinder. It really does not need bigger rads, although I have yet to experience a really cold spell. The Daikin high temp design is quite clever. Check outline here.  The downstairs rooms are nice and warm.

 

Shortly, probably 1st April, coinciding with the energy hike, will turn off the heating and get the system drained and TRVs and heads installed. Still have several rads without TRV or 26 year old incompatible and clogged up TRVs.

[Marvin]

51 minutes ago, ASHP-user said:

It really does not need bigger rads, although I have yet to experience a really cold spell.

It would be a good thing to do a room by room assessment of the heating requirement to be sure before you get the alterations done.

[RobLe]

We have TRVs on all rads, but I leave all downstairs ones full open so there is a guaranteed heat load, and the thermostat is in the central hallway.  

 We have a well insulated house (1.6 kW peak loss), so internal air circulation equalises any temperature imbalances.  Bedroom ones are adjusted by user preference.  Rads are original 1963, but loads of insulation means they are now ‘oversized’, flow temp of 32C generally.

I’m a believer of insulation first, low flow temperatures, clever smart controls last.