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Daikin Altherma 3 ASHP and Evohome Controller

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 KenM
(@kenm)
Active Member Member
50 kWhs
Joined: 1 year ago
Posts: 2
Topic starter  

Hi all, 

This is my first post, after monitoring and reading many posts over the past while, this is such a helpful and informative forum that I felt the need to  eventually get my act together to seek some advice on my ASHP setup.

I had 16kW Daikin Altherma 3 (split) installed in September 2022, Outdoor unit - EPGA16DAV37 and Indoor Unit - EABH16DF6V7. Having run this for the 12 months, it was serviced in September 2023 before the start of the heating season. SCOP for space heating after the first season was 3.048, however the service engineer found that there was quite a bit of debris in the filter so I'm hoping that that the cleaning of that will help improve the SCOP.

To improve the COP/SCOP of my system I would like to understand what actions I could possibly take which may improve performance. It is current controlled by Honeywell Evohome and I'm unsure if this is hindering the performance of the ASHP or not. 

Evohome UFH heating controller, with 5 UFH zones downstairs (12 loops) and 5 radiator zones upstairs. I don't have any schematics of the UFH loop lengths etc, so have been attempting to manually adjust the flows in the main area we use downstairs (kitchen )to attempt to get delta t of 7c( this room has 3 loops and losses the most amount of heat of underfloor heated rooms, always struggles to maintain or attain target temperature - currently set to 21c). On the whole, I have left most of the other flow untouched bar some of the smaller rooms which have single loops and I have decreased the flows slightly on these).

Last year I spent some time monitoring and attempting to adjust heat curve settings on the ASHP to try minimize electricity usage while maintaining comfort, but I was never sure if this was ever right. Original installer set it to: 45c@0c and 35c@15c external temperature. The service engineer in Sept 2023 changed this to 43c@-10c and 25c@15c. I'm not sure which one is right to follow and which is the most econcomical, but last year I just left the ASHP operate with some setbacks at nighttime and didnt have much vibisility on how the heat pump was consuming energy ona an hourlyu basis/ cycling/if zoning was causing issues etc. I was a little disappointed on the whole with the performance so would like to improve on this.

This summer past I installed solar PV and now have CT clamp in place (and linked solar PV app) so I have an idea of what the heat pump is consuming during winter, and some visibility on how power usage patterns look. This has been a bit of an eye opener as it appears that the ASHP is cycling about 3 times per hour once room temps get within 1 degree of target ( or when temps are c.7+ degrees outside): firstly I will see almost base load in the first 5 minute window reading, with spiking power usage in the next 10 and 15 minute snapshots/ windows and then back to base load again after 20 minutes), only for the cycle to be repeateded over and over in conditions mentioned above. Could this be down to cycle rate per hour settings and minimum on time setting on Evohome?

What I would appreciate is some guidance or input on is how to best manage my heat pump based on my 3rd party controller and overall setup. I really had a good handle on how to manage the heating with the Evohome with my previous oil boiler but not sure sure how this should be set up now with ASHP, how I should manage UFH and actuators etc.

See some information on the house below:

House - 330sq mt, 2 story, ducon slab 1st floor, rated at 1.76 W/Kelvin/m2

Walls - Steel frame, 162mm neopor insulated with block outer leaf

ASHP - As above plus 40 litre buffer tank

Emitters - UFH downstairs and Aluminium Radiators upstairs

Zones - 5 downstairs, 5 upstairs

Windows - mix of double and triple glazing (double to south, east & west facing window downstairs, north triple glazed downstairs, all upstairs are all triple glazed.

Any thoughts/ observations/criticism etc. most welcome.

Many thanks in advance.

Ken

 

This topic was modified 6 months ago by KenM

   
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 Gary
(@gary)
Reputable Member Member
983 kWhs
Joined: 1 year ago
Posts: 111
 

The cycling is probably due to different rooms calling for heat at different times so you have a very small amount of water being heated as only some of your UFH loops and/or rads are calling for heat.  So the heat pump can't modulate down low enough so has to turn off.

Unfortunately, you have controls that were designed to cycle a boiler on and off so that any one room didn't get too hot, while this will work with a heat pump it won't work efficiently.

You also have a buffer tank which was again probably installed due to the 10 zones in the house which with a house your size probably isn't required if all the zones were open.

You  may have already read that the best way to run a heat pump is with all TRV's, thermostats above the temp you want the house at, then to control the heat of the house via the flow temperature of the heat pump this is your weather compensation curve.

The installer will never be able to set it correctly for your house you will have to play with that yourself over the course of winter to get it dialled in, @derek will be along shortly and he has a good method of getting that sorted which he can explain better than I can.  There are plenty of youtube videos on how to set your WC curve up so should be straight foward.

The good news is that you are already getting a SCOP of 3 so its not disastrous and you can get better from there.

Good luck, I look forward to the updates.

 

 


   
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(@iancalderbank)
Noble Member Contributor
3640 kWhs
Joined: 2 years ago
Posts: 644
 

@kenm so I have an evohome controller also, was used to run my house with gas boiler. it is still there but I have slowly reduced its role in the system to almost nothing. The cycle rate you have seen is very likely to be the evohome controller trying to flick a boiler on and off and/or evohome TRV's partially closing zones so the available emitter area reduces and the HP doesn't have enough output available, so the HP cycles due to too high an RWT. Either way, same result - running it like this is just not designed for an ASHP.

tips based on what I have done (after quite a few steps, just giving you the end)

  1. Do not use the evohome controller to call for heat from the heat pump.  The "call for heat" output of the BDR goes nowhere (bear with me).
  2. Instead, Use the heat pumps own controller / thermostat, placed in a suitable living space. make sure that this will be calling for heat 99% of the time. (thus you don't need the BDR to activate the HP).
  3. take the TRV heads off ALL the radiators in the downstairs rooms, and the circulation spaces.   So they are always on.
  4. The same with your UFH, run it always on.
  5. Leave the TRV heads on in the bedrooms if you prefer cooler rooms for sleeping. Use the evohome controller only to set those as you require.
  6. Tune the flow temperature (via the weather compensation settings), and balance the radiators (and UFH flow rates), so that all rooms stay at a stable comfort temperature all the time. This will take a LOT of iterations and is where the hard work is (but also the reward - get it right you get a stable efficient system).
  7. (doesn't relate directly to evohome) Install something that monitors in real time your heat pumps usage and gives historical tracking.  It will really help you with seeing the effect of any tuning you do. plenty of discussion on this on other threads (I don't know what daikin has natively)

 

as for weather comp : 45c@0c and 35c@15c   vs  43c@-10c and 25c@15c . the former implies a higher water temp for the same outdoor temp. Its just a line on a graph, fairly easy to understand if you draw it. The former will therefore use more energy. you want to have your weather comp set to the lowest possible water temp, that keeps your house at a constant temperature with all the radiators on and the heat pump running at a steady output (ref point 6).

My octopus signup link https://share.octopus.energy/ebony-deer-230
210m2 house, Samsung 16kw Gen6 ASHP Self installed: Single circulation loop , PWM modulating pump.
My public ASHP stats: https://heatpumpmonitor.org/system/view?id=45
11.9kWp of PV
41kWh of Battery storage (3x Powerwall 2)
2x BEVs


   
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 KenM
(@kenm)
Active Member Member
50 kWhs
Joined: 1 year ago
Posts: 2
Topic starter  

Thanks @gary, I've been working to optimise the WC curve, but as you said, it will take some time to get it dialled in. 

 

Thanks @iancalderbank. I unforunately only have the Evohome controller controlling my ASHP, I do not have any Daikin controller / thermostat in place, so rely in the Evohome controller. Following the general advice found on some other threads on renewableheatinghub, and as you have referenced above, I removed all actuators on the UFH downstairs and bumped my Evohome controller temperature up to 25 degrees for the past week. The weather here has been pretty mild (7-10 degrees) so maybe not the ideal conditions to attempt to dial in WC curve, it has still been cycling but when the temps drop it seems to run at a more constant clip. What i need to understand now is the balancing of all of the loops within the UFH to see which ones need to be opened/closed more to allow equal distrbution of temperatures between zones.

Just on another note that I forgot to mention previously, my ASHP is set up as if if it is feeding radiators, which means that Daikin has defatulted to delta t to 8c (just more an FYI than anything).

A couple of thoughts/questions I have:

- Is the buffer tank likely to have a considerable negative impact on performance, as I've now essentially decided to use the entire UFH as 1 zone by removing the actuators?

- I have my UFH circulation pump set to speed 2, this is an older pump. There are a number of pumps in the system. After the buffer there is a variable speed pump. On the UFH, there is the 3 speed pump. And there is also a pump on the feed to the radiators/towel rails upstairs. The towel rails are left open therefore this pump runs regularly too to ciruculate water through these, this is also set to speed 2.

How do I go about finding the optimum speed setting for all of the radiator and UFH pumps, and could all of these pumps be negaively impacting the overall system performance?

So many different things to consider when trying to squeeze some improvements out of the system 🤔 


   
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(@iancalderbank)
Noble Member Contributor
3640 kWhs
Joined: 2 years ago
Posts: 644
 

@kenm with a buffer tank (or LLH) you always have the possibility of imbalance in flow rates between each side. which will mean any or all of mixing of cold into hold within the buffer, different DT,  lower flow temps, all of which means less efficient.

the way to optimise the buffer in this context is to aim for the same flow rate on each side. that gives the least efficiency loss across the buffer. But given your multiple secondary pump setup , all of those pumps will make a difference. fundementally you need to try to track the flow rate each side: best option flow metering on both sides if you have it, the next best thing to flow metering is to measure flow and return temps on both sides of the buffer, accurately and over long periods. you are aiming for the flow and return temps each side to be the same. this diagram from here is where I always suggest people to start to visualise this. ideally you want the one on the left. Slightly higher flow on the HP side is ok (the one on the right) because  the flow temp across stays the same. To be avoided is a large drop in flow temp across into the secondary side (middle one).

image

 in terms of the flow rate of each of your multiple secondary pumps vs the others, it'll just be question of careful iterative balancing, making sure each gets enough flow to keep that area warm (because you are no longer relying on higher flow temps and thermostats)

the "set DT" in the controller may not be the actual DT. measuring it will tell you. don't be surprised if its way lower. if flow rate is higher, DT will be lower, thats just physics.

always wait at least an hour after a change to see the effect. HP's take ages to adjust to system changes.

cycling in milder temperatures is a standard problem , in that situation optimising the flow rates , temperatures/DT's and emitters so that its balanced is if anything more crucial - you need to get it right for the system to have any chance of running at a stable dialled-down temperature.

as for controller, I don't know daikin but I assume it has some kind of control panel, with many HP vendors this panel is capable of operating as a thermostat? but anyway, uf you're running the evohome at 25C though that's effectively disabled it so that its "always calling", all the system's heat input tuning is them with WC and flow rates, so thats a good approach.

My octopus signup link https://share.octopus.energy/ebony-deer-230
210m2 house, Samsung 16kw Gen6 ASHP Self installed: Single circulation loop , PWM modulating pump.
My public ASHP stats: https://heatpumpmonitor.org/system/view?id=45
11.9kWp of PV
41kWh of Battery storage (3x Powerwall 2)
2x BEVs


   
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