This is my first post and I’m hoping for some advice regarding the poor running efficiency of our Ecodan 8.5 kW. I have a COP of around 1.7
Our system is currently running in weather comp. mode with all thermostats and rads fully open.
There is no zoning control as such however there are separate circ pumps for upstairs rads and the downstairs underfloor which take supply from what looks to be a pre-plumbed low loss head.
I’m getting a flow rate of 14 l/min on the heat pump ring and cannot increase pump speed any more. Is this where the problems lies?
Also these are two screen shots taken from Melcloud showing a 1 hour caption of the flow/return @ 02:00 and 13:00 today.
Is the system cycling or is it normal behaviour just maintaining flow temp given the small scale/deviation between upper and lower limits?
Do these pumps turn on at the same time, or are they controlled separately?
This is within spec for that model heat pump, so is probably fine. When was it serviced last?
Yes, that is cycling 6 times an hour, which is not ideal. Do you seem the same when it’s cold out?
Is there a room thermostat that is calling for heat? What type is it?
Your flow temperature is very low, and my guess is that there’s not enough emitter surface to shed the heat being generated. Raising the flow temperature will reduce the cycling, but then you’ll have too much heat and will need to cycle the room temperature instead.
So the system was installed on a new build and commissioned almost 4 years back when we moved in. During this time we’ve accepted the system was costing more to run than our previous 3 bed semi (now 4 bed detached)
Following a recent service its come to light that the system isn’t running at optimum. The filter was cleaned during service however I’m going to have the system flushed too given a poor water test result.
Initially it was set at 45’C flow temp setting and getting a COP of 1.3.
Ive opted the weather curve/all thermostats calling for heat and seen slight improvement but nowhere near what others appear to get.
I mentioned the no zoning control although i suppose up+downstairs are zoned but with no mixing valve/separate temperature control. Just a separate circ pump with underfloor manifolds.
There are no buffers and questionable whether it has a LLH.
I’ll get some images of the install uploaded soon.
Cheers again
Vince
What was the calculated heat loss for your property? How big is the property (in m²)?
On January 18th, what was the average outside temperature, and how much electricity (kWh) did the heat pump consume that day? Was the house warm enough?
Sorry, one more: what is your weather compensation curve set to?
To pre-empt answers to my question, and mostly so I don’t forget it, I checked the performance measurements from HeatpumpMonitor.org for some other, similar-sized systems on that day:
System #73 consumed 23 kWh and generated 78 kWh of heat, COP of 3.4. Average -1.5 °C.
System #67 consumed 33 kWh and generated 94 kWh of heat, COP of 2.8. Average -0.3 °C.
System #56 consumed 43 kWh and generated 103 kWh of heat, COP of 2.4. Average 1.0 °C.
This shows the sort of consumptions you might expect to see on “design day”.
The other thing I notice about your flow temperature is that it is very low at 25°C. This will most certainly result in cycling. I would recommend adjusting the curve so the minimum is, say, 30°C, and see how that changes the behaviour. Hopefully the room thermostat will step in if the house gets too warm?
You’re right Tim and looking at last nights colder spell below 10’c i can see how the cycling stabilised. I have to admit here this is my doings/experiment with the weather curve trying to find lowest flow temp setting to achieve 18’c seen in a bedroom for the higher ambient temp setting (i hope this makes sense because it even confuses me reading it back).
Does this conclude its impossible to opt the method of running with thermostats set to max/calling for heat as recommended for highest COP because anything over 10’c outside and the system will just cycle as we’re seeing.
I’m thinking the next test it to try the auto adaption and see how that performs being the ‘smart’ method.
I feel it may be worth need more temp data from the system too for the up and downstairs legs?
While this is the “optimal” way to run a heat pump, it doesn’t work if the heat pump is oversized for the property. The minimum heat output of your unit is maybe 3 kW, and if your emitters cannot output* that heat at 25° then there’s no where for that heat to go. Flow temperature goes up until it exceeds the weather compensation limit, and the heat pump shuts down for a few minutes before restarting. Those short cycles will typically have poor performance, and wear out the compressor.
*At 5° above room temperature, your radiators will only be able to output 5% of their rated output.
Anecdotally, this has worked quite well for some owners, myself included. In this mode, the flow temperature is left to go up to where it stabilises, and will produce long runs with good performance. When the room temperature reaches 1° above set point, the heat pump turns off (eventually). It’s worth experimenting with, even if only to better understand how your heating system responds.
Here’s a snapshot from my system, running with room auto-adapt. The flow temperature tends to reach 40°C regardless of the outdoor temperature, cos the heat pump is about twice the size it needs to be.
Though 14 l/min is within the flow range for the 8.5kW unit I would expect the max pump speed of 5 to be producing something closer to the 24.4 l/min top of the range.
If you have the Ecodan pre-plumbed cyclinder, which I am inferring you have from the LLH reference, then the literature mentions a required primary flow rate of 25.8 l/min. I’m not exactly sure of the reasons for that, but if I am reading the pump chart right for the secondary pump installed on the pipework then even on the lowest speed setting it is just balancing the flow rate at the highest setting for the primary pump. So there might be quite a difference between when you have two running.
This is good feedback Tim and hopefully I also see positive results once switch to the auto adaption.
I just need to relocate the controller as its currently in the cupboard with the tank and seeing 25’C room temp. I’ll require this for the temperature feedback as don’t have a wireless thermostat.
Hi Nigel. Thank you for checking the specs and interesting regarding the pump speed. The controller doesn’t seem actually change the speed of the pump if changed between 1-5, only by pressing the buttons on the pump itself. Perhaps this could suggest its wired into the controller incorrectly?
This very much depends on the pipework - mine can barely manage 16/17 l/min at the top end, due to how far away the outside unit is. I have the pump speed turned down, so am running down 13/14 l/min, which is on the very edge of the manufacturer’s spec, but it works okay.
Yes, that is the low-loss header that comes with pre-plumbed cylinders. You’ll have a main pump that circulates water to the outside unit and back, and secondary pump that circulates water around the radiators/UFH.
So I’ve just managed to relocate the main controller and have now set it to auto adapt.
I might need to change some settings but this now seems to control the circ.pumps for outside unit and the upstairs zone. I believe I might need to get another wireless thermostat for downstairs as when the UFH stats call for heat the circ pump activates on the UFH manifold however the heat pump isn’t kicking in as the main control upstairs isn’t activated.
I’ll let it do its thing overnight and see how it performs.
I’ll flush this system over the weekend too and hopefully might see some increase in flow/thermal transfer.
is 
