I think you still have some misconceptions on what Vaillant does. They are not cooking numbers - and that’s coming from someone who once also thought they were .
Here’s what they are measuring:
electrical energy via a built-in power/energy meter
usable heat going into the house by measuring flow rate as well as flow- and return temperature. Heat is computed from these metrics. Physically, this is truly the heat energy being put into the heating circuit by the compressor.
What they are then doing is subtracting electrical energy from the heat energy to show how much energy was extracted from the environment. The reasoning is simple: Any heat energy measured by the heat metering components that is in excess of what was supplied by electricity must come from the environment by conservation of energy. They call this excess energy “yield”.
COP however must be computed by relating heat to expended electrical energy; and that’s exactly what they do: divide the measured heat by the measured electrical energy.
I don’t have EN 14511 in front of me now, but I am very confident that this must be the definition in there as it is also just what makes sense from a physics perspective.
Thanks Andre,
That makes perfect sense now.
You gotta love physics
I can now relate the useful heat output obtained from the flowmeter and temperature sensors (Q=mCpdT) and electrical output from the CT clamp.
The EN 14511 does state COP= Heat output/Electrical output.
Apologies are due to Valliant. I only wish they had not coined the term Energy Yield.
I thought I’d be able to help a colleague with her poorly performing Arotherm+, knowing my way around most of the settings. She’s getting a COP around 2 on days when I would expect something closer to 4. I checked the obvious things: weather curve is down at 0.6, sensible schedule and setback, TRVs open, flow rate at 1200l/h (it’s a 7kW). Now I’m a bit stumped. Looking through the live monitor on the control panel, it was reporting 0.8kW electrical consumption and 0.8kW cooling capacity @ 30C flow / 0C outdoors. I’m wondering if there could just be a sensor fault, and it’s actually producing much more heat than reported at higher COP. The only thing I’ve spotted is that it’s clocked up 19,500 on/off cycles in under a year, which I reckon is something like 20x more cycling than mine. I checked the energy integral settings, and “comp. start from” was at the default 60 degree-minutes. I bumped this up to 100 to try to ease the cycling, but I still don’t think this can explain the terrible COP. Is there anything else obvious to check?
19500 cycles in.a year, that’s awful. Mine averages less than one cycle every two hours if operation.
There is something majorly wrong with this installation, vast oversizing, buffer or something else. My guess is that if you fix that you will fix the COP.
If you can put some monitoring on it so you can see what’s happening but otherwise take a look round and sense check loss calculation to see what’s causing it. Is it being run with thermostats and trvs not open loop, if so that could be a contributor.
No thermostat, just the manufacturer control with room temp mod inactive. Flow rate looks fine making me think TRVs aren’t causing problems. I do think the system looks oversized. I’m seeing it running at 750W electrical at -1°C outside. But even so, when my Arotherm cycles in mild weather, it still returns good COP. And it’s not cycling in today’s temperatures, yet reporting a COP of 2. There’s got to be something other than oversizing going on.
I tried to sense check the building heat loss from the design quotation, but it left me none the wiser. It stated a design heat loss of 6kW, yet an annual heat demand of 6,000kWh. Those don’t match up! I can believe 6,000kWh/year is the correct figure, and true heat loss is perhaps closer to 2.5kW.
6MWh/year is indeed about 2-3kW loss, so yes a 7kW heat pump is definitely well oversized. This will definitely cause a lot of cycling. However the frequency is particularly high so I am wondering a few things
What is your system volume?
Do you have a buffer, heat exchanger or Low Loss Header between heat pump and emitters?
Are there any other restrictions in the system or secondary heating sources?
I would stick with inactive for now whilst you diagnose, but wouldnt rule out active or expanded once you know whats going on. I would also turn TRVs to max just to rule them out.
One possible thing to consider given the gross oversizing is to batch heating. With radiators this is less successful than with UFH because you dont have a slab to act like a storage heater, but it may just work without your house temperature changing too much.
You really could do with some basic monitoring. If you are even faintly computer literate then setting up Home Assistant (if you have one on a Raspberry Pi, but otherwise on any other computer you can leave on permanently) would be well worthwhile. It can read the same data as the app and a plot of flow temperature will tell you so much about whats going on!
The 0.6 heat curve setting is likely way too high. Our Victorian solid brick house with the same 7kW Vaillant needs a 0.45 curve setting to keep the whole house at 22degC using ‘Active’ WC mode.
The cycle count on your colleague’s system is egregiously high; are you certain that there’s nothing but the Vaillant controls installed? A cheeky little third party UFH valve controller perhaps? Something is making it cycle way more than it ought to be.
What’s a “normal” range of cycling. I have a low heat-loss home (1.8kwh) according to heatgeek. 3.5kwh system and its cycling an average of 1.5 times per hour and COP at 2.8. Yesterday was fairly mild, 12c or so and it did 3.05 COP. Low flow rate of 0.45. Temps are 20.5c through out the day.
Welcome to the forum @Thabo.
Your cycle rate is perfectly reasonable, especially with mild conditions outside.
Anything less than 2-3 cycles per hour should not be a cause for concern.
In expanded mode, does the energy integral still have effect? I thought it was ignored, but seems not.
For a variety of reasons we dropped to 18.8C internally today (on active with target of 20C). I switched to expanded hoping it would turn the machine back on and heat till 20 then turn off, but it didn’t seem to do this.
Plus it’s annoying you can’t do this from the app, but that’s another story.
I run my system in Expanded all the time. Energy Integral can lead to shutting the heat pump off if it reaches its trigger point before the set temperature is exceeded.
The data below shows this clearly. I have just come back from holiday and so the house was returning from running at 15°C and is returning towards it’s normal target of 20°C
The top blue line shows flow rate. When this drops slightly the heat pump is shutting down on Energy Integral (and the circulator pp keeps running). When it drops to zero the heat pump is shutting down because the temperature set point has been achieved (and the circ pp shuts down as well).
Okay thanks. So it appears expanded doesn’t ignore integral.
It’s a shame there isn’t a setting that’s like ‘ignore energy intergral if temp current < temp desired’. This would deal with some of my issues. And or another setting that’s ‘heat continuosly until temp current > temp desired’
What I have done is use Home Assistant to adjust the Heat Curve based on the difference between the actual temperature and the target temperature. The setting I use is to set a curve of 0.8 if the actual is 0.5°C or more below target. I decrease the Heat Curve by 0.05 for each 0.1°C increase of the actual temperature until at 0.1°C above target the Heat Curve is set to 0.45.
Thanks for the comment, that’s a good idea. Are you able to DM me a screenshot of how you did that?
I wanted to avoid using 3rd party tools to manage things, and keep it as simple as possible, but shoulder seasons and lack of sun see to be our trouble point.
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