I just had a 10kw Vaillant Arotherm installed in August, and have a few questions about COP and SCOP
How accurate are the figures generated in the My Vaillant app? I am confident that the energy used is accurate, based on my Octopus agile account.
Can I add my details to the ‘league tables’ using the Vaillant data?
Surely the COP figures are based on the number of people in the house? Ie 4 people will consume more hot water than 1 person? Thus more water needs to be heated up. Therefore comparing COP figures are meaningless. Am I missing something?
When is the best time to heat hot water? I am thinking around 2-3 pm because it’s generally warmer then. The heat pump will be more efficient? Also the flow temperature will still be warm, and can be used for the heating process during the Agile peak times of 4pm to 8pm.
Welcome to the forums - and to your first heating season with your Vaillant Aerotherm.
I don’t have any experience with the Vaillant app so I’ll let others comment on the accuracy of the built-in metering on your system, which will depend on what mechanisms Vaillant use to estimate the heat output. Some people will have added third-party heat meters to their Vaillant installations so will be able to provide back-to-back comparisons.
You’re free to add your system to the ‘league tables’ based on the Vaillant data - just be sure to select the correct options with respect to metering. In particular your system won’t comply with the “MID Metering” requirements, so don’t tick that box.
It would be wrong to say it’s meaningless to compare COP figures. Overall energy inputs and outputs certainly vary hugely between installations, but by looking at the ratio of input energy to output energy a lot of that variation gets filtered out. However, there are certainly factors which influence heat pump performance - based on the flow temperature the heat pump is required to deliver:
Installations with a lower indoor target temperature tend to perform better
Installations with more ‘effective’ heat emitters tend to perform better - e.g. bigger radiators and larger-diameter pipework (or underfloor heating)
Installations requiring a lower proportion of stored hot water heating (compared with space heating) tend to perform better
Due to having fewer occupants, alternative sources of water heating (e.g. solar thermal), or just simply needing a huge amount of space heating which then ‘drowns out’ the stored hot water energy usage
Somewhat counter-intuitively, installations in very well-insulated properties tend to show mediocre efficiency, because so very little space heating is required and hot water usage tends to dominate
These installations tend to be at the top of the ‘Costs’ and ‘Fabric’ league tables though
In terms of the best time to heat hot water: “it depends…” - especially on your electricity tariff, whether you have solar panels and / or battery storage - and what time of day your household mostly uses hot water (and how much hot water you use, compared with the capacity of your hot water cylinder)
Some people are on an electricity tariff which is much cheaper overnight (e.g. 1/4 of the daytime rate) so choose to take a slight hit on efficiency for a significant cost saving by heating stored hot water overnight - especially if they use most of their hot water for showering in the morning
Having battery storage coupled with a cheap overnight tariff potentially makes this ‘low-rate’ electricity available at any time of day though
Even the best-insulated hot water cylinders will lose heat over the course of a few hours (e.g. mine lost 5C over 16 hours yesterday) - so if you’re heating water at 3pm but mostly using hot water at 7am you’ll need to heat the cylinder to a higher temperature than if you’re heating at 5am - which could easily offset the efficiency gain of the warmer outdoor air in the afternoons
Note we generally aim to use the term Seasonal Performance Factor (SPF) to refer to the measured, real-world efficiency of a complete heating system. One of the industry researchers pointed out that COP and (especially) SCOP are performance predictions used by heat pump manufacturers, based on laboratory conditions.
For me, the main value of the HeatpumpMonitor dataset is in demonstrating that there are plenty of real-world heat pump installations that are genuinely delivering an SFP of about 4 in a wide range of properties, to counteract the assertions that ‘heat pumps don’t work’ or that they cost more to run than gas boilers.
The community forum has good insights on the Valliant App shared by Michael de Podesta “Protons for breakfast”. You should be able to find it under “heat pump learning resources”. In summary, the Valliant App appears to present a “predicted COP” value and not an accurate COP value.