Heat Pump SCOPs – The Truth Might Not Be What You Think

David Stanford · 2024-12-03T10:19:27Z

When it comes to ASHP efficiency, there’s often a lot of discussion and misunderstanding. SCOP (Seasonal Coefficient of Performance) is a key measure of efficiency, but what does it really tell us, and how can we interpret it? After analysing data from the top 20 heat pumps on heatpumpmonitor.org – all with SCOPs above 4.0 over the past 365 days – I’ve uncovered some insights that might surprise you. What the Data Reveals (At Time of Writing) Air Source Dominates: Of the top 20 heat pumps, 19 are air source, and only one is ground source. System Volume is Often Overlooked: Surprisingly, 75% of users don’t calculate or record their system volume. For those that do, systems with 15 litres per kW of peak capacity or more perform best. The top-performing system has 16 l/kW. However, going far beyond 15 l/kW offers diminishing returns, and there isn’t enough data to confirm its benefits. Manufacturer Diversity: The top-performing models come from a range of manufacturers, including Viessmann, Nibe, Vaillant, Grant, Samsung, Mitsubishi and Acond. This highlights that system design is often more critical than the brand. Refrigerants Don’t Make a Big Difference: Among the top six ASHPs, there is an even split between those using R290 and R32 refrigerants, suggesting no significant efficiency advantage to either. Single-Zone Systems Rule: Every system achieving a SCOP above 4.0 is a single-zone setup. Multi-zone systems seem to struggle to match this level of efficiency. Flow Temperatures are Key: Systems with a maximum flow temperature of 45°C or lower dominate the top-performing list. Higher flow temperatures tend to drag down efficiency. Modest DHW Settings Win: The top six ASHPs have domestic hot water (DHW) set to an average temperature of 45°C, reinforcing the importance of keeping DHW temperatures modest for better efficiency. Building Efficiency is Less Relevant: Interestingly, building efficiency (measured in W/m2) varies wildly among the top systems, from 19 to 76 W/m2. This suggests that SCOP is influenced more by system design than the property’s insulation or efficiency level. Supplementary Technologies Enhance Results: Over half of the top 20 systems either don’t heat DHW or use supplementary technologies such as hybrid boilers, photovoltaic (PV) panels or solar thermal systems to improve performance. Notable Features in Top Systems Buffer Vessels: These are present in many high-performing systems. 10mm Microbore Pipework: Often considered suboptimal, this pipework appears in some top-performing setups, proving that careful system design can overcome perceived limitations. Thermostatic Radiator Valves (TRVs): Despite some reservations, TRVs are used in many systems, likely in specific zones like bedrooms. Key Takeaways From this analysis, a few clear lessons emerge: Aim for 15+ l/kW System Volume: This seems to be a reasonable rule of thumb for optimising efficiency. Focus on System Design: The manufacturer matters less than a well-designed, balanced and commissioned system. Refrigerant Choice Isn’t Critical: Both R290 and R32 perform equally well in top systems. Stick to Single-Zone Systems: Multi-zone setups don’t achieve the same efficiency levels. TRVs Are Acceptable: While they may reduce efficiency slightly, TRVs can work well if carefully implemented, likely in specific areas like bedrooms. Keep Flow Temperatures Below 45°C: Lower flow temperatures are crucial for high SCOPs. Lower DHW Temperatures: Reducing DHW temperatures has a substantial positive impact on system efficiency. Don’t Stress About Building Age or Efficiency: A correctly sized heat pump can deliver excellent results in properties with varying levels of efficiency. Supplementary Technologies Help: PV, solar thermal, and hybrid systems can boost overall system performance.

Page 2 / 2 Prev

Air Source Heat Pumps (ASHPs)

Last Post by Old_Scientist 2 days ago

13 Posts

9 Users

3 Reactions

638 Views

RSS

Old_Scientist

(@old_scientist)

Honorable Member Member

Joined: 1 year ago

Posts: 239

04/09/2025 10:00 am

Posted by: @mike-h

↑

Posted by: @david-stanford

↑

Aim for 15+ l/kW System Volume: This seems to be a reasonable rule of thumb for optimising efficiency.

Can you explain the mechanism for this effect? Could it just be coincidental rather than causal? System volume may prevent short cycling, but there are other ways of achieving that.

Sufficient system volume is also essential for ensuring there is enough energy in the system to perform effective defrost cycles (unless there is some form of additional heater present). Without sufficient volume, constant defrost cycles will quickly kill efficiency in colder weather, and leave the house cold.

This post was modified 2 days ago by Old_Scientist

Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.

ReplyQuote

Page 2 / 2 Prev

26 Forums
2,153 Topics
47.3 K Posts
33 Online
5,673 Members

Forum Icons: Forum contains no unread posts Forum contains unread posts

Topic Icons: Not Replied Replied Active Hot Sticky Unapproved Solved Private Closed

RE: Failing heat pump system - seeking thoughts on a rebuild

@jamespa I think that's a good interim solution James. ...

By bontwoody , 8 minutes ago
RE: Electricity price predictions

Community energy installations are a great idea, but th...

By Scalextrix , 4 hours ago
RE: Can you help with our research: solar panels, EV chargers, home batteries, heat pumps?

I have signed up as well. @belsnugg could you outline ...

By JamesPa , 12 hours ago
RE: New Vaillant aroTherm Plus in black - When will it come to the UK?

Ooh, heat pumps in neon blue wrap 🤣 🤣 &...

By Old_Scientist , 12 hours ago
RE: Samsung problems

@profzarkov Good to know in case it ever happens to me...

By bontwoody , 1 day ago
RE: Are Octopuses Slowing Consumer Adoption of Heat Pumps?

I mean, is this surprising? The local installers in my ...

By Alex , 1 day ago
RE: Samsung Controls

@old_scientist sorry, I should have made it clear that ...

By GrahamF , 1 day ago
RE: Mitsubishi Ecodan 11kw Defrosting Issue.

@thundermink can you provide photos to illustrate your ...

By Morgan , 1 day ago
RE: Boiling Mad: Exposing Radiatorgate

Hi @Rob, I’d be more than happy to contribute. I have ...

By DREI , 1 day ago
RE: Solar Power Output – Let’s Compare Generation Figures

@andris a great year - very happy with our system

By Profzarkov , 1 day ago
RE: A Customer's Lessons Learnt from a Heat Pump Installation in a Large House

After our rather lengthy meander off piste, I thought I...

By GrahamF , 2 days ago
RE: Midea ASHP – how to set weather compensation

@pash44pump - to collect the IAT/OAT data, can I sugges...

By cathodeRay , 2 days ago
RE: Ecodan software update. Real or scam?

@vinz86 Contact Mitsubishi and an engineer attends and ...

By ASHP-BOBBA , 2 days ago
RE: Seeking Help for In-Principle Quote to fix a botched heat pump installation by Heat Geek Installer

@drei When I was in local government we were of cours...

By JamesPa , 2 days ago
RE: Heat Pump SCOPs – The Truth Might Not Be What You Think

Sufficient system volume is also essential for ensuring...

By Old_Scientist , 2 days ago
RE: Flexi-Orb Heat Pump Scheme: A Game-Changer for the UK's Heat Pump Industry

As someone who has suffered from a Heat Pump installati...

By DREI , 3 days ago
RE: What crazy nonsense are inverter limits and why are they imposed?

I’ve also got a dual fuel Rangemaster. We originally ha...

By Majordennisbloodnok , 3 days ago
RE: Octopus tariffs - a quick comparison

@tim441 I’d agree wholeheartedly with that, with 2 x Po...

By Toodles , 3 days ago

Forums

Heat Pump SCOPs – The Truth Might Not Be What You Think

Join Us!

Podcast Picks

Latest Posts

Members Online