Welcome to the forums @hawxby

My personal take on SCOP is that it's a marketing and promotional metric which is only semi-useful. Look at our ASHP as an example. In the enclosed image (a plaque taken off our ASHP), all calculations are based on flow rates of 30/35C, and I think that if we ran our heat pump at 35C, we would probably have a COP of over 3. Given our property, a renovated period farmhouse, insulation is good (not excellent) so we have no choice but to set our flow rate to 45C. Our heat pump's lifetime COP is 2.7. There is no way (after using the pump for two years) that we will ever get above 2.8 unless we consider dropping our flow rate to 35C. 

We are upgrading some rads next week to K3s - if they're effective, we'll consider dropping our flow rate to 40C and see what that does to COP. 

Not sure if that's helpful at all - will have a look at your attachments tonight.

Thanks @Mars. I actually included the Caernarfon in my table above and according to the MCS database they tested it at 4.11 @ 35C and 3.26 @ 55C, which if you're saying you've for a lifetime COP of 2.7 @ 45C shows just how much the lab differs from the real world. At 45C the MCS database shows 3.46.

That being said, I didn't really expect to hit the lab numbers with any heat pump but it was more a question as to whether the lab numbers can be gamed in a way that makes a less efficient pump appear better than a more efficient competitor in lab conditions, VW emissions style. I ask because I had a call from the installer speccing for the LG today and I directly asked "Would you install a Grant? Their SCOP is incredible", and he flat out said no, there's no way they really got that number and the reality is once installed it would perform basically identically to the LG, perhaps even worse seeing as they're a little company that don't have much HVAC experience. LG and the like are drawing on years of experience making air con and heat pumps systems. 

Aside from that, as a test before getting a ASHP installed we've been running our radiators at 50C for the last couple of weeks and even with a dip down to -3C a couple of nights ago we've not had any issues in terms of temperature and we haven't even had our cavity walls sorted or radiators upgraded yet. For reference we're in a semi-detached with a rough 50:50 split between the original 1920's farm cottage and a 2008ish extension. We've got 17 radiators in the house of varying quality and sized but the intention is to replace/upgrade 6-10 of them.

@hawxby, the published COP numbers are similar to car mpg figures.  They are created under very controlled conditions.  They will give a general guide but that's all.  The construction of your house and the way you use the system will have a much greater effect on COP than the manufacturer.  I would also say that finding a good installer is just as important as choosing the right ASHP.  Also, you obviously know about the permitted development rules and choosing one that fits within them might be worth doing. In case you haven't seen it, look at this.

https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/planning-permission-for-air-source-heat-pumps#post-540

It's good sign that you can heat your house at 50 degrees.  That's what our newly installed system is set at (it's a Mitsubishi) and in the week that it's been running (1 April to now) COP is about 3.3. 

@hawxby, I went through the list and a lot of the numbers are 'inflated' as a result of lab environments that they're tested in, which can never be replicated in reality (as you've pointed to). Our pump is a clear case in point: 3.46 versus 2.7 is world's apart.

The conversation with your installer is an interesting one. While the argument of LG, Mitsubishi and Samsung being dominant in ASHPs because of their AC experience is a valid one, you're also dealing with global multinationals that have a mixed track record when it comes to service and after sales support.

@sam, as an example, purchased a house with an LG ASHP and it's been a nightmare story from the get-go and it's only because @bobbt9866 got involved (who has LG connections) that things are happening – we're awaiting her latest update which might entail legal action. 

We went down the route of a "small" manufacturer in Global Energy Systems, but the after sale support has been excellent. It also comes down to the competence of the installer and that they design, size, install and commission the heat pump correctly. There are so many moving parts and loads of places where things can go wrong.

As for your test, that's a sensible approach. As it transpires, some of our issues have been related to pipework, so we'll be adding a stronger distribution pump next week and we're also upsizing five rads to K3s from Stelrad. Radiators are important  when to heat pumps – do you have K2s, and it's interesting to hear you'll be changing a few - the heat loss survey and emitter guide are very important. 

Yep @kev-m, planning permission is something I've been looking at and staying clear of anything that will require it. We have about 300L of oil left (we had 1000L fill in January) so I'm trying to time the heat pump install with the oil tank being almost empty. I was initially concerned that LG would not fit within the permitted development volume but the installer forwarded over a brochure with slightly different dimensions compared to the documentation I could find online, but both LG and Veissmann websites are absolutely awful for getting specific figures. 

@editor I agree about the installers. We actually already had a 4th installer provide a quote already but I cropped it out of my image. First they turned up without even notifying us of an appointment, then the guy didn't give me a great feeling as he was looking around, his estimate then came back with 8kW when everyone else recommended 12+, but most amusingly he recommended installing it on top of the garage. We don't have a garage. Staggeringly bad.

The rads we have already are a bit of a mixture. Given what I've been reading I'm thinking I will change out more than what is suggested below and going to K3's and wider where possible to reduce the flow temperatures as low as possible. It seems a lot of people that are suffering with cold houses or horrible power bills have either undersized rads, undersized heat pump or poor insulation, my intention is to have none of them. I've got a company round next week to quote an a PU cavity fill. Combined with 300 - 1000mm of loft insulation I'm hoping our heat losses will be much lower than the EPC. 

Much like the websites you can enter real world economy data for cars, there should be a way to do the same for heat pumps on a month by month basis, eve better if there was a way to have the data automatically flow through. 

@hawxby, there are a lot of cowboy installers out there. We had six in total quoting, and three were shockers.

We are putting in K3 rads from Stelrad in next week Tuesday and Wednesday. I’ll be able to let you know what the difference is like in rooms that have been underperforming. The new rads have 50% more metal surface, so we hope they do the trick.

@hawxby SCOP should be ignored.

@editor

I reduced my boiler temperature settings two month ago, as an experiment and have reduced my gas bills by a third by that alone. Wish I had done it sooner.

I have not changed from a boiler to a heat pump, as someone will no doubt ask, because we were going to downsize and i could justify the cost in the short term. We have decided to stay in the property so might have to review.

Our house is well insulated and we have replaced three windows recently and are about to replace/upgrade two radiators.

Posted by: @bobbt9866

@hawxby SCOP should be ignored.

Could you please explain why @bobbt9866?

@bobbt9866, I suppose that makes sense. This winter, with the new distribution pump and K3 rads, I might experiment dropping our flow to 40C to see if that helps at all with running costs.

@editor

Rather typically, of course, the temperature has dropped but the house is still maintaining 20DegC and my better half is still not sitting in the lounge wearing a Parka.