heat pumps anyone ?

If you have a working smart meter. Currently waiting for my 5th one in 4 years.

Tim

I’ve never really got my head around SCOP. Between March and October my gas boiler twiddles its thumbs doing bugger all so I’m not that interested in a system’s efficiency for much of the year when it will scarcely be operating.

Tim

I spend as much on oil in Dec-Jan-Feb as I do the whole rest of the year.

The reason is the ambient temperature is well below the average UK of about 9°C

And sometimes below 0°C

That is the efficiency that really matters to me, and I suspect everyone, is the efficiency when ambient is below 4°C .

And that's exactly when an ASHP is crap. When its cold outside and you need the hottest water inside to heat the house.

As with all eco s*it it lets you down when you need it the most.

In the end all that is important to most people is what their final bills are.

Exactly. CH in at least the more southerly parts of the UK only operates between November and April and even then the big burn is december january and february

A modern well insulated house will stay warm most of the time simply on account of the trickle of power its using anyway to do other things.

The problem is that's too simplistic an example.

A lot of the heating degree-days come in spring and autumn. It's 10C outside and the house needs to be heated to 20C. That means the emitters only need to run at (say) 30C to get the heat output, and that's when the HP is at its most efficient, with a deltaT of 20C.

Contrast that with taking hot water on the same day from 10C to 50C and the HP has to work harder with a deltaT of 40C.

If instead you heat the water with a solar panel then the HP only has to make deltaT=20C water and it's very relaxed and the COP is better. The more days with a better COP you have, the better the SCOP.

When it's -10C outside you drink big chunks of energy which makes a sizeable contribution to the SCOP, but it's about degree days again: 5 days at -10C (needs 5*(20-(-10)) = 150 deg-days at thermostat=20C) in winter versus 50 days at 10C (needs 50*(20-10) = 500 deg-days). Obviously that's a caricature but just to illustrate the point.

SCOP doesn't include cooling. That's SEER.

Theo

Interestingly, this year the house thermostat brought on the heating in July. We are in Surrey!

Sadly our house in not modern - 113 yeasr old.

Why include solar into the equation? The SCOP figures are only for the ASHP and not a hybrid system? My point is any use of the hp in the summer is going to make the SCOP figures look better albeit very marginally better if only used DHW.

I would still question the validity of the SCOP values for the Octopus ASHP. Does the SCOP testing assume that the higher output temperatures are only going to be used for DHW and for CH running at a lower temperature into large radiators or always with higher output temperatures for CH feeding existing radiators that would have been sized for a 60+C feed temperature?

On a given spring day where ambient = 10C.

For heating the ASHP has to make deltaT = 20C For hot water the ASHP has to make deltaT = 40C You get a COP which is based on the (weighted) average of those two numbers, let's say deltaT = 30C for this example.

In reality you may use more heating than hot water, but that depends on various factors like your house size and usage of hot water.

On the same day, if you have solar and heat water via the immersion or solar thermal, not the ASHP:

For heating the ASHP has to make delateT = 20C for heating. For hot water the ASHP does not run. You get a COP which is based on heating alone, ie deltaT = 20C

deltaT=20 is less work for the HP than deltaT=30 and so a higher COP.

In summer (without solar) it's even more significant.

For heating the ASHP does not run. For hot water (maybe 15C mains temp) the ASHP has to make deltaT = 35C

deltaT=35 so the HP is working harder than it does on a spring day, and that drags the SCOP down.

Obviously there are a ton more varying factors which make any calculation specific to a particular installation, but it illustrates the effect on the SCOP. The SCOP is not the be-all-and-end-all, but it's the sort of thing to be aware of when understanding what the SCOP number means, especially for the SCOP of a specific installation.

The MCS table you linked to shows SCOP at different output temperatures. AFAIK those are calculated based on a constant output temp, ie no weather compensation, no varying between heating and hot water.

Effectively they put the HP in different conditions (air temp at X degC, water temp at Y degC) and ask it to make water at Z degC. That gives the COP figures for different conditions. Then they take a model of some average UK weather conditions to give the daily temps and number of degree days for that location and use that to calculate the SCOP for different values of output temp Z. That test doesn't care what you're using the water for - it just comes out of the unit in a pipe.

What they do not do is put it in a house and measure what happens with radiators or UFH or a family of teenage girls. All those are things that are specific to particular installations, which is why everyone gets their own SCOP, which is not the same as the standardised SCOP on the spec sheet.

Theo

That's modern from where I am. We're keeping our oil boiler as long as we can. The Listed status might make anything external, like the cold end of an ASHP, impossible.

Andy

Bravo!

"what their final bills are"

People are selectively rational.

They will pick apart a solution based on comparing energy cost.

But hardly anyone considers the economics of insulation. Insulation would have reduced our heating season bill and paid for itself, but people don't do that. There are plenty of houses out there, that are energy pigs and hard to heat even with powerful heating solutions.

Even if you don't agree with ASHP, insulation would make the world a better place.

Paul

I think every single private home that can benefit and whose occupants can arrange the capital has already insulated it as much as possible.

I don't think that's true - there's lots of structural reasons why people don't insulate. eg because it means disruption which they can't cope with, or they have other things like work or health problems to worry about. People are not rational economists.

Also once you've done cavity walls and loft, the next lowest hanging fruit may be windows. Some houses have a lot of glass and older even double glazing isn't very good. Unfortunately changing windows is very expensive so many people don't do it.

Plus a number of homes are rentals and landlords just don't care, they're quite happy for their tenants to live in a crap home paying high bills with no power to do anything about it.

One thing not mentioned about ASHP is how much nicer it is. The house is at a nice smooth constant temperature all day long, you get none of the temperature swings and draughts you get by cycling a boiler on and off and pumping scalding water about. I'd never go back to that.

If I had cooling installed (or UFH) you can also set the ASHP to maintain a constant temperature in summer too - it'll decide whether it needs to heat or cool, and how much. It's proper climate control rather than a crude box of fire.

Theo

Earlier this year I stopped at some traffic lights, behind a van that was sign-written ‘DAMPREMOVERS’ under which was written ‘Cavity Wall Insulation Removers’.

They didn’t seem to be cowboys, and were getting enough business to run a dedicated firm.

A couple of decades ago we decided to upgrade the 1” of loft insulation with that space-blanket stuff, bought in a sale. It certainly cut the heat loss. Unfortunately the loft became quite damp, water dripping on the insulation we’d put in, and the wood felt quite moist.

We moved shortly after.

That means they cant. Not that they wont

Windows are the lowest hanging fruit and ex of loft insulation, the cheapest

They score because of draught proofing more than the double glazing

Even things like taking up carpets and tacking hardboard over a suspended wooden floor to cut down draughts makes a huge difference.

Cavity wall is quite expensive and not possible if there is no cavity

I specified privately owned for that reason

You are an idiot. Thats not ASHP. Thats underfloor heating. My oil fired UFH is the same. You cant retrofit UFH to solid concrete floors.

Well that's the danger of uninformed retrofitting.

Like Grenfell towers.

In reality if you have adequate soffit venting you wont get condensation in the roof space above the insulation.

It's a problem in certain situations - typically, a narrow cavity (so quite early examples of cavity wall), exposure to wet (leaking gutters, driving rain etc.), little direct sun, and/or high ground level (typically, raised above the inside floor level). In those situations damp can penetrate the outer skin, bridge the cavity, and introduce damp indoors. Joist ends particularly susceptible.

I know - because my home is affected. My architect neighbours who've just moved in are having their cavity insulation removed - quoted £5k. I don't think I'll bother, partly because I don't think it's possible, having seen how 'clumpy' and stuck together it is when I replaced a couple of bricks. And partly because I've fixed some of the causes of the bridging. Not the main ones though, so I'm keeping an eye on it, and expect it to take a long time before it ever dries out.

I think a firm of solicitors near here (Sheffield) went broke because they took on a number of no win-no fee cases on behalf of affected households who had cavity fill. It's quite difficult to prove negligence ISTR, even if you can catch the installer. Hence the removals firms.

Indeed - takes a lot of thinking through. I had a new roof recently and the roofer went for 'warm roof' - celotexed between the rafters. It seems OK but quite a few cold spots need sorting at some some point, or I'll be getting damp too. The 'Spray foam insulation' thread covers some of this.

Not a bad idea :-)

I don't have UFH, I have radiators and a concrete floor. It still applies.

Theo

My insulation was pumped through the outside wall to the cavity, with no disruption at all. It has proved very successful.