Air Source Heat Pumps, SCOP and humidity

According to hansard The average coal use per household in 1950 was "a little over two tons at 90 shillings a ton" The actual debate linked is discussing the fact that at the time miners were being partly paid in coal rather than just in money, and therefore mining households burnt quite a lot more than the average household, and if in a time of austerity and needing to import coal from the USA, this was the fairest way to do things.

According to my reference texts burning typical coal is 7MW hours per metric tonne  and more like 9 for 'best quality steam coal'  so the two tons was probably about 15-18 megawatt hours, but I bet more than half of that went straight up the chimney.

Mike

There is a lot of misinformation in this thread.

Firstly, insulation of the house has nothing to do with HP's, it affects all heating sources, so I really dont know why HPs are singled out as 'they dont work on old properties', as, clearly they do! Of course insulation helps, and more insulation is the biggest thing to do to save energy.

Ground vs Air. I used to be an advocate of Ground source, but no longer. I had a call out to one, it had frozen where the pipes came out of the ground, and the frozen ground went around 3 feet down. Research later showed that this was a known problem if the pipes are too close to each other in a vertical excavation, and also happens if they are too close to the surface in a horizontal format. The UKs typical air temperature is above 5 deg. C for 95% of the year, the ground will drop to to 5 deg before christmas on a horizontal excavation, and a bit later on a vertical piled array. They wont benefit from a daytime at 10 degrees, which is quite common, even in January. Vertical arrays are far better, but the install cost is beyond most normal people, and unlikely to ever pay back the install cost, even the excavations for a horizontal array at 2 metres deep may not be cost effective for 20+ years.

Have a back up. Well, you've answered that, a gas boiler or immersion wont work if there is a power cut. A gas boiler will only consume around 250 watts power, so a generator can easily supply the power to make that run. If you have a heat loss of 3kW, then a larger generator, of 2kW or so would run the HP succesfully. Being as you have a log burner, with a back boiler,you are sorted anyway. Yes, a HP, and solar/solid fuel can be combined succesfully.

Frost. Yes, they do frost up in humid conditions below 5 deg C. The defrost cycle will take some of the water from either the central heating, or hot water cylinder supply loop, run it in reverse (not actually in reverse, a valve opens inside the HP), run that for 2 or 3 minutes, and the defrost is finished. Of course, the COP does drop because of that, but, the HP should, if designed and fitted correctly, achieve a COP of 3.5 or higher. I was on a course last week, the Owner of the Training Centre is a bit of a researcher into HPs, and he regularly gets a COP of 6, all year round. He said on the day before, it was almost 9.

Cost. Install cost can be almost free now with Octopus et al falling over themselves to fit them. However there is a downside to the cheap install cost. BG guarantee that their HPs will keep your house warm, but they dont say at what cost. From some inquiries, they set them to run at 50 deg.C which is not at all efficient. Octopus are similar in that they do a 'one size fits all' approach. If its cold, they just turn up the flow temperature, which gets the house warm, but adds energy costs.

If you do want one, then it shoud be designed correctly, with a good heat loss survey done before anything else. From that, it can be decided if the current system needs upgrading. At a 3kW heat loss for the whole house (getting toward passive levels?), then you will probably be ok for the piping through the property if they are 15mm+. Radiators/emitters may have to be changed.UFH pipes are generally ok, as they usually run at a lower temperature anyway (27-30 Deg C?) The flow temperature will certainly be lower with a HP compared to a gas boiler. From the flow and return temperature is the Delta T, temperature difference. On a gas boiler it'll be 20-40 deg. on a HP it'll be 5 to 7 if designed correctly. This is what causes the need for larger emitters, not the flow temperature, basically, with a smaller DT, there is less heat given out on each revoltuion of the heated water, so, to make it up, a larger emitter is required.

Running costs. Without good research, it can be hard to justify a HP against a gas boiler. Install cost is the big problem, as said, it can be fitted cheaply, with the 7.5k grant, can be almost free, but I wouldnt trust the Company who fitted such a HP. There are better Companies out there who do a far more detailed design and installation, and give proper after service (at the least, i would expect a revisit after a week, then a month, and then 6 months on to ensure all of the settings are optimised, being as you are technically minded, that could be something you do yourself). You would not get that kind of service from Octopus, or, indeed, any of the larger Companies who have jumped onto the £7.5k grant bandwagon.

If you get a SCOP (years average) of 3.5, then the running cost will compete with gas. If designed properly, I think you could expect a SCOP of over 4. Get below 3.5, and gas will be cheaper. But, who is saying gas will not increase in price? It certainly wont decrease by much, whereas electricity could come down in price slightly, some suppliers are actually giving free power at certain times now as wind and solar need to be used up in their generating peaks.

Whether to get one. The main advantage is their lack of emissions at source. Yes, there is still some coal, and a lot of gas generation, but that percentage is slowly falling, so you can say, without doubt, that you are running a greener form of heating, which will only get greener in future as renewables increase their production.

Cost, install is certainly more than a gas or oil boiler. Running costs should be comparable to, or better than, a gas boiler. If it isnt, then the design and / or install has been done badly.Ongoing costs should be similar. They should be serviced every year (Grant do a 7 year warranty on their HPs if serviced to their spec), the service cost is typically £150. If you have a pressurised cylinder, that should also be checked every year, so combine the 2. Servicing costs are a little more than gas boilers, but, most gas services do not do a correct service, look into your service manual for any recent boiler, and there is a long list of items needing to be removed and cleaned etc, whereas most Gas Servicers clean out the combustion chamber, do a combustion and gas leak test and say it has been serviced. BG were notorious for this lack of actual servicing.

It's a difficult choice, I'm getting a ASHP myself after looking into it a lot for my own house. Over the last few years I've done a lot of Courses about heating, and manufacturers courses on their own HPs. I wouldnt recommend one make over the other, but I'm going for a Daikin 4kW unit. Nibe was a close second, and has a better set of controls, Grant was in the frame too, but the training and back up from Daikin won the day, and the price was a bonus too, in being very slightly cheaper than the Grant, the Nibe was a lot more expensive, but I think it is a better overall unit, with better controls, but the extra cost did not justify that over the Daikin. Vaillant have been the market leaders for the last 18 months or so, but many of he other makers have caught up with them. Its a minefield, if you were buying a gas boiler, it is far easier to make a choice, as most of them are very similar, HPs are harder, as they all have their own proprietary controls, and the controls and setting them up are a big part of making them easy to use. If you are still looking next June, then get yourself along to the Installer Show at the NEC Brum, as all the Makers have their products on show in one big hall.

mapj1 said:

In the newer ones, the gas might have been original for lighting and then electricity was added at some point

Probably neither when our place was built in around 1902. The gas lighting seems to have been put in when the house was extended circa 1923, but there was no mains gas available at the time so it would have been only for lighting.

Coal consumption would have been several tons per year then, about 5 cwt now.

Thats a really good point actually, better insulation and building standards mean less heat loss and thereby less demand for heaitng appliances and heat pumps can be more effective.

But the flip side of that would also mean less gas consumption required!

Plus if you factor in global warming (not that it really is much warmer in the winter) then there should be higher temperatures and again less heat demand, in theory at least.

Indeed - that coal fire would have been lucky if it was equivalent to 2 or 3 kW when well made up, and there would have been ice on the bedroom windows inside in the morning in winter - the only time a bedroom fire was lit if some one was really ill. - I recall that time too, but I was young..

Of course if it is the same temp inside and out, there is not a lot of  point in double glazing either.

I'm not advocating for this by the way, quite the reverse, but I wish to make it clear where I think the 'do nothing' scenario ends up.

We can change the designs of future houses of course, the problem is more the rows and rows of hundred plus year old solid walled terraces that are the majority in many older cities. In the newer ones, the gas might have been original for lighting and then electricity was added at some point, then a phone line, and now in the next hundred years or so, for sure,  the gas is going to end.

Mike.

mapj1 said:

that is not to heat houses very much at all

Modern houses should not need to be heated very much at all, which is why electric heat pumps may suffice.

When I was a lad, many people did not heat their bedrooms and there would have been a coal fire downstairs. That's no good at least in England now.

This year we have managed to get our gas consumption down to 60 MWh. I don't think that there is currently a viable alternative to gas.

Weeell, there is a viable and very cheap alternative - but it certainly involves a drop in living standards and possibly lifespans- and that is not to heat houses very much at all.  This would revert to where we were before central heating - there is a reason for all those sleeveless jumpers in old photos, after all,- but we have had at least one generation, probably two,  that know nothing else but instant warmth, and would certainly struggle to adapt to that.

At the moment folk talk about choosing to eat or heat, as if both are equally essential, while really to some degree food fuel and clothing can be interchanged, but then some folk think electricity and or the internet connection is essential too..... 

It really depends how it pans out - even if climate change does not get us, the gas fields running flat certainly will at some point, so some adjustment will have to happen. If it is not planned, then simply being priced out  will do it, but just waiting for that to happen is not an outcome I would favour.

Mike.

Yes thats true, I think the 2025 date will stick for new builds but the way things are going with targets and so called called climate crisis the farther away dates may yet come in!  But hopefully common sense will prevail and they will realise there is no viable alternative and scrap it.

I'll buy a replacement before they are banned so will be running a gas boiler in my house at least until 2060, or until the gas supply is off or I am deed.

well, where we are now, is that it is gas heating in new build houses that will be phased out from 2025, and replacement boilers in existing housing from 2035 onwards. That in turn suggest to me that most older houses will still be running gas fired heating until perhaps the mid to late 2040s as the last decade or two of installations start to fail beyond repair, though a sharp rise in gas price may lead to the switch off of working systems.

I think you have a good while to organize a replacement, and if you wish to stay with gas (and if you already have it I would at the moment) then there is at least a decade or so to do so.

Mind you this is govt policy we are considering, so it may be cast aside at any point, but I'd be surprised if the dates go much nearer, I'd not be at all surprised by a slight delay when the deadline gets closer.

Mike.

Don't let the greenwashing fool you, buy a gas boiler before they are banned!

For most of us there is no viable alternative at the moment.  (Air source) Heat pumps are not working aswell as advertised, especially at lower temperatures.  Ground source can be effective but again has limitations as you need the deltaT, also huge installation costs and this is crucial for their effectiveness.

The boiler in my house is over 30 years old and still going strong.  But I am worried when it fails I might not be able to buy a gas boiler replacement.