Peter wrote:
Radiators sized for 80C water is a fairly aggressive cost reduction tactic You also need a big boiler to achieve that. Very wasteful.A heating boiler should do HW as well. That provides you with hw at a small cost, and negligible when the heating is used.
Can anyone work out how the above Mitsubishi heat pump avoids evaporator icing?
That was the standard UK post-war central heating design – it assumed a boiler providing 80 degrees C (or thereabouts) flow to the radiators and approx 60 degrees C return. You don’t need a particularly large boiler because it isn’t a very high volume of water.
The boiler was here when I got here. It’s a combi boiler, so even if connected it wouldn’t work like that. They are separate circuits and give no free lunch. I agree that when a gas/oil boiler also indirectly heats a water tank (which is incidentally what our Aga does) you may as well use it. I could modify the CH circuit to take a loop through the hot water tank, but it’s not worth the capital cost and the amount of mess/hassle necessary to put the pipework in. If we ever got rid of the Aga I’d consider it doing it, but we still wouldn’t be using the boiler as it was designed to be used – i.e. on-demand hot water heating.
The whole thing has provided an interesting lesson in practical thermodynamics. It was extremely satisfying to experience the evenly-warm radiators, much better heating and lower gas consumption (boiler condensing) having increased the system capacity and adjusted the boiler to pump it round more quickly. You also get less sludging in the system because of the greater fluid velocity.
@Inkognito I wasn’t suggesting people run air sourced heat pumps with 80 degrees flow temp. Just that most legacy CH systems in UK housing stock have radiators sized for 80 degrees flow temp, and obviously if you want a heat pump to work well with that system (at a much lower temp) then you usually need to make extensive modifications – at the very least adding radiators or considerably upsizing the existing ones. Depending on the house, this is often completely impractical to the point of an entirely new CH system being a better idea.
Is that a warm-air blowing heater? Does it sit on the inside of an external wall, exchanging with the air outside and heating a single room? What do they cost?
Not sure what they cost, €2-3k I think. My pump came with the house. It heats the entire house actually. It circulates/heats lots of air at a modest velocity. It shuffles air around very efficiently. It works much better in all respects than I would ever imagine a year ago 
Think of it as a fireplace with a big but gentle fan on top.
However, using an outside air sourced heat pump to first heat up water to 80 deg, and then use that water to heat up the house to normal room temperature, 22 degree perhaps. That sounds to me to be a very inefficient way to use a heat pump.
@Inkognito when I referred to over insulating I was talking of the many people living in old stone houses who block every
entry and exit point for air, including air bricks, and the air intakes for wood burning stoves and fires, so that the air has to be pulled from all over the house causing draughts and a lack of air.
@Graham from your post I assume you have a gas condenser boiler. I thought that might be the way to go in one of my listed buildings until Putin decided to invade Ukraine. However, I was put off by all the reports on the internet of a toxic air/liquid waste product. How are you dealing with this and is it really a problem?
LeSving wrote:
Not sure what they cost, €2-3k I think. My pump came with the house. It heats the entire house actually. It circulates/heats lots of air at a modest velocity. It shuffles air around very efficiently. It works much better in all respects than I would ever imagine a year ago Think of it as a fireplace with a big but gentle fan on top.However, using an outside air sourced heat pump to first heat up water to 80 deg, and then use that water to heat up the house to normal room temperature, 22 degree perhaps. That sounds to me to be a very inefficient way to use a heat pump.
If they only cost 2-3k then I would buy one, but might struggle to fit it bearing in mind my walls are solid stone ~60-70cm thick. Amazing that it can heat the whole house – if so then it sounds like a no-brainer. How much electricity does it consume to do this?
I think I pointed it out before, but they don’t use them here to heat water up to 80 degrees. They run CH systems at some much lower flow temperature, but the problem is that the legacy CH systems they fit them to were originally sized for 80 degree flow, so work is necessary (more and larger radiators) to make them work passably.
gallois wrote:
@Graham from your post I assume you have a gas condenser boiler. I thought that might be the way to go in one of my listed buildings until Putin decided to invade Ukraine. However, I was put off by all the reports on the internet of a toxic air/liquid waste product. How are you dealing with this and is it really a problem?
Yes a gas condensing boiler. Mine burns LPG from a tank in the garden, since the village does not have mains gas piped to it. Most others in the village have oil boilers instead. Oil offers more supply flexibility (buy from whoever, order and they deliver) whereas with LPG you get stuck with contracted suppliers in fixed-price deals lasting 2 years. On the flip side, oil boilers and tanks are smelly, and oil boilers cannot generally modulate – they are 100% output or nothing – so the issue I have had to solve with my system would have been much worse with oil.
The gas from the flue is just the by-product of combustion. You probably wouldn’t want to breathe it directly, but then you don’t generally. Well over half the houses in the country have a gas boiler – the only models available have been condensing ones for some time now – and the exhaust isn’t thought to be a particular problem. While operating it empties the condensate trap periodically, ejecting maybe 100ml liquid / hour. The condensate is basically water but is quite acidic, maybe pH 3-4. In my installation it is piped through the wall and just drops onto the earth on a small flower bed next to the house – I plant that area with plants that like acidic soil and they do fine. Some people pipe the condensate outlet to a sewer or soakaway, or alternatively to a wastewater drain within the house – I don’t think there are any rules and no-one seems unduly concerned about it.
Thanks for the information Graham. I have a listed building in limestone. Walls 60cm thick etc.
Currently it has an oil fired boiler approx 40Kw feeding what are really good radiators, the type you would have found in an old UK school.
It doesn’t supply the hot water system although it probably could.
The boiler was installed more than 50years ago. It heats the building really well and the costs are quite competitive with other forms of heating and cheaper than some.
At over 50 years old I am aware that it might not continue working for very much longer.
If the time comes soon, because of new rules set by the French government, I can no longer replace it with a more modern oil heating system. The choice is gas fired boiler, heat pump, or granule fuelled (this is a non starter as I don’t live on the premises.
So I am very interested to absorb all knowledge of both heat pump systems and gas fired boilers, and the prosband cons. Thanks euroga.
Sounds like a great system. Why shouldn’t it keep going? I certainly wouldn’t change it unless I had to, and it might be worth sourcing spares if you can and keeping them in reserve in case they become unobtanium?
A ground-source heat pump is, I understand, a better proposition that an air-source one, assuming you have the space. With old-fashioned (high capacity?) radiators I presume heating at a low flow temperature would work well enough. High capital cost though. The gas boiler is a drop-in replacement at low capital cost, but is there mains gas or would you need a tank?
Apart from that it’s just a gamble on gas/elec prices going forward.
You can do a google on condensing boiler efficiency but it is a lot better than a non condensing boiler, especially a 50 year old one which is probably basically a dustbin with a burner underneath it. We have a condensing one now and I reckon it halved the oil usage. The condensate comes out of a pipe and by regulation, if entering the soil directly, needs to be x cm away from the house walls. Basically about 1m away. The chimney outlet also need to be x cm away from any window – that’s obvious anyway. Condensing boilers are not as reliable as the old ones.
A ground source heat pump is the way to go, but you either need a field to bury the pipes in, or pay 10k+ for a borehole. But even with a GS HP you still need underfloor heating, or loads of radiator area.
Radiator style is not important but obviously the modern ones can be smaller for the same heat output. I got a whole new system put in in 1999, with Faral rads. They are about half the size of the old “Soviet Bloc classroom” ones And I am using +60C boiler output.
You should definitely heat your hot water from this boiler. That circuit needs its own motorised valve (2-port) which is opened when the hot water is calling for heat – typically this is a cylinder thermostat (set for about +45C) and a timer. Each zone has its own 2-port motorised valve. Each valve has a switch which closes when the valve is fully open; all the valves’ switches are wired in parallel so any valve open turns on the boiler+pump. That’s the standard way. There are refinements like a delayed turnoff on the pump, which gains you a little bit by extracting the remaining boiler heat. Some boilers implement the pump power internally, including this delay. If you do all this, further gains are minimal.
40kW is a huge boiler – enough for a 10 bedroom house
Problem is, he’s not allowed a new oil boiler.
I’m surprised that a new one should halve the oil consumption, that sounds optimistic to me. At the end of the day you’re just burning it and using the heat. Obviously the old one won’t be condensing, but no way round that as he can’t put a new one in. It’s always a case of looking at the payback, and in this regard most consumers have poor literacy and are easily sold a lemon. UK consumers are always having ‘new more efficient’ boilers pushed on them, ‘save £££ on your heating bills’, etc. Not many have the nous to ask how much gas the capital cost would buy.
I agree, but it depends on how bad the old one was. And in the oil boiler business, it could be “pretty bad”. Gas boilers tend to be a more modern design anyway.
