goiḃniuFeb 20
After much consideration and research, I think I've finally settled on a heating system for my #Retrofit of an old house, which avoids the typical compromises and would suit a lot of people.
Key features:
* Constant hot, potable water (no legionella cycle)
* Responsive, underfloor heating
Key technologies:
* High temp heat pump (R290)
* Super insulated buffer tank (thermal store)
* Heat exchangers (BPHE)
* Low profile UFH, with metal sheets for dissipation (low thermal inertia)
Show threadgoiḃniuFeb 20
The sole job of the heat pump is to keep the buffer tank hot (~75°c). Fresh water is heated from the water in the buffer tank via an external, brazed plate heat exchanger to provide potable, hot water. This means there is only a small amount of stagnant water, in the pipes, so there is practically no risk of legionella. Super insulated tanks loose very little heat are simple and readily available, so they make more sense than, say, a phase change material, thermal store.
Show threadgoiḃniu
UFH is typically installed in the slab, which works as a cheap thermal store, but it has some serious disadvantages. It is extremely unresponsive, taking a day or so to bring a house up to a comfortable temperature. It relies heavily on insulation, to be efficient at all. By using a low profile system on top of the slab, or wooden floor, this can mostly be avoided. You can even heat the area quickly by boosting the temperature, since it will cool down quickly too.
Feb 20 at 3:27pmWeb
Show threadgoiḃniuFeb 20
This is also nice because it can be used on upper floors, without any need for screed etc. If you already have a reasonably insulated floor, it can be installed on top, only adding a few cm and without the need for digging up your existing floor. A leaking pipe, would not be such a massive job to fix, either. This setup allows you to upgrade in more affordable phases, rather than doing everything at once. If you already have radiators, you could use them instead.
Show threadgoiḃniuFeb 20
Overheating is another common problem with systems that use the slab as a thermal store e.g. from solar gain.
Show threadBen AvelingFeb 20
One claimed advantage for UFH is that you can heat using off-peak power. I have no idea if that works in practice.
@goibhniu
Show threadgoiḃniuFeb 20
@BenAveling Thanks, maybe I'm wrong, but I'm thinking it makes even more sense to charge a buffer tank (and battery) with off-peak power, which you can then use when you need it.
Show threadBen AvelingFeb 20
If you've got enough battery, then I guess it's an option.
I think it used to be impractical to run heating from a typical home battery, but the technology has improved a lot, so maybe. @goibhniu
Show threadPadjoFeb 20
@goibhniu very interesting, would love to hear more about the exact setup. I'm going to have to ditch my gas boiler at some stage!
Show threadgoiḃniuFeb 20
@Padjo great! I can update this thread as I go, but I expect it will be a while before I actually start buying stuff and installing it. It might make sense to go for solar first, if you're in a position to do that.
Show threadOrange MenaceFeb 20
@goibhniu we considered fitting a similar system a couple of years ago. I went through most of the same ideas. In the end, I stuck with a traditional radiator wet heating system. Adding insulation, replacing all the windows and doors with very efficient triple glazed units, and working on air tightness means it takes very little heat input to warm the house.
I was dead set on a thermal store, but it takes a lot of input to heat it and in summer we wouldn’t need that much hot water!
Show threadOrange MenaceFeb 20
@goibhniu I’m still considering a heat pump, but there was a fairly recent condensing oil boiler that came with the house. I added a 3-way valve so we can heat just the water in the summer, and a proper control unit with room and cylinder thermostats.
We use less than 1000l oil in a year, and house is at a fairly constant 20-21C.
Show threadgoiḃniuFeb 20
@OrangeMenace fantastic, thanks! My understanding is that it takes very little energy to keep it hot, if you're not using it. If that's not the case, I suppose an additional, smaller buffer tank for use in Summer, could do the trick. I think the high temperature heat pumps and super insulated buffer tanks are what make this feasible at all. I'd love to know what you think.
Show threadOrange MenaceFeb 20
@goibhniu it was about 3 years ago I looked at this, things might have moved on. I’d looked at all the same tech - thermal stores, plate heat exchangers, metal plate UFH, but decided to work on the fabric first, then see how much heat input I actually needed..
How thermally efficient can you get your house? Replacing all the windows and doors wasn’t cheap, but it transformed our house.
Show threadgoiḃniuFeb 21
@OrangeMenace Excellent, thanks. I have an old stone house and I'm going to need to gut it. It has no insulation, I need to replace the roofs, windows, dig up the floors, the whole thing. It's daunting and going to cost a fortune, and I'm wary of making a mistake now which will cost more in the long run e.g. heating the slab. At the moment, I only heat a single room, with an electric heater. I'm going to have to rent part of the house to pay for the job.
Show threadOrange MenaceFeb 21
@goibhniu you’ve got quite the project! We looked at some stone houses but ended up with a more modern timber frame construction. From what we read at the time, stone houses seem to like constant heat, to keep the structure warm and push the moisture out. In the old days people had an Aga, but under floor heating would be the modern equivalent.
First winter here, we had a draughty house and electric heaters so I know what that’s like!