Reducing flow temperatures normally makes gas boilers more efficient, not less. They stay in their condensing mode longer and cycle less often.
Heat Pumps: anyone have one/thought about it?
- Thread starter fish
- Start date
Modern heat pumps don’t need an immersion heater assist for hot water. Even the ‘low temperature’ ones.
We know you like a YouTube video, have a look at the 2 links I posted above.
Heating hot water generally lowers SCOP thought as it has to get hotter. 50-55c is normally more than fine for hot water and they’ll push it up above 60 once per week for legionnaires.
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It's a combi, so while that's true in theory. What actually happens is it can't manage the low requirements at it lowest output so starts cycling. If I set the whole house to 22c it'll happily stay on pretty much on its lowest.
But with only some rooms on maybe even one and asking for 18c it doesn't work.
I'd need something like a 5kw boiler.
Lowest mine can do is about 3.7kw which from a 32kw boiler isn't bad.
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(I find written descriptions more trustworthy) - but had posted on high temp heat pumps before ...
https://www.homebuilding.co.uk/advice/high-temperature-heat-pumps - talks about 35-45C, unless you have heat pumps using more esoteric compressor gases (like that on vw ID3)
maybe you can go with a bigger hot water tank though (is that already part of the game plan), to compensate for lower temperatures and the higher volume of that water you would use in a shower, or kitchen use.
The written medium can just as easily be out of date and lack specific detail 
Modern low temperature heat pumps will happily go to 60C for hot water. Most target 50C for hot water which is fine and only go up to 60 for the legionnaires cycle. Performance obviously reduces when going to 60c.
It’s pointless heating it more to then mix it with cold water to cool it down. It’s more efficient to just make more when you need it.
Modern low temperature heat pumps will happily go to 60C for hot water. Most target 50C for hot water which is fine and only go up to 60 for the legionnaires cycle. Performance obviously reduces when going to 60c.
It’s pointless heating it more to then mix it with cold water to cool it down. It’s more efficient to just make more when you need it.
I'd be more than happy with around 50c.The written medium can just as easily be out of date and lack specific detail
Modern low temperature heat pumps will happily go to 60C for hot water. Most target 50C for hot water which is fine and only go up to 60 for the legionnaires cycle. Performance obviously reduces when going to 60c.
It’s pointless heating it more to then mix it with cold water to cool it down. It’s more efficient to just make more when you need it.
When my heating is on flow temps range from around 25c to 40c so sounds like they can easily do those temps.
See what Octopus come back with.
Soldato
Interesting I hadnt figured on them being self DIYable.
I had assumed they would fall under the permitting of greenhouses gases (like AC units)
Pretty good. We've got a 35kW boiler (which is beyond overkill in the first place), which can only modulate down to 7kW after about 5-10 seconds so it's always cycling when we lower the flow temperature
We need a smaller boiler and one with a mega modulation rate, the closer to 1kW output the better.
Monoblock units are sealed, it’s just water in and water out for the heating loop and power.
Soldato
Pretty good. We've got a 35kW boiler (which is beyond overkill in the first place), which can only modulate down to 7kW after about 5-10 seconds so it's always cycling when we lower the flow temperature
We need a smaller boiler and one with a mega modulation rate, the closer to 1kW output the better.
I have this same problem and it really ****** me off. The plates should be sized differently for the DHW and the HTG like an HIU would be. Man I’m angry
Soldato
I have this same problem and it really ****** me off. The plates should be sized differently for the DHW and the HTG like an HIU would be. Man I’m angry
Isn't that the result of our historically really badly setup houses.
They were super leaky for heat so we needed bonkers immediate kw capacity so we could heat from cold to hot in a short time.
If the houses held the heat really well we would probably keep them warm, and only need to add small amounts of energy to keep them warm.
So you have a monoblock with some pumps either locally or remotely plus some/a fan in order to move the air across the monoblock?
If thats the setup then the long term maintenance and things "to go wrong" are very minimal.
Compared to a gas boiler in that case then you would expect to see far less repairs of any consequence over time I agree.
The annual service is sounding like an EV annual service in that case!
Pretty much, the service will be check the physical condition, clean the fan/condenser, check the control panel and do a functional test. Done and dusted in no time. The only real physical maintenance is to clean the fan and condenser.
The manufacturer can’t even really tell you what they do:
www.vaillant.co.uk
The manufacturer can’t even really tell you what they do:
What to expect from a heat pump service | Vaillant
If you've recently had a heat pump installed, it's important you keep the maintance up! Learn more about heat pump servicing.
www.vaillant.co.uk
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Soldato
Spotted this earlier
heatpumpmonitor.org
Interesting to see some real world ones
HeatpumpMonitor.org
Interesting to see some real world ones
Soldato
Pretty much, the service will be check the physical condition, clean the fan/condenser, check the control panel and do a functional test. Done and dusted in no time. The only real physical maintenance is to clean the fan and condenser.
The manufacturer can’t even really tell you what they do:
What to expect from a heat pump service | Vaillant
If you've recently had a heat pump installed, it's important you keep the maintance up! Learn more about heat pump servicing.
Start at £250+VAT!
Edit : £250 inc VAT
Bargain.
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Numbers vary so much.Spotted this earlier
HeatpumpMonitor.org
Interesting to see some real world ones
probably need to do a simulation of what 50C would be like in the hot water tank (by turning current one down to 50) ,
how long that volume of water would last, whether a pressurized system is needed, we have quite a lot of temperature loss from downstairs combi to upstairs bathroom,
the 35KW boiler can deal with it, just about, would probably need larger diameter hot feed pipes at the lower temp too.
coincidentally r4pm / ethan davis had experts on answering heat pump questions extolling the propane refrigerant based ones for the higher temps.
and also reiterated there are 10K UK installers at the moment but need 60K so installers market, as we knew.
I don't have a water tank at the minute but boiler is set to 52c currently for your water.
Feed pipes are all 22 and 15mm.
Redone my maths
Gas £309/year
Heatpump COP 3
80% Boiler efficiency = £328
70% Boiler efficiency = £287
Minus the £100 gas standing charge a £122 a year saving.
Once Octopus get back to me ill factor in the cost of the install and years to repay, now and again ill update the input data such as tariff prices and install costs see if it ever becomes worth it. But say its £3000 install thats 25 years just to recover the costs before i start saving.
With how little energy we use i cant see it being worth it.
Averages are 373kwh of gas a month @ £46. 219kwh of electric @ £85.
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Soldato
Indeed which I think is the main issue/criticism
A dodgy gas install will probably still be semi efficient since its basically inefficient in all installs.
But heatpumps can be super efficient, but equally super inefficient.
So the margin between them can be really significant.
What was interesting is when you look at the older systems, with 1 year or so, and compare to the newer ones. The ones say a year old have seen a full cycle of seasons. The ones installed for 3 months have only seen summer.
Its probably still far too light on data right now to really pull any conclusions. But if it gets added to more and over time more systems see full season cycles it will hopefully start to show more real world data.
Yes a couple of years with of data is what's needed.
Am I right in thinking SCOP is the figures to look at, is that weighted for winter?
I think I could arrange the garage so a thin cylinder would fit.
Good I wish having a heatpump and solar was easy and affordable right now I'd love the lot, margins are just so tight.
Why are the government not making it an absolute no brainer.
Soldato
What pricing did you use on elec, and I would test some sensitivity on the COP personally.
Since its fairly critical I would probably run the COP testing at 2, 2.5, 3, 3.5 and 4
So you have an idea of likely range of costs. 2 could be pretty nasty, albeit also unlikely to be that bad, but its possible.
I agree however that right now it doesn't look likely that a heat pump is likely in the vast majority of cases to lower bills.
But the simple numbers tell us that already.
Its more about how bills move, current state of gas boiler etc.
If you can come out close to neutral on bills and you may need a boiler soon the maths is easier I think.
Unlikely to change overall I think until the gas price is closer to the elec price.