It will be better than 1:1 otherwise they wouldn’t be able to produce a greater output than input.
True but some have a large drop off in actual energy they can produce in low temperatures (probably worse on the bigger end of the domestic models up to 16kw). Still not hitting 3:1 in mid winter.
Hiya,
My house is a very old stone house with reasonable insulation but obviously not enough with the solid walls. We looked in ASHP's but the advice seems that with the house as it is, that it probably wouldn't work.
For us a wood burner back boiler seems to be a better idea. I may revisit the ASHP in the future, when I can figure out a better way to insulate the house, but for the moment the wood burner seems to be the better way to heat this house. The Gas boiler which is a modern condensing one we will keep obviously.
Maybe we will then switch the gas CH to ASHP, with the wood burner in the depths of winter providing a top up.
BR
JeZ
I’m probably in a position where we could probably dig up a big chunk of garden. So a ground source heat pump is an option. Doees that generate water at a higher temperature? Are we less likely to need to replace the pipes?
We're very well insulated and airtight in a passivhaus-style house. We've only got electric underfloor heating and it's been ruinously expensive to the extent that i've turned it right down and we're all wearing 5 jumpers.
We've got no radiators but I had a look at fitting wet ASHP system and got quotes between £40 and 75K.
Instead, we looked at air to air heat pumps - basically air conditioning. They have the advantage of being able to heat or cool and because they don't have to heat the air as much as a water system, the efficiency is better - I think 4-500% is realistic.
It's about 2.5K per unit with something like 5kw heating power. If the government hadn't moderated the cost of electricity I would have got one, but as it was we decided to leave it and see if we could manage the house better (it's only our second winter).
You can get hot water tanks with built-in heat pumps for hot water needs. Presumably you can still use your excess PV with those systems, but its cheaper to run in winter.
I’m probably in a position where we could probably dig up a big chunk of garden. So a ground source heat pump is an option. Doees that generate water at a higher temperature? Are we less likely to need to replace the pipes?
Nope.
Lower flow temperatures than ASHP and similar temperature differential.
Bigger rads and bigger pipes.
Can be fudged to a degree with a buffer running a higher temperature differential but rads will still be undersized.
Instead, we looked at air to air heat pumps – basically air conditioning. They have the advantage of being able to heat or cool and because they don’t have to heat the air as much as a water system, the efficiency is better – I think 4-500% is realistic.
You could basically just stick AC in. It's a heat pump. Obvs as soon as you use it to cool you are throwing your green credentials and carbon savings out of the window.
I assume the high ASHP prices are due to difficulty routing pipework around the house and therefore costly refit. AC could be a similar issue but pipes are smaller.
You could basically just stick AC in. It’s a heat pump. Obvs as soon as you use it to cool you are throwing your green credentials and carbon savings out of the window.
We haven't had ours over a summer yet, but as we have solar PV and a battery I'm hoping to justify it to myself that we'll only need it on days when the PV has generated way more power than we could use anyway so some of it may as well be used to cool the place down...
As for phiiiil, if it's hot enough for AC, then we have plenty of excess power. But even this summer it wasnt too bad and it probably would get much use.
The installation is very easy if you don't have it ducted - just a hole in the wall between the compressor outside and the fan unit inside. We have mvhr, but the air volume isn't enough to distribute the heat effectively.
One thing to keep in mind with just reducing gas boiler temperature is that you still need bigger pipework for the ASHP as it runs at a lower temperature differential to achieve the same output.
Thanks for that, it's something I didn't know but I don't understand the physics; can you expand a bit for me, please? If I'm sending enough 45ºC water round my radiators to maintain 18ºC room temperature, why does the pipe diameter matter? Is it to do with the temperature of the return flow, and if so, how does pipe size affect that?
Just turning down flow temperature isn't enough, you've got to lower the temp difference across the flow and return to mimic a heat pump.
You could do that using the lockshield valve on the radiator though. Also I would suggest a 50 deg flow for rads unless you are in a modern well insulated house.
And most heat pumps will be weather compensated so you would not be getting the maximum flow temp with the mild conditions that are above the south east at the moment.
No chance it’ll be running much closer to 1:1 as it needs some warmth in the air to do it’s black magic.
Well unless this ASHP supplier is lying an ASHP ha smuch better COP than 1:1 in the temps we've just had
Urban Plumbers have just posted a YouTube vid covering an ASHP installation. Its worth watching this guy's other stuff as he does some impressive work.
If you were running a heat pump last night it was definitely lower CO2 than a gas boiler:
https://twitter.com/winderful_uk/status/1605125913158746114?s=20&t=FQgitHg2jR****_uL_zJAQ
No chance it’ll be running much closer to 1:1 as it needs some warmth in the air to do it’s black magic.
Well unless this ASHP supplier is lying an ASHP ha smuch better COP than 1:1 in the temps we’ve just had
Point conceded earlier but I'd not be believing the manufacturers either the figure is going to be massaged up and then different manufacturers will have different performances.
Don't know the exact split but we've used something like 3500 kWh for an entire year of heat and hot water, with a permanently warm 4 bed house. That would suggest we have had a very decent percentage of "free" energy from the ashp.
Even if it was only 1:1 for one week (which it wasn't) then it is still better (cheaper, less energy and arguably less carbon) than bottled gas or oil which are my alternatives.
I like the way people are very quick to contest ashp cop figures but no one contests manufacturers claims about boiler efficiency. Same deal with ice vs electric cars. We have long since given up believing mpg figures for petrol and diesel from the manufacturers but people are all over claims of mileage on an ev.