Lewis Bowick

A secondary frustration with the "solar makes HPs make sense" concept is that upfront cost is HPs' greatest challenge IMO. To mainstream this for ordinary households, the last thing we need is to say "you just need to drop a further £8k for it to be worthwhile"

What's screwey is that fixed cost are recovered via the energy consumption charge. As a result, electrifying makes you overcontribute to fixed costs, while generation lets you undercontribute. The two cancel each other out, causing the illusion that micro solar complements heat electrification.

The idea that micro generation, costing 2-3x as much as grid-scale generation, with a generation profile inversely correlated to the heating season, makes electric heating more economic than using the grid should tell you something's screwey with the price signals

I'm pretty sure it does more harm than good. Only one third of the retail price of electricity is for energy, so the "true" saving of rooftop PV must be about 8p/kWh of self consumption. The other two thirds are just shifted to everyone else's bills, making electrification even less appealing.

Ooft. Hadn't thought it might get that bad

Because of politics?

The whole reason for CP30 was, I think, that in 2022 it looked like any additional renewable capacity would bring down bills. Now that wholesale has come down and CfDs have risen, I'm not sure there's any merit to a 2030 sprint (besides being the right direction of travel for carbon overall)

District cooling is a thing, though I'm not convinced that would be easier than an individual building approach, given the need for co-ordination across many building owners and civil works. It would still need fan coils to be installed indoors. New build is an ideal opportunity for A2A I'd say

Efficiency of air-to-water is very sensitive to the water temperature required by the radiators. If you've got underfloor heating or very big radiators then great, but if not you can get COPs much worse than you would with warm air. I think retrofitting refrigerant pipes more likely!

Yep air-to-water is the default path for our homes. Just seems like a shame to be rolling out heat-only systems right when we realise we're gonna need AC. If we could combine the cooling perk with decarbonisation it would be a much easier transition.

UK here, been trying to figure out if mini-splits could work for us at scale. The trouble is we all have whole house hydronic systems, so would need to double up with splits in every room. And how do you deal with bathrooms? More likely is people just put splits in bedrooms and keep using gas heat

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I was recently talking to Christoph at goeconic.com who are offering this setup

You can have fan coils connected to the pipework as well as radiators, which can provide effective cooling with proper moisture removal. The pipework needs to be insulated to avoid condensation. Probably quite hard to find installers who will do it atm

True, heat pumps will only introduce about 30% as much additional heat to the environment as other forms of heating. So no cooling, but a reduced contribution to urban heat island in winter

I'd be interested to know if these studies have taken into account that the portion of heat being blown onto the street which has been removed from the building is being cancelled out by that building absorbing heat through its leaks. Only the portion covered from electricity is a net addition.

In both heating and cooling mode, heat is moved between indoors and out, plus heat is generated by electricity being burnt off as friction. So in both cases there's a net addition of heat. The hot air blown out is a combination of the heat moved from indoors and the heat added from electricity.

Heating just adds heat to a building at the same rate it escapes to outdoors. It's an equilibrium to maintain a steady temperature, so there's no net removal of heat from the environment.

Raises the question of whether we should be insulating pipes at installation to make them cooling-ready

Not sure about easy. Freeholder permission needed, and often difficult to pass noise limits due to being close to neighbours' windows. Maintenance at height could be awkward. Feels like flats need fully indoor HPs which duct to outside air

I suppose you can have bypass for the cool night air, then heat exchange to *cool* the fresh air in the afternoon, right? Whereas I have to seal up in the afternoon if I want to keep peak temperatures out, which feels weird!

I suppose I'm basically describing PIV, except timed to run only during cool hours in a heat wave

I'm not sure how much relief extract would provide, pulling air into the rooms from other warm rooms? Having supply at outdoor night time temperatures sounds nicer! I guess some of the extract makeup might come through the trickle vents though

I reckon all it would take would be a fan to duct cool night air into the bedrooms from a quiet side of the house

What I notice in heatwaves is we'd be able to keep cool if we weren't so restricted with ventilation. Security overnight, road noise, curtains to block 5am sunrise (also blocking cool air) and outdoor temps above indoor between midday and 9pm. Precious little opportunity for passive cooling!

Poor bloke should have just followed the handy steps on his EPC. Move out of his downstairs to do underfloor insulation, stick a wind turbine on the back wall and put in flue gas heat recovery to save 2% emissions and get a 150 year payback

Does reducing output on a within-day timescale meaningfully reduce fuel costs? I've been wondering if the renewables which displace French nuclear actually have value. Had it in my head nuclear is virtually all fixed cost

I'd assume there's some crossover point with the design flow temperature of A2W where it becomes more efficient. Like maybe it beats A2A at 35C design but not at 50C

Looking at the datasheets for A2A products, they usually have a tested heating SCOP above 4

Do you have any sources for that? HP efficiency is mainly about the temperature of the condenser, and if anything A2A can probably run cooler than A2W in many cases

I put a heat pump in my 1900 terrace. Works great. Does the same thing the boiler before it did