News for hackers. Stuff that matters.

A comment on Do heat pumps work in cold climates?. Parent comment

Re:Do heat pumps work in cold climates? by leoedin on Thursday January 12, 2023 @08:09AM (#34352916)
The other issue is that a heat pump has to keep the output temperature relatively low to stay efficient - so just dropping a heat pump in to replace a wet heating system with a gas boiler will have two problems - the total power is less, and the amount of power the existing radiators can deliver to the room is too low. Effectively heating a house with lower temperature water needs big radiators or wet underfloor heating.
[ Parent | on HN ]
Re:Do heat pumps work in cold climates? by blitzar on Thursday January 12, 2023 @08:17AM (#34353011)
"The Daikin Altherma 3 H HT air source heat pump can provide water with temperatures up to 70°C – the same level as gas boilers – and can work when it’s as cold as -28°C outside."

https://www.theecoexperts.co.uk/heat-pumps/high-temperature-...

Given that there are a lot of existing houses out there, surely drop in replacements should be more prevalent.

[ Parent | on HN ]
Re:Do heat pumps work in cold climates? by Tor3 on Thursday January 12, 2023 @08:45AM (#34353374)
That article was generally informative, but they forgot (as far as I could tell after a quick read) to include something very important: How much heat can that Daikin heat pump provide? 3kW? 6kW? 10kW? Can it provide more than a standard air-to-air heat pump which typically can provide less than 7kW under optimal (read: Not that cold outside) conditions? This is important to know before buying one (any type of heat pump)
[ Parent | on HN ]
Re:Do heat pumps work in cold climates? by blitzar on Thursday January 12, 2023 @09:23AM (#34353877)
"from £12,500" I guess it comes in different sizes

To be honest the prices I see out there are still generally 'luxury' anyway. If i am spending £20k on a boiler, then an extra £2k to have a secondary gas system that never/very rarely gets used wouldn't bother me at all.

[ Parent | on HN ]
Re:Do heat pumps work in cold climates? by sokoloff on Thursday January 12, 2023 @09:39AM (#34354113)
It can make leaving water temps (LWT) of 70°C. It can work when it's as cold as -28°C outside.

What it can't do is make 70°C LWT when it's -28°C outside. It can only do that down to -15°C and starts to lose both max LWT and heating capacity below that.

[ Parent | on HN ]
Re:Do heat pumps work in cold climates? by hedgedoops2 on Thursday January 12, 2023 @03:43PM (#34359982)
Heat pumps can't be more efficient than the theoretical Carnot heat engine running in reverse, whose efficiency is T_outside / delta_T. In this case it's (273-28)K/98K = 2.5.

I guess being 2x as efficient (cheap) as electric resistive heating isn't super-terrible, but it's not great either.

Compare this to a favorable groundwater heat pump configuration with good radiators and insulation where the 'outside' (groundwater) is maybe 10°C and the target temp 30°C (close to room temp): (273+10)K/20K = ~14.

[ Parent | on HN ]