Comment by joaodlf | Hacker News Reader

Comment by joaodlf | Hacker News Reader

> The load also depends on unique characteristics of the home like the amount of insulation or the type of windows and doors. A home built in 1850 with no insulation requires more energy than a brand new home. The load is just a technical way to describe and measure all of this.

No kidding. The site is all about switching from carbon, which I am all for, as would anyone that cares even slightly about the planet.

BUT. If you do live in a 1850s house with no insulation, getting a heat pump is a colossal waste of money that will not do the job. No matter how many fancy biased graphs and numbers someone comes up with.

Any responsible heat pump installer will firstly look at your home to determine if a heat pump is remotely feasible. Unfortunately, in the UK, only very recent new builds can comfortably accommodate a heat pump. That or older properties that have had CONSIDERABLE insulation work done to them (and I am talking the expensive kind like internal/external wall work, not just the easy jobs like loft insulation).

Be very careful with heat pump cowboys, if you are getting quotes that don't include a site inspection, run.

Could you elaborate a bit? My parents live in a not-very-well insulated wooden house from around 1900, and use a heat pump as their primary means of heating the house. This is Scandinavia, so it might be that this house (despite not even coming close to modern insulation standards) still has better insulation than most British houses, but it would surprise me (older British houses are generally built in brick, which should provide a better base level of insulation than a wooden house, and I'd think Britain isn't warm enough that nobody would build a house without any insulation whatsoever).

Maybe I don't understand what you mean by the word "feasible" – they don't have a goal of getting their living room above 23 C at most in winter, and I guess heat pumps are insufficient in such a house if you desire ambient temperatures above that. However, while other means of heating could plausibly bring the temperatures higher, that would end up being very expensive also because of the poor insulation – it's just harder in general to heat a drafty house and keep the temperature up, and I don't see how heat pumps are a uniquely bad choice for homes like that.

Edit: This is coastal Norway, so the climate in winter is quite similar to somewhere like Edinburgh, with temperatures usually above 0 C in January. The heat pumps would probably be insufficient somewhere the temperatures regularly reach -10 or -20 C, but that's a very infrequent event both here and in the UK.

British houses generally have terrible levels of insulation and if built before roughly 1930 are likely solid walled, so have no wall cavity to insulate. There is also the issue that a lot of people live in terraces and semis and there may simply be no suitable place to install a heat pump. When I looked into it for my house a couple of years ago the fitters basically said they couldn't do it because of lack of space.

I live in an apartment in a UK 1850s house, it just has solid exterior walls.

I think there are now heat pumps that are a similar size to a gas combi boiler and are designed to be inside a building, not a big box outside.

Interesting - https://groundsun.co.uk/small-home-and-apartment-heat-pumps/

There isn't that much to elaborate on. Commercial heat pumps just aren't good for the average UK house. They would be "alright" if the costs weren't prohibitive.

I don't know the specifics of your parents. A "wooden house" with a heat pump acting as the primary heating system in a country like Norway sounds fairly bad on the surface. But I don't know the insulation specifics, nor do I know what other heating element might come at play when the heating pump fails to keep up with the heat loss. Also, what heating pump are we talking about?

Heat pumps work extremely well in the Nordic countries and are therefore very popular. That's because due to the cold winters houses are already well insulated, though very old houses less so. Which means the houses are in general reasonably energy efficient to start with, so a heat pump providing 3.5-6kW of heat is generally sufficient. That would be to the main area of the house, so yes the heat pump is the primary heating system (for those who use them) in the sense that it's the heater used for the main parts of the house - think living room, kitchen area. There may well be normal electric heaters in other rooms, if deemed necessary, but other rooms (food storage, bedrooms etc) don't usually need much, if any, heating).

Of course in the Nordic countries you also have areas very far from the ocean, and there it can get very cold. Down to -50C in some cases, and regularly -30C or colder. I imagine heat pumps aren't used much there. But elsewhere (i.e. most places) they are great. In those places you see them absolutely everywhere now.

As long as the heat pump was properly sized for such an uninsulated home it would still heat it more efficiently than a resistive element heater and just as completely. Of course, if saving money is what you want to do, then yes, insulate before throwing dollars at anything else.

The costs are totally prohibitive, though. We're talking tens of thousands of pounds, whatever direction you decide to take.

You could spend 10s of thousands of pounds in a "properly sized" heat pump system. Or you could spend 10s of thousands of pounds in insulating your home + a more moderate heat pump.

Insulation always pays for itself in the long run, but the period of payoff like peruod of payoff on a mortgage - 10-20 years. We need very generous finance on making home improvements

Yes, it's more efficient than resistive electric heating, but in the UK that is typically not the alternative it's being compared to. The usual existing heating system would be a gas-fired central heating boiler, and the cost of gas vs cost of electricity means that gas is still cheaper, I think.

I'd argue that insulation should be the first thing people consider unless they know their home is already well insulated. It's all very well having energy efficient heating systems but if most of the heat generated leaks straight outside then I'd question whether that's efficient overall. Particularly in smaller dwellings, you can reduce the amount of heating you require each day during winter - often to nil.

In theory I'd agree that you should insulate first. But as others have pointed out, on some older houses, insulation can be difficult to accomplish (especially true in non-wood-framed housing). In such cases it is still a better idea to use LESS energy (because of a COP above 1) to heat that space than it is to use resistive or combustion methods (which have a COP less than 1).

The key issue is despite claims that cold doesn’t affect heat pumps it absolutely does. We have an old house. When very cold the heat pump struggles to put out enough heat. It works well enough, but something to be aware off - go bigger in system than you think you need maybe

"go bigger" will result in short cycling during the hot summer resulting in high humidity and mold problems in the summer.

Untrue. All modern heat pump systems use DC motors ("inverter technology") and will run continuously at variable speed until target temperatures are exceeded by a (programmable) margin. They do not turn on and off and on and off.

Nobody says that it has no effect. Only that efficiency decreases. And that even at diminished efficiency it's still better than a boiler.

I dont understand how heat output from a heat pump vs heat output from a gas / oil / wood burner / resistive heater are at all different.

Heat is heat, a joule of heat output by the system is a joule of heat ... or am I missing something?

Heat pumps take much longer to heat the system, to get it to the desired temperature. Combine that with a property that is not insulated to very high standard, and you get a heating system that is incapable of keeping you warm.

Of course, you could throw more money at it. But it won't be cheap, and you won't see a return on your investment any time soon.

Speed / response is a perfectly valid difference. Had not considered it.

Leaky houses are already throwing money at the heating problem, and perhaps with a slower response time you would 'idle' the heating circuit at a passive 25C against 18C room temperature, and throttling up from there. Throwing money at it works!

Maybe they're referring to cases where the heat pump can't supply heat faster than what the building is losing through the uninsulated walls. In such cases, you must first move out of the holey tent before installing a heat pump.

You just need a bigger pump!

I think what the post you replied to meant is that when your home needs a 10kW-20kW heater to actually be able to heat your home, then spending tons of money on a heat pump which (for the largest models) can maybe pump out 7kW of heat (equivalent) under optimal conditions (when it's not that cold outside) then you have paid a lot of money and you're still freezing. So you may as well install something else, even a simple wood stove can provide 10kW or more, sometimes much more.

If you need 20kW and you install a 7kW (equivalent) gas boiler you are in just as much trouble.

If you need 20kW and install a system that can output 20kW under the worst situation (resistive heating), you are probably averaging about 7kW of electric usage when the heating is on to generate 20kW (about 3:1 ratio on average)

Setting aside capital costs that's going to cost you 7kWh per hour of heating. An oil boiler will cost 20kWh per hour of heating.

If your oil costs 40c per litre/$1.50 per gallon and each litre delivers 10kWh, that's about 80c/hour to heat

If your electricity costs 10c per kWh, that's 70c/hour to heat, that's a win

If your electricity fosts 15c per kWh, that's $1/hour to heat, that's a loss

Absolutely - but the important thing is that you can actually get a 20kW gas boiler, but you can't get a consumer 20kW heat pump. You can buy the most expensive consumer heat pump you can find, and it won't do at all if you actually need 20kW. So you can as well save the money as you'll have to install a gas heater (or oil or wood heater) anyway.

> Absolutely - but the important thing is that you can actually get a 20kW gas boiler, but you can't get a consumer 20kW heat pump.

If even you could, you may not want to. Instead one external heat pump handle heads on the top floor, which is generally bedrooms, and not occupied during the day; a second external unit to handle heads on the main floor, which are generally not occupied overnight.

Each individual smaller unit runs less because the load is more focused in 'zones'.

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.

"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.

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)

"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.

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 both at the same time: make 70°C LWT when it's -28°C outside. It's designed for 65°C LWT (some models 60°C) and can only reach 70°C at a performance penalty (year-round) and can only maintain 70°C LWT down to -15°C and starts to lose max LWT, heating capacity, and even more efficiency below that. (Losing efficiency a few days out of the year is a minor concern. Not being able to meet the heat loss and heat transfer for the building for a few days is a much more serious issue for health and comfort.)

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.

To understand the difference in a short and simplyfied way:

1. Your examples are heating up the inside air by using energy (burning fuel). Doing so will always be less than 100% efficient, some heating technologies are as little as 10-20% efficient (energy per kWh)

2. Heatpumps are instead using energy to do heat transfer. Moving heat from the outside to the inside.

The latter is way more efficient, with easily 300-400% efficiency. But obviously the colder it gets outside, the less heat is in the air to extract and the efficiency goes down.

It's not different but the amount of heat that each system can be generated is different. And when it's cold (i.e. when you need the extra heat to be compensate for your draft home) your heat pump is going to struggle most.

> I dont understand how heat output from a heat pump vs heat output from a gas / oil / wood burner / resistive heater are at all different.

A gas/oil/wood burner are not 100% efficient in creating heat, and release carbon into the atmosphere.

A resistive heat is at most 100% efficient: all the electrons go to making the coil glow, like old school light bulbs. So 1 kW of electricity is 1 kW of heat (which has some BTU equivalent for old fashioned folks).

A heat pump does not create heat, but moves it from one place to another with refrigerant and pumps. So 1 kW of electrical usage can move 3 kW of heat at times:

* https://en.wikipedia.org/wiki/Coefficient_of_performance

* https://energyeducation.ca/encyclopedia/Coefficient_of_perfo...

So if you input 1 kW of energy, do you want 0.9 kW of heat out (carbon), 1 kW of heat out (resistive), or >2 kW of heat out?

The $/capacity may be quite different. The capacity of burner systems is generally cheap, so you oversize them and if you need more heat, you just burn more fuel. The capacity of a heat pump is relatively expensive, so you size it up to something reasonable, and in an unusually cold day you may hit the limits of how much joules you can get out of it.

Also, the $/fuel is different - if one system gets three times more joules from the same fuel, it doesn't mean it's more efficient as the other system may be using four times cheaper fuel; so a 300%-efficient heat pump is more efficient than a resistive heater but may be less efficient than a furnace burning cheap fuel.

+1 to this. I had a hpwh installed for my radiant system and after paying >7k to get it up and running, I learned that this model is entirely unsuited to that setup and Rheem refuses to accept a return.

If anyone wants a barely used 120 volt hpwh in the bay area, get in touch.

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