4 ms·

> require quite a lot of conditions that simply are not met by many older buildings. Such as?

fabian2k 5y ago
The temperature you achieve is lower than for older gas heating equipment, so your radiators are likely not dimensioned correctly if you switch. You really want floor heating for heat pumps, and very well insulated walls. The moment the heat pumps can't provide enough heating you have to heat with electricity, and that is incredibly expensive especially in Germany.
- diordiderot 5y ago
  Modern heat pumps work well below freezing, in Chicago 2021 there were 4 days that gas heating would be more efficient. Maybe don't use a radiator? American heat pumps hear air directly.
  - rad_gruchalski 5y ago
    > Maybe don't use a radiator? And how do you do this in a building never designed for this king of system?
  - cycomanic 5y ago
    Heating the air is less efficient, by a significant margin (you need a high temperature for the same comfort level). Using US houses as an example is quite laughable, the energy consumptions of US households is much higher than German ones.
    - hedora 5y ago
      I doubt heating air to a higher temperature with a heat pump is less efficient than natural gas heating. The heat pump will have a coefficient of performance over five for small temperature differentials. For huge differentials, the thermal loss of the building is linear in the differential, and dropping the thermostat a few degrees only drops a few percent of thermal loss. In those scenarios, the COP of the heat pump is still something like 1.5 or 2.
    - scythe 5y ago
      >Using US houses as an example is quite laughable, the energy consumptions of US households is much higher than German ones. It's an extremely heterogeneous dataset, but a cursory analysis does not agree: Germany: 136 kWh/m^2 https://bpie.eu/wp-content/uploads/2018/01/iBROAD_CountryFactsheet_GERMANY-2018.pdf https://bpie.eu/wp-content/uploads/2018/01/iBROAD_CountryFac... US: 47000 Btu/ft^2 — because we like dumb units — 148 kWh/m^2 https://constructionphysics.substack.com/p/looking-at-energy-use-in-us-residential?s=r https://constructionphysics.substack.com/p/looking-at-energy... That's a slight win for Germany, but it's not by much. For the most part, US houses are simply larger than German ones, which is where that energy use comes from. (US temperatures are also harsher, in both directions.)
- deleted 5y ago
  [deleted]
fmajid 5y ago
The technology is improving by leaps and bounds: https://www.theguardian.com/environment/2022/jan/07/new-heat-pump-could-ease-uk-shift-to-low-carbon-homes-say-developers https://www.theguardian.com/environment/2022/jan/07/new-heat... My parents in France ditched their 40 year old gas furnace for a heat pump, more than 50% subsidized by the French government, and they couldn’t be happier.
- rad_gruchalski 5y ago
  Where in France?
  - fmajid 5y ago
    Paris outskirts, halfway between Versailles and St Germain en Laye. They did have to install an external compressor/heat exchanger unit which would have been harder if they didn’t own a single-family detached home.
munk-a 5y ago
I think the biggest ask the article is making in an unreasonable way is to somehow find millions of contractors who can actually go home by home and refit the heating systems in a timescale that'd actually be relevant for the war in ukraine. If Germany wanted to switch everyone over to a different kind of lightbulb they'd need to ensure the production capacity to make the new bulb exists and set up logistics to actually distribute it. You'd have a fair amount of non-compliance due to paranoia and other factors but I think you could probably get it done with a year or two of warning... Once you hand the household the lightbulbs they just go through and replace them all and dispose of the old bulbs... To change out a heating system you need to remove large appliances, install other large appliances, fiddle around with gas lines and the breaker panel (probably you'd need to replace a fair number of breaker panels in older houses to handle the higher throughput), deal with the wiring which might be unsafe for the power you'll be sending over them... then you'd need to actually install the radiators, that involves tearing up floors to do it right (floor radiation can be extremely efficient and generally creates a higher apparent heat than traditional radiators placed next to windows for fire hazard reasons), or else popping in some other more module style of radiator. Those radiators might use direct electric generation or you might opt for additional boiler capacity (much more sane for efficient stand-radiators) which comes with piping requirements along with a lot more wiring work. All of that is in addition to all the problems I mentioned around lightbulbs - you're still going to need to actually produce and distribute all the material needed to execute this change. If you, as a person, want to swap out the heating in your house it'll be a weeks (maybe if you're lucky) or months long renovation - imagine trying to do that on the scale of a country, the only way it'd be even plausible is if you essentially drafted large portions of the population and trained them up on trades - that might not be a terrible economic investment, but it certainly isn't going to happen fast.
- diordiderot 5y ago
  This was a great answer and well thought out! Thanks for taking the time. My only rebuttal is heat pumps can heat the air directly. No need for a radiator or plumbing.
  - namibj 5y ago
scythe 5y ago
A vapor-compression heat pump generates hot air. But many old buildings transmit heat using hot water. This only works if the water is quite a bit hotter than a heat pump usually gets, because the water heats by blackbody radiation, the radiation power is proportional to T^4, and the effective surface area of the existing radiators is calibrated to the old drive temperatures. Heat pumps are a drop-in replacement if you have forced-air heating, but if you have hot-water radiators, it's not so easy. In theory, you could add another stage, but now you're sacrificing a lot of COP. New buildings should always be built with heat pumps (and heat exchangers) but old buildings take a lot of work to fix.
- ajmurmann 5y ago
  > But many old buildings transmit heat using hot water I thought hot water heating was still by far the norm in Germany for homes with new homes having water heated floors. Has this changed recently?

The temperature you achieve is lower than for older gas heating equipment, so your radiators are likely not dimensioned correctly if you switch. You really want floor heating for heat pumps, and very well insulated walls. The moment the heat pumps can't provide enough heating you have to heat with electricity, and that is incredibly expensive especially in Germany.

diordiderot 5y ago
Modern heat pumps work well below freezing, in Chicago 2021 there were 4 days that gas heating would be more efficient. Maybe don't use a radiator? American heat pumps hear air directly.
- rad_gruchalski 5y ago
  > Maybe don't use a radiator? And how do you do this in a building never designed for this king of system?
- cycomanic 5y ago
  Heating the air is less efficient, by a significant margin (you need a high temperature for the same comfort level). Using US houses as an example is quite laughable, the energy consumptions of US households is much higher than German ones.
  - hedora 5y ago
    I doubt heating air to a higher temperature with a heat pump is less efficient than natural gas heating. The heat pump will have a coefficient of performance over five for small temperature differentials. For huge differentials, the thermal loss of the building is linear in the differential, and dropping the thermostat a few degrees only drops a few percent of thermal loss. In those scenarios, the COP of the heat pump is still something like 1.5 or 2.
  - scythe 5y ago
    >Using US houses as an example is quite laughable, the energy consumptions of US households is much higher than German ones. It's an extremely heterogeneous dataset, but a cursory analysis does not agree: Germany: 136 kWh/m^2 https://bpie.eu/wp-content/uploads/2018/01/iBROAD_CountryFactsheet_GERMANY-2018.pdf https://bpie.eu/wp-content/uploads/2018/01/iBROAD_CountryFac... US: 47000 Btu/ft^2 — because we like dumb units — 148 kWh/m^2 https://constructionphysics.substack.com/p/looking-at-energy-use-in-us-residential?s=r https://constructionphysics.substack.com/p/looking-at-energy... That's a slight win for Germany, but it's not by much. For the most part, US houses are simply larger than German ones, which is where that energy use comes from. (US temperatures are also harsher, in both directions.)
deleted 5y ago
[deleted]

fmajid 5y ago

The technology is improving by leaps and bounds: https://www.theguardian.com/environment/2022/jan/07/new-heat-pump-could-ease-uk-shift-to-low-carbon-homes-say-developers https://www.theguardian.com/environment/2022/jan/07/new-heat... My parents in France ditched their 40 year old gas furnace for a heat pump, more than 50% subsidized by the French government, and they couldn’t be happier.

rad_gruchalski 5y ago
Where in France?
- fmajid 5y ago
  Paris outskirts, halfway between Versailles and St Germain en Laye. They did have to install an external compressor/heat exchanger unit which would have been harder if they didn’t own a single-family detached home.

munk-a 5y ago

I think the biggest ask the article is making in an unreasonable way is to somehow find millions of contractors who can actually go home by home and refit the heating systems in a timescale that'd actually be relevant for the war in ukraine. If Germany wanted to switch everyone over to a different kind of lightbulb they'd need to ensure the production capacity to make the new bulb exists and set up logistics to actually distribute it. You'd have a fair amount of non-compliance due to paranoia and other factors but I think you could probably get it done with a year or two of warning... Once you hand the household the lightbulbs they just go through and replace them all and dispose of the old bulbs... To change out a heating system you need to remove large appliances, install other large appliances, fiddle around with gas lines and the breaker panel (probably you'd need to replace a fair number of breaker panels in older houses to handle the higher throughput), deal with the wiring which might be unsafe for the power you'll be sending over them... then you'd need to actually install the radiators, that involves tearing up floors to do it right (floor radiation can be extremely efficient and generally creates a higher apparent heat than traditional radiators placed next to windows for fire hazard reasons), or else popping in some other more module style of radiator. Those radiators might use direct electric generation or you might opt for additional boiler capacity (much more sane for efficient stand-radiators) which comes with piping requirements along with a lot more wiring work. All of that is in addition to all the problems I mentioned around lightbulbs - you're still going to need to actually produce and distribute all the material needed to execute this change. If you, as a person, want to swap out the heating in your house it'll be a weeks (maybe if you're lucky) or months long renovation - imagine trying to do that on the scale of a country, the only way it'd be even plausible is if you essentially drafted large portions of the population and trained them up on trades - that might not be a terrible economic investment, but it certainly isn't going to happen fast.

diordiderot 5y ago
This was a great answer and well thought out! Thanks for taking the time. My only rebuttal is heat pumps can heat the air directly. No need for a radiator or plumbing.
- namibj 5y ago

scythe 5y ago

A vapor-compression heat pump generates hot air. But many old buildings transmit heat using hot water. This only works if the water is quite a bit hotter than a heat pump usually gets, because the water heats by blackbody radiation, the radiation power is proportional to T^4, and the effective surface area of the existing radiators is calibrated to the old drive temperatures. Heat pumps are a drop-in replacement if you have forced-air heating, but if you have hot-water radiators, it's not so easy. In theory, you could add another stage, but now you're sacrificing a lot of COP. New buildings should always be built with heat pumps (and heat exchangers) but old buildings take a lot of work to fix.

ajmurmann 5y ago
> But many old buildings transmit heat using hot water I thought hot water heating was still by far the norm in Germany for homes with new homes having water heated floors. Has this changed recently?