8 ms·

To heat, you just run the electricity through resistance. To cool down, you need to run a compressor, it's pretty energy-intensive. Anyway, each place has a d

To heat, you just run the electricity through resistance. To cool down, you need to run a compressor, it's pretty energy-intensive. Anyway, each place has a different cold/warmth quota so you can't issue a universal rule.

danmaz74 8y ago
Actually, heating with a heat pump is much more efficient than using a resistance.
- Tharkun 8y ago
  That's mostly true, but only if the temperature difference isn't too high. During the coldest days of winter -- or when boiling water, I'd imagine -- the COP can be as low as 1, ie the same as resistive heating.
JaimeThompson 8y ago
In most cases doesn't it take less energy to move head (aircon) and more to generate heat (resistive heating)?
- deleted 8y ago
  [deleted]
sp332 8y ago
Heating using resistance is inefficient and gets you at most 1 unit of heat energy per unit of electrical energy. Heating and cooling using heat pumps can move more than one unit of heat energy per unit of electrical energy.
- timr 8y ago
  Heating via electrical resistance is 100% efficient. All energy goes into generating heat. There is no loss. Gas heating is something like 90% efficient now. People, stop. Downvoting doesn't change facts.
  - klodolph 8y ago
    Yes, 100% is inefficient because you can get higher ratios if you use heat pumps. The loss is that you are using more energy compared to how much energy you would use if you had a heat pump instead.
    - timr 8y ago
      That's not efficiency. That's an efficiency ratio, which is different. Heat pumps have a higher EER, but also higher parasitic losses, which is the source of confusion on the whole thread. It's like claiming that rockets are "more efficient" than cars because they move you faster.
      - deleted 8y ago
        [deleted]
      - jdmichal 8y ago
        The only reason behind that difference is because it's not generating heat, but moving heat. The difference to users is unimportant. As long as BTUs are pumped into / out of their closed environment, their needs are being met. And the bottom line is that for the same unit of energy used to generate 1 BTU from resistance heating, we can move several BTUs. EDIT: I'd also like to note that heat pump systems which include resistance heating systems will typically mark them as "emergency heating". Because they are less efficient, unless it's so brutally cold outside that the heat pump has dropped below 1 EER or can't even operate properly. EDIT2: I forgot that the units in SEER are not the same on both sides of the ratio. (That is, it's not actually a ratio, since those are supposed to be unitless.) So my original "13+ BTUs" was high. Changed it to a non-descript weasel-word instead.
      - deleted 8y ago
        [deleted]
      - klodolph 8y ago
        The reason you are being downvoted is because your argument basically boils down to having an unreasonably narrow definition of what “efficient” means. In context, it’s obvious that “efficiency” here is the ratio between the amount of heat provided and the amount of energy spent. You might call it EER, I might call it COP, but it’s irrelevant because in context the word “efficient” is unambiguous. Narrow interpretations of definitions to support a point don’t actually provide much useful insight to the topic being discussed, and are seen as distracting. So these non-useful comments are being downvoted to make them less visible. It is not an issue of whether they are technically correct. You could probably make an interesting point about the electrical efficiency of heat pumps, or you could make a comment about terminology and explain that “technically” the correct term is X, but instead you chose to interpret a term in a way that contradicts the contextually obvious meaning and then base an argument on top of that.
Eire_Banshee 8y ago
Actually, compressors use very little energy if you keep them running. They use a lot of energy when they turn on initially, after that, its very little . Ive been working on smart thermostats that take advantage of this phenomenon to lower HVAC costs.
- 21 8y ago
  So you are saying that it's better to run a modern AC (inverter, all that) continuously on a low power than every hour or so? I'm thinking in context of cold leak (through windows, ...)
  - Eire_Banshee 8y ago
    Yes, exactly.
  - jdmichal 8y ago
    Actually, yes. The most high-efficiency central AC systems on the market use variable flow for exactly this reason. Below that are two-stage systems (low and high flow), then single-stage systems. Reliability and cost does play a part in all of this, though. [0] AFAIK, the most efficient residential systems are ductless split systems, where you basically have a centralized compressor and distributed air handlers in individual rooms. This allows for variable flow and localized control, which reduces need. [0] https://en.wikipedia.org/wiki/Seasonal_energy_efficiency_ratio#US_government_SEER_standards https://en.wikipedia.org/wiki/Seasonal_energy_efficiency_rat... > But when either replacing equipment, or specifying new installations, a variety of SEERs are available. For most applications, the minimum or near-minimum SEER units are most cost effective, but the longer the cooling seasons, the higher the electricity costs, and the longer the purchasers will own the systems, the more that incrementally higher SEER units are justified.
dogma1138 8y ago
That’s not how heat pumps work, heat pumps in air con can essily get 1:5 ratio the best radiative heating can do is 1:1.
saalweachter 8y ago
Heat loss through a surface is proportional to the difference in temperatures from one side to the other. So if you are cooling a house to 70 degrees in 90 degree weather, you are fighting a 20 degree difference. If you are heating a house to 70 degrees in 30 degree weather, you are fighting a 40 degree difference. In a severe heatwave, you might spend weeks with much of the day at 100 degrees; during a cold snap last winter, there was a span where I live where the temperature was usually around 0, and never higher than 10 degrees. Meanwhile, a furnace works by directly converting energy to heat; for simplicity, let's assume a heater generates 1 unit of heat for 1 unit of energy (it's 100% efficient). An air-conditioner, however, moves heat, moving heat from inside to outside. An air conditioner doesn't use 1 unit of energy to move 1 unit of heat; an air conditioner might move 3 units of heat using 1 unit of energy. So putting the two together, it takes roughly 6 times as much energy to heat my house on the coldest days as it does to cool my house on the hottest days. The full answer is a lot more complicated than that, because other things in houses are generating waste heat and you need to look at the deviations above and below your target temperature range over the full year and across many different places. Someone else has already posted a link to US energy usage showing that total energy spent on air conditioning is a fraction of that spent on heating, but from the above you should be able to get an intuitive feel for why that's so.
- _fizz_buzz_ 8y ago
  > An air-conditioner, however, moves heat, moving heat from inside to outside. An air conditioner doesn't use 1 unit of energy to move 1 unit of heat; an air conditioner might move 3 units of heat using 1 unit of energy. Be careful, you're angering the thermo gods! If that was true, I would simply use an air-conditioner to heat my house. Cool, the outside and move the heat inside. In reality, you have the efficiencies backwards. Cooling is more energy intensive than heating.
  - carry_bit 8y ago
    > If that was true, I would simply use an air-conditioner to heat my house. It's true, and people do. Install a heat pump, and save your traditional heat source for when it's sufficiently cold outside.
kragen 8y ago
This is backwards; while it's true that a resistor is less mechanically complicated than a compressor-expander-condenser heat pump like an air conditioner, the coefficient of performance for a resistor is limited to 1 (and is very nearly 1, say 0.9999), while the coefficient of performance for such heat pumps is 2–6. That is, for every joule of energy you burn up in the compressor, you transfer 2–6 joules out of your living space into the outdoors. I know, that sounds crazy, and sometimes the CoP is given as an "efficiency", which makes it sound even crazier — a CoP of 2.0 is "200% efficient"! But it's not science fiction; it's a simple consequence of the Carnot cycle being reversible and the Carnot efficiency of heat engines at ordinary temperatures being quite low.
deleted 8y ago
[deleted]
Robotbeat 8y ago
For the same amount of heat moved, resistive heating is much more energy intensive than the A/C compressor. Heat pumps are about the same, though.

danmaz74 8y ago

Actually, heating with a heat pump is much more efficient than using a resistance.

Tharkun 8y ago
That's mostly true, but only if the temperature difference isn't too high. During the coldest days of winter -- or when boiling water, I'd imagine -- the COP can be as low as 1, ie the same as resistive heating.

JaimeThompson 8y ago

In most cases doesn't it take less energy to move head (aircon) and more to generate heat (resistive heating)?

deleted 8y ago
[deleted]

sp332 8y ago

Heating using resistance is inefficient and gets you at most 1 unit of heat energy per unit of electrical energy. Heating and cooling using heat pumps can move more than one unit of heat energy per unit of electrical energy.

timr 8y ago
Heating via electrical resistance is 100% efficient. All energy goes into generating heat. There is no loss. Gas heating is something like 90% efficient now. People, stop. Downvoting doesn't change facts.
- klodolph 8y ago
  Yes, 100% is inefficient because you can get higher ratios if you use heat pumps. The loss is that you are using more energy compared to how much energy you would use if you had a heat pump instead.
  - timr 8y ago
    That's not efficiency. That's an efficiency ratio, which is different. Heat pumps have a higher EER, but also higher parasitic losses, which is the source of confusion on the whole thread. It's like claiming that rockets are "more efficient" than cars because they move you faster.
    - deleted 8y ago
      [deleted]
    - jdmichal 8y ago
      The only reason behind that difference is because it's not generating heat, but moving heat. The difference to users is unimportant. As long as BTUs are pumped into / out of their closed environment, their needs are being met. And the bottom line is that for the same unit of energy used to generate 1 BTU from resistance heating, we can move several BTUs. EDIT: I'd also like to note that heat pump systems which include resistance heating systems will typically mark them as "emergency heating". Because they are less efficient, unless it's so brutally cold outside that the heat pump has dropped below 1 EER or can't even operate properly. EDIT2: I forgot that the units in SEER are not the same on both sides of the ratio. (That is, it's not actually a ratio, since those are supposed to be unitless.) So my original "13+ BTUs" was high. Changed it to a non-descript weasel-word instead.
    - deleted 8y ago
      [deleted]
    - klodolph 8y ago
      The reason you are being downvoted is because your argument basically boils down to having an unreasonably narrow definition of what “efficient” means. In context, it’s obvious that “efficiency” here is the ratio between the amount of heat provided and the amount of energy spent. You might call it EER, I might call it COP, but it’s irrelevant because in context the word “efficient” is unambiguous. Narrow interpretations of definitions to support a point don’t actually provide much useful insight to the topic being discussed, and are seen as distracting. So these non-useful comments are being downvoted to make them less visible. It is not an issue of whether they are technically correct. You could probably make an interesting point about the electrical efficiency of heat pumps, or you could make a comment about terminology and explain that “technically” the correct term is X, but instead you chose to interpret a term in a way that contradicts the contextually obvious meaning and then base an argument on top of that.

Eire_Banshee 8y ago

Actually, compressors use very little energy if you keep them running. They use a lot of energy when they turn on initially, after that, its very little . Ive been working on smart thermostats that take advantage of this phenomenon to lower HVAC costs.

21 8y ago
So you are saying that it's better to run a modern AC (inverter, all that) continuously on a low power than every hour or so? I'm thinking in context of cold leak (through windows, ...)
- Eire_Banshee 8y ago
  Yes, exactly.
- jdmichal 8y ago
  Actually, yes. The most high-efficiency central AC systems on the market use variable flow for exactly this reason. Below that are two-stage systems (low and high flow), then single-stage systems. Reliability and cost does play a part in all of this, though. [0] AFAIK, the most efficient residential systems are ductless split systems, where you basically have a centralized compressor and distributed air handlers in individual rooms. This allows for variable flow and localized control, which reduces need. [0] https://en.wikipedia.org/wiki/Seasonal_energy_efficiency_ratio#US_government_SEER_standards https://en.wikipedia.org/wiki/Seasonal_energy_efficiency_rat... > But when either replacing equipment, or specifying new installations, a variety of SEERs are available. For most applications, the minimum or near-minimum SEER units are most cost effective, but the longer the cooling seasons, the higher the electricity costs, and the longer the purchasers will own the systems, the more that incrementally higher SEER units are justified.

dogma1138 8y ago

That’s not how heat pumps work, heat pumps in air con can essily get 1:5 ratio the best radiative heating can do is 1:1.

saalweachter 8y ago

Heat loss through a surface is proportional to the difference in temperatures from one side to the other. So if you are cooling a house to 70 degrees in 90 degree weather, you are fighting a 20 degree difference. If you are heating a house to 70 degrees in 30 degree weather, you are fighting a 40 degree difference. In a severe heatwave, you might spend weeks with much of the day at 100 degrees; during a cold snap last winter, there was a span where I live where the temperature was usually around 0, and never higher than 10 degrees. Meanwhile, a furnace works by directly converting energy to heat; for simplicity, let's assume a heater generates 1 unit of heat for 1 unit of energy (it's 100% efficient). An air-conditioner, however, moves heat, moving heat from inside to outside. An air conditioner doesn't use 1 unit of energy to move 1 unit of heat; an air conditioner might move 3 units of heat using 1 unit of energy. So putting the two together, it takes roughly 6 times as much energy to heat my house on the coldest days as it does to cool my house on the hottest days. The full answer is a lot more complicated than that, because other things in houses are generating waste heat and you need to look at the deviations above and below your target temperature range over the full year and across many different places. Someone else has already posted a link to US energy usage showing that total energy spent on air conditioning is a fraction of that spent on heating, but from the above you should be able to get an intuitive feel for why that's so.

_fizz_buzz_ 8y ago
> An air-conditioner, however, moves heat, moving heat from inside to outside. An air conditioner doesn't use 1 unit of energy to move 1 unit of heat; an air conditioner might move 3 units of heat using 1 unit of energy. Be careful, you're angering the thermo gods! If that was true, I would simply use an air-conditioner to heat my house. Cool, the outside and move the heat inside. In reality, you have the efficiencies backwards. Cooling is more energy intensive than heating.
- carry_bit 8y ago
  > If that was true, I would simply use an air-conditioner to heat my house. It's true, and people do. Install a heat pump, and save your traditional heat source for when it's sufficiently cold outside.

kragen 8y ago

This is backwards; while it's true that a resistor is less mechanically complicated than a compressor-expander-condenser heat pump like an air conditioner, the coefficient of performance for a resistor is limited to 1 (and is very nearly 1, say 0.9999), while the coefficient of performance for such heat pumps is 2–6. That is, for every joule of energy you burn up in the compressor, you transfer 2–6 joules out of your living space into the outdoors. I know, that sounds crazy, and sometimes the CoP is given as an "efficiency", which makes it sound even crazier — a CoP of 2.0 is "200% efficient"! But it's not science fiction; it's a simple consequence of the Carnot cycle being reversible and the Carnot efficiency of heat engines at ordinary temperatures being quite low.

deleted 8y ago

[deleted]

Robotbeat 8y ago

For the same amount of heat moved, resistive heating is much more energy intensive than the A/C compressor. Heat pumps are about the same, though.