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How can heating be any less efficient than 100%? I get that engines can be less efficient than 100% since the remaining energy is dissipated as heat and heat is

by leni536 12y ago

How can heating be any less efficient than 100%? I get that engines can be less efficient than 100% since the remaining energy is dissipated as heat and heat is the not desired energy in that case. What happens with the remaining energy if you heat with less than 100% efficiency? Does it start to rotate things?

DanBC 12y ago
Energy is used to heat something, which is then used to heat a room. Some devices will use more energy to get a room to X Celsius. Those devices are less energy efficient than the other devices.
- leni536 12y ago
  Electric heating has near 100% efficiency regardless how you use it[0]. Heating with furnace is less efficient since some of the heat escapes through the chimney directly and efficiency is typically disproportional to the heating power so it's better to heat constantly[1]. [0] https://en.wikipedia.org/wiki/Electric_heating#Environmental_and_efficiency_aspects https://en.wikipedia.org/wiki/Electric_heating#Environmental... [1] experience
abelsson 12y ago
Heating can be more than 100% efficient. Before you go "what, lol, no" - let me clarify. Obviously it can't be even 100% thermodynamically efficient, but a heat pump for example can generate 3-4 kW of heat from 1 kW of power. The rest of the energy comes from the environment obviously, but naively assuming that the 100% efficient power-into-heat is the best you can do is not true.
- leni536 12y ago
  Are there any efficient electric heating systems for a household based on a thermodynamic cycle with the environment? I think the most electric heating systems I have seen are using the rather bruteforce and inefficient (only near 100%) method. The basic principle that they heat a resistor and something quickly transfers the heat away so the resistor doesn't burn out and/or your house doesn't catch on fire. An other fun method to increase the "efficiency" of electric heating would be heating with bitcoin miners. It wouldn't make the heating more efficient in the sense it would cost the same energy but at least you could get some of your money back spent on heating.
  - abelsson 12y ago
    I'm not quite sure what you mean your first question, but I think heat pumps using air, ground or water as heat reservoirs would qualify. They are in common household use at least where I am located, and have a input-power-to-heat efficiency of up to 400% (the Carnot cycle imposes a limit of roughly 7-10x depending on which exact scenario you calculate) Here's an example of one manufacturer and products: http://www.nibe.eu/Domestic-heatingcooling/Airwater-heat-pumps/ http://www.nibe.eu/Domestic-heatingcooling/Airwater-heat-pum...
roel_v 12y ago
'Efficient' not in the thermodynamic sense, but in the sense that you need to put in x % less energy to have the same comfort level (i.e, have the house at a comfortable temperature at the times you need it). And to add another use of 'efficient' to the mix, just to keep things interesting ;) , when people say 'heating a house with a CV (water) based system powered by natural gas is more efficient than using electricity', what they mean is that A) electricity is generated from other sources and there are losses in the conversion/transport/etc, whereas for gas that's not so; and B) that it's just much cheaper. So yeah, sorry for the confusion, but in energy use land, 'efficient' is a highly overloaded word.

by leni536 12y ago

DanBC 12y ago

Energy is used to heat something, which is then used to heat a room. Some devices will use more energy to get a room to X Celsius. Those devices are less energy efficient than the other devices.

leni536 12y ago
Electric heating has near 100% efficiency regardless how you use it[0]. Heating with furnace is less efficient since some of the heat escapes through the chimney directly and efficiency is typically disproportional to the heating power so it's better to heat constantly[1]. [0] https://en.wikipedia.org/wiki/Electric_heating#Environmental_and_efficiency_aspects https://en.wikipedia.org/wiki/Electric_heating#Environmental... [1] experience

abelsson 12y ago

Heating can be more than 100% efficient. Before you go "what, lol, no" - let me clarify. Obviously it can't be even 100% thermodynamically efficient, but a heat pump for example can generate 3-4 kW of heat from 1 kW of power. The rest of the energy comes from the environment obviously, but naively assuming that the 100% efficient power-into-heat is the best you can do is not true.

leni536 12y ago
Are there any efficient electric heating systems for a household based on a thermodynamic cycle with the environment? I think the most electric heating systems I have seen are using the rather bruteforce and inefficient (only near 100%) method. The basic principle that they heat a resistor and something quickly transfers the heat away so the resistor doesn't burn out and/or your house doesn't catch on fire. An other fun method to increase the "efficiency" of electric heating would be heating with bitcoin miners. It wouldn't make the heating more efficient in the sense it would cost the same energy but at least you could get some of your money back spent on heating.
- abelsson 12y ago
  I'm not quite sure what you mean your first question, but I think heat pumps using air, ground or water as heat reservoirs would qualify. They are in common household use at least where I am located, and have a input-power-to-heat efficiency of up to 400% (the Carnot cycle imposes a limit of roughly 7-10x depending on which exact scenario you calculate) Here's an example of one manufacturer and products: http://www.nibe.eu/Domestic-heatingcooling/Airwater-heat-pumps/ http://www.nibe.eu/Domestic-heatingcooling/Airwater-heat-pum...

roel_v 12y ago

'Efficient' not in the thermodynamic sense, but in the sense that you need to put in x % less energy to have the same comfort level (i.e, have the house at a comfortable temperature at the times you need it). And to add another use of 'efficient' to the mix, just to keep things interesting ;) , when people say 'heating a house with a CV (water) based system powered by natural gas is more efficient than using electricity', what they mean is that A) electricity is generated from other sources and there are losses in the conversion/transport/etc, whereas for gas that's not so; and B) that it's just much cheaper. So yeah, sorry for the confusion, but in energy use land, 'efficient' is a highly overloaded word.