4 ms·

This doesn't explain how they work though? I've found the following simplified model of how heat pumps work useful, and why they have > 100% efficiencies (Typic

This doesn't explain how they work though? I've found the following simplified model of how heat pumps work useful, and why they have > 100% efficiencies (Typically 300% - 400% or more compared to burning/ resistance heating which can only reach 100% efficiency). Heat always flows from a high temperature to a low temperature. However, we want heat to go the opposite way (i.e. from the cold outside to our warm houses). There's a technique to do this. We use a gas (the refrigerant) to transfer heat. We first expand the gas (which cools it) until it cools below the cold outside. We then bring it near the cold outside where it now starts absorbing heat until it matches the cold outside temperature. We then move the gas and compress it until it's temperature matches/exceeds our desired warm inside temperature. Then, we bring it to the warm indoors where heat will now flow out of it. During the entire cycle, the gas is inside a closed loop. It exchanges heat through radiators. The compression & expansion cycles uses energy (technically they can be offset against each other a bit) which is added to the gas (conservation of energy) raising its temperature. Thus by supplying a little electricity, we're able to move heat from the cold outdoors to the warm indoors. The high efficiencies are because for using X units of energy, we're able to heat the house by X+Y units where Y is the heat transferred from the outside. Typically Y >> X.

cubefox 3y ago
By that measure of energy, burning oil or gas also has >>100% efficiency, as you only need energy to get it out of the ground, transport, and to light it. The energy stored in the oil is analogous to the "outside heat" for heat pumps.
- duckmysick 3y ago
  That's the thing though: the energy is stored in natural gas or oil but I still need to extract it. I can't heat my room by pumping it full of natural gas or filling it with oil. To raise the temperature of my 300 square feet room by one degree I need the same amount of energy, no matter the source. But the ways of delivering that energy aren't the same. If I have a simple gas burner, I need to know how much gas do I have to burn to heat my room. It will keep me warm, but it's not a good idea. Burning gas with a flame makes other gases that I don't want inside. I need to vent them, but I will lose some heat through that. I can also get a gas furnace that condenses those byproduct gasses in a second heat exchanger for extra efficiency. Maybe seal it up better too. It needs a little electric power for ignition, so I need to take that into account. But overall, it would be more efficient. I would need less gas to heat my room. Even though I'm using gas in both examples, the efficiency is different. It depends on how I convert that gas into heat. I can also burn that gas in a generator to produce electric power. Then I can use that electric power for a resistive heater. Not a great idea, but it's an option. I don't have to burn the gas myself. I can delegate generating power to a gas-fired power plant and buy power from them. And I can use a heat pump instead of a resistive heater. My heat pump will use less power than a resistive heater, so that's good, I suppose. The question remains: how much gas do I (or a power plant) have to burn to heat my room. The answer depends on what do I use the gas for and how. That's the efficiency.
- stubish 3y ago
  The measure really is how many joules of energy is required to heat something a certain amount of joules. By burning oil or converting electricity to heat, 1 joule of stored chemical or electrical energy converted to heat energy will raise the heat of that something by a maximum of 1 joule. A maximum of 100% efficiency. By using 1 joule of energy to compress cold gas into warm gas, we can raise the heat of that something by 3-4 joules. Moving heat energy around is more efficient that generating heat energy. Commercially available technology 300%-400% efficient.
- ppsreejith 3y ago
  > The energy stored in the oil is analogous to the "outside heat" for heat pumps. This isn't correct. Here's a thought experiment to clarify: If we burn X MJ of oil, we transfer X MJ of energy as heat to our house. Otoh, if we set up a generator (say 40% efficient) which produces electricity from oil and dumps waste heat into our house, and use that to power a 300% efficient heat pump, we get 0.6X (generator waste heat) + 1.2X (300% * 0.4X) = 1.8X MJ of heat using the same X MJ of oil. Thus,we get an additional 0.8X MJ of heat (80% extra heating) from the same X MJ of oil just by using a heat pump (& generator) compared to burning it. I.e we're using the energy stored inside the oil more efficiently.
  - cubefox 3y ago
    Here you are comparing oil to oil + heat pump, but the original comparison was just between oil and heat pump.
Projectiboga 3y ago
It's able to do this via a temp change as part of the compression cycle. When gas expands it's container gets cold. These systems can move heat from outdoors to inside in cooler weather. Your Air Conditioner doesn't make cold, it moves your heat outside. So being able to move or collect heat is how efficiencies over '100%' can happen, it isn't free just more efficient than space heaters.

cubefox 3y ago

By that measure of energy, burning oil or gas also has >>100% efficiency, as you only need energy to get it out of the ground, transport, and to light it. The energy stored in the oil is analogous to the "outside heat" for heat pumps.

duckmysick 3y ago
That's the thing though: the energy is stored in natural gas or oil but I still need to extract it. I can't heat my room by pumping it full of natural gas or filling it with oil. To raise the temperature of my 300 square feet room by one degree I need the same amount of energy, no matter the source. But the ways of delivering that energy aren't the same. If I have a simple gas burner, I need to know how much gas do I have to burn to heat my room. It will keep me warm, but it's not a good idea. Burning gas with a flame makes other gases that I don't want inside. I need to vent them, but I will lose some heat through that. I can also get a gas furnace that condenses those byproduct gasses in a second heat exchanger for extra efficiency. Maybe seal it up better too. It needs a little electric power for ignition, so I need to take that into account. But overall, it would be more efficient. I would need less gas to heat my room. Even though I'm using gas in both examples, the efficiency is different. It depends on how I convert that gas into heat. I can also burn that gas in a generator to produce electric power. Then I can use that electric power for a resistive heater. Not a great idea, but it's an option. I don't have to burn the gas myself. I can delegate generating power to a gas-fired power plant and buy power from them. And I can use a heat pump instead of a resistive heater. My heat pump will use less power than a resistive heater, so that's good, I suppose. The question remains: how much gas do I (or a power plant) have to burn to heat my room. The answer depends on what do I use the gas for and how. That's the efficiency.
stubish 3y ago
The measure really is how many joules of energy is required to heat something a certain amount of joules. By burning oil or converting electricity to heat, 1 joule of stored chemical or electrical energy converted to heat energy will raise the heat of that something by a maximum of 1 joule. A maximum of 100% efficiency. By using 1 joule of energy to compress cold gas into warm gas, we can raise the heat of that something by 3-4 joules. Moving heat energy around is more efficient that generating heat energy. Commercially available technology 300%-400% efficient.
ppsreejith 3y ago
> The energy stored in the oil is analogous to the "outside heat" for heat pumps. This isn't correct. Here's a thought experiment to clarify: If we burn X MJ of oil, we transfer X MJ of energy as heat to our house. Otoh, if we set up a generator (say 40% efficient) which produces electricity from oil and dumps waste heat into our house, and use that to power a 300% efficient heat pump, we get 0.6X (generator waste heat) + 1.2X (300% * 0.4X) = 1.8X MJ of heat using the same X MJ of oil. Thus,we get an additional 0.8X MJ of heat (80% extra heating) from the same X MJ of oil just by using a heat pump (& generator) compared to burning it. I.e we're using the energy stored inside the oil more efficiently.
- cubefox 3y ago
  Here you are comparing oil to oil + heat pump, but the original comparison was just between oil and heat pump.

Projectiboga 3y ago

It's able to do this via a temp change as part of the compression cycle. When gas expands it's container gets cold. These systems can move heat from outdoors to inside in cooler weather. Your Air Conditioner doesn't make cold, it moves your heat outside. So being able to move or collect heat is how efficiencies over '100%' can happen, it isn't free just more efficient than space heaters.