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> heat pumps: electrical devices Just to be pedantic, but not exactly. The typical design in a domestic heating unit, or refrigerator is mechanical. A fluid
by retrac 4y ago
> heat pumps: electrical devices
Just to be pedantic, but not exactly. The typical design in a domestic heating unit, or refrigerator is mechanical. A fluid is pumped and cyclically compressed/expanded. While electric motors are usually used, they can be driven by any source of mechanical energy; driven directly by a combustion engine is not too unusual.
There are also heat pump cycles that can be driven directly with heat. Refrigerators based on that are relatively common here in Canada in areas without reliable grid electricity. Usually a propane or natural gas flame.
Thermoelectric coolers are actual electric heat pumps; directly moving heat across a semiconductor junction. Not very efficient and quite expensive practically. They're used in those USB drink coolers and to cool down lab equipment. Finding a high-efficiency thermoelectric material that works at normal temperatures and pressures is nearly as much of a Holy Grail as finding a high temperature superconductor.
- the_other 4y ago> Finding a high-efficiency thermoelectric material that works at normal temperatures and pressures is nearly as much of a Holy Grail as finding a high temperature superconductor. Are they two sides of the same problem?
- deleted 4y ago[deleted]
- fnordpiglet 4y agoNo, TECs operates on a quirk related to semiconductor properties and are using electricity to move heat from one side to another but necessarily have resistance. Superconductors however are seeking zero electrical resistance. Current TECs produce 5x heat vs heat moved, and have a limited range of operation and a small range (30c) for the delta in heat between the two sides. I’ve been fascinated by TECs for years and I aspire to freeze CO2 with them, but it’s actually been really difficult to get cryogenic temperatures. You need to build a pyramid that has increasingly powerful TECs drawing heat away faster than it can accumulate. Even then I’m hitting walls in the -30c range because efficiency falls off a wall at both ends as you exceed the optimal ranges for the semiconductor materials.
- juujian 4y agoYou are not adding anything to the conversation, but I still love pedantic comments like these.
- NikolaNovak 4y agoHmm, as somebody who knew a bit about heat pumps but not much, I did find it added to clarify/distinguish between the main mode of operation of heat pump, used to accomplish the actual heat transfer; and what power / mechanism is used to move the mechanical bits. I.e. an internal combustion engine implicitly uses some kind of burning fuel; if on the other hand you want to use electricity as energy source, it needs a different kind of engine entirely. But that, as I understand from the post, is not the case here - heat pump as described here can operate on same principle and look broadly similar in its core parts, whether powered by electricity or something else.
- zozbot234 4y agoStrictly speaking you don't need a phase change in the fluid for a viable heat pump; pressure change is enough albeit with worse efficiency. Even something as simple as a Stirling engine with forced circulation of the fluid works as a heat pump.
- elil17 4y agoIf you are referring to transcritical CO2 that is absolutely right. However you can't just use any pressure change in any gas, it would work but it would not be economically viable due to that inefficiency.
- ars 4y ago> There are also heat pump cycles that can be driven directly with heat. They are called https://en.wikipedia.org/wiki/Absorption_heat_pump https://en.wikipedia.org/wiki/Absorption_heat_pump But they are much less efficient that electrical ones, adding even a small amount of electricity to the cycle (even if the primary energy is heat) can dramatically improve efficiency.
- rootusrootus 4y ago> There are also heat pump cycles that can be driven directly with heat. Refrigerators based on that are relatively common here in Canada in areas without reliable grid electricity. Usually a propane or natural gas flame. Notably, the propane fridges used in RVs (which AFAIK usually use ammonia for the refrigerant) are extremely inefficient. They have the huge upside of requiring very little electrical power to operate, but would never be my choice if I wasn't tightly limited on electrical power.
- namibj 4y agoThey're inefficient because they skimp on a motor for a forced circulation pump. Otherwise, ammonia/water absorption chillers are quite efficient.
- crznp 4y agoAs you said: a Peltier heat pump is a purely electrical device, so if you're using a broader definition of the term, it could be a variety of different types of devices. But that is the introductory paragraph, the author is defining what they mean by "heat pump": a device for heating a house which is powered by electricity. You could power it with something else, but the point is to replace natural gas furnaces.
- usrusr 4y agoMy mind parses the term "heat pump" as a device that works on temperature by compressing some medium. Works out just fine for most heat pumps, but not at all for e.g. the Peltier element which is about moving heat from one side to the oher ("pump") but does not involve compression at all.
- xpe 4y agoTLDR: for a heat pump, "electromechanical device" is more descriptive than "electrical device"