Incredibly simple yet incredibly useful. Rather than note what a heat pump is, it's probably easier to note what is a heat pump. A fridge. A freezer An Air conditioner. A heat pump. Want to know way more than you'll ever need?, Enjoy a video or two from [[Technology Connections]] - [Heat Pumps: The Future Of Home Heating](https://www.youtube.com/watch?v=7J52mDjZzto) - [Why Heat Pumps are Immensely Important Right Now](https://www.youtube.com/watch?v=MFEHFsO-XSI) Basically, they move heat energy from one place to another. Hence making the area they took heat from, colder. This means a common object is often called two different things depending on climate. In Australia, we tend to call a Heat pump designed for controlling the climate in a room, an "Air Conditioner", as most of the time we're making the area cooler. In the US, or Europe, they are referred to as "Heat Pumps", as they are generally more interested in the heat, to heat their home. There are two common heat pumps. - Peltier - Vapor Compression ## Peltier The heat pump that nobody likes, but can be pretty useful. A Peltier heat pump is solid state. Input voltage, move heat energy from one side of the thin sheet of material to the other side. Want to reverse it? Reverse the polarity. Unfortunately, it is not very efficient. A peltier device tends to have a Coefficient of Performance (COP) between 0.3 and 0.6. This means for every Watt of energy consumed, you only move 0.3 to 0.6 watts of heat energy. If you put in 1 Watt, you heat the hot side by 1.3 to 1.6 Watts, and cool the cold side by 0.3 to 0.6 Watts. Hot side gets dramatically hotter than the cold side gets colder. They can however be extremely compact, and precisely controlled, so have their uses. They are becoming somewhat popular with neck fans, where they can press a cold surface directly to the neck and cool the body. 10 Watts of power consumption may not last too long on an integrated battery, but could last a whole day from a USB battery in your pocket. And 5 watts of energy taken directly from your neck and blood is a lot more than you would expect. Sure, you can cool a whole room with Vapor Compression very efficiently, but it's pretty dang efficient to only cool a body. ## Vapor Compression The type everyone is familiar with, and probably what you expected to read about. It's the heat pump that everyone likes, because it actually works well. A vapor compression heat pump uses a refrigerant that cycles through evaporation and condensation. It absorbs heat from one place and dumps it somewhere else. Want to reverse it? Just reverse the flow — now it’s a heater. It’s not solid state, but it’s very efficient. A typical vapor compression system has a Coefficient of Performance (COP) between 2.5 and 4.0, depending on conditions. That means for every Watt of energy consumed, it can move 2.5 to 4 Watts of heat energy. If you put in 1 Watt, you cool the cold side by 2.5 to 4 Watts, and heat the hot side by 2.5 to 4 Watts, and heat the compressor (normally outside due to noise) by 1 Watt. A large amount of energy moves, despite the small amount put in. They’re not compact, and they need compressors, fans, and refrigerant plumbing — but they’re the backbone of modern cooling and heating. From fridges to air conditioners to heat pumps, vapor compression is everywhere.