Description:

Introduction: A heat pump is a type of Heating, Ventilation, and Air Conditioning (HVAC) equipment that can provide both heat and cooling. A heat pump uses mechanical energy to remove heat from the air and move it either inside or outside, depending on whether your space needs heat or air conditioning. 

In HVAC applications, a heat pump is typically a vapor-compression refrigeration device that includes a reversing valve and optimized heat exchangers so that the direction of heat flow (thermal energy movement) may be reversed. The reversing valve switches the direction of refrigerant through the cycle and therefore the heat pump may deliver either heating or cooling to a building. In cooler climates, the default setting of the reversing valve is heating. 

The default setting in warmer climates is cooling. Because the two heat exchangers, the condenser and evaporator, must swap functions, they are optimized to perform adequately in both modes. 

Powerful electrical systems in EVs also generate huge amounts of heat, and its negative effect on range and battery charging time is perplexing. Where the strategy was once to waste it, now the focus is on saving every last joule and forcing it to earn its keep. That is where the role of heat pump, a kind of back-to-front refrigerator, comes in. 

In an EV, reversible heat pumps can be used to both warm the battery and cool it. When cooling it, the excess heat from the battery can be sent to the cabin heater. A heat pump can also move heat from the ambient air to the cabin heater. The Nissan Leaf was the first to do this, but not all EVs have embraced this technology yet.

Maturity Timeline:

Advantages: Heat pumps have two major advantages: They can operate in both directions and they can transport more heat than the energy required operating them. Other advantages of heat pumps are: 

• Lower Energy Expenses. According to energy.gov, a heat pump can deliver as much as 3 times more heat energy to a space than the electrical energy it uses. That translates to greatly reduced energy bills for you. An average home might save as much as $1,000 per year.
• Lower Repair and Maintenance Costs:  If you’re using a heat pump as your sole source of heating and cooling, there is only one system to maintain, and one system to diagnose and repair if anything goes wrong. That also lowers your total cost to operate.
• Environmentally Friendly. Heat pumps do use electricity, but they don’t consume fossil fuels to produce heat. When you don’t have to rely on an oil or gas burning furnace, you’re doing your part to reduce the use of fossil fuels.

Limitations: The big drawback to heat pumps is that they lose efficiency in climates with extended periods where the temperature drops below freezing.

Process: When comparing the performance of heat pumps the term 'performance' is preferred to 'efficiency', with coefficient of performance (COP) being used to describe the ratio of useful heat movement per work input. An electrical resistance heater has a COP of 1.0, which is considerably lower than a well-designed heat pump which will typically be between COP of 3 to 5 with an external temperature of 10 °C and an internal temperature of 20 °C. A ground-source heat pump will typically have a higher performance than an air-source heat pump. 

The "Seasonal Coefficient of Performance" (SCOP) is a measure of the aggregate energy efficiency measure over a period of one year which it is very dependent on region climate. One framework for this calculation is given by the Commission Regulation (EU) No 813/2013:[26]. 

A heat pump's operating performance in cooling mode is characterized in the US by either its energy efficiency ratio (EER) or seasonal energy efficiency ratio (SEER), both of which have units of BTU/(h·W) (note that 1 BTU/(h·W) = 0.293 W/W) and larger values indicate better performance. Actual performance varies, and it depends on many factors such as installation details, temperature differences, site elevation, and maintenance.

Commercialization: Nissan, The BMW i3, Volkswagen e-Golf, and Kia Soul EV (1st-gen) and Hyundai Ionic.