A basic ‘monoblock’ heat pump system comprises six components: a compressor, an expansion valve, a fan, an external radiator, a heat exchanger, and internal radiators, all interconnected by a refrigerant-filled pipe with a low-temperature boiling point liquid. When the refrigerant is warm, it exists as a vapor (essentially a gas), and when cooled, it returns to a liquid state.

Upon activation of a heat pump, the compressor initiates the process. Constrained by the expansion valve, this elevates the pressure of the refrigerant gas on one side of the system. Compression of the gas causes its molecules to densely pack together, collide, and rapidly heat up.

Visualize a deodorant can: when released, it cools in your hand; if forced back in, it heats up. This heating effect transfers to the heat exchanger, which then imparts heat into the water circulating through our radiators. As the water cycles through the radiators, it returns cooler, consequently cooling the plate and condensing the refrigerant gas into a liquid.

This compressed refrigerant traverses the expansion valve, decompressing and dropping below the outside air temperature. This now very cold, low-pressure liquid flows through an outside radiator to extract heat from the ambient air, aided by a fan. It warms up, boils, transitions back to a gas state, and returns to the compressor.

This entire process leverages latent heat and phase change principles. Any liquid converting to gas absorbs latent energy (energy absorbed without altering temperature), while any gas converting to liquid releases this latent energy as heat, warming objects without cooling itself.

The outside air serves as the source of our thermal energy, with the electricity powering the heat pump facilitating the transfer of heat from the outside air and concentrating it into our geysers. The heat energy doesn’t originate from the electricity; rather, it comes from the air. Various iterations of heat pumps, such as air-to-air, ground source, and water source, operate on the same fundamental principle.

A heat pump boasting over 400% efficiency? What precisely are we measuring?

With gas geysers or boilers, we gauge the gas input and the resultant heat output. For instance, if we input 1 kWh of gas and obtain 0.9 kWh of heat, we achieve 90% efficiency. Conversely, when employing heat pumps, if we input 1 kW of electricity and extract 4 kW of thermal energy, our efficiency registers at 400%. Allow us to elaborate!

To convert gas energy to heat, we combust it, burning 1 kWh of gas to release 0.9 kWh of heat, with the remaining 0.1 kWh lost as uncaptured latent energy in water vapor. Crucially, you pay for the power utilized, not the heat acquired.

In contrast to gas geysers or boilers, where the energy source is the gas, for a heat pump, it’s the external air, not the electrical power input. Efficiency in this context denotes how effectively input energy is converted into useful output energy or work, calculated as output divided by input, expressed as a percentage.