As the world strives to eliminate the use of greenhouse gases, the term heat pump gets thrown around a lot as a solution for heating without natural gas. Unless someone is knowledgeable on what heat pumps are, most times a person has a very fixed idea of them and does not know that the term ‘heat pump’ can cover many different technologies.
What exactly is a heat pump?
A heat pump is a system that transfers thermal energy from one area to another using a refrigeration cycle. For the refrigeration cycle everything starts and ends at the compressor. In heating mode, the compressor removes the refrigerant vapour from the low side of the system and pumps it to the high side where is then transferred to an indoor coil where the hot vapour heats the air and the refrigerant then condenses. A thermal expansion (TX) valve is then used to separate the low side from the high side, which then passes through a heat exchanger to transfer the heat energy elseware. The colder refrigerant then goes back through the reversing valve and finally to the compressor where the cycle starts again. For a heat pump in cooling mode the system reacts the same except the indoor coil now becomes the evaporator and the heat exchanger after the TX valve comes the condenser
What types of heat pumps are there?
Generally speaking, there is 2 main types of heat pumps; air sources and water sourced. Within the water sourced heat pump category there are standard water sourced and also ground sourced categories.
Air sourced heat pumps
Think of your air conditioner at home. There is an indoor coil located in the duct work and a condensing unit located outside. In summer (cooling mode) the indoor coil acts as the evaporator, absorbing heat and rejecting it to the outdoor condensing unit. For winter (heating mode) it is opposite and the indoor unit is now the condenser and the outdoor unit is the evaporator
Water sourced heat pumps
The concept of a water sourced heat pump compared to an air sourced heat pump is still the same except now the compressor is moved to the indoors and is replaced with an external coil with a heat exchanger which utilizes water to reject/absorb heat. The heat exchanger loop can be coupled with many different systems or options to maintain loop temperature including cooling towers, bodies of water and boilers. For cooling and heating, the loop temperature does not have to be the same but we do have to ensure that the temperatures fall within the selected heat pumps operating range in both operating modes.
Ground sourced heat pumps
Ground sourced heat pumps (also known as geothermal heat pumps)act the same as a standard water sourced heat pumps but instead of external systems to maintain loop temperature, it instead uses the ground to absorb or reject heat.
Conclusion
Overall, each heat pump solution comes with their own benefits and challenges and therefore each individual application must be reviewed to ensure the best option is selected. In the end, a heat pump is a great solution for decarbonization in heating and cooling and the efficiencies that come with a heat pump make it that much more appealing.
