The environmental impacts of heat pump systems (air to air, water, geothermal) can be summarized in two categories; total emissions of CO2 and the environmental safety of refrigerants used.
Environmental Aspects of Operation
Too fully account for the total emissions of heat pumps evaluation of the system and the energy required to operate the system must be takin into account. A report from the European Union has tackled this problem and created an equation that evaluates such aspects of a heat pump and produces a value in total mass of CO2 produced. This equation is called the Total Equivalent Warming Impact (TEWI) (below).
When looking at an example of a geothermal heat pump, it’s clear the most emission intensive component is not the pump itself but the production of electricity to run the pump.
The total TEWI value can be greatly reduced then by the source of the electricity to run the pump, thus a solar powered heat pump has very low carbon emissions. Below is an example of European countries and their production of CO2 based on electricity generation. Norway has the smallest emissions because the majority of electricity production is from renewables.
Overall the operation of a heat pump is a low emission process that can greatly reduce carbon emissions, but ultimately depends on the source of the electricity powering the pump.
Environmental Aspects of Refrigerants
Once the emissions of the pump are taken into account for environmental sustainability the refrigerant used in the system must also be assessed. The refrigerants must have certain thermodynamic requirements to efficiently operate a heat pump and this requirement leads to the use of flammable and toxic refrigerants. The type of refrigerant is determined by the specific requirements of the heat pump namely industrial vs household systems. The most common refrigerant was R-22(HCFC) or Freon until is ozone depleting effects were realized. Currently this refrigerant is being phased out for a non-ozone depleting option R-410A which is more efficient. Although less energy is a benefit it is still over 1000 times more powerful of a greenhouse gas than CO2. Thus mitigating any leaks is extremely important. The biggest issues for refrigerant loss are due to leaks in operation lifetime and dismantling/demolition. The use of refrigerants is necessary for the operation of heat pumps but the properties required promote the use of potentially dangerous chemicals. Ideally we will phase out these harmful refrigerants but science and technology needs to produce a better, affordable, efficient replacement.