A gas heat pump it can be of the 'compression' or 'absorption' type. The first is a variant of the heat pump 'traditional' electric equipped with a compressor which, instead of electricity, uses the mechanical energy generated by a gas engine (methane or LPG). In the case of the absorption heat pump, without a compressor, it is instead a completely different technology based on absorption refrigeration cycles.
Given that there are advantages and disadvantages of the heat pump compared to other technologies, the gas heat pump compared to the electric one, it has the advantage of ensuring greater stability of performance, but the disadvantage of being more expensive when purchasing.
The main advantage is that in the cold season, when the outside temperature approaches zero, the heat recovery guaranteed by the gas engine allows not to have the drop in efficiency typical of electric air heat pumps.
A gas heat pump it can work with an external air temperature of -20 ° C providing an efficiency comparable to that of a condensing boiler. A comparison between the technologies of these machines and a similar efficient system for producing thermal energy (for example a condensing boiler) confirms a better efficiency of the gas heat pumps compared to the electric version.
With the reversible models of gas heat pump it is also possible to use the appliance not only in the winter cycle, therefore for the production of hot water, but also in the summer cycle for the production of chilled water. The interest in these machines may also derive from the fact that their use can also be foreseen where there is not much electricity available.
We say 'a lot' because some electricity is still needed to power the circulation pump, but it is a minimal amount. The LPG power supply makes the suitable gas heat pumps also to places not served by the distribution networks. The absence of mechanical moving parts (apart from the circulation pump) increases their useful life and the absence of a compressor makes them silent.
According to data from the Politecnico di Milano, in Italy at the end of 2013 there were about 400 thousand installations of compression heat pumps (almost all electric) and 150 thousand absorption heat pumps (all gas). In fact it is in the absorption technology (more recent than the compression one) that the greatest advantages of the gas heat pump compared to the electric one.
Operation of a gas absorption heat pump
There gas absorption heat pump it is based on an alternative refrigeration cycle in which the compressor is replaced by a closed circuit crossed by a refrigerant fluid, ammonia or lithium bromide. Depending on the temperature and pressure conditions in which it is found, the refrigerant takes on the liquid or vapor state. The closed circuit consists of:
Condenser and evaporator consist of pipes placed in contact with the service fluids (in ammonia absorption gas heat pump it is water or air) in which the refrigerant flows. The latter transfers heat to the condenser (high temperature side) and extracts it from the evaporator (low temperature side).
The transformations that the refrigerant undergoes constitute the cycle of gas absorption heat pump: supplying energy with the gas burner, the refrigerating fluid in evaporation absorbs heat from the external fluid and, through the condenser, transfers it to the deck to be heated.
An interesting advantage of the gas absorption heat pump is that the energy input in the form of heat necessary for operation can also be provided directly by systems such as a solar thermal system, a cogeneration plant, or come from thermal waste.
Another advantage of the heat pumps, both electric and gas, is to be able to benefit from the incentive provided for by the Thermal Account (Ministerial Decree of 28 December 2012 on economic development) intended to support the interventions of 'replacement of existing winter air conditioning systems with winter air conditioning systems equipped of heat pumps, electric or gas, using aerothermal, geothermal or hydrothermal energy '.
The heat pumps they are also tax deductible at 65% until 31 December 2014 (afterwards the deduction will drop to 50%). For owners of electric heat pumps, from 1 July 2014 the electricity tariff D1 is available on an experimental basis, based on a constant price per kilowatt hour. Membership is voluntary.