22 May 2002
Replacing boilers by a combination of cogeneration units with electric heat pumps can double the energy efficiency in producing low temperature heat. Even when replacing boilers in older dwellings by heat pumps and cogeneration units, a total energy performance factor of about 1.5 can be attained. However, this requires heat pumps with a smaller drop of heating capacity at higher temperature lifts, a lower compressor outlet temperature and a higher energy efficiency.
In order to meet these requirements the development of a new type of retrofit heat pump has been initiated by the Swiss Federal Office of Energy. This development leads to new cycles for small heat pumps: two stages with two compressors, vapour injection with an economizer, va-pour injection with an economizer and a suction gas superheater, and a separate heat pump loop for the subcooling of the condensate. The experimental results of these cycles are presented and compared with those of a conventional heat pump cycle.
For HFC refrigerants a promising retrofit heat pump with vapour injection is now in the phase of field tests. A retrofit heat pump with ammonia as refrigerant and an adsorptive ammonia trap is still in the stage of a bench system.