IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C1 Report, 31 October 2010
7 Steam jet chillers
Clemens Pollerberg (Fraunhofer UMSICHT, Germany)
7.1 Brief description of the technology
The Steam Jet Ejector Chiller (SJEC) is a thermo-mechanical chiller for cold generation. A
refrigerant boils at a low pressure in the evaporator. The necessary heat of evaporation is
provided by the water to be chilled. The vapour refrigerant is then compressed by a steam jet
ejector to a higher pressure level and fed into a condenser. The driving energy of the steam
jet ejector is supplied by motive steam, which can be generated by solar energy. The motive
steam and vapour refrigerant are mixed in the steam jet ejector and both are liquefied in the
condenser. The condensation takes place at a higher temperature than the ambient
temperature, so that the heat from the condensation process can be rejected to the
atmosphere. The condensate from the condenser is fed back to the evaporator and to the
motive steam generator. Figure 33 depicts the principle of a solar driven SJEC.
Figure 33: Principle sketch of a solar driven SJEC with water as working fluid and refrigerant.
A SJEC can use water as the working fluid, which is used for generating the motive steam
and as a refrigerant. In that case, an open process can be constructed without hydraulic
separation between the solar collector and the SJEC or the chilled water network and the
SJEC. The evaporator can be designed as a flash evaporator and the condenser as a direct
contact condenser, such that both devices are basically vessels. The steam jet ejector
consists of a motive steam nozzle, a mixing chamber and a diffuser. Thus the whole solar
cooling system is simple in design and a high reliability of operation can be expected.
Besides using water as both a working fluid and a refrigerant, different types of fluid have
been discussed too. In particular, halocarbons, hydrocarbons and ammonia have been
proposed for solar driven SJECs. The advantage of these proposed fluids is a reduction of
the required temperature level of the driving heat, while still allowing adequate COP values to
be reached. An overview of the possible types of fluid and an investigation of their
applicability in a SJEC is given in [181].
SJECs in the higher cold capacity range are designed as two stage chillers and have several
steam jet ejectors. In this case, the delivery rate of the ejectors could be different from each
other in order to obtain a capacity control of the chiller by switching steam jet ejectors on/off.
New approaches to increasing the efficiency of SJECs focus on the use of multiple ejectors
in series and the use of two different types of fluid as working fluid and as refrigerant.
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