Active Thermal Cooling Technologies - Low Energy Cooling for Sustainable Buildings - page 157

Conventional gas- or electrically driven diffusion-absorption refrigerators (DARs)
with their directly powered generator/gas bubble pump were theoretically and
experimentally investigated in numerous research projects for the operative range of
refrigeration as well as air-conditioning (Watts and Gulland, 1958; Stierlin, 1964;
Narayankhedkar and Maiya, 1985; Kouremenos et al ., 1994; Chen et al ., 1996;
Smirnov et al ., 1996; Srikhirin and Aphornaratana, 2002). The Electrolux AB com-
pany, Sweden (today Dometic AB), brought out the first refrigerator in 1925 (Nieber-
gall, 1981). The cooling power of these diffusion-absorption refrigerators is between
40 and 200W. Another company, Servel Inc. in Evansville, USA (today Robur SpA,
Italy), produced refrigerators with small capacity under licence starting in the 1930s
and later, according to their own design, Servel developed and produced a gas-driven
heat pump in 1937. This pump was water cooled and the auxiliary gas used was hy-
drogen. The unit had a COP of 0.192 with a cooling capacity of 1.75 kW and a heating
capacity of 9.12 kW (Plank and Kuprianoff, 1960).
In the 1990s, these domestic DARs were modified and improved for use as directly
heated, gas-driven diffusion-absorption heat pumps (DAHPs). Values of the COP for
heating applications, COP heat , were between 1.2 and 1.35 for a heating capacity of 80
to 205W and with a cooling capacity between 25 and 51W (Herold, 1996). Another
group of researchers developed a directly gas-heated DAHP with a heating capacity
between 3.0 and 3.5 kWat heating temperatures of 150 ◦ C and evaporator temperatures
ranging from

15 to +5 ◦ C (Schirp, 1990; Stierlin and Ferguson, 1990). The COP for
heating was between 1.4 and 1.5. The industrial conversion of this directly heated, gas-
powered DAHP was carried out by BBT Thermotechnik GmbH, formerly Buderus
Heiztechnik GmbH, in combination with a condensing boiler for a near-market unit,
but is not yet commercially available. The output heating capacity of the DAHP is
approximately 3.6 kW at COP heat of 1.5 and it requires a 1.2 kW power input out of
environmental heat through the evaporator (e.g. by a solar air collector) and a 2.4 kW
heating capacity through the gas burner/generator (Schwarz and Lotz, 2001). Another
industrial conversion of the DAHP has been done by Entex Energy Ltd. The company
realized DAHPs with a 2.6 kW up to 8.0 kW heating capacity with COP heat of about
1.5. The company also realized a gas-driven DACM with a 1.0 to 3.5 kW cooling
capacity (Entex, 2004).
Current thermally driven DACMs with ammonia/water (NH 3 /H 2 O) and a pressure-
compensated auxiliary gas circuit (helium or hydrogen) are only commercially used
in the smallest power range up to 100W. The priority operating criterion is the abso-
lute noiselessness (hotel mini-bars) and the autonomous power supply (camping gas
refrigerators).
Some prototypes of commercial absorption refrigerators with indirectly solar-
powered generators and hydrogen or helium as the inert gas have also been ex-
perimentally and theoretically investigated. In these studies, COPs of 0.2 to 0.3
and cooling capacities between 16 and 62W were reached at heating temperatures
between 160 and 230 ◦ C and evaporator temperatures of

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18 ◦ C (Keizer,

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