Active Thermal Cooling Technologies - Low Energy Cooling for Sustainable Buildings - page 111

5
Active Thermal Cooling
Technologies
If a building cannot be cooled by passive means such as night ventilation or earth
heat exchange alone, active cooling technologies have to be employed. Today, the
dominant cooling systems are electrically driven compression chillers, which have
a world market share of about 90%. The average coefficient of performance (COP)
of installed systems is about 3.0 or lower and only the best available equipment can
reach a COP above 5.0. To reduce the primary energy consumption of chillers, thermal
cooling systems offer interesting alternatives, especially if primary energy neutral heat
from solar thermal collectors or waste heat from cogeneration units can be used. The
main technologies for thermal cooling are closed-cycle absorption and adsorption
machines, which use either liquids or solids for the sorption process of the refrigerant.
The useful cold in both cases is produced through the evaporation of the refrigerant in
exact analogy to electrical chillers. For air-based cooling systems, desiccant cooling
cycles are useful, as they directly condition the inlet air to the building.
Thermal cooling systems are mainly powered by waste heat or fossil fuel sources.
Solar cooling systems in Europe have a total capacity of about 6MW only (Nick-
Leptin, 2005). The type of solar thermal collector required to drive the sorptionmaterial
regeneration depends on the heating temperature level, which in closed systems is a
function of both cold water and cooling water temperatures. In open sorption systems,
the regeneration heating temperature depends on the required dehumidification rate,
which is a function of ambient air conditions.