Geothermal Cooling - Low Energy Cooling for Sustainable Buildings - page 83

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Geothermal Cooling
Research into ground-coupled cooling systems, which are more energy efficient than
conventional compression cooling systems has been carried out for many years. The
initial interest was in direct coupling of buildings with the earth, in order to take
advantage of the fact that the sub surface soil temperature in many regions falls below
or is within comfort conditions (Labs, 1989; Dahlem, 2000). Direct contact with the
ground allows heat to dissipate into the earth, and stabilizes building temperature at or
near the temperature of the adjacent soil. In order to be effective, most of the envelope
of the building must be in contact with soil at a sufficient depth to eliminate the effect
of variations in the surface temperature. A principal disadvantage of direct coupling
is that the missing thermal separation leads to additional heating demand in winter.
Where direct contact with the soil is not possible (as is usually the case, due to
a variety of constraints), the ground may still be used as a heat sink by means of
either earth to air or earth to water heat exchangers. Examples are given by Fink
et al . (2002). If air is used as the cooling fluid, the heat exchangers are typically pipes
buried beneath the surface, through which air is drawn into the building by electric
fans (Kumar et al ., 2003). As air moves through the pipe, energy is transferred to the
adjacent soil. Since air has a much smaller heat capacity than any type of soil (by
several orders of magnitude), its temperature will become equal to that of the soil
after a certain distance with only a small disturbance to the earth's temperature field.
The air drawn into the building may be either ambient air, in which case the system is
referred to as 'open-loop', or interior air, circulating in a 'closed-loop' or multi-pass
system. Argiriou (1996) presents several models for calculating the time-dependent