Abstract
This study investigates the use of a direct ground cooling system (DGCS) using active chilled beams for the cooling of office buildings in Sweden. The methodology of the study entails laboratory experiments to develop and validate a simulation model of the cooling system. The sensitivity of the input parameters, such as borehole heat exchanger (BHE) length, internal heat gains and room temperature set point, are studied with respect to BHE outlet fluid temperature and room thermal comfort. The results provide a practical insight into designing DGCSs with regard to borehole outlet fluid temperatures. The results also show that the thermal comfort criteria in the room are met by applying the DGCS even under the most critical design conditions of undisturbed ground temperature and internal heat gains. The sensitivity study quantifies the influence of the room temperature setpoint and internal heat gain intensity on the BHE length. The BHE outlet temperature level is more sensitive in shorter BHEs than in the longer ones, and BHE length and room temperature levels are highly correlated. Thus, the sizing of DGCS can benefit from a control system to allow the room temperature to float within a certain range.
Highlights
Systems utilising ground as a heat source or heat sink are among the most viable solutions for the provision of energy-efficient space heating and cooling
The results show that the ground loads per borehole heat exchanger (BHE) unit length are inversely proportional to BHE length
The results suggest designing the building temperature control system so that the room temperature increases to a certain extent during the peak period in order to reduce the peak cooling load
Summary
Systems utilising ground as a heat source or heat sink are among the most viable solutions for the provision of energy-efficient space heating and cooling. Ground-coupled systems benefit from exchanging heat with the ground, which has a lower temperature than the ambient air in summer. The reversible ground-source heat pump system is a wellknown ground-coupled cooling technology. The heat pump uses the ground as a heat sink in summer to cool the refrigerant in the condenser. Ground-source heat pumps yield better energy performance than air-cooled chillers do [4e6], this technology demands significant amounts of electricity for the refrigeration cycle. It is possible to use direct ground cooling systems (DGCS) to provide cooling to buildings. These systems do not use compressors and use natural ground temperatures to provide cooling [8]. The cooling performance ratio of the systems is as high as 13e25 [8,10]
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