Free cooling reduces energy consumption of cold water systems

Cooling systems account for a major part of operating costs in buildings with cooling applications. In the winter periods, the demand for cold energy is often much lower because of diminished need for air conditioning. As a consequence, the chillers are operated at part load because they are usually designed for the warmest periods of the year. This leads to low efficiencies and therefore unnecessary high cold water production costs. An approach to avoid the operation of chillers in low-demand periods is the utilization of free cooling. Free cooling means the exploitation of low ambient temperatures to directly generate cold water without the use of chillers and refrigerants. At the Fraunhofer IISB, possible applications and energy savings of free cooling were investigated. Extensive simul ations of relevant cooling components (i.e. chillers, cooling towers, pumps) in cooling networks have been conducted in order to determine the efficiency potential in a virtual environment.The simulation results promised a high contribution of free cooling to the overall cooling demand of the installed cold water system as well as high energy saving potentials. In order to validate the models and demonstrate the energy savings, the concept of free cooling was implemented at the Fraunhofer Institute. This was accomplished by integrating a recooling unit from a separate cold water system for air conditioning into the feed line of the main cold water system for process cooling. The existing installation manages a cooling capacity of about 120 kW at an ambient temperature level of 3 °C. At low er ambient temperatures much higher cooling capacities can be achieved. In operation, free cooling doubled the system performance (COP) compared to the regular cooling components in the regarded season.