Free cooling in commercial buildings. Application with evaporative cooling tower and chilled beams

Licentiatavhandling, 2004

The use of electricity in commercial buildings has increased over the last decades. One major cause is the rapid escalation of air conditioning equipment together with a growth of internal heat gains originating mainly from an increased amount of office equipment, which also use electric energy, and high levels of solar irradiation. The purpose of this thesis is to examine an alternative comfort cooling system consisting of a hydronic cooling system with an evaporative cooling tower and chilled beams. The system has no conventional chiller and is therefore completely free of environmentally hazardous refrigerants. The thesis also deals with the topic of how to decrease the use of electricity from internal heat sources by using a rational and methodical approach during the design phase of a building project. The analysis of the comfort cooling system is made through simulations in a building simulation tool, IDA Indoor Climate and Energy (IDA ICE). A mathematical model of a cooling tower is developed in this project and added to IDA ICE. The base case condition comprises a normal office building with a normally sized cooling system. The total internal heat gain, including solar radiation, is between 50 – 70 W/m2 and the climate conditions is equal to those in northern Europe, i.e. north of latitude 48 – 49°N. The results form the simulations indicate that the comfort cooling system can maintain a thermal climate where the annual maximum indoor air temperature is between 24 – 26°C in a Nordic climate, and between 25 – 27°C in the rest of the northern Europe. The annual duration of indoor air temperature during working hours exceeding 24°C is between 1 – 5% in Nordic climates and between 3 – 8% in the rest of the northern Europe. The annual maximum relative humidity seldom exceeds 80% and at maximum indoor temperatures, the relative humidity is between 60 – 70%. The annual COP of the cooling tower and the cooling system is about 24 at base case conditions. Thus, the use of electric energy is about 10% of the energy used in a conventional cooling system. A hydronic cooling system with a cooling tower can be applied to both new and refurbished buildings. This comfort cooling system represents well-established techniques and no parts of the system are new or unproven on the market. Preliminary data from other sources indicate approximately equal total investment costs for a hydronic cooling system with a cooling tower compared to a conventional hydronic cooling system with a mechanical chiller.