Evaporative Cooling Tower and Chilled Beams. Design Aspects for Cooling in Office Buildings in Northern Europe.

Doctoral thesis, 2009

The purpose of this thesis is to examine a comfort cooling system consisting of a hydronic cooling system with an evaporative cooling tower and chilled beams. The system has no conventional chiller. The analysis of the comfort cooling system is made through simulations in a building simulation tool, IDA Indoor Climate and Energy (IDA ICE) and monitoring of a pilot plant equipped with this system. A mathematical model of a cooling tower is developed and validated 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 pilot plant consists of an office space of 450 m2 which is cooled by a free cooling system. The free cooling system has an outdoor evaporative cooler which is connected to a chilled beam system in the office building. The monitoring was made during May – August 2007. 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 COP of the cooling tower and the cooling system is about 7 at base case conditions. Thus, the use of electric energy is about a third of the energy used in a conventional cooling system. The outcome from the pilot plant basically confirms the results regarding the indoor climate. The COP of the evaporative cooler during the measured period is however lower compared to the results from simulations. A hydronic cooling system with an evaporative 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.