Diploma's thesis Julian Kremeyer


Impact of the control strategy at energetic and exergetic efficiency of a cooling system with passive night re-cooling

Diploma's thesis Kremeyer Copyright: EBC Scheme of Dymola simulation model

For the student competition Solar Decathlon Europe 2012, the team of RWTH Aachen developed and built a two-person residential building. The installed building technology uses a cooling system that employs a nightly radiative cooling instead of a chiller. In this system, water is dispersed at night over the photovoltaic modules installed on the roof and cools down. The cooled medium is stored in tanks. During daytime, the water is used for the chilled ceiling and the air-cooling of the air conditioning.

In this work, three optimized control strategies of the cooling system are compared with the original control by means of simulation. For this reason, the building technology and building shell are modeled in the simulation tool Dymola. The model is connected to a Programmable Logic Controller (PLC) on which the control algorithms are executed. The coupling between Dymola and the PLC is done via the Modbus protocol.

The evaluation shows that the reduction of the mass flow rate in the radiative cooling increases the coefficient of performance and the exergetic efficiency. The use of a rotational speed control of the chilled ceiling’s pump reduces the electricity consumption significantly, without decreasing the cooling power of the chilled ceiling. It has been proven less efficient to primarily use the air-cooling to dissipate the cooling load and utilize the chilled ceiling only if the power of the cooling radiator is exceeded. This is drawn back to the low performance potential of the cooling radiator.