Self-Regulating Active Chilled Beams

Doctoral thesis, 2020

By designing comfort cooling systems to operate with higher chilled water temperatures, electricity driven chillers may be replaced by natural sources of free cooling. It also enables the possibility of self-regulation which, due to simplicity and robustness, brings cost-savings both during installation and maintenance of the building. Active chilled beams is one technology especially well suited for this high temperature cooling.

The objective of this thesis is to investigate the function of self-regulating active chilled beams in order to improve design and operation of such systems. Based on experience from existing systems, a hypothesis is that current models and knowledge do not fully capture the behavior of self-regulating active chilled beams.

The work has been carried out through measurements in an experimental facility, building performance simulations and analysis of operational data from an actual building. The purpose of the measurements was to develop a model of an active chilled beam and also to validate a modified zone model used to simulate the thermal climate in a room equipped with an active chilled beam. The purpose of the simulations was to determine the peak shaving effect of self-regulating active chilled beams and to study the influence of central control of the chilled water temperature. The purpose of the analysis of operational data was to study the performance of an actual self-regulating active chilled beam system with respect to energy use and indoor air temperatures.

The results show that a higher chilled water temperature generates more induction of room air in the active chilled beam, which is beneficial for the cooling capacity. Induction of room air also increases the internal convective heat transfer in the room, which reduces the required heat transfer area of the active chilled beam. As a consequence of self-regulation, buildings are precooled prior to the peak cooling load, further reducing the required heat transfer area. By increasing the chilled water temperature outside of the summer season, overcooling is avoided without causing thermal discomfort. The analysis of operational data demonstrates the ability to achieve the desired indoor temperatures with self-regulating active chilled beams without the use of a chiller.