Development of a new controller for simultaneous heating and cooling of office buildings

This paper aims to develop a new controller to regulate the supply water temperature of a room-temperature loop integrated in a novel HVAC for office buildings.
The main feature of the room-temperature loop is its ability to provide simultaneous heating and cooling by circulating water with a temperature of about 22 °C. Therefore, the same supply water temperature is delivered to all the thermal zones in the building, no matter whether a single zone needs heating or cooling. In previous studies, the supply water temperature varied between 20 °C and 23 °C, according to outdoor air temperature. However, a dependency with the outdoor air temperature showed some limitations in terms of energy use and indoor thermal comfort.
A new controller for the supply water temperature was developed in Dymola, a modelling and simulation environment based on the open Modelica language. The controller was fed by signals of actual room air temperatures and return water temperature. Depending on the minimum and maximum air temperatures in the rooms, the supply water temperature was set by adjusting the return water temperature with two offsets, one for heating demand and one for cooling demand.
The behaviour of the controller was tested by modelling two office rooms connected to the room-temperature loop. Standard internal heat gains and construction thermal properties were selected. To evaluate potential energy savings, the new controller was compared with the simple controller previously developed. Simulations with Dymola showed that energy savings of approximately 44% were achieved for both the winter and summer day thanks to the integration of the new controller.