Simulation of temperature in office with building integrated heating and cooling system

In this paper a numerical investigation of the thermal indoor environment has been performed for an office with building integrated hydronic heating and cooling system. Today office buildings are designed in such a way, and have such high internal heat loads and solar gains, that some kind of cooling is normally necessary for most of the year. Even in as cool climates as in the Nordic countries. The way the cooling is often achieved is through air conditioning. This can in many cases lead to sick building syndrome (SBS) symptoms, and furthermore it results in high energy consumption periods by raising the temperature of the concrete to slightly above the desired room temperature. Another way of solving the problem of cooling is by using building integrated cooling in floors. This technique utilizes the thermal mass of concrete in the floors, by integrating PEX pipes in the floor. By maintaining the temperature of the concrete to a level slightly below the desired room temperature, the concrete will work as an absorber for the excess heat in the office. This can significantly reduce the need for air conditioning, which will give both improved indoor climate and lower energy costs in the building. At the same time the building integrated system can also heat the office during cold periods. To examine a building integrated heating and cooling system, a simulation model has therefore been created and implemented in Matlab. The model is able to calculate heating and cooling demand, temperatures and thermal comfort parameters. The model is based on a numerical Finite Control Volume (FCV) method for the heat transfer in walls, ceiling, windows and floor. The model uses both convective and radiative heat transfer to the room air and between the room surfaces. The simulation model can be used for calculating situations with both cooling and heating demands. Using the model it is therefore possible to assess the thermal environment, and furthermore to calculate the energy consumption required for both heating and cooling. In the paper different construction types of the floor are examined, as well as various heat loads in the office. The effect of different control strategies and supply temperatures are examined. It has been found that building integrated heating and cooling to a large extent can replace air condition without decreasing the thermal comfort, while only ventilating for fresh air. For high heat loads, however, an air condition system is still required. It has also been found that in supply temperatures close to room temperature is sufficient for both heating and cooling.