Nowadays it is almost the norm for companies to equip offices with at least one computer terminal per person and it is not uncommon to see other heat generating equipment such as laser writers and telefaxes stacked on desks. To couple this kind of heat generating equipment and heat produced by people and lighting with limited ability to combat solar gains, you will reach some rather high cooling loads. Usually ventilation air is used for cooling in the Scandinavian countries. The current trend for meeting cooling and air quality requirements of the building centres on the integration of ventilation systems and cooling ceiling panels. The main purpose of the present study is to establish if the two systems work in harmony. The cooling ceiling panel systems have shown to be good complements to more traditional systems like displacement ventilation and mixing ventilation. There can be several advantages with such cooling systems, e.g. energy savings, better thermal comfort and more silent operation. There are, though, some disadvantages too. The cooling system cannot by itself remove air pollutants, odours or latent heat, this has to be taken care of by the ventilation system. Therefore, it is important that the cooling system can co-operate with the ventilation system. The objective of this research will be to explore the flow-rate and velocity characteristics created by chilled beams in rooms. The introductory work done so far has been focused to quantitatively explore the air flow pattern created by chilled beams.
The experiments have been performed at the Royal Institute of Technology, Department of Built Environment during the autumn of 1998. A (L x W x H, 4.2 m x 3.6 m x 2.5 m) test room was set-up to provide a realistic office environment. Figure 1 shows the two different layouts used during the experiments and table 1 shows the nondimensional magnitudes.
For lighting the room was equipped with four fluorescent tube fittings with a heat load of approximately 80 watts each. To simulate common office environment the room was furnished with a PC-model with variable heat-load and a “manikin" with approximately the same area and heat load as a human. Electric heating foil was used to simulate solar irradiated windows. Thermo-couples were used to measure temperatures along the surface of a wall, at the floor and ceiling surfaces and of the air in the interior of the room. For the evaluation of the cooling effect the temperature of the inlet and outlet water were measured together with the water flow rate. Table 2 shows typical heat-balances from the experiments. The differences are caused by heat losses to the environment. To document the flow pattern under the chilled beam a digital camera and slit illumination were used together with a smoke generator with the outlet above the chilled beam.
When the heat load increases the chilled beam is unable to remove the total heat and the temperature will rise. The temperature measurements show, see figure 2, that although the temperature increases, the temperature gradient remains almost unchanged.
Figure 2: Temperature gradients
Figure 3 shows the flow below the chilled beam. The flow is very unstable and oscillates from one side to the other. This oscillation is of very low frequency and also very irregular, although there seem to be a core in the middle of the flow which is relatively stable.
Figure 3: Smoke visualisation
The next step in this project is to measure the air flow-rate created by the chilled beam. As the results above indicates there is also a need to examine the oscillation flow. The slow drift might influence the thermal comfort causing a sensation of draught to the occupants. The change in flow direction will, by the occupants be interpreted as an intermittence of the velocity field. To evaluate this flow behaviour the idea is to use video recording, temperature measurements and hot wire anemometry.