On the improvement of thermal comfort in indoor spaces conditioned by split-type systems

Abstract

Conventional on/off-based control split-type appliances are widely used in classrooms and offices, in Brazil and in many other countries, due to their low cost and ease of installation. However, occupants often complain about thermal discomfort depending on their position within the conditioned space, especially in positions that are directly affected by the draft, since those equipment provide high cold air velocities as a result of their high cooling capacity relatively to their air supply area. In order to improve the indoor thermal comfort in spaces conditioned by this kind of system, a simplified empirical model for controlling both the supply airflow and the temperature set-point is proposed in this work. In view of that, the comfort conditions in an occupied classroom were experimentally evaluated according to ISO 7730 Standard, which defines the thermal satisfaction in occupied environments based on the PMV index. Specifically, the speed, temperature and relative humidity of the air and the mean radiant temperature of the room were measured at 8 positions within the air conditioned space, for the three original air flows (high, medium and low) of a 10.5-kW cooling capacity appliance and three set-point temperatures (23, 24 and 25 °C). The simplified model, correlating thermal comfort and the variables that could be directly controlled by the split-type system (airflow rate and temperature), was obtained by adjusting several curves from 72 measuring assemblies (8 measuring points, 3 set-point temperatures and 3 supply airflows). The correlation that best represents the distribution of thermal comfort throughout the conditioned environment was provided by the non-linear regression method of Levenberg-Marquardt.