On the development of a simplified model for thermal comfort control of split systems

Despite split-type systems for cooling purposes became popular in countries such as China, Japan. India, Indonesia and Brazil, their use commonly promote high gradients of both temperature and air velocity in rooms which may cause considerable thermal discomfort. Hence, this work aims at developing a simplified thermal comfort index, based on temperature and air speed, in order to develop controllers for those types of air conditioning systems, replacing the traditional on-off temperature set-point control by an effective and inexpensive thermal-comfort based control. The work is focused on the assessment of comfort in classrooms by carrying out measurements according to ISO 7730 and ASHRAE 55 Standards, 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 eight positions within the space. The field experiments were performed considering two 10.5-kW cooling capacity appliances installed in different positions relatively to the layout of the room, considering three levels of supply airflow (high, medium and low) and three set-point temperatures (23, 24 and 25 °C). An analysis of uncertainties is presented for PMV measurements and a regression analysis was applied to the measured data to determine a simplified correlation between thermal comfort (by means of the PMV index) air temperature and air velocity, aiming at developing afterwards a control device based on thermal comfort instead of temperature setpoint only. Results are shown in terms of distribution of air speed, air temperature and PMV index for the two configurations of equipment installation, as well as the resulting empirical model correlating thermal comfort index with both temperature and air speed. In addition, thermal comfort opinions from a survey are contrasted with the simplified thermal comfort model.