Overcooling Index of Air Conditioning

The purpose of air conditioning systems is to lower the air's Heat Index (HI) from an uncomfortable level to a comfort level of temperature and humidity. Heat Index is the “feel like” air temperature that combines the actual temperature and humidity. The publication “Comfort Heat Index – Thermostatic Control of Air Conditioning Units” [6] defined the comfort level of the Heat Index as a Comfort Heat Index (CHI) equal to 26.6°C (79.9°F). The publication [6] also introduced the Optimum Comfort Air Conditioning (OCAC), a thermostat setting that achieves thermal comfort with minimal cooling hours, reduced energy consumption, and a Heat Index (HI) that remains below the Comfort Heat Index (CHI = 26.6°C). The current work adds a minimum OCAC, MinOCAC = 25.35°C (77.63°F), the thermostat setting that achieves thermal comfort (CHI=26.6°C) even at 100% relative humidity. Cooling below the Comfort Heat Index not only wastes energy but also causes serious discomfort and health hazards to many people. In this work, Heat Index above or below the Comfort Heat Index is considered equally uncomfortable conditions. This work introduces two new terms related to air conditioning overcooling: Overcooling Heat Index (OCHI) and Overcooling Index of Air Conditioning (OverAC). OCHI is the difference between the Comfort Heat Index and the actual Heat Index, and OverAC is the product of OCHI and the extended time it lasts. For example, if the operation of air conditioning system results in a Heat Index 2°C below the CHI on average, and 1,000 hours more than CHI, the OCHI index will be 2°C and the OverAC index will be the product of 2°C per 1,000 hours, 2,000 degree-hours (dhr). Running the BESOO simulation program for Jerusalem and Tel Aviv shows that setting the air conditioning thermostat to 16°C results in an OverAC index for Jerusalem of 51,434 dhr and for Tel Aviv of 45,265 dhr. The BESOO Online Building Energy Simulation and Optimization programs, used in this work, are available at: https://nowagreen.ct.ws/BESO/544Jm https://nowagreen.ct.ws/BESO/544TA