B076 Lunch hour ventilation

Thermal energy saving potential for transient ventilation demands at lunch hours of air-conditioned offices of Hong Kong

Brief:

A ventilation system which supplies fresh air to a room consumes a considerable portion of thermal energy in an air-conditioning system of an air-conditioned office and affects the indoor air quality (IAQ). A successful control on the ventilation system would reduce the thermal energy consumption. In an occupied office, the IAQ would be surrogated by the carbon dioxide (CO₂) concentrations and the amount of fresh air which primarily related to the occupant load. In this study, regarding a significant occupant load reduction at lunch hours in offices, the ventilation demands due to occupant load variations during the lunch periods were examined against certain IAQ subjects. This study also examines the potential thermal energy saving in different operating schedules of ventilation in lunch periods for typical air-conditioned offices in Hong Kong. The estimation is based on an earlier developed transient ventilation demand model using the mass balance of carbon dioxide (CO₂) volume fractions for occupant loads, with the parameters determined from a year-round occupant load survey in Hong Kong. The results showed that the energy consumption of a ventilation system would be correlated with the transient occupant load and its variations in the air-conditioned office. An open-plan office (area of 1200m²) in Hong Kong was used as an application sample to evaluate the potential energy saving due to the reduction of occupant load in the lunch hours. Compared with the ventilation system operating for the maximum occupant load in office, the results showed that, regarding the same IAQ objective, the ventilation system operating for the transient occupant loads would reduce the thermal energy consumption by 40% in the lunch hours. A better understanding on the transient characteristics of occupant loads is important in evaluating the ventilation demands in air-conditioned offices.

Further Information:

Mui KW, Wong LT, 2009. Thermal energy saving potential for transient ventilation demands at lunch hours of air-conditioned offices of Hong Kong, The 11^th International Conference on air distribution in rooms (ROOMVENT 2009), 24-27 May, Busan, Korea, pp. 131-138.