Thermal energy impact for IAQ Improvement by Dilution

Brief:

Dilution is one of the means for IAQ improvement approaches adopted in many air-conditioned offices of Hong Kong. See IAQ of Hong Kong offices with such improvement approach.

Energy impact for IAQ improvement by dilution

Treatment of fresh air in ventilation systems for air-conditioned offices consumes a significant amount of energy and affects the indoor air quality (IAQ). Energy impact on the ventilation systems was examined against certain IAQ objectives for indoor airborne bacteria exposure risk in air-conditioned offices of Hong Kong. The relationship between thermal energy consumptions and indoor airborne bacteria exposure levels based on regional surveys were investigated. The thermal energy consumptions of ventilation systems operating for CO₂ exposure concentrations between 800 ppmv to 1200 ppmv for typical office buildings and the corresponding failure probability against some target bacteria exposure levels were evaluated as a demonstration of method. The results showed that, in this example, for a reference indoor environment at a CO₂ exposure concentration of 1000 ppmv, the predicted average thermal energy saving of ventilation system for a unit increment of the expected risk of unsatisfactory IAQ of 1% was 55 MJ m⁻² yr⁻¹; and for a unit decrement of 1%, the predicted additional thermal energy consumption was 58 MJ m⁻² yr⁻¹ respectively.

We did the analysis for another example air pollutant, HCHO. Thermal energy consumptions for ventilation systems and indoor formaldehyde exposure concentrations based on some regional surveys of typical offices in Hong Kong were reviewed. The thermal energy consumptions of ventilation systems operating for CO₂ exposure concentrations between 800 ppmv to 1200 ppmv for typical office buildings and the corresponding formaldehyde exposure risks were evaluated. The results showed that, for a reference indoor environment at a CO₂ exposure concentration of 1000 ppmv, the average thermal energy saving of ventilation system for a unit increment of the acceptable formaldehyde exposure limit of 1 hour (loss of life expectancy of 0.0417 day) was 280 MJ m⁻² yr⁻¹; and for a unit decrement of the exposure limit of 1 hour, an additional average thermal energy consumption of 480 MJ m⁻² yr⁻¹ was expected.

Building energy issues

The development of thermal energy consumption model for air-conditioned office. See Building Energy.

Further information:

Wong LT, Mui KW, Chan WY, 2008. An energy impact assessment of ventilation for indoor airborne bacteria exposure risk in air-conditioned offices, Building and Environment 43(11) 1939-1944.

Mui KW, Wong LT, Chan WY, 2008. Energy impact assessment for the reduction of carbon dioxide and formaldehyde exposure risk in air-conditioned offices, Energy and Buildings 40(8) 1412-1418.