Design, Evaluation and Techno-Economic Analysis of a Demand Controlled Ventilation in Hot and Humid Climate

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The British University in Dubai (BUiD)
Buildings consume 40% of world’s total energy and produce more than 30% of global CO2 emissions. “The heating and (cooling) of homes and buildings shares 56% of total energy consumed by buildings and homes.” (Fink, H.S., 2011, Aldossary, N.A., et. al, 2013). Future global HVAC energy demand is expected to rise further due to increase in population growth, rapid urbanization and demand for new residential and commercial units, and rising global temperatures due to climate change. The objective of the research was to develop an efficient ventilation system that lowers the ventilation energy consumption and reduced HVAC system sizing in Buildings. As part of the research, ventilation system in an existing building was modeled on IESVE (Baseline case model; Constant Air Volume-CAV) and its energy usage recorded. The model was updated by introducing a CO2 sensor (Proposed Case Model-CO2-based-DCV) and the energy model was re-run to compare against the baseline case model. Significant energy saving was found in the proposed case model. In the baseline case model, intake airflow (outside air) is constant and configured based on maximum occupancy in the building whereas in reality the occupancy in the building is variable touching the maximum only for a portion of the duration, thereby creating an inefficient system, which contributes to energy wastage, higher CO2 emissions, and larger system sizes. Further, in cases when the real occupancy of the building is higher than configured, deterioration of indoor air quality occurs in the baseline case model. In the proposed case model, intake airflow is configured to be modulated based on the occupancy profile, which is determined by set value of CO2 concentration (Maximum level of 800 PPM) as recommended by ASHRAE standard 62.1-2010 and Dubai Green Building regulations and specifications, 2011. As a result the air supply varies according to the building occupancy thereby creating an efficient ventilation system that reduces energy consumption, lowers CO2 emissions and results in smaller HVAC systems. The IESVE energy model results of the two cases were compared, and it was found that the energy consumption and system capacity were lower in the proposed case model by 18.61% and 22.38% respectively. The test building consisted of 3 basements, ground floor and 43 floors and had mixed-usage: residential, commercial and hotel. The proposed case model considered occupancy profile based on ASHRAE standard 90.1-2010 and occupant density and the airflow based on ASHRAE standard 62.1-2010 (maximum amount of outside air limiting to 800 PPM CO2 concentration). In conclusion, the proposed case model was found to lower system capacity, thus lowering the CAPEX needs, lower energy consumption, lowering OPEX needs throughout the life-cycle of the building, and reduced CO2 emissions, promoting sustainability of the built environment.
controlled ventilation, energy consumption, CO2 emissions, ventilation system, sustainability