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Description of HVAC Systems
Published in David W. Bearg, Indoor Air Quality and HVAC Systems, 2019
Demand-controlled ventilation (DCV) is an approach for regulating the quantity of outdoor air delivered to a zone in response to the number of people present in that space. Just as occupancy sensors are being used to save energy by turning off lights when spaces are unoccupied, DCV can save energy in certain situations of low occupancy. In order for this approach to be cost effective, the occupancy needs to be variable, such as would be occurring in a theater, an auditorium, a meeting room, or a classroom.
Terminal Systems and Components
Published in Herbert W. Stanford, Adam F. Spach, Analysis and Design of Heating, Ventilating, and Air-Conditioning Systems, 2019
Herbert W. Stanford, Adam F. Spach
Demand controlled ventilation (DCV) is considered a key approach to help minimize building energy consumption by HVAC systems, as it allows the amount of outdoor introduced for dilution ventilation to be reduced in proportion to any reduction in the number of people occupying a space.
Energy savings and ventilation performance from CO2-based demand controlled ventilation: Simulation results from ASHRAE RP-1747 (ASHRAE RP-1747)
Published in Science and Technology for the Built Environment, 2020
Zheng D. O'Neill, Yanfei Li, Hwakong C. Cheng, Xiaohui Zhou, Steven T. Taylor
Demand-controlled ventilation (DCV) has proven to be a cost-effective and energy-efficient strategy compared with systems that provide a constant outdoor air ventilation rate. DCV is a ventilation rate control strategy to modulate the volume of fresh air taken into an occupied zone based on the current population of the zone. ASHRAE Standard 62.1 requires that the minimum outdoor air be based on the sum of ventilation rates required to dilute pollutants generated by occupants (e.g., bioeffluents) and building sources (e.g., off-gassing from furniture and other building materials). One way to monitor the concentration of bioeffluents generated by occupants indirectly is to measure zone CO2 concentration since, in general, CO2 generation rate is proportional to odorous bioeffluent generation rates (Lin et al. 2013). CO2-based DCV has been popular in the HVAC industry for years and it is mandated in ASHRAE Standard 90.1 for most densely occupied spaces. CO2-based DCV offers the possibility of reducing the energy penalty of over-ventilation during periods of low occupancy, while still ensuring adequate levels of outdoor air for ventilation. Numerous simulation-based studies and some actual field case studies show that CO2-based DCV can offer up to a 60% energy savings compared with constant ventilation rate systems (Mysen et al. 2005; Lin et al. 2013). Table 1 summarizes the savings based on a NIST report (Emmerich and Persily 2003) and ASHRAE RP-1547 (Lin et al. 2013).
Assessment of CO2-based demand controlled ventilation requirement for a flexible work environment with ductless split air conditioners
Published in Science and Technology for the Built Environment, 2019
Demand-controlled ventilation (DCV) provides fresh air at periods of requirement, thereby maintaining adequate indoor air quality and improving energy efficiency. DCV can be employed when the occupancy rate varies with time and the energy requirement for space is high (heating or cooling). Fisk and De Almeida (1998) state that the concentration of predominant contaminant varies with time and other contaminants' concentrations are relatively low. An appropriate ventilation rate is determined based on the level of this contaminant inside the work environment. The common surrogate used for monitoring is carbon dioxide (CO2). The CO2-based DCV (CO2-DCV) uses sensors to control the ventilation duration and frequency. The sensor detects a particular threshold level and triggers a ventilation strategy accordingly. The ventilation rates vary with the lower and upper set points (using dampers) or with the occupant density criteria (proportional control) as indicated in Table 2.
Energy and ventilation performance analysis for CO2-based demand-controlled ventilation in multiple-zone VAV systems with fan-powered terminal units (ASHRAE RP-1819)
Published in Science and Technology for the Built Environment, 2020
Xing Lu, Tao Yang, Zheng O’Neill, Xiaohui Zhou, Zhihong Pang
Demand-controlled ventilation (DCV) is defined as a system that achieves “automatic reduction of outdoor air intake below design rates when the actual occupancy of spaces served by the system is less than design occupancy” (ASHRAE 2019). Measuring the zone carbon dioxide (CO2) concentration could be an indirect approach to monitoring the level of bioeffluents generated by occupants since, in general, the CO2 generation rate is proved to be proportional to odorous bioeffluent generation rates (Lin and Lau 2014; Lin, Lau, and Yuill 2014).