Analyzing CO2-Based DCV for Multiple-Zone VAV Systems With Multiple Recirculation Paths
From ASHRAE Journal Newsletter, Feb. 23, 2021
The original CO2-based demand-controlled ventilation (DCV), which has been popular in the HVAC industry for 40 years, is only applicable to single-zone mechanical systems. A Science and Technology for the Built Environment article presents research that applied DCV for multiple-zone variable air volume (VAV) systems with multiple recirculation paths.
Researcher Zheng O’Neill, Ph.D., Member ASHRAE, an associate professor of mechanical engineering at Texas A&M University, spoke with ASHRAE Journal about this work.
1. CO2-based DCV has been popular in the HVAC industry for the last 40 years. Why is it important to explore this topic now?
CO2-based demand-controlled ventilation (DCV) has been popular in the HVAC industry, as it is widely acknowledged to be energy efficient by altering ventilation rates based on the surrogated indications of CO2 levels. In the last 40 years, we have seen the maturation and deployment of the technologies in hundreds of thousands of buildings in the U.S. We also have seen the penetration and acceptance of this technology in the industry and its mandatory stipulation in many building codes regarding energy efficiency and building health. From the standards and regulatory context changes regarding DCV, we could conclude that this technology has transformed from an engineering research topic to more practical applications.
However, the original CO2-based DCV is only applicable to single-zone mechanical systems, and research efforts toward the enhancement and expansion of this technology is needed. Our research is applying DCV for multiple-zone variable air volume (VAV) systems with multiple recirculation paths. This is an expansion of our other related ASHRAE research (RP-1747) on single-duct, multiple-zone VAV system DCV, and split air-conditioning systems. DCV for multiple-zone VAV systems with multiple recirculation paths includes VAV systems with series fan-powered terminal units (SFPTUs), parallel fan-powered terminal units (PFPTUs) and dual-fan dual-duct (DFDD) systems. In this research, we developed practical and code-compliant DCV control sequences for this type of system configuration and investigated the energy and ventilation performance of the control sequences.
2. What lessons, facts, and/or guidance can an engineer working in the field take away from this research?
We developed practical and code-compliant DCV control sequences for multiple-zone VAV systems with multiple recirculation paths. The developed control sequences can be used with ASHRAE Guideline 36-2018, High-Performance Sequences of Operation for HVAC Systems. Our simulation studies show that the developed DCV control logic could lead to 7% to 14%, 7% to21% and 1% to 8% HVAC source energy savings for SFPTU, PFPTU, and DFDD systems, respectively, compared with the baseline ASHRAE Standard 62.1-2016 approach.
3. How can this research further the industry's knowledge on this topic?
We filled in gaps in understanding how much energy could be saved while providing the code-compliant ventilation performance for different climate zones using DCV for the multiple-zone VAV systems with multiple recirculation paths.
4. You indicate that future work includes the testing of the DCV control sequences in a real facility and the validation of the simulation results. Do you have plans to carry out this research? If so, when?
We hope ASHRAE can continue to support the field validation of DCV controls for multiple-zone systems. We will also work with industry stakeholders to find other funding sources for the field studies.