Demand control ventilation (DCV) with dedicated outside air

Published: February 18, 2016

  • OVERVIEW
  • GUIDELINES
  • REFERENCES

Buildings require a certain amount of ventilation, or outside air (OA), in order to ensure good indoor air quality. Typically the required amount of ventilation is calculated using the building’s maximum occupancy.

Buildings, however, are rarely at full capacity, which means more outside air is supplied than necessary, resulting in unnecessary energy spent heating and cooling that air. DCV reduces OA based on the number of people in the building. Building energy codes now require DCV in some spaces. But there are several cost effective ways to use this energy conservation measure beyond those required by code.

Sensors
The two primary methods for controlling OA use either carbon dioxide sensors or occupancy sensors. A carbon dioxide sensor modulates OA proportionally to the number of people in the space and works best in large spaces with variable occupancy. An occupancy sensor works better for smaller spaces as it either toggles ventilation completely on or off based on occupancy. Typically using a combination of these two approaches within the building will save the most energy while maintaining good indoor air quality.

Fan energy
For most systems, DCV saves only heating and cooling energy. However if ventilation air is supplied by a dedicated outside air system, DCV will also save fan energy. Fan energy is cubically proportional to fan speed, so reducing fan speed can save significant energy. In a recent study of six buildings, the average annual energy savings from implementing DCV was $0.59 per CFM of design OA.

ASHRAE 2010. 62.1 User’s Manual ANSI/ASHRAE Standard 62.1 Appendix A.

Brandemuehl, M., and J. Braun. The Impact of Demand Controlled and Economizer Ventilation Strategies on Energy Use in Buildings. ASHRAE Transactions 105 (2): 39-50.

EDR 2007. Design Brief: Demand-controlled Ventilation. Energy Design Resources. http://energydesignresources.com/

Hackel, Scott, Saranya Gunasingh, Ben Auchter, Melanie Lord, and Alisa Petersen. Energy Savings from Implementing and Commissioning Demand Control Ventilation. Seventhwave, 2015. Web.