Energy & Cost Impacts: Carbon Dioxide (CO2) Sensors

California’s 2019 Building Energy Efficiency Standards (Title 24) specify that the minimum ventilation for a fixed ventilation rate system must be the greater of 15 CFM/person or a calculation based on floor area, where the minimum area outdoor air rate (Ra) is specified in Table 120.1-A of the 2019 Building Energy Efficiency Standards. A demand control ventilation (DCV) system is applicable in a subset of occupancy categories (Table 1). In these categories, the minimum area outdoor air rate can be reduced (Min Air Rate for DCV) when occupancy is reduced, as determined by monitored CO2 levels. In occupancy categories other than Table 1, Title 24 does not allow a DCV system to reduce ventilation because rates are already low based on low occupant design density (e.g., private offices) or because ventilation is needed to mitigate other indoor pollutants specific to the occupancy category (e.g., chemicals used in a nail salon).

Table 1–Occupancy categories from 2019 Building Energy Efficiency Standards (Table 120.1-A) for which DCV systems are applicable

Energy savings estimates for implementing DCV in a packaged heating, ventilation, and air conditioning (HVAC) system are provided from a 2016 workpaper by Pacific Gas and Electric [1] that used eQuest to model the impact of DCV on energy consumption in California climates for a range of building types. Both packaged heat pumps and air conditioning with a gas furnace were simulated. Annual electricity, natural gas, and cost savings for DCV were compared to a baseline fixed ventilation system for eleven building types (Error! Reference source not found) assuming an average commercial electricity cost of $0.1944 per kWh and an average commercial natural gas cost of $0.9354 per kWh. Results are normalized by ton of nominal cooling capacity. The savings were driven by a reduction in energy used for heating and were most significant in mountain and coastal climates.

Figure 1 – Estimated annual impact for DCV on cost, electricity, and gas consumption by building type for three regions of California based on 2016 analysis by Pacific Gas and Electric(4).

1. Work Paper PGECOHVC168 Demand Controlled Ventilation. Demand Controlled Ventilation for Single Zone Packaged HVAC.