Estimating HVAC Energy Savings from Installing Comfy
Quantifying Comfy’s impact on HVAC energy can be a challenge. Energy usage in buildings varies greatly with weather, inside activity, and mechanical equipment operation. Furthermore, HVAC energy is rarely metered separately, so it can be hard to assess if changes in energy usage stem from Comfy, or from something else. To isolate Comfy’s impact, this approach uses research from UC Berkeley, which specifically correlates how changes in heating and cooling setpoints affect HVAC energy usage. Changing temperature setpoints is the core of what Comfy does, and such measured data is easily available, making this approach well suited to estimate how much energy Comfy is saving.
HVAC Energy Comparison Methodology
Energy savings from installing Comfy are estimated with a methodology developed by the Center for the Built Environment at the University of California, Berkeley. This methodology, published paper and link below, uses EnergyPlus to perform parametric simulations of Department of Energy Models to compare annual HVAC energy usage of different types of buildings operated with different heating and cooling setpoints.
Iterations vary the following criteria to allow for comparisons between measured before and after conditions in a range of climates, mechanical systems, and operating conditions.
- Location (ASHRAE Climate Zone)
- Heating Setpoint
- Cooling Setpoint
- Building Construction
- Mechanical Systems
- Equipment Sizing
- Minimum Airflow %
- Extending Air Temperature Setpoints: Simulated Energy Savings and Design Considerations for New and Retrofit Buildings, Tyler Hoyt, Edward Arens, Hui Zhang, Center for the Built Environment, University of California at Berkeley, USA
To assess the energy impact of Comfy, the following measured data is used for each zone. These values are calculated from 5-minute interval BMS data to get time-averaged values for occupied hours.
- Cooling Setpoint before Comfy (˚F)
- Heating Setpoint before Comfy (˚F)
- Cooling Setpoint with Comfy (˚F)
- Heating Setpoint with Comfy (˚F)
- Maximum Airflow (cfm)
Using the Center for the Built Environment methodology, the following inputs are used to estimate the percent change in HVAC energy usage on a zone by zone basis.
|Inputs||Outputs (Change in Energy Usage)|
|Building Location (same for all zones)||Fan (%)|
|Heating Setpoint Before Comfy (˚F)||Terminal Heating (%)|
|Cooling Setpoint Before Comfy (˚F)||Central Heating (%)|
|Average Heating Setpoint With Comfy (˚F)||Cooling (%)|
|Average Cooling Setpoint With Comfy (˚F)||Total HVAC (%)|
Total HVAC Energy Savings from Installing Comfy
After using the CBE tool, the total HVAC energy savings are adjusted by performing a weighted average of the setpoints for each zone using each zone’s maximum airflow. Taken together, this approach yields the estimated percent change in HVAC energy usage from installing Comfy.