MODELING CONTROL STRATEGIES OF A HIGH-PERFORMANCE ENERGY RECOVERY VENTILATOR IN NIST'S NET ZERO ENERGY RESIDENTIAL TEST FACILITY

Abstract

With the acceleration of climate change causing increased global temperatures, reduced polar ice caps, and more severe weather, reducing carbon emissions is more important than ever. Residential buildings are responsible for 57 % of the greenhouse gas emissions in the building sector. This sector provides a clear opportunity to reduce emissions and energy consumption. Net Zero Energy Buildings (NZEB) are a more recent answer to this need where the building generates more energy over a year than it consumes through renewable sources. NIST’s Net Zero Energy Residential Test Facility (NZERTF) was constructed and instrumented to serve as a test bed for NZEB research at the residential scale. This facility has a previously uncharacterized Energy Recovery Ventilator with opportunities to implement a bypass mode to avoid any heat exchange between the fresh and stale air streams. This bypass mode allows for free cooling in the shoulder seasons by using cooler outdoor air to cool the inside of the building. To test the energy savings potential for temperature-based and enthalpic-free cooling control schemes, a TRNSYS model was updated and tuned to accommodate more recent building performance and shifting operation patterns. These updates included heat pump performance curves, adjustments to HVAC airflow modeling, moisture capacitance models, and a complete evaluation of the ERV’s fan power and sensible and latent effectiveness. This model was run for annual simulations without bypass mode, with bypass mode enabled based on the outdoor temperature, and with bypass mode based on the outdoor enthalpy. The temperature-based control required an additional 2.4 % of heat pump energy relative to the baseline along with a slight degradation in thermal comfort. The enthalpic control saved 0.2 % and maintained a similar thermal comfort to the no bypass mode case. These bypass controls do not offer significant opportunities for this facility in this climate zone but could be implemented in lower-humidity climates or more extensive facilities with more substantial sensible loads. I plan to continue this work by testing the enthalpy bypass control at the NZERTF, characterizing, modeling, and testing bypass options with the ventilator’s HRV core, and by integrating CONTAM into the TRNSYS model to improve the airflow modeling for more accurate zone level conditions.