HVAC engineers have a significant opportunity to downsize the volume of refrigerant needed by reducing a system’s cooling capacity. This is achieved with energy reduction strategies, such as utilizing thermal storage for peak shaving, designing high-efficiency central plants, selecting airside energy-recovery systems, and specifying high-performance envelopes. These strategies will lower the building’s cooling demand, thereby reducing the plant size and thus the volume of refrigerant used.
In milder climates, design teams can also consider natural ventilation to downsize or eliminate mechanical cooling requirements. Strategically located operable windows coupled with large fans or boosted exhaust can significantly decrease the amount of cooling needed in a building. For example, on a recent project in Santa Barbara, California, the mild climate supported a natural ventilation and mixed-mode cooling design. In a baseline comparison with HFC refrigerant R-410A, with its GWP of 2,090, Buro Happold and Autocase estimated the quantity of carbon emissions avoided for the 150,000-square-foot facility. With a refrigerant charge of 550 pounds, a conservative 2% annual leakage rate, and an assumed 10% end-of-life leakage, it was estimated that by using natural ventilation, the building owner will avoid 200 tons of CO2 equivalent emissions, which is the equivalent of 476 MWh of electricity in Southern California.
Engineers should consider the opportunity to currently be active in specifying low-warming refrigerants, such as HFOs or natural refrigerants, where possible. Natural refrigerants have already been adopted in the food refrigeration industry, for example, but unique challenges have slowed its acceptance in the HVAC market. For example, ammonia offers high energy performance, is easily detected by smell, and is available at a low cost, but it’s toxic in higher concentrations, according to the U.S. Occupational Safety and Health Administration (OSHA). Carbon dioxide can be used as a natural refrigerant, but equipment compatible with CO2 may often be expensive.