Night Flush Cooling uses ventilation of outdoor air during cool nighttime hours to remove stored building heat and pre-cool thermal mass for the following day. This passive cooling strategy minimizes daytime mechanical cooling requirements by leveraging temperature differences between indoor and outdoor environments.
Technical Operation
Night flush cooling activates when outdoor temperatures drop 5-8 degrees below the previous day’s peak indoor temperature, typically between 10 PM and 6 AM. Ventilation fans move 4-8 air changes per hour through the building for 4-6 hours, cooling the structure’s thermal mass to lower daytime baseline temperatures. Systems require outdoor air dampers, return air dampers, exhaust dampers, and controls to prevent backflow.
Building Requirements
Effective night flush cooling requires buildings with substantial thermal mass (concrete floors and ceilings), outdoor air temperatures dropping to 60-65°F, and low nighttime humidity. Urban heat islands and high ambient humidity reduce effectiveness. Buildings must prevent noise complaints to neighbors and secure openings from intrusion.
Energy Impact
Night flush cooling can reduce daytime cooling energy by 30-50% in suitable climates, particularly in dry regions with 15-25 degree diurnal temperature swings. It works best in office buildings that can accept 72-75°F morning temperatures.