Cool Building Mass at
Night
for Energy & Demand Savings
For buildings
and spaces that are not occupied at night, such as offices and
retail businesses, control the HVAC systems to cool the building
mass late at night, when outdoor temperatures are cooler and demand
charges are lower. Night cooling can save up to 50% of cooling
energy and reduce peak demand by up to 40%, compared to standard
night temperature setback strategies.
Night cooling
can be done with either air or water cooling systems. For air
systems, late night and early morning outdoor air temperatures
in Santa Monica allow use of the economizer cycle for much of
the year, greatly reducing compressor run-time and energy. Similarly,
for water systems, the chiller can be bypassed to use water from
the cooling tower. For greatest demand cost savings, ensure that
the HVAC systems start before the onset of higher demand charges.
The major
drawback of night cooling is the potential for cold space temperatures
at the beginning of the occupied period. Stopping night cooling
an hour before occupancy typically ensures comfortable conditions
for early arrivals. If a few late-night occupants are expected,
ensure local systems are in place, with temperature controls for
occupants that provide comfort for small occupied areas.
Cautions
- Not suitable
for buildings with high occupancy between midnight and dawn.
