'Precooling' Office Buildings Cuts Peak Energy Costs

PhysOrg reports that Purdue University engineers say they've developed a method for "precooling" small office buildings to cut energy costs.

According to James Braun, a Purdue professor of mechanical engineering, precooling would reduce energy consumption during times of peak demand, promising not only to save money but also to help prevent power failures during hot summer days.

Precooling involves running air conditioning at cooler-than-normal settings in the morning and then raising the thermostat to warmer-than-normal settings in the afternoon. The method has been shown to reduce the cooling-related demand for electricity in small office buildings by 30 percent during hours of peak power consumption in the summer, Braun said.

As PhysOrg points out, small office buildings represent the majority of commercial structures, so reducing the electricity demand for air conditioning in such buildings could help prevent rolling blackouts, such as those that plagued California during the summer of 2000.

Braun said the study focused on California because research was funded by the California Energy Commission, but the same demand-saving approach could be tailored to buildings in any state.


Reducing peak power demands is very important. Not only does it help prevent rolling black-outs which occur when peak demand exceeds generating capacity, but in the longer run, reducing peak demand avoids the construction of new power plants.

Power generating capacity must exceed peak power demands at all times, not just average demands. Peak demand can be two to three times higher than average demand (the exact amount varies regionally due to climate and local building/efficiency codes).

When peak demand exceeds generating capacity, power companies are forced to buy power from the 'spot market' - the open energy trading market; i.e. where Enron made all its money - often at prices significantly higher than the price they charge their customers. If peak demand exceeds capacity too often, utility companies are forced to build more power plants or contract for more output from other plants - i.e. increase capacity.

In short, additions to plant capacity are driven by increasing peak power demand, not increasing total consumption.

Technologies and practices like this that reduce peak demand are thus critical in maintaining the effectiveness and integrity of our power generation infrastructure while mitigating the need for new infrastructure investments. They are thus nearly always very cost effective, both for the business or home owner as well as for the utility company that gets to avoid the costs of adding new capacity or purchasing power at peak periods from the spot market.

[BTW, Interface Engineering of Portland used a simiar 'precooling' technique for their new Oregon Health Sciences University River Campus One building in Portland's new South Waterfront development district, which is expected to be (by far) the largets building to achieve LEED Platinum certification while cutting mechanical and electrical costs by 10%! Expect more on this soon...]