Using off-peak precooling

ASHRAE Journal, March, 2009 by Kurt Roth, John Dieckmann, James Brodrick

Kurt Roth, Ph.D., is group leader, building efficiency, with the MIT-Fraunhofer Center for Sustainable Energy Systems, Cambridge, Mass. John Dieckmann is a principal with TIAX LLC, Cambridge, Mass. James Brodrick, Ph.D., is a project manager with the Building Technologies Program, U.S. Department of Energy, Washington, D.C.

* In a building with natural ventilation, OA ventilation would begin when [T.sub.OA] < [T.sub.Z] (assuming acceptable OA moisture levels).

([dagger]) Diurnal variations in wet bulb temperatures are usually much smaller than those in dry bulb temperatures.

([double dagger]) "Weak" = $0.20/kWh throughout the day, $10/kW on-peak (9 a.m.-6 p.m.), $5/kW off-peak; "Strong" = $0.20/kWh on-peak and $0.05/kWh off-peak; $10/kW on-peak and $0/kW off-peak.

([section]) Demand charge of $16/kW and on- (9 a.m.-10 p.m.) and off-peak electric rates of $0.052/kWh and $0.023/kWh, respectively.

(#) Demand charge of $5.60/kW and on- and off-peak electric rates of $0.0388 and $0.0268, respectively.

([parallel]) Phoenix: $14.82/kW, $0.051 (11a.m.-9 p.m.) and $0.027/kWh. Miami: $6.25/kW, $0.028 (12PM to 9PM) and $0.011/kWh.

** Mixing return and OA increases the supply air temperature, greatly diminishes the value and viability of the OA-based strategy.