Analysis of Pickup/Pulldown Load in Buildings: Part I — Mathematical Analysis

In large commercial buildings, air handlers for HVAC systems are shutdown during unoccupied periods to save on utility bills. During the shutdown time, some of the heating or cooling load accumulates and is stored in the building. Consequently, on start up, there is an added load that must be removed by the HVAC system. The stored load can be divided into preconditioning load (fast load) and storage load (slow load). In this paper, mathematical analysis is used to study the preconditioning and storage loads after system shutdown. The governing mathematical equations, that represent an analytical model, were solved using Laplace transforms. Simplifications to the analysis are presented. It is found that the ratio of storage area to the exposed area plays an important role in the determination of shutdown loads.