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A mathematical model for estimating recovery response is developed based on the dimensionless step response of room temperature to zone heat input. Separate transfer functions are used to represent the walls, floor, and ceiling of a prototypical zone. Additional transfer functions are defined for each of several layered constructions made to represent the contents of a typical office building. A grid of three construction weights (light, medium, and heavy) and five one-node model time constants (5, 10, 20, 40, and 80 hours) is defined to represent a range of zone thermal characteristics. Dimensionless step responses of the resulting 15 prototype zones are generated by simulation. A design method, based on the generalized response curves, is presented as a graphical hand calculation procedure. A microcomputer implementation is developed based on a reduced order, single-input, single-output z-transfer function model and a corresponding analytical expression for each of the 15 dimensionless simulated step responses. The recovery response model is experimentally verified by monitoring thermal responses of three commercial buildings. The buildings were monitored during recovery from night setback under a variety of conditions. The thermal characteristics of the subject buildings and the instrumentation and test procedures are described. One day plots of indoor, outdoor and supply air temperature give an overview of how each zone responds during occupied, unoccupied and recovery periods. Plots of normalized measured recovery temperatures show that room temperature recovery trajectories for a given zone are similar in shape regardless of plant capacity and indoor-outdoor temperature difference. The thermal properties of different zones that cause the shapes of their trajectories to differ are discussed. The responses of one monitored building are used to verify the general theoretical model by comparison with response simulated by the transfer function model. The results of project 491-KP pertain to heating and cooling load calculation, Chapters 25 and 26 of the ASHRAE (1989) Handbook of Fundamentals.