This paper presents the development of a multi-evaporator load emulation unit (ME-LEU) for air conditioning and refrigeration (AC&R) systems. Through a combination of on-line real-time modeling and hardware actuation, LEUs are able to mimic the dynamics of a variety of cooling loads. A virtual container model simulates the thermal dynamics of the cooled space and determines the appropriate return air temperature to the evaporator for a given application. The LEU uses an actuated slide to mix warm return air with colder supply air to track the desired return air temperature from the model. Depending on the physical design of the LEU, control of the return air temperature may become difficult due to non-monotonic and nonlinear dynamics. The presented LEU design achieves monotonic and nearly linear dynamics between the actuation mechanism and the return air temperature, allowing for a simple yet robust controller to be designed for the system. The experimental implementation of the ME-LEU on a dual evaporator AC&R system permits independent loading of each evaporator, thereby increasing the emulation capabilities to a larger set of real world systems.
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