Development, validation, and application of general gray-box models for ductless and ducted residential heat pumps
Abstract
Space conditioning accounts for a large portion of the energy usage in residential buildings. The use of reversible heat pumps has been increasing recently as an efficient method of meeting both heating and cooling loads. With more stringent energy efficiency standards on the horizon and the introduction of ductless heat pumps into the North American market as higher efficiency alternatives to conventional ducted split systems, there is a need for accurate and representative heat pump models to aid in equipment selection and LEED certification. This thesis presents generic equipment models that capture the performance of families of similar heat pump equipment and that can be used in building simulation programs. Mapping has been carried out for families of single and dual compressor speed ducted split systems and the correlations have been implemented as components for building simulation. The units mapped ranged in nominal cooling capacity from 1 to 5 tons (3.5–17.6 kW) and 2 tons to 5 tons (7.0–17.6 kW) for the single and dual speed units, respectively. A family of ducted variable speed heat pumps was also mapped ranging in nominal cooling capacity from 3 to 5 tons (10.6–17.7 kW). Ducted equipment models for building simulation were generated based on the ASHRAE secondary toolkit direct expansion model. All ducted heat pump models were generated using data from a detailed component based simulation. The generalized ducted single speed heat pump models generated in this study were first compared to established performance models based on the ASHRAE toolkit model for cooling and the DOE-2.1 RESYS routine for heating mode. It was found that using default coefficients can lead to large performance prediction errors, particularly at conditions away from the equipment rating conditions. Finally, a decoupled model of a ductless heat pump with two indoor units was developed from experimental data for both heating and cooling operation. The ductless heat pump had a nominal cooling capacity of 2 tons (7.0 kW). The decoupled modeling approach models each of the major components of the system, namely the heat exchangers and the compressor. This approach reduces the number of tests required to characterize the system since component models from tested combinations of indoor and outdoor units can be used to predict performance of untested combinations.
Degree
M.S.M.E.
Advisors
Braun, Purdue University.
Subject Area
Architectural|Mechanical engineering
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