HVAC, Cyclic degradation, Rating standards, Code Tester
Building Heating, Ventilation and Air Conditioning (HVAC) is one of the largest primary energy consumer in the United States. Vapor compression systems (VCS) at the heart of building HVAC are typically sized for peak operation and operate at part load most of the time. Rating standards have been conceived to provide credit to the designs that have higher efficiency in the part load operation. However, the current evaluation procedure is not sufficiently uniform and the same system tested in different testing facilities provides different results. The deviations arise from the thermal inertia of the test setup referred to as the code tester, which is not captured in the current procedure. The current article aims at quantification of these effects and its impact on the evaluation of cyclic degradation coefficient in a split air conditioning system. A new term called “loss factor” is added to the formulation of the cyclic degradation coefficient to account for the thermal inertia of code tester. A conventional residential split air conditioning system is tested in two different code testers to obtain two different values of the cyclic degradation coefficient. A physically based model of code tester is developed using Modelica and validated with experimental data. Loss factors for both these code testers are evaluated using this model and the new equation is able to predict the cyclic degradation coefficient obtained in the second setup from the results of the first setup and the loss factor of the second. The current study is the first study of its kind and is expected to normalize the existing test procedures by removing variations arising from differences in code tester designs at various laboratories. Parametric studies by changing materials, air flow rates and temperatures of systems in the code tester are carried out to quantify the loss factor and understand the effect of various factors on it.