On-field validation of a seasonal performance calculation method for chillers in buildings

Abstract

In the last years the importance of part load conditions in the estimation of chiller performance in real world operation has been completely acknowledged. As a matter of fact, chillers are sized for peak loads, so they usually run under part load conditions, far from the full load ones, taken as references in catalogues. Some methods for these calculations already exist, both in Standards and in building energy simulation programs, but they lack an extensive validation in actual HVAC systems. In this regard, the present paper compares the chiller performance estimated via the calculation method contained in Standard EN 14825 against monitored data taken along an entire cooling season, both in a small HVAC plant and in a large one.In the present paper a variation of the calculation method contained in Standard EN 14825 is used indeed. In particular, in this variation of the EN 14825 calculation method, the interpolation between the values of EER rated under part load conditions is performed by means of intermediate parameter Z, equal to the ratio of the electrical power consumption under part load conditions to the electrical power consumption under full load conditions. This interpolation method allows the HVAC designer to draw more reliable profiles of PLF (Part Load Factor) versus the capacity ratio (CR), in order to increase the accuracy in performance prediction under part load conditions. As a matter of fact, this interpolation method allows the HVAC designer to achieve a better estimation of the EER at low values of the part load ratio, especially when compared with the linear interpolation method suggested in Standard EN 14825.