Parameter Estimation for HVAC System Models From Standard Test Data

Abstract

Nearly all cooling systems, and an increasing proportion of heating systems, utilize the vapor compression cycle (VCC) to provide and remove heat from conditioned spaces. Even though the application of VCC’s throughout the built environment is ubiquitous, effective and accessible models of the performance of these systems remains elusive. Such models could be important tools for equipment and building designers, and building energy managers and those who are attempting to optimize building energy performance through the use of model-based control systems. A quasi-steady state, spreadsheet-based model has been developed which requires knowledge of 10 system-specific parameters. A method utilizing manufacturer’s test conditions to derive these values is presented. The model is applied to three commercially available units and a subset of test conditions is used to identify the model parameters. The model is validated over the entire range of conditions with modeling errors ranging from 2 to 4%.

Parameter Estimation and Dynamic State Observer Design for Vapor Compression Systems

“…Much of the research performed in modelling VCC systems to date is primarily focused on steady-state and empirical methods. However, an increasing number of researchers have been turning their focus toward more dynamic models and simulations (Luthman, 2016).…”

“…Through extensive experimental testing, this model was shown to be relatively effective at capturing the main dynamic characteristics of a VCC. Most recently, research was conducted that led to the development of a quasisteady state model to identify the heat transfer characteristics of both the evaporator and condenser of a VCC from performance data provided by the manufacturer (Luthman, 2016). This approach utilizes the moving boundary method used by Li (2009) and various others including McKinley & Alleyne (2008), Frink (2005), and Rasmussen (2005), all of whom rely heavily on the work presented in He (1996).…”

“…Therefore, these models are specific to the unit tested. Luthman (2016) and Gardner & Luthman (2016) introduced the concept of utilizing effective heat transfer coefficients identified through performance data provided by a systems manufacturer, to incorporate the effect of the fins throughout each heat exchanger. Utilizing these effective coefficients, could potentially eliminate the need for obtaining and testing a physical system prior to predicting the response or performance of a specific unit.…”

“…As described in Luthman (2016) and He (1996), a thermodynamic analysis of the heat exchangers used throughout a VCC system can be used to mathematically define the heat transfer phenomenon occurring in each. To do so, the following assumptions were made:…”

“…Gardner & Luthman (2016) and Luthman (2016) proposed that effective heat transfer coefficients can be developed from performance data provided by the manufacturer. These coefficients can then be used to capture the effect of the fins.…”