Overview

The Building Energy HVAC System Performance (TSPR) tool incorporates a chiller's integrated part-load value (IPLV) by analyzing a handful of performance metrics through Copper, a performance curve generator for BEM applications. In TSPR's implementation, Copper ingests the following user inputs to define their chiller's performance curve:

  • Compressor type: (options: Scroll/Screw, Reciprocating, Centrifugal)
  • Condenser type (options: Air, Water)
  • Reference capacity in tons
  • Full-load efficiency
  • Part-load efficiency

The TSPR analysis tool leverages Copper's command line interface to generate chiller IPLV-specific curves for baseline and user models. Details into how these inputs get transformed into a performance curves can be found in the Modeling Strategy section of this article.

Modeling Strategy

The integrated part-load value or IPLV of a chiller is a metric aiming to indicate how well a particular chiller will perform at off-rated conditions. Codes and standards tend to provide two compliance paths. While not explicitly stated, one is aimed at constant speed chillers while the other is aimed at variable speed chillers. The IPLV is calculated as weighted average efficiency at four distinct load points and 4 sets of environmental conditions (AHRI, 2023). Part load performance of chillers in BEM tools is modeled using sets of performance curves, typically through quadratic and bi-quadratic (two independent variables) equations. Determining a set of curves that matches both a full load efficiency and part load efficiency value for a specific type of chiller involves solving an underdetermined system of equations.

Copper is a performance curve generator for BEM applications. It can be used to generate IPLV-specific performance curves for chillers when only general characteristics are known. Copper uses a two-step data driven process. First, it leverages its data library to generate typical performance curves that corresponds to the user's targeted characteristics such as chiller capacity, chiller compressor type, chiller compressor speed control, chiller condenser type (water-/air-cooled), and chiller targeted efficiency. The generation process aggregates calculated a subset of the data library to generate the curves. At this point, while the curves might be representation of the general performance of the target chiller, the set of curves might not fully match the targeted efficiency. The next step deals with modifying these curves to match the targeted efficiency. Since the problem relies on an underdetermined set of equations, there exist an infinite number of solutions. Copper finds solutions by treating the problem as an optimization type problem and uses a genetic algorithm to converge to a solution.

Users looking for detailed documentation on the Copper process, please refer to the References section found below:

References