HVAC Design

Chiller
Carrier 80 GT Reciprocating Chiller

Carrier Corporation, a division of United Technologies Corporation, is one of the largest manufacturers and distributors of Heating, Ventilating, and Air Conditioning (HVAC) equipment worldwide. For over ten years, Carrier has been using VisSim to model, simulate, and validate product designs ranging in scope from single zone air conditioners to hundred-ton chillers used in hospitals, university campuses, and office complexes.

Richard Kolk, manager of controls and simulation, explains why and how Carrier uses VisSim:

"Due to its power, flexibility, ease of use, and low cost, VisSim has been Carrier's choice for system modeling, simulation, data acquisition, and rapid prototyping. VisSim has mathematical power to model all aspects of Carrier's designs, but more importantly, it is easy to learn, easy to use, has fast execution, and has a block interface to Carrier Comfort Net (CCN), Carrier's building communication network.

VisSim enables complex real world HVAC systems to be rapidly modeled, simulated, and debugged. Modeling of essential matrix-based control elements, such as state space controllers, observers, and Kalman filters becomes particularly easy with the new matrix operations.

Carrier uses VisSim to develop and test all of its electronic controls and depends on the resulting shortened development times to continually merge new technology into its products. Products which would have taken two to three years to develop in the past are now routinely completed using VisSim in less than one year."

A VisSim modeling effort conducted by Dr. Fred Cogswell, senior scientist at United Technologies Research Center, focused on the development of a reciprocating chiller model for simulating faults. The reciprocating chiller consisted of two refrigerant circuits, each with the following components:

  • One to four reciprocating compressors in parallel to compress the refrigerant vapor
  • A water-cooled or air-cooled condenser to remove heat from the high pressure refrigerant and condense it to liquid
  • A stepper motor controlled expansion valve to meter the refrigerant flow as it goes from high to low pressure
  • An evaporator to transfer heat from the chilled water to the refrigerant, thus boiling the refrigerant to vapor while providing cooling. The model, which consisted of approximately 6,000 blocks, performed a dynamic simulation of the chiller system tracking the migration of refrigerant between components as well as the control interactions. On a standard PC it was capable of running many times faster than real time.

This reciprocating chiller model is just one of the many ways Carrier Corporation uses VisSim to significantly decrease its design cycle time.