Carrier
Uses VisSim for HVAC Desig
Dynamic Simulation of a 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 more
than five years, Carrier has been committed to 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, senior staff engineer in 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 for each of the past five years. Version 4.0 further
extends VisSim's power to cover both scalar and vector block diagrams
including such features as matrix operations, matrix output displays,
expression blocks, and a model tree.
These features enable complex real world 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 recent 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:
Carrier 30GT reciprocating chiller.
The controller was designed using VisSim.
- 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. It ran at an update time of 1 second in order to maintain
stability between the components; however, on a Pentium computer it was
capable of running many times faster than real time.
This reciprocating chiller model represents one of the many ways Carrier
Corporation uses VisSim to significantly decrease its design cycle time
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