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 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, manager 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. VisSim's power is
extended 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:
- 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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Carrier 30GT reciprocating chiller.
The controller was designed using VisSim.
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