Mydax, Inc. 1M9W-S Water Cooled Chiller
Lawrence Berkeley Laboratory 2
SYSTEM OVERVIEW
System Fluid Schematic
Refer to drawing #B2343, the fluid schematic. The heart of the design is the evaporator valve. This is a thermal-electric
expansion valve, controlled directly by the system's embedded microprocessor. Hermetically sealed, it consists of a
spring-loaded needle valve in contact with a bimetallic plate. The plate is wound by a coil of wire connected to terminals
on top of the valve. The curvature of the plate, and therefore the position of the needle valve, varies with its temperature
which is controlled by electrical current flow through the coil. So by controlling the duration of electrical pulses applied
to the valve terminals, the microprocessor opens the valve to a precisely determined point. This passes a precisely
determined flow of freon to the evaporator, allowing for exceptionally stable recirculating temperatures. This system
is designed to control the recirculating output temperature to
±
0.05°C across the system operating range.
The microprocessor sets the exact position of the valve based upon the system heat load. If the load increases, the
evaporator valve is opened slightly, passing more refrigerant. If the load decreases, the valve is closed slightly, passing
less refrigerant. During normal operation, the position of this valve stays nearly constant. Only major changes in heat
load or system-wide power cycling cause large changes in the valve opening. In the case of a step-wise change in heat
load, the microprocessor quickly drives the valve to the new setting and refrigerant flow soon settles at the proper level.
The valve drive setting is based primarily upon data received from RTD's (resistance temperature devices) located about
the circuit. The drawing shows RTD's at the evaporator valve, at the discharge line from the pump, at the reservoir and
between the condenser and receiver. The microprocessor "reads" these and other sensors constantly and sets the
refrigerant valve accordingly.
Thus refrigerant flow is truly proportioned, through a valve which only rarely cycles all the way open or shut. Besides
precise temperature control, this allows continuous compressor operation without the normal addition of cycling, and
therefore failure-prone, pressure-actuated hot gas bypass valves. All other refrigeration circuit components are used as
in conventional systems. All permanent copper joints in the refrigeration circuit are brazed for extra strength. Much of
the circuitry is insulated to eliminate cooling capacity loss and unpredictable operation due to drafts or fluctuating
ambient air conditions.
This system is designed to recirculate water. It is not designed to recirculate solutions of automotive antifreeze.
Approximately 10 gallons are required to fill the polypropylene reservoir. The heating elements are stainless steel
cartridge heaters. The freon evaporator is a coaxial heat exchanger, located in the recirculating return line leading to the
reservoir.
The reservoir is fitted with two level sensors. One level sensor drives a FILL TANK alarm at the main panel, indicating
coolant level has dropped somewhat. The second sensor, the TANK EMPTY sensor, is connected to the safety interlock
loop and shuts the system down if tripped. Note that "empty" is a relative term only. The real function of this sensor
is to prevent the coolant level from dropping so low as to expose the pump suction line.
Содержание 1M9W-S
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