Recirculating chillers are liquid cooling systems that offer precise temperature control and/or cooling below ambient temperatures. Chillers have many options so they can be integrated easily into many applications. Recirculating chiller options include features to satisfy special applications, fluid compatibility issues, equipment protection concerns and convenience. This article will look at special application and fluid compatibility options.
Special ApplicationsOptions to customize a chiller for a special application include adding a heater, an internal insulation package, low-temperature operation, water-cooled condenser and a 0.1°C setpoint.
Heater. When the ambient temperature is below the required chiller setpoint temperature, a heater may be needed. This option is especially helpful when equipment is turned off nightly or turned on and off in a cold environment. Typically, the type of heater used is a submerged 2,000 W, 230 V electric-resistance unit that allows a setpoint temperature to be reached faster during cold startups or during frequent coolant setpoint cycling. Often, it wil have a built-in overtemperature shutoff. When the coolant is within 5.4°F (3°C) of the set temperature, the heater shuts off, and the refrigeration cycle takes over until the set temperature is reached.
Internal Insulation Package.An internal insulation package reduces the formation of condensation on the tank, pump head and coolant lines when the chiller coolant setpoint temperature is below the ambient dewpoint. The insulation helps prevent corrosion within the chiller as well as damage to electronics from drips. An internal insulation package is recommended for applications where the setpoint temperature is 50°F (10°C) or less as well as when the ambient temperature is above 77°F (25°C).
Low-Temperature Operation.For low-temperature setpoints of 23 to 77°F (-5 to 25°C), the low-temperature operation option maximizes performance and provides more low-temperature cooling capacity than a standard chiller. Internal insulation is required when selecting this option. For instance, low-temperature operation may be required in applications for lasers, X-ray cooling and analytical instrumentation.
Water-Cooled Condenser.Another option is a water-cooled condenser. This option allows for rejecting heat to an external liquid coolant source via a brazed-plate, liquid-to-liquid condenser instead of rejecting it to ambient air with a liquid-to-air condenser. This option prevents room warming and possible air-conditioning overload.
Often, water-cooled chillers are quieter because a condenser fan is not used. The liquid coolant source is typically facility water, but it can also be another chiller located in a different room. The chiller cooling capacity is based on a facility water temperature of 75°F (24°C) at a pressure less than 100 psi.
Setpoint Options. With a standard chiller, the user can set the temperature to the nearest degree. With the 0.1°C setpoint option, temperature can be set to the nearest tenth of a degree, allowing for more precise control of the coolant delivery temperature. This feature is recommended when temperature stability is critical. Laser cooling and analytical instrumentation cooling are two applications for which this option might be selected.
Fluid Compatibility IssuesFluid compatibility options for recirculating chillers include a deionization (DI) water cartridge, high purity plumbing and PAO compatibility.
DI Water Cartridge.A DI water cartridge removes ions from the coolant, maintaining a fluid resistivity level between 1 to 3 Mohm/cm by partial flow through the bed. The filter cartridge is externally mounted on the return to the chiller. High-purity plumbing should be selected with this option due to the corrosivity of deionized water. The filter should be replaced every three to six months with normal operation. Resistivity can be tested to determine if the cartridge should be replaced sooner.
High-Purity Plumbing.When high-purity plumbing is added, all wetted components are fully compatible with DI water. High-purity components can include a nickel-brazed evaporator; a stainless steel, positive-displacement pump; and nickel-plated or nylon fittings. The high-purity plumbing option is strongly recommended when selecting a DI water cartridge.
PAO Compatibility.Standard chillers typically use filtered water and inhibited ethylene glycol and propylene glycol water solutions. However, polyalphaolefin (PAO) can by used as a coolant as well. PAO is a heat transfer fluid used frequently in military and aerospace industries for its dielectric properties and wide operating temperature range. When using this fluid, the appropriate wetted materials must be selected.
It is plain to see that there are many options for recirculating chillers. Coolant compatibility and temperature control options are just a few of them. Understanding the options available on a chiller is important in determining how a chiller will meet an application’s specific liquid cooling needs.