recirculating chillers are "off-the-shelf" liquid cooling systems that offer precise temperature control and/or cooling below ambient temperatures. they are used to cool various types of equipment, including medical equipment, lasers, microscopes, analytical instrumentation, semiconductor processing equipment, power supplies, electronics, and many other applications. chillers have a number of options to configure the system to your particular application. these options include protection options, convenience options, special applications options, and fluid compatibility options.

protection and convenience options, featured below, include external flow valves, external pressure relief valves, anti-siphon systems, air filters, water filters, and remote start capabilities. (special applications and fluid compatibility options will be featured in a later application note.) selecting the appropriate options can make operation and maintenance of your chiller easier, help to minimize the risk of premature system failure, and ensure optimal system performance.

valves and filters are considered protection options. valves help manage the flow and pressure to your application:

external flow valve

a highly recommended option is the external flow valve. an external flow valve is a manually adjustable globe valve that is used to control the coolant flow rate to your application. as the valve is opened, more flow bypasses the application and is redirected back to the return line of the chiller. the external flow valve is installed on the back of the chiller in parallel with the chiller coolant supply/return. figure 1 shows a standard external flow valve configuration on lytron's kodiak® recirculating chiller.

this option is useful in applications where the process pressure drop is unknown or a specific flow is required. it also provides maximum flexibility for the chiller to be used at different flow rates.

external pressure relief valve

another option is an external pressure relief valve. this valve allows the recirculating chiller to continue to run and maintain temperature and pressure if the flow to the application is temporarily interrupted. for example, his could be helpful if your application is cycling on and off. the external pressure relief valve can also be used to prevent the chiller supply from exceeding a predetermined pressure setting. the external pressure relief valve and the external flow valve options should not be selected together, as the interaction between them may be difficult to control.

the external pressure relief valve is a manually adjustable check valve that can be set to 50-100 psig. when flow is interrupted, the valve opens and bypasses flow to the chiller's return. this valve is typically installed externally on the back of the chiller in parallel with the chiller coolant supply/return. when using a positive displacement pump in conjunction with an external pressure relief valve, the pump's integral bypass valve setting is usually increased to 90 psi. this is to prevent the pump from bypassing flow and creating a low flow condition on the return line, causing the chiller to turn off. minimal flow rates of 0.5 gpm for lytron's rc006 through rc022 chillers and 1.5 gpm for lytron's rc030 and rc045 chillers are required to prevent this low flow condition. figure 2 shows the standard external pressure relief valve configuration on the back of a recirculating chiller.

anti-siphon system

a valve option that offers both protection and convenience is an anti-siphon system. this system allows a chiller to be installed at an elevation below that of the application. the chiller tank is vented, so when the chiller is shut off, coolant in the hoses between the chiller and the application will flow back to the tank if the application is at a higher elevation than the chiller. in this situation, the fluid can overflow the tank if there is no anti-siphon system installed. the anti-siphon system option is most beneficial when space is an issue, and the only location available for the chiller is below the application or in a clean room application.

this anti-siphon system consists of an internal check and solenoid valves that are installed on the supply and return lines respectively. the check valve allows coolant flow to the application, but it also prevents it from flowing back to the chiller. the solenoid valve is open to allow coolant flow when power is on and closed to prevent coolant from flowing back to the chiller's vented tank when power to the chiller is shut-off. figure 3 shows an anti-siphon check valve.

like valves, filters help to protect your chiller and your application:

air filter

for dusty and/or dirty environments, an air filter is highly recommended. an air filter will help to prevent dust build-up that could lead to decreased chiller cooling capacity. it also reduces the need to clean the condensing coil and other internal refrigeration components. mounted internally to the chiller behind the front grill, the air filter is easily accessible. lytron recommends replacing the air filter periodically depending on the level of dust in the air. for example, in a clean environment, such as in an air-conditioned laboratory, the air filter may only need to be replaced every 6 months. however, in a very dusty or dirty environment, such as on a machine shop floor, the filters may need to be replaced as often as every month. figure 4 shows an air filter being installed.

5-micron coolant filter

just as important as an air filter is a water or coolant filter. as the name implies, a 5-micron filter removes particles up to 5µ (0.197 mils) from the coolant supplied to your application, protecting equipment from blockage or damage due to particulate buildup. it is located on the supply line of the chiller. all of the coolant flow is directed through the filter. if a chiller has both a coolant filter and a pressure relief or flow valve, the filter will be installed after the valve. in this situation 100% of the coolant flow to the application will pass through the filter. lytron recommends that the filter be inspected the day after initial set up and on a weekly basis after that. failure to replace filter cartridges can lead to a decrease in flow and consequently a decrease in chiller cooling capacity or a system shutdown.

these filters can be used with turbine and positive displacement pumps. they are especially beneficial when using positive displacement pumps, which are sensitive to particles. coolant filters are not recommended with centrifugal pumps because the pressure drop through the filter is too high. figure 5 shows a standard water filter configuration.

the remote start option is considered a convenience option:

remote start

the remote start option allows an external circuit to control the chiller on/off function via dry contacts on the rear of the chiller. an auto-restart is included with the standard chiller controller package, however, a remote start is beneficial for those who would like to simultaneously start their equipment and the recirculating chiller from a computer or relay for ease of operation. the remote start can also prevent accidental operation of the applications without the chiller and vice versa, which could cause damage, unnecessary energy consumption, etc.

conclusion:

there are many options available with recirculating chillers. valves, filters, and remote start are just a few of the options available on standard cooling systems. selecting the right options can help make your system operation and maintenance easy as well as keep your costs down. modified cooling systems can also be designed to meet other additional requirements. for example, custom chillers can be designed for reduced acoustic levels, for additional cooling capacity or wattage, for various shapes and sizes, with or without "skins", and more. ask your chiller manufacturer for more information on recirculating chiller options and how your cooling requirements can be met with a standard or custom liquid cooling system.

written by joao castro, lytron applications engineer and harold bufe, lytron service manager