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Tools & Technical Reference


Low Coolant Flow From Your Recirculating Chiller

One of the most common chiller application issues is low coolant flow. A high system pressure drop or a frozen evaporator typically causes a low flow problem. All Lytron chillers contain a flow switch that shuts the system down in a low flow condition. Fortunately this situation can easily be prevented.

The most common sources of low flow is a high pressure drop through your equipment. This can be caused by kinks in your hoses, long lines, small diameter hoses, or high pressure drop fittings such as self-closing quick disconnects.

Figure 1: Recirculating Chiller Flow Control Valve Figure 1: Recirculating chiller
flow control valve

In these situations the pump's safety bypass valve can produce low flow. To prevent an over-pressure situation every Lytron chiller has a pump bypass. This valve is either built into the pump, as with all positive displacement pumps 5 gpm or less, or is a secondary valve behind the pump. As pressure builds this valve opens and decreases the water flow to your equipment.

In order to prevent this from happening, Lytron offers a flow control valve as a standard feature or as a retrofit kit (See Figure 1). A globe valve, connecting the supply and return, regulates the flow between the equipment and the bypass. This keeps the flow rate above the minimum required by the flow switch and still provides cooling to the equipment.

The second common low flow problem occurs when the chiller operates at a low set point, usually below 50oF (10oC). At this temperature the coolant should always be a mixture of water and antifreeze. The refrigerant temperature in the evaporator is typically 20oF below the set point. If coolant does not contain antifreeze, it can freeze in the evaporator, the site of refrigerant/coolant heat transfer. Low flow is an early warning of freezing. The solution to this situation is to use antifreeze in the water. Lytron recommends a 30/70 mixture of ethylene glycol and water. This provides freeze protection well below the temperature found in the evaporator and should prevent any problems.

High pressure drop and freezing the evaporator can be real problems. By following these simple steps, you can prevent costly damage and downtime and your cooling loop will provide years of reliable service.