How to protect cooling towers from cold weatherbrought to you by Michael Collins of Eagle Bay Refrigeration. We will discuss a few tips with basic information--please contact us for a more detailed description of any tip, or with any other questions you may have.
{Please note that you should always check with your manufacturer or with us for specific recommendations for your application.}
Delta Induced Fan Cooling Towers provide good protection against freezing. The counter flow cooling tower isolates the heat transfer fill from outside elements. This post presents some general guidelines to be followed when designing our tower installation for cold weather applications.
Heating the Sump May not be Enough
Resistance sump heaters are a good alternative for applications with occasional cold weather shutdowns, or when a separate gravity feed indoor storage tank is not feasible. For applications where more extensive cold-weather operation is expected, a remote sump provides more comprehensive freeze protection.
A Remote Sump Can Eliminates most Freeze Protection Issues
Draining water from the tower to a remote sump, usually located indoors, eliminates most freeze up issues.
TOP TEN CONSIDERATIONS
The load on the tower should be kept as high as possible, and the flow rate should not be allowed to drop below the minimal design flow to avoid dry spots prone to freezing. Modulating cooling tower flow during cold water operation should only be attempted after consultation with the manufacture.
If you expect operation with minimal heat load during winter operation, a bypass should be installed that, when activated, bypasses 100% of the return water directly to the sump.
The MINIMUM leaving temperature of the cooling tower should not be allowed to drop below the minimum set point. See your manufacturer for the appropriate set point for your application.
The most critical periods of operating during cold-weather are startup and shutdown, as during these times the tower is operated with minimal heat load. On systems with a bypass, the bypass should be opened during startup as the heat rejection load is building up. The shutdown procedure is essentially the reverse of the startup procedure.
The remote sump sizing is critical; please see your manufacturer for the proper sump size for your application. A properly sized sump provides: a) Sufficient volume to accept water from everything upstream, including piping and any system components between the tower and the sump. b) Enough retention time of the water for proper air separation. If the buffer volume is not sufficient, water may leave the tank before proper air separation. c) Inlet/outlet connections and a tank design that avoids vortexing and air entrainment.
A drain line should be installed connecting the inlet water piping to the remote sump, with a control valve that drains the line whenever the pump is off. The drain line and valve should be installed indoors close to the remote sump. This will ensure that all outdoor piping will drain to the sump when the tower is not in operation.
All exposed water piping that does not drain to the remote indoor sump should be heat traced.
Proper control of the cooling tower fans is critical to avoid freeze up. A variable speed drive is recommended as it provides superior water temperature control.
De-Icing fan control for winter operation can help avoid ice build-up. Several control sequences are used; please see your manufacturer for recommendations for your application.
A vibration safety switch is recommended to protect against damage caused by ice build-up on the fan and fan blades.
[Bonus Tip] A Water-side Economizer should be considered for Free-Cooling for most cold weather applications. This option can often result in significant energy savings by eliminating mechanical refrigeration by meeting the cooling load directly from the cooling tower as ambient conditions allow.
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