Frequently Asked Questions

A dry bulb switchover temperature refers to the temperature at which a closed circuit cooler can run fully dry (with just the fans running, without the spray pumps on) and reject 100% of the design heat load. This is an important term in the engineering community as a higher dry bulb switchover temperature results in reduced water consumption throughout the year.

Since the process fluid is contained within a steel coil, when ambient conditions are colder than the dry bulb switchover temperature, closed circuit coolers can utilize airflow over the coil to achieve the required heat rejection with just the fans operating.

When a fluid cooler is sized for a dry bulb switchover temperature, this means that the pumps are off and the fans are running at 100%.

Hybrid coolers utilizing coils with extended surface fins can achieve much higher dry bulb switchover temperatures due to the additional surface area on the coil.

EVAPCO eco-coolers utilize finned coil technology and can achieve dry bulb switchover temperatures for full load (95/85/78 degrees F design conditions) up to 45 degrees F.  EVAPCO eco-Hybrid coolers can achieve dry bulb switchover temperatures for full load (95/85/78 degrees F design conditions) up to 65 degrees F.

No, the recirculating pumps supplied on EVAPCO closed circuit coolers are ON/OFF and require full flow to maintain system efficiency and prevent premature scaling of the coil. They are not designed to operate on a variable frequency drive (VFD).

Every fluid cooler pump is sized for a set flow rate to adequately wet the coil and provide 100% heat transfer via evaporation from the coil. If a recirculating pump is operated on a VFD at a lower speed and flow rate than required at 100%, not only will the system efficiency decrease, but premature scaling of the coil could occur from continuous wetting and drying of certain areas of the coil.

Please note that pump starters are not supplied by EVAPCO and must be provided by other manufacturers.

Glycol has antifreeze properties that protect coils in a closed circuit cooler from potential freezing during winter operation in northern climates.  Glycol solutions are rarely used for closed loop systems in warmer climates, such as Florida or Arizona, unless they are being used as corrosion inhibitors.

In general, about half of closed circuit cooler applications use water and about half use glycol.  Which is better for a closed loop system and why?

Water has superior heat transfer properties compared to propylene or ethylene glycol and is more frequently used in the southern half of the United States.  Water is also cheaper than glycol and, in most cases, will result in a smaller unit selection while requiring less pumping HP.

In most cases, the reason to convert a closed loop system from water to glycol is to prevent freezing and the associated coil damage that results when a closed circuit cooler is exposed to lower ambient temperatures.

If water is being utilized in a closed loop system in a northern climate, it is imperative that a minimum flow be maintained at all times. The temperature inside the coil must never drop below 45 degrees F.  Discharge hoods with dampers and padded insulation on the outside of the coil casing section can also help to prevent freezing of the coil if water is being used in a cooler during winter operation. The most foolproof method of protecting a coil from freezing/bursting in northern climates is to use either an ethylene or propylene glycol inhibitor which have antifreeze properties.

Reasons for not converting a closed loop from water to glycol include the capital cost of glycol (especially for larger systems), the reduced heat transfer rate of glycol (i.e., a larger unit would be required to achieve the same heat transfer capacity), and the increased pump HP required for glycol.

All of the above must be weighed when considering whether water or glycol is right for your closed loop system. For more assistance, please contact your local EVAPCO sales representative.

You can find the coil volume of your closed circuit cooler in 3 places. Each model’s product brochure contains this important information. Visit our comprehensive Document Library to locate up-to-date materials related to your specific fluid cooler. You may also find the coil volume in the project submittal, or within EVAPCO’s selection software, Spectrum.

If you do not have access to any of the above or the unit is an older unit and no current brochure is available, please reach out to your local EVAPCO sales representative for more information.

Please be sure to double check the following three locations for more details: 

1.  Each EVAPCO closed circuit cooler product brochure.  All current brochures can be found within this website; search the Document Library for your specific unit’s information.
2.  If you have access to EVAPCO’s selection software, Spectrum, coil volumes are listed with each unit. 
3. All EVAPCO closed circuit cooler submittals from the year 2020 and newer have a section on the technical data sheet that provides the coil volume.  

A minimum flow needs to be maintained in all closed circuit coolers to prevent potential freezing/bursting of the coil(s) during cold weather operation. Also, when the flow falls below a certain threshold it becomes laminar, which will significantly reduce performance during normal operation. The recommended minimum flow for each EVAPCO fluid cooler is located in its respective marketing product brochure. You can find all up-to-date materials in our comprehensive Document Library.

Regarding cold weather operation, the most foolproof method to prevent freezing is the use of ethylene or propylene glycol.  Draining a coil should only be done in an emergency situation.  Care must be taken to ensure that the piping is sized to allow the water to flow quickly from the coil.  Coils should not be drained often, or for an extended period of time.  Leaving the coil drained and open to the atmosphere can cause interior corrosion, which may lead to premature coil failure. Please contact your local EVAPCO sales representative or Mr. Goodtower® Service Center if you need additional assistance with winter operation/maintenance.