Evaporative cooling pads
Providing maintenance for a longer life
By Richard S. Gates and Brett C. Ramirez
As we begin to settle into late spring and realize the warm weather is coming or already upon us, this article aims to recap the fundamentals of maintaining evaporative cooling pads. Evaporative cooling pads can be a significant expense and their regular maintenance is often ignored or simply hasn’t been taught to users.
The following are some guidelines for regular maintenance that can be used throughout the season. Following these guidelines will often yield several years of extra use before replacement pads are needed and will ensure that the pads are performing well while in use.
Evaporative cooling pads can be quite effective for reducing the interior air temperature in a facility. As incoming hot outside air moves through the saturated pad media, the water evaporates.
When water evaporates, it changes phase from a liquid to a vapor, which requires energy. That energy is removed from the water itself and the incoming air, as a result, the temperature of the incoming air decreases. Consequently, the amount of moisture in the air entering the facility increases, too.
The degree of cooling achieved depends on the wet-bulb temperature depression, which is the difference between air (dry-bulb) temperature and air wet-bulb temperature. Typical design wet-bulb depression values in the Midwestern U.S. range from 14°F to 20°F during the daytime in summer.
Evaporative pads can provide up to 80% or greater efficiency, measured by the reduction in air temperature above the wet-bulb temperature. Modern evaporative cooling pads, in conjunction with a well-designed ventilation system, can achieve incoming air temperature reductions of 5°F to 15°F and consequentially reduce heat stress exposure in livestock buildings.
Continuous maintenance
Evaporative system water quality is probably the most important factor effecting the frequency and extent of pad maintenance. To start, water pH should be between 6 to 8. If higher (more basic), acidification may be advised.
It is also critical to bleed off some of the water in the system because salts and mineral concentration builds as the water is evaporated and these are left behind in the water. Bleeding off water is the simplest way to ensure that fresh water will dilute those mineral concentrations. In extreme cases, if insufficient bleed-off is provided, deposits will build up on the surfaces of the evaporative pad (Figure 1). This build-up reduces evaporation efficiency.
How much to bleed off? Follow recommendations from the pad manufacturer. One pad manufacturer recommends bleeding off a portion (3% to 5%) of the re-circulating water. Or, simply start with 1 gallon/hour per foot of length (for a 4 ft high pad that is 6 inches thick). Reduce bleed off rate for softer water and increase for harder water (even up to 10% or more of the re-circulating water).
One common installation point for a bleed off valve is on the discharge side of the pump, with water passing by a partially opened (and plumbed) ball valve to achieve the desired percentage or numerical bleed off rate. The bleed-off discharge water must be managed, for example, route it to the surface drainage system for the site.
The following equation can be used to determine time to fill a 5-gallon bucket for bleed off.
60 min. / GPH bleed off needed * 5 gal. = time to fill 5-gal. bucket (min.)
Example: for a 50 ft long 6 inch thick pad measuring 6 ft high (1.5 gallons/hours per linear foot), start with a bleed off rate of 75 gallons/hour. Note that 75 gallons/hour will fill a 5-gallon bucket in 6 minutes and 15 seconds, which is easily checked. This example is applicable for systems with good water quality. Remember, harder water more rapidly accumulates scale, mineral deposits, and support slime/algae growth.
Other things to watch: make sure that there are no dry sections when the system runs. The flow to the pads should be great enough such that all of the pad is uniformly wetted. Typical values are about ¾ gallon per minute per foot of pad. If the system becomes fouled with scale or algae the holes in the distributor pipe can plug. Ensure water levels in the trough/sump are not over filled. Water level should be roughly 1 inch below the pads for correct normal operation.
Weekly maintenance
Watch for algae. Algae is bad for the pad media, and as it builds up it will increase the airflow resistance of the pads and decompose the cellulose pad material. Strategies to control algae include:
Proper chemical treatment (see below).
Avoid direct sunlight exposure to the pads and the sump area if there is one.
Take action to ensure that the pads become fully dry once every 24 hours. This can be accomplished several ways, for example, set the ventilation controller to only activate the system at a temperature that is higher than the night time temperature, or put the system on a 24 hour timer to shut out operation for a few hours in the early morning hours.
Visually inspect all sections of the pads for any sagging, and for damage including bird nests and holes. Look for dry sections that indicate insufficient flow in the distribution line, a failing pump, or plugged water distribution pipe holes.
Check the sump for debris, such as algae, insects, dust, tree seeds and leaves, and grass clippings from mowing that have been washed into the system.
This is all food for more algae to grow, so keep it out first, and clean it out if it gets into the sump, so less need for more maintenance.
Monthly maintenance
Watch for scale build up. If present, increase bleed off rate.
Watch for algae appearance. If noted, adjust daily drying time and review chemical treatment practices (below).
Clean any filters that are in the system.
Quarterly maintenance
The system should be completely drained and disinfected. See chemical treatment below. For evaporative cooling systems in the upper Midwest that run from May into October, do this at the start of the season, in July and again when the system is closed down.
The start-of-season cleaning is particularly important if pads remain installed year around, accumulating debris. The distribution pipes and upper assembly must be thoroughly cleaned of debris, and the sump and gutters should have all accumulated solids removed.
Chemical treatment guidelines
Two treatment regimes are generally advised, continuous and quarterly cleaning (or as needed). Follow pad manufacturers’ recommendations.
Some general guidelines include: never add bleach (chlorine) or bromine, as they will shorten the pad life. But, check with your pad manufacturer, because some do recommend bleach (with correct dilution).
Compounds with quaternary ammonium are generally recommended for continuous treatment as an algaecide. For cleaning, seek compounds that contain detergent along with organic acid to reduce pH and help with descaling.
Remember that when cleaning pads and distribution lines, the return water to the sump should not be “re-used”. This avoids further “seeding” by dislodged organic biomaterials and algae as it is redistributed into your cleaned system.
Selected resources:
Connover, C.A., R.D. Caldwell and R.C. Flohr. 1995. Screening for control of algae in cooling pad systems. Proc. Florida State Hort. Soc. 107:202:204.
Kuul Vitality Maintenance and Service Guide. Accessed May 2019.
Munters Celdek Maintenance Guide. Accessed May 2019.
AP Komfort Kooler Installation Manual. Accessed April 2023
Grower Select Evaporative Cooling System Installation Manual. Accessed April 2023.
Gate is the director of the Egg Industry Center and Ramirez is an assistant professor in Department of Agricultural and Biosystems Engineering and assistant director of the Egg Industry Center, both at Iowa State University.
