Evaporative Cooling Pads
Beat the heat with cooling pads.
Hot weather cooling for livestock and poultry includes sprinkling or misting combined with high enough air velocity to promote evaporation, or direct cooling of the air via fogging or evaporative cooling pads as part of a mechanical ventilation package.
Evaporative cooling pads can be quite effective for reducing the interior air temperature in a facility. They work by drawing hot outside air through the saturated pad media, where it absorbs water and cools in the process.
Extent of cooling
The degree of cooling realized depends on the wet-bulb temperature depression, which is the the difference between air (dry bulb) temperature and air wet-bulb temperature.
- Typical design wet-bulb depression values in the Midwestern US range from 14 to 20 oF 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 to 15 oF and consequentially reduce heat stress exposure in livestock buildings and improve growing conditions in greenhouses.
Evaporative cooling pads are a significant investment and their regular maintenance is essential.
Evaporative system water quality is important, starting with water pH between 6-8. If higher, acidification may be advised. It is 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. These reduce evaporation efficiency. How much to bleed off? Follow recommendations from the pad manufacturer, or simply start with 1 gallon/hour per foot of length (for a 4' high pad that is 6" thick).
Example: for a 50' long 6" thick pad measuring 6' high, 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. Reduce bleed off for softer water and increase for harder water. The bleed-off discharge must be managed, for example route it to the surface drainage system for the site.
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 that all 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.
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
- 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.
- 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.
- The system should be completely drained and disinfected.
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.
- Compounds with quaternary ammonium are generally recommended for continuous treatment as an algacide.
- For cleaning, compounds that contain deterent along with an organic acid to reduce pH and help with descaling are used.
Author: Richard S. Gates, Ph.D., P.E., June 201
- Screening for Control of Algae in Cooling Pad Systems. Connover, C.A., R.D. Caldwell, and R.C. Flohr.
- Kuul Control Evaporative Media Guide.
- Munters Celdek Maintenance Guide.