How Are Evaporative Cooling Pads Engineered for Poultry Houses?

The engineer starts from the design tunnel airflow and works to pad area. Using the rule of roughly 1 square foot of pad per 150 to 200 cfm, a house moving 2 million cfm needs on the order of 10,000 to 13,000 square feet of pad — typically split across the full inlet end wall in stacked sections. Media depth and flute angle are selected from manufacturer performance data at the design face velocity, and the engineer confirms the published cooling efficiency — usually 70 to 85 percent of the wet-bulb depression — against the local design wet-bulb temperature to predict the actual temperature drop the house will see on a design day. Pressure drop is the check that closes the loop. Pads typically add several hundredths of an inch of water column, and the engineer adds that to the house static pressure budget — pads, tunnel doors, and inlets together must stay within what the fan bank can pull at rated capacity. Pad frames are drawn with airtight seals to the wall so air cannot bypass around the pads, and the engineer specifies pad retention and support details that survive years of wet-dry cycling without sagging into the airstream.

The recirculating water loop is sized like a small process system. The engineer sizes the sump tank for the pad area's water inventory plus operating surge, selects pumps for the distribution head at full flow, and draws the header with balancing valves so the top and bottom of tall pad sections wet equally. Makeup water is metered and the bleed-off rate is set from the supply water's hardness — in hard-water regions the bleed runs higher to keep dissolved solids from crusting the pads. Where water quality is poor, the engineer specifies treatment: softening, acid feed, or algaecide dosing, each with proper chemical storage and feed equipment. Pad houses — the doghouse enclosures at the inlet end — are drawn as part of the design. They shade pads from direct sun, which cuts algae growth and evaporation loss, and they give maintenance access to pumps, sumps, and distribution without entering the bird area. The engineer details the pad-house floor with drainage to daylight, specifies corrosion-resistant materials for the constantly wet environment, and screens openings so the sump and pad area do not become mosquito breeding habitat. Winterization is designed in: drain-down valves and freeze protection for the loop where climate demands it.

Use this checklist before the cooling design is released: • Pad area sized near 1 sq ft per 150 to 200 cfm at low face velocity for rated efficiency • Temperature drop predicted from local design wet-bulb and published pad efficiency • Pad pressure drop included in the fan static-pressure budget with sealed bypass-free frames • Sump, pumps, and distribution sized for full pad area with even wetting top to bottom • Bleed-off and makeup water designed from supply hardness; treatment specified where needed • Controller staging: pads wet only on temperature demand, with humidity lockout and bird-age interlocks • Shaded pad houses with drainage, corrosion-resistant materials, and screened openings • Winterization: drain-down and freeze protection for the recirculation loop