Progress Report Series No. 90 Agricultural Experiment Station AUBURN UNIVERSITY b 68 20 1968 V mctor ku urn, Alabm AIR FLOW THROUGH POROUS CURTAIN WALL MATERIALS C. A. ROLLO, W. GRUB i , and J. R. HOWES 2 Department of Agricultural Engineering THE USE OF POROUS wall-covering material on the sidewalls of poultry houses is increasing. Such material, used as an intake device, supposedly provides low-velocity incoming ventilation air over a wide area, creating a so-called breathing wall. Ma- terials used range from burlap to tightly woven plas- tic. These are. often accepted by the poultry producer as satisfactory methods of supplying ventilation with- out drafts from high-velocity air currents. The poul- try producer attempts to control the air flow through such material and the air exchange through the ani- mal shelter by fan ventilation. Fans located in the sidewalls or ceiling are usually designed to exhaust air from inside the building, causing fresh air to flow through the porous wall material. Fans are controlled by thermostats, humidistats, or time clocks. These devices supposedly regulate the rate of air exchange and provide the necessary control for one or more environmental parameters. A study was begun at the Auburn University Ag- ricultural Experiment Station to determine air-flow characteristics of various porous wall materials and to investigate, under actual field conditions, the utili- zation of such materials. In theory, air flow through porous wall materials is dependent upon the differ- ence in pressure across the material. As the difference in pressure increases, the rate of air flow increases. The air flow is from the area of high pressure to the area of low pressure. A pressure difference can be created with a fan, which can be arranged either to increase or decrease the pressure in the building relative to the prevailing SPresent address, Texas Tech., Lubbock, Texas SPresent address, Texas A & M, College Station, Texas atmospheric pressure. The pressure differential and consequent air flow through the porous wall material can be regulated by using variable-speed fans or sev- eral individually controlled fans. Pressure differences on a side wall can also be created by natural air movement. The force of wind against the sidewall of a building creates a positive pressure on the outside surface and causes air to flow into the structure. This same wind causes a negative pressure on the opposite side of the building, causing air to flow out of the building through that sidewall. When a wind hits a wall at an angle of less than 90' with the wall, varying patterns of air pressure de- velop along the length of the building. These cause uneven flow patterns into and out of the building, depending on the wind direction and length of build- ing walls. In all cases, the actual pressure developed is dependent upon the wind direction and velocity. The higher the wind, the greater the pressure differ- ential. Various porous wall materials were tested in the mass air-flow device (1,2,3) of the Station. Air flow through square samples, measuring 3 feet on each side, were tested. Air flow through the different porous wall materials was measured in cubic feet per minute per square foot of wall material. These meas- urements were made at pressuredifferentials ranging up to 2 inches of water, Materials tested were various types of wire screen- ing, burlap, woven plastic, and perforated hardboard. The materials fell into 8 distinct generalized patterns. The various metalic screening materials were the least restrictive and provided little difference in pres- sure, less than 5/100 inch of water, at air flow rates of 700 cubic feet per minute per square foot of ma- terial surface. The burlap materials were intermedi- ate in restricting air flow, while the perforated hard- board and woven plastic materials were most restric- tive, Figure 1. 700. SCREENING 6600 60 BURLAP 500 al- 4WOVEN PLASTICS -00AND PEG BOARD 0 J- 0 .2 .4 .6 .8 1.0 1.2 14 16 18 Static Pressure Differential- Inches Water FIG. 1. Air flow through porous materials. Three woven plastics, each with a different trade name, were tested. Results are shown in Figure 2. No significant difference was noted within the pres- sure range tested. The three materials reacted sim- ilarly to static pressure ranging up to 1.6 inches of water. a_ 400 a- 300 200 0 0 0 2 4 ,6 .8 10 12 14 16 1.8 Static Pressure Differential - Inches Water FIG. 2. Air flow through woven plastic materials. Metallic materials tested were 18- to 1-inch hard- ware cloth, 1- to 2-inch poultry wire, and aluminum and galvanized screening. Results are shown in Fig- ure 8. Aluminum screening, the wire mesh with the greatest projected surface, restricted air flow the most. The material with the least projected surface, 2-inch poultry mesh, restricted air flow the least. Both 1- and 1 4 -inch perforated hardboard were tested in single sheets and double sheets separated by a 1-inch air space, Figure 4. The ' 8 -inch peg board was perforated with one l/s-inch diameter hole per square inch of board surface. The 1i-inch peg board sheet was perforated with one ' 4 -inch hole per square inch. The l-inch perforated board of- fered less resistance per unit rate of air flow than did the ' 4 -inch board. GALV ALUM. 12 2" /2" 1/8" SCREEN SCREEN 8i- 6- 4- 0 Static Pressure Differential- Inches Water FIG. 3. Air flow through metallic screening materials in hundreds of C.F.M. -- AI IBORDL FIG. 4. Air flow through single and double thickness peg board. Double sheets separated I in. with holes in line. Static pressure per unit air flow rate was deter- mined also with the 1-inch air space between the two sheets filled with 1-inch thick fiberglass batt. Little difference was noted in the static pressure at the same rate of air flow, Figure 5. These tests all used new, clean, porous material. Tests conducted with material exposed to dusty and dirty conditions showed a considerable decrease in air flow. This air flow decrease was a result of plug- ging of holes in the material. Analysis of these data presents definite possibilities when applied to specific practical design problems. In the case of a hypothetical laying house 40 feet wide with a bird density of 2 square feet per bird, an arbi- trary ventilation rate of 2 c.f.m. per bird would only require a 61/ 2 -inch wide strip of woven plastic or perforated board if a pressure differential of 1 /s-inch static pressure were maintained across both faces of the material. If the static pressure were increased to 14 inch of water, only a 4-inch strip of woven plastic or perforated hardboard would be required. . 400 I. 300 100 Wateo nateri 180 .2 .4 6 8 10 12 14 16 Static Pressure Differential - Inches Water 400 LL 0" 300, a_ 0 X 200 0 I f. 0 .2 .4 .6 .8 O 1.2 1.4 1.6 Static Pressure Differential- Inches Water FIG. 5. Air flow through double sheets of Va-in. peg board. In- sulation 1 in. thick used between sheets in one test and no insula- tion used in other. In the case of a typical broiler house with a bird density of 3 square foot per bird, an arbitrary venti- lation rate of 1 c.f.m. per bird would require only an 8 i2-inch wide strip of woven plastic if the fan system provided a differential static pressure of 1/8 inch of water. If the static pressure were increased to 1/4 inch of water, the width of the continuous porous strip, could be reduced to 5 inches. These arbitrary ventilation designs may be of in- terest because the continuous strip of porous material on a typical commercial house is at least 86 inches wide. This information is presented as a possible ap- plication of porous wall material. The design might DOUBL DOUBL be a tight building lined with a porous wall material and with a wall cavityto serve as an air duct system. This system would be of significance for reasons other than utilizing porous materials for the wall and ceil- ing surfaces. It would allow ventilation without con- centrated air streams and accompanying cold areas. The air would be heated as it passed through the wall and ceiling cavities. Heat loss from the structure would be at a minimum because incoming air would return most of the radiated heat to the living area. Porous wall materials have an important place in the construction and ventilation of animal structures, especially where there is a need for continuous venti- lation. Although these porous materials are widely accepted in the poultry industry, these research find- ings indicate the large surface areas now being used must be questioned. Further study is to be con- ducted in the use of these materials. LITERATURE CITED (1) Cox, W. T., 1966. Instrumentation for the Measurement of Air Velocities Surrounding Poultry in Environmental Test Chamber. Unpublished Thesis, Auburn University. (2) Cox, W. T., C. A. ROLLO, W. GRUB, AND J. R. HOWES, 1966. A Device for Studying the Effects of Air Movement on Poultry. Proceedings of"Southern Agricultural Work- ers Conference 62nd Meeting. (3) Cox, W. T., W. GRUB, C. A. ROLLO, AND J. R. HOWES, 1966. A Wind Tunnel for Studying Effects of Air Move- ment on Small Animals. Abstracts of Papers for 55th Annual Meeting Poultry Science Association.