UNDERSTANDING MESH SPECIFICATIONS
The openness factor of screen mesh is specified by the yarn density and yarn diameter. The “warp” and “fill”, that is, the number of yarn threads per inch “warp” by the number of yarn threads per inch “fill” specifies the yarn density. Thus, 18X14 mesh is eighteen threads per inch warp, and fourteen threads per inch fill. The larger the warp and fill numbers and the larger the yarn diameter the tighter the weave, the smaller the openings between the threads, the smaller the insects it will control, the greater the reduction in air flow and the greater reduction in light and visual transmittance. Solar factors are specified for screen mesh also. Each screen mesh is specified as to its solar transmittance, solar reflectance and solar absorbance.
SCREENING FOR INSECT CONTROL:
For maximum control of insects, including the smallest ones, you want to select the screen mesh for smallest openness factor. This means high warp and fill and yarn diameter. However, the downside of small openness factor is reduced air flow and light transmittance. The room will be darker and on hot days it will suffer from lack of air movement. Therefore, it must be kept in mind that screen selection is a compromise. If the room is fitted with lights and fans a screen mesh can be selected to minimize the openness factor such as 20X30. If you are depending on air movement from outside, a mesh with a higher openness factor such as 20X20 will allow more air flow and restrict all (including no-seeums) but the smallest insects. For maximum airflow 18X14 mesh is best. If the lights are going to be on at night you will want to use 20X30 and fans for cooling. This is because at night the smallest insects, attracted to the light, will land on the screen and squeeze through and continue to the light.
SCREENING FOR SUN CONTROL
Solar transmittance is the amount of solar energy that passes through the openings and thus is proportional to the openness factor. The tighter the weave the less solar transmittance can result. Solar reflectance is the amount of solar radiation reflected. Again, a tighter weave gives more solar reflectance, but the lighter the color also the higher the reflectance. Solar absorbance increases with tighter weave and darker colors. The problem with high absorbance is that approximately one half the solar energy absorbed by the screen mesh is re-radiated back into the room. The sum of the percentages of transmittance, reflectance and absorbance must equal one hundred percent of the solar energy incident on the screen mesh. Ideally you want to maximize reflectance and minimize absorbance for any particular mesh density. This means the lighter the mesh color the better for sun control. Again, air flow is compromised by lowering the transmittance since to do so means to reduce the openness factor.
SCREENING FOR PRIVACY CONTROL
Privacy control using screen mesh works the same way that one-way mirrors work. The darker side of the screen can see clearly through to the lighter side. The more reflectance on the lighter side the more privacy offered to the darker side. Therefore, to get daytime privacy inside we want to use a light screen color. This reverses at night if lights are on inside the room. From the lit inside of the room you will see nothing outside, whereas anyone outside can see everything inside. The brighter the light side and the darker the dark side the more privacy is on the dark side. In addition to color, visual transmittance is a factor in privacy control. The lighter the color and the lower the visual transmittance the more privacy. A higher transmittance mesh such as white 17X14 super screen means more lightening of the dark side that somewhat reduces the privacy. However, a lower transmittance mesh such as white NANO95 has a lower openness factor and lower air movement. A better compromise is a semi-open white colored mesh like white Solar screen. This is because in addition to these optimum physical characteristics of the screen the physiological characteristics of the eye also come into play. The bright glare of the lighted side of the screen closes down the iris of the eye so that the visual transmittance through the openings in the mesh cannot be processed effectively by the eye and brain.
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