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1-800-633-0405 For the latest prices,please check www.automationdirect.com. <br /> Enclosure Heating and Heater Selection <br /> Why Heat an Enclosure? Heater Location <br /> Today's miniaturization of enclosure components results in high Ideally, most heaters will perform optimally when mounted <br /> packing densities,which in turn results in higher temperatures near the bottom of an enclosure and used in conjunction with <br /> within the enclosure.These high temperatures are harmful a control device,thermostat, and/or hygrostat.The control <br /> to electronic components. In response, cooling systems have device may be a separate device,or it may be integral to the <br /> become standard in many applications. However,just as critical heater.With the controller located in an area of the cabinet <br /> and widely underestimated,are failures caused by the formation that is representative of the average temperature or humidity <br /> of moisture. requirement,the heater should then be placed in a position near <br /> Under certain climatic conditions, moisture can build up not the bottom of the enclosure. If a separate control device is used, <br /> only in outdoor or poorly insulated enclosures, but also in highly the heater should not be located directly beneath the controller <br /> protected and well-sealed enclosures. to ensure that the controller is not influenced by direct heat from <br /> the heater. <br /> Moisture and Failure Heater Calculation <br /> Moisture,especially when combined with aggressive gases and Follow Steps 1-5 to determine the heating requirement of an <br /> dust, causes atmospheric corrosion and can result in the failure of enclosure(US units - left column, metric- right) <br /> components such as circuit breakers, busbars, relays, integrated <br /> circuit boards and transformers.The greatest danger lies in STEP 1: Determine the Surface Area (A) of your enclosure which is <br /> conditions where electronic equipment is exposed to relatively exposed to open air. <br /> high air humidity or extreme variations in temperature,such Enclosure Dimensions: <br /> as day-and-night operation or outdoor installation. Failure of <br /> components in such cases is usually caused by changing contact height = feet meters <br /> resistances,flashovers,creepage currents or reduced width – feet meters <br /> insulation properties. <br /> depth = feet meters <br /> Eliminate Moisture Choose Mounting Option from next page, and calculate the <br /> surface area as indicated <br /> Moisture and corrosion will remain low if relative air humidity A – ft2 or m2 <br /> stays below 60%. However, relative humidity above 65%will <br /> significantly increase moisture and corrosion problems.This can STEP 2:Choose the Heat Transmission Coefficient(k)for your <br /> be prevented by keeping the environment inside an enclosure enclosure's material of construction. <br /> at a temperature as little as 9°F(5°C) higher than that of the painted steel – 0.511 W/(ft2K) 5.5 W/(m2K) <br /> ambient air.Constant temperatures are a necessity to guarantee <br /> optimal operating conditions.Continuous temperature changes stainless steel = 0.344 W/(ft2K) 3.7 W/(m2K) <br /> not only create condensation but they reduce the life expectancy aluminum = 1.115 W/(ft2K) 12 W/(m2K) <br /> of electronic components significantly. Electronic components plastic or insulatedstainless = 0.325 W/(ft2K) 3.5 W/(m2K) <br /> can be protected by cooling during the day and heating at night. <br /> k = W/(ft2K)or W/(m2K) <br /> Thermal Management STEP 3: Determine the Temperature Differential (AT). <br /> Modern enclosure heaters are designed to protect against A. Desired enclosure interior temp. _ of—OC <br /> condensation.They heat the air inside enclosures, preventing B. Lowest ambient(outside)temp. __OF_oC <br /> Tem <br /> water vapor from condensing on components while providing Subtract B from A = diff. <br /> the greatest possible air circulation and low energy consumption. p (AT <br /> ) _ of oC <br /> Other heating element technology improvements include: For these calculations,AT must be in° Kelvin (K).Therefore, divide <br /> AT(OF) by 1.8.AT = K <br /> • Longer operating life <br /> STEP 4: Determine Heating Power(PV), if any(generated from <br /> • Greater energy efficiencies existing components, i.e.transformer). <br /> • Quick wiring options <br /> • Easier mounting PV = W or W <br /> • Fan heaters should be considered for larger enclosures to ensure that STEP 5:Calculate the Required Heating Power(PH)for your <br /> the entire enclosure is heated uniformly enclosure based on the above values. <br /> If enclosure is located inside: <br /> PH = (AXkXAT) - PV = W <br /> If enclosure is located outside: <br /> PH = 2x(AXkXAT) - PV = W <br /> www.automationdirect.com Enclosures Thermal Management tENT-75 <br />