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Environmental Management of Enclosures AutomationDirect Logo


  1. Scope:
    The scope of this document is to aid the user in environmental management of enclosures.

  2. When choosing cooling methods there are only two choices.
    • 2.1. Maintaining a NEMA rating
      • 2.1.1. A/C's, heat exchangers, Fins, vortex coolers.
    • 2.2. Not maintaining a NEMA rating
      • 2.2.1. Vents, fans, fans/filters
  3. Enclosure cooling:
    • 3.1. No cooling devices
      • 3.1.1. Determining temperature rise will give you the required temperature range to determine the correct method of cooling for your project.
      • 3.1.2. Temperature rise =
        • DT = 4.08 (Q/A) + 1.1
          • DT = temperature rise in *F
          • Q = heat generation in Watts
          • A = exterior surface area in sqft
      • Q (heat generation) = summing of all heat dissipation of all internal equipment and components (not power consumption.)
      • Exterior surface area =
        • A = (2dw + 2dh + 2wh) / 144
          • A = area in sqft
          • d = depth, w = width, h = height
      • 3.1.3. Example:
        • 1200 watt internal heat generation (Q)
        • 55.6 sqft external surface area (A)
          • DT = 4.08 (1200 / 55.6) + 1.1
          • DT = 90*F
            • If your ambient is 72*F then inside your enclosure will be 162*F
        • If you were to double the width A = 85.6 sqft
          • DT = 59*F
            • Your enclosure temperature reduces to 130*F at 72*F ambient

  4. Fan selection:
    • 4.1. Temperature drop is dependant on the amount of flow generated by the fan. It is difficult to estimate a true DT because of pressure drops and enclosure turbulence.
      • 4.1.1. Temperature Drop calculation
        • DT = 3.1 Q / V
          • V = fan flow rate in cfm
          • Q = heat generation in Watts
      • 4.1.2. Example:
        • 1200 watt internal heat generation (Q)
        • 300 cfm fan selection
          • DT = 3.1 (1200 / 300)
          • DT = 12*F
            • If the temperature rise is 90*F; deduct 12*F for the new temperature rise accommodating the additional fan.
            • If the ambient temperature is 72*F then the enclosure internal temperature is 150*F.

  5. Vortex/AC cooling:
    • 5.1. Vortex tube sizing is the same as a standard enclosure A/C unit. It is based on Capacity expressed in BTU/HR.
      • 5.1.1. Capacity (C) calculation in BTU/HR
        • C = 3.413 Q + (W/Ft^2 * A * 3.413)
          • Q = heat generation in Watts
          • A = sqft external surface area
          • W/Ft^2 will come from the heat rise chart for the enclosure for the allowable temperature rise required
          • DT = Difference between ambient and max desired temperature inside enclosure. Note that this value will be negative if the ambient temperature is less than the maximum internal temperature.
      • 5.1.2. Example:
        • 12" x 12" x 12" box (6 sqft)
        • 200 watts
        • 70*F ambient
        • 100*F maximum inside temperature
          • (3.413 x 200W) - (6.7W/ft^2 x 6ft^2 x 3.413)
            • C = 545.4 BTU/HR
            • 6.7W/ft^2 is from heat rise table for enclosure
      • Please use the tool located here (https://ftp.automationdirect.com/pub/stratus_ac_btuh_calculator.zip) to access an online calculator to perform these calculations for you.

  6. Additional tips:
    • 6.1. Fans can be used for both blower and exhaust functions on enclosures.
      • 6.1.1. It is always recommended to put the fan as a blower pressurizing the enclosure to help keep all the dust and dirt out while cooling.
    • 6.2. The inlet size must be equal to the outlet.
    • 6.3. The outlet must be located at a point to prevent short cycling of air.
      • 6.3.1. Short cycling is when the air does not circulate throughout the enclosure because there is a low-pressure zone at the outlet where it immediately exits (I.E. inlet too close to the outlet.)
    • 6.4. If two fans are used in parallel or in series.
      • 6.4.1. They have to be the same size.
    • 6.5. Altitude is sometimes a factor to be aware of because of air density affecting cooling.
    • 6.6. Filters must be cleaned periodically to maintain CFM.

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