Environmental Management of Enclosures

Scope:
The scope of this document is to aid the user in environmental management of enclosures.
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
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
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.
Vortex 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 visit the Hubbell-Wiegmann page at http://www.hubbell-wiegmann.com/930_wie_kool.htm to access an online calculator to perform these calculations for you.
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.