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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

- 2.2.1. Vents, fans, fans/filters

- 2.1. Maintaining a NEMA rating
**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

- DT = 4.08 (Q/A) + 1.1
- 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

- A = (2dw + 2dh + 2wh) / 144
- 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

- Your enclosure temperature reduces to 130*F at 72*F
ambient

- DT = 59*F

- 3.1. No cooling devices
**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

- DT = 3.1 Q / V
- 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.

- 4.1.1. Temperature Drop calculation

- 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.
**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.

- C = 3.413 Q + (W/Ft^2 * A * 3.413)
- 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

- (3.413 x 200W) - (6.7W/ft^2 x 6ft^2 x 3.413)

- Please use the tool located here (http://ftp.automationdirect.com/pub/stratus_ac_btuh_calculator.zip)
to access an online calculator to perform these calculations for you.

- 5.1.1. Capacity (C) calculation in BTU/HR

- 5.1. Vortex tube sizing is the same as a standard
enclosure A/C unit. It is based on Capacity expressed in BTU/HR.
**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.

- 6.1. Fans can be used for both blower and exhaust functions
on enclosures.

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