Enclosure Thermal Management: Product Types and Selection Overview

Enclosure Thermal Management
Product Types and Selection Overview

Reasons to Control Enclosure Climate
Industrial facilities have lots of enclosures housing
automation and electrical/electronic components, many of
which need cooling and/or heating.
When fluctuating temperatures exist, heating and cooling
are required to maintain optimal operating temperatures
that keep components from overheating or condensation
from forming.

Heat Transfer
Controlling an enclosure’s climate is done by transferring heat into or
out of the enclosure. There are three basic heat transfer mechanisms:
1. Convection: The movement of heat through a moving fluid (a gas
or a liquid) or from a moving fluid to the surface of a solid.
2. Conduction: The flow of heat through solid material or between
two solids.
3. Radiation: The transfer of thermal energy via conversion to and
from electro-magnetic energy (light).
Convection is the primary mechanism used to control the climate inside
an enclosure because the air inside the enclosure is the most effective
means to transmit heat between the enclosure components and the
heating and/or cooling devices.

Convection
One of the factors that affects the rate of heat transfer inside an enclosure is the
movement of the air inside the enclosure. The faster the air moves inside the enclosure,
the faster the heat transfer occurs. This results in two basic types of convection:
• Natural Convection: Air expands (becomes less dense) as it warms and contracts
(more dense) when it cools. So whenever the air meets a heat source inside an
enclosure, that air expands and rises. The space that air occupied is then replaced by
cooler air, which is heated, expands, rises and gets replaced. This continuous cycle
causes air to circulate inside the enclosure.
• Forced Convection: Air movement created by an artificial means, typically a fan.
Within the context of enclosure climate control, forced convection is utilized when
higher heat transfer rates (more heating or cooling) is needed. But don’t discount the
power of natural convection – natural convection can create a hurricane;
there’s no fan big enough for that!

Reasons for Enclosure Heating
• Enclosure heating is NOT for keeping internal components warm.
Electric and electronic components typically perform better at colder
temperatures.
• As temperature drops, the capacity for air to hold water vapor is
reduced, so the relative humidity of the air increases (even if the
amount of water vapor remains constant).
• Moisture and corrosion become a problem when relative air humidity is
above 65%. So the goal of enclosure heating is to keep the relative
humidity inside the enclosure below 65%.
• Temperature must be consistent to guarantee optimal operating
conditions and prevent condensation.

Enclosure Heating Considerations
• In some applications, an enclosure may need to be cooled during day
and heated at night.
• Heater placement is important. Ideally, optimal performance is achieved
by placing heater near the enclosure bottom to allow natural convection
to distribute the heat. Review specific heater recommendations.
• Larger enclosures often require fan heaters to distribute the heat
throughout the enclosure. Generally, heaters over 150 Watts will include
an axial fan to move the heat throughout the enclosure.

Selecting an Enclosure Heater
This answer is provided using the calculations found
on the next few slides.
What size heater do I need?
These calculations will find PH
(Heating Power) required in Watts
to efficiently heat your enclosure.

Selecting an Enclosure Heater
1. Determine the Enclosure Surface Area (A) exposed to open air
• Height (feet or meters) • Width (feet or meters) • Depth (feet or meters)
(Choose one mounting option representation from the graphics shown on this slide or the next three
slides, then use the formula below the picture to calculate Surface Area A):
1. Free-Standing
A = _____ ft2 or m2
Area (A) =
1.8 (HxW) + 1.8 (HxD) + 1.8 (WxD)
Area (A) =
1.8 (HxW) + 1.4 (HxD) + 1.8 (WxD)
Area (A) =
1.8 (HxW) + (HxD) + 1.8 (WxD)

Selecting an Enclosure Heater (continued)
(Choose one mounting option representation from the graphics shown on this slide, previous slide, or the
next two slides, then use the formula below the picture to calculate Surface Area A):
2. Wall-Mounted
A = _____ ft2 or m2
Area (A) =
1.4 (HxW) + 1.8 (HxD) + 1.8 (WxD)
Area (A) =
1.4 (HxW) + 1.4 (HxD) + 1.8 (WxD)
Area (A) =
1.4 (HxW) + (HxD) + 1.8 (WxD)

(Choose one mounting option representation from the graphics shown on this slide, previous two slides, or
the next slide, then use the formula below the picture to calculate Surface Area A):
3. Ground
A = _____ ft2 or m2
Area (A) =
1.8 (HxW) + 1.8 (HxD) + 1.4 (WxD)
Area (A) =
1.8 (HxW) + 1.4 (HxD) + 1.4 (WxD)
Area (A) =
1.8 (HxW) + (HxD) + 1.4 (WxD)

(Choose one mounting option representation from the graphics shown on this slide or previous three
slides, then use the formula below the picture to calculate Surface Area A):
4. Ground and Wall
A = _____ ft2 or m2
Area (A) =
1.4 (HxW) + 1.8 (HxD) + 1.4 (WxD)
Area (A) =
1.4 (HxW) + 1.4 (HxD) + 1.4 (WxD)
Area (A) =
1.4 (HxW) + (HxD) + 1.4 (WxD)

2. Choose a Heat Transmission Coefficients (k) value (imperial or metric)
from the table below based on the enclosure construction material:
Enclosure Material Coefficient (W/(ft2•K) Coefficient W/(m2•K)
Painted Steel 0.511 5.5
Stainless Steel 0.344 3.7
Aluminum 1.115 12
Plastic or Insulated Stainless Steel 0.325 3.5
Coefficient (k) Value selected = (Imperial) ____ W/(ft2•K) or (metric) _____ W/(m2•K)

4. Determine Component Heating Power (PV), if any
(heat generated by internal components, i.e. transformer)
PV = _____ Watts (total of all devices)
3. Determine the Temperature Differential (ΔT)
a. Decide the desired enclosure interior temperature = ___°F or ___°C
b. Ascertain the lowest ambient (outside) temperature = ___°F or ___°C
Subtract b from a = Temperature Differential (ΔT) (°F or °C)
(ΔT) must be in degrees Kelvin (°K). If Fahrenheit was used for this calculation, then divide
ΔT (°F) by 1.8. If Celsius was used, no conversion is needed.
ΔT (°K) = _____ ΔT (°C) or ΔT (°K) = _____ ΔT (°F) / 1.8

5. Calculate the required Heating Power (PH) for your enclosure based on the
previous values
• If enclosure is located inside:
PH = (A x k x ΔT) – PV (Watts)
• If enclosure is located outside:
PH = 2 x (A x k x ΔT) – PV (Watts)
Where:
PH = Heating Power (from this Step #5)
A = Enclosure Surface Area (from Step #1)
k = Heat Transmission Coefficient (from Step #2)
ΔT = Temperature Differential (from Step #3)
PV = Heating Power in Watts (from Step #4)

Other things to consider
• Fan or No Fan: In most cases, this is determined by the heater capacity. However, there are
somesizeswhereauserhastochoosebetweenaheaterwithafanandonewithout.
• Operating Voltage: Heaters are available in a variety of operating voltages. Choose one
compatiblewithavailablepowerinsidetheenclosure.
• Control: Heaters should always be controlled with a thermostat or a hygrostat to turn them OFF
when the enclosure internal temperature and/or relative humidity is sufficient to prevent
condensation. Controls may be adjustable or preset to fixed ON/OFF setpoints. Control devices
maybeintegratedintotheheater,ormaybeanindependentdevice.
• Element type: Cartridge heaters are a common type of heating element in industrial
applications; they typically include a nickel-chromium (Nichrome) resistor at their core. Positive
Temperature Coefficient (PTC) heaters use a ceramic or polymer resistor whose electrical
resistance increases with temperature. This makes them self-limiting in the temperature that
theycanachieve.

Other things to consider (continued)
• Touch Safe Heater: Heaters, by definition, get hot. Touch-safe heaters
have a shroud covering the heating element to protect against
inadvertent contact by persons working inside the enclosure.
• Protection Rating: Since heaters are inside the enclosure, in most cases
protection rating is not a concern. However, in hazardous locations an
explosion-proof heater may be required.
• Heater Mounting: Most heaters can be DIN rail mounted or panel
mounted. Some are foot mounted, allowing them to be mounted
directly to the floor of the enclosure.
• Space Available: Heaters are available in various shapes and sizes to
allow for appropriate fit in the enclosure.

Ways to Heat Enclosures
Stego heaters offered by AutomationDirect:
• PTC heaters, 5W – 13W, for heating small enclosures,
panel mount.
• Touch-Safe PTC heaters, 10W – 150W, 35mm DIN rail mount,
optional integral fixed-range thermostat.
• Explosion-proof (IP 6X) heaters, 50W & 100W, high-
performance cartridge, 35mm DIN rail mount.

• Touch-safe PTC heaters, 150W – 400W, axial fan, 35mm
DIN or panel mount.
• Touch-safe PTC heaters, 250W – 400W, axial fan, integral
fixed-range thermostat, 35mm DIN rail or panel mount.
• High-performance cartridge heater, 500W – 700W, axial
fan, 35mm DIN rail or panel mount, compact design ideal
for limited spaces.

• PTC heaters, 550 – 650W, axial fan, integral adjustable
thermostat, 35mm DIN rail mount.
• High-performance cartridge heaters, 950W, axial fan,
optional fixed hygrostat or adjustable thermostat, 35mm
DIN rail, panel or foot mount.

• PTC heater, 1000W, axial fan, 35mm DIN rail or panel
mount, optional fixed-range thermostat, compact design
ideal for tight spaces.
• PTC heater, 1200W, axial fan, optional adjustable
thermostat, 35mm DIN rail, panel or foot mount.

Reasons to Control Enclosure Climate
Reasons for Enclosure Cooling
• Heat may be added to enclosure from both internal
components (drives, power supplies, etc.) or external
sources (furnaces, foundry equipment, ovens, etc.).
• Heat decreases life expectancy of components such as
PLCs, HMIs, AC drives, etc.
• Heat may cause electrical/electronic component faults
(i.e., overload tripping, change in performance of
circuit breakers and fuses, power failures, and more).

Ways to Keep Enclosures Cool
Selecting a cooling method depends on several factors:
• How much heat must be removed? The cooling capacity of the
method selected needs to be greater than the combined internal
and external heat load.
• The desired internal enclosure temperature and the ambient
temperature around the enclosure: Heat will naturally flow from
higher temperatures to lower temperatures. The higher the ambient
temperature relative to the enclosure temperature, the harder it is
to move heat from the enclosure to the atmosphere.
• The protection rating of the enclosure: Some NEMA enclosure
ratings preclude allowing outside air to enter the enclosure as part
of the cooling system, since other outside contaminants (water,
dust, oil, etc.) could enter via the same path.

Ways to Keep Enclosures Cool
How can you keep an enclosure’s interior air temperature cool?
Heat can be generated to raise the temperature of an enclosure but
cold cannot be generated. Cooling an enclosure is accomplished by
removing heat from the enclosure to the surrounding atmosphere.
There are several types of cooling methods, all of which will be
described in greater detail:
• Natural Convection: Typically for small heat loads. The ambient
temperaturemustbelowerthanthedesiredtemperatureinsideenclosure.
• Forced Convection: The ambient temperature must be lower than
the desired temperature inside the enclosure.
• Closed Loop Cooling: Used when the ambient temperature is as
high or higher than the desired internal temperature. This method
is also used for areas with harsh environments.

Natural Convection Cooling
• Use when outside is clean, dry,
and cooler than enclosure interior.
• Heat is transferred to the
enclosure surface, and then
dissipates to atmosphere.
• Louvers or grilles with filters can
be used to dissipate heat more
quickly by allowing warm air to
escape enclosure and be replaced
by cooler air from surrounding
atmosphere.

Natural Convection Cooling
• STEGO Enclosure Exhaust Grilles with Filters: Available for no-screw
installation with optional mounting screws for additional support and
indoor or outdoor installation options.
• Hubbell-Wiegmann Enclosure Exhaust Grilles and Filters:
Polycarbonate, fire-retardant plastic grilles with durable reusable filter mat.
• Hubbell-Wiegmann Vents, Louver Plates and Filters: Open
louvers and vents for both metal and fiberglass enclosures.
• Integra Labyrinth Vent: For Integra polycarbonate enclosures.
Natural Convection Cooling Devices offered by AutomationDirect:

Forced Convection Cooling
• Use when clean and cool
outside air is available.
• Use filter fan and grille to force
cool ambient air into enclosure.
• Use exhaust grille to allow hot
air in enclosure to exhaust as
cool air is forced in.

• STEGO Enclosure Filter Fans: Create constant air flow
through the enclosure to prevent localized heat
pockets and protect components from overheating.
• Hubbell-Weigmann Enclosure Fans: Cooling fans and
exhaust grilles that provide high quality cooling.
Enclosure fans provide optimum climate in enclosures channeling cooler
filtered outside air into the enclosure and expelling hot internal air.
The following forced convection fans are offered by AutomationDirect:

Sometimes the enclosure cooling system has the capacity to dissipate the total
heat load in an enclosure, but if a high heat load from one or more components
or a “hot spot” develops because the arrangement of the components, this
restricts air movement in one area. These situations can create a “bottleneck” in
the flow of heat from the enclosure to the outside.
In such cases, STEGO StegoJetCompact Fansfrom AutomationDirectcan
provide spot cooling by creating a focused stream of air inside the enclosure to
move the heat away from the hot spot or high heat load component, allowing
the enclosure cooling system to move the heat to the outside.

Closed Loop Cooling
Closed loop cooling devices are used when there is a need to maintain temperature
inside an enclosure at or below safe levels for the equipment/components without
introducing outside air into the enclosure.
Closed loop cooling is typically used in:
• Harsh environments
• Areas where washdown is required
• Areas with heavy dust and debris
• Areas where chemicals are airborne
Closed loop cooling options offered by
AutomationDirect:
• Enclosure Heat Exchangers
• Enclosure Air Conditioners

Closed Loop Cooling
How closed loop cooling systems work:
• The heart of the system is a refrigerant the
circulates through a sealed system that
passes from an evaporator coil inside the
enclosure to a condenser coil on the outside
and back.
• As the refrigerant circulates, it acts as a
conveyor belt for heat, picking up heat from
inside the enclosure at the evaporator and
dropping it off to the outside air at the
condenser.

Closed Loop Cooling
How closed loop cooling systems work (continued):
• A fan circulates air from inside the enclosure
across the evaporator coil. Since the refrigerant
in the evaporator is colder than the air in the
enclosure, it absorbs heat from air and cools it.
• A second fan circulates ambient air across the
condenser coil. Since the refrigerant in the
condenser is hotter than the ambient air, heat
from the refrigerant is rejected to the
atmosphere.

Closed Loop Cooling
Closed loop cooling options offered by AutomationDirect:
• Stratus Enclosure Air-to-Air Heat Exchangers
• Stratus Enclosure Air Conditioners
The primary differences between the
operation of an enclosure heat exchanger and
an enclosure air conditioner is the refrigerant
and how it is circulated through the
evaporator and the condenser.

Closed Loop Cooling
Enclosure Heat Exchangers: Air-to-Air Heat Exchangers use the
heat pipe principle to exchange heat inside an electrical enclosure
to the outside:
• A liquid refrigerant is sealed in a bundle of copper
tubes under a partial vacuum. The partial
vacuum lowers the boiling point of the refrigerant.
• The tube bundle is mounted diagonally, with the
top section forming the condenser and the
bottom end forming the evaporator.
• The condenser and evaporator sections are
separated by a permanent baffle.
• Since the refrigerant is under a partial vacuum,
the heat absorbed in the evaporator boils the
refrigerant (changes it from liquid to vapor).

Closed Loop Cooling
Enclosure Heat Exchangers (continued)
• The refrigerant vapor is lighter than the liquid refrigerant, so the heated refrigerant
rises to the condenser section at the top of the tube.
• The cooler ambient air passing over the
condenser section cools the refrigerant vapor
until it condenses (returns to liquid phase).
• Liquid refrigerant falls to the evaporator, replacing
the refrigerant vapor that is rising.
• The cycle repeats endlessly as long as ambient air
is cooler than the air inside the enclosure. If the
ambient temperature equals or exceeds the
enclosure temperature, the flow of refrigerant
stops.

Closed Loop Cooling
• Heat exchangers typically afford similar cooling
as filter fans: the cooler the ambient air is
relative to the enclosure air the faster the
enclosure air is cooled.
• Like filter fans, heat exchangers are not effective
when ambient temperatures can exceed the
desired enclosure temperature. Enclosures
located in ambient temperatures may require an
air conditioner or vortex cooler.
• Though the cooling capabilities are similar to
filter fans, heat exchangers can maintain higher
NEMA ratings than filter fans.

Closed Loop Cooling
• The Stratus heat exchanger design has a
top-to-bottom enclosure air flow pattern
with maximum separation of the inlet
and outlet.
• The units use aluminum end plates and
baffles which improve conduction and
reduce corrosion for longer life.
• The center aluminum baffle, which is
swaged into the heat pipe coil, provides
an air tight seal between the two air
systems.

Closed Loop Cooling
Enclosure Air Conditioners work essentially the same way as heat
exchangers, except that the refrigeration system is more complex.
• The evaporator and condenser are still in separate compartments,
but are separate coils connected by a loop of piping.
• Upstream of the condenser coil is a compressor, which acts
like a pump to force the refrigerant through the system. The
compression of the refrigerant vapor also makes it very hot,
so when it enters the compressor it is hotter than the
ambient air (even on a hot day) enabling it to reject heat to
the atmosphere.
• The compressed refrigerant condenses at a much higher
temperature than it does uncompressed. So even though it is
hotter than the outside air it still changes to liquid form when
it passes through the condenser.

Closed Loop Cooling
Enclosure Air Conditioners (continued)
• Just upstream of the evaporator, the hot, pressurized refrigerant passes through
an expansion valve, which causes a large drop in the
refrigerant pressure.
• Just as compression caused the refrigerant vapor to get
very hot, the sudden reduction of pressure causes the
refrigerant liquid to get very cold as it enters the
evaporator. The cold liquid is very effective at absorbing
heat from the enclosure air that is being blown across the
evaporator coils.
• The low pressure refrigerant evaporates back into vapor
form. Its expansion pushes the vapor to the suction side
of the compressor, where the cycle starts again.

Closed Loop Cooling
• The compression and expansion of the refrigerant (and the
accompanying temperature extremes they produce) means
that an air conditioner can maintain enclosure temperatures
that are lower than ambient temperatures. This makes air
conditioners useful in environments that have high ambient
temperatures, where fans or heat exchangers would be
ineffective.
• The effectiveness of the air conditioner does come at a
price. The compressor uses much more electrical power
than a filter fan or a heat exchanger.

Closed Loop Cooling
Stratus air conditioners feature
• Highly energy-efficient compressors
• A programmable temperature controller with visible
alarm features
• Protective coatings on the condenser coils of NEMA 4
and NEMA 4X models for corrosion resistance
• Active condensate evaporation system with safety
overflow (for elimination of water vapor that may
form on the outside of the evaporator coils when the
enclosure air is cooled)
• Anti short-cycle compression protection

Closed Loop Cooling
Stratus Refrigerant-free Vortex Coolers
(Technically, vortex coolers aren’t closed loop, they are actually displacing hot air inside the enclosure with
cold air from the outside. However, since the cold air comes from a filtered compressed air system, they
stillmaintainhighNEMAenclosureratingslikeairconditionersandheatexchangers.)
• The vortex generator inside the cooler creates a vortex
that rotates the compressed air supply at speeds up to
1,000,000 rpm.
• The rotation air separates the air into hot and cold air
streams.
• The hot air stream is vented to the atmosphere, while
the super-cooled air is forced through the center of the
incoming air stream, through the cold air exhaust port,
and into the enclosure.
• Hot air from the enclosure is forced out through a vent.
Vortex coolers generate a stream of cold air using nothing except compressed air
– no fans, no moving parts, no electricity required.

Closed Loop Cooling
Stratus Refrigerant-free Vortex Coolers (continued)
• Stratus vortex coolers are useful when air conditioner or heat
exchanger cooling is not possible. (i.e., small to medium size
enclosures, non-metallic enclosures, areas where the size of
cooling devices is restricted, areas where access to electrical
power is limited but compressed air is available).
• Vortex coolers are very inexpensive up front and require no
maintenance. But they do consume a lot of compressed air,
which must be accounted for in their operating cost.
• Like an air conditioner, a vortex cooler is effective even in high
ambient temperatures.
• Unlike competing brands, the cooling capacity of a Stratus
vortex cooler can be changed by simply replacing the vortex
generator. The vortex generator costs less than $10, and can be
changed in less than five minutes with common hand tools.

Sizing of Cooling Devices
After choosing the most appropriate cooling method (natural convection,
forced convection, or closed-loop), calculations are needed to determine
the size/capacity of the cooling components.

Sizing an Enclosure Fan
To select the proper size (CFM) fan, determine the amount of heat to be removed and
the maximum temperature differential that needs to be accommodated.
Cubic Feet per Minute (CFM) calculation
CFM = (3.17 x Pwatts) / ΔT °F
Where:
P = Power to be dissipated in watts
ΔT = (max. allowable internal enclosure temperature °F) –
(max. outside ambient temperature °F)

Fan Sizing Example
A NEMA 12 Hubbell Wiegmann N12302412 enclosure (30ʺ high x 24ʺ wide x
12ʺ deep) contains a GS3-2020 AC drive (20 HP 230 volt) that has a
maximum allowable operating temperature of 104°F and is located in a
warehouse with a maximum outside ambient air temperature of 95°F.
Power to be dissipated is stated in the specifications of the GS3-2020 and is
found to be 750 watts, so P = 750 watts.
ΔT = 104°F (max. operating temperature for the GS3-2020)
– 95°F (max. ambient air temperature) = 9°F
Sizing an Enclosure Fan (continued)
CFM = (3.17 x 750 watts) / 9°F = 264

Informative video for AutomationDirect’s STEGO line of enclosure filter fans and
exhaust grilles.
Sizing an Enclosure Fan

Sizing an Air Conditioner or Vortex Cooler
To select the proper size unit, consider the worst-case conditions, but do not oversize.
Two main factors when choosing for an indoor uninsulated metal NEMA rated enclosure:
• Internal heat load: The heat generated by components inside the enclosure.
The preferred method to determine this is to add the maximum heat output
specifications that the manufacturers list for all the equipment installed in the
cabinet. Load is needed in BTU, but the values are typically given in Watts,
so use the following conversion:
BTU per Hour = Watts x 3.413
Example: The Watt-loss chart for the AutomationDirect
GS3 Drives shows that a GS3-2020 AC drive has a
Watt-loss of 750 watts.
BTU per Hour = 750 watts x 3.413 = 2559

Sizing an Air Conditioner (continued)
Note: 1.25 is an industry standard constant for metal enclosures;
for plastic enclosures use 0.62.
• Heat Load Transfer: The heat lost (negative heat load transfer) or gained
(positive heat load transfer) through the enclosure walls with the surrounding
ambient air. Calculate using the following formula:
Heat load transfer (BTU/H) =
1.25 x surface area (sq. ft. ) x (max. outside ambient air (°F) –
max. allowable internal enclosure temperature air (°F)) Surface Area (sq. ft.) =
2 [(H x W) + (H x D) + (W x D)] / 144 sq. inches
Cooling capacity (BTU/H) = Internal Heat Load ± Heat Load Transfer
Once you determine the Internal Heat Load and the Heat
Load Transfer, you can choose the proper size unit
by calculating the needed cooling capacity.

BTU per Hour = 1290 watts x 3.413
BTU per Hour = 4403 BTU/H
Heat load transfer:
Heat load transfer (BTU/H) = 1.25 x 19 sq. ft. x (115°F – 104°F)
Heat load transfer (BTU/H) = 261 BTU/H
Air Conditioner Sizing Example
A NEMA 12 Hubbell Wiegmann N12302412 enclosure (30ʺ high x 24ʺ wide x 12ʺ
deep) contains a GS3-4030 AC drive (30 HP 460 volt) that has a maximum allowable
operating temperature of 104°F and is located in a warehouse that has a maximum
outside ambient air temperature of 115°F. Power to be dissipated is stated in the
specificationsoftheGS3-4030andisfoundtobe1290watts.
Internal Heat Load:

Air Conditioner Sizing Example (continued)
Cooling Capacity:
• Cooling capacity (BTU/H) = 4403 BTU/H + 261 BTU/H = 4664 BTU/H
Now review the cooling capacity charts
for Stratus air conditioners on the
AutomationDirect website for an air
conditioner that can provide at least 4664
BTU/hour at 115 at an operating
temperature of 104°F and a 115°F
ambient temperature.
Select a TA10-060-46-12 Stratus air conditioner

Informative video about AutomationDirect’s Stratus™ enclosure 480V air
conditioner models.

Sizing a Heat Exchanger
To select the proper size unit, consider the worst-case conditions. For a heat exchanger
to work, ambient air temperature must be lower than the desired internal enclosure
air temperature. There are three main factors in choosing a heat exchanger for an
uninsulated metal NEMA rated enclosure located indoors:
• Internal heat load: The heat generated by components inside the enclosure.
The preferred method to determine this is to add the maximum heat output
specifications that the manufacturers list for all the equipment installed in the
cabinet. This is typically given in Watts.
• Delta T (ΔT):
ΔT = (max. allowable internal enclosure temperature) –
(max. outside ambient air temperature °F)
Example: The Watt-loss chart for the AutomationDirect GS3 Drives
shows that a GS3-2020 AC drive has a Watt-loss of 750 watts.
BTU per Hour = 750 watts x 3.413 = 2559

Sizing a Heat Exchanger (continued)
Note: Only include exposed surfaces.
Heat Load Transfer (W/°F) = 0.22 W/°F sq. Ft. x Surface Area
Note: Use 0.22 Watts/°F sq. ft. for painted stainless and non-
metallic enclosures. Use 0.10 Watts/°F sq. ft. for stainless
steel and bare aluminum enclosures.
Once you determine the Internal Heat Load and theHeat Load
Transfer and the Delta T, you can choose the proper size unit
by calculating the needed cooling capacity.
• Heat Load Transfer: The heat lost (negative heat load transfer) or gained
(positive heat load transfer) through the enclosure walls with the surrounding
ambient air. Calculate using the following formula:
Surface Area (sq. ft.) = 2 [(H x W) + (H x D) + (W x D)] / 144 sq. inches
Cooling capacity (W/°F) = Internal Heat Load / ΔT - Heat Load Transfer

Surface Area (ft.2) = 2 [ (30 x 24) + (30 x 12) + (24 x 12) ] / 144 sq. inches = 19 ft.2
Heat load transfer = 0.22 x 19 ft.2 = 4.2 Watts/°F
Selecting a Heat Exchanger (continued)
Heat Exchanger Selection Example
A NEMA 12 Hubbell Wiegmann N12302412 enclosure (30ʺ high x 24ʺ wide x 12ʺ
deep) contains a GS3-4010 AC drive (10 HP 460 volt) that has a maximum allowable
operating temperature of 104°F and is located in a warehouse that has a maximum
outside ambient air temperature of 90°F. Power to be dissipated is stated in the
specificationsoftheGS3-4010andisfoundtobe345Watts.
Internal Heat Load = 345 Watts
Delta T (ΔT ) = 104°F – 90°F = 14°F
Heat load transfer:

Heat Exchanger Sizing Example (continued)
Cooling Capacity = 345 Watts/°F – 4.2 Watts/°F = 20.4 Watts/°F
In this example, we can determine that a Stratus heat exchanger, with a
capacity of at least 20.4 Watts/°F is needed, such as a TE30-030-17-04.
Note: This selection procedure
applies to metal and non-metal,
uninsulated, sealed enclosures in
indoor locations. This selection
procedure gives the minimum
required size; be careful not to
undersize when purchasing.

Informational video of AutomationDirect’s Stratus™ line of air-to-air heat
exchangers in 120VAC and 24VDC models.

Enclosure Thermal Management Controls
Enclosure heaters controlled with thermostats,
humidistats (hygrostats) and hygrotherms provide the
most consistent temperature and humidity control
• Many enclosure heaters include integrated
thermostats or other controls
• Certain heaters may allow for or require
external controls

The need for control of cooling devices depends on the type of device:
• Filter fans and Stratus heat exchangers do not require a thermostat since they
consume very little power. However if they do not need to operate
continuously, a control device will prolong the life of their filters.
• Stratus air conditioners have an integral thermostat, so an external control
device is never needed.
• Stratus vortex coolers should ALWAYS be controlled by a thermostat to
minimize compressed air consumption (and in some cases, to prevent
freezing of components inside the enclosure).

Climate control components offered by AutomationDirect:
• Tamperproof Thermostats (DIN Rail-mounted): Tamperproof
(pre-set) NC (normally closed) thermostat opens on temperature
rise above fixed setpoint. Tamperproof NO (normally open)
thermostatclosesontemperaturerise.
• Adjustable Thermostats (DIN Rail-mounted): NC adjustable
thermostat opens on temperature rise above setpoint. NO
adjustablethermostatclosesontemperaturerise.
• Adjustable Dual Setpoint Thermostats for Enclosure Heaters
(DIN Rail-mounted): Houses two separate thermostats, allowing
independent control of heating, cooling or other equipment. The
NC thermostat (red dial) opens on temperature rise above set
point. TheNOthermostat(bluedial)closesontemperaturerise.
NOTE:Red(NC)thermostatscontrolheating;blue(NO)thermostatscontrolcooling.

Enclosure Heating Controls
Hygrostats/Hygrotherms from AutomationDirect:
• Electronic Hygrostats for Enclosures (DIN Rail Mounted): Electronic
hygrostats (humidistats) sense relative humidity in an enclosure and
turn on a heater at the setpoint. This helps prevent enclosure
condensation formation.
• Electronic Hygrotherms for Enclosures (DIN Rail Mounted): Electronic
hygrotherms sense ambient temperature and relative air humidity.
Depending on the selected contact combination, the hygrotherm will
turn a connected device ON or OFF if either the temperature is below
the setpoint, or the humidity is above the setpoint. Typically used to
control PTC heaters, fan heaters, condensation heaters, or other climate
control devices.

Instructional video for AutomationDirect’s thermostats and hygrostats.

Weather keeping your enclosure cool, or safe and dry, we have
the climate control solution at prices that won’t make you sweat!

Enclosure Thermal Management: Product Types and Selection Overview

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