Wiegmann WPG Series - Manual (Page 3)

K3
www.hubbell-wiegmann.com
Data Subject To Change Without Notice
E N V I R O N M E N TA L C O N T R O L S
A I R C O N D I T I O N E R S - A P P L I C AT I O N I N F O R M AT I O N
S T E P F O U R
(Watts x 3.413) +
[1.25 x Area ft.2 x
Δ T (°F)]
=BTU/HR.
Capacity
Required BTU/HR.
Capacity Rating
1oC or 1oKΔT=1.8oF T
Determine the tempera-
ture differential by sub-
tracting the maximum
allowable temperature
inside the enclosure
(Ti) from the maximum
ambient temperature
outside the enclosure
(To) To-Ti=ΔT
S T E P T W O S T E P T H R E E S T E P O N E
1 Watt = 3.413 BTU/HR.
Determine the internal
heat load in Watts that
must be dissipated. 1 m2 = 10.76 ft.2
Calculate the exposed
surface area of the
enclosure: 2(h’ x w’) +
2(h’ x d’) + (w’ x d’) =
Area (ft2)
C o o l i n g A n d C o n t r o l C a b i n e t s
The effect of significant restrictions in
the cabinet air flow path are as follows:
The obstructions cause pressure drops,
which leads to cool air flow reduction.
This reduction in cool air flow will
decrease the effective capacity of the
cooling unit. When selecting the
proper cooling unit, allowance must
be made for pressure drop.
Heat Load From The Surroundings
Ambient conditions can cause a heat
gain in the enclosure. The rated
capacity of the cooling unit must be
sufficient to handle this heat gain.
When evaluating the additional heat
load gained from the surroundings,
the subject more or less breaks down
into two situations: (1) the cabinet is
insulated and well sealed, or (2) the
cabinet is not insulated (most cabinets
are uninsulated.)
(1) Cabinet Insulated — Normally, well
insulated cabinets will not gain suffi-
cient ambient heat to affect air condi-
tioner’s operation. Maximum operating
temperature for our air conditioners is
125°F. When the air conditioner oper-
aties in ambient temperatures below
125°F, the cooling capacity of the air
conditioner substantially increases.
(2) Cabinet Not Insulated —
Obviously, this design placed more of
a burden on the cooling unit. Heat is
conducted to the cool side. Thus,
high ambient heat will be readily
transmitted into the cooler enclosure.
To determine the additional capacity
required of our air conditioner installed
in an uninsulated cabinet, the surface
square footage of the enclosure must be
Cooling Control Cabinets
Most electrical & electronic control
systems generate a substantial
amount of heat during operation. This
heat factor is intensified as controls
are made more compact, perform
more functions, and are placed in more
confined areas. Additional problems
are encountered when the electronic
process control system is located on-
site in an industrial setting, rather than
in a clean computer room. The factory
environment can be hostile to the
point that performance and effective
life of the electronic components are
materially reduced, or the control sys-
tem fails completely. Ambient temper-
ature might be excessively high, as
that found in a steel mill. Moisture-
laden air and air-borne particulate
matter might be present to adversely
affect the electronic components, as
in the paper manufacturing industry.
Air conditioners are designed to perform
reliably under many of these harsh
conditions and to provide the cooling
and environmental protection required
by sensitive electronic production
control systems.
Factors Affecting Model Selection
This selection is presented as a basic
outline or checklist of the various
conditions to be considered when
choosing a cooling unit for a certain
application. The following are factors
which must be considered when
selecting a cooling unit:
Internal Heat Load — This is the heat
dissipated by the electronic controls.
It is expressed in watts. One watt
equals 3.413 BTU/HR. Thus, to obtain
the approximate cooling capacity
required to remove a specific heat load,
the following formula can be used:
Watts x 3.413 = BTU/HR
For example, a heat load of 800 watts
requires an air conditioner capable of
removing at least 2,730 BTU/HR.
Resistance to Air Flow in the
Enclosure
Air Flow is measured in cubic feet per
minute (CFM). To create an air flow of
any desired velocity requires that
pressure be produced by the blower
in the air conditioner. Resistance to this
blower-produced air flow is created by
obstruction within the cabinet in the
air flow path. The resistance itself is
called pressure drop (P.D.) and is
measured in inches of water column.
calculated to obtain the total effective
heat transfer area. For this calcula-
tion, use the surface area of the
sides, plus the area of the top, and
omit the bottom area of the cabinet.
Air movement outside the uninsulated
cabinet will increase the heat conduct-
ed from the ambient into the enclosure.
When there is little or no air circulation
outside the cabinet, the layer of air
immediately adjacent to the exterior
cabinet walls acts as an insulating
film. Exterior air movement dissipates
this insulating layer of air in proportion
to the velocity of the air flow. Substantial
am-bient air circulation will increase
the transmitted heat load imposed on
the cooling unit.
If the cabinet being cooled is not air
tight, then high ambient relative humidity
will adversely affect the cooling effec-
tiveness of the air conditioner. When
humid air infiltrates a poorly sealed
enclosure, the air conditioner is required
to use up valuable BTU/HR capacity
just to condense the moisture from the
internal air. Conversely, if the cabinet
is well sealed, high ambient relative
humidity, has very little effect on the
heat capacity of the air conditioner.
Steps For Sizing an Air Conditioner
Proper selection of an air conditioner
is determined by the following criteria:
• Required cooling capacity BTU/hr.
(complete Steps #1-4)
• Mounting requirements (top or side
mounting options)
• Dimension of air conditioner and
enclosure