t67 Calculate Enclosure Heat Load
t67 Calculate Enclosure Heat Load
t67 Calculate Enclosure Heat Load
HARMFUL HEAT
Like people, industrial electronics can over-heat, causing malfunction and even complete failure.
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The good news is that electronic components can be kept cool to extend their life and prevent expensive operations downtime.
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LEARNING OBJECTIVES
Understanding why temperature variation can be a problem Understand the consequences of over-heated electronics Learn the benefits of cooling industrial electronics Identify the sources of damaging heat Learn how to size a cooling unit for your cabinet
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VARIABLE FREQUENCY DRIVE (VFD) SERVO DRIVE PROGRAMMABLE LOGIC CONTROLLER (PLC) STARTER KIT POWER SUPPLY INVERTER RELAYS TERMINAL BLOCKS INDICATOR LIGHTS TRANSFORMER*
* Typically outside the control panel, but can sometimes be included inside the enclosure
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Electrical characteristics Threshold voltage = Applied voltage to the gate The higher the temperature , the higher the threshold voltage trigger point requirements May cause the transistor to drift out of design requirements The higher the temperature, the longer it takes for the gate to open The higher the temperature the greater the internal resistance the gate may not open at all HOFFMAN MCLEAN SCHROFF Result: the gate does not open when it is designed to, which HOFFMAN MCLEAN SCHROFF adversely affects other components on the circuit Life Expectancy Properties of silicon oxide used in the components changes with temperature fluxuations
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In Wiring Insulation Elasticity and strength are reduced Ductility increases temporarily Atomic Mobility increases
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42 C / 108 F
32 C / 90 F
50% 100%
22 C / 72 F
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40
50
60
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90
100
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Lost production+ direct repair cost + lost opportunity cost= Cost of downtime
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VARIABLE FREQUENCY DRIVE (VFD) APPROX. 95 TO 98% EFFICIENT SERVO DRIVE >85% EFFICIENT POWER SUPPLY APPROX. 60 TO 83% EFFICIENT TRANSFORMER* APPROX. 95-99% EFFICIENT
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* Typically outside the control panel, but can sometimes be included inside the enclosure
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IRON FOUNDRY MINING Heat radiates into the HOFFMAN MCLEAN SCHROFF HOFFMAN MCLEAN from SCHROFF control cabinet outside
WELDING PROCESS INTENSE LIGHTING Applies extra heat load to the automation electronics inside
SOLAR HEAT GAIN HOT WEATHER Dark-painted enclosures collect more heat than light-colored cabinets
DRYING OVEN BLAST FURNACE Many factories around the world are hot environments and use automation equipment
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TMAX
Heat Load TA
The difference between the Maximum Internal System Temp. and the Ambient Temperature. T = TMAX - TA
AMBIENT
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CONVERSIONS/ASSUMPTIONS
1 Watt = 3.413 BTU/HR 1 HP = 746 Watts 1 HP = 2546 BTU/HR If the efficiency of the drive is known, Watts lost to heat can be estimated if it is not supplied by the manufacturer. 50 HP drive = 37,300 Watts potential power consumption. If 93% efficient, and operating at full capacity, MCLEAN 2,611 SCHROFF Watts lost to heat = 8,911BTU/HR cooling required. MCLEAN SCHROFF
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A/Cs and HXs create air movement over a cool surface which pulls heat out of the enclosure.
A/Cs cooling source is refrigeration system therefore, capable of temps below ambient. Heat exchanger cooling source is ambient air therefore, can never create temps below ambient. HOFFMAN MCLEAN SCHROFF HOFFMAN MCLEAN SCHROFF Forced Convection (open loop)cooling source is ambient air therefore, can never create temps below ambient.
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CONDUCTIVE COOLING
Cooling that maintains the protective seal of the cabinet, typically with an air conditioner or heat exchanger
Cooling that circulates fresh air through the cabinet to take damaging heat away
Cooling that allows the heat to simply radiate through the cabinet
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AMBIENT TEMPERATURE The maximum temperature outside the enclosure. ELECTRONICS TEMPERATURE The rated or desired temperature for the electronics inside the enclosure.
Electrical Enclosure
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IF ELECTRONICS TEMPERATURE MUST BE LOWER THAN AMBIENT TEMPERATURE Then air conditioners, air-to-water heat exchangers, thermoelectric coolers or vortex coolers are selected.
IF ELECTRONICS TEMPERATURE CAN BE HIGHER THAN AMBIENT TEMPERATURE Then filter fans, axial fans, fan trays or air-to-air heat exchangers are chosen.
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-48/105
-47/106
-47/118
-47/118 -39/113 -36/116 -40/118
-42/111
-37/114 -37/112
-30/110
-40/128
-50/122
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-27/120
-29/120
-22/113
-34/110
-23/120
-10/111
-80/100 12/100
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-2/109
VFD
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METHODS TO DETERMINE INTERNAL HEAT LOAD 1. Data from Each Electronics Component 2. Component Power Component Efficiency 3. Incoming Outgoing Power 4. Automated Equipment Horsepower
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VFD
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GATHER HEAT LOAD DATA OF EACH ELECTRONIC COMPONENT Ask your customer . . . How much heat is being generated from each electronic component in your enclosure?
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System uses two components that draw 115 VAC at 15 amps. Each has a rated efficiency of 90% (10% of each device becomes heat).
Estimated internal heat load is: Device Power = 115 x 15 = 1725 W Total Power = 2 x 1725 = 3450 Less Efficiency = 3450 x (1 - .90) Total Heat Load = 345 W
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An enclosure has three input lines of 230 VAC at 11, 6 and 4 A. It has one output control line of 115 VAC at 9 A.
Estimated internal heat load is: Incoming Power = (230 x 11) + (230 x 6) + (230 x 4) = 4830 W Outgoing Power = 115 x 9 = 1035 W Total Heat Load = 4830 1035 = 3795 W
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A cabinet has three 5-hp VFDs with 95% efficiency Estimated internal heat load is: VFD Watts = 5 hp x 745.6 x 3 = 11184 Adjusted Watts = 11184 x (1 - .95) = 559 Total Heat Load = 559 x 1.25 = 699 W
1.25 is an assumed safety margin for other minor heat producing components.
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METHODS TO DETERMINE HEAT TRANSFER LOAD 1. Simple Chart Method 2. Equation Method
REMEMBER The higher the ambient temperature and/or the presence of solar heat gain on the enclosure, the more cooling capacity is required.
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SURFACE AREA (ft.2) = [2AB (in.) + 2BC (in.) + 2AC (in.)] 144 SURFACE AREA (m2) = [2AB (mm) + 2BC (mm) + 2AC (mm)] 1000000 Total Heat Transfer Load = Heat Transfer per ft.2 or m2 x Cabinet Surface Area
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A painted steel enclosure has 80 ft.2 of surface area and will be located in a maximum ambient temperature of 95 degrees F. The rated temperature of the electronics is 75 degrees F. Estimated internal heat transfer load is: T = 95 75 = 20 F Heat Transfer = 4 W/ft.2 (from chart) Total Heat Transfer Load = 80 x 4 = 320 W
If system will be deployed outdoors, solar heat gain will need to be added. We recommend utilizing the online Product Selection Tool in these instances.
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Definition of Variables q = Heat transfer load per unit of surface area To = Maximum ambient temperature outside the enclosure Ti = Maximum rated temperature of the electronics components ho = Convective heat transfer coefficient outside the cabinet Still air: h = 1.6 Relatively calm day: h = 2.5 Windy day (approx. 15 mph): h = 6.0 hi = Convective heat transfer coefficient inside the cabinet Still air: h = 1.6 Moderate air movement: h = 2.0 Blower (approx. 8 ft.3/sec.): h = 3.0 R = Value of insulation lining the interior of the enclosure walls No insulation: R = 0.0 1/2 in. or 12 mm: R = 2.0 1 in. or 25 mm: R = 4.0 1-1/2 in. or 38 mm: R = 6.0 2 in. or 51 mm: R = 8.0
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Online Product Selection Tool: Total heat load = 1733 W BTU/Hr. = 1733 x 3.413 = 5914
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HOFFMAN HOFFMAN
POWER INPUT 115 VAC 50/60 Hz 230 VAC 50/60 Hz 230 VAC 50 Hz MCLEAN SCHROFF 460 VAC 50/60 Hz single-phase MCLEAN SCHROFF 460 VAC 50/60 Hz three-phase 24 VDC 48 VDC
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As you select a Fresh Air Cooling product, you will use Air Flow
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HOFFMAN MCLEAN SCHROFF
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Static Pressure is the air flow restriction caused by electronic components. Here are three examples:
(187 Pascal)
(436 Pascal)
You will also use Static Pressure to choose Fresh Air Cooling
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Determine Delta-T The difference in maximum desired temperature for the electronics and maximum temperature outside the enclosure Electronics vs. Ambient Temperature Difference (T)
Maximum Ambient Temperature
Example
Delta-T = Delta-T = 35C (95F) Maximum Electronics Temperature 10C (18F)
Determine Heat Load The amount of heat to be removed from the enclosure Electronics Heat Load
Example
System Efficiency Heat Load = 10000 Watts Drawn by the Electronics System
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Free Air Flow Requirement
2000
180 306
Under-Sized
Below 180 CFM (306 M3/Hr) target
Light Airflow Restriction SF13 376 CFM (638 M3/Hr) Filter Fan
Light Airflow Restriction SF13 473 CFM (803 M3/Hr) Filter Fan
Right-Sized
At the 180 CFM (306 M3/Hr) target
Over-Sized
Above 180 CFM (306 M3/Hr) target
Designers should confirm the filter fan model with a system test
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HOFFMAN MCLEAN SCHROFF
Static Pressure
2 1 0 0 200 400
249
(in. of H20)
600 400
800
(Pa)
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Static Pressure
Fans - High Volume Low Pressure MIs - High Volume Medium Pressure Centrifugal Blower - High Volume High Pressure Radial Blower - Low Volume High Pressure HOFFMAN MCLEAN SCHROFF
5 4
680 498
374
1000
1200
1400
General vs. concentrated air flow Amount of air volume Ability to overcome air flow restrictions caused by electronic components Component price Power input (AC or DC volt) Ability to protect the electronics from dust and water
You will need to carefully consider your Fresh Air Cooling options
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A typical application. An extra exhaust grille HOFFMAN cabinet MCLEAN to SCHROFF is added to improve Pressurizes HOFFMAN MCLEAN help keep out dust. SCHROFF air flow and cooling.
Pull design is less desirable because dust can be sucked inside the cabinet.
Push / pull is used to increase air flow through more tightly packed cabinets.
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Air mover type (fan tray, blower, etc.) Air flow (CFM or M3/HR) Enclosure system air resistance Static pressure (air flow drive)
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AIR-TO-AIR HEAT EXCHANGER Quickly radiates heat away from the enclosure by circulating cool air through a metal core
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COMPACT AXIAL FAN Circulates cool air through or within the electrical enclosure 19 FAN TRAY AND BLOWER Fits a standard 19 data rack, blowing fresh cool air through the electronics
VORTEX COOLER Cools electronics lower than temperatures outside the enclosure using compressed air
ENCLOSURE HEATER Used to warm electronics rather than cool them. Also reduces condensation inside the electrical enclosure
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SUMMARY
Understanding why temperature variation can be a problem Understand the consequences of over-heated electronics Learn the benefits of cooling industrial electronics Identify the sources of damaging heat Learn how to size a cooling unit for your cabinet
PENTAIR
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