Heating with Compressed Air

Sords Electric and Convectronics offer Compressed (flameless) Air Heating, up to 1400 degrees F.

The energy (kW) requirement is calculated from the following formula:

 

KW = SCFM x (Texit – Tinlet) (ΔT) / 2500

SCFM = Air flow in Standard* Cubic Feet per Minute

Tinlet = Inlet Air Temperature (°F) (typically 70°F)

Texit = Desired Exit Air Temperature (°F)

[The temperature difference is also know as delta T (ΔT) ]

Example: Heating 10 SCFM from ambient temperature (70°F) to 800°F:

KW = 10 SCFM x (800°F – 70°F) / 2500 = 2.9 kW

Conversion Formulas:

(Liters per Minute)/28.3 = Cubic Feet per Minute

°C = 5/9 (°F – 32)

°F = 9/5°C + 32

Using an Air Heater:

If used properly, heater life of 5000 hours or greater can be expected. To ensure long heater life and safe operation, follow these guidelines. Also read and understand your heater Operating Manual before use. Failure to follow these guidelines can result in heater damage, failure, or personal injury. 

Air Sources:

In general, compressed air, and air from regenerative blowers may be used to supply Convectronics flameless air heaters. Your air source should be clean and dry. Dirt, grease, oil, or oil vapors, or corrosive or reactive gases will damage an air heater. Also, use air or inert gas only. Do not use with volatile or combustible gases.

Regenerative Blowers:

Regenerative blowers are compact and inexpensive clean air sources. They can provide large amounts of low-pressure air for your air heating system. 

Compressed Air:

Compressed air is commonly available in most factories. It is high-pressure regulated air (typically to 100psi), and often contains oil for lubricating pneumatic valves and equipment. You must filter this oil to prevent fouling and damage to Convectronics electric air heater elements.

When measuring compressed air flow rates, be sure you are measuring Standard CFM or Standard LPM units. The "Standard" means that the units are measured at standard temperature and pressure. Many flow meters are labeled SCFM, but this is incorrect at the higher pressures produced by compressed air. For accurate flow measurements, you must consult your flow meter manual for converting CFM to "Standard" CFM. In the diagram below, the flow meter reading (CFM) is converted to SCFM using a Dwyer ball-type flow meter conversion.

Controls:

A good control system is critical for long heater life. Before turning your control system on, you must have sufficient airflow through the heater before applying power. (Applies to heaters without over-temperature protection.) Only qualified individuals should install Convectronics heaters and controls. Follow all applicable electrical codes and use proper wiring, fusing and safety procedures.

Open-Loop (Manual) Control:

This simple method of control uses a manually operated power controller to apply a fixed voltage to the heating element. Using this system, the operator manually adjusts the controller to change heater temperature. Note that if the airflow is suddenly interrupted, the element could fail. The open-loop controller is generally used with Convectronicss Series heaters.

Closed-Loop (Feedback) Control:

A closed-loop heater control system uses a power controller, temperature controller, and thermocouple to provide a constant output temperature, regardless of changes in airflow. The temperature controller also provides a convenient display of your process air temperature.

Power Controller:

Phase angle fired SCR (Silicon Controlled Rectifier) power controls will provide the smoothest power regulation for  Air Heaters.

Temperature Controller:

Use only digital temperature controls with type-K thermocouple inputs. The temperature control output must match the input of the power control. (i.e. 4-20mA, or 0-10VDC).

A standard PID-type control with a wide proportional band setting will work best to minimize temperature overshoot. PID parameters may be auto-tuned, but only at temperatures well below the maximum of the heater. If the temperature rises too high during auto-tune, turn power off immediately.

When using a Solid State Relay power control, the temperature controller cycle time should be set for 100ms or less.

Thermocouple:

Use only a fine-wire (.030" max wire dia.), exposed-junction, type-K thermocouple placed within 1" of the heater exit for accurate temperature readings. Other thermocouple styles, or varying the distance from the heater exit will result in temperature measurement errors and/or heater failure.

Air Flow Conversions:

SCFM = SCFH / 60 = SLPM / 28.3
SLPM = SCFH / 2.12
SCMH = SCFH / 35.3
SCFM = (Pounds of Air Per Minute) / (.080 lbs/ft3)

SCFM = Standard Cubic Feet per Minute
SCFH = Standard Cubic Feet per Hour
SLPM = Standard Liters per Minute
SCMH = Standard Cubic Meters per Hour

Single Phase Wiring:

V = I x R (Volts = Amps x Ohms)
I = W / V (Amps = Watts / Volts)
W = V2/R (Watts = (Volts x Volts) / Ohms)
Use our Ohms Law Calculator

Three Phase Wiring:

Delta Configuration:

R = R1 = R2 = R3
Wdelta = 3(VL2)/R
Wdelta = 1.73 x VL x IL
IP = IL/1.73
VP = VL

Wye Configuration:

R = R1 = R2 = R3
Wwye = (VL2)/R = 3(VP2)/R
Wwye = 1.73 x VL x IP
IP = IL
VP = VL/1.73

Percent Loss of wattage with lower than rated voltages applied:

230-volt heater on 208 volts - 82% (18% loss)
240-volt heater on 208 volts - 75% (25% loss)
480-volt heater on 277 volts - 33% (66% loss)
480-volt heater on 440 volts - 84% (16% loss)
480-volt heater on 318 volts - 44% (56% loss)
550-volt heater on 480 volts - 76% (24% loss)

To convert KiloWatts to BTUs:

Multiply  KW x 3413 = BTUs

°F (Farenheit)	=	(9/5°C) + 32
°C (Celsius)	=	5/9 (°F - 32)

For application help, please call Sords Electric - 216-765-4230
www.sordselectric.com