This document discusses energy conservation in compressed air systems. It provides an introduction to compressor capacity testing and calculations for determining actual free air delivery and specific energy consumption. Common methods for improving compressed air system performance are also outlined, such as addressing leakages, intercooling between stages, and optimizing operating pressures. Statistical data indicates that 10-20% of industrial electricity is typically used for compressed air, but only around 50% of the air supplied is actually used for production.

1. -Vishnu RC Vijayan
Energy Conservation In
Compressed Air Systems

2. Context
 Introduction
 Capacity/Pump-Up Test
 Methods To Improve Performance
 References

3. Introduction
 Every manufacturer specifies the FAD of the Compressor as the Motor
rating
 For Eg a 1000 Scfm (Standard cubic feet per minute) Compressor requires
a 220 KWH Motor
 So, 1000 x 60 Std. cu. ft of air per hour requires 220 KWH
 i.e 220 KW generates 60000 std cubic feet
 So, 1 KW generates 273 std cubic feet
 Cost of 1 KWH is @ Rs. 5.00.
 So, power cost of 1 cu. Ft. is @ 2 paise, or 0.02 Rupees
 Thus, the running cost for a 1000 Scfm Compressor, at 80% load, becomes:
1000 x 60 x 0.8 x 0.02 x 24 = Rs. 23K per day, or ~ @ 75 Lacs p.a.
 And we have not taken the Capital cost of the Compressor into account

4. Why Energy Conservation is Needed
Study Conducted by Forbes Marshall
 Air compressors account for significant amount of
electricity used in Indian industries. The average
for all Industries is around 10%

5. Statistical Data
 Between 10% and 20% of electricity consumed is for generating
compressed air itself
 Of the total cost, 76% is attributed to electricity, 12% to Maintenance
and 12% to Equipment and Installation
 Only 50% of a compressor's air supply is used for production
 The rest is lost through waste and air leaks

6. Pump-Up Test
To find out:
 Actual Free Air Delivery (FAD) of the
compressor
 Specific power requirement

7. Methodology of Capacity Test
 This test needs less skill and simple arithmetic calculation and
any skilled person can conduct the test under the supervision of a
qualified engineer
 Instruments needed for the test are:
(1) stopwatch (2) Clip on power meter which measures KW
 Use of conventional multi-meter to measure line current to
calculate the power should be avoided because the value of
power factor cannot be assumed and this may lead to wrong
conclusion
 Therefore, only clip on power meter should be used to measure
the actual power drawn by the air compressor panel meter
installed can be used

8.  The steps involved in conducting the test are- Isolate the air receiver from
the air network by closing the delivery valve after the receiver
 Measure the approximate volume of piping network and filters like oil
filter, intercooler and after cooler etc, between compressor and receiver in
m3
 Hold the clip on power meter in any one of the phase in the switch panel
Empty the air receiver and set the pressure gauge at 0 bar (gauge)
 Drain water from the receiver and do not forget to close the drain valve
Start the compressor and start the stop watch once the compressor comes to
loading mode
 Simultaneously measure the KW in the clip on power meter for each
pressure till the compressor reaches the normal working pressure Note
down the time in seconds taken to fill the receiver to the normal operating
pressure, i.e. compressor reaches unloading mode

9.  The compressor capacity is estimated using the equation.
Free air delivered using the following formulae:
Actual Free Air Delivered (Q) = [(P2-P1)/P0]*[V/T]
P2 = Final pressure after filling [kg/ cm2]
P1 = Initial pressure [kg/cm2 ] after bleeding
P0 = Atmospheric Pressure [kg/cm2]
V = Storage volume in m3 which includes receiver, after cooler,
and delivery piping
T = Time take to build up pressure to P2 in minutes.
 The above equation is relevant where compressed air
temperature is same as the ambient air temperature, i.e., perfect
isothermal compression
 In case the actual compressed air temperature at discharge, say
t2O C is higher than ambient air temperature say t1O C (as is
usual case), the FAD is to be corrected by a factor (273 + t1) /
(273 + t2)
Calculations

10.  Specific Energy Consumption
(SEC) = KW/FAD
 Isothermal Efficiency = Isothermal power / Input
power
Isothermal power kW= P xFAD x log(r)/ (36.7)
Volumetric efficiency= FAD/ (Compressor
displacement)
Compressor displacement = (∏/4 )X D2 x L x S x n
 ISO 1217:2009/Amd 1:2016

11. Methods to Improve Performance
 Location and Size of Filters
Low inlet temp
Filter to reduce Wear
 Elevation
Less to avoid Volumetric Efficiency
 Inter-cooling in between Stages
Economy in size and Cost of Receiver
To avoid Condensation in Receiver
 Optimizing Pressures

12.  Leakages
Estimated as major drawback
 Use of Blowers
 Pneumatic Tools

13. References
 Forbes Marshall
Surveyon Energy Conservation
 National Productivity Council
Website: http://www.em-ea.org/
 Bureau of Energy Efficiency
Website: www.beeindia.gov.in