SCREW COMPRESSOR CALCULATION

 SCREW COMPRESSOR  CALCULATION:

A small machine shop has installed 220 cfm screw compressor to meet air requirement for various operation. The operating details are given below:

Shift reference

(8 hrs/ Shift)

Load time in sec

Un-Load time in sec

I

60

10

II

45

25

III

25

45

Load Power = 37 KW

Un-load power = 11 KW

Calculate the following:

1. Energy loss per day 

2. Shift wise average air requirement in cfm 

3. The plant has proposed to install a VFD for the compressor. Calculate the energy savings after installing the VFD operated compressor, if the VFD loss is 3 % of load power.

CALCULATION:

Ist shift consumption = ((60 / 70) x 37) + (10 / 70) x 11) x 8)

= (31.71+1.57) x 8

= 266.24 kWh

IInd shift consumption = ((0.64 x 37 + 0.36 x 11) x 8 )

= (23.68 + 3.96) x 8

= 221.12 kWh

IIIrd shift consumption = ((0.36 x 37 + 0.64 x 11) x 8)

= (13.32 +7.04) x 8)

= 162.88 kWh

Daily Total Energy consumption = (266.24 + 221.12 + 162.88)

= 650.24 kWh

Daily Energy loss due to unloading = (1.57 +3.96 +7.04) x 8

= 100.56 kWh

Daily load cycle Energy consumption = (650.24 – 100.56)

= 549.68 kWh

Daily energy consumption with VFD = (549.68 / 0.97)

= 566.68 kWh

Paper 3 Code : Pink

_______________________

Bureau of Energy Efficiency

15

Daily Energy loss due to VFD = (566.68 – 549.68)

= 17 kWh

Daily Net Energy savings with VFD compressor = (100.56 – 17)

= 83.56 kWh

Ist shift air requirement = (0.86 x 220)

= 189.2 cfm

IInd shift air requirement = (0.64 x 220)

= 140.8 cfm

IIIrd shift air requirement = (0.36 x 220)

= 79.2 cfm