Science

A metal foundry uses an average of 215 kW to produce compressed air at 125 psig to satisfy plant pressure requirements. The compressed air system operates 6,000 hours per year.

Pressuredrop in the compressed air system at the metal foundry has been attributed to the following components:
1. Dirty coalescing filters – 4 psig drop
2. Compressor room piping – 3 psig drop3. “Tee” piping junction in compressor room – 6 psig drop
4. Undersized distribution piping – 6 psig drop
5. Standard 3/8 inch quick disconnects – 11 psig drop

If the aboveequipment is replaced with the following, what will the annual cost savings be given an electric price of $0.07/kWh?
1. New, low differential pressure filters – 1 psig drop
2. Upgradedcompressor room piping – 0 psig drop
3. Angle piping junctions – 0 psig drop
4. Upgraded distribution piping – 2 psig drop
5. Industrial ½ inch quick disconnects – 4 psig dropCalculate the energy consumption of the current system-


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EU = Energy usage (kWh/yr)
P = Power draw (kW)
t = hours of operation (hrs/yr)


Calculate the costreduction due to reduced pressure drop-


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ES = Energy savings (kWh/yr)
pR = Pressure reduction due to reduced pressure drop (psig)
ECS = Energy cost savings ($/yr)ER = Energy rate ($/kWh)

*For every 1 psig reduction in compressor output pressure, compressor power consumption will be reduced by approximately 0.5%.Solution-


The pressure drop in the existing system totals 30 psig. By upgrading equipment, the pressure drop will be reduced to 7 psig. Therefore, the compressorout put power can be reduced by 23 psig while maintaining plant pressure requirements.


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Reduce Energy Consumption

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