Manufacturing client in Boise. The compressed air system is the single largest contributor to demand charges. Three 100 HP compressors running load-unload cycling. During unloaded periods the compressors still draw about 60% of full load power. When all three cycle into loaded mode simultaneously the demand spikes. Interval data shows demand swings of 150 kW entirely from compressor cycling. How common is this?
Compressed air systems ? the hidden demand charge killer
Margaret ? compressed air is typically 20-30% of total electrical demand in manufacturing facilities and its almost always the most inefficient system. Load-unload compressors at partial load are particularly wasteful. VFD compressors that modulate speed to match demand virtually eliminate the cycling spikes. Replacing one of three fixed-speed compressors with a VFD trim unit typically reduces compressed air demand by 25-35%.
Ruth ? the client is resistant to capital expenditure. A VFD compressor to replace one unit would cost $45,000-55,000. Any lower-cost alternatives?
Margaret ? before replacing compressors, check the system for leaks. Most compressed air systems lose 25-35% of output through leaks. Fixing leaks reduces the total air demand which means compressors run less and demand drops. An ultrasonic leak survey costs $2,000-3,000 and typically identifies enough leaks to reduce compressor load by 15-20%. Much cheaper than new equipment.
Thomas is right about leaks. Also check the system pressure. Many plants run compressed air at 110-120 PSI when equipment actually needs 80-90 PSI. Every 2 PSI reduction in system pressure reduces compressor energy by approximately 1%. Dropping from 110 to 90 PSI ? a 20 PSI reduction ? cuts compressor demand by roughly 10%. Zero cost to adjust the pressure regulator.
Thomas and Clifford ? great suggestions. The leak survey found 47 leaks ranging from tiny hose fittings to a major pipe joint. Estimated leak volume was 30% of total compressor output. Fixing the leaks allowed one of three compressors to be shut down entirely during normal production. System pressure was also reduced from 115 to 95 PSI. Combined demand reduction: 95 kW. At Idaho Power demand rates thats $760 per month or $9,120 annually. Total cost for leak repairs and pressure adjustment: $4,800. Two of three compressors now handle the load that previously required all three.