For a plant running three shifts, you need a screw compressor built for continuous operation, with variable speed, sized so that it does not run at 100% all the time. The S 220 PM, with its permanent magnet motor, is the starting point for sites that run a lot. Above 22 kW, the S series goes up to 132 kW on quotation. A piston compressor, designed for intermittent use, should be ruled out.
Our page on compressors for industry and production describes a plant's compressed air installation. This article covers what changes when the plant never stops: the hours, the electricity, the heat and the maintenance.
How many hours does the compressor run?
Take a plant on three 8-hour shifts, 5 days a week, with 50 production weeks a year. This is an assumption: replace it with your own calendar.
- Hours per week: 24 × 5 = 120 hours.
- Hours per year: 120 × 50 = 6,000 hours.
- Running 7 days a week, all year: 24 × 365 = 8,760 hours.
By comparison, a single 8-hour shift, 5 days a week, is 2,000 hours a year. On three shifts, the compressor works three times as much, and everything that depends on hours is multiplied by three: electricity, wear, maintenance.
Electricity becomes the biggest cost
Over 6,000 hours, the compressor's electricity bill weighs far more than its purchase price. An order of magnitude, with a simple assumption: a 22 kW compressor running at 70% of its power on average.
- 22 × 0.7 = 15.4 kW on average.
- 15.4 × 6,000 = 92,400 kWh per year.
Multiply by your price per kWh, or run the figures in our compressor electricity cost calculator. Three actions weigh most on this figure on three shifts:
- Set the pressure to what you really need. Every extra bar is paid for over 6,000 hours.
- Fix the leaks. A leak also blows at night and at weekends. The leak cost calculator shows what they cost.
- Follow demand. That is the job of variable speed, covered below.
The three shifts do not use the same air
In many plants, the night shift runs fewer machines than the day shift. Measure consumption shift by shift before you choose.
Example: 3.2 m³/min at 8 bar during the day, 1.2 m³/min at night.
- One machine: the S 220 PM delivers 3.6 m³/min at 8 bar and covers the day. Its variable speed reduces flow at night.
- Two machines: an S 220 PM for the day and an S 110 (1.7 m³/min at 8 bar) that handles the night on its own. The small machine works in its best range, and the plant keeps air if one of the two stops.
For a smaller site, under 2 m³/min, the S 150 delivers 2.2 m³/min at 8 bar. Our article on variable speed or fixed speed explains why variable speed matters on a changing profile.
Heat, day and night
Almost all the electrical energy a compressor draws ends up as heat in the plant room. On three shifts, that heat never stops, summer nights included. The room must remove it continuously: fresh air in low down, hot air out high up, without recirculating hot air to the intake. See the compressor room and why a compressor overheats.
Condensate, with nobody there to drain it
At night, nobody thinks of opening a drain valve. In continuous operation, fit an automatic condensate drain on the receiver and filters, and a dryer sized for the compressor's maximum flow. See which air dryer to choose.
Maintenance without stopping the plant
Our screw compressors need a first service at 500 hours, then one every 1,500 hours. Over 6,000 hours a year:
- 6,000 ÷ 1,500 = 4 services per year, after the first one.
- Over 8,760 hours: 8,760 ÷ 1,500 = nearly 6 services per year.
Schedule them during planned shutdowns or at weekends, keep the service kits in stock and log the hours. The controller shows a reminder at each due date. If the plant never stops, a second machine or a rental compressor supplies the air during the service. Our rental screw compressors range from 5.5 to 132 kW.
For a site of this size, see also our industrial projects, or send us your consumption per shift with a quote request.
For your trade: Compressor for industry and production.