Energy consumption and energy efficiency is a major issue for many compressor operators.
While there are a number of fairly well known methods for keeping on top of energy consumption, and often we think we know it all – fix the leaks; change the filters; regularly maintain your compressor; ventilate; recover generated heat; invest in VSD, there are some lesser known yet clever ways to cut your bills further down.
1- Use two compressors instead of one: Although it may sound strange it works. As an example, if you have a required capacity of 10.5 m3/min, instead of investing in a 75 kW screw compressor with VSD (with a capacity of 11.7 m3/min) an alternative option is to purchase a 55kW machine for base load supply and combine it with a small piston compressor to cover peak demand.
To begin with,initial investments can be much lower in this scenario. Secondly, significantenergy savings can be made by reducing the base load operating pressure. A rule of thumb is that every 2psi increase in operating pressure requires an additional 1% in operating costs of energy, and vice versa.
Another example is combining a fixed speed with a VSD unit.This configuration, as depicted in the schematic below, allows for nearly 100% turn-down capabilities (as would be the case for a single large VSD unit with twice the capacity). In this example, all the benefits of a single-duty, large VSD unit can be achieved for a smaller upfront cost by combining smaller VSD unit with a fixed-speed unit for base-load supply.
2 – Energy savings with fixed speed compressors: Although variable speed units are generally believed to be the best option to achieve energy savings, they may not be the best option for your scenario. If your compressor operates most of the time at full load, look for a modern fixed speed compressor, possessing energy saving features. A good example is Hitachi Hiscrew compressors series NEXT. With new increased capacity, an energy saving cooling fan system and ECOMODE operation there are many energy saving features to be found in the fixed-speed models.Also by lowering the cut-off pressure as per the load ratio of your compressor,you’ll get a great combination of relatively low initial investments (compared to a VSD unit) with 2-4% energy savings through the lifespan of the equipment. 4% savings could save you several thousand dollars per year – makes sense, doesn’t it?
3 – Not all VSD’s are the same: New VSD compressor models feature constant pressure control which maintains constant pressure at all times, without a pressure drop.
This reduces pressure undershoot under fluctuating load situations and enables the minimisation of control pressure setting to reduce power consumption. New, Hitachi VSD models have the ability to operate in PQ Wide-mode – giving the ability to operate at 105% flow capacity (at slightly reduced pressure) or at a higher then specified pressure (at a reduced flowrates) and still be energy efficient.
4 – Air Auditing: The last point won’t be revelation, as the importance of air auditing is hard to overestimate, with over 70% of the total costs of the compressor being energy consumption.