By Ron Marshall
The pressure at which you operate your system has a significant effect on the energy efficiency of your air compressors, and can affect the air consumption of the compressed air powered tools and equipment in the plant. Running at higher pressure than desired causes higher system flow and more power consumption, increasing the cost of your compressed air, often with no additional benefit to the end user.
It takes a specific amount of energy to squeeze atmospheric air into compressed air. There is no way around it, this is governed by the laws of physics. A rule of thumb applies to compressed air, at around 100 psi it takes about one percent more power to produce a given amount of compressed air for every two psi increase in pressure. If you don’t use the compressed air at that higher pressure, the energy is just wasted as the compressed air is regulated to lower pressure.
For unregulated compressed air demands, for every one psi in higher pressure the flow increases by about 0.9%. This extra flow is called “artificial demand.” This additional flow increases the loading on the air compressor and causes it to consume more power—this is on top of the extra power it uses to produce the higher pressure in the first place.
For example, a 50 hp compressor that is fully loaded would consume about $900 in extra power at 10 cents per kWh if it ran about 4,000 hours per year (a two shift operation) at 10 psi higher pressure. The extra costs if running 24 x 7 would be about $1,800 per year.
The artificial demand costs due to extra flow might increase the costs another $800 for the two shift operation or $1,600 for full time operation if about 50% of the plant demand, including leaks, is unregulated (typical).
Often compressor room operators do not know why their compressors are running at high pressures. If your plant is running at 100 psi system pressure or higher there is likely a good potential opportunity to reduce operating costs by lowering system pressure.
Many times, one or more faulty devices, or something as simple as a clogged filter, may have forced the plant pressure to higher levels in the past to compensate. If you have high pressure it is time to investigate!