Energy Savings through Tank Storage

The case for installing a tank receiver

There is no simple formula to calculate the savings from installing a larger receiver tank, but the logic is fairly simple. The key benefit of a receiver tank is that it consumes zero energy and requires no maintenance.

Switching from load to idle

A fixed-speed compressor, Kaeser or any other, will typically use its full motor horsepower (and, therefore, full kilowatt draw) when it is fully loaded and making compressed air. When the machine achieves your system set pressure, it receives a signal to switch from load to idle. When it runs in idle, the power consumption is reduced by 60 percent.

Let’s use a fixed-speed 75 horsepower Kaeser CSD compressor to demonstrate how this works:

• 75 hp translates to 55 kW.
• At full load, a 75-hp Kaeser compressor consumes 55 kW. In idle, it consumes 22 kW.
• If the plant operates 8,000 hours per year, the power consumption costs $57,200 (55 kW x 8,000 hours x $0.13 for energy).
• The loaded hours run without a receiver tank are 20,600.
• The total hours run without a receiver tank are 31,000.
• This confirms that the loaded power is reduced by 60 percent (when we switch load to idle for approximately 32 percent of the time).

So, it’s clear that if we are able to increase the amount of time a compressor runs in idle we can reduce electricity costs.

Increasing tank size

Increasing the tank size can result in even greater energy savings. For example, upsizing from a 660-gallon tank to a 1,060-gallon tank (a percent capacity increase), should increase idle time by 62 percent.

The example above covers a fixed-speed compressor. Using a tank with a variable-speed compressor will not achieve energy savings to the same extent because the compressors are more efficient, but it will still increase idle time.

Additional benefits

Beyond idle time, there are additional benefits associated with adding a receiver tank to any compressed air system, whether fixed or variable speed.

When a Kaeser compressor switches to idle, it automatically engages a 4-minute, factory set, run-out timer. If no compressed air is called for in this 4-minute period, the compressor automatically stops and the energy consumption becomes zero. Getting the compressor to time out should always be the target, which is why we always say “you can never have enough storage.”

In addition, the tank acts as a buffer for the compressor’s control valving. This prevents rapid cycling and premature wear and tear of valves inside the machine, which, in turn, reduces maintenance costs.

The tank also slows the velocity of air and creates a cyclonic motion as the air passes through it. This reduces the oil/water condensate load on all downstream clean air treatment filters and dryers, further reducing filter and other maintenance costs.

That sums up the cost-benefit analysis of adding or upsizing a receiver tank. Let us know if you have any questions. We’d be happy to do a site visit and provide recommendations to help you optimize your compressed air system and reduce your total cost of ownership.