Compressed air efficiency, part 3: the energy study

Peter Moore, BC Hydro Energy Management Engineer

If your plant uses compressed air, there's a good chance you could save significant amounts of energy (and money) with some simple improvements. Compressed air (CA) is the most expensive utility in most plants, and it's easy to use it inefficiently.

But where's the best bang for your retrofit buck? Our compressed air efficiency series has already outlined multiple ways to save on compressed air (including managing demand and managing supply). However, to compare improvements and know which will pay back first, you need an energy study.

"Many experienced companies and their employees come up with good ideas about how to save energy, but they don't know how much those ideas are worth, or how much to spend on a retrofit," says Pete Moore, an energy management engineer for BC Hydro. "An energy study takes the opportunities and quantifies them in terms of how many kWh per year each one will save and what each retrofit project will cost. It builds a business case."

Financial support available

BC Hydro's Power Smart Industrial Program offers financial support to conduct an energy study (in some cases, an end-use assessment may be required first, also eligible for financial support). "Once each customer has an energy study report, then it's up to them to choose which measures they want to implement," says Moore. BC Hydro project incentives can then help cover capital costs.

What is an energy study?

An energy study is done on a discreet system within a facility — defined as a collection of machinery that operates on the same material. Although compressed air snakes throughout a plant, it is a discreet system because it carries compressed air from the point it is generated to the point where it is used. (If a plant has more than one distinct compressed air system, it might need two or more separate compressed air energy studies.)

A compressed air energy study assesses how compressed air is produced, filtered and dried, stored, distributed and used, as follows:

"A lot of the compressors in the province are very old and not very efficient," says Moore. "In the energy study, the main thing the consultant will do is measure the efficiency of the compressor itself, typically in cfm/kW." This helps determine whether a modern, more efficient compressor should be considered.

Filtering and drying
Compressing air causes the moisture that it holds to condense. This water must be removed so it doesn't damage equipment downstream. Some dryers use compressed air in their internal process (to dry out saturated dessicant); newer models use a blower or blower/heater combination to do the same job with less energy. Depending on system requirements, a refrigerant dryer may be used in place of a dessicant dryer.

Using appropriate storage can save money by reducing the amount of time a compressor must operate, or allow additional production with the same size of compressor. An energy study helps assess usage patterns to determine the most efficient combination of compressor size and storage volume for a plant's needs.

Distribution and usage
"Leakage is the biggest and most common inappropriate use of compressed air," says Moore. A single 1/4 inch leak at 100 psi costs more than $6,000 in wasted electricity. Reducing leaks and ensuring compressed air is only used in appropriate ways helps you reduce the compressor effort required in your system, for compounded savings. The energy study considers all these elements together — then provides a road map for improvement.

"Many of our customers have large compressed air systems that were built decades ago," says Moore. "But because energy was cheap, a lot of these systems aren't as efficient as they should be. Basically, any time you can do a job with anything other than compressed air, you are going to save money. Compressed air is expensive."

Read about experiences other companies have had with compressed air retrofits:

More detail about compressed air efficiency: