The idea
Some compressors are most efficient at full load, while others, such as variable-speed machines, are efficient across a range. In a base and trim arrangement, the efficient fixed-speed machines carry the steady load and a variable-speed machine adjusts to follow demand.
When it fits
Good conditions for base and trim:
- Demand that has a steady part and a variable part
- A mix of fixed-speed and variable-speed machines
- A requirement for a stable pressure
- Enough capacity that the trim machine is not working outside its useful range
Things to check
Before adopting it:
- The usable turndown of the trim machine
- The pressure bands and how the machines are ranked
- What happens when the trim machine is down
- Whether the controls can actually coordinate the machines
Verify the benefit
Compare power and pressure before and after under similar demand. The benefit depends on the plant and must be measured, not assumed.
What to prepare
Information that helps us advise:
- Number, make, model and size of the compressors
- Current controllers and how they are connected
- Pressure settings and the lowest pressure the process needs
- Demand pattern across shifts and any known problems
Frequently asked questions
What is a trim compressor?
A machine that adjusts its output to follow the changing part of demand, often a variable-speed machine.
Can I run two variable-speed machines instead?
Sometimes, but two machines both running at low speed may be less efficient than one trimming and the other at steady load. It depends on the machines.
Does base and trim need a master controller?
Usually some form of coordination is needed so that the machines do not fight each other.
Field guide
Base and trim: let each machine do what it is best at
Most plants have a steady base demand and a variable part on top of it. The efficient arrangement is to run one or more fixed-speed compressors fully loaded on the base, and let a single trim machine, ideally a variable-speed compressor, follow the variable part.
Rules that make base and trim work
- Only one trim machine at a time. Two machines trimming together both run part-loaded.
- Size the trim range to cover the swing. If the trim machine's range is smaller than the step between base machines, there will be a "control gap" where a fixed machine unloads and the trim machine cannot fill the hole.
- Keep the VSD in its efficient range. Below its minimum speed a VSD starts to load and unload like a fixed-speed machine.
- Give the system enough storage so that pressure does not collapse while a base machine starts.
A quick check
Look at the hours meters. If a fixed-speed machine shows a large share of unloaded hours, it is acting as a trim machine and wasting energy. Look at the VSD's speed trend: if it spends most of its time at full speed, it is too small for the swing; if most of its time at minimum, it is too big or the base is too small.
What to send for a quotation
- Make, model and serial number of every compressor and dryer in the station.
- Running hours and a typical week of operation (shifts, weekends).
- Current pressure settings and controller type on each machine.
- Any alarm or fault history you have.
Send it through find my part or the spare parts enquiry, or call +91 99590 60718 or +91 92468 88812.