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Master Controllers

1.1           Scope

Master controllers are microprocessor-based controllers that can be used to improve the control of compressed air systems with two or more compressors. They realise energy savings by reducing the pressure fluctuations that are normally present in compressed air systems when simple cascade or sequence controls are used to maintain system pressure, and by allowing users to schedule compressor operations that reflect working patterns.

To be eligible for inclusion on the Energy Technology List (ETL), products shall meet the requirements as set out below.

1.2           Definitions

Master controllers are products that are specifically designed to control the operation of multiple air compressors in a manner that maintains the operating pressure of the compressed air system within a narrow band, thereby minimising energy consumption.

1.3           Requirements

1.3.1       Eligibility requirements 

To be eligible, products shall:

  • Be able to automatically control the operation of:

1.    At least two air compressors.

2.    Both fixed speed and variable speed compressors.

3.    Any positive displacement compressor that is capable of accepting a remote load/unload control signal via a volt-free switching circuit or electromechanical pressure switch, or in the case of variable speed drives capable of accepting a speed control signal or a remote pressure set point adjustment.

  • Incorporate a microprocessor based controller that is pre-programmed to provide facilities for users to:

1.    Detect/determine efficiency to load level curve for Variable speed compressors.

2.    Prioritise the use of more efficient compressors over less efficient ones, whilst making optimal use of any variable speed compressors being controlled (including optimal efficiency of variable speed compressors).

3.    Schedule the times of the week (in intervals of five minutes or less) when the compressed air system should be switched on and off and be operated at a reduced pressure.

4.    Schedule at least two different operating pressures for the compressed air system (to enable for example operation at lower pressure at off peak times).

5.    Define the minimum and maximum limits for the operating pressure (or pressure band) that the controller must maintain the compressed air system within.

  • Incorporate an anti-tampering mechanism that prevents automatic control from being disabled, except during commissioning, maintenance or testing.
  • The Master controller shall be capable of controlling any air compressor, regardless of compressor manufacturer.
  • Incorporate a pressure transducer that has a measurement accuracy of at least (i.e. <=) +/- 0.5% of full scale across its rated operating pressure range and across a rated temperature range of –25 to 80 degrees Centigrade.
  • Incorporate automatic control algorithms that monitor rate of change in system air pressure/flow and prevent compressors from being brought on load or unloaded in response to small fluctuations in demand.
  • Be capable of automatically regulating the operating pressure of the compressed air system (where all compressors in the system are situated at a single location), based on the output of a single pressure transducer, to within +/-0.1 bar of the operating pressure set-point, as air demand varies in 60 seconds between 10% and 100% of the maximum combined, continuous, rated output of air compressors being controlled.
  • Conform with the requirements of The Electromagnetic Compatibility Regulations 2016, and have an appropriate Conformity Assessment mark.

Where products provide facilities for operators to override automatic control, they must be pre-programmed to return to automatic control at the next scheduled time for system switch off / on, and to automatically reset the override within 24 hours.

Where products are also designed to control desiccant air dryers, they must also satisfy the eligibility criteria for ‘energy saving controls for desiccant air dryers.

Automatic control may be implemented either directly by means of an analogue or digital signal connection, or indirectly by means of another control device or network. Where products are designed to indirectly control variable speed compressors, they must be capable of monitoring the operating speed of the variable speed compressors, and of remotely adjusting the speed or pressure set points (or pressure or speed range limits) within the variable speed compressor’s control device.

Products that cannot directly control the speed (or speed range) of a variable speed compressor, or indirectly control their speed of operation by adjusting their pressure set points, are not eligible.

1.4           Verification for ETL Listing

There are no testing requirements, however manufacturers shall provide sales and technical brochures to evidence the conformity of their products against the requirements from section 1.3.

1.5           Conformity testing

Products listed on the ETL may be subject to the scheme’s conformity testing programme in order to ensure listed models continue to meet the ETL requirements.

1.6           Review

1.6.1       Indicative review date

This technology specification will be reviewed in 2022-23

1.6.2       Illustrative future direction of the requirements 

Future changes in Technology Specification may include:

  • Master controllers shall enable a much tighter running of compressors to match demand. Software upgrades could be upgraded to detect if there is excess demand due to a leak in the system.
  • Master controllers shall monitor and report the energy savings achieved by the end user as a result from its installation. Through this monitoring, the device would be capable of making recommendations to the user for better system performance.