Page 12 - INDEX Summer 2024

VICE CHAIRMAN ’ S VICE CHAIRMAN ’ S
S AY
C O MMIS SIONING – B A CK T O B ASIC S ?
There is no doubt that the building service industry has made great strides in the last few years in terms
of achieving and maintaining improved space conditions in buildings and promoting better air quality.
This progress has been achieved through more sophisticated equipment and better controls and
software. The result is that today’s commissioning engineers need to have at least a working knowledge
of some complex systems.
However, it is worth reminding ourselves that the basis of all of these systems is still a fan moving
air through ductwork or a pump circulating water round pipework. For example, unless a ventilation
system has the correct amount of air moving at the most effective speed throughout all the distribution
ductwork, achieving the required specified conditions will be difficult, irrespective of the sophistication
of the controls.
To that end, the CSA thinks that it is time to remind everyone of some of the basic requirements of the
commissioning process.
First and foremost is understanding the fan laws. There are three of them and, although usually referred
to as the fan laws, they also apply to pumps:
Number one: flow rate is directly proportional to rotation speed. If the fan or pump speed is
increased by 10%, the amount of air or fluid moved through the system will also
increase by 10%.
Number two: system pressure is proportional to the square of the rotation speed. That 10%
increase in rotation speed will result in a (1.1 * 1.1) = 1.21 (that is 21%) increase in the
pressure at the fan/pump discharge.
Number three: power absorbed is proportional to the cube of the rotation speed. The 10%
increase in speed results in an increase in electrical current drawn of (1.1*1.1*1.1) =
1.33, or 33%.
The other basic premise of air and water systems that requires a reminder is that the current drawn by
a fan or pump motor is related to the amount of air / water passed. More flow means more amperage
and less flow means less amperage. It is still common to encounter building services engineers that are
sure that if you close a fan discharge damper or pump discharge valve while it is running, the current
drawn will rise. No, it will not. It will drop.
Having got those basic tenets in place, there are five further elements that the commissioning engineer
(and designer / installer) all need to focus on:
Calibrated Instruments
Whether it is a micromanometer and pitot tube being used on a ventilation system, or an electronic
manometer being used on a heating / cooling system, the instrument must have a valid and indate
calibration certificate. Commissioning engineers also need to be honest with themselves. Did
you accidentally drop that instrument? If you did, you know it has to be checked against another
calibrated instrument and recalibrated if necessary.
Keith Barker – CSA Vice Chair & Director of TTL
S A Y C ONTINUED . . .
Test Point Locations
This leads to an associated element of functional testing and regulating systems that needs
underlining. A pitot tube traverse location or the location of an orifice plate must be as detailed in
the relevant CIBSE commissioning code or BSRIA Guide. These provide detailed guidance on siting
measurement points with sufficient straight, uninterrupted ductwork or pipework up and downstream
to ensure accurate readings. Any location that does not comply with the recommendations in those
documents will, by definition, cast doubt on readings. Providing suitable locations is as much a task
for the designer and installer as for the commissioning engineer.
Initial Readings
The commissioning engineer MUST record the initial total system flows and fan/pump pressures,
ensuring in excess of 100% of the design flow rate. For traditional systems (not VAV/PICV systems),
the commissioning engineer MUST record the initial indicated rates of flow at all terminals. Index
terminals should also be indicated on the test sheets. Any issues identified at this stage must
be investigated prior to proceeding with system regulation. Records of the initial readings are
invaluable in indicating the extent of the balancing required on the system. They may also be useful
in the investigation of any problems, such as excessive noise or system resistance, experienced
with the system once it is balanced.
Correction Factors
Ventilation system correction factors should be established, wherever possible, for each type of
terminal and flow capture hood in use. Where this is not possible, the commissioning engineer
must agree a suitable compromise with the design team and/or witnessing agent.
System Reports
The nature and complexity of some systems requires a narrative to describe the system, the
operating parameters, commissioning/proving process, and the reasoning behind this. An example
would be explaining how the system diversity was set up, or filters/strainer dirty condition was
simulated. This report should also include a pressure profile of the Fan/AHU and pump system
pressures including closed head readings. This makes it clear and easier for the consultant or
witnessing authority to understand or the process to be repeated at a future stage.
If commissioning engineers can reabsorb any of these basics back into their daily work ethics, the
individuals and the projects they are involved with will benefit greatly.
With my other hat on, it's great to see that the success of last year's CSA Awards is heading for a
repeat performance.
As well as our long term category sponsors Ashford Environmental Services, BSRIA, HDR, MBS Magazine,
Media Control and RED Engineering, we are now joined by Banyards and Core Emirates. We are also being
approached by other organisations wishing to support the Awards – look out for further developments.
Make sure you have booked your seats – and submitted your entries!
You can also find this full press release in the June edition of Modern Building Services.
Keith Barker – CSA Vice Chair & Director of TTL