Page 13 - INDEX Summer 2024

VICE CHAIRMAN ’ S VICE CHAIRMAN ’ S

S AY S A Y C ONTINUED . . .

C O MMIS SIONING – B A CK T O B ASIC S ? Test Point Locations

There is no doubt that the building service industry has made great strides in the last few years in terms This leads to an associated element of functional testing and regulating systems that needs
of achieving and maintaining improved space conditions in buildings and promoting better air quality. underlining. A pitot tube traverse location or the location of an orifice plate must be as detailed in
This progress has been achieved through more sophisticated equipment and better controls and the relevant CIBSE commissioning code or BSRIA Guide. These provide detailed guidance on siting
software. The result is that today’s commissioning engineers need to have at least a working knowledge measurement points with sufficient straight, uninterrupted ductwork or pipework up and downstream
of some complex systems. 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
However, it is worth reminding ourselves that the basis of all of these systems is still a fan moving for the designer and installer as for the commissioning engineer.
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 Initial Readings
ductwork, achieving the required specified conditions will be difficult, irrespective of the sophistication
of the controls. 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),
To that end, the CSA thinks that it is time to remind everyone of some of the basic requirements of the the commissioning engineer MUST record the initial indicated rates of flow at all terminals. Index
commissioning process. 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
First and foremost is understanding the fan laws. There are three of them and, although usually referred invaluable in indicating the extent of the balancing required on the system. They may also be useful
to as the fan laws, they also apply to pumps: in the investigation of any problems, such as excessive noise or system resistance, experienced
with the system once it is balanced.
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 Correction Factors
increase by 10%.
Ventilation system correction factors should be established, wherever possible, for each type of
Number two: system pressure is proportional to the square of the rotation speed. That 10% terminal and flow capture hood in use. Where this is not possible, the commissioning engineer
increase in rotation speed will result in a (1.1 * 1.1) = 1.21 (that is 21%) increase in the must agree a suitable compromise with the design team and/or witnessing agent.
pressure at the fan/pump discharge.
System Reports
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) = The nature and complexity of some systems requires a narrative to describe the system, the
1.33, or 33%. 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
The other basic premise of air and water systems that requires a reminder is that the current drawn by simulated. This report should also include a pressure profile of the Fan/AHU and pump system
a fan or pump motor is related to the amount of air / water passed. More flow means more amperage pressures including closed head readings. This makes it clear and easier for the consultant or
and less flow means less amperage. It is still common to encounter building services engineers that are witnessing authority to understand or the process to be repeated at a future stage.
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. 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.
Having got those basic tenets in place, there are five further elements that the commissioning engineer
(and designer / installer) all need to focus on: 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.
Calibrated Instruments
As well as our long term category sponsors Ashford Environmental Services, BSRIA, HDR, MBS Magazine,
Whether it is a micromanometer and pitot tube being used on a ventilation system, or an electronic Media Control and RED Engineering, we are now joined by Banyards and Core Emirates. We are also being
manometer being used on a heating / cooling system, the instrument must have a valid and indate approached by other organisations wishing to support the Awards – look out for further developments.
calibration certificate. Commissioning engineers also need to be honest with themselves. Did Make sure you have booked your seats – and submitted your entries!
you accidentally drop that instrument? If you did, you know it has to be checked against another
calibrated instrument and recalibrated if necessary. You can also find this full press release in the June edition of Modern Building Services.

Keith Barker – CSA Vice Chair & Director of TTL Keith Barker – CSA Vice Chair & Director of TTL