October 9, 2012

HVAC – A Fight for Control

We see it in everyday life and politics – fight for control over practically everything – territories, power, and supremacy. Well, looks like even the HVAC industry is not left out.

Are you really in control of a building if your BAS cannot give information virtually whenever and wherever we need it? This is a classic question the building facilities team often ask themselves. The building operator feels in control of his building through his mastery of the BAS system.

In an age of competitive selling, more and more HVAC equipment manufacturers supply their HVAC equipment like AHUs, Boilers & Chillers etc. complete with on-board logic controllers, e.g.: C-Trac & W-Trac for ‘Engineered Air’ AHUs, Tracer Summit for Trane AHUs, Microtech-III for ‘McQuay’ AHUs, and CoolLogic for ‘HTS’ Chillers. The list seems to grow every day.

This, in a way, seems to elbow into the scope of design for the conventional BAS provider. The BAS contractor usually has to be content with providing just an ‘enable/ disable’ point and sometimes a set point control. The ‘intelligent’ on-board controller usually takes care of the various control functions like economizer, set point resets, time-of-day schedules etc. No doubt, they offer excellent control of the various control loops, but do throw up some challenges.

From a commissioning point of view though, the above scenario does pose a few challenges. For the Cx Consultant, the grand rule is to ensure that the HVAC equipment operates according to the ‘Design Intent’. He relies on the BAS to verify the functioning of the various control loops. Usually the BAS contractor demonstrates this by inputting different setpoints or by using simulation techniques and trending. However, when it comes to the units with integral controls, (these controllers are sometimes termed as Black Boxes), there is very little that can be verified. Some controllers allow BAS to pick up monitoring points. It is worse in some cases, where the on-board controller is unable to communicate with the BAS protocol without a suitable interface card. Often we see situations where the BAS has all the capabilities to provide complete customized control of the system, but then, when the HVAC equipment is installed, someone suddenly discovers that it has its own on-board control module with a mind of its own. But can this module provide the sequences and algorithms exactly as per the design intent? Can this controller be totally by-passed to have full BAS control? One doesn’t know for sure.

There is also a cost-factor to it. The BAS contractor usually prices the programming portion of the project based on the number of I/O points that is being controlled, and also by the complexity of the control algorithms. Likewise, the equipment supplied with on-board controller comes with a price tag. Not all suppliers offer an option with or without on-board controllers. The Design Consultant has an important role here. The specification should clearly state who controls what, in order to avoid overlap of functions.

So there you have it – a good example of how the Cx Consultant can add value and expertise by highlighting subtle, but relevant issues, and work with the team towards an effective resolution.
This is just a collection of my thoughts, and I welcome your views.

Why Commissioning