All the right signals?

The Orwellian vision of "big brother" also very accurately describes God-will-provide controls systems. You know, the ones with the incomprehensible systems which require the users to have a masters degree in IT.

Thankfully, things are getting better. We have learnt a lot in the last few years about what constitutes manageable complexity. Controls systems are getting smaller and simpler, and industry-agreed protocols for the exchange of data are making communication between subsystems much easier.

The latest technical guide from the CIBSE has attempted to pull together this learning into one source of information. An overdue update of an earlier applications manual issued in 1985, CIBSE Guide H: Building Control Systems contains a multiplicity of controls advice, from controls fundamentals right down to control strategies for m&e subsystems.

The Guide starts with the basic types of controllers available, such as sensors, valves, dampers and actuators. Sections 3 – 6 deal with the practical design of control systems, starting with hardware and moving on to the links between components and the software used to control entire hvac systems. Advice on lighting controls is conspicuous by its absence, but the subject is covered by other CIBSE Guides.

Young engineers will appreciate the background information on control fundamentals, such as proportional and integral control, and their various combinations. Digital, cascade and logic control methods are also described, with some good sections on optimisation and weather compensation. There are some good sections on system tuning, as well as advice on the use of "fuzzy" controllers. Tables 1 and 2 show some of the information in the Guide on the pros and cons of different controls devices.

The sections covering systems, networks and integration will prove useful to the layperson and the specialist alike. The text is thankfully and probably uniquely free from the marketing hype that surrounds the various bus protocols, such as LonWorks and EIBus (figure 1).

Without wishing to appear a Luddite, it is clear that the functionality that can be derived from an integrated hvac controls system is rarely understood or actually needed on a day to day basis. All specialists – not just m&e designers – rarely appreciate this fact. To paraphrase Scott Adams¹, more and more people are getting relatively more stupid every year, as smarter technology forces them to drop below their 'incompetence line'.

Inappropriately designed and poorly commissioned controls networks fall into this category. Hapless building managers can quickly plummet below their threshold of incompetence as they try and fathom, with rapidly increasing resignation, the unilateral actions of a complex, integrated controls system.

Clearly such situations are not the product of a sensible design strategy. To avoid these problems services engineers need to be thoroughly sure about the level of building management after handover before going anywhere near designing integrated controls. However, where an integrated system is deemed to bring benefits, the Guide's unbiased descriptions of the communication protocols will be useful.

The Guide then goes into the controls issues of various m&e subsystems, such as boilers, pumps, chillers and the like. There is an interesting section on the controls issues associated with ice stores, but the section could have benefited from a list of the advantages and disadvantages of each controls strategy. Some in-use information would also have been welcome.

The sections on subsystem design are interesting and extensive, but they contain so much background data, such as on the detailed design of hydraulic circuits, that the controls element is difficult to extract. Services engineers might appreciate it, but the layperson will be lost. On the other hand there is a useful amount of design advice on ventilation, particularly the control issues of mixed-mode systems.

The Guide contains a few controls case studies, which, while welcome, are annoyingly not as detailed as the aforementioned sections covering subsystem design. Rather oddly, given the Guide's subject, there is a separate short section on 'information technology', which turns out to cover energy monitoring and targeting.

The Guide finishes off with a section called Management Issues (section 8), which yet again turns out to be misnomer, in this case for advice on controls procurement, design and specification and tendering. Clearly this would have been better at the start of the book; readers are advised to go here first before getting wrapped up in the nitty-gritty of proportional plus integral control.

As usual with CIBSE publications, there is extensive referencing at the end of each chapter and a very good glossary of terms.

The authors of the Guide are keen to point out that the operation of controls is heavily dependent on the right amount of time being spent on commissioning. It can take up to six months for a controls system to be commissioned, a period which can easily extend into infinity once the occupants have moved in and the building is supporting the client's business.

On that subject, the Guide stresses that irrespective of whether the controls management of a building is in-house or contracted-out, there should be clear and unambiguous responsibility for its successful operation.

It is important, say the Guide's authors, that controls be considered from the earliest stages of the design process. Occupant feedback data, particularly when obtained as part of a broader energy and design analysis², can also be a useful design and commissioning tool.