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Where do fan coils go from here... again!

Change is happening faster in the fan coil sector now than ever before, according to Peter Lowther. Here, he outlines the main developments and their impact on the sector
There must have been a dozen articles published recently from fan coil unit manufacturers that have attempted to define where fan coil unit technology goes from here.

While they all proffer slightly different visions of the future, there is no doubt that fan coil technology, in all its respects, nowadays moves further every month than it used to in a decade so there is always a story worth telling.

While some visions of the future do not make happy reading for all, it is certain that if new and innovative technical solutions work, save money, save time and save energy, then their eventual acceptance and implementation is inevitable.

Consider that the designer and fan coil manufacturer are both charged with delivering a cost effective solution that provides a comfortable environment within defined temperature limits and within a defined noise level limit - no more, no less.

Let us tackle the first of these issues - that of being more cost effective. Many projects now use PICC pressure independent characterised control valves. These remove some valve sizing issues and possibly offer rationalisation of the valve parts that have to be purchased but in terms of overall cost do they save any money?

Some would argue not, because they still require commissioning and beyond that, they are often charged with introducing as many problems as they claim to solve.

The real problem with commissioning PICC valves, however, has nothing to do with the valves themselves, but rather that they require certain criteria to be met before they are able to perform correctly. They need in particular, an adequate supply of clean, deaerated water at a suitable minimum pressure differential and if these conditions are not met, as is sometimes the case, they can appear to misbehave. Unfortunately, because PICC valves are the 'new kids on the block', the finger of suspicion is all too quickly pointed at them without any closer move to find the real, underlying causes.

Everyone in the industry appreciates that in the short timeframes available towards practical completion and handover, meeting all these conditions on a building site is not easy. That does not, however, remove the need for them.

The question is sometimes put: 'Why was everything so much easier and apparently so much better before PICC valves?' The answer is: probably, it wasn't. It might have appeared easier, but was it better? Almost certainly not.

Previously, flow regulating valves were set when everything was believed to be correct and settled. But without cross checking, who is to say it was? If current buildings fitted with PICC valves have problems that affect the valves' capability to perform, what evidence is there to suggest those same issues were not present pre-PICC valve?

Combine the tolerances of previously installed regulating valves and measuring stations, add in a bit of air and a couple of actuator heads left off for good measure and the flow rates, even in a conventional system, could have been way off without anyone realising.

Less than satisfactory
Is the increasing call for 'Soft Landed' handovers the evidence that some buildings were, albeit unknowingly, handed over in a less than satisfactory state? While PICC valves are often held up as the culprit for poor flow control, are they actually the messenger, the missing cross check that has highlighted some of the problems that would have previously gone unnoticed?

Having dealt with the need to deliver a cost effective solution and the effect of PICC valves in that aspect, let us move on to the second obligation of designers and manufacturers: that of providing a comfortable indoor environment.

Consider the manner in which fan coil units are specified and selected. When a fan coil manufacturer receives a specification for a project, it will include cooling and heating duties and noise level requirements; it will also include design conditions and any number of physical constraints. This is because they are all definitions of what is wanted.

Items that are not specified, however, include values such as fan voltages and water flow rates. This is because these are not in themselves requirements, but are simply means to an end. Accepting that the sum of the total water flow is required for pump and pipe sizing etc, designers are not really interested in water flow rates per se, only insofar as they are a necessary component in the overall scheme to provide what the client really wants, which is to be comfortably cool.

Here is the evidence. When does an occupier with a poorly performing fan coil ever say: 'the temperature in here is way too hot - the water flow rate must be down'? The answer is never. Providing a fan coil unit does what it is expected to do (that is to provide a comfortable working space), how it does it should not concern the occupier.

When is providing the maximum design water flow rate important? Actually, only on days when maximum or peak load is being experienced. At all other times, the valves will be happily modulating away, controlling to a lower water flow rate sufficient to provide the right amount of cooling on that day.

Returning to the problems with the commissioning process: what would silence the debate is a valve control strategy that self-corrects to ensure that the primary requirement of a comfortable space is always maintained?

In the not too distant future, if the water flow is not commissioned with the prescribed accuracy, it will no longer matter. If the water temperature at the far end of a branch has degraded and is not at design level, it will no longer matter.

Why? Simply because every unit will be monitoring its own little part of the environment and if the controlling strategy senses that the unit appears to be struggling, it will temporarily self-correct the design water flow position to deal with the problem until it passes.

This means that, although PICC valves might still be affected by pre-handover vagaries in the system, and while they might still have their critics, it will no longer matter because the valves will merely, 're-tune' to cope with almost any eventuality, be it man made or system made.

It's really a question of focusing on the primary purpose of a fan coil, which is to provide a comfortable environment for the occupants of a building.

The author is director and chairman of Ability Projects
10 September 2012

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