By pioneering parametric design and linking CAD systems to factory machinery, manufacturers can ensure repeatable and consistent quality with every component - totally bespoke units, without the tailored price tag, says Alun Thomas
Ventilation systems are interlaced into building fabric and are a large and crucial part of the overall building design. Every building is created and constructed to meet the customers exact requirements and are bespoke in every way - yet, we insist on using our 'Tetris Toolkit' of ventilation components (fans, coils, filters) to try to create an adequate solution with the parts available to us from our supplies - the proverbial 'Square peg in a round hole'. In this current economic climate, there is fear that the supply chain is being pressured to cut costs in order to be competitive.

As far as fixed unit sizes are concerned this restriction is in place for many air handling unit (AHU) manufacturers, where economy of scale and set engineering resource drives to develop a number of fixed unit models in set ranges and defined performances. These units are normally launched as a range with fixed model numbers.

What if the customer needs a unit which is just outside of one of the performance curves as per the Red Dot indicated? What options are available?

Tweaking occupancy levels
The consultant can look at the ventilation loads in more detail; tweak the occupancy levels and heating/cooling loads to suit the unit or the space available. The unit would then perhaps deliver the duty under ideal conditions; however, once the filters become loaded and the coils become fouled, the end result would be an underperforming system running 24/7 with no additional capacity.

For example, financial pressures and economic climate can force a contractor to take a risk and offer the size 8 unit, hoping that there would be enough of a safety factor. We have all seen projects cutting corners when times are tough, and implications may only be evident in the longer term performance and cost analysis.

Other contractors may convince a client that they should purchase the oversized unit and then de-rate it. The client may pay for the additional unit cost but there are also costs associated with the infrastructure to support the larger unit including increased cable, contactor and breaker sizes for the larger motors, additional plant area and service requirements, increase running costs due to oversized system inefficiencies (Controlling coil temperatures at low flow conditions and so on).

Some might consider developing a custom or bespoke unit. This involves design engineers developing a new or unique product to deliver the performance required. This would include contact with suppliers and perhaps bespoke products further down the supply chain. Custom data sheets and performance information is created.

CAD Engineers then convert this design into an AHU that can be manufactured. This includes developing 300 or so sheet metal parts needed to build the unit and then writing the punching and folding programs to allow these to be run through the machinery. The production facility would then need to deal with a bespoke AHU potentially requiring testing and validation to ensure the quality of the unit is of the highest standard.

The increase in cost of bespoke designs is predominantly due to the additional processes mentioned above. The bespoke unit is optimised for size and duty and can be more expensive than a larger standard selection; however we cannot forget inherent risks of human error through bespoke designs.

The secret of parametric design
So what if we could make you an AHU with the individual components you need, in sizes that can grow and shrink to the millimetre to fit your exact requirements? We can through parametric design. Parametric design is where components can be scaled up or down and to keep design integrity for manufacture.

Imagine a typical panel on an AHU. Some are larger/thicker than others; some have handles, hinges or portholes. But at the end of the day, it is still a panel.

The basis of the system starts with software, such as Nuaire's AireCAD system, which allows us to drag and drop components into position to create the basic AHU you are looking for. The overall dimensions of the unit can be specified, the components can be customised and the data sheets can be provided to the consultants for discussion and approval. Up until this point, the system is very fluid and allows all parties to change the AHU as they wish - tracked using unique reference numbers and revision control.

A great example of this was a recent project where we were asked to slice the unit sections to fit through a doorway by providing this 'cheese slice' effect. Parametric design enabled us to ensure the quality and integrity of the unit was maintained. Once the unit had been finalised and ordered, it could then be launched into the second stage of the system - this is where the magic happens.

From this point, there are no further changes permitted and the unique product is loaded into a 'Parametric Design' system. Individual parts are imported into a CAD model and then stretched or shrunk in order to ensure a perfectly designed AHU. Every part in the system is uniquely numbered and can be traced back to the parent unit without fail. All of the components are fully designed, developed and tooled ready for the machine without any human intervention.

For Nuaire, as a supplier of AHUs, this is where the cost considerations come into play. Assuming the design time has been minimised with this technique how can you keep the manufacturing costs down?

Manufacturers benefit most where the CADCAM (Computer Aided Design Computer Aided Manufacture) is linked. Through automated machinery that links to CAD systems parts are automatically punched, folded and delivered to the production area ready to be assembled.

For companies that have this capability it can be as easy to build truly bespoke units on software as it is to tweak existing units using the traditional method.

// The author is commercial office manager at Nuaire //