WHEN planning a project involving terminal units, such as fan coils or chilled beams, one key decision is whether to adopt conventional pipework assembly techniques or use prefabricated assemblies. The right choice can make a significant difference in terms of finances, performance and completion on time.

While it is sometimes tempting to stick with familiar procedures, it is worth looking at all of the factors before making a decision. Prefabrication is not be the right solution for all projects but it could be the best option for more jobs than you think. And any concerns about lack of familiarity can be put to rest by teaming up with an experienced prefabricator.

Fifteen years ago, the idea of prefabricated pipework assemblies would have been seen as innovative in its own right. Now, the concept is established but that should not detract from the innovation. It is this which ensures prefabrication techniques continue to evolve and to offer even more value to projects.

A case in point is the use of prefabricated manifolds in an insulated manifold box. This is a fairly basic arrangement but the use of innovative valves and features to aid installation and commissioning ensures that the benefits extend beyond the minimum. For instance, providing capacity for additional fan coil connections in the manifold box can make future changes to the design much easier to accommodate. It is not rocket science, but it is surprising how rarely such foresight is applied.

Similarly, the choice of valves included in the assembly will make a big difference to commissioning. This could include the use of commissioning valves with inter-changeable venturis, or a range of other control valves, such as pressure-independent flow-limiting valves. The important thing is to adopt a flexible approach that looks at the needs of the project and comes up with the best solution.

To that end, it is important to plan early for prefabrication and, if it is being outsourced, to involve the fabricator at an early stage. This will facilitate production of drawings and hydronic performance data in time to spot any potential problems. Opting for prefabrication also provides cost surety, as the project will be less prone to fluctuations in material costs during the course of the project.

It also makes on-site installation work up to 50% faster, so the time of skilled operatives can be used to maximum effect, with a consequent reduction in costs.

The fact that prefabricated manifolds bring all of the control valves for a group of terminal units into one location brings a number of benefits. For example, the boxes can be installed early on in the project making it relatively easy to pipe to and from them as the project proceeds.

And if there are changes to the layouts of the terminal units - and when aren't there? - they are easier to accommodate.

In our experience, combining prefabricated manifold boxes with a flexible multilayer pipe running directly from the manifold to the terminal unit brings even more advantages. At installation stage, this eliminates the need for soldering. It also means fewer joints and less risk of leaks. This has implications for insurance premiums, particularly if the joints are confined to safe areas such as corridors.

Flexible pipe also makes it easier to reposition terminal units at either shell and core or fit-out stages. Rather than undoing up to a dozen connections between the manifold and the terminal unit, there are just two. Furthermore, if the ceiling has already been put up, there are only two tiles to remove to access these connections. And the same length of pipe may possibly be used for the new connection, meaning less waste.

Many of these benefits also apply at commissioning stage. Rather than taking measurements at each fan coil, the commissioning engineer can access, perhaps, up to six fan coils in one space. Clearly, the time savings simply from not having to move from one fan coil to another, and complying with the Working at Height Regulations at each location, are enormous. With a properly considered control solution the need to revisit each manifold more than once is unnecessary, often reducing the commissioning process to a read and record exercise.

In addition, if the ceiling has already gone up by commissioning stage, there are fewer tiles to remove, so less time is wasted. And, if extra terminal units are added after commissioning, subsequent recommissioning can all be carried out in the manifold box, if needed at all.

These are just the most obvious considerations that need to be applied to the decision-making process. Use of prefabrication often brings associated benefits that impinge on the whole culture of the project.

The key thing is to keep an open mind and go for the most appropriate solution, working with a prefabricator that offers a flexible range of products.

www.marflow.co.uk