Pre-fabricated packages can overcome obstacles and cut costs.
There are many reasons for wanting to improve the efficiency of building services systems, such as heating and hot water, but when working with existing buildings there are often many practical challenges that can impact on the viability of such projects. In many cases, making use of pre-fabrication techniques such as skid-mounted plant will often facilitate smooth project implementation and may even make the difference between project viability and non-viability. The same techniques can also be used to good effect in new-build projects.

In the case of plant upgrades, the driving forces behind such projects may relate to the age and reliability of plant, or an aspiration to improve overall energy efficiency and reduce carbon emissions. Or they may be a 'consequential improvement' requirement under Part L of the Building Regulations.

Limited access to plant rooms

However, replacing existing plant or introducing additional plant to a system in an existing building isn't always easy. Access to plant room space may be limited, or the layout of the plant room may restrict working space - particularly where 'hot work' is required.

Or there may be restrictions on getting new plant into the site. Hospitals, for example, often only have limited time-windows where large vehicles can enter the site without critically disrupting the core activities of the site. So any such time availability needs to be exploited to the full.

In all of these situations, adopting a pre-fabrication approach to the central plant can offer many of the advantages that are already accepted for distribution systems such as pipework or cable tray.

This can be illustrated by considering the retrofit of a biomass boiler to an existing heating system. This could be to replace older fossil fuel boilers or to supplement existing plant and reduce overall emissions.

Using traditional installation methods the new biomass boiler would be installed and then connected to the stoker and an auger would be installed to connect to the fuel store (wood pellets or chips). Additional work would include connecting up power, pipework and control wiring from the control panel to motor control centres, with additional connections to thermostats. Then the assembled system would be tested in situ and any issues rectified.

So this is quite a lot of time-consuming work that has to be carried out in plant room conditions, often with other trades working in the same space and getting under each other's feet. During this time, services are often disrupted and the whole site may be disrupted by movement of people, plant and materials.

Using the pre-fabrication approach, the majority of the work is carried out in a factory under controlled conditions. The boiler and stoker, complete with controls, are mounted on a skid and all connections between them are made, followed by dry run testing - including witness testing where required. The entire assembly is then delivered to site and dropped into place, ready for quick connection to the auger, flow and return pipework and a flue, followed by commissioning.

Alternatively, if access to the plant space is restricted, the pre-tested assembly described above can be broken down to allow the elements to pass through doorways and then re-assembled in situ. The benefits of factory-controlled assembly and testing still apply. And where space for extending plant is at a premium, pre-fabricated assemblies in weatherproof housings can be used to utilise space outside the building, though planning permission and drainage may be required.

The same principles can be applied to the biomass fuel storage. Rather than building a traditional bunker for the wood pellets or chips, a pre-fabricated silo can be delivered to site, erected and connected to the auger in just a few hours. This may be an indoor fabric silo supported by a frame, or an outdoor glass reinforced polyester (GRP) silo that is placed in position by a special delivery vehicle.

CHP can be integrated

Nor are these techniques restricted to biomass heating plant; they can be used for any large plant items. For instance, a complete combined heat and power (CHP) package, comprising engine, generator and controls can all be integrated into an acoustic housing on a skid assembly ready for delivery to site, where all that is required is a few connections.

In all cases the time-savings are significant, there are fewer workers on site and fewer deliveries to site, so less storage space is required for components awaiting installation. Plus, there is less hot working, which reduces health and safety risks.

Pre-fabrication of skid-mounted plant is not a new concept but it has seen a resurgence in the last few years as building operators try to improve the energy performance of existing building stock. It is also often used in new build projects, again because of the time savings on project schedules and reduction in on site staff levels. It's not the best solution for every project but is certainly worth considering at the planning stage - and has the potential to make the project manager's life considerably easier.

• Kevin Stones is engineering and service director of Hoval