Flexible, efficient ventilation for sheds-type buildings

Operators of high-ceilinged shed-type buildings need to maintain comfort levels with optimum efficiency and flexibility, says *Ian Dagley of Hoval

When it comes to maintaining good indoor air quality (IAQ) and thermal comfort, with optimum energy efficiency, ‘shed’ type properties require a flexible approach that accommodates several key criteria.

For example, the layout and usage of the space(s) are almost certain to change during the lifetime of the building, so the design of the ventilation systems needs to include some inherent adaptability. And, of course, energy efficiency needs to be optimised.

Design options include centralised air handling plant serving ducts and diffusers, decentralised ventilation units operating independently of each other or integrated systems that combine several units, each configured to the space it is serving.

Centralised systems tend to lack adaptability, so that any change is disruptive and expensive. In contrast, decentralised ventilation systems, or ‘hybrid’ systems combining the characteristics of both, are increasingly popular because of their versatility.

Decentralised systems

Unlike central air handling units, decentralised systems normally work without supply and extract ductwork, making design easier and reducing installation costs. They can also be combined with heat pumps to provide low carbon heating.

Decentralised systems also make it possible for each space – or each zone within a large space – to be controlled independently of units in other spaces/zones. This means ventilation rates can be matched to the actual demand within each space (demand-controlled ventilation).

Latest generation decentralised units also incorporate air injectors, so that the air distribution pattern can be changed automatically, infinitely variably between vertical and horizontal, for very effective air distribution using lower air volumes. Air injectors also minimise thermal stratification, which can be very wasteful in high-ceilinged buildings.

Additionally, this decentralised ‘island solutions’ approach ensures that there is no contamination of one zone by another, which can be an issue with central plant serving ductwork distribution. For large installations this also facilitates phased investment to spread the capital costs.

Lifecycle costs are clearly a consideration and one key element in lowering running costs is heat recovery, where much of the heat energy in the extract air is recovered and transferred to the incoming supply air via a plate or rotary heat exchanger. We have seen paybacks as low as two years for these kinds of installation.

A system approach

A ‘system’ approach is based on a three-module concept, comprising a heat source, ventilation units providing recirculation or air changes, and a control system. The system approach may also include zone control which, in conjunction with temperature- and time-based zone control, can optimally adapt the heating times and space temperatures to logistical and energy-related requirements.

In all cases, it is particularly important to take account of installation and maintenance factors at the design stage of the project. The fact that decentralised units are installed at high level, or on the roof, means that installation has minimal impact on the activities below and the units are easily accessible from the roof for servicing and filter replacement – whilst occupying valuable floor space.

Summary

Whether for retail, events, manufacturing or logistics, the different uses and requirements of shed type buildings are most easily met with a system based on decentralised units, operating on a standalone basis or as part of an integrated system. The adaptability of this approach not only makes it straightforward to meet current requirements but also helps the building to adapt to changing usage in the future.

*Ian Dagley is General Manager of Hoval Ltd

Website – www.hoval.co.uk
Email – info.uk@hoval.com