Decentralised ventilation - the answer for larger spaces?

Published:  07 March, 2017

Factories, warehouses and other ‘shed’ type buildings provide special challenges for HVAC systems. Eduard Kovac of Hoval explains how decentralised ventilation units can meet many of these challenges.

Creating and maintaining good indoor air quality (IAQ) in a factory or warehouse is essential in terms of assuring both the health and comfort of staff. It may also be important in ensuring stability of stored goods and components, and the operation of machinery. High humidity resulting from insufficient ventilation, for example, can have a negative impact on health, damage materials and machines and lead to condensation that creates slip hazards.

Of course, the same general considerations are true for any space in a building but these larger buildings with high roofs pose particular design challenges, for two main reasons.

The first of these is obvious: the buildings are large and conventional systems are designed for smaller spaces. The second depends on the type of space. For example, an electronics assembly area has different requirements to a paper production hall or a print shop. And, of course, these are very different from warehousing/logistics spaces, which themselves exhibit considerable variation depending on types of products stored, racking density etc.

In addition, such buildings frequently change their use over time. Where today’s screws will be produced, tomorrow’s cultural events could take place. The manufacturers of indoor climate systems try to satisfy these demands and provide specifiers with the products they need to meet the end client’s requirements.

To that end, decentralised ventilation systems are proving particularly versatile in meeting a wide range of requirements.

One reason for this is the inherent adaptability of such units. For example, in industrial buildings problems often arise due to high oil contamination of extract air. The separation performance of a normal extract air filter is insufficient and, consequently, the filter life is much too short – resulting in increased lifecycle costs.

Moreover, where inappropriate designs are used, there is a risk of oil dropping from the unit into the working area, or being removed with the exhaust air. As a result, the unit quickly becomes very dirty.

Ventilation manufacturers can provide a solution that uses special two-stage filters, whilst exposed unit parts are protected with coatings, and vulnerable materials such as seals are replaced by oil-resistant materials. The oil-laden condensate is filtered and separated inside the unit and removed via an oil and condensate drain.

Avoiding draughts

As noted earlier, each area will have its own particular requirements. For instance, people who are sitting at an assembly area all day need to be protected from draughts caused by the ventilation system. By using air injectors that distribute supply air at different temperatures, draughts are eliminated. The air distribution pattern can be changed automatically and is infinitely variably between vertical and horizontal.

Noise levels may also be an issue in some areas, so it may be necessary to incorporate special sound insulation to ensure that low noise levels are maintained.

Looking ahead

In such spaces it is particularly important to take account of installation and maintenance factors at the design stage of the project. Avoiding, or at least minimising, disruption of manufacturing and other key processes is critical during the installation phase and later on through the life of the plant.

This is another reason for the growing popularity of roof-mounted decentralised units, as they offer several advantages in this respect. The fact that they 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.

A further benefit is that they do not occupy any valuable floor space, so they can be positioned optimally without conflicting with the layout of the area below.

Island solutions

Ensuring optimum performance and efficiency throughout the life cycle of the installation is essential, in terms of both running costs and environmental impact. With decentralised ventilation systems this is addressed by providing each space – or each zone within a large space - with its own single ventilation unit. Each unit can then be controlled independently of other units in other spaces/zones, thereby catering for specific requirements in each area.

For instance, different zones may have different occupancy patterns through the day, so that ventilation requirements vary accordingly – perhaps laying on an extra shift during peak times. The ability to adjust ventilation rates to the actual demand within each space (demand controlled ventilation) minimises running costs without compromising on comfort.

Furthermore, this arrangement provides the flexibility to adapt the ventilation if the usage of the space or zone changes in the future. This may be in terms of changing work patterns, different activities or variation in line with the seasons of the year. The adjustable air injection system also makes a re-adjustment of airflows very straightforward, where necessary.

Additionally, this ‘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 systems. For large installations this also facilitates phased investment to spread the capital costs.

Short amortisation

Unlike central air handling units, decentralised systems normally work without supply and extract ductwork. Not only does this make the design easier, it also facilitates the operation of cranes or – as is often necessary – installation of new production machinery.

The installation costs also decrease as a consequence. Nowadays, installation is very simple, using pre-wired units that are easy to change at a later date. Also the air injectors give very effective air distribution, allowing a lower air volume to be used, resulting in a further reduction in investment.

Most savings, though, can be realised by means of lower running costs. Facilities management data shows that the construction cost of a building in relation to the whole life cycle is only 30 per cent. The remaining 70 per cent is the running costs, so that reducing running costs can deliver a fast return on investment.

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. In such cases, it is important that the system works automatically and is ‘user-friendly’.

We have seen paybacks as low as two years for these kinds of installation, due to lower running costs – which then contribute to increased profits through the remaining life of the plant.

Aiming for ‘win-win’

Whether for process, manufacturing or logistics buildings, different uses and requirements can be met with a decentralised ventilation system. The adaptability of the units as well as their quality guarantees a long-term cost-effective and efficient solution for the building owner and manager.

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