INDOOR AIR QUAL I TY

Pushing air up the agenda

Many expensive air movement and air conditioning systems are undermined because the final part of the design has been overlooked, says David Fitzpatrick, Sales and Marketing Director of Ruskin Air Management.

Meet the challenge

The challenge is making sure the mechanical element is as energy efficient as possible and how the tempered air is delivered meets the design criteria required. When supplying fresh air for

ventilation during the winter months, a tempering process is often required to raise its temperature to an acceptable level. This is typically achieved through air handling units (AHUs) with heating via hot water coils, DX circuits, or by making use of ground source heat pump or solar heating technologies. All very laudable and well designed to minimise energy costs and improve indoor conditions. There is much emphasis

C

onsulting engineers spend a lot of time working on the design of air movement and ventilation systems,

but sometimes the whole thing falls over at the final hurdle. How the treated air is finally distributed into the occupied space is, in too many cases, overlooked and can fall victim to last minute cost cutting. Financial pressures are, of

course, greater than ever, but so too are the demands of regulators for good air quality and low energy consumption. With buildings becoming more insulated and better sealed to reduce heat losses it is important to make sure that indoor air quality is not compromised. Designers have to juggle with

the requirements of Part L of the Building Regulations to minimise energy use; Part F to deliver healthy fresh air rates; and Part E to avoid disruptive levels of noise from the ventilation system. Air terminal devices, such as diffusers and grilles, play a more important role in ensuring the finished product meets all these seemingly conflicting demands than is often recognised. As a result, the air distribution market has become dominated

by commodity products that offer a basic function at a far reduced price, but the cost of using these devices can be severe and far-reaching. A properly designed four-way

diffuser, for example, is a complex piece of engineering and should be manufactured from high quality materials. Yet there are products on the marketplace available for less than £20. These may well have their place, but they signify that air distribution is not given the attention that it needs.

In the lifetime of a building,

Critical

How the airflow is treated in the plenum box behind a diffuser can be absolutely critical to the conditions experienced by building occupants. If the terminal device is not properly designed the result can be air velocities that are too fast leading to cold air dumping and high noise. Similarly, if there is turbulence behind the diffuser, you will not achieve the distribution patterns intended for the room. Poorly designed and positioned devices will end up forcing the air movement system to work harder in an attempt to improve comfort conditions, so driving up energy costs.

VISIT OUR WEBSITE: www.bsee.co.uk

the occupants are by far the most expensive element. Salaries and other overheads account for over 90% of the total lifecycle cost. Keeping those expensive people productive and healthy must, therefore, be the top priority for any commercial building operator. As a result, more specifiers

are leaning towards natural ventilation. However, the 100% natural approach does not work for all buildings due to factors such as internal partitioning and the location of server rooms etc. A degree of mechanical ventilation is often required to achieve sufficient air changes to keep the internal environment healthy.

MAY 2010 BUILDING SERVICES & ENVIRONMENTAL ENGINEER 29

placed on the efficiency ratings of these heating, cooling and ventilation systems, particularly in light of tightening up of planning regulations. However, an area that is often neglected is the

actual conditions experienced by the occupants.

Intensive

No matter how efficient our heating and cooling equipment, if air distribution is not satisfactory then the design is fundamentally flawed. Not only will occupants be dissatisfied with their working environment, they will take additional – usually energy intensive – steps to make things better. A common problem is the

poor positioning of grilles and diffusers. A four-way diffuser placed close to a wall will, for obvious reasons, not perform well because it will not be able to diffuse in all four directions. Similarly, if the airflow is not properly managed in the plenum box the air may not emerge from the whole of the grille so undermining the overall design strategy. How air moves within occupied areas should be taken into account as part of the lifecycle costing of a project. Full CPD modelling of the area will show optimal airflows,

Financial pressures are, of course, greater than ever, but so too are the demands of regulators for good air quality and low energy consumption. With buildings becoming more insulated and better sealed to reduce heat losses it is

important to make sure that indoor air quality is not compromised

but the designer cannot be certain that they are delivering that result if the specification of air terminal devices is undermined.

Value for money

As specifiers and end users look for ever more value for money, this is an area that cannot be ignored. In many cases, the air distribution system is delivering excellent results proving that the industry clearly has the necessary skills and equipment. However, in far too many instances the system is compromised for want of a little care at the final stage and the results can be expensive – in more ways than one. Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52