Tackling air quality from the design stage
Andy Cardy of Fläkt Woods discusses the need for a holistic approach to system design in modern ventilation systems to optimise working environments and reduce energy costs
Throughout the year, battlegrounds are drawn in many offices. Two opposing teams are destined to clash over an imperative decision making process, which could affect the output of the entire company: should the thermostat be turned up or down?
Ok, so this is a slightly exaggerated scenario, but coping with cold, damp or stale air in the winter months, as well as overcoming the dry, hot and balmy summer, can be a tough challenge for a workforce and a facilities manager. However, whereas the temperature might be the main protagonist in an office conflict, it is actually the indoor air quality as a whole that needs greater consideration.
Many of the non-domestic buildings in the UK will not be equipped with centralised ventilation systems, and will rely on more traditional methods i.e. opening a window. Although some consultants might argue that this can still be an effective way of improving indoor air quality, the UK Building Regulations have driven commercial property design to become increasingly airtight to conserve fuel and power. This has led to the potential degradation of indoor air quality becoming an issue for system designers. After all, for occupants of commercial premises, such a problem can often trigger a notable reduction in productivity and comfort levels, so designing an effective system for all months of the year is essential.
Unfortunately, there isn't a 'one solution fits all' option and, instead, maintenance of good indoor air quality can be a complex task, both in its initial design and ongoing monitoring. In the first instance, ventilation rates have to be designed to a set occupancy level, but this can often be exceeded, causing a reduction in stale air removal and, consequently, a higher concentration of pollutants. If this scenario is coupled with a high density of occupants in a relatively small space, it
can also lead to various problems, including increased levels of odours and noise, or increased transmittance of colds and flu. Other challenges include maintaining moisture levels and keeping energy usage to a minimum.
There are many factors to consider when ensuring that a new building has an optimised indoor climate. Building services engineers need to look at ventilation rates, temperature, humidity, air purity and noise. One approach that is regaining momentum and is an ideal method for maintaining indoor air quality, is demand controlled ventilation. This helps keep the temperatures and ventilation rates at the required level and can be achieved by carefully specifying a range of products - such as air handling units (AHUs), axial/centrifugal fans, and air terminal devices (ATDs) - that can intelligently 'communicate' with each other to provide the optimum air quality.
A common component in commercial ventilation systems (especially offices) is an air terminal device, or room diffuser. It might not always be considered a crucial element of a system but, when specified correctly, can provide some useful energy reductions. For this reason, manufacturers such as Fläkt Woods have developed 'active' room diffusers, which not only improve the performance of demand controlled ventilation systems, but also maintain excellent comfort levels for occupants.
By regulating the air distribution and controlling the flow rate, these room diffusers can ensure a constant air throw. In addition, where occupancy rates increase (a common occurrence in an office environment) and a higher ventilation rate is required, the diffusers can adjust air discharge velocity accordingly.
Another key factor that should be at the centre of an effective ventilation system design is controls. According to the Carbon Trust, it is estimated that up to 90 per cent of heating, ventilation and air conditioning building control systems are inadequate in some way, costing industry and commerce over £500 million per
year in additional energy costs. Good controls are essential within a building to optimise levels of service, comfort and safety in an energy efficiency manner, so designing them in early to a project can ensure a reduction in overall running costs by preventing wasteful out-of-hours operation and reducing excessive wear and tear.
Control systems are also an essential component for optimising indoor air quality. For example, ventilation speeds can be regulated based on the levels of carbon dioxide in the air. Connecting such sensors to demand controlled units allows airflow to drop when there is less demand for fresh air or increase where the demand is higher. Of course, lowering ventilation rates provides energy savings through reduction of ventilation fan speed, as well as decreasing heating/cooling loads.
While demand controlled ventilation is an effective way to manage air quality, reducing overall energy consumption is another key consideration. And, one type of air climate technology in particular is making a resurgence: heat pumps. Although this technology has not always been associated with a ventilation system, manufacturers have started combining reversible heat pumps with a recovery wheel as an integral component of air handling units.
One key benefit of an integrated heat pump unit is that this 'packaged solution' reduces the amount of refrigeration related work to a minimum, as components are factory assembled. Of course, whilst this does not totally remove the need for facilities managers to carry out regular leakage checks, it does reduce the work needed to comply with Building Regulations.
So, as discussed, maintaining good indoor air quality is a key consideration for modern commercial buildings. The developments in ventilation technology - such as demand controlled systems, controls and the latest AHUs with integral heat pumps - are all helping building services engineers meet the challenges of the latest legislation.
Balancing these technologies with the overall running costs will require greater collaboration throughout the supply chain, from manufacturers to consultants and facilities managers. This will provide a building with the most effective indoor climate solution, and ultimately help reduce the problems of poor indoor air quality in the future.
// The author is the product manager at Fläkt Woods //
11 March 2014