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For further information,
please contact:
Neil Yule
+44 (0)1206 222 593
neil.yule@flaktwoods.com
As prepared for
Building Engineer
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Architects may design and specifiers may specify but, when it comes to providing building services, the buck stops with building engineers. Whatever systems are specified, they have the responsibility of ensuring that these are correctly installed and work efficiently and cost-effectively on a continuing basis.
That burden of responsibility includes a duty diplomatically to disagree when a specified system is not the best solution. Simply, building services engineers should know more than architects about ventilation, for example, and must strongly recommend a better option when they know of one.
Traditionally, not an onerous duty maybe. Past choice for any given situation was narrower than today’s and, in terms of technological advantage, with very little difference between rival systems. All would work in much the same way and offer very similar running costs. Selection on the basis of initial installation price-tag appeared to make a lot of sense.
But the world has changed. Now, building engineers are seeing the increasing convergence of two building design issues of ever-increasing importance: indoor air quality and energy efficiency.
Whether the aim is to raise productivity in workplaces, to improve comfort levels in hotels or to deliver optimum environmental conditions in hospitals, there has never been a greater focus on improving air quality in buildings. At the same time, the drive for energy efficiency is not merely a vital challenge for today, but for the foreseeable future. It all adds up to growing pressure on those responsible for creating and maintaining buildings: to view these issues in tandem, and deliver systems that not only offer the best possible indoor climate, but do so in the most energy-efficient way on a continuing basis.
Indoor air quality is highest when there’s an optimum combination of five factors: ventilation, temperature, humidity, air purity and noise. The architect or specifier — guided by relevant experts, the building services engineers — has to create a system which supplies fresh air without uncomfortable draughts; provides cooling or heating to optimum levels; maintains a proper humidity balance for personal comfort; reduces CO2 and harmful or irritating particulates; and does all this without distractions from functioning systems.
Any competent building services engineer can design such a system by bringing together the best-in-class from a range of component manufacturers. (In a perfect world, of course, they would be able to benefit from synergies and cross-functional expertise by finding a single manufacturer able to supply everything – but there are few companies like Fläkt Woods.) The challenge is to create a system that delivers all this while taking into account costs that go beyond initial purchase price.
During the lifespan of an indoor air system — 20 years or more — the total cost will comprise three main elements: original investment, running costs and maintenance costs. Viewed over that period, and at current plant and energy prices, the initial system price will ultimately represent only about 10% of overall cost – and maintenance a further 5%. The overwhelming bulk of the system’s cost, around 85%, will be for the energy needed to run it. (A fourth, and final, cost element would be removal and recycling – but in our case at Fläkt Woods, with all of our products more than 95% recyclable, it’s small.)
So far, so good. We know we need a good working solution and that it needs to be energy-efficient in the long term. However, today, there are further factors that must influence system design. Legislation now lays down stringent requirements relating to the provision of quality indoor air. Meanwhile, standards relating to energy usage continue to evolve. ISO 13790:2008 Energy performance of buildings, (covering space heating AND cooling) is the latest update on its 2004 Thermal performance predecessor which focused solely on heating. Building engineers need to remain constantly abreast of such evolving standards, as well as implementation consequences of the European Energy Performance in Buildings Directive [EPBD]. This defines and requires minimum standards for energy performance in both new and refurbished buildings, as well as covering energy certification.
More specifically, the 2006 update to Building Regulations Part F Ventilation raised the mandatory minimum fresh air quantity per person in buildings by 25% — from 8 litres to 10 litres per person per second. It also set out other detailed criteria for air cleanliness and humidity. At the same time, the updated Building Regulations Part L – Conservation of Fuel and Power focused on energy use in buildings. This included mandatory airtightness testing, targeting lower rates of air leakage, and tighter targets for CO2 emissions. Among other matters, one major update objective was reduction of CO2 build-up within occupied spaces. However, reduced inhalation levels of CO2 can be achieved by changing the method of introducing fresh air into the space.
A potential solution in use in the UK for some years, although its benefits are still not widely understood, is displacement ventilation. This addresses both indoor air quality and energy issues – supplying clean fresh air directly into the occupied area at low level, at the correct temperature. The area’s warm, contaminated air is shifted upwards — hence, displacement — for extraction through the exhaust air system.
As the warm air rises, carrying any particulate contaminants, it is replaced by clean air. Provided that the supply air flow is adequate, the system is entirely self-regulating. Displacement ventilation has been shown to offer a ventilation efficiency of around four times the effectiveness of traditional mixing systems when introducing fresh air into a target zone. This increased effectiveness is consistent, unaffected by whether the space is occupied.
Such a system is not only capable of meeting CO2 requirements, it also provides a suitable room temperature while functioning at relatively low flows. In general, displacement ventilation systems operate at both low velocity and very low pressure. This delivers an immediate additional benefit of low operational noise combined with minimal draught within the occupied area.
In the temperature gradient associated with displacement ventilation, the ceiling-level air temperature is higher than that of the occupied zone. The first effect of this is that the supply temperature can be higher than that of traditional mixing systems. The reduced cooling requirement means reduced energy usage, throughout the system’s lifetime.
A higher return air temperature also renders the system ideal for use with an energy recovery device within an air handling unit [AHU]. There is a consequent dramatic reduction in the heating energy needed to meet room conditions after the energy recovery device. In some cases, particularly if energy recovery is via a thermal wheel, the heating energy requirement can be removed altogether. There are also bonus benefits: the higher supply temperature enables free cooling to be available for much of the year.
With a thermal wheel in the AHU and an evaporative humidifier in the extract, the cooling load required by any chiller or condensing unit can be cut by 50%. This indirect evaporative cooling system not only reduces peak cooling loads, but also significantly increases the amount of time cooling recovery can occur. The energy recovery capabilities are key to minimising energy usage in such a system.
The life-cycle benefits can be understood best by considering the working of a specific system. In Econet, Fläkt Woods has created a packaged liquid-coupled energy recovery system. It delivers highly energy-efficient usage, with space and installation flexibility, through a unique optimising control system. The package includes supply and extract coils, invertor driven pump set, valves and sensors. The pump pack is supplied pre-piped, pre-configured, pre-programmed and pre-commissioned, ready to connect directly to the supply coil. Coils are mounted within the AHU.
Energy recovery from extract air is maximised by large coils, with water used as the most efficient recovery medium. Using up to 76 waterways and 12 rows of coils permits energy recovery efficiencies of up to 70-75% at equal supply and extract airflow. Complete heating and cooling is supplied with the same coils when the system is supplemented by injecting energy from hot water or chilled water through plate heat exchangers. Due to the efficiency of the large coils, this supplementary energy can be low grade, waste or renewable energy. In short, condenser water from chillers at 35oC can be used to supply all the heating, and bore hole water temperatures of around 11oC used to cool the supply air down to 14oC.
The Optimising Controls work by sensing the water temperatures in the Econet system and calculating the optimum way — recovery, waste heat etc. — of delivering the required temperature. Consistent efficiency throughout derives from the combination of the optimiser and invertor-driven pump: if 73% efficiency is achieved, 73% is maintained through all airflow and system variables. The result is energy saving, plus high-quality indoor air, with a further benefit that, because supply and exhaust airstreams are separated, it’s ideal for hygiene-critical applications.
It should now be clear that achieving a cooling airflow at low installation cost does not equate to delivering high air quality with optimised life-cycle economics. With an AHU’s 20-year running cost approaching roughly 10 times initial investment, reducing its continuing energy demands brings important whole life-cycle savings. If the building engineer pushes for a system to be specified with Econet capabilities, then free cooling, winter energy recovery and indirect evaporative cooling can all be delivered for the benefit of occupiers, building owners and specifiers alike for the whole life of the system.
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