The growing need for energy-efficient ventilation

Published:  08 December, 2007

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As the air tightness of dwellings increases, so more sophisticated methods of ventilation become appropriate and necessary. The simplest approach is individual fans for the kitchen and each wet room, preferably with energy-efficient DC motors such as Xpelair’s ultraDC (top right), and trickle vents in windows to provide make-up air. Mechanical ventilation units such as the Xcell 150 (bottom right) and Xcell 270 (top left) also provide make-up air and incorporate heat recovery to temper the incoming air.

Ventilation is essential for buildings. As their energy performance improves, the proportion of energy required to deliver ventilation increases. Joe Barasso discusses strategies for efficient ventilation.

With the advent of the Climate Change Bill in the Queen’s speech, climate change continues at the top of the political agenda, with the Government proposing a legal requirement to reduce carbon-dioxide emissions by at least 26% by 2020.

Transport, power generation, industry and households all have their part to play in the reduction of greenhouse-gas emissions. However, with carbon dioxide from the UK’s 22 million households making up 27% of the total, increasing focus is being placed on reducing energy waste where we live and work.

Everybody can and should do their bit to reduce energy consumption at work. The greatest energy savings can be achieved through a genuine commitment to energy reduction and the careful selection and installation of efficient equipment and automated controls. Businesses have seen their energy costs more than double in three years. They are being urged to analyse their energy use and develop a plan to reduce it. All Government departments are now required to meet tough targets on energy as part of The Framework for Sustainable Development with an uptake of renewables such as solar thermal collectors and heat pumps.

Ideal opportunities

Given the will, energy use in existing buildings can be measured and reduced, but new-build and major refurbishments present ideal opportunities for the largest carbon savings. There has been a shift from building at the lowest cost to designing for future low running costs and lowest carbon impact. At an application level, advice is readily available from reputable manufacturers. Ventilation is no exception. In densely occupied public areas, body heat and odours can be the overriding consideration. Ventilation controls such as Xpelair Active Response Systems automatically vary ventilation rates with varying usage, air quality and changing seasonal temperatures with a real impact on energy costs.

Air-handling units designed to reduce energy costs, such as Xpelair’s CustomVent, feature variable-speed drives, heat recovery, zone controls to provide ventilation only for occupied areas and timed controls for business hours — in addition to mandatory local energy metering and interfacing with building-management systems to monitor and control usage. Moving from manual intervention to automated controls means equipment operates only when required, minimising energy use whist maintaining good air quality. These measures, taken together, can achieve significant energy savings and, therefore, reduce carbon emissions.

Companies such as Xpelair Ventilation, Redring, Creda, and Xpelair CustomVent (all part of Applied Energy Products) have advisory teams who are fully conversant with current and forthcoming regulations and able to provide assistance to businesses and local authorities on strategies using standard products appropriate to their premises and activities.

On the new-home front, there has been a dramatic change in attitudes to ventilation in the last 12 months. Revisions to Building Regulations Parts L and F1 and F2, together with the road-map standards set by the Code for Sustainable Homes, are changing the way in which domestic and commercial buildings are designed and built.

Displaying the SAP rating to potential buyers is mandatory. 45% of UK carbon-dioxide emissions come from buildings, and 40% of the emission savings are expected to be derived from the domestic residential sector, so Parts L1 and F1 of the Building Regulations focus on improving energy efficiency and reducing carbon impact, whilst preserving a healthy environment and protecting the fabric of the dwelling.

Part L requires the air leakage of buildings not to exceed 10m3/h/m2 with a 50 Pa pressure difference between the outside and inside of the building. Many developers are choosing to better this figure as they discover air-tightness is one of the most cost-effective ways to reduce carbon impact and meet their target carbon emission rate (TER). To police these air-tightness standards, mandatory leakage testing has been introduced. Part F already cites more demanding levels of air tightness to 3 or 4 m3/h/m2 at 50 Pa as being achievable using normal construction methods. With such low leakage, a controlled ventilation strategy is essential.

So ventilation is now linked to energy efficiency. The new SAP appendix Q procedure promotes carbon efficiency through new technologies, which can be factored into the SAP rating.

StrategiesB>

Three controlled ventilation strategies are attracting much interest.

1. Decentralised constant extract systems. These use individual fans in the kitchen and each wet room running constantly at a preset low extract rate defined in Part F1. Products fitted with DC motors invariably provide lower energy use than equivalent AC motors and have a longer motor life. This approach requires window trickle vents to provide air replacement.

2. A single extract unit with ducts connected to the kitchen and wet rooms. Best-practice products in this category have to demonstrate a specific fan power of 0.6 W/l/s and are usually fitted with UltraDC motors. Again, window trickle vents are required to provide air replacement.

3. Mechanical ventilation with heat recovery (MVHR) combines an extract system from the wet rooms and a controlled air-input system to other habitable parts of the dwelling whilst transferring a large amount of heat to temper the incoming airflow. Cross-flow heat exchangers are typically 50 to 70% efficient, depending on air volume. Contra-flow exchangers can offer efficiencies of 85 to 93%. In the UK, MVHR systems are also very effective in reducing condensation. Trickle vents are not required.

A list of MEV and MVHR units which can be factored into SAP calculations is available on the Building Research Establishment SAP Appendix Q web site. Leading manufacturers have submitted their MEV and MVHR units for test. The published results show specific fan power, the tested efficiency of heat-recovery cells. The logo of the Energy Savings Trust signifies that the product has met the best-practice criteria. The Xpelair Xcell 270 MVHR unit and Xplus MEV units for example are Appendix Q listed and best-practice compliant.

Products that are compliant with best practice and their test declarations are listed at www.sap-appendixq.org.uk, or visit www.xpelair.co.uk.

Joe Barasso is with Xpelair.



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