By Tim Pendleton of Better Blind Company, a KNX UK Association Member
In 2006, driven by targets of reducing CO2 emissions by 20% by 2015 and 60% by 2050, the UK Government set out its objective that all new homes and commercial buildings should be carbon neutral by 2016 and 2019 respectively. We don’t have to look far for statistics which support the emphasis on energy performance of buildings – most strikingly, 40% of UK emissions can be attributed to buildings.
Document L of the Building Regulations, 2010 came into effect in October 2010 and broadly speaking, applies to new building work and refurbishments and in comparison to the 2006 Document L, the 2010 revision is more stringent, demanding a 25% improvement in energy performance. In addition, the document differentiates energy targets by building function – such as usage type and number of people accommodated.
Importantly, there is now an emphasis on monitoring, meaning energy certificates must be provided to authorities both prior to development and after completion. This ensures that the energy performance upon which planning approval was granted is indeed met by the occupied building.
One need only look at the predominant style of modern architecture to understand the focus of the regulations on solar gains and heat losses. Large glass surfaces are aesthetically pleasing, however, such expanses of glass increase potential for solar gain in summer, increasing energy consumption through artificial cooling, and heat loss in winter, leading to energy consumption through artificial heating. Therefore, Document L advocates the use of glazing with appropriate U (heat transmittance) and G (solar gain transmittance) values.
Comfort and stability
Consider the façade of a building to be like a jacket. You wouldn’t wear the same jacket in summer as you would in the depths of winter. Glazed façades, even when supplemented with manual blinds or fixed external shading, offer this degree of inflexibility. This means that the effect of the dynamic external conditions have to be compensated for by artificial lighting, artificial cooling/ventilation and artificial heating in order to achieve comfort and stability indoors.
Energy intelligent solar shading in the form of automated internal blinds, curtains and external shading can use interior temperature, exterior weather sensors and sun tracking technology to trigger automated behaviour. When used in conjunction with the most appropriate level of glazing, solar shading provides the ability for a building facade to be dynamic and respond to changes in external conditions, thus reducing the load on HVAC and lighting systems.
Energy-intelligent solar shading, HVAC and lighting experts from each industry agree that the days of independent systems and controls for the management of each have now passed, and the ambitious CO2 emission targets in Document L can only be met by adopting a joint and integrated approach to planning and implementation.
A guide book ‘How to Integrate Solar Shading in Sustainable Buildings’ published in 2010 by REHVA (Federation of European Heating, Ventilation and Air-Conditioning Associations) advocates that selection of solar shading should always be one of the first steps in the design of HVAC systems, as the demand for power and the energy consumption are greatly influenced by solar shading.
The BELOK Project was conducted in Sweden during 2006-7 and demonstrated that electricity consumption for artificial cooling could be reduced by as much as 80% by adopting a holistic approach. The project also proved a positive correlation between energy savings and the use of energy intelligent solar shading with dimmer controlled roof lighting.
Barriers to acceptance
There are a number of barriers to acceptance of this holistic approach. Firstly, Document L itself, like many building regulations is not prescriptive. Both the British Blinds and Shutters Association (BBSA) and the Building Controls Industry Association (BCIA) have expressed concerns that the regulations are not specific enough about shading and building controls respectively. Both associations are lobbying for further clarity in future revisions of the document, with the BBSA contesting that the benefits of solar shading are not represented correctly in standard building models (SBEM and SAP).
Fragmentation is a second barrier. Many different parties feed into the building design and construction process, and as a result, the purchasing processes for building controls for HVAC, lighting and façade are fragmented. This is also engrained in purchasing regulations meaning that tendering of building controls is broken up into smaller packages. This effectively inhibits the purchasing of integrated building management systems, leading to fragmented systems and compatibility issues, resulting in energy savings not being fully realised.
Despite the above, experts from solar shading, HVAC, lighting and building control disciplines agree that now is a pivotal moment. The rate of change towards a holistic approach and integrated solar shading, HVAC and lighting systems is going to accelerate and 2013 and 2016 revisions to Document L will be a key driver.
It is suggested that building automation system integrators bring together suppliers from solar shading, HVAC, and lighting disciplines at the outset of the building specification process. Many building automation systems integrators offer blinds and curtains on an ad-hoc basis; some profess to be able to derive energy saving benefits by automating HVAC and lighting. However, few offer HVAC, lighting and solar shading as a holistic energy saving solution.
Partnering with a solar shading company will therefore be key to achieving real energy savings. Modelling software traditionally used by mechanical engineers in building energy performance modelling takes into account lighting and HVAC. It touches upon solar shading but does not accurately represent its benefits because the software hasn’t been developed with input from the solar shading industry.
Modelling software such as Somfy’s DISC or the British Blind and Shutters Association’s (BBSA) Shade Specifier enables solar shading companies to liaise with mechanical engineers and architects to model the energy savings provided by different combinations of glazing, shading product types and fabrics.
There is a variety of shading-specific control systems available, ranging from proprietary bus control systems to open control systems designed to integrate with building control systems using open bus networks, such as KNX or LON. All offer integration with DALI lighting systems.
Building automation control systems based on open protocol bus networks, such as KNX, offer a greater degree of integration, customisable behaviour and compatibility between different types of controls and systems and are therefore more suited to the holistic and integrated approach. Your solar shading partner will work with you to choose the appropriate type of shading control, depending on the automation system that is being specified.
Most solar shading companies will also offer a site survey service and will liaise with the end user or interior designer on your behalf with regards to the aesthetics of the solution. As a final justification, solar shading specialists will be able to perform Life Cycle Cost (LCC) analysis which will assist in the justification of capital expenditure to the building owner or investor by demonstrating pay back.