090 GGP 0813

GGP August 2013

LETTER FROM AMERICA remember reminder of the importance of access to daylight for our body’s health. At this point though, I feel that I must insert a note of translation, since this is a classic example of being ‘divided by a common language’, and you are probably wondering if there are other effects of light that I haven’t mentioned! In the US the word ‘drug’ is used to describe any form of medicine prescribed by a doctor – that is, it’s the good stuff that makes you better – not just the illegal, bad, stuff! With the impact on health and well-being in mind, I turn now to our battle for the wall which continues to be waged in the US. In my last letter I mentioned that there is a specific proposal being made to reduce the allowable window to wall ratio (WWR) from 40% to 30% for buildings less than 25,000 ft2 (approximately 2,500 m2), which are designed using the prescriptive compliance path of the ASHRAE 189.1 green building standard. This standard was developed to codify the US Green Building Council’s Leadership in Energy and Environmental Design (LEED) rating system (similar to the UK’s BREEAM) and includes sections for energy efficiency, daylighting and views and other sustainable design practices such as water management, for example. It is ironic that the reduction in window to wall ratio is being proposed in a standard where provision of daylight and views are also a key focus. Now you might think that since this change relates only to buildings of size less than 2,500m² that this isn’t going to have a big impact, but according to the Commercial Building Energy Consumption Survey (CBECS) 89% of the buildings in the US are in fact under this size! The public review period for the proposal closed a couple of weeks ago with an overwhelming response: 72 public comments from 57 different commenters – all negative and asking for withdrawal of the proposal. To understand the enormity of the response, you have to know that in the normal course of business there are generally only 5-15 comments per proposal, and in some cases none. Even more importantly, the commenters were not just from glass and window companies who obviously have a business interest in maintaining higher window areas, but they spanned a wide range of independent organisations from across the broader building industry, including the International Association of Lighting Designers, lighting control companies, academics and many daylight experts. In addition to the fact that the proposal ignores the human health and wellbeing benefits of windows, there were actually quite a number of other distinctly different reasons cited for why the proposal should not be adopted, which I have attempted to summarise below: • Conflicts with the provisions for daylighting and views. Since ASHRAE 189.1 is a sustainable design standard, compatibility with its requirements for daylight and views is critical. During development of the original standard, the constraints on the fenestration in the energy chapter were tested thoroughly against the provisions for daylighting and views to ensure that there were no significant conflicts or unintended consequences. Reducing the window area will certainly make it more difficult to comply with the IEQ provisions and to provide a comfortable glare-free day lit space. • Reduces the potential for achieving better overall performance. This is an interesting point. The design of a high performance building involves the optimisation of many competing goals and optimisation of energy performance “I now turn to our battle for the wall, which continues to be waged in the US” can have a detrimental effect on others. Attempts to constrain too prescriptively the parameters such as WWR, visible light transmission, orientation, etc. limits innovation in design and new product adoption and the potential for better performance. For example, there are many available product technologies that allow dynamic optimisation of daylight and sun management for fenestration (such as automated shading systems, dynamic glazing, light redirecting films), that respond to changing climate conditions and occupant preferences. Taking the simplistic approach of reducing window to wall ratio will reduce the incentive for adoption of technologies that allow designs that can be optimised for daylighting and views without compromising energy performance. . • The limitations of an energy model used to justify the WWR reduction. Although there are many arguments specific to the particular modelling analysis used to support this particular proposal, the bottom line is that the results of a modelling study are only as good as the assumptions made and the model used and it is important to understand these in order to understand the applicability and limitations of the results. • Using whole building energy modelling for compliance is not a realistic alternative for small buildings. One of the arguments in the proposal for the reduction in WWR in the prescriptive compliance path is that there is still an option for using a compliance path which uses whole building energy modelling (the performance path). However, for small buildings, this not a realistic alternative because of the cost associated. Moreover, the modelling only takes into account the energy performance and says nothing about the IEQ of a high performance building. Whilst the list is neither exhaustive nor fully detailed, it at least gives you a flavour for the main points that have been made, some of which may be transferable to similar future situations. Much of the credit for the extent of the public comment response should be given to the Glass Association of North America (GANA) which, through its Building Standards Subcommittee and its code consultant, Tom Culp, worked diligently to get the word out during the public comment period to both its membership and a wider audience, and helped educate the community on the concerns. At this point the ASHRAE 189.1 energy work group is reviewing the comments and we should hear more in the next few months. To be continued… 090 August 2013 Glass & Glazing Products


GGP August 2013
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