Energy Bill

Memorandum submitted by the National Association of Rooflight Manufacturers (EN 37)

Reducing Energy Use and Associated CO 2 emissions by use of daylighting through rooflights, in conjunction with automatic control of lighting systems

E nergy use of the lighting system is a key issue when considering overall energy use in a builidng , often being the primary source of CO 2 emissions in many non-domestic buildings . C orrect use of daylight in conjunction with automatic daylight-sensing control of the lighting system is critical to reducing lighting energy and overall CO 2 emissions in many building types. Total CO 2 emissions arising from all aspects of operation of a building can be increased by more than 50% if this is not employed.

This is widely recognized and a main focus for consideration by Working Groups addressing Part L 2013. But whilst most new build stock may benefit from these savings in order to meet the targets of Part L, most existing industrial and storage buildings do not currently benefit from these dramatic savings - they may have lower levels of daylight and no a utomatic lighting control so electric lights often remain on permanentl y, wasting energy throughout the day.

 

In many forms of non-domestic building daylight cannot be provided via windows (which only provide illumination within a few metres of the wall into which they are fitted) but rooflights are often suitable for providing daylight into many building types. They are particularly suited to large open plan buildings such as warehouse, distribution and manufacturing facilities (which accounts for over 1/3 of current non-domestic building work) as well as schools, sports halls, hospitals, atria and many more.

As demonstrated below, r enewing the rooflights (or fitting new rooflights to the recommended percentage of the roof area) in conjunction with installation of a current lighting control system can halve the total CO 2 emissions for many existing buildings, without any other measures. This is likely to give by far the largest saving in energy use of any possible measures in any such b uilding over 10 years old .

NARM (National Association of Rooflight Manufacturers) has carried out a lot of analysis using the SBEM model developed by BRE for compliance with Part L Building Regulations, investigating the effects of various lighting systems, control systems for lighting, and different levels of daylighting through rooflights.

 

The findings for new build have been published in the NARM Guidance Note "Designing with Rooflights: Supporting the Guidance in AD L2A and AD L2B (2006)" which is an approved second tier document to the Building Regulations, approved by DCLG.

 

This has recently been updated to reflect the latest 2010 revisions to Part L and SBEM software, copy attached.

 

Graph 1 of this document, duplicated below, shows that if all aspects of a typical large warehouse match those specified for the current Part L notional building, including the specification of rooflights at 12% of roof area, the efficiency of the lighting system and the use of proportional lighting controls then the actual building matches the performance of the notional building - but if rooflights are removed then energy use and CO 2 emissions from use of the lighting system more than double, and the total CO 2 emissions from all aspects of operation of the building increase by 50%

 

Graph 2 of the document, also duplicated below, shows that if rooflights are retained but there is no automatic control of the lighting system (to turn off the electric lights when there is natural light available) then the total CO 2 emissions from the building increase by almost 60%.

 

This provides evidence that the combined effects of use of natural daylight and lighting control systems on energy use, and associated CO 2 emissions, are dramatic.

However, m ost existing industrial and storage buildings do not currently benefit from these dramatic savings - they may have had lower rooflight area originally, and older rooflights may now be giving less light transmission so levels of daylight are likely to be much lower, whilst use of automatic lighting control was rare so electric lights often remain on permanently throughout the day in many such buildings.

 

F itting new rooflights to replace existing (or to an increased percentage of the roof area) in conjunction with installation of automatic control of the lighting system can capture these savings, more than halving the energy consumption of the lighting system, and probably by far the largest saving in energy use of any possible measures in m any building s over 10 years old .

NARM has therefore also carried out SBEM analysis on an "old" building, estimating the effect of various improvement measures.

This assumed typical 1995 fabric values, and that the original building has 10% double skin rooflights, and with metal halide lights without any automatic controls.

A new 2010 notional building (which by definition has 12% triple skin rooflights, and electric lights based on a power density of 2.2 W/m 2 K per 100lux, with a geometry correction) would have emissions of approx 16 kgCO 2 /m 2 whilst the 1995 building would be 54 kgCO 2 /m 2 (3.5 times greater)

T he effects of the following possible measures were then assessed:

(i) adding simple on-off controls of the lighting system to the existing building with no other changes – reducing emissions to 43 kgCO 2 /m 2

(ii) replacing the rooflights (with alternative areas of 10, 12, 14 or 16%), whilst retaining the original electric lights, with on-off controls, reducing emissions to 37 to 34 kgCO 2 /m 2

(iii) alternatively replacing the metal halide lights with T5 fluorescents with on-off controls, whilst retaining the original rooflights - reducing emissions to 34 kgCO 2 /m 2

(iv) as (iii) above, but adding proportional controls rather than on-off controls with T5 fluorescents and retaining the original rooflights - reducing emissions to 32 kgCO 2 /m 2

(v) combining (ii) and (iv) above, replacing the rooflights (with alternative areas of 10, 12, 14 or 16%), and replacing the metal halide lights with T5 fluorescents and proportional controls - reducing emissions to 28 to 27 kgCO 2 /m 2

These results are all shown on the graph below – the blue points are where on-off controls and the red where proportional controls have been modelled , whilst the square points are where metal halide lights the cross where T5 fluorescents have been modeled. T he lines show where new rooflights are used at different rooflight areas:

As you would expect this shows both new rooflights and new lighting systems offer very significant savings when combined with simple on-off controls, and these are improved further when combined with proportional controls.

Furthermore, when both measures (new rooflights and new lighting systems) are incorporated, in conjunction with proportional lighting controls, then overall CO 2 emissions are halved.

However, as you would also expect, these results show that even after these improvements, overall building performance does not match the 2010 notional building, as the rest of the fabric and efficiency of the heating system is significantly poorer than 2010 standards, which new rooflights and lighting systems cannot be expected to compensate for.

June 2011