By Chris Pearce
Last October saw the latest changes to the Part L2 Regulations (Conservation of Fuel and Power in buildings other than dwellings). This is the latest revision as part of an ongoing programme of carbon dioxide (CO2) emission reductions to achieve zero carbon non domestic buildings by 2019. Part L 2010 Regulations required a 25% (on average) improvement on the 2006 Regulations, which in turn were a 25% improvement on the 2002 Regulations.
The 2002 Regulations were primarily focused on improving the insulation and the air leakage of the external fabric of the building. This was further improved in 2006 together with a focus on improving the efficiency of the building services – heating, air conditioning, hot water and artificial lighting. 2010 Regulations require further improvements to the fabric of the walls and roof, but these are subject to the law of diminishing returns. Further increases in insulation thickness add additional cost (often requiring additional structure) but with ever decreasing benefits. The focus of Part L 2010 is increased efficiency and control of building services, reducing the impact of excessive solar gain that could create an increased requirement for air conditioning, and further improvements in build quality to avoid air leakage.
For a new non domestic building, compliance is achieved when the CO2 emissions of an actual building (the Building Emission Rate or BER) are less than or equal to the CO2 emissions of a Notional building (the Target Emission Rate or TER). The Notional Building is re- defined for 2010: it is the same size and shape, and used for the same activity as the actual building, with performance of all elements of the fabric, the building services, and system controls are based on current good practice, all defined in the National Calculation Methodology.
Performance of the actual and Notional buildings are calculated and compared using approved simulation tools, such as SBEM (free-of-charge computer software from the Government).
Part L 2010 for New Build Non Domestic buildings (ADL2A) also sets out worst acceptable values for the performance of both the building fabric, and the efficiency and control of building services. These are designed to allow some flexibility in building design; the Notional Building is based on improved values. If an actual building was designed using the worst acceptable values as set out in ADL2, for all design considerations, it would fail to achieve the performance of the Notional Building by a considerable margin. If worst case values are adopted in some areas, significant improvement will be required in others to compensate.
One of the most important aspects of a non domestic building is the energy use of the lighting system, and use of natural daylight to minimise this: uncontrolled, lighting can often be one of the biggest single energy uses when operating a building. This is particularly important when CO2 emissions are considered, as much more CO2 is emitted to generate each kWh of electricity used for lighting systems than is emitted to generate similar levels of energy from most other sources (such as natural gas typically used for heating systems).
Control of the lighting system to capture the benefits offered by natural daylight is vital: human nature means that in non-domestic buildings lights can often be left on all day despite the availability of natural light. If the lights remain on permanently regardless of the natural daylight available, or there is no automatic control of the lighting system, then for a typical warehouse or industrial building, the CO2 emissions from the use of the lighting system alone can be 4 times greater than for the heating, and greater than the total permissible emissions for the whole building!
Two fundamental design issues must be considered here: good levels of natural daylight must be designed in, then control systems must be used to turn off artificial lights to gain the benefit of this. Firstly we must design in plenty of natural daylight.
In smaller or narrow buildings, correctly specified windows can provide good levels of natural light for areas within 6 metres of a window wall. However, for larger buildings where the space is greater than 6m from a window, roof glazing or rooflights, typically to 15-20% of the floor area, is the best way to put natural light on to the floor of the building. The Notional Building assumes rooflight area of 12% for appropriate building types.
Having provided the natural light, control systems are needed to turn the artificial lights off, and on when needed – electric lights should be on and bright when needed, dimmed or off when the natural light gets brighter, or switched off when there is no one in the area. Control systems can either be switching (on-off) or ideally proportional (dimming), using sensors to detect the amount of available natural light, and can be supplemented with occupancy sensing and timers. The Notional Building assumes proportional control of lighting systems in rooflit areas.
By introducing rooflights coupled with automatic control of artificial lights, the energy saving is considerable and essential to achieve compliance to the 2010 Regulations. The following graphs show the effect of altering rooflight area, and lighting system controls, for a typical industrial building otherwise specified in accordance with the Notional Building.
These graphs demonstrate that for a typical industrial building:-
1. At 12% rooflight area and with proportional lighting control, overall CO2 emissions are exactly the same as the Notional Building and will be compliant.
2. If rooflight area is reduced, CO2 emissions increase and the building will not be compliant unless other savings are made
3. If lights are left on permanently (either without rooflights, or without automatic lighting controls) the CO2 emissions associated with use of the lighting system alone are
a. greater than the maximum permissible total emissions
b. 3 times greater than when rooflights and lighting control are correctly specified
c. 4 times greater than the emissions for heating the building
4. If lighting controls are switching rather than proportional, emissions are increased, but increases in rooflight area can compensate for this
It should also be noted that
1. If rooflights with lower U-value (eg 1.3 W/m2K) are used, heating demands will be reduced and further benefits are seen as rooflight area increases above 12%, providing an opportunity for the designer to compensate for other areas of the design that may be less efficient.
2. Rooflight area should not normally exceed 18-20% to avoid risk of solar overheating
It is clear that the benefits of designing with rooflights coupled with sensor controlled artificial lighting are fundamental to achieving compliance to Part L2A 2010 .
And there is a real fundamental added bonus – rooflights provide natural daylight across the entire floor space of the building making the building a pleasant place to be and where people work (or play) more efficiently. Natural daylight is fundamental to our daily routine and self esteem. It has been shown that hospital patients get better quicker when in a ward with plenty of natural light, students results improve when learning in naturally lit classrooms, retails sales are higher in naturally lit stores, and productivity rises and absenteeism reduces in naturally lit workplaces.
Thus 15-20% rooflights coupled with sensor controlled artificial lighting provides both designers and building owners a win:win solution.
The National Association of Rooflight Manufacturers (NARM) have now issued a 2nd tier document to ADL2A 2010 to advise full details for designers and contractors on achieving compliance to Part L by using rooflights and artificial lighting control. It provides advice on the use of SBEM and how to input rooflight data, the effect of varying rooflight area, thermal and light transmission properties, worst case U-values and solar gain limits, as well as looking at the requirements for refurbishment detailed in AD L2B.