Benchmarks for office energy
For several years 'Econ 19' has been one of the clearest energy benchmarks for designers. This month the DETR publishes a revised edition of Econ 19 (its full title is 'Energy Consumption Guide 19: Energy Use in Offices'*). Based on measurement of energy consumption it sets out 'typical' and 'best practice' performances, suggesting new buildings should aim to do better than the current best practice figures.
Econ 19 is not a general guide for designers, clients and facilities managers. While it acknowledges the significance of strategic design decisions on form, orientation and the like, its main focus is to set out benchmarks on an annual per m2 basis for delivered energy use, energy cost and carbon dioxide emissions.
In dealing with current performance it must characterise current office design. It uses four representative office types.
Type 1: naturally ventilated, cellular, typically 100-3000m2 , sometimes in converted residential accommodation. A domestic-scale approach to design, with few common facilities.
Type 2: naturally ventilated, open plan, typically 500-4000 m2 , largely open-plan with some cellular offices and special areas. New or converted building; more use of lighting and shared controls with lights thus often being left on.
More office equipment, vending machines, etc.
Type 3: air-conditioned, standard, typically 2000-8000 m2 , largely purposebuilt, often speculative. Similar to Type 2 in occupancy and planning, but deeper plan. May be more intensively used.
Type 4: air conditioned, prestige, typically 4000-20,000 m2 , often a national or regional head office. Purpose-built or refurbished to a high standard. Diverse occupancy with longer running hours.
Energy consumption of catering and computing facilities can be high; also parking and leisure facilities.
As Table 1 illustrates, there are very great energy cost differences between the types, resulting both from their use patterns and design. Recent claims that well-designed air-conditioned buildings might consume no more energy than passive designs is not yet being born out by current general practice. And this despite the fact that larger organisations typically pay less for their fuel - Table 2.
Per formance in practice Econ 19 points out that, overall, the benchmarks will be higher than most design estimates 'which often assume essentially perfect performance and operation, and ignore some end uses and practices' such as catering, vending machines, lifts, computer suites, reception areas, etc. In terms of building use, optimistic assumptions are often made about user behaviour, such as light switching, and the effective management of the building over its life. The bar charts given of fuel use, cost and CO for actual buildings need interpreting in this light.
While much of Econ 19's content is about presenting and interpreting the data, there are a range of pointers to how design can be improved, ranging from general points about understanding the motivations of different players in tenanted buildings, to specific tips like saving on the often energy-wasteful process of catering by making the catering fuel bill part of the catering contract. And there are data - see Table 3 - for making the case to clients that IT heat loads are not as high as sometimes claimed.
Econ 19 could improve on a couple of points. It could be clearer on the need for submetering; if facilities managers don't know what fuel is being used for what application how can they manage it? The other point is the issue of space-use intensification. Measuring energy, its cost and CO 2could well penalise a smaller but more efficient building. That is, one that uses more energy per m2 but less overall. With changing patterns of office work, dense occupation is becoming increasingly pertinent. Even without data to spell this out, the issue should have been raised in the document. That said, this is an important set of benchmarks aiming to push forward the mass of office building practice.
*FreefromRECSU Enquiries Bureau, BRE, Garston, Watford, WD2 7JR, tel 01923 664258