Table 1
UK energy and carbon metrics and some consequences.
| Date | Example | Metric | Some consequences |
|---|---|---|---|
| 1974–90s | ‘Yellow Booklet’ Normalised Performance Indicators (NPIs) | Stress on reducing total delivered energy (EU = final energy, US = site energy) | Normalised for weather and occupancy-hours. Some later revisions included fuel/electricity splits. Caused some buildings to change from fuel to much more expensive and high-carbon electricity. Normalised performance was sometimes confused with raw |
| 1980s | e.g. Monergy campaign, 1986 | Stress on cost and efficiency: not conservation, which politicians still do not favour | Considerable effort on energy management. Motivation slackened when energy prices fell. Once price competition was introduced, contract negotiations could save a lot of money easily, so why bother with investment and management? |
| 1991–2001 | Energy consumption guides | Separate benchmarks for delivered fuel and electricity | Some guides included cost and CO2 indicators, and breakdowns by end-use. For a while this improved the focus of designers on all elements of energy performance in use |
| 2002–08 | In-use benchmarking neglected by government and its agencies | Dominated by building regulations requirements in CO2 metrics | Policy emphasis on CO2 shifted activity towards low-carbon and renewable energy, too often at the expense of basic energy savings. A ‘design for compliance’ culture burgeoned, with design thinking narrowed to modelled calculations of ‘regulated loads’: the heating, hot water, cooling, ventilation and lighting prescribed in the EU Energy Performance of Buildings Directive |
| 2008 on | In-use benchmarking continues to be neglected | Regulations and building energy certificates largely based on CO2 | Compliance culture continues. Poor support to Display Energy Certificates based on metered energy use, which also failed to be extended to the private sector (Cohen & Bordass 2015) |
| 2018 on | Revisions to building regulations pertaining to the conservation of fuel and power (Part L) MHCLG (2019) | Primary energy (Source Energy in the US is similar) and CO2e | Could create new unintended consequences, in particular too fast a shift from fuel and heat to electricity, even though electricity is much more expensive and its capacity to do useful work should not be squandered |
Table 2
Denominators often used in energy-use indicators (EUIs) and carbon performance indicators (CPIs).
| Denominator | Strengths | Weaknesses | Comments |
|---|---|---|---|
| Floor area (m2 or ft2) | Measure of useful space. Often recorded, but not always accurately | May reward lightly used buildings, unless intensity of use is also taken into account in some way | Floor area conventions (e.g. gross, net, usable, internal, external, treated (heated) etc.) and definitions can vary widely between sector and country |
| Volume (m3 or ft3) | Used in some sectors, e.g. historically in UK health buildings, but its justification is not at all clear | Not routinely recorded. Tall ceilings help natural ventilation and light. With air-conditioning, lower ceilings aggravate differences in EUI | Not normally very helpful. May suit sectors (e.g. warehouses) where height can contain useful volume. Often better to have separate sector benchmarks by area |
| Number of workstations, occupants or occupant-hours | Indication of ‘productivity’ of the building in some sectors | Occupant numbers (and occupant-hours) are difficult to count reliably. Overestimates have often been used to ‘improve’ EUIs | Best as a secondary indicator, or where occupancy metrics are robust (e.g. school rolls). Should become more useful as systems for monitoring occupancy improve |
| Volume of production or sales | Useful where production or sales are well defined | Relationship is often quite weak | Used for some industrial processes, restaurant meals and supermarket sales |
| Other commercially relevant factors | Relates to business drivers | Relationships need to be demonstrated to be relevant and useful | For example, type and quality of hotel and number of bedrooms |
Figure 1
Boundary of premises energy use (PEU) and operational rating (OR).
Note: CHP/Cogen = combined heat and power/co-generation.
Source: Cohen, Bordass, & Field (2006).
Figure 2
The Landlord’s Energy Statement (LES) process for a rented office.
Note: HVAC, heating, ventilation and air-conditioning.
Figure 3
Chartered Institution of Building Services Engineers (CIBSE) TM22 ‘Tree diagram’ for lighting in an office.
Figure 4
Three complementary approaches to benchmarking.
Note: DEC, Display Energy Certificate.
Figure A1
Landlord’s Energy Statement (LES), extract from page 1.