Robert Cohen discusses how best to improve the energy performance of commercial properties
Buildings in the UK offer the most cost-effective and largest opportunity for carbon abatement. The fourth carbon budget review for buildings, published in December 2013 by the committee on climate change, forecasts that emissions from public and commercial buildings could be close to zero by 2030.
That is the scale of the challenge facing owners and managers of non-domestic buildings. Yet, over the past 20 years, the energy performance of commercial properties in the UK has failed to improve at a rate commensurate with the acknowledged potential for cost-effective savings. Although energy use for heating has typically fallen, albeit by less than might have been expected, this has been counteracted by growth in electricity use, with its higher primary energy and carbon factors.
Information shortfall
A primary reason for the shortfall has been the over-emphasis by policymakers on computer models of theoretical energy use, specifically how much energy is needed to create a comfortable working environment under standard conditions of use. But the carbon at stake in this approach represents a diminishing proportion – often well under half – of a non-domestic building’s carbon footprint in operation.
There needs to be more focus on operational energy use: measuring how buildings perform, making all stakeholders aware of how that compares with the design-stage assessment and what is causing the differences, aka the notorious performance gap. Persuading everybody to engage with reality rather than, or at least in addition to, a contrived metric is the only rational way to deliver on expectations.
The Building Regulations 2002 introduced a requirement to install energy sub-meters in new non-domestic buildings. However, this is too often treated as a tick-box exercise, with the meters forgotten when the building opens. Unsurprisingly, this has led to poor quality delivery – for example, meters that are faulty or incorrectly commissioned, and a lack of resource to interpret the data they provide (which is difficult to recover in any case) to identify the improvements needed. As a result, the energy management of most new buildings is no better than it was before the requirement for sub-meters was introduced.
Such behaviour is not inevitable. Supermarkets, for example, routinely deploy an array of energy sub-metering to monitor targets, and have delivered remarkable improvements in their energy performance as a result. Their behaviour is not altruistic; they know that energy efficiency helps their business to avoid the negative impacts associated with a poorly performing building, even before taking into account the financial savings from lower running costs.
Why has this not become standard practice across the non-domestic sector? Partly because energy costs are higher for supermarkets and partly because it is a sector dominated by well-honed, pattern-book specifications delivered by suppliers that are often long-term partners and focused on retaining the repeat business. Supermarkets expect bug-free sub-metering systems, know how to capitalise on them, and in many cases use sub-meter data to support evidence-based rolling programmes to determine which new energy-saving approaches or technologies are worthwhile.
Spreading the word
Energy measurement is a powerful and indispensable tool for identifying energy and cost reduction, but it is critical to limit the number of sub-meters to match the energy management capacity available. Make the meters useful and they will be used. Ensure sub-meters are fully commissioned, calibrated correctly and delivering data in a suitable format.
Once a system is handed over, it is important to include the sub-meters in maintenance schedules and ensure there is a user-friendly infrastructure for processing sub-meter data. If only to cope with staff changes, a sub-metering system should always be described by a short “start-to-end” guide, which tells the person taking over responsibility everything they need know to continue delivering the appropriate level of energy management.
It is exasperating how common it is for there to be doubt about which plant or equipment is on each sub-meter. The meters are at best marked on complex electrical distribution diagrams, often with opaque descriptions of the loads being measured, such as motor control centre, building management system (BMS) control panel, and landlord meter. And it is not unusual for reality to be slightly different from what is shown on design drawings.
System design
The cause of the problem is that many mechanical and electrical engineers and contractors install a sub-meter system without anticipating how to do so to ensure energy management is relatively easy. A better approach is to define first the energy management system and the necessary sub-metering, and then design a system, clearly documented by a meter tree, to deliver that strategy (see panel above). The electrical distribution diagram should be the last resort to confirm which equipment is fed from each sub-meter.
CIBSE, the Chartered Institution of Building Services Engineers, has developed a tool called TM22 to enable energy managers to understand a building’s energy use and diagnose improvements. At a building’s design stage, it can also be used to define an optimum sub-metering arrangement.
The key to effective energy management is to know how much energy you are expecting a sub-meter to measure – this could be over a day, week, month or year – and to determine if and why use is exceeding this level. TM22 can tell you this if you enter the power ratings of the main equipment, such as chillers, pumps, fans, and small power and lamp asset registers, and their expected hours of use. It can also benchmark each energy end use’s roots of consumption (installed power and service levels and hours of use), leading to diagnoses of excess and then to energy-efficiency improvement measures.
Half-hourly electricity (and gas) data are increasingly available and an unerring guide to waste, especially that occurring during the long periods when many buildings are unoccupied. It is always worthwhile to benchmark the base load in watts per square metre (W/m2). If this is too high, a night survey would identify the sources of out-of-hours energy use and check whether they should be switched off – for example, by fine-tuning the BMS controls.
Transparency
Transparency and understanding about energy use are critical drivers. Establishing an effective reporting hierarchy can create appropriate levels of engagement.
Start by encouraging supportive behaviour by the building’s occupants – this may take some determination and charisma. Instil a sense of purpose and even fun, while recognising the importance of occupant satisfaction with their working environment. Display screens in the reception area are increasingly popular for reporting energy performance and motivating improvement.
More formal reporting should be at the following three levels:
- reports for the internal team with energy management responsibilities;
- annual report to the main board, ideally receiving director sign-off and budget approval for making improvements; and
- public transparency – for example, producing annual corporate responsibility reports and displaying energy certificates.
