Evaluating energy performance in buildings: Why? When? How?
Author: Date: 20/03/2017
Faced with the urgent and important demands that buildings and Energy Managers are presented with every day, it's understandable that the equally important but less immediate challenge of understanding and optimising energy often has to take a back seat. It's often difficult and complex to understand how much energy your building is using, and how it breaks down into uses, time periods, zones and even tenants. Then there's the question of differentiating the building's intrinsic energy use from that needed to run its operations and activities. All told, it isn't surprising that, in spite of the rhetoric surrounding energy performance of buildings, all too often, relatively little is done in practice.
Why and when to evaluate energy performance in buildings
There are many reasons for evaluating the energy performance of your building under different circumstances. If you’re taking over ownership or tenancy, whether it’s a newly built, refurbished or an established building, you shouldn’t rely on a theoretical performance assessment – an EPC or BRUKL is based on assumptions about how well the ‘as built’ building matches the ‘as designed’ building and reflects the performance of its fabric and services. In theory, theory and practice are the same, but in practice they aren’t. Recent studies under the Innovate UK's Building Performance Evaluation programme (and others) have found that, on average, non-domestic buildings use 2 ½ times more energy than predicted; irrespective of its sector. This performance gap arises from a combination of factors but evaluating the energy performance of your building as part of the hand-over process will enable you to ensure that the fabric performance comes up to scratch, and that its services are installed and commissioned properly. The flip side of this is; if you’re responsible for marketing a property, demonstrating its ‘as built’ performance will be of increasing interest to potential tenants and purchasers.
For buildings you already own or occupy, evaluating the energy performance equips you to manage energy use better on a daily basis and to identify and prioritise opportunities for energy-related improvements – whether they’re capital investment, education programmes or building management modifications. One well-known property owner found that even without capital investment, it was able to save at least 20% of landlord energy use through basic, low-tech measures and good procedures. In addition to saving energy and hence expense, if you get really smart at managing energy use in real-time, there are opportunities for negotiating more attractive tariffs through dynamically adjusting demand.
Comparing the performance of your buildings with each other and with others of similar design or use gives a real sense of how big the opportunities for improvement might be, and it enables you to focus clearly on the low-hanging fruit of energy inefficiencies. A number of web-based tools are available, such as Carbon Buzz and Energy Deck, some of which are free. Carbon Buzz, for example, compares energy intensity (annual energy use per m2) of a given building to CIBSE TM46 sector benchmarks and to all buildings held on the database, filtered to include those similar to yours.
Even if you don’t compare energy use in your own building(s) with others, tracking energy use over time enables target setting and underpins investment decisions. For example, if service equipment becomes inefficient as it ages, monitoring energy use can alert you to equipment failures, unauthorised reprogramming of controls or changes in occupancy; enabling you to act quickly to respond to occupant needs without wasting energy.
The final reason for evaluating energy performance is to protect the value of property assets arising from the potential future threat of regulatory obsolescence if building performance falls behind standards required at transfer of ownership or tenancy.
How to evaluate energy performance in buildings
The old adage: “If you don’t measure it, you can’t manage it” applies but what should you measure, how, how often and how should you interpret the data?
Energy performance evaluation is a significant subset of overall building performance evaluation and, I would argue, undertaking a broader performance evaluation of the building gives valuable additional insight into why energy is being used where and when.
For in-use buildings, best practice is to carry out a periodic study - say summer and winter - plus additional studies triggered by changes in use or replacement of key equipment. The evaluations should draw on data captured over the whole year, e.g. half-hourly meter data, internal and external temperature records and services operating records. Using a spread sheet-based tool such as CIBSE TM22, you can capture and document the energy used by occupants and, combining this with an occupancy profile, predict the building’s expected energy uses. If your building has a good and reconciled sub-meter arrangement, you can record measured and disaggregated energy use, which can identify and quantify discrepancies (and hence any opportunities).
In order to use a spread sheet such as TM22, you’ll need data from sensors, thermostats, meters, etc. However, even if your building is minimally monitored, has no BMS or only has a main electricity/gas meter or a simple programmable timer on space and water heating, you can still use this information, together with counting and estimating hours of use for energy-using services and equipment (e.g. lights, computers), to get a pretty good estimate of where, when and how energy is being used in your building.
If this is starting to sound a bit complex, think of the savings you’re almost guaranteed to make. It’s also reassuring to know that specialist help is available through numerous consultancies and charities such as the National Energy Foundation, and many offer advice with no up-front cost but for a share of the savings made.
There are two other key aspects to building performance evaluation that contribute significantly to energy performance evaluation – site inspection and occupant survey. Site inspection is about taking a good look (and listen) at your building; from top to toe, inside to outside, board room to plant room. Look at the fabric of the building; look for hot spots in summer, cold spots in winter, draughts, doors that don’t quite close, cracked or broken windows, gaps around services penetrations or where modifications have been made. Look at the services themselves, especially heating and air conditioning, checking for lagging of pipes, excessive fan noise, programming that doesn’t fit occupancy patterns.
Consider the settings and controls in the building. Are offices and meeting rooms too hot or cold? Do they have both heating and air-conditioning (potentially fighting each other)? Do factory floors and loading bays have large doors that stay open for longer than necessary? What about compressed air leakage? Is internal or external lighting left on overnight? How do cleaning staff leave the building? Is office equipment left on when not in use?
Look for the kind of poor operating practices we see all too often:
- Building management systems not properly commissioned or set up at handover - complex controls, poor operating instructions, inadequate labelling and systems inappropriately programmed for their occupancy.
- Inadequate training on operating the building efficiently.
- No interlock on heating and cooling systems, allowing occupants to have both running simultaneously.
- Air-conditioning that is too high capacity for the areas it serves, and installed without calculating the relevant load.
- Heating and air-conditioning systems that are set either too high or too low, instead of providing a comfortable environment for most people while allowing them to dress according to their own personal comfort.
- Air-conditioning systems that are left on in unoccupied areas when sensors would solve the problem.
- Heat rejection pipes from portable coolers poked into the ceiling void or behind furniture - as if this can magic the heat away!
- Ventilation fans that run overnight, removing heat from the building and increasing the morning re-heat load. Either fit better controls or re-configure the operating hours.
- No natural light or inappropriate lighting. Lighting is often inefficient, has zoning deficiencies or uses poor controls. It can be too dim or too light, and is all too often left permanently on. Adjusting the amount of lighting, fitting LEDs with lux levels suited to the location and use, or installing motion sensor controls are often affordable, and offer short paybacks.
- Heating on, windows open. Fit window sensors that switch the heating off automatically when they are opened.
- Poor implementation of sub-metering, made worse by no clear understanding of how to use it properly and the benefits it can provide.
- Loading bay doors that are left open unnecessarily.
- Poorly maintained refrigeration – missing doors, broken hinges and worn seals.
- Doors in shops and offices either left permanently open or open/close too frequently.
- Uninsulated hot water tanks, pipework, valves, flanges and pumps.
- Hot water overheated to combat diseases such as legionella, but without doing a realistic risk assessment.
- South-facing, highly-glazed buildings, without shading - leading to overheating and an increased requirement for cooling. Solutions include blinds, window film or brise soleil shading.
Ideally, carry out one site inspection during occupied hours and another when the building is not being used. Ask yourself: How much energy is my building using when I’m not using it? Because the vast proportion of this energy is, quite simply wasted, it can be a quick win, offering a potential saving without impacting any of the building’s normal activities.
The final piece, and not to be underrated, is the perspective of occupants. A structured survey method such as Building Use Survey (BUS), which has been honed over 30 years and includes a large database of properties already surveyed, provides maximum benefit to the surveyor as well as benchmarking against other buildings in terms of a range of comfort factors. Alternatively, occupant feedback can be captured using a ‘home grown’ survey at very low cost and, most importantly, the individual and collective survey data can be cross referenced with other information from site surveys and energy monitoring to identify wasted energy. Consider, for example, glare on computer screens. This might result in occupants drawing window blinds and using additional artificial lighting during daylight hours. A change in office layout could tackle the root cause and remove the need for extra artificial light whilst also improving the working environment.
Energy performance evaluation will increasingly be an essential responsibility of Energy Managers, and will benefit all building stakeholders from shareholders to employees to customers. Whilst you’re likely to need external expertise for complex buildings and a detailed evaluation, you can carry out a basic evaluation with a little help, training and support, a common sense approach, good observational skills, and a willingness to act on the results.