Mind the gap06 May 2021

Engineered systems support people living and working indoors. However, there is often a gap between the way those systems were designed to work, and what happens in reality. Enter the growing field of building performance evaluation. By Tom Austin-Morgan

According to the UK’s National Energy Foundation, there is significant and growing evidence that buildings do not perform as anticipated in their design stage, especially energy performance. The reasons for this stem from various areas including design, construction, handover and operation. This is often referred to as the ‘performance gap’.

Building performance evaluation (BPE) is a tested and defined method that can be adopted to measure and monitor building performance before, during and after building projects with post-occupancy evaluation being one of its major parts. It can be carried out in new, existing and refurbished domestic and non-domestic buildings.

In any organisation, energy can’t be efficiently managed unless it’s monitored effectively, and results are targeted and acted upon. BPE can help organisations set up robust energy monitoring systems, provide results to agreed timescales and ensure that identified anomalies are resolved.

Anthony Coates-Smith, managing director of Insite Energy, says that one of the reasons that buildings often don’t perform the way they are designed to is down to British design standards and consultants’ unwillingness to push boundaries to improve efficiency by downsizing their buildings.

“It’s far easier to oversize a building and never run out of heat capacity at peak demand than it is to take a risk and design to tighter specifications,” he says.

“If you designed a system that’s smaller, tighter and more in line with likely peak loads, it’s going to be more efficient when it’s not at peak load. But oversized systems are being churned out time and time again and they benefit no one.”


Christian Engelke, director of climate solutions provider Viessmann, adds that he sees generic building designs being chosen for projects where that particular design may not be the most efficient for the way the building will be used.

Commonly, the most power-consuming aspect of building operations is the heating, ventilation and air-conditioning (HVAC) system. Thus, it is also the most important to focus on to increase efficiency. Engelke says: “Some buildings are run in a regimented way: the heating is switched on at 6am and off at 5pm, and it will not be turned back on from Friday evening until Monday morning. People think they’re saving energy doing this because they don’t want the building heated when it is empty.

“In the UK a lot of buildings use convector heating, pumping high-temperature air from radiators or air handling units as quickly as possible. But the walls and other surfaces are cold, so extra heat must be pumped in to make people feel warm. There are ways of maintaining a certain fabric temperature so you use less energy to heat it up the next morning.”

Viessmann’s energy monitoring facility in its controllers shows how hard HVAC compressors are being run. Compressors work inefficiently if heat pumps are providing high temperatures.

“The best example is pumping up your bicycle tyre,” Engelke explains. “The higher the pressure in the tyre, the hotter the air pump gets because more effort is being put through it. It’s the same thing with a compressor, the higher the temperature the heat pump must produce, the more electricity is required, and therefore efficiency goes down. You can see on our energy management controllers how hard the compressors are running and we can advise customers what changes and improvements are needed.”

Even simple things that aren’t technically operation engineers’ responsibilities, such as managing the procurement of gas at the best price (if you have a gas-led system) and understanding heat network performance, is critical to operations and maintenance (O&M). If you can’t see how the network is performing, how can you fix it?

“Check metres have been mandatory since 2014 in residential buildings,” explains Coates-Smith. “One of the failures of the Heat Network (Metering and Billing) Regulations 2014, in my opinion, was while it required meters to be installed, they weren’t required to be connected to an automated meter reading system; you have to physically go and read the dial.”


From an O&M point of view this is crucial, because it means that you can’t know how efficiently the building is working. Insite Energy is involved in BPE, though mainly on heat networks, looking at performance evaluation to advise clients where they can improve. One example Coates-Smith gives is of a site in Scotland where it took a year for its client to realise why the revenue from residents wasn’t covering the gas bill.

“This well-known big six utility company that also does field engineering, was adamant our metering system was wrong,” he says. “We looked at the data on our cloud-based system and found that two of the cores had constant, massive flow. We had to explain to them that there are bypasses in the system for maintenance and if, during commissioning, they’ve been left open at the top of the riser, that bypass allows hot water to flow through at a constant rate, as determined by the pump set.”

As a result, these pumps which were designed to operate on average 12-14 hours a day, were running 24 hours a day full-bore. This also reduced their operating life from 10 years to three.

“One person made a mistake when they were commissioning but nobody noticed and it took a year to identify,” Coates-Smith continues. “It cost nearly £50,000 for that medium-sized site, which is unrecoverable. And that’s a client who did look, there are lots more who don’t.

“Don’t stop at the regulatory requirement. Go to the best-practice requirement. It’s not there because somebody felt like writing it, it’s there to protect operators.”

The Chartered Institution of Building Services Engineers recently updated its CP1 code of practice (https://is.gd/tucika). Consultants must specify equipment that is fit for purpose, which in turn removes the possibility that contractors will make the wrong choice based solely on price. By specifying, mandating and being strict, systems will perform better.

For new-builds specifying components, equipment and the supplies needed at the earliest stage in the design, and maintaining an interest in having sign-off on deviations from that spec, is crucial. “One of the key things for me is to see it through into operation,” Coates-Smith says. “Once you’ve designed it – whether it’s at your cost at the client’s – stick around, revisit, see what was built, see how it works. One of the criticisms we see of new building designs is that the people who design it too rarely come back to see how it’s working.”


For O&M companies coming into an existing site looking to improve it, the first order of business should be to see if the site complies with the metering regulations from 2014 onwards, because there are many sites that don’t.

The second is, if you are able, speak to the team that operated the site before you. If there are known issues that clients haven’t been willing to fix for either financial reasons or perhaps simply not understanding why, look at how you can get data out of the site. Clamp-on meters that don’t require invasive cutting-in can be cost-effective solutions.

“If you can see the data it’s a lot easier to identify where improvements can be made,” Coates-Smith concludes. “On heat networks that are operating badly, the costs can be huge, and the relative cost of putting in data-gathering equipment and then making interventions to improve performance can pay back incredibly quickly.”

However, Engelke adds that it’s not just about collecting the data; it’s also about learning what to do with it. He observes: “There’s still a learning curve in industry to use data effectively, to understand what it actually means and how to prepare it. What’s your baseline and what you want to do with it?”


Nonprofit timber building group Wood Knowledge Wales commissioned a guide to BPE for domestic buildings written by the not-for-profit building association Good Homes Alliance. The 160-page guide and accompanying toolkit were published in January (https://is.gd/tunoka).

Wood Knowledge Wales says: “New homes often fail to meet low-energy targets, and to satisfy residents with fundamental issues such as ease of use, summer comfort and energy costs. There is little Building Performance Evaluation (BPE) happening routinely on projects to close the performance gap. A step change is needed to transition to net zero carbon while making our homes comfortable, healthy and enjoyable.”

It says that the aim is to embed building performance throughout the project stages and empower project teams to deliver high performance. At the design stage, that means predicting performance and informing the design; during construction, checking implementation; at completion and handover, checking as-build versus objectives; during occupancy, checking in-use performance versus objectives, as well as monitoring and assessing.

This guidance recommends a ‘core’ BPE scope for clients and project teams wanting to understand and improve the performance of their homes. This includes:

  • Design and documentation review
  • Handover review
  • Early stage overheating analysis
  • Energy strategy review
  • Thermal bridging and moisture review
  • Site inspections and visits
  • Airtightness review, checks and tests
  • Commissioning
  • Acoustic checks and testing of ventilation system
  • Energy use audit
  • Water use audit
  • User surveys.

In addition, it also recommends, if possible, thermography spot checks and IEQ (indoor environmental quality) spot checks and short-term monitoring.


In October 2020, architecture trade association RIBA recommended post-occupancy evaluations as standard practice to make sure all new buildings meet energy efficiency ratings. The recommendations were made in an October 2020 report: www.is.gd/okugif.

RIBA president Alan Jones said: “As Dame Judith Hackett noted in her report on the disaster at Grenfell Tower, a complete change in construction industry culture is needed to address issues of quality, safety and sustainability. The message is very clear. We need to embrace a culture of accountability and continuous improvement, and that starts with checking the true performance and impact of buildings on the environment. If the government is serious about reaching net zero by 2050, post occupancy evaluation must be embedded into all projects that receive full or partial public funding now for the future of our planet and its people.”

The report defines three levels of POE. Light-touch POE is said to be ‘a simple but meaningful rapid evaluation undertaken post-occupancy, before the building contract concludes.’ Diagnostic POE picks up from there, providing a more detailed building review as required. Finally, detailed or forensic POE involves a comprehensive investigation by independent evaluators to identify and resolve significant and persistent performance issues, it says.

Tom Austin-Morgan

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