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  • Writer's pictureThomas McCrossin

Energy Management at The Leadenhall Building

Author: Thomas McCrossin, Cavendish Engineers.

Energy sub-metering has long been used to monitor and manage energy consumption within the industrial sector, however its potential for use within the commercial sector has lagged. While the United Kingdom’s regulatory provisions for sub-metering have been around since the early 2000’s under the Part L Building Regulations, up until recently most commercial members viewed the requirements for sub-metering as a check-box rather than a real opportunity to cut costs and reduce CO2 emissions. It has taken a combination of increased media attention on the climate emergency as well as the transition to cloud computing for commercial sector energy management to come into focus.

This recent interest into reducing one’s carbon footprint has resulted in a surge in advanced software solutions to managing energy consumption, but it has also highlighted that the skills required to translate this new data source into meaningful actions are not commonplace.

Cavendish Engineers Energy Bureau aims to remedy this disconnect and in January 2019 Savills Property Management partnered with Cavendish Engineers to implement the Energy Bureau at 122 Leadenhall Street.

As one of London’s largest commercial offices and a 24/7 demand-led operating environment, The Leadenhall Building presents a challenge to simply maintain consumption levels, let alone reduce them. With over 300 electrical sub-meters and 100 thermal sub-meters, The Leadenhall Building has deep visibility into its energy consumption and countless insights into its operation that are not typically available through a BMS.

The energy data is collected via EP&T Global’s EDGE software and collated into a cloud-based platform where interrogation of the collected data can be performed rapidly and remotely from the site. Cavendish Engineers are experienced in interpreting this data and cross-referencing observed consumption levels against a series of other relevant data sources such as BMS trends, physical asset inspection, as-built commissioning reports, asset data sheets, and anecdotal site evidence.

Once an issue is identified, it is logged with supporting graphs/trends/documentation and a dialogue started with all stakeholders. While some issues are resolved overnight, others are ongoing and are progressed by monthly in-person meetings with the Savills Property Management team.

Informed assessment of this data stream, which is separate both in type and functionality to that from the BMS, has identified a combination of asset failures and opportunities for permanent energy reductions at The Leadenhall Building. As of the end of FY2020 electricity Cavendish Engineers and Savills Property Management have reduced by electricity consumption by over 250,000kWh when compared to FY2019.

There are many items behind this annual saving. Some of them large and readily visible while others barely warrant an investigation. But if an issue is visible and it can be resolved then the Energy Bureau will address it regardless. Some of the items that have helped create this 250,000kWh reduction are as follows.

Elevated Chilled Water Pump Loading

122 Leadenhall Street utilises a singular primary CHW circuit with each floor connected via a plate heat exchanger to the occupiers’ secondary CHW circuit. The speed of the CHW pumps are controlled via riser differential pressure sensors. Through an automated alert in late April 2019, the Energy Bureau was notified of elevated CHW energy loading. Inspection of the electrical and thermal sub-metering found the CHW pumps drawing approx. 40kW more than usual and delivering approx. 65l/s more than expected. Savills Property Management were notified and the incumbent maintenance company were tasked to check the CHW pump controls.

It was found that the differential pressure sensor was reading a smaller than normal value, which in turn increased the demand on the CHW pumps. The site team kludged the pump controls into an acceptable speed and a replacement sensor was ordered.

As per the included graphs, the issue was identified and resolved within one day (Monday 29th April 2019) some 48 hours after the issue occurred – the is very quick for a relatively invisible issue. With the Sunday consuming 900kWh more than usual in just 24 hours and a projected weekly increase of 4,000-5,000kWh, this issue alone would cost £500 per week until noticed. Given that the observed flowrates matched expected business hours flowrates, it might not have been discovered until quarterly PPMs came around.

24/7 AHU Operation

While the prior item illustrates erroneous asset operation due to sensor failure, issues arising from human error are frequently identified too. In mid-July 2019, overnight operation was identified over the basement changing room AHU. Typically scheduled to turn off at 21:00 during weekdays, the energy data showed that it ran continually.

The Savills Property Management were notified and after a short investigation it was found that the AHU scheduling had been overridden. The schedule was returned to normal and correct loading was confirmed the following day. While not a large load at 2kW, sustained operation does add up over time and it reduces the asset’s lifespan. This simple mistake could have added up to £1,000 over the year had it gone unnoticed. It only took 10 minutes to identify, communicate, and resolve – a very good payback in the end.

Elevated Cooling Tower Fan Loading

External contractors always represent a higher than normal risk to maintaining energy consumption levels on site. The nature of their work whereby they typically repair and/or test assets leaves their work prone to human error – whether it be via forgetting to return the asset to its original control state or by making a narrow-viewed decision that does not holistically consider how the BMS controls the assets on site.

In early April 2019 irregular loading was observed over the cooling towers and by mid-April 2019 there was a sustained elevation over the towers. While the profiles were not significantly different to what would be expected during warmer conditions, the relatively mild conditions combined with no notable occupier operational differences raised alarm bells. After the elevations were referred to Savills Property Management, contact was made with the cooling tower contractors who confirmed that they put two towers into hand to increase their run hours to match the others. Unfortunately, this override negated the capacity for the system to modulate and resulted in elevated loads. With an additional 6,500kWh per week being recorded, this issue could have cost several thousand pounds before the contractors were back on site to rectify.

Managing Occupier CHW Consumption

The Energy Bureau does not only look at landlord assets, it also supports Savills Property Management in their quest to manage occupiers’ consumption – even when the occupiers have their own demised engineering team.

Monitoring of thermal sub-metering within the commercial sector is not commonly performed, but the insights that can be developed are invaluable. At the end of the day landlord consumption is driven via occupier demand. Floors with higher numbers of occupants or assets will have higher heat gains. Further to this, floors with occupants who improperly control their FCUs without consideration to how each change ripples through the floor will also see increased energy consumption – both theirs and the landlords.

The Energy Bureau regularly informs Savills Property Management of high-uses occupiers. At this point Savills Property Management will inform the demised engineering team or landlord incumbent maintenance team that there has been an increase and an investigation will commence. While the demised engineering teams are under no obligation to investigate, communications of potential costs tend to motivate anyone. This is where thermal sub-metering really shines, as the 15-minute data provides easy to interpret graphs that can be shared with the occupiers as well as hard evidence of impending invoice increases.

As-built Chiller CHW Delivery

Reviews and evidence-based changes to the as-built operation of any building represent the hardest of all Energy Bureau pursuits, but they also present the largest potential savings. The sites that the Energy Bureau operate at are typically “broken in” and are good candidates for design reviews. This is because the collected empirical data supersedes design information when assessing whether a system is operating correctly.

One such identified opportunity that is currently being investigated centres on the CHW flowrates through the chillers. All available design information states that flowrates through the chillers should be approx. 100l/s yet sub-metering data frequently shows flows well over 160L/s. Not only does this not benefit the chillers, but it also indicates that energy reductions could be achieved through lowered pumping power. Given the design of the primary CHW circuit, we know there are competing demands between the CHW riser and chillers. We have also collected evidence to show that no ill effects are incurred during sub-design riser differential pressure readings and that reductions in pumping power will be considerable if implemented on a permanent basis.

Even without the current COVID-19 environment and reduced floor demands, this item has the potential to save around 100,000kWh per year or more.

What is Next?

Cavendish Engineers and Savills Property Management will continue to partner to maintain and reduce energy consumption at The Leadenhall Building. There is no doubt that there is a place for this process and the progress made so far is encouraging. We expect more human errors to be made and more sensors to fail – that is the nature of any building – and we will be there to ensure neither costs more than it need to. There are numerous as-built reviews going on as of writing and even best-practices from other countries being implemented, and these will generate substantial reductions. Someday it will no longer be possible to reduce consumption and it will stabilise – but until then Cavendish Engineers and Savills Property Management will ensure it is one step forward, no steps back.

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