How heat network integration underpins "London's most sustainable building"

Named after the large grocers that once occupied this prominent corner site in London's Smithfield – home to the City of London's only remaining wholesale market – the 19,000m building sits in the heart of what is now one of the UK capital's most desirable districts for both work and play.

Offering ten floors of office space, outdoor terraces on three levels, and retail units on the ground floor, JJ Mack reflects the increasingly porous lines between business and pleasure. But it also speaks to something far grander and more significant in scope: the need to find innovative, workable ways to decarbonise our built environment at speed and scale. It is among London's smartest and most sustainable buildings, with environmental performance having been integral to every stage of its design, construction and operations.

JJ Mack was the UK's first building to be assessed as BREEAM Outstanding at the design stage and has an energy performance certificate (EPC) rating of A. Its carbon emissions are more than 50% lower than the regulated UK Buildings Regulations' Targeted Emissions Rate. These qualities make it a genuine international flagbearer for sustainability.

"The idea was always to make JJ Mack a showcase for sustainability and technology," says Pavlos Clifton, Senior Development Executive at Helical, who, with their joint partners AshbyCapital, are the developers behind the project. "In terms of sustainable building design, London has firmly established itself as a world leader, so to have the best in class in this city means to be a true global leader.”

Some of the headline sustainable features of the building are high above street level, where one will find solar PV panels feeding energy back into the grid, 885m of biodiverse green roof, and even two bee colonies. However, a key component of JJ Mack's decarbonisation agenda is actually buried deep underground and located almost literally next door: the Citigen district energy network.

Operated by E.ON, Citigen is a renewable energy plant, providing electricity for the grid as well as heating and cooling to local homes and businesses via a district heating network across the City of London, saving an estimated 5,000 tonnes (t) of CO₂. "It offers significant benefits, both in terms of sustainability and economically," Clifton says of using such a district heating system. "The case for plugging the building into the network was undeniable."

Antony Meanwell, E.ON's head of decarbonisation and heat zone development for its City Energy Solutions division, agrees that inner-city boroughs like the City of London, Islington, Newham and Tower Hamlets are prime candidates for benefitting from such heating schemes. "London generates lots of waste heat from sewage treatment works, industrial processes, data centres and office cooling and this heat is effectively wasted and released into the atmosphere. It is believed that almost 50% of the heat needed for London could come from these sources."

Meanwell continues, "Being able to utilise that is a great way of delivering cost-effective and low-carbon heating to residents."

For Clifton, the case for integration in regard to office space can be broken down into three key components: the absence of in-building plant providing significantly more space for tenant use; removal of fears around obsolescence, breakdowns, and on-site repair and maintenance costs; and JJ Mack benefitting from E.ON's continual investment into renewable and progressive heat and energy generating technologies.

But that only tells part of the story. The truth is that there remains some hesitancy on the part of private developers when it comes to heat networks, which currently supply just 3% of the UK's heat demand. The Climate Change Committee believes that proportion could rise to 18% – and significantly higher in densely populated areas such as the City of London or Islington – but only with the right incentives, investments and education in place.

There was no hesitancy for Clifton or Helical seeking to explore new options, rather the natural next step in a relationship with heating networks dating back over ten years. In 2011, the developer acquired a site that was to become Barts Square , a redevelopment of the old Barts Hospital facility located less than half a mile from JJ Mack, on the other side of Smithfield. The project created 235 apartments and 254,700ft of offices across three buildings connected for its heating and hot water to Citigen.

"Even back then, we were very interested in ways of driving efficiencies and improving environmental performance," Clifton recalls. "I was aware of Citigen, but there had always been some reluctance to use a heat network on the private development side. Having looked into the possibilities, I made the case and we plugged in all of the residential and two of the office buildings successfully."

That success saw Kaleidoscope, a five-floor Smithfield office building that opened in 2019 and is now rented in its entirety as the UK head office for TikTok, also integrated into Citigen, making JJ Mack Helical's fifth participating building. Clifton jokes that he's hoping he'll be able to present the stamps on his loyalty card and get the sixth one free. "All that experience made bringing JJ Mack into the network a simple decision," he says.

But the case was not always so easy to make. When pushed on the reasons for initial reluctance, and any lingering doubts among Helical's peers, Clifton points to both a lack of precedent and some cultural and behavioural hesitancy that needed to be overcome. "Tenants like the idea of being able to control their own systems," he explains. "The heating and cooling of a building is tantamount to the ability to operate and enjoy one's space. I think people are, to some extent, moving past that as they embrace the green agenda and there's a more open feeling from tenants as they see the benefits of such a system, in terms of the environment, cost and resilience."

The fact that the journey began with a mixed-use scheme made it easier, Clifton expands, given the Barbican and other local residences were already plugged in, but commercial offices amounted to something of a leap into the dark. Having been among the first to make that jump, he has fielded countless enquiries from other developers over the years since, seeking input, advice and observations from Helical's experience.

Despite the case now being far easier to make than it was 12 years ago, dialogue, education and promotion are still required – not least because regulations and information around heat networks remain in their infancy.

Meanwell agrees that for the decarbonisation of heat to fulfil its potential in delivering successful urban energy transition, the right frameworks must be in place to ensure proper engagement and integration of heat network schemes into a city's wider net-zero efforts.

The key driver for this is heat network regulation, so everyone understands the specifications and requirements and is heading in the same direction. "Without the necessary regulation, we'll not see the step changes required," Meanwell explains. "Then it comes down to ensuring participation is incentivised correctly, as heat networks become more efficient the more users they have. If they're under-utilised you don't get that efficiency."

"A heat network is by its very nature a collaborative project," Meanwell continues. "Engagement is paramount, but the lack of a clear framework can make the message hard to articulate."

That process of proper articulation is still a work in progress. "When we first started the journey, the efficiencies that were provided by getting your heating and cooling from an energy network were not properly recognised by the various accreditation and regulatory bodies," Clifton explains. "The feedback I was getting was that we could unlock the same levels with a very efficient on-site plant.

"What this didn't take into account is that an on-site plant would deteriorate faster and you'll have to replace it within ten to 15 years. This speaks bout the longevity of a building's life cycle. Replacement of capital equipment in a building is often a trigger for redevelopment or disposal. Buildings that should last 60 years are getting major works done at 15 years to keep them marketable. This is not sustainable.

"That carbon life cycle wasn't being captured ten years ago. Things are better now, but probably still haven't gone quite far enough. There are some political and accreditation incentives for connecting into a district heating system, but not as much as I think there should be."

Back in the City of London , the business case has also changed due to the sheer levels of investment and decarbonisation that Citigen has introduced over the past decade, and plans to in the near future. JJ Mack is also plugged into private wire for electricity, the first of Helical's buildings to do so, meaning it is drawing its power, as well as heating and cooling, from Citigen – Clifton mentions that a neighbouring building is now doing the same. The business is also in discussions with E.ON about a green tariff agreement that would put JJ Mack in a zero-carbon position.

"Having heating and cooling off-site has enabled us to convert the tenth floor for accommodation and significantly lowers the on-site service charge," says Clifton. "The point that can get missed, however, is that Citigen will be perpetually improving its systems. When we first joined in 2012, we didn't know they were proposing a borehole heating solution, for example."

That solution is the addition of geothermal and heat pump technologies that deliver a significant drop in emission levels – 200m-deep boreholes provide direct access to the Thames Basin Aquifer that runs beneath Citigen. The geothermal energy is fed into a heat pump that extracts the energy and increases the temperature of the naturally sourced heat.

This is further added to by waste heat produced by the existing central heating and cooling plant to deliver the greenest possible heating solution.

Meanwell is proud of the work being done at Citigen, with a new Department for Energy Security and Net Zero (DESNZ) study under way by the design and engineering consultancy firm Ramboll, which will map out the path Citigen can take to fully reach net zero.

"This is the next phase in the decarbonisation journey, to understand the different steps and technologies required to reach net zero for the entire Citigen network by certain dates," he explains.

Such efforts benefit all parties. "The fact that E.ON has its own green agenda and decarbonisation goals is now something that we also significantly benefit from," Clifton says.

Helical's positive experience with Citigen across the past decade means that the feasibility of heat network integration is a consideration baked into all projects – Clifton says he always has the district heating installation map ready for consultation.

He acknowledges that there remain variations in the quality of feedback, support and services delivered, something he thinks greater government focus will help to change, and believes Citigen provides a template for how such business models can be delivered and sustained.

"Being a proponent for heat network connection is certainly now less of an outsider position for a private developer to take. We are seeing perceptions and mindsets change," Clifton says. "Having a facility like Citigen on one's doorstep makes it a no-brainer decision – and a significant wasted opportunity for those not engaging."