How Sustainable Infrastructure Helped St George's College Respond to the Recent Heatwave

by Greg Cole, Bursar

As the UK experienced another period of exceptional heat, schools across the country faced difficult decisions about how best to protect students and staff. Every school site presents different challenges, and responses varied according to the buildings, facilities and infrastructure available.

At St George's College, our priority remained the wellbeing of our students and staff. We adapted where necessary, cancelling after-school activities and some evening events, moving many sports sessions indoors, encouraging regular hydration and making full use of our temperature-controlled learning environments. These measures enabled the College to continue delivering its full academic programme, with the school day running as normal from 8.40am until 4pm.

While these were practical operational decisions, they were underpinned by something much less visible: long-term investment in sustainable infrastructure.

A Vision That Has Stood the Test of Time

When the College commissioned its ground source heat pump system in 2022, it was one of the most ambitious sustainability projects in our history.

The system is built around four ground source heat pumps, drawing on a ground array of 132 boreholes, each drilled to a depth of 140 metres and containing some 40 kilometres of piping, through which flows around 36,000 litres of glycol. Using the stable temperature beneath the Earth's surface, it provides low-carbon heating across much of the College estate while dramatically reducing our reliance on natural gas. Because the installation qualifies for the government's Renewable Heat Incentive, the income it earns broadly matches the cost of running it, so the heat it generates in winter is effectively break-even.

The project was expected to deliver a substantial reduction in the carbon emissions from heating the College, cutting our reliance on natural gas. It reflected the College's long-standing commitment to environmental responsibility and to investing for the future. Four years on, that investment is delivering benefits beyond those originally imagined.

Sustainability Meets Resilience

The recent heatwave reinforced an important lesson: sustainable infrastructure is also resilient infrastructure. The same long-term thinking that keeps the College warm and low-carbon in winter also helps keep it cool and comfortable during periods of extreme heat.

But it would be too simple to credit any single piece of technology. The College stayed comfortable, and kept running, because of several systems working together: efficient cooling, clean electricity we increasingly generate ourselves, and buildings designed to stay comfortable using little or no energy at all. Each began as an environmental decision. The heatwave showed that each is also a resilience decision.

Keeping Cool, Efficiently

The College cools its buildings in two complementary ways.

In our science and languages buildings, cooling is delivered in an unusually efficient way that surprises most people when they hear it. Rather than relying on conventional air conditioning, we draw on the naturally low temperature of the ground itself. A fluid is circulated through the borehole array, cooled by the ground, and passed through a heat exchanger to provide cooling to those classrooms. The heat pumps play no part in this: during cooling they are bypassed entirely, and the cooling comes directly from the ground. It does away with the energy-hungry condensing units that conventional air conditioning depends on, and with them the refrigerant gases those units contain, many of which are themselves potent greenhouse gases if they leak. The system still uses some electricity, to run the circulation pumps and the fan coil units that distribute the cool air within each classroom, but far less than conventional air conditioning would draw.

There is even a neat circularity to it. Drawing warmth out of the buildings in summer returns heat to the ground, which in turn improves the system's efficiency when it comes to heating in winter. The two work in harmony.

Across the rest of the estate we use conventional air conditioning. This includes our main classroom block and the dining room, along with the theatre, performance and sports studios and other key spaces. Both approaches are electrically powered, which raises an obvious question for any school serious about its environmental impact: where does that electricity come from?

Powered by the Sun

For St George's, increasingly, the answer is the sun.

The College has invested steadily in solar generation over many years. This is not a single installation but an extensive network of around 16 separate rooftop arrays across the campus, with a combined capacity of more than 600 kilowatts.

The recent heatwave was, in a sense, the perfect demonstration of why this matters. The very conditions that drive up the demand for cooling, bright sunshine and long days, are also the conditions in which our solar arrays generate the most. Much of the electricity used to keep buildings cool was therefore generated on site. Indeed, through the summer the College frequently generates more electricity than it uses, running for periods entirely free of the grid. The electricity we do draw from the grid comes from certified renewable sources.

So even at the height of a heatwave, keeping our students cool did not come at the expense of our environmental commitments.

The Power of Passive Design

Not every space relies on mechanical cooling at all.

The Trailfinders Hall, our large indoor sports hall, is not air conditioned. It is naturally ventilated, its airflow designed to keep the space comfortable with no mechanical cooling whatsoever. During the heatwave it performed remarkably well. On one of the hottest afternoons of the week the hall was in full use for cricket and a range of other sport, at an indoor temperature comfortably cooler than outside, and cool enough for normal activity to continue. Even the hospitality area at the very top of the building, which has no air conditioning, stayed cool enough for a game of table tennis.

It is a reminder that the most sustainable cooling of all is the kind that needs no energy: thoughtful, passive design, built in from the start.

Efficient by Design

One of the most striking outcomes of the recent heatwave was that maintaining comfortable learning environments did not require a corresponding increase in energy consumption.

We know this because we measure it. The College monitors its energy use in detail, which lets us see how the estate is really performing. Over the heatwave week of 22 to 26 June, even with cooling running across the campus, the College imported less than half the grid electricity it used during the equivalent week before our heat pump and solar investments.

This is one of the greatest strengths of how the College is now set up. Unlike conventional cooling, which sharply increases electricity demand in hot weather, our combination of ground-sourced cooling, on-site solar generation and well-designed, naturally ventilated spaces allows us to stay comfortable while continuing to operate sustainably.

Investing in the Future

When the project began, the ambition was clear: reduce the College's environmental impact and invest responsibly for future generations.

The recent heatwave has shown that those same decisions are now helping the College respond to another emerging challenge. Climate resilience is becoming an increasingly important consideration for schools. As periods of extreme weather become more frequent, the quality of school estates, the efficiency of their infrastructure and the flexibility of their learning environments will play an ever-greater role in supporting student wellbeing.

"We set out to reduce our carbon footprint, and we have ended up with a campus that is far better prepared for a changing climate as well. Sustainability and resilience, it turns out, are two sides of the same investment."

For St George's College, sustainability has never been simply about reducing carbon emissions. It is about making thoughtful, long-term investments that benefit our students, our community and the environment. The recent heatwave has shown that those investments are delivering exactly that.