Borders College - Pioneering Wastewater Heat Recovery System Cuts Carbon Emissions

Sustainability Projects, Insights

About

Borders College in Galashiels, Scotland, sought to reduce its reliance on gas for heating as part of its ongoing carbon reduction efforts.

The campus comprised of three distinct buildings, heated by five plant rooms containing ageing gas boilers in varying conditions.

Main Building: A modern facility with lecture halls, offices, a library, and catering.
TTC: A technical training centre with open workshops and office spaces.
High Mill: A historic Victorian textile mill shared with Heriot-Watt University, featuring old cast iron heating infrastructure.

The Challenge

The challenge was to transition to a renewable heating system without imposing major changes to the internal heating infrastructure.

We considered various options.

Biomass boilers were ruled out due to limited space for fuel storage and delivery constraints.
Connection to a local district heating network was deemed too complex and slow to implement.
Heat pumps were identified as the best solution, as they could efficiently convert low-grade heat into high grade heat.

The Heat Pumps Solution

Heat pumps work by extracting local, low carbon thermal energy from natural sources. This can be air, ground or open water sources, or by extracting heat from waste sources and upgrading it to a higher temperature for heating buildings.

Wastewater heat recovery was chosen for this project due to accessibility (the sewer line ran at the rear of the college), reliability and efficiency.

Sewage water from the local sewer typically has a temperature of around 20ºC, even in winter. A heat exchanger extracts this warmth, and the heat pump compresses and upgrades it to a usable temperature. This energy is then distributed via underground pipes to heat the college buildings. The existing gas boilers would be retained as a backup.

Project Implementation

HI Group were asked to lead the technical design and project management, ensuring seamless integration of the new systems with the existing plant rooms.

Throughout the design and pre-construction our team provided advice and support to the various stakeholders to move the project to delivery.

Key steps included:

Energy analysis to assess heating demand.
Technical design of the heat pump system, Energy Centre and underground heat distribution network.
System integration with the five plant rooms.
Collaboration with the local water authority to access wastewater from the sewer.

Pioneering Approach

This project was the first in the UK to use wastewater heat recovery at scale, showcasing innovative ways to decarbonise heating for multiple buildings.

Heat pump retrofit: successfully integrated into the existing heating system.
Fourth-generation district heating network: a modern, low-temperature system with retained boiler infrastructure was designed for future energy flexibility.
Funded business model: using HI Group’s corporate finance expertise, Borders College limited its financial risk through the use of heat supply contracts and commercial finance, rather than by upfront capital investment. This was a game-changer for the college, with commercial risk being taken by the technology providers and funding partners and the college paying for heat supply at a competitive rate whilst continuing to reduce carbon emissions.

Overcoming Technical Challenges

As a first-of-its-kind project, some challenges arose, which required modification:

Sewer debris: Solid waste like wipes required additional screening and filtration.
Low wastewater flow in summer: low flow periods also coincided with warmer water temperatures, so a solution was developed to circulate water multiple times for efficient heat extraction.
Cold temperature effects: The system was modified to automatically switch to gas backup during extreme conditions.

Results and Project Impact

Since launching in December 2015, the system has performed exceptionally well, achieving consistent efficiency.

1 GWh of renewable heat generated annually, significantly reducing gas consumption.
Carbon savings of around 180 metric tonnes per year.
Recognition for pioneering achievement through two prestigious awards in 2017: the EAUC Green Gown Awards (Newcomer of the Year) and the Scottish Green Energy Awards (Best Innovation)
Hosting over 300 site visits in the first 3 years of operation from organisations keen to replicate the model.

Borders College continues to build on this success, with plans to:

Add solar energy and battery storage to mitigate grid electricity costs and improve carbon reduction
Integrate the boiler plant with the 4^th generation network and decommission the five satellite plant rooms, thereby reducing service and maintenance costs.

Conclusion

The Borders College wastewater heat recovery project proves that innovative renewable energy solutions can be retrofitted into existing infrastructure and can lead to significant decreases in carbon load,

HI Group were delighted to work alongside Borders College to shape a project that has become a model for sustainable heating in the education sector.

Testimonial

“Working with HI Group to deliver an innovative low-carbon heat solution for Borders College, I can thoroughly recommend them as an innovative leader in sustainability practice. From project inception to completion, their professionalism and flexibility ensured that we were able to significantly reduce our carbon footprint, while also realising revenue savings, and with minimal capital outlay.”

Pete Smith, Principal and CEO at Borders College