4. Current Policy Approach: Contradictions and Failures
4.1 The Greater London Authority's Approach
The GLA has acknowledged the UHI challenge through various policies and programmes:
- London Environment Strategy: Includes policies to minimise new developments' contribution to UHI and reduce overheating impacts
- London Plan Policy 5.9 (Overheating and Cooling): Establishes a cooling hierarchy that prioritises passive approaches over active cooling
- London Heat Map: Interactive GIS tool identifying opportunities for decentralised energy projects
- Urban Greening Initiatives: Tree planting and green infrastructure programmes
- Climate Resilience Review: 2024 independent review recommending accelerated adaptation measures
Critically, the London Plan explicitly acknowledges that 'air conditioning systems are a very resource intensive form of active cooling, increasing carbon dioxide emissions, and also emitting large amounts of heat into the surrounding area.' This recognition is important—it demonstrates policy awareness of the waste heat problem. However, the solutions proposed remain inadequate.
4.2 The Thermodynamic Contradiction
Despite acknowledging the waste heat problem, current policies contain a fundamental thermodynamic contradiction:
- Carbon Metrics Over Efficiency: Policies prioritise 'low-carbon' credentials over actual energy efficiency. An electric heat pump powered by grid electricity may have lower direct emissions than a gas boiler, but if the waste heat from centralised power generation (rejected at 50-60% efficiency losses) plus the waste heat from the building cooling system both contribute to the UHI, the net thermodynamic effect is negative.
- Ignoring Centralised Generation Losses: Policies that mandate electrification ignore the fact that approximately 50-60% of primary energy is lost as waste heat at centralised power stations. This heat is rejected to the environment (often via cooling towers or water discharge), and then additional heat is rejected at the point of use by cooling equipment.
- Discouraging Gas-Based CHP: Regulatory frameworks discourage combined heat and power systems that use gas (even bio-methane) because they focus on point-of-use emissions rather than system-wide efficiency. This penalises the most thermodynamically efficient available technology.
- Individual Building Focus: The regulatory approach treats buildings as isolated units rather than components of an urban thermal system. Each building optimises its own 'carbon performance' without regard to collective waste heat impacts.
4.3 The Bunhill Case Study: Promise and Limitations
The Bunhill Heat Network in Islington demonstrates both the potential and limitations of current approaches. This £16.3 million project recovers waste heat from London Underground ventilation shafts to provide district heating to approximately 1,350 homes, a school, and two leisure centres. Key features include:
- 1 MW heat pump connected to Underground ventilation shaft
- Two 237 kWe/372 kWth CHP gas engines
- Reversible fan system that can cool the Underground in summer
- Estimated 500 tonnes CO₂ reduction annually
The project has been lauded as 'a blueprint for decarbonising heat' and 'the first of its kind in Europe.' However, expert analysis has raised important criticisms:
- The waste heat from Underground ventilation is only 3-4°C above ambient temperature, meaning heat pumps must provide most of the temperature lift (~55-60°C) to reach the 70°C district heating temperature
- The system requires gas-fired CHP engines to power the heat pumps when electricity prices are high, raising questions about actual carbon savings
- The cooling benefit to the Underground is limited—ventilation provides wind chill effect but does not fundamentally reduce tunnel thermal mass
- Infrastructure costs are substantial for relatively modest heat recovery
The Bunhill project reveals a critical point: even showcase 'green' infrastructure projects rely on gas-fired CHP as a backup/support system. The question then becomes: why not design around CHP as the primary system, maximising its thermodynamic advantages, rather than treating it as supplementary? This is precisely what the bio-methane CCHP approach proposes.