Tim Knights
Operations Director, Hoare Lea
Pragmatic decarbonisation: cities set on Net Zero.
PEOPLE
Fresh perspectives
New voices of the built environment
The scale of the UK Net Zero Carbon existing buildings challenge is undeniably daunting. Even more so when viewed through the lens of the ‘fabric first, all electric’ approach typically adopted for new-build developments or extensive refurbishment schemes.
When compared against new-build developments, the opportunities to decarbonise existing buildings are usually governed by more onerous site constraints, typically:
- Capex: a project that’s decarbonisation focused requires dedicated funding
- Viability of operational disruption: significant decarbonisation interventions are likely to require prolonged shutdown periods to implement required works, which may not be viable (it’s difficult to close a hospital, for instance)
- Plant space availability: heat pumps require significantly more footprint per unit of energy than fossil fuel equivalents
- Available electrical capacity: the availability on an existing site may not be sufficient to cater for a 100% all-electric heating system
- Planning and governance: extensive works that impact on the external visual appearance of a building/site are likely to trigger a requirement to seek planning permission
- Acoustics: air source heat pump installations are noisy – the larger the installation, the greater the impact to background noise levels
When staring down the barrel of such a huge challenge, feeling like a rabbit in the headlights, down-to-earth realism and practicality are key.
Navigating the roadblocks: a pragmatic approach
I’m sure many of you reading this will have encountered one, if not all, of these ‘roadblocks’ when working with existing buildings or estates. So, what can we do about it? Well, there’s one potential route that we’ve found success with so far when it comes to city-wide solutions. If we introduce heat pumps into existing heating systems in a lead heat source capacity (with the heat pump sized to consider the existing site constraints), the majority of the existing annual heating consumption can be transferred from gas to electric –significantly decarbonising the system.
Work like this can be generally confined to external areas and internal plant areas, with heat pumps integrated into existing heating systems at the end of the works period… Electrical capacity, planning/governance, acoustics and plant space issues? All solved – in one swoop!
So, what remains on the list? Capex costs and operational disruption… Well, when coupled with other pragmatic carbon reduction measures, the adoption of a relatively small heat pump installation in a lead heat source capacity represents a majorly cost-efficient solution. The key? That it makes a considerable reduction to the overall carbon footprint of a building while simultaneously being a solution that can be implemented without significant shutdown periods.
What would the haters say?
While this approach does not fully transfer all emissions associated with the existing heating system from fossil fuel to electric, it can represent a significant first step towards a 100% electric heating system, forming part of a modular/phased approach to decarbonisation. The remaining fossil fuel heating plant will only operate during low ambient temperature conditions, when the duty of the heating system exceeds the duty of the heat pump installation, or when heating system secondary circuits require elevated flow temperatures (e.g. space heating circuit during low ambient conditions).
Most importantly, the implementation of additional decarbonisation measures over time will enable the complete transfer of the heating system’s fossil fuel emissions to cleaner all-electric solutions.
So how do we know it works?
To robustly assess the impact that heat pump installation will have, existing half-hourly utility meter data (i.e. gas and electricity) can be utilised to fully understand the existing building heating and electrical demand profiles. When combined with weather data and heat pump part-load data at the proposed design conditions, the impact to the site’s annual fossil fuel and electrical load consumption can be established (through adopting a performance engineering approach) which, in turn, defines the impact to the site’s overall carbon footprint.
When assessed against many other potential decarbonisation intervention measures, the adoption of a modest heat pump installation in a lead heat source capacity typically results in a very low £/tCO2eLT figure (i.e. the cost to save a tonne of CO2e over the lifetime of an application), maximising the benefit of the investment.
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