Carbon mitigation unit costs of building retrofits and the scope for carbon tax, a case study

doi:10.1016/j.enbuild.2019.109415

Energy and Buildings

Volume 203, 15 November 2019, 109415

https://doi.org/10.1016/j.enbuild.2019.109415 Get rights and content

Highlights

•
Unguided markets cannot produce price signals for heating decarbonisation.
•
Decarbonising heating sector can achieve similar unit costs ($/tCO₂e) as CCS.
•
Robust fuel carbon content can inform least-cost heating decarbonisation routes.
•
Moderate carbon taxes cannot enable CapEx recovery of low carbon heating solutions.
•
Centralised biomass and GSHP recover their CapEx only via government subsidies.

Abstract

Energy and environmental data is collected from 5 tower blocks each containing 90 apartments to create two representative calibrated energy models. Three towers (heated by individual natural gas boilers) characterise medium (137.3 kWh/m²/yr.) and two (heated by electrical night storage heaters) characterise low (75.4 kWh/m²/yr.) thermal demands when benchmarked against actual UK domestic portfolio. Across 2020–2040 time horizon, an uncertain landscape is represented by 12 fuel carbon intensity and 14 economic scenarios in order to examine building fabric upgrade, without or in conjunction with centralised CHP engines, GSHP and biomass boilers in the case study towers. Out of 18 retrofit options examined, 7 or 8 solutions (under annual fuel price rises of 2% or 5.2% respectively) can provide lifetime CO₂e mitigation at unit costs that fall below the upper bounds of carbon capture and storage technologies (US$143/tCO₂e). If carbon taxation were to be used to enable full recovery of retrofit capital expenditure with no government subsidy, the lowest tax level observed belongs to a transition to centralised biomass from decentralised natural gas boilers requiring US$111/tCO₂e (in 2020), while deep retrofits (i.e. plant and fabric) require much more punishing carbon taxes with 2020 figures ranging from US$233/tCO₂e to US$1665/tCO₂e.

Introduction

Severe housing shortage following WWII and post war development of modular design techniques led to the construction of a large number of tower blocks in Europe. Together with the need to house a growing post-war population, high-rise buildings offered a fast, simple and comparatively cheap replacement of the damaged domestic housing stock. Towers with prefabricated elements and modular construction became an integral part of the 20th century modernist movement which incorporated technological advances into underlying design principles with the aim of modernising not only the housing stock, but also society [1]. What remains of post war high rise buildings rank poorly against current building performance criteria. These towers form the hard-to-treat building stocks that the Commission of European Union recast directive [2] expects member states to transform into very low energy buildings. The UK Government is also currently seeking low carbon heating solutions and heat networks [3] to decarbonise space heating in the domestic sector, which in combination with the industry and transport sector is expected to achieve 50.6% carbon reduction over 2020–2040 time span (see 2.2). This work utilises extensive field data and occupant engagement from five 15-storey tower blocks to develop two representative calibrated models of [a] three towers heated via individual natural gas boilers and [b] two towers heated via individual night-time electrical storage. Calibrated model predictions are benchmarked against actual UK housing in order to derive ‘scalable’ techno-economic results of 18 retrofit options based on [a] upgrading the tower fabrics in isolation or in combination with [b] centralising the supply of thermal demand using ground source heat pumps, natural gas fuelled CHPs or biomass boilers. The inevitable landscape of techno-economic uncertainty is treated as follows:

a)
Fuel decarbonisation pathway uncertainty: A combination of 3 grid electricity (containing 50, 75 and 100 gCO₂e/kWh) and 4 natural gas (containing 0, 5, 12.5 and 20% of bio-fuel) fuel characteristics. These values are assumed to have been achieved by the end of 5th UK carbon budget (2032) resulting in 12 future primary fuel decarbonisation scenarios to inform retrofit carbon savings.
b)
Future economic landscape uncertainty: Discount rates of 2% to 8% to represent the price of time in the assessment of Net Present Value of each retrofit option as well as historically-driven moderate (2%) and high (5.2%) annual fuel price rises. These assumptions result in 14 future financial scenarios to assess the extent to which each retrofit solution can recover the capital expenditure.

These techno-economic results are used to provide the following comparative benchmarks:

a)
Identification of retrofit solutions that can deliver carbon reduction in line with 2020–2040 UK emission targets.
b)
In order to illustrate a broader least-cost route to economic decarbonisation, the standardised carbon abatement ability of all retrofits (i.e. tonnes of CO₂e saved per unit of $ investment) is benchmarked against the best current economic alternatives (i.e. carbon capture and storage). This allows identification of economic sectors that can deliver most carbon abatement per unit expenditure.
c)
The level of carbon tax obligations which can enable retrofit solutions to fully recover their capital expenditure (CapEx) within a typical 20 year lifetime set against the idealised energy-economy-climate model carbon tax recommended by Intergovernmental Panel on Climate Change.

Section snippets

Low carbon retrofits

Field studies and evaluation of sustainable retrofit opportunities particularly in high-rise buildings have so far been a rather neglected area [4]. Ownership type (i.e. private, corporate, institution or governmental) has been found to have the most impact on the way retrofit decisions are made [5]. Retrofitting is often more economical and has less environmental impact when compared to complete demolition and rebuild [6], [7]. Arriving at sustainable retrofit options for clusters of social

Description of case-study buildings

The case study buildings are five 15-storey brick-clad towers built in the 1960s, of which three have natural gas supplies enabling central heating systems and gas cooker use (type 1), and two have only electricity supply and are heated by electric storage heaters charged using off-peak electricity (type 2). Originally built with brick and block infills, both tower types had double glazing upgrades in the early 2000s. Additionally the type 2 towers were retrofitted with both insulated external

Energy model calibration

EnergyPlus is a first-principle based building energy modelling tool that has been developed over several decades by the US department of energy in close collaboration with research institutions. EnergyPlus uses fundamental heat and moisture balance equations to complete building thermal behaviour whereby a multiplicity of differential equations within integrated modules are solved iteratively to produce a convergence that honours parameter inputs and achieves target temperatures using three

Model calibration

Electricity data (recorded at 60 s intervals) was logged on transformer substations of two towers and additionally in 20 apartments (i.e. clamp-on sensors). These were aggregated into hourly time steps to guide hourly model calibration. However the only practical way of collecting gas consumption (supplied to type 2 only) was manual recording at daily intervals (see next paragraph). Privacy and ethical reasons limited project team's data collection efforts to a maximum of 9 months. To further

Conclusion

CO₂ remains the most important anthropogenic radiative forcing agent and capping (and reversing) cumulative CO₂ emissions in all sectors of economy remains a global priority. Deep decarbonisation of the economy is principally underwritten by economic investment. The uncertain carbon content of fuel and economic landscape across 2020–2040 propagates into substantial uncertainty bands (and hinders conclusive results) in the case study presented in this work, with the largest uncertainties

Limitations

The non-monetary value of improved occupant comfort in a thermally efficient building or the rebound effects of lower fuel costs were not considered. Collecting high quality natural gas consumption data remained the biggest challenge in this work which effects precise calculation of heating and DHW use and benchmarking. The useful lifespan of fabric retrofit is more than 20 years yet it was assumed so to enable a comparison with other retrofit solutions over 2020–2040. While CO₂ remains the

Declaration of Competing Interest

We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.

Acknowledgements

The authors would like to thank Engineering and Physical Sciences Research Council (EP/P001173/1), Northern Gas and Northern Electricity network for providing the financial support to enable this work. Sincere thanks to Malone Engineering Services for their invaluable input on Hydronic systems design and costing.

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Carbon mitigation unit costs of building retrofits and the scope for carbon tax, a case study

Highlights

Abstract

Introduction

Section snippets

Low carbon retrofits

Description of case-study buildings

Energy model calibration

Model calibration

Conclusion

Limitations

Declaration of Competing Interest

Acknowledgements

Procedia Eng.

Energy Build.

Energy Build.

Renew. Sustain. Energy Rev.

Energy Build

Int. J. Sustain. Built Environ.

Build. Environ.

Energy Build.

Procedia Econ. Finance

Energy

Renew. Sustain. Energy Rev.

Energy Policy

Energy Policy

Int. J. Greenhouse Gas Control

Energy Procedia

Appl. Energy

Energy Build.

Energy Build.

Energy Build.

Atmos. Res.

Energy Convers. Manag.

Procedia Manuf.

Appl. Energy

A History of Architecture: Settings and Rituals

Tall Buildings and Sustainability

Meeting Carbon Budgets - 2016 Progress Report to Parliament

Do energy efficiency investments deliver?

Evidence from the Weatherization Assistance Program

Climate Change Act

Decarbonising the Gas Network

Carbon pricing in climate policy: seven reasons, complementary instruments, and political economy considerations

Wiley Interdiscip. Rev.