This table is taken from my review paper and a full discussion of these points is included in that article; Table 3, Hurst and O’Donovan (2019) “A review of the limitations of life cycle energy analysis for the design of fabric first low-energy domestic retrofits” Energy & Buildings, 203, 109447. Please cite this paper when using any content from this table.
| Measure for Fabric First Retrofit LCEA | Why the measure is relevant | Effect of Measure |
| Standardisation of the EE definition and life cycle stages included in the analysis | Variations in approach to LCEA mean that results between studies cannot be compared, and therefore the relationship between OE and EE is not clear. | Enables straightforward and robust comparison between building LCEAs, thereby driving down LCE globally through benchmarking, competition etc. An understanding of the OE and EE relationship can be developed. Simplification of the LCEA and interpretation of the results. |
| Report LCEA as final energy | Temporal and spatial variations present in primary energy do not influence final energy. Avoids the need to estimate or forecast PEFs for EE or OE. Ensures OE corresponds only to changes in the building fabric or function, rather than to changes in the PEF. Enables EE values in an LCI to be relevant over time, regardless of changes, for example, in energy supply to a manufacturing process. | Building fabric performance can be reported purely as a function of the physical characteristics of the building fabric, and the materials constituting it. Focuses design decisions on factors over which a building designer has the most knowledge and influence, i.e. building design; leaves issues of energy supply to experts in that field. |
| OE reported as absolute final energy required for space conditioning, excluding appliances and other infrastructure. EE physical boundaries set as the parts of the building making up the thermal envelope and systems relating to building conditioning, such as heating and ventilation, but excluding décor, furnishings and non-conditioned spaces. | Appliance energy consumption is not affected by, nor does it affect OE. Value derived for EE is directly relatable to space conditioning, and therefore to OE consumption. | A direct relationship can be established between OE and EE. Therefore retrofit design decisions focus on building fabric performance and are not conflated by other OE or EE loads or inputs to the building. |
| Report LCEA spatial functional unit as “per unit floor area within the thermal envelope” (i.e. m2), with reference made to the designed occupancy (i.e. persons/m2). | Reporting with a spatial functional unit allows for standardisation between studies which consider dwellings of different sizes, however the functional unit must be delimited according to the same parameters between studies. Reference to designed occupancy gives indication of intended density, and hence similarities or differences when comparing studies. | Relates building energy performance to the area being conditioned. Retrofit design decisions focus on fabric performance and are not conflated by inclusion of spaces outside the thermal envelope, e.g. a garage, or unheated loft. |
| OE reports all energy sources including renewable and non-renewable, either within or beyond the building’s physical boundary. Could report Renewable Embodied Energy Ratio (REER) if relevant for a specific study. | Energy use is dependent on the building’s physical characteristics, not on the source of energy. Understanding fabric performance is only possible with knowledge of the space conditioning absolute energy demand. Reporting only non-renewable energy cannot provide a true indication of the building’s energy performance. | Prevents the acceptance of poor building fabric performance by compensating with on-site renewables. |
| Omit “sunk” LCE at the time of retrofit | “Sunk” LCE has already contributed to historic emissions and cannot contribute to current or future emissions targets. It is therefore not useful in the analysis of effective retrofit design. | Ensures that design decisions are based only on the proposed retrofit interventions and ignores those impacts which occurred historically and can no longer be changed. |
| The approach and boundaries for developing the LCI should be clearly stated with the LCEA report. Quantified uncertainties should be reported alongside LCE data. | The different methodological approaches to LCEA lead to widely different outputs, and so cannot be readily compared. | Case studies from different sources could be readily compared if the approach was the same, or considered in the context of their different approaches or uncertainties if this information has been provided. |
| Life spans for retrofit LCEA should be determined for a specific building by a building professional with due consideration to condition and the proposed retrofit approach. | Use of standardised life spans is unrealistic, and could lead to unrealistic estimates for recurring maintenance, or even an unsubstantiated decision to proceed with a retrofit or demolish the building. | Ensures a realistic annualised LCE accounting for variations in condition between dwellings of the same typology, age and location, and the proposed retrofit approach, component lifespan and replaceability. Allows informed decisions to be made regarding the most suitable retrofit approach, or alternatives such as demolition and rebuild. |
| Report actual quantities of OE and EE, rather than proportions | The shifts in proportions of OE and EE either between “conventional” and “low-energy” buildings, or with time does not offer insight into the total LCE, which is the only measure which can be used to address energy use reductions. | Enables comparison of values between case studies. Provides data which can be used to map spatial or temporal trends in LCE |
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