Abstract
The performance gap is a measure of the difference between design assumptions and actual in field data. Estimating terms, specifically the operational hours of use, when making such design assumptions in order to predict the impact of lighting upgrades can potentially result in either an overestimate or underestimate of the savings to be made. In this paper, the background of performance gap measurement is outlined and field measurements are gathered and applied retrospectively to lighting upgrades in corridors. The lighting upgrade projects in three university buildings and their assumptions are explained in relation to the operational hours proposed using the industry ‘Energy assessment and reporting method’. We then describe a simple and relatively inexpensive means of taking in field measurements using small unobtrusive environmental loggers to record the lighting use and occupancy. This method, which can be implemented prior to upgrade works or energy efficiency retrofits, reveals substantially different patterns of annual electricity consumption and carbon dioxide equivalent emissions from those assumed by a priori estimates. Patterns of use emerge that include additional hours of use by cleaners, out of hours working, and weekend working not anticipated in original estimates. These results also suggest a valuable distinction between lighting on hours and occupancy hours not captured in the current ‘Energy assessment and reporting method’. The results find the differences between predicted vs. actual data are considerably different, with lights on hours ranging from -67% lower to 25% and 138% higher when compared to predicted operational hours. We conclude that the estimates the industry uses in calculating energy efficiency upgrades should be accompanied by clear and adequate information about occupancy use. In our study, the consequence of reporting energy savings using assumptions and estimates in calculations resulted in a substantial overall underestimate of the savings achieved in practice.
Highlights
In 2014, lighting comprised 18% of all United Kingdom electricity use and consumed 58,000 TWh per year (Lighting Industry Association, 2014)
This paper aimed to measure and assess how automatic lighting controls in corridor areas performed in practice, in comparison with consultants estimates of energy savings
This study provided original empirical evidence on lights on hours and occupancy hours in corridors which was previously unknown and found that neither of these are synonymous with operational hours
Summary
In 2014, lighting comprised 18% of all United Kingdom electricity use and consumed 58,000 TWh per year (Lighting Industry Association, 2014). Having recognised the need for verification and evolving improvement of building systems the “European Committee for Standardization Technical Body CEN/TC 169—Light and Lighting” is in the course of updating their documentation to include the “Lighting Design Process” (LightingEurope, 2017). The “Lighting Design Process” details five stages: (1) Design, (2) Installation, (3) Commissioning, (4) Verification, and (5) Operation and Maintenance. These stages have been illustrated alongside the building life, frequency of lighting upgrades in Figure 1 (LightingEurope, 2017). Stage 4 Verification of the “Lighting Design Process” is key to the credibility of business cases for supporting lighting upgrades (Lighting Industry Association, 2014). The lighting sector and leading European Union member states are making significant changes to include verification as part of their evolving practises; the lighting performance gap is crucial to all stages but is distinguished in the verification stage
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