Lighting offices with LEDs: A study on retrofitting solutions

Global energy consumption is rising and the relative contribution of lighting in buildings to that total is also increasing. In offices, the dominant form of lighting is fluorescent, but this will soon be surpassed in terms of performance by LED lighting, which are already starting to be more widely used. Considering that most buildings and offices are of older building stock, this presents a great opportunity for making energy savings by using more efficient light sources within offices. This thesis investigates the application of LEDs as a retrofitting solution to existing fluorescent lighting systems and assesses their potential to provide an equivalent lighting environment with no adverse effects on performance and investigates their impact on space conditioning load demands and CO2e emissions on a range of case study buildings in the UK. Savings in lighting cannot only be made through reduced electrical consumption, but also through space conditioning loads, by reduced lighting heat gains. Currently used lighting technology is reaching its limit of performance, whereas LEDs offer the potential to meet energy saving targets with their rapidly improving performance. LEDs emit most of the heat generated to the back of a luminaire, rather than directly to the occupied space and this can lead to reduced heat gains and thus savings on space cooling demand loads, in addition to the electrical savings due to higher efficacies, for operating them. In this thesis, simulation software were reviewed that would allow for the lighting specification of custom LED replacement luminaires and assessment of their thermal performance. Methodologies were developed on simulating their light output and designing custom LED replacement luminaires with the use of RADIANCE, thus providing a novel use for this extensively used and validated software. For validation purposes a test room was used where custom LED replacement luminaires were fitted and measured for their performance, where good agreement in predicted and measured results was found. A visual performance study was also conducted using a range of age groups, to ascertain if there is a difference in task based performance on paper and VDU screens between fluorescent lighting and LED lighting, in an office environment. Subjective opinions on preference between the two light sources was also investigated. An assessment of space conditioning load demands was performed on five case study buildings, where custom LED luminaires were specified to retrofit the existing fluorescent lighting. Results showed lighting levels and distribution in each building could be replicated with good agreement, offering a cooling load demand reduction, however with an increase in heating load demand. In terms of CO2e emissions, the use of LED lighting instead of fluorescent also proved to be beneficial, providing reductions in emissions