LIGHTING OFFICES WITH LEDS: A STUDY ON RETROFITTING SOLUTIONS SPYROS STRAVORAVDIS A thesis submitted in partial fulfilment of the requirements of Cardiff University for the degree of Doctor of Philosophy Welsh School of Architecture 2013 SUMMARY 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. i DECLARATION This work has not been submitted in substance for any other degree or award at this or any other university or place of learning, nor is being submitted concurrently in candidature for any degree or other award. Signed ……………………………………… (candidate) Date ………………………… STATEMENT 1 This thesis is being submitted in partial fulfillment of the requirements for the degree of …………………………(insert MCh, MD, MPhil, PhD etc, as appropriate) Signed ……………………………………… (candidate) Date ………………………… STATEMENT 2 This thesis is the result of my own independent work/investigation, except where otherwise stated. Other sources are acknowledged by explicit references. The views expressed are my own. Signed ……………………………………… (candidate) Date ………………………… STATEMENT 3 I hereby give consent for my thesis, if accepted, to be available for photocopying and for inter-library loan, and for the title and summary to be made available to outside organisations. Signed ………………………………………… (candidate) Date ……………………… STATEMENT 4: PREVIOUSLY APPROVED BAR ON ACCESS I hereby give consent for my thesis, if accepted, to be available for photocopying and for inter-library loans after expiry of a bar on access previously approved by the Academic Standards & Quality Committee. Signed ……………………………………… (candidate) Date ………………………… ii ACKNOWLEDGEMENTS I would like to express my thanks to my supervisor Prof. Chris Tweed for his guidance, support and critical comments for this thesis, as well as the many useful discussions had throughout the period of this thesis. I would also like to thank Katrina Lewis for her administrative support on issues related to this thesis and Dr Ian Knight for his comments. A special thanks to Dr Andrew Marsh and Caroline Raines, for their continuous support throughout the period of this thesis. The critical comments on my work and the long and useful discussions that kept me going and motivated. I would also like to thank the Welsh Energy Research Centre for providing funding support through the EU for the Low Energy Design of LEDs (LEDLED) research project, which forms part of the work presented in this thesis. The author of this thesis was the principal investigator of this research project and was the one who conceived the idea, formulated the research questions and prepared the funding application. The aim of this research was to design and develop four LED lighting demonstrator products and assess their potential impact in buildings. There were four university partner departments in this project, all located within Wales, UK. These were the Department of Optometry and Vision Sciences (Cardiff University), the Department of Electrical and Electronic Engineering (Swansea University), the Department of Chemistry and Material Science (Bangor University) and the Welsh School of Architecture (Cardiff University), which was leading this project. Each department was commissioned by the author to perform a range of tasks required by the project. iii The author of this thesis served as both principal investigator in this project and as project manager, with responsibilities ranging from co-ordinating all aspects of the project on a daily basis, devising methodologies, running computer simulations, analysing results and writing reports. A number of research assistants were commissioned by all five departments involved in this project, throughout its duration, to perform a series of tasks setup by this author and other co-investigators, for their respective work packages. The following list outlines the contributions of others in the work presented here, together with additional information on how this work was used by the author in this thesis: • Site measurements in a test room: This involved the use of lux level meters and temperature measurement devices obtained from the environmental lab of the Welsh School of Architecture. The specification on how measurements should be taken was defined by the author of this thesis, who also took part of the measurements and then used the data obtained to make comparisons between measured and simulated data, as presented in Chapters 6, 7 and 8. I would like to thank Li Qian and Shareful Shickder for their help in this aspect of the work. • The construction of LED luminaires, as well as combined fluorescent and LED ceiling tile luminaires to be used for testing: The Department of Electrical and Electronic Engineering at Swansea University was commissioned to conduct this work, to the specifications provided by the author of this thesis. The luminaires constructed were then placed in a test room for measurements to take place, as described in Chapters 6 and 7. • Task based performance and perception study: The Department of Optometry and Vision Sciences of Cardiff University was iv commissioned to run an experiment in a test room, that was specified and setup according to the specifications of the author, by measuring the task based performance of subjects under fluorescent and LED lighting conditions. The author used this data to make comparisons between the two conditions, as presented in Section 7.4, Chapter 7. I would like to thank Rachel North and Andrew Bullyment for their help in this aspect of the work. In all cases, the author of this thesis oversaw the above work, developed the methodology and setup for experiments, unless otherwise stated in the following chapters. Finally I would like to thank my parents Dimitris and Niki, for their constant support throughout all my studies, as without their support this would not have been possible. v CONTENTS Chapter 1. Introduction ........................................................................................................ 1 1.1 Research Background ......................................................................................................... 1 1.2 Defining the Problem ........................................................................................................... 4 1.3 Aims and Objectives ............................................................................................................ 7 1.4 Method Overview ................................................................................................................ 8 1.5 Contributions of this Thesis ................................................................................................. 9 1.6 Outline ..............................................................................................................................