HYBRID LIGHTING SYSTEMS: COSTS AND BENEFITS

Introduction

Daylight is the preferred source in buildings due to its beneficial effect on human well-being and performance. Its potential to conserve energy and hence protect the environment has stimulated interest as an electric lighting substitute. The recent development of ‘daylight guidance technology’ allows redirection of daylight into areas of buildings that cannot be lit using conventional glazing. The two main guidance types are the commercially successful tubular daylight guidance systems (TDGS) and the newer hybrid daylight/electric systems (HLS). This study of costs and benefits of hybrid systems makes the case for utilizing this form of daylight provider as an alternative to TGDS in combination with a conventional electric lighting system (ELS).

Evaluation method

The methodology used to evaluate system costs and benefits is Whole Life Cycle Costing (WLCC). This provides more realistic comparison data than the simple payback method which is commonly used for lighting system evaluation.

Whole life cycle costing (WLCC)

WLCC takes into account the costs of running and operating buildings (or components) over their lifespan as opposed to a specified period of time. The concept of ‘time value’ reflects the fact that present capital is more valuable than a similar amount of money received in the future. Its computation is based on present value, compounding and discounting techniques [3], which can be computed according to the formulae:

PV = FV (1 + r)-t (1)

FV = K (1 + i)t (2)

Where: PV = present value, FV = future value of capital, K= annual cost, r = discount rate, i = inflation rate, t = period of analysis.

Net Present Value (NPV)

NPV is a variation of WLCC where the PV of cash flow is subtracted...

... middle of paper ...

...ars is used as being a typical life of lighting equipment. The results of this study are expressed in terms of payback period (PB). For each system in every location the PB curves use electricity prices ranging from 10p/kWh to 50p/kWh. The electricity price median over EU-27 countries in 2009 is 14.01p/kWh, which has risen some 46% in 5 years [7]. The PB shows the annual variation for both system, and electricity, price variation.

Works Cited

Boussabaine H. & Kirkham R. (2004). Whole life-cycle costing, risk and risk responses, Blackwell publishing Ltd.

European Commission (2010). Statistics on focus, (Available at: http://epp.eurostat.ec.europa.eu/portal/page/portal/publications/collections/sif_dif/sif).

Mayhoub M. & Carter D. (2009). Hybrid lighting systems: a feasibility study for Europe, in proceeding of the 11th LuxEuropa, Istanbul, Turkey, 1, 265-272.