It is common knowledge that lighting contributes to more than 30% of the total energy consumption of a building. Nowadays lighting systems in so-called smart buildings are optimised to ensure the minimum energy consumption. Such lighting systems are composed of energy efficient luminaires and daylight control, offering additional savings due to the natural light entering the building. In some applications occupancy control is also present. Comprehensive studies have been performed to ascertain how daylight harvesting can contribute to, and increase, energy savings in association with automated and manual control systems. Using numerical [1,2] (RELUX, MATLAB SIMULINK) and analytical methods [3-5], daylight utilization was analysed where dimming systems were generally ascertained to be the most suitable means for integrating the sustainable development concept. Calibrating the lighting system as well as continuing user and operator education were procedures deemed to be extremely important when using sophisticated control systems that include continuous daylight control and occupancy sensors [6]. A fuzzy logic based approach is described [7] and its implementation is analyzed in conjunction with DIALux^®. Since daylight is a dynamic, highly variable, season and location dependent, source of lighting, fuzzy logic may be a promising alternative to classical, mathematical modelling. In this paper the authors demonstrate a simple, straightforward and time efficient paradigm of including daylight harvesting calculations in electrical lighting designs. An example is provided where the Electrical and Computer Engineering ECE Department of the University of Auckland is chosen for performing measurements due to its accessibility, familiarity and, most important, due to the availability of software modelling files “.DWG”. These files offer the layout of given locations and are appropriate for use with the lighting design software DIALux^®. State of the art appliances (ETAP luminaries and associated sensors/dimming ballasts from the Belgian company ETAP Electro Technische Apparaten) and measuring equipment (power meter, lux meter) are used for data gathering.

The definitions of specific lighting quantities and their depiction for an appropriate understanding of the described assessment technique are subsequently presented.

Illuminance E Illuminance (Figure 1) is the amount of light coming from a light fixture that lands on a surface. It is measured in lux (lx).

Luminance L Luminance describes the amount of light leaving a surface in a particular direction. Units: candela/m².

Maintenance Factor The maintenance factor (light loss factor) is a value

designed to account for the reduction in light output from a lighting system due to ageing, dirt and dust on the light fittings.

Reflection Coefficient The reflection coefficient (reflectance) is used to calculate the amount of light transmitted through a medium if the only losses considered are reflection losses.

Uniformity Level The uniformity level is a dimensionless quantity that represents the ratio of

Standards The prescriptions of the Australian/New Zealand Standard™ (AS/NZS 1680.0:2008) and of the New Zealand Green Building Council (NZGBC) were used for design purposes [8]. Table 1 presents the illuminance levels on the workplane according to the Interior and Workspace Lighting for Educational and Training Facilities section of the Standard.

Luminaire L A luminaire is a complete light unit consisting of lamps, reflectors and other parts that hold the lamp in place and protect it. Choosing luminaires with the right type of lamp and reflector type, which efficiently provides the appropriate lighting patterns, is also an important part of energy efficient lighting design. Figure 2 shows a typical luminaire arrangement [9].

Ballast Ballast is a device used to start a lamp by providing a shot of voltage and also control the current flow during its operation. There are 2 types of ballasts, magnetic and electronic. The electronic ones are preferred more because of their robustness and improved functionality and efficiency. The dimming ballast [10] reduces the amount of current entering the lamp in accordance with the daylight available and helps reduce power usage. A typical dimming ballast is depicted in Figure 3.

Sensor The sensor, clipped onto the luminaire, regulates and shuts down the artificial light output in accordance with the level of natural light available [11]. The sensor used

Table 1. Lighting levels on the workplane.

for this project maintains a maximum illuminance level of approximately 500 lx at all times and operates at a voltage range of 1 - 10 V. Figure 4 show a sensor on a luminaire (4a) and the layout of a complete unit (4b).

The sensor has a measuring field of ø3 meters at a height of 2.8 meters. It takes into account the luminance of the available daylight and of other artificial sources along with the reflection coefficient of the material present underneath. The dimming electronic ballast reduces the amount of current entering the lamp in accordance with the information received from the sensor.

Power Meter A power meter provides the power reading of the luminaire. When used in connection with a sensor the power readings vary due to the amount of daylight available.

Lux Meter A lux meter (Figure 5, next to a power meter) provides the illuminance reading in locations of choice.

A novel technique is proposed where a sensor’s power P versus illuminance E curve is determined and subsequently used in inferring the power (energy consumption)

of the luminaire-sensor unit, for various levels of daylight affected illuminance E.

To illustrate the concept measurements were performed by placing an ELS (ETAP Lightig control System) sensor equipped ETAP luminaire (one lamp fixture) onto the ceiling at a height of 2.8 m, as specified in Standards. Illuminance E, as seen by the ELS sensor, was varied, and the corresponding ETAP luminaire active power P measured (Figure 6). The measurements were performed using a lux meter that measured the illuminance E at the ELS sensor’s height, and a power meter, that measured the corresponding active power P of the ETAP luminaire. On the workplane the illuminance was maintained according to Standards.

The dependency P/E is the basis for accurately evaluating the energy consumed by a particular sensor/luminaire based lighting system designed using specialized lighting software (in this instance ELS sensor/ETAP luminaire unit and DIALux^® software).

For the purpose of the present research an open lighting simulation software, DIALux^®, was selected and used. The software supports luminaire data for numerous global manufacturers in the form of “plugins” as well as “.DWG” file format that enables the user to reproduce/ use/transfer analyzed location’s dimensions accurately. Some of DIALux^® essential features are:

-       it can simulate daylight for different weather patterns;

-       it can take into account the geographical location of the model to simulate the season’s weather patterns as well as the analyzed location’s position in respect to the sun;

-       it has the unique capability of incorporating interior and exterior objects taking into account their reflection coefficients and interference in the spread of light;

-       it provides a variety of useful lighting design quantities, like luminance L, average illuminance E_average, uniformity level, that allow an adequate description of the task.

Some key parameters set in DIALux^® for the purpose of the present research are presented in Table 2.

Areas within ECE department were analyzed and specific design improvements were proposed for a chosen location (Undergraduate Lab UG4). UG4 lighting system consists of 34 luminaires, each possessing two T5 lamps with a total active power of 28 W × 2 = 56 W, and a 5 W ballast. The lab also has 3 windows that allow daylight to supplement lighting.

According to Standards a minimum of 320 lux must be maintained on the workplane (0.7 m height). The luminaires consume full power throughout the working day (9 am to 6 pm).

A superior lighting system ultimately comprising ELS sensors equipped ETAP luminaires (one lamp fixture, Figure 7) is proposed and analysed. The system complies with the illuminance level on the workplane required by Standards while providing significant energy savings.

The following steps were undertaken during the analysis process.

Considering the cost per kWh of energy as described in [13], that is $0.235/kWh, the financial costs for one year are depicted in Figure 12, from where it can be inferred that the operating cost of UG4 can be reduced by $680.4 per year. The total cost of retrofitting UG4 using the ELS sensor/ETAP luminaire (one lamp fixture) new lighting system amounts to $2380 and can be recovered in 3.5 years.

In order to assess the reduction in the amount of CO₂ the energy savings generate, from [14] it is determined that for every kWh of electricity consumed a quantity of 0.23 Kg of CO₂ is produced. The results obtained are presented in Figure 13.

It is ascertained that the proposed ELS sensor/ETAP luminaire (one lamp fixture) new lighting system contributes to an annual reduction of 665.9 Kg in CO₂ emissions.

The data used for Figures 12 and 13 are summarized in Table 5.

Table 4. Energy data for the ELS sensor system.

Table 5. Costs and CO₂ emissions and savings.

A novel technique to design smart building lighting systems or evaluate existing ones, based on a three steps approach that includes daylight harvesting (optical sensor P/E characteristic evaluation, room properties calibration, photometric and energy savings calculations), is proposed and tested in conjunction with a specialized lighting design software (DIALux^®) [15]. The results show an improvement in energy utilization, since important energy savings were obtained, resulting in significant financial and CO₂ savings. The approach is highly advantageous for designers, investors, future tenants and environmentalists.