STRATEGY 4
Installation of automatic daylight control in site offices
Contents Introduction Installation Control Settings Energy Savings Equipment Grants Reference

   

            1. Introduction

 Examining the cabin accommodation on the site under investigation it can be shown that the proportion of glazing in the cabin accommodation provides a significant amount of space lighting by natural lighting, hence reducing the requirements for artificial lighting.

 

Hence, in window offices where the employees work the majority of the day at their desk the most efficient method to reduce lighting costs is to install automatic daylight control.

 

Additionally, occupancy sensors could be installed in offices that are not occupied during the whole day. A typical layout of a control system is presented in the figure below.

 

		Layout of control system for artificial lighting [3]

 

Photoelectric daylight control can take two forms, either simple on/off switching or dimming. Photoelectric switching can cause sudden and noticeable changes in lighting level that can lead to occupant complaints. [1] In order to avoid this as well as to maximise energy savings, the control system should be a proportional system directly linked to the artificial lighting system so that the lighting output will vary inversely with daylight availability.

 

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            2. Installation

 

The photo sensor can either be mounted externally or facing out of the window to sense the daylight only or mounted inside the space to measure the total amount of light, comprising natural daylight and artificial light.     This report will consider use of the photo sensor mounted on the inside of the office and electric lights will be controlled by dimming.   Daylight sensors should be mounted in locations representative of the task area, as shown in the picture beside.
		Fisheye view from a sensor located on the ceiling [3]

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            3. Control Settings

 

A setpoint value can then be entered which typically comprises 500lux illuminance and a daylight factor of 5% for office use. If this value is exceeded the artificial lighting will be turned down until the setpoint value is reached again.
Low  outdoor illuminance				High  outdoor illuminance
This way the artificial lighting load varies continuously to achieve a constant illuminance on the working plane. Set points should reference the daylight incidental on the working plane.
Most high frequency dimmable control gear will allow dimming down to 1% of full light output. Over the most dimming range, the percentage energy savings roughly equates to the reduction in light output for electronic HF dimming as demonstrated in the graph beside.
			Indicative energy savings against light levels [3]

 

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            4. Energy Savings

It is a complex matter to calculate the amount of energy that can be saved by installing daylight control systems. Many factors will influence the performance, such as:

 

In order to identify the feasibility of daylight control in construction site offices and assess the amount of energy savings a case study has been conducted on the use of automatic daylight control in a commonly sized office room. This case study can be accessed from the Lighting part of the Project Web Site.   

Based on this case study it has been identified that the installation of automatic daylight control systems in office accommodation in construction villages can enhance energy savings between 45% and 65% for office lighting.

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Daylight control can be realised either by using a control system for the whole building, space etc. or stand-alone products like ballasts equipped with photo sensors.

A lighting design, which is suitable to be used for daylight controlled office lighting, is the Kanby T5 Smart (Thorlux Lighting Ltd).

This lighting system provides T5 fluorescent lamps with high frequency ballasts combined with a daylight sensor as well as a Passive infra-red (PIR) sensor.

It is a twin lamp system consisting of either two 35W lamps or two 28W lamps.

 Properties of the Kanby T5 Smart System [2]

The prices for both types of lamps indicate that installing a daylight control system would require significant initial investment and a change to the current lighting design of new cabin accommodation. 

However, economies of scale mean that there are normally discounts on these items dependent on quantities ordered but typically it would be around 20%.

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 It should be noted that Enhanced Capital Allowances (ECAs) apply to the installation modulating lighting controls. ECAs allow the cost of selected energy efficient equipment and its installation to be written of against Corporation Tax in the year of purchase. This can result in significant reduction in the cost of installing energy efficient lighting.

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            (1)                 Commission of the European Communities, Energy Efficient Lighting in Buildings, Directorate-General for Energy (DGXVII)

            (2)                 http://www.thorlux.com/controls_products.html#Smart

            (3)                 Tsangrassoulis A et al, SynthLight Handbook- Integration of electrical lighting-daylighting, February 2004

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