3. Electrical Savings from Daylight

The Orientation Factor is used to compensate for the different orientations of the windows.

The Datum Internal Illuminance for Daylight Linking (lux) should be set at the minimum acceptable illuminance. This value is then used to calculate the Datum External Illuminance and hence to find the Percentage of Year External Illuminance is Exceeded and the Energy Savings from Using Photoelectric Dimming, from the graphs below.

The Uncontrolled Lighting Hours of Operation are those expected if the lights are turned on when the centre is opened and only turned off when the centre closes. The value should reflect opening times. The Occupancy Sensor Controlled Lighting Hours are those estimated if the lights are only on when the hall is being used. If the hall is likely to be used more then the hours should be increased. Average sports hall is

Graph for Edinburgh - Percentage of Year a Given External Horizon Diffuse Illuminance is Exceeded

Graph for Edinburgh - Percentage of Energy Savings from Daylight Linked, High Frequency Dimming of Lighting.

4. Payback Period

The payback period is the number of years that it will take to pay back the extra cost of including fenestration and is calculated from the estimated costs of the various measures.Some approximate costs are given. In some instances there may be additional implications when using such large areas of glazing due to the extra weight and problems associated with solar and thermal control with large glass areas.

5. Greenhouse gas emissions

The Greenhouse gas emissions for the initial building are based on full lighting for an uncontrolled period and no additional heat loss. The Co2 emissions due to the daylit buildings take account of the increase in emissions due to the heating and decrease due reduction in electrical demand.

Lighting controls have the most beneficial effect on running costs but none of the structural aspects have short payback periods. This is in part due to the absence of any thermal advantages gained from the glazing. For example:- The additional capital cost over a “black box” hall of achieving a DF_ave of 2% from apex rooflights, including daylight linked fluorescent lighting (with occupancy sensors) is approximately £34,000. Cost savings are approximately £1,040 per year. A simple payback of 33 years which unless there are recognisable amenity benefits is unlikely to be acceptable.

Understanding Daylighting of Sports Halls

The Spreadsheet Model

This guide contains a Microsoft Excel spreadsheet to allow experimentation and comparison of average daylight factor and cost savings for different scenarios. This followed a design exercise which investigated a range of daylighting options for two outline designs of ‘black box’ halls and incorporated architectural, cost and engineering concerns. The spreadsheet takes account of:

1. sports hall dimensions, glazing provision, reflectance values of surfaces and transmittance of glazing to generate an average daylight factor;

2. glazing u-value, hours of heating operation and fuel cost to generate the additional heating requirement as a consequence of heat loss through the glazing;

3. installed lighting, lighting control, hours of operation and fuel cost to generate electrical savings and hence net running costs or benefits of including glazing;

4. cost of glazing and controls to determine the simple payback;

5. The savings in greenhouse gas emissions on a yearly basis due to inclusion of glazing.

It can be opened and altered to the user’s preferences, in order to examine various scenarios, after saving to the hard-disk. It is suitable for PC and Macintosh. PC users click HERE to view the spreadsheet in your browser or right click and "save as" to save the file to your hard drive.

1. Average Daylight Factor

The average daylight factor is the sum of Daylight contributions from all the openings as described in the section ‘Designing for Daylight’.

2. Cost of Heat Loss through Glazing

The additional heat loss associated with the inclusion of glazing into the hall is found from multiplying the sum of the heat loss from each surface by the total annual heating hours. Holidays are excluded only if the heating system is intended to be turned off during that time. It is assumed here that sport centres would be closed on 25th December and 1st & 2nd January.

The differential U-value of the glazing is used as it is to be compared to the otherwise opaque and better insulated structure. Only the windows are considered as it is the difference in heat loss from the black box scenario which is of relevance. The differential U-value (ie Uvalue of Window 2.3 - Uvalue of wall 0.35 = 1.95) is multiplied by the average temperature difference between inside and outside during the heating season.

No account is taken of the energy benefits of solar gain as sports hall design relies on avoidance of direct solar ingress and it is assumed that all solar access is blocked by shading. Natural ventilation is assumed.

unoccupied for 39% of the time it is open. The total lighting in the installation should be included.

The Uncontrolled Consumption is the Annual Total of Uncontrolled Lighting Hours of Operation multiplied by the installed lighting load. The Occupancy Sensor Controlled Consumption is calculated in the same way. The Consumption after Illuminance Exceedance Savings is calculated by multiplying the Occupancy Sensor Controlled Consumption by the Percentage of Year External Illuminance is Exceeded. The value is then multiplied by the Energy Savings from Using Photoelectric Dimming to give the figure for the Consumption after Photoelectric Dimming. Multiplying the Consumption after Photoelectric Dimming by the Cost per Unit Electricity gives the Cost with Savings. The percentage of these savings over the original, uncontrolled cost is given for interest.

The final Cost Saving is calculated by subtracting the Annual Cost of Heat Loss through Windows from the Savings due to daylighting.




		3. Electrical Savings from Daylight The Orientation Factor is used to compensate for the different orientations of the windows. The Datum Internal Illuminance for Daylight Linking (lux) should be set at the minimum acceptable illuminance. This value is then used to calculate the Datum External Illuminance and hence to find the Percentage of Year External Illuminance is Exceeded and the Energy Savings from Using Photoelectric Dimming, from the graphs below. The Uncontrolled Lighting Hours of Operation are those expected if the lights are turned on when the centre is opened and only turned off when the centre closes. The value should reflect opening times. The Occupancy Sensor Controlled Lighting Hours are those estimated if the lights are only on when the hall is being used. If the hall is likely to be used more then the hours should be increased. Average sports hall is

	Graph for Edinburgh - Percentage of Year a Given External Horizon Diffuse Illuminance is Exceeded



	Graph for Edinburgh - Percentage of Energy Savings from Daylight Linked, High Frequency Dimming of Lighting.


	4. Payback Period The payback period is the number of years that it will take to pay back the extra cost of including fenestration and is calculated from the estimated costs of the various measures.Some approximate costs are given. In some instances there may be additional implications when using such large areas of glazing due to the extra weight and problems associated with solar and thermal control with large glass areas. 5. Greenhouse gas emissions The Greenhouse gas emissions for the initial building are based on full lighting for an uncontrolled period and no additional heat loss. The Co2 emissions due to the daylit buildings take account of the increase in emissions due to the heating and decrease due reduction in electrical demand. Lighting controls have the most beneficial effect on running costs but none of the structural aspects have short payback periods. This is in part due to the absence of any thermal advantages gained from the glazing. For example:- The additional capital cost over a “black box” hall of achieving a DF_ave of 2% from apex rooflights, including daylight linked fluorescent lighting (with occupancy sensors) is approximately £34,000. Cost savings are approximately £1,040 per year. A simple payback of 33 years which unless there are recognisable amenity benefits is unlikely to be acceptable.
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