Combination Artificial & Daylighting Daylight as a primary lighting source Artificial lighting as a secondary source Room 102 Architecture Building

Recall in the discussion on artificial lighting, for a level of illumination of 70 footcandles for room 102 of the architecture building, the calculation called for sixteen fixtures. The arrangement of the fixtures for consistent coverage was four rows of 4 fixtures each. The following diagram indicates the four rows of fixtures. The plan also shows the approximate location of the values of illumination that daylight provides, calculated from the previous discussion.

From the daylight calculation problem, none of the 3 figures found are sufficient to serve the room if 70 footcandles are desired. However, each of the levels of light is a percentage of that required, which, if daylighting is primary, then less artificial light, and therefore energy, is needed for the task. At minimum, daylight = 10/70 = 14% At 2x min, daylight = 17.48/70 = 25% At 4x min, daylight = 34.96/70 = 50%

50% 25% 14%

The next illustration is a cross section of the room with the windows on the left. This drawing shows the amount of light across the room that is provided by daylight. The area in the section above the slanted, dashed line and the horizontal dashed line at the top indicates the amount of artificial light that must be provided by fluorescent fixtures.

By utilizing daylight for room 102, from the diagram it seems it would take a minimal amount of energy of supplementary artificial lighting to attain 70 footcandles at the work level near the windows, a moderate amount at the center and less than full illumination at the wall opposite the windows. But, if artificial lighting is installed to accommodate the room at night, what type of controls could be utilized to satisfy both conditions and conserve energy during the day? A system of switches? A) First a master switch to turn on or off all the lights at once – for nighttime use. B) Sub switches: An individual switch for each row of lights, so during the day, the two inside rows can be left on, while the two outside rows are turned off.

The primary task is to determine how to provide full artificial illumination for nighttime And at the same time control the amount of power as needed during daylight.

A manual setup using individual switches would probably work to some degree - but the process would be simply a guess – and then at best, from someone concerned with energy conservation. Human nature being what it is, what person in charge is really going to be sensitive to the process and turn on the proper switches and leave off the ones not needed? Most will probably simply turn on all the switches and to heck with energy conservation. That’s the way of society today. We are an ocean of waste!! Like this room . . . how much light do we need here just to do what we do?

A better system of switches might be if each row of fluorescent tubes across each row of 4 fixtures could be controlled. Each row of fixtures would have the flexibility of control in 25% increments.

But who is going to know if the proper number of rows are on or not? Particularly since the average person cannot distinguish between about a 25 - 50 footcandle range. So a system of positive switches sophisticated enough to have the range of flexibility to be practical – would probably go unused, simply because the user would not be disciplined to the system. Plenty of electronic control equipment is available, but clients are not quick to utilize the additional expense because they do not realize the long term benefits. But remember, daylight is free !

Since the input of energy can easily be controlled to each light fixture, an electronic control that has an infinite number of settings will adjust the light output in a manner that for the most part would go unnoticed. And no matter what the level of daylight was available, the electronic control would adjust automatically with the proper type of photoelectric cell.

Incandescent and fluorescent lamps are both capable of having light output controlled by automatic switches, which can adjust the amount of voltage to the fixture. An electronic sensor is a device that can be set to do a task at a given setting. Computer software is available to prescribe settings to control lighting, the performance of heating and air conditioning equipment, or as reminders when a squeaky wheel needs a shot of wd40. Even check on maintenance requirements of equipment, such as a time duration for filters, operating temperature of compressors, etc.

So how would this information benefit room 102? If a sensor is installed at some strategic point to measure the level of light required for each row of lights, say on the ceiling, then light output can be controlled from zero to maximum by the reading the sensor takes. So if a sensor is set to maintain 70 footcandles, it doesn’t care from whence the light comes. If daylight provides 40% of the setting required, the artificial source will be activated by the electronic sensors to provide the other 60%

And what is all this good for? In the drawing cross section, the total watts required for all artificial (nighttime) is 16 x 200 = 3200. But with daylight at minimum conditions, only 2000 watts are required of the artificial lighting. A saving of 1200 watts for the room at the worst conditions of daylight, and remember the worst conditions do not occur very often.

Electrical energy use is measured by a meter that records the amount of watts consumed per hour. And in order to make the numbers smaller, one-thousand watt increments are used, called kilowatts. One kilowatt of energy consumed in one hour is called a “kilowatt-hour.” Since electricity is charged to the customer based on an amount per kilowatt-hours, (say $ .08 per kilowatt hour), then in a 10 hour workday period the 1200 watts that are saved by utilizing daylight, relates to 1200 x 10 = 12,000 watts, or 12 kilowatt - hours.

The cost of 12 kilowatt hours is 12 x. 08 = $. 96 per day The cost of 12 kilowatt hours is 12 x .08 = $ .96 per day. Not a breathtaking amount, but consider that it amounts to .96 x 22 (number of workdays in a month) = $ 21.12 per month, and 21.12 x 12 = $ 253.44 per year. Still, not an impressionable sum, but consider an office building similar in area to the architecture building, with 8 such rooms per floor 10 stories tall = 80 such rooms

Eighty rooms x $ 253. 44 per year would amount to $ 20, 275 Eighty rooms x $ 253.44 per year would amount to $ 20, 275. 20 per year saving. $ 20,275 is an impressionable sum – and that is a positive amount of client money that would not be spent. But consider that the process would at the same time conserve 1200 watts x 10 hours x 8 rooms x 10 floors = 960,000 watts of electrical energy per year – just for taking advantage of free daylight.

The amount of heat generated by one watt of electrical power is 3 The amount of heat generated by one watt of electrical power is 3.4 btu per hour. During air conditioning times, this heat must be removed in order to provide comfort conditioning – say five months out of the year. At 960,000 watts of electrical energy, the amount of heat created that must be removed during air conditioning periods equals 960,000 x 3.4 x 5/12 = 1,360,000 btu of heat. In terms of air conditioning load, this number amounts to 113 nominal tons of air conditioning. At a price of $ 1500 per ton of installed air conditioning, that amounts to $ 169,500 of equipment that does not have to be installed.

If the 113 tons of air conditioning were to be operated, electrically, a direct expansion compressor uses approximately 1000 watts per ton of air conditioning. This amounts to another 1000 x 113 = 113,000 watts of electricity that does not have to be used. The electrical operational cost of the 113 tons of equipment would amount to 113,000/1000 = 113 kw x 10 hours = 113 x 10 x .08 = $ 90.40 per day, or 90.40 x 22 x 5 = $ 9,944.00

Aside from energy, consider the monetary savings: Savings in electricity for lighting $ 20,275.00 Savings in air conditioning equipment: 169,500/15 years $ 11,300.00 Operation of air conditioning equipment $ 9,944.00 Or a total of $ 41,519 per year Just for utilizing free daylight.

The energy code for the State of Texas requires a limit on the amount of electricity used for lighting, for heating and air conditioning, all of which affects heat loss and heat gain conditions. By their standards, there would certainly be a limit as to how much window area of what type of glass could be used in a design. That does make your task as designers more difficult.

But your task as a designer would be made more simple if in your projects, daylight is taken into account as free energy. Not only does it save money in operation . . . It also frees the designers of the restrictions of the limit of wattage allowed for specific tasks. If the model energy codes required daylighting as a part of the requirements for conserving energy we would realize that To complain about the price of gasoline is hypocritical if people are not willing to take advantage of free energy – whether it be designer or client.