This article was originally published in the May/June 1993 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
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Home Energy Magazine Online May/June 1993
Building an Energy-Efficient Home Office
by Christine Geltz
How does one person manage to make clients feel right at home? Her prescription for a home office makeover begins with energy-efficient lighting.
The Geltz Communications office started as half of a double garage in a two story town house. Despite its humble origins, I tried to make it as energy-efficient as possible. Good lighting was crucial, so I employed an expert, Bernie Bauer of Integrated Lighting Concepts. We discussed my lighting needs and developed an energy-efficient solution. Factors we considered were:
* Room uses. This 200 ft2 room was to contain a computer workstation, a drafting workstation, a conference area, and a gallery highlighting framed examples of company projects. Each of these functions required its own set of lighting specifications, in terms of illumination and color rendering.
* Energy efficiency. This varies among lamps and ballasts. Even small differences are important in maximum-efficiency design. We made a careful review of the most efficient and readily available products on the market.
* Natural daylighting feel. Because the office lacked windows, there was no spill lighting, or daylighting available for general lighting or visual brightness.
* Costs. Quality lighting was important because I was going to spend long hours in the office. Still I could not afford the Taj Mahal of lighting schemes.
Bauer came up with a task-oriented lighting plan but tempered it with small scale fixtures to meet the need for a blend of office and residential feel. It's designed to harmonize the color aspects throughout the room. It's also quite energy-efficient. The design features a multiple switching scheme that highlights each of the home office functions: mood or low level lighting for the entrance and exit, gallery lights which highlight framed work samples for show and tell or presentation, and conference table lighting which does not interfere with contrast needed for other tasks (see Table 1). There's also an occupancy sensor by the office entrance which controls the entire lighting circuit.
The difference in the feel and functionality to the room from its former state is amazing: It's bright and inviting, and feels much more professional and sophisticated.
How Much Energy Does the Office Use?
With a mix of compact fluorescent and halogen lamps, the lighting system uses about one-third as much energy as a conventional design, yet puts out roughly the same amount of light. It includes 12-20W halogen bulbs which, with their 5W ballasts, draw only 25W each, for a total of 300W (see Table 1). By comparison, 12 conventional 75W incandescent reflector lamps would draw 900W. Similarly, instead of 75W or 100W incandescents the design features two 13W compact fluorescent lamps inside of the wall sconces. The total lighting system should use 490W, whereas an equivalent incandescent system might draw 1,535W. With all of the lights in the office turned on, the design should use 2.45 W/ft2. A comparable incandescent design would draw 7.7 W/ft2--which is quite high.
Although the added cost of installing energy-efficient fixtures and lamps rather than conventional assemblies was about $750 (this estimate is based on average prices) the improved fixtures and lamps will pay for themselves through energy savings and significantly longer lamp life. Incandescent lamps have an average life of 750 hours, halogen spotlights last about 50% longer than incandescent spotlights, and compact fluorescent lamps last about 10,000 hours--12-13 times the life of incandescents. Longer lamp life translates into less maintenance for the home office owner. The energy-efficient lighting design will likely pay for itself within 18 months (see Table 2). This assumes that the lighting system is used for 50 hours a week and that all lights are on. However, it should be noted that with the motion sensor and multiple zone task switching, the system seldom draws its full load.
Rated versus Metered Energy Use
I worked with a local electrician to monitor the electricity use of my home office. When we metered the lighting demand for one hour and with all lights on, average demand was actually about 520W, 30W higher than the design specifications. We haven't been able to determine the reason for the disparity, but minor variations between printed specifications and a fixture's actual usage are not uncommon. Wattage ratings of lamps, ballasts, and transformers are based on standard voltages and these can also vary.
The electrician also monitored the energy use of the rest of the office, which is on a separate circuit from the lighting. We monitored the combined load of all of those devices except the copier at five-minute intervals (see Table 3).
Including the computer, printer, copier, fax, and scanner the whole office never draws more than 400W. We also measured the energy use of each office device. I compared that to the nameplate values and--not surprisingly--found that the nameplate never actually indicated actual power draw.
The following are some additional recommendations Bauer makes for people interested in a home office lighting system.
Windows. If there are windows, daylight should be used as part of the lighting scheme. Glare control can be addressed with commercial blinds or similar screening devices.
Dimmers. These generally provide more lighting control, and models that work with compact fluorescent lamps are just coming on the market. If one plans to dim fluorescent fixtures, fixtures should have suitable ballasts and lamps.
Occupancy Sensors. These can also add to an energy-efficient lighting plan. An electrician can install them so that just those lights one needs for traffic or general lighting sources will come on when the room is occupied. Occupancy sensors are also more expensive than regular switches. They can cost $60-$100, and are somewhat more difficult to install. In addition, occupancy sensors do take a bit of time to get used to. For instance, sometimes while I'm working, the sensor doesn't see me and turns the lights off, so I have to wave my arms around to turn them back on.
Rebates. Another consideration is that a number of utilities offer rebates for energy-efficient lighting purchases.
Installation. A qualified electrician should come out for a pre-inspection. The electrician should make sure there is proper capacity on the circuit to support the equipment, and that the power quality is good enough to run state-of-the-art equipment. (Not all electricians know how to do this.) It is also vital that the installation be done according to code. The Geltz office installation took a day and a half, with very few wall modifications. n
A Lighting Lexicon
Lumens. This is visible light output, or how bright the light is. It is measured in foot-candles (fc).
Illuminance. Measured in foot-candles (fc) illuminance is the amount of light on a surface. For paper tasks, the higher the illuminance, the easier it is to see, but too much can cause glare, which worsens vision. Computer screens do not require illuminance.
Lighting Ratio. This is the ratio between the brightness of the task and other areas in the visual field. If the lighting ratio is too low, it makes the visual environment too uninteresting. If it is too high, occupants pupils will adjust to the bright ambient light and not to the task. A good rule of thumb is to maintain a 3:1 lighting ratio between a video display terminal (VDT) and adjacent dark surroundings, 1:3 between a VDT and paper based tasks. Ambient lighting levels should remain 30-50 foot-candles
Color. Lighting color definitions are influenced by two factors:
Chromacity. The chromacity of a light source defines its whiteness, its yellowness or blueness--its warmth or coolness. Chromacity is measured in kelvins (K), based on the absolute temperature of metal as it heats up and progresses in color from red to yellow to white to blue-white.
Color Rendering. The chromacity of a light source does not tell how natural or unnatural colors of objects will appear when lighted by it. Two lamps can have the same chromacity, but render colors very differently. For example, a warm-white fluorescent lamp has about the same chromacity as a high wattage incandescent, but red colors do not appear as bright under it, because it has less deep red in the color spectrum it projects. To measure color rendering, an internationally agreed upon color rendering index (CRI) has been devised based on a scale of 100. Outdoor north sky daylight is defined as a perfect 100 CRI, and incandescent lamps are defined as nearly 100 CRI.
For an in-depth consumer guide to lighting, see Lighting the Way Towards More Efficient Lighting, HE, Jan/Feb '89, p. 16.
Table 1. Foresight Brings Needs to Light: Standard versus Geltz Office Design
STANDARD DESIGN ENERGY-EFFICIENT DESIGN
Number Luminaire and lamp Watts Luminaire and lamp Watts Watts saved
12 75W R30 Holder and lamp 900 20W MR16 Holder and lamp(1) 300 600 3 100W A19 Holder and lamp 300 18W PL18 Holder and lamp(2) 66 234 2 75W A19 Sconce and lamp 150 13W PL13 Sconce and lamp(3) 34 116 1 185W 4/F40 T12 185 90W Light Tube 3/F32 T8 95 95
Totals 1,535W 490W 1,045
Source: Bernie Bauer, Integrated Lighting Concepts.
1. MR16 requires a transformer which draws 5W, so lamps actually require 25W.
2. PL fluorescents require ballasts which draw 4W.
3. Assumes residential decorative milk-white lensed surface 2 ft 2 4 ft fluorescent with standard ballast and F40 lamps.
Table 2. Geltz's Lighting Energy Savings Payback
kW x Number of x Average = Annual Savings annual operating cost per kWh energy savings hours
1.045 kW x 3,500 hours x 11.5cents/kWh(1) = $420
Cost of project = Simple payback Annual savings
$750 = 1.8 years $420
Note: 1. Average residential electricity rate.
Table 3. Nameplate Ratings versus Actual Loads
Equipment Rated (W) Idle Active
Copier Cannon PC-2 (instant ready) 575 6 400
Personal computer IBM PS/2 Model 70, 386 400 62 62
Video monitor NEC MultiSync 3D VGA 180 60 60
Laser printer Hewlett Packard Laserjet III 874 80 200
Fax Panasonic KX-F110 (facsimile, telephone, answering machine) 96 14 30
Figure 1. Plans used for the Geltz home office lighting retrofit.
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