ENME808WAdvanced Topics in Mechanical Engineering:

Energy Efficiency/Energy Audit and Conservation

Week Eleven Lecture I:

Dr. Michael Ohadi Class: Mon. 4:00 – 6:40 PM

Office: 4164C Glenn L. Martin HallOffice hours: As Per the Syllabus

Light System Audit

Lighting Terminology

Lighting Terminology

• Illumination - The distribution of light on a horizontal surface. The purpose of all lighting is to produce illumination.

• Lumen - A measurement of light emitted by a lamp. As reference, a 100-watt incandescent lamp emits about 1750 lumens.

• Footcandle - A measurement of the intensity of illumination. A footcandle is the illumination produced by one lumen distributed over a 1-square-foot area.

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Lighting Power Density (LPD):

It is a measurement of the watts per square foot consumed by the lighting system. “Total system wattage / total square footage = LPD”

In Maryland state Codes are based on lighting power allowances based on the type of building or space type and are used as a basis for design.

LPD is how most utility programs measure and qualify new construction lighting projects.

Lighting Terminology, cont.

• Efficacy – The amount of visible light (lumens) produced for the amount of power (watts) expended

• Color Temperature – Measure of the color of a light source relative to a black body at a particular temperature (K)– Incandescents have low color temperature (~2800K)– Daylight has a high color temperature (~6000K)

Lighting Color Temperature

Lighting Terminology, cont.

• Color Rendering – Describes how a light source renders a set of colored surfaces with respect to a black body light source at the same color temperature– Color Rendering Index (CRI) 0 – 100

Lighting Terminology, cont.

Blast Factor (BF) BF is the ratio of lamp lumens produced when

lamp(s) are operated on a given ballast versus equivalent lamps on a “reference” ballast.

Higher BF will increase wattage consumed as well as lumen output

Optimum Lighting Efficiency

The energy efficiency of the lighting system in a project is measured by the LPD (watts / square foot).

Energy codes may contain maximum LPDs based on the type of building or the type of space.

Keep in mind the optimum goal is to provide quality lighting at the lowest possible lighting power density.

Lighting System Audit

• Lighting accounts for a significant portion of electrical energy consumed in a building– Typically, more of an issue in commercial buildings

as opposed to residential buildings– Contributes to cooling loads

• Methods of reducing lighting energy– Reducing illumination levels– Improving lighting system efficiency– Curtailing operating hours– Taking advantage of daylighting

Lighting Audit Steps

1. Asses what you have– Room Classification: Office, warehouse, storage, etc.– Room Characteristics: Height, width, length, color and

condition of surfaces– Fixture Characteristics – Lamp type, number of fixtures, lamp

wattage, condition, etc.

2. Evaluate lighting levels and lighting quality– Measure foot-candles using a light meter– Sketch luminaries types and layout in room– Check for excessive glare or contrast– Talk to occupants about lighting levels, controls, and quality– Compare foot-candle measurements to IES recommendations

for the task performed

Illuminating Engineering Society (IES)Functional Area Light Level Lighting Power Density Classrooms Standard 50 FC 1.2 W/SF High Task - Drafting 75 FC 1.5 W/SF Science Labs 50-75 FC 1.2 - 1.5 W/SF Home Economics 50-75 FC 1.2 - 1.5 W/SF Industrial Arts 50-75 FC 1.2 - 1.5 W/SF Cafeteria Eating Area 20 FC 0.6 W/SF Food Preparation 75 FC 1.5 W/SF Computer Rooms 35 FC 0.8 W/SF (1) Conference Rooms 35 FC 0.9 W/SF Hallways/Lobbies 20 FC 0.7 W/SF Gymnasium General 30 FC 1.0 W/SF (2) Exhibitions/Matches 50 FC 1.4 W/SF (2) Library Reading Area 50 FC 1.2 W/SF Stacks 35 FC 1.0 W/SF Check in/out 75 FC 1.5 W/SF Offices Private w/o task lighting 50 FC 1.2 W/SF Open w/ task lighting 35 FC 0.8 W/SF Computer Work 30 FC 0.7 W/SF (1) Rest Rooms 20 FC 0.7 W/SF

Recommending Lighting Levels

Lighting Audit Steps, cont.

3. Estimate electrical consumption– Calculate total watts (watts/fixture × # of fixtures)– Calculate power density (watts/sq. ft)– Compare existing power density to code of design guidelines– Estimate annual hours of use– Estimate annual lighting energy cost

4. Calculate energy savings– Determine new total wattage after retrofit– Determine change in annual operating hours if lighting

controls are changed– Calculate energy savings– Calculate energy cost savings

Secondary Effects

• Reduction in lighting energy can also– Increase heating energy consumption– Decrease cooling energy consumption

• Heat of light is often an expensive and inefficient heating source

• General rules of thumb– If a building is heated only Decrease energy savings by 20%– If a building is heated and cooled Increase energy savings by

20%• If cooling system is being replaced in conjunction with

lighting upgrades, often cooling capacity can be reduced

Lighting Design Considerations

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Design GuidelinesSeveral factors can contribute to energy

efficiency: Choose the most efficacious source you can afford Select high-efficiency luminaires

–Advanced, low-glare fixtures for offices! Consider new technologies as an alternative

–Consider LED downlights vs. Halogen

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Go with the right Light LevelsUnder-lighting spaces can cause safety issues

and hinder productivity.

Over-lighting spaces simply wastes energy!

“Dial it in” the first time; don’t be afraid of multiple light levels for multiple spaces

Lighting Sources

Incandescent Lamps

• Have lowest lamp efficacies of the commonly used lamps

• Most common type of lighting in homes (~85%)

• Light up instantly and are dimmable

• Provide warm color• Short life span• Most expensive to operate

Tungsten Halogen

Incandescent Lamps, cont.

• A-Type – standard incandescent light bulb• Tungsten-Halogen – slightly higher efficacy than A-

Type due to halogen gas filling• Reflector Lamps – Interior aluminum coating directs

light to the front of the bulb

A-Type Reflector Lamps

Fluorescent Lamps

• Use 25-35% of the energy used by incandescent lamps

• Last about 10 times longer as incandescent lamps

• Require a ballast to regulate operating current and provide a high startup voltage

• Recent improvements have been made in color temperature and color rendering that compare to incandescent lamps

Fluorescent Lamps, cont.

• Fluorescent Tubes – Second most popular

light source– Preferred for ambient

lighting in large indoor spaces due to reduced glare

– Types: T12, T8, T5

Fluorescent Lamps

• T12’s are obsolete and should be replaced.• T12’s are 12/8 = 1.5 inches in diameter (least

efficient)• T8’s are 8/8 = 1 inch in diameter (more

efficient)• T5’s are 5/8 inches in diameter (most efficient)

Fluorescent Lamps, cont.

• Compact Fluorescent (CFL’s)– Efficiency of fluorescents– Convenience of

incandescent bulbs– ~75% energy savings

over incandescent lamps– Require recycling due to

mercury

CFL vs. Incandescent

Assumes $0.113 per kW-hr and 6 hours of use per day.

High Intensity Discharge (HID)

• Highest efficacy and longest service life of any lighting type

• Require a ballast and take up to 10 minutes to produce light– Most suitable in applications where lights remain

on for long periods of time• Commonly used outdoors and large indoor

arenas

HID’s, cont.

• Mercury Vapor Lamps – oldest HID, commonly used in street lights

• Metal Halide Lamps – best color rendering amounts HID’s, commonly used in sport arenas

• High Pressure Sodium Lamps – becoming most common type of outdoor lighting, most efficient HID

Light Emitting Diodes (LED’s)

• One of today’s most energy-efficient and rapidly developing lighting technology

• Last longer, more durable, and offer better lighting quality than any other light source

• Near monochromatic light source• Directionality makes LED’s ideal for recessed

down lights and task lighting• LED’s emit almost no heat

Light Emitting Diodes (LED’s)• The high efficiency and mono-directional structure of

LEDs makes them ideal for many industrial uses.

• LEDs have largely replaced incandescent bulbs in traffic signals.

• They are also increasingly common in street lights, automobiles (interior and exterior), walkways, computer components, and signs and displays.

• Because light-emitting diodes provide such strong lighting in one direction, they are ideal for lighting countertops for cooking and reading recipes.

Light Emitting Diodes (LED’s)

• Recessed downlights are commonly used in kitchens, hallways, and bathrooms in homes, and have largely replaced ordinary street lights

• Decorative light strings such as Christmas tree lights are among the most popular and most affordable LED consumer products on the market. Not only are the LED bulbs far brighter and less yellow in color than incandescent ones, but they save 90% or more in utility costs, operate at cooler temperatures, and have an operational life span of roughly 20,000 hours (enough to last for 40 holiday seasons).

LED Uses

Recessed Down LightsKitchen Under-Cabinet Lighting

Refrigerated Showcases

Holiday Lights

Lighting Type Efficacy(Lumen/Watt)

Lifetime (hours) CRI Color Temp. (K)

IncandescentType-A 10-17 750-2000 98-100 2700-2800Tungsten-Halogen 12-22 2000-4000 98-100 2900–3200Reflector 12-19 2000-3000 98-100 2800FluorescentStraight Tube 30-110 7000-24,000 50-90 2700-6500CFL 50-70 10,000 65-88 2700-6500Circline 40-50 12,000High Intensity Discharge (HID)Mercury Vapor 25-60 16,000-24,000 50 3200-7000Metal Halide 70-115 5000-20,000 70 3700High Pressure Sodium 50-140 16,000-24,000 25 2100Light Emitting Diode (LED)

Cool White LED’s 60-92 35,000-50,000 70-90 5000

Warm White LED’s 27-54 35,000-50,000 70-90 3300

Low Pressure Sodium 60-150 12,000-18,000 -44

Lighting Controls

Dimmers

• Suitable for indoor lighting for incandescent and dimmable fluorescent lamps

• Reduces lumen output more than wattage– Makes incandescent lamps

less efficient• Decrease service life

significantly

Motion Sensors

• Automatically turn off outdoor lights on when they are needed and turn them off a short while later

Occupancy Sensors

• Detect activity within a certain area

• Provide convenience by turning on lights when someone enters a room

• Two types– Ultrasonic– Infrared

Timers

Programmable Light Switch

Preset On Times(10, 20, 30, 60 minutes)

Receptacle Timer(for plug-in lights)

References

• Thurman, Handbook of Energy Audits• EnergySavers.gov

– http://www.energysavers.gov/your_home/lighting_daylighting/index.cfm/mytopic=11980