Energy Efficient Buildings
Energy Efficient BuildingsEnergy Efficient LightingThe electricity to power lights and electrical equipment is a significant fraction of total building electricity. Moreover, heat gain from lighting, electrical equipment and people are significant components of building heating and cooling loads. Thus, energy efficient buildings utilize natural lighting and efficient electrical lighting and equipment to reduce both primary and cooling energy use. Residential Building Energy Breakdown Commercial Building Energy BreakdownLighting Introduction In the U.S., about 19% of all electricity is used for lighting (ACEEE, 2000). Typical lighting power densities are about 1-2 W/ft2 in the commercial sector and 1-1.5 W/ft2 in the manufacturing sector (UD-IAC, 2008). Modern lighting systems are much more energy efficient that previous systems. Thus, upgrading older lighting presents an opportunity for energy savings. However, an effective lighting system must do more than deliver light efficiently. Effective lighting must provide the right quantity of light, with good color rendition and minimal glare. Quality lighting and day lighting has been shown to improve productivity and enhance worker satisfaction. In most cases, small improvements in worker productivity greatly outweigh lighting energy costs. Thus, when considering upgrades to reduce lighting energy use and costs, it is essential that the changes maintain or improve the quality of light.End use lighting savings opportunities include:Turn off blocked lights and lights in unoccupied areas.Use motion sensors to turn off lights in seldom used areas such as warehouses.Turn off unnecessary lights near windows or skylights.Use photo sensors to turn on/off outdoor lights.Determine required light level and disconnect lights in overlit areas.Replace colored glass and fiberglass with corrugated polycarbonate, and turn off unnecessary lights.Add windows or skylights, and turn off unnecessary lights. Lighting distribution system savings opportunities include: Clean dirty lenses and replace yellowed lenses.Add reflectors to fluorescent strip lights.Add task lighting over critical areas and decrease general lighting.Lower lights beneath scaffolding.Paint ceilings and walls lighter color.Lighting replacement savings opportunities includeReplace incandescent and halogen lights with compact fluorescent lights.Replace T12 fluorescent lights with T8 or T5 lights and electronic ballasts.Replace HID lights with HBF lights.Productivity and Lighting Several studies have documented productivity improvements due to lighting upgrades and the increased use of sunlight for interior lighting. A few examples are listed here.Lighting UpgradesIn the post office in Reno, Nevada, a lighting retrofit with a six-year payback increased the number of letters sorted per hour by 6% and decreased the rate of sorting errors to 0.1% making the Reno Post Office the most efficient in the Western US. Energy savings were about $22,400 per year, but the increase productivity was worth about $400,000 per year (Romm and Browning, 1999).Boeing recently went through a lighting upgrade with a two-year payback. In addition to energy savings, “the things that people tell us are almost mind boggling”, said one manager. Machinists report being able to read calipers and tools more easily. The improved contrast improves workers ability to detect imperfections in the shop by 20%. This is important because “most of the errors… weren’t picked up until installation in the airplane, where it is much more expensive to fix” (Romm and Browning, 1999).Hyde Tools lighting upgrade reduced electricity costs by $48,000 per year. However, “the quality of work improved significantly because we could see things we couldn’t see before”. The manager estimates that the improved lighting results in about $250,000 per year in additional revenue (Romm and Browning, 1999).Pennsylvania Power and Light saved $2,000 per year from their lighting upgrade, but the time required to produce drawings decreased, saving them another $42,000 per year. In addition, sick leave decreased from 72 to 54 hours per year. It was apparent that “low quality seeing conditions were causing morale problems among employees” (Romm and Browning, 1999).West Bend Mutual Insurance Company’s move to a new building with advanced HVAC and better lights reduced electricity costs from $2.16 /ft2 to 1.32 /ft2, and improved productivity by 16.8% (Romm and Browning, 1999).Day LightingThe Herman Miller company built a new manufacturing plant with a large portion of its lighting provided by skylights. Production output has consistently been over 20% higher than in the previous electrically-lighted plant. Employees report that working conditions are excellent (McDonough, 2008). Lockheed Missiles and Space Company commissioned a new office building in California in which the cost of extensive day lighting added an extra 4% to the buildings cost. However, electricity costs will be reduced by about $500,000 per year for a four- year payback. In addition, absenteeism dropped by 15%, which paid for 100% of the first cost in the first year (Romm and Browning, 1999).Skylights were installed on one half of the roof of a Wal-mart in Lawrence, Kansas. Sales data indicated that the departments under the skylights sold more than the departments under the electric lighting, and more than similar departments in other stores. To test whether this was due to the skylights, the departments were switched from one side of the store to the other. As before, sales from departments under the sky lights increased (Romm and Browning, 1999). A 1999 study conducted for Pacific Gas and Electric evaluated elementary student test scores and found that, in classrooms with daylight, test scores improved by over 20+%. Retail sales in a chain of 100+ similar stores were also evaluated. Sales were found to be as much as 40% higher in stores with skylighting (Heschong Mahone Group, 1999). Lighting Fundamentals Effective, energy-efficient lighting systems provide the right quantity of light, with good color rendition and minimal glare, while minimizing energy-use. Each of these concepts is described briefly in the sections that follow.Light QuantityThe quantity of visible light radiated by a light source is measured in lumens. The theoretical upper limit for the conversion of energy to light is 683 lm/W. Natural daylight has luminous efficacy of about 110 lm/W. Electric lighting ranges from about 10 to 100 lm/W. Illuminance is the quantity of light divided by the area on which it is incident. Illuminance can be measured by light meters. The common measure of illuminance in U.S. units is footcandles. One footcandle is one lumen per square foot. 1 fc = 1 lm/ft2The Illuminating Engineering Society of North America (IESNA) publishes recommended lighting levels for various tasks and spaces. IESNA recommended lighting levels for some common spaces are shown in the table below (IESNA Handbook, 9th Edition). In general, recommended lighting levels increase as the size and contrast of the visual task decrease. Thus, the recommended lighting level will be near the lower level of the range shown in the table below when the size and/or contrast of the visual task is large, and will be near the upper level of the range when the size and/or contrast of the visual task is small. For example, 15 fc may be sufficient for warehouses with large bulk items, but 25 fc may be needed for warehouses with hand-stocked items. Similarly, 30 fc may be sufficient for general manufacturing, but 50 fc may be required for manufacturing tasks requiring visual precision.Space/FunctionRecommended Lighting Level (fc)Offices and classrooms30-50Corridors5-10Restrooms5Dining rooms10Merchandise Display50Warehouse5-30Manufacturing30-50Inspection50-100Light QualityOur eyes evolved to see in natural sunlight; thus, we distinguish colors best in sunlight. Light from electric lamps is generated at lower temperatures than sunlight and reduces our ability to distinguish between colors. Color Rendering Index (CRI) describes the effect of a light source on the color appearance of an object. CRI varies between 0 and 100. Approximate CRIs of various types of lighting are shown in the table below. Light TypeCRISunlight100Incandescent99T8 Fluorescent 75-85Metal halide65T12 Fluorescent (cool white)60High-pressure sodium22Some tasks, such as inspection and painting, clearly require high-quality light. In addition, most people prefer to work and live in light that is as close to sunlight as possible; thus the CRI of a light source should always be a consideration when selecting lights. For example, most people report seeing better under fluorescent lights with a CRI of 85 than under high-pressure sodium lights with a CRI of 22, even when the illuminance under the high-pressure sodium lights is higher. Light ColorThe color of light is often characterized by temperature. Many people prefer “warm” white light with a temperature of about 2,700 K. “Bright” white light is at about 5,000 K.GlareGlare is uncomfortably high illuminance. Glare can be problematic with large windows with direct sunlight and with direct high-intensity artificial lighting. For this reason, windows are often equipped with some type of shading and luminaries are often designed to diffuse light.Electric LightingCommon types of electrical lighting fall into three categories: incandescent, fluorescent and high-intensity discharge. Important characteristics of each category are described below. Incandescent Lights Thomas Edison invented the incandescent light bulb and it remains essentially unchanged today. Incandescent lights produce light by simple radiation from a heated tungsten filament. The lighting efficiency is generally low since most of the energy is released as infrared radiation rather than visible light. In recent years, halogen has been added to the filament increasing the efficiency and light output by about 30% in ‘halogen lights’. Incandescent lights are inexpensive, require almost no warm-up time, and the lighting output does not degrade significantly over time. However, because of their inefficiency, they are being replaced by compact fluorescent lights that use about 30% as much energy and last about seven times longer.Fluorescent LightsFluorescent lights work by energizing Ar, Ar-Ne or Kr gasses inside a tube. The gasses produce UV radiation that is converted to visible light when it interacts with phosphor coatings on the inside of the tube. Fluorescent lights have a higher lighting efficiency than incandescent lights. They start quickly and lighting output degrades only moderately over time. Fluorescent lamps are labeled using “F” and “T” notion. The “F” notation refers to the nominal wattage of the lamp. The “T” notation denotes the diameter in units of 1/8 inch. Thus, Thus ‘F32T8’ refers to a lamp with nominal power draw of 32 W and 1 inch diameter. Over time, the progression has been toward thinner lamps, from T12 to T8 to T5, with corresponding improvements in energy efficiency and color rendition. Tubular fluorescent lamps with low mercury content are generally marked with green end caps. All fluorescent lights require ballasts. The ballast regulates voltage and uses some energy itself. Old-style T12 lamps used magnetic and electro-magnetic ballasts. T8 and T5 lamps use electronic ballasts. New electronic ballasts are more energy-efficient, eliminate the flicker associated with old-style magnetic ballasts, are quieter and contain less heavy metals than old-style ballasts.The actual power draw of the lamp, and the corresponding lamp output are determined by the power supplied to the lamp by the ballasts. The relative power delivered by the ballast to the lamps is called “ballast factor”. For example, lamps powered by a ballast with a ballast factor of 0.87, will draw about 87% of their rated wattage and deliver about 87% of their rated lighting output. The fixture that houses the lamps and ballast and directs the light onto the work plane is called a luminaire. The most common types of fluorescent luminaries are recessed-troffer and suspended luminaires. Many offices employ recessed-troffer luminaires. The troffers are typically equipped with acrylic lenses or parabolic grids to diffuse the light. Although acrylic lenses transmit more light than parabolic grids, parabolic grids produce less glare and are therefore widely used in rooms with video displays.Recessed parabolic and lensed troffers.In industrial applications, fluorescent luminaires are typically suspended from the ceiling. Simple “strip” lights without reflectors attached to the sides lose a significant amount of the light sideways and upwards. Adding reflectors to the sides of the luminaire pushes more light downward onto the work plane, and reduces the number of lights required to generate a given lighting level on the work plane. The most efficient fluorescent luminaires employ polished metal mirrors above each lamp to direct the maximum possible light onto the work plane. High-bay fluorescent (HBF) luminaires employ these polished reflectors, and are displacing HID lights in industrial applications due to their improved energy efficiency, color rendition and other attributes. A) fluorescent strip light, B) fluorescent strip light with side reflectors, C) high-bay fluorescent light with individual polished mirror reflectors.High-Intensity Discharge LightsHigh-intensity discharge (HID) lights are primarily used in applications with high ceilings or for outdoor lighting. The most common types of HID lights are metal halide (MH) and high-pressure sodium (HPS). MH lights produce a white light with a CRI of about 65, and have a lighting efficiency of about 70 lm/W. HPS lights have a lighting efficiency of about 95 lm/W, but produce a yellow light with poor color rendering (CRI = 20); thus, these lights are best suited for outdoor and warehouse applications. All HID lamps require a ballast. The ballast for a typical 400-W HID lamp uses 50 to 65 W. HID lamps take about 3 minutes to start-up when cold and about 25 minutes when warm. Thus, most HID lighting systems include a few fluorescent safety lights that start up immediately in the advent of a power interruption. Two-stage and dimmable HID ballasts with occupancy sensors are available, Two-stage HID ballasts typically have a low-lighting stage that produces 35% of the light while using 50% of the rated energy. Luminaries for HID lights typically use acrylic or spun-aluminum reflectors. Acrylic reflectors spread about 10% of the light horizontally and toward the ceiling. Because of this, they are often used in retail applications where bright ceilings are more visually attractive. Spun aluminum reflectors are the most common type in industrial applications and direct all light toward the floor. HID luminaries are classified as high-bay for placements higher than about 25 feet, and low-bay for placements less than about 25 feet. Low-bay luminaries have acrylic lenses that spread the light outward over a wider surface area.A)acrylic high-bay luminaire, B) aluminum high-bay luminaire, C) aluminum low-bay luminaire with acrylic lens.Light emitting diodes (LEDs)Light emitting diodes (LEDs) are semiconductor materials that emit light when electricity is passed through them. LEDs are used in thin-screen computer monitors, thin-screen televisions, watches, exit signs, flashlights, traffic lights and many other applications. Their appeal lies in their energy efficiency and longevity. A principle challenge for white light LEDs is converting the colored light produced by an LED into white light, which a combination of many colors of light. To do so, many LED produce UV light to stimulate phosphors which emit red, green and blue light in the proper proportion to make white light. Another approach is employed by organic LEDs, which may someday be mass-produced using ink jet technology on a substrate. The efficiency of white light LEDs is approaching the efficiency of fluorescent lights at about 25%. Theoretically, LEDs could be 100% efficient, which is equivalent to 683 lm/W. Current commercial and household LEDs produce about 50-100 lm/W. Lab prototypes can produce up to 200 lm/W at 2,700 K. The rated lifetime of LEDs is about 50,000-100,000 hours. A principle advantage of LEDs is that they produce uni-directional light. Thus, light from LEDs can be aimed directly at target without a reflector and the associated losses. In contrast, incandescent, fluorescent and HID lamps produce light in all directions and use reflectors to direct light onto a target.LED lights in a Walmart in Suzhou,ChinaThe combination of high efficiency, long life and unidirectional light is often very powerful. For example, many older traffic lights use 150-W incandescent light bulbs that last about 1 year and are covered by red, yellow and green filters. Replacement LED lights that directly generate red, yellow and green light consume about 15 W and last about 5 parative CharacteristicsThe efficiency of converting electricity to light can be measured as the ratio of light output (lm) and electrical power (W). All common types of electric lights except incandescent lights require a ballast to regulate the voltage to the lamp. Thus, the lighting efficiency should include the electricity consumed by both the lamp and ballast. The lighting output of most types of lights degrades over the lifetime of the light, thus the mean lighting output should be used when calculating energy efficiency. The approximate lighting efficiencies of common types of lighting systems (including ballasts), and other characteristics are shown in the table below.Light TypeEfficiency(Lm/W)*CRILifetime (hours)LumenMaint.Restrike TimeIncandescent1899750GoodInstantCompact fluorescent706010,000OKImmediateT12 Fluorescent 586020,000GoodImmediateT8 Fluorescent 1007520,000GoodImmediateMetal halide706520,000Fair30 minHigh-pressure sodium962220,000Good30 minLEDs1208080,000GoodImmediate*Typical lm/W calculated using mean lighting output (lm) and energy use (W) including ballast.Performance MetricsTypical performance and cost data for common lamps and ballasts are shown below. Fluorescent and HID lamps are generally specified by a nominal power draw and nominal light output. However, the power to a lamp is regulated by a ballast. Thus, the actual power draw of the lamps plus the ballast, and light output of the lamps is determined by the ballast. Example 4-ft T8 fluorescent lamps have a nominal power draw of 32 W each and nominal light output of 2,710 lm each. Using data from the tables shown below, calculate the actual power draw and lighting output of two 32-W lamps when powered by a single low-output electronic ballast, and when powered by a high-output electronic ballast. The power consumption of a single low-output electronic ballast is 51 W and the power consumption of a single high-output electronic ballast is 77 W. Thus,Power input of 2 lamps and the ballast for low output ballast = 51 WPower input of 2 lamps and the ballast for high output ballast = 77 WThe actual light output of a lamp is the product of the nominal rated light output and the ballast factor associated with the ballast. Thus, the actual light output of two 32-W lamps with nominal rated output of 2,710 lm each, when powered by a low-output electronic ballast with ballast factor 0.75 is:Light output (low output ballast) = 2 lamps x 2,710 lm/lamp x 0.75 = 4,065 lmIf the same lamps were powered by a high-output electronic ballast with ballast factor 1.20 the actual light output would be:Light output (high output ballast) = 2 lamps x 2,710 lm/lamp x 1.20 = 6,504 lmSimilarly, a metal halide lamp may be labeled with a nominal power draw of 400 W and nominal light output of 23,500 lm. However, as shown in the tables below, the lamp and the ballast together draws 460 W. HID ballasts generally have a ballast factor of 1.0. Thus, the actual light output of HID lamp is equivalent to the nominal light output of the lamps. Fluorescent Lamps TypeNominalPower (W)RatedLife(hr)Mean Output (lm)CRICost($)4-ft T1248-in T12 34-W3420,0002,280621.4048-in T12 40-W4020,0002,910734.004-ft T848-in T8 32-W3220,0002,710781.9048-in T8 32-W, long life, low merc3224,0002,710752.6048-in T8 32-W, cover guard3220,0002,6257811.008-ft T1296-in T12 60-W6012,0005,060623.9096-in T12 95-W9512,0006,960606.0096-in T12 110-W11012,0007,7406013.008-ft T896-in T8 59-W5915,0005,310757.8096-in T8 59-W, cover guard5915,0005,1507524.1096-in T8 86-W8618,0007,2007517.70Fluorescent Ballasts TypeLampsLamp Power (W)BallastPower (W)BallastFactorCost($)4-ft T12Fluor F34T12 Electromagnetic 23468.874-ft T8Fluor F32T8 Electronic (Low Output)23251.75$36Fluor F32T8 Electronic (Normal Output)23258.87$15Fluor F32T8 Electronic (High Output)232771.20$368-ft T12Fluor F96T12 Electromagnetic 260112.88Fluor F96T12 Electromagnetic295203.91Fluor F96T12 Electromagnetic2110237.958-ft T8Fluor F96T8 Electronic 259110.85$25Fluor F96T8 Electronic 286160.88$29Metal Halide Lights 175 W250 W360 W400 W1,000 WLamps/fix11111kW/fix0.2100.2950.4200.4601.080Lum/fix8,80013,50023,50023,50066,000Hours/lamp10,00010,00020,00020,00012,000Cost/lamp$27$26$50$23$74Cost/fix*: Low Bay$225$215$250$250$205Cost/fix*: High Bay------$110$110$235CRI6565656565High-Pressure Sodium Lights70 W100 W150 W250 W400 W1,000 WLamps/fix111111kW/fix0.0880.1280.1850.3000.4651.110Lum/fix5,4508,55014,40027,00045,000126,000Hours/lamp24,00024,00024,00024,00024,00024,000Cost/lamp$27 $23 $21 $21 $19 $83 Cost/fix*$163 $165 $160 $196 $216 $360 CRI 222222222222High-Bay Fluorescent LightsT8T8T8T5T5T5Lamps/fix468468kW/fix0.1560.2340.3120.2360.3540.472Lum/fix 13,68020,52027,36024,00036,00048,000Hours/lamp24,00024,00024,00024,00024,00024,000Cost/lamp$2.50$2.50$2.50$15$15$15Cost/fix* $120 $150 $200 $170$230$300Cost/occ sen$70$70 $70$70 $70 $70 CRI858585858585* Fixture cost includes lamp, ballast and luminaire High-Bay LED LightsLEDLamps/fix4kW/fix0.080Lum/fix **8,000Hours/lamp***100,000Cost/lamp80Cost/fix*340Cost/occ sen70CRI80* Fixture cost includes lamp, ballast and luminaire Lighting DesignThe Illuminating Engineering Society (IES) lumen method calculates the illuminance on a workplane, Ew (fc), as:Ew = Cu x F / Awwhere Cu is the coefficient of utilization, F is the total lumens produced by the lamps, and Aw is the area of the work plane. Cu is a calculated from a manufacturer-supplied table based on the type of luminaire, room geometries and surface reflectivities. Typical Cus range from about 0.2 to 0.6 (Kreider and Rabl 1994) Heating and Cooling of Buildings.This equation can also be written as Ew = Cu x (LPF x N) / AwWhere LPF is the lumens per fixture and N is the number of fixtures. In fluorescent lights, lumens per fixture LPF is the product of the number of lamps, NL, lumens per lamp, LPL, and the ballast factor, BF. LPF = NL x LPL x BFTo determine how many fixtures are needed simply solve this equation for N.N = (Ew x Aw) / (Cu x LPF) Values of the coefficient of utilization, CU, for typical 4-lamp fluorescent troffer fixtures, 400-W high-bay metal halide fixtures and 6-lamp high bay fluorescent fixtures are shown in the tables below. CU values for recessed 2’ x 4’ fixture with acrylic lens and 4 lamps ()CU values for 8-ft 4-lamp or 4-ft 2-lamp fluorescent fixture ()CU values for high-bay 400-W MH or HPS fixture ()CU values for high-bay six-lamp ORION 416 HPM fluorescent fixture ()In each table CU depends on the room cavity ratio, RCR, whereRCR = 5 x h x (w + l) / (w x l) CU also depends on the reflectivity of the ceiling, rc, and the reflectivity of the walls, rw. Most paint color chips report Light Reflecting Value (LRV), which is the reflectivity. Light surfaces have a high reflectivity.Source: Lighting Design ExampleDetermine the number of 400-W metal halide fixtures and 230-W high-bay fluorescent fixtures required to light a space with the following characteristics:Ew = 40 fcW = width = 50 ftL = length = 100 ftH = height = 25 ftRc = reflectivity of ceiling = 50%Rw = reflectivity of walls = 50%Solution:RCR = 5 x h x (w + l) / (w x l) = 5 x 25 x (50 + 100) / (50 x 100) = 3.75 ~ 4.0CU (400-W metal halide) = 0.57CU (230-W high-bay fluorescent) = 0.69LPF (400-W metal halide) = 23,500 lmLPF (230-W high-bay fluor, w/ 3 2-lamp, 1.2 BF, 78-W ballasts at 8,000 hrs) = 3 x 6,840 lm = 20,520 lmN = (Ew x Aw) / (Cu x LPF) N (400-W metal halide) = (40 x [50 x 100]) / (.57 x 23,500) = 14.9 ~ 15 lightsN (230-W high-bay fluorescent) = (40 x [50 x 100]) / (.69 x 20,520) = 14.1 ~ 14 lightsLamp Replacement CostsOvertime, lamps fail and need to be replaced. Thus, economic analysis of lighting upgrades should consider lamp replacement costs.The number of lamps that must be replaced each year, Nr, can be calculated as:Nr = Nt x AOH / LLWhere:Nt = total number of lamps in operationAOH = annual operating hoursLL = lamp lifetimeLamp Replacement Cost ExampleConsider lamp replacement savings from replacing 320 400-W MH fixtures with 320 6-lamp HBF fixtures if the lights operate 8,000 hours per year.The number of lamp replacements would be about:MH: (320 fix x 1 lamps/fix) x 8,000 hours/year / 20,000 hours = 128 lamps/yearT8: (320 fix x 6 lamps/fix) x 8,000 hours/year / 30,000 hours = 512 lamps/yearThe cost of a 400-W MH lamp is about $23, and T8 lamps cost about $3 each. The hourly wage for a skilled-trade electrician, including all benefits, is about $65 per hour. Assuming it would take one worker about 30 minutes to replace either a single MH lamp or 6 T8 lamps, the annual maintenance costs are about:MH: 128 lamps/year x ($23 /lamp + (30/60 hours/lamp x $65 /hour)) = $7,104 /yearT8: 512 lamps/year x ($3 /lamp + (30/60 hours / 6 lamps x $65 /hour)) = $4,309 /yearThus, the annual maintenance savings would be about:$7,104 /year - $4,309 /year = $2,795 /yearEconomics of Lighting UpgradesThe methods described above can be used to determine the economics of lighting upgrades. The method typically involves the following steps.Calculate how many of the proposed lights are needed to deliver the required number of footcandles in the space.Calculate the annual energy cost savings of replacing the current lights with the proposed lights.Calculate the annual relamping cost savings, including both labor and material costs. Calculate total annual cost savings including both annual energy and annual relamping savings.Calculate the one-time implementation cost of replacing the current lights with the proposed lights.Calculate the simple payback of the investment.The performance and coefficient of utilization data from the preceding sections can be used in these calculations.Lighting Upgrade Economics ExampleA facility has 25 fixtures with 400-W high pressure sodium (HPS) lamps. A lighting upgrade to 6-lamp T8 high-bay fluorescent (HBF) fixtures is proposed. The lights operate 6,000 hours per year and the average cost of electricity is $0.10 /kWh. The hourly wage for an electrician is $50 per hour. It takes an electrician 15 minutes to replace either a single HPS lamp or 6 T8 lamps. It takes an electrician 30 minutes to replace a HPS fixture with a new HBF fixture.Determine annual cost savings including energy and lamp replacement costs, the implementation cost, and simple payback of the project. The space has the following characteristics:Ew, required = 50 fcW = width = 150 ftL = length = 100 ftH = height = 25 ftRc = reflectivity of ceiling = 70%Rw = reflectivity of walls = 70%Solution:The number of HBF fixtures required would be:RCR = 5 x h x (w + l) / (w x l) = 5 x 25 x (150 + 100) / (150 x 100) = 2.0CU (HBF) = 0.93LPF (HBF) = 20,520 lmN (HBF) = (Ew x Aw) / (Cu x LPF) N (HBF) = (50 x [150 x 100]) / (.93 x 20,520) = 34 fixturesThe energy cost savings would be:Esav = [(25 fix x .465 kW/fix) – (34 fix x .234 kW/fix)] x 6,000 hr/yr Esav = 22,014 kWh/yrECsav = 22,014 kWh/yr x $0.10 /kWh = $2,201 /yrThe number of annual lamp replacements would be:HPS: (25 fix x 1 lamps/fix) x 6,000 hours/year / 24,000 hours = 6 lamps/yearHBF: (34 fix x 6 lamps/fix) x 6,000 hours/year / 24,000 hours = 51 lamps/yearThe annual lamp replacement costs would be:HPS: 6 lamps/year x ($19 /lamp + (.25 hr/lamp x $50 /hr)) = $189 /yrHBF: 51 lamps/year x ($2.5 /lamp + (.25 hr/ 6 lamps x $50 /hr)) = $234 /yrThe annual lamp replacement savings would be:$189 /year - $234 /year = -$45 /yearThe total annual savings would be:$2,201 /year - $45 /year = $2,157 /yearThe implementation cost and simple payback would be:IC = 34 fix x [$200 /fix + (.50 hr/fix x $50 /hr)] = $7,650SP = $7,650 / $2,157 /yr x 12 mo/yr = 43 monthsNatural Lighting DesignNatural lighting uses light through skylights in the roof of a building or windows in the walls of a building. Illuminance from SkylightsThe Illuminating Engineering Society (IES) lumen method to calculate the illuminance on a work plane, Ew (fc), from the illuminance on a horizontal skylight Esl (fc) is:Ew = Esl x Cu x transmissivity of the skylight x transmissivity of the well x Asl / AwWhere Cu is the coefficient of utilization, Asl is the area of the skylight and Aw is the area of the work plane. Cu is a function of ceiling reflectivity, pc , wall reflectivity, pw, and the room cavity ratio, RCR. Values of Cu for skylights are tabulated in Table 13.5 of Kreider and Rabl, 1994, Heating and Cooling of Buildings. An adequate approximation is given by:Cu = 1.016898 + 0.074074 pc + -0.14778 RCR + 0.111111 pw + 0.037037 pc2 + 0.008133 RCR2 + 0.125 pw2The room cavity ratio, RCR, is:RCR = 5 x h x (w + l) / (w x l) where h is the height of the skylight over the work plane, w is the width of the room and l is the length of the room. Design values of the illuminance on a skylight, Esl, can be found in Figures 13.4 – 13.6 of Kreider and Rabl, 1994, Heating and Cooling of Buildings. Alternately, Esl can be calculated from the total radiation on a horizontal surface Ih (Btu/hr-ft2) by assuming that the illuminance of sunlight is 110 lm/W.Esl (fc) = Ih Btu/hr-ft2 / 3.413 Btu/W-hr x 110 lm/W x 1 fc/(lm/ft2)According to a local roofing company in 2002, the material and installation for a 4 ft by 4 ft skylight with a 10-foot shaft would cost about $2,000.Illuminance from Skylights Example A 50 ft by 50 ft room with a 25 foot ceiling has 50 ft2 of skylights. The total solar radiation on the skylights is 300 Btu/hr-ft2. Calculate the illuminance on the floor. The reflectivity of the walls is 0.70 and the reflectivity of the ceiling is 0.70. The average transmissivity of each skylight is 0.80 and the average transmissivity of each skylight well is 0.90. Assuming that the illuminance of sunlight is 110 lm/W, the illuminance on a skylight, Esl, is: Esl = Ih Btu/hr-ft2 / 3.413 Btu/W-hr x 110 lm/W x 1 fc/(lm/ft2) = 9,669 fcThe room cavity ratio, RCR, is: RCR = 5 x h x (w + l) / (w x l) = 5The coefficient of utilization, Cu, is:Cu = 1.016898 + 0.074074 pc + -0.14778 rcr + 0.111111 pw + 0.037037 pc2 + 0.008133 rcr2 + 0.125 pw2 = 0.690The illuminance on a work plane, Ew (fc), is:Ew = Esl x Cu x transmissivity of skylight x transmissivity of well x Asl / Aw = 96 fcIlluminance from Vertical WindowsThe IES recommends an illuminance of about 20 fcs for warehouse spaces and 50 fc for precision work. The general equation to calculate the illuminance on a work plane, Ew (fc), from the illuminance on a vertical window Ev (fc) is:Ew = Ev x Cu x transmissivity of the windowWhere Cu is the coefficient of utilization. Cu is a function of the window length and height, room depth and the distance between the window and the work plane (expressed as a fraction of the room depth). Values of Cu for windows are tabulated in Table 13.8 or Kreider and Rabl, 1994, Heating and Cooling of Buildings.Design value of the illuminance on a vertical window, Ev, can be found in Figures 13.4 – 13.6 of Kreider and Rabl, 1994, Heating and Cooling of Buildings. Alternately, Ev can be calculated from the total radiation on a vertical surface Iv (Btu/hr-ft2) by assuming that the illuminance of sunlight is 110 lm/W.Ev (fc) = Iv Btu/hr-ft2 / 3.413 Btu/W-hr x 110 lm/W x 1 fc/(lm/ft2)If the window is shaded from direct solar radiation, then the Iv should be the diffuse component of solar radiation.LightSim Daylighting Analysis SoftwareLightSim daylighting analysis software simulates hour-by-hour illuminance on a work plane using TMY2 meteorological data. It is specifically designed to assess the feasibility of daylighting in buildings. LightSim can quickly determine the fraction of time that various daylighting designs can meet or exceed a target illumination on a work plane. LightSim is available at no cost from the University of Dayton IAC.Photo Controls Photo controls turn lights on and off depending on lighting levels or occupancy. In indoor lighting applications, photo controls are most often used with fluorescent or incandescent lights since these lights turn on and off quickly. Photo controls are seldom used with HID lighting in indoor applications, because of the 15-minute restrike time required for HID lighting to regain full output. Photo SensorsPhoto sensors measure light levels and control lights based on the difference between the measured light level and a set point. In outdoor applications, photo sensors turn lights off during the day and on during night, with an average on-time of 12 hours per day. Most outdoor HID lights come with a ?-inch knockout or an 11/16-inch hole for easy screw-in mounting. Most photo sensors have built-in delays to prevent false cycling from headlights, etc. Photo sensors typically cost less than $15 each and can be installed in less than ? hour. Thus, it is virtually always cost-effective to install photo sensors on outdoor lights to prevent lights from running during daylight hours. In indoor applications, photo sensors turn off unnecessary lights in day lit spaces. Occupancy SensorsOccupancy sensors turn lights on when a space is occupied and turn lights off about 4 minutes after the space is unoccupied. Most occupancy sensors use infrared sensors to detect body heat in motion. In commercial buildings, occupancy sensors are especially effective in lightly used areas, such as lavatories or conference rooms, or in rooms where lights may be left on inadvertently. In manufacturing facilities, occupancy sensors are especially effective in ware house areas with limited traffic between rows of stacks. Residential occupancy sensors cost about $15 each and commercial/industrial quality occupancy sensors cost between $80 and $200 each.Ballast and Lamp DisposalBallasts manufactured before 1979 contained wet-capacitors with the hazardous waste PCB. After 1979, ballasts used dry capacitors and contain no appreciable hazardous wastes. Because very few pre-1979 ballasts remain, most states allow post-1979 ballasts to be disposed of in normal waste streams.Fluorescent and HID lamps contain small amounts of mercury in the phosphor powder. Mercury is a potent neurotoxin and is harmful to both animals and humans. When unbroken lamps are disposed of in landfills, virtually no mercury leaches into the environment. However, if lamps are incinerated, the mercury is transported through the atmosphere to water, animals and humans. Spent lamps can also be recycled; however, some studies indicate that more mercury is released into the environment during recycling than by placing the lamps in landfills.Currently, lamp disposal is regulated on a state-by-state basis, or indirectly by the 1990 RCRA, which recognizes mercury as a hazardous waste. In many states, all traditional spent lamps from businesses are considered hazardous waste irrespective of the number of lamps being disposed. In this case, spent lamps should be sent to a registered recycler or hazardous waste contractor. Under RCRA, small quantity generators that dispose less than 350 4-foot lamps per month can legally dispose of spent lamps into the municipal solid waste stream. In any case, if the municipal waste is incinerated, it is recommended that the lamps be sent to an EPA-registered recycler or hazardous waste disposal company. Be sure to research the credibility of the recycler or waste management company. If the waste is not disposed of properly, the original generator may be legally liable. Recyclers and hazardous waste handlers typically charge about 40 cents per lamp for disposal or recycling. For new lamp purchases, specify low-mercury lamps, which are commonly marked with green end-caps. Low-mercury lamps have about 5 milligrams of mercury compared to about 48 milligrams for 1985 vintage lamps. The additional cost for low-mercury lamps is usually negligible, and in most states, spent low-mercury lamps can be deposited directly in landfills instead of being sent to a lamp recycler. This saves disposal costs and reduces potential environmental legal liability pact fluorescent lamps contain about 4 mg of mercury. However, the 75% reduction in energy use compared to incandescent lamps displaces mercury emissions from coal fired power plants. The U.S. EPA estimates that the use of CFLs in place of incandescent lamps results in over three times less mercury emissions.Source: U.S. E.P.A., Information on CFLs and Mercury, 10/2010Heating and Cooling InteractionsReducing the lighting energy added to a conditioned space decreases the space cooling load and increases the space heating load. From simple energy balances, the air conditioning electricity savings can be estimated as:[(Plights,pre - Plights,post) x hours/year ] / ?coolingThe additional heating energy can be estimated as:[(Plights,pre - Plights,post) x hours/year] / ?heatingWhere Plights is the power draw of the lights and ? is the efficiency of the space conditioning equipment. Heating and Cooling Energy ExampleIf the lighting load were decreased from 50 kW to 40 kW, for 2,500 hours per year during the cooling season, and the average efficiency (coefficient of performance) of an air conditioner is 3.0, calculate the air conditioning savings: The air conditioning savings would be:[(50 kW - 40 kW) x 2,500 hr/yr ] / 3.0 = 8,333 kWh/yr If the lighting load were decreased by the same amount for 2,500 hours during the heating season, and the average efficiency of a furnace was 75%, calculate the additional heating energy needed. The additional heating energy would be about:[(50 kW - 40 kW) x 2,500 hr/yr ] / 0.80 x 3,413 Btu/kWh = 107 x 106 Btu/yrNote that when the heating and cooling periods are about the same length, as in this example, the increased air conditioning and decreased heating costs may be nearly equal. For this reason, they are sometimes ignored. In buildings with complex HVAC systems, heating and cooling interaction effects can be more accurately modeled by building energy simulation software. Internal Heat Gain from People Typical sensible, latent and total heat rates given off by people are shown in the table below (ASHRAE Fundamentals, 2005). The sensible heat gain results from radiation and convection from the human body to the air. The latent heat gain is the energy required to condense the water vapor given off by human respiration and perspiration. The latent heat gain is the product of the mass of water vapor from humans and the enthalpy of evaporation for water vapor at atmospheric pressure. Average PersonQtotalQsensibleQlatentAt rest350 [Btu/hr]210 [Btu/hr]140 [Btu/hr]100 W60 W40 WLight work640 [Btu/hr]315 [Btu/hr]325 [Btu/hr]185 W90 W95 WHeavy work1600 [Btu/hr]565 [Btu/hr]1035 [Btu/hr]470 W170 W300 WInternal Heat Gain from Electrical EquipmentAll electricity consumed in a building is eventually converted into sensible heat. Thus, the heat gain from electricity is equivalent to the electricity use inside a building. The average American house in uses about 11,000 kWh/yr. To gain intuition about how much heat this is, assume a house uses 8,760 kWh/year. If so, the average rate of heat gain is about:Only the electricity consumed indoors becomes heat gain to the space. If 25% of this electricity was used for outdoor lighting or consumed by the outdoor air conditioner compressor and condenser fan , the average internal heat gain from electricity use would be:Alternately, the following table shows average operating characteristics of residential electric appliances. Residential electric equipment energy use. Source: DOE, Building Energy Data Book, March 2011In commercial buildings, lighting energy density is typically about 1.5 W/ft2 and the plug load density for computers, copiers, etc. is about 0.5 W/ft2. All of this becomes heat gain into the space. 405828541846500Reducing Energy Use and Cooling Loads with Energy Efficient Appliances and EquipmentEnergy Star is a standard created by the United States Environmental Protection Agency to identify energy efficient lighting, equipment and even buildings. Energy Star certified products typically use 30% or more less energy than conventional products. The table below shows the increased energy efficiency of Energy Star rated products compared to conventional products.Energy Star Equipment efficiency gain compared to typical product.ExampleConsider a house that uses the following electric equipment: cloth washer, dish washer, refrigerator-freezer, desktop PC, desktop monitor, television, microwave oven, toaster oven and coffee maker. a) Using data from the “Residential electric equipment energy use” table, calculate the total annual energy use of the equipment (kWh/yr). To demonstrate how to calculate annual energy use, consider the case of “Desktop PC”. The annual consumption is calculated as:The annual energy use for all equipment is the sum of the annual consumption of all the individual equipment.b) Using data from the “Energy Star Equipment efficiency gain compared to typical products” table, calculate the total annual energy use of Energy Star equipment (kWh/yr). The annual energy use for Energy Star equipment is:c) Calculate the overall percent energy use reduction of the energy star equipment compared to typical equipment. Lighting ReferencesAmerican Council for an Energy-Efficient Economy, 2000, “Guide to Energy-Efficient Commercial Equipment”, Washington, D.C. Energy Information Administration, 1996, “Residential Lighting Use and Potential Savings”DOE/EIA-0555(96)/2, U.S. Department of Energy, Washington, DC, Information Administration, 2002, “U.S. Lighting Market Characterization, Volume 1: National Lighting Inventory and Energy Consumption Estimate”, U.S. Department of Energy, Washington, D.C. Granger, 2001, “Grainger Industrial Supply Catalog 2000-2001”, No. 391. Heschong Mahone Group, 1999, “Daylighting in Schools” and “Skylighting and Retail Sales”, Pacific Gas and Electric, , J.F. and Rabl, A., “Heating and Cooling of Buildings”, 1994, McGraw-Hill Inc.McDonough, 2008, , Plymouth WI, Romm and Browning, 1999, “Greening the Building and the Bottom Line”, Global Energy Conference, Vancouver, May.Suozzo, M., Benya, J., Hydeman, M., Dupont, P., Nadel, S. and Elliot, N., “Guide to Energy Efficient Commercial Equipment”, 2000, American Council for an Energy Efficient Economy.Technology Review, 2003, “LED vs. the Lightbulb”, May, pgs. 30-36.University of Dayton Industrial Assessment Center, 2008, Dayton, OH ................
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