LIGHTING

Lighting falls into the general functional categories of ambient lighting (for security and safety), task lighting (to illuminate the space where tasks are performed), and accent lighting (usually on walls to make a space more visually comfortable).

Other distinctions in lighting include ...

• Efficacy

     This is a term denoting the efficiency of lighting, again comparing energy- in to energy- out, in this case lumens per watt. For example, a 100              watt incandescent lamp (bulb) produces about 1,750 lumens, giving it an efficacy of 17.5.

• Illumination

     llumination is the distribution of light on a horizontal surface and is measured in footcandles. A footcandle of illumination is one lumen                        distributed over one square foot.

• Color Rendering Index

     This is the degree to which the color of light from a lamp resembles the color of sunlight. Incandescent lighting has a color rendering index of              97-100, almost the same as sunlight. Compact fluorescent lambs have a range of 81-90.

• Lighting Types

     The most common types in residential use are ...

• Incandescent

    This century-old technology is still prevalent in homes, despite the fact that is very inefficient, with an efficacy of 10-23. As an electric

     current passes through a tungsten filament, approximately 10% from the energy output of this type of lamp is in the form of light; the rest

    in the form of heat. A halogen incandescent lamp is filled with halogen gas, enabling it to operate at higher temperatures and efficacy. 

• Compact Fluorescent (CFL)

    Light bulbs (lamps) of this, now-common type are 3-4 times more efficient than incandescents and their life is about 10 times longer.  

    When they are energized, a small amount of electricity excites mercury vapor in the bulb, producing short- wave ultraviolet light, which  

    causes a phosphor coating on the glass to glow. Because of the mercury in the bulb, it is prudent to hold your breath if you break one.

• Light Emitting Diode (LED)

     LEDs are tiny bulbs that have no filament and do not get very hot. They are illuminated solely by the movement of electrons in a    

     semiconductor material and, unlike incandescent and fluorescent lamps, they emit light in a targeted direction. They last 6 times longer

    than CFLs and are twice as efficient.

• Light Quality

      Light quality describes how well people in a lighted space can see to do visual tasks and how visually comfortable they feel in that space. The           elimination of glare is essential for light quality. Direct glare is strong light from a window or bright lamp shining directly into your eyes.                         Reflected glare is strong light reflected off a shiny surface into your eyes. Veiling glare is glare from a work surface such as a computer

      screen.

      A general good practice for designers of interior spaces is to hide a light source from direct line-of-sight. Can lights recessed in a ceiling often

      allow the light source (the light bulb) to be seen by occupants. This confuses the pupil of the eye, which attempts to open up to let in enough

      light to see the task at hand - and to simultaneously close down in response to a bright light source in direct line of sight. These two                             conflicting signals can result in discomfort. If recessed cans lights must be used, it is good practice to install very deep cans so that bulbs can

      be recessed deeply in them and not seen directly. The goal is to provide illumination without seeing the bulb. This concept seems

      foreign to designers of outdoor (street) lighting, who usually create lighting that exposes the bulb, thus creating glare that makes it more

      difficult to see both the lighted area. and the night sky. An organization called The International Dark Sky Association was created to educate

      citizens and governments about this subject and has created model lighting ordinances that are being adopted by more conscious

      communities.

PASSIVE HOME DESIGN

Unlike active solar design, which might use solar PV systems to increase the energy

available in a home, passive design attempts to reduce energy consumption simply by

the way a house is designed. These design principles include making the house compact

in shape to reduce surface area, orienting the building with its long axis running East/West,

reducing solar heat gain with shade trees and vines, using cool roof design, superinsulation,

thermal mass, advanced window technology, air tight building envelopes, and

natural ventilation.

RADIANT BARRIERS

A radiant barrier in residential construction is a reflective metalized material, often an aluminum foil, or the powderized metal coating used in "low-e" windows, and metal surfaces roof. Radiant barriers emit (give off by radiation) only 5% of the heat they absorb. The physics of radiant heat transfer describes how radiant barriers work. [see Cool Roof, above]

In an existing home, 4' wide foil, with tiny holes punched in it to allow water vapor

to pass through, can be stapled to the attic side of the roof rafters.

When solar radiation strikes the roof, the shingles (which for some inexplicable

reason are dark) heat up. This heat moves by conduction to the felt paper

underneath, thence to the plywood or OSB roof sheathing. At that point, the heat

reaches an open space, which it can move across only by radiating. As heat is

radiated to the foil radiant barrier attached to the underside of the rafters, most of

the heat is reflected back to the roof. The remaining heat is absorbed by the

radiant barrier, which - because of its low emissivity - holds onto most of this heat,

emitting only 5% of what was absorbed into the attic below. Note that this radiant

barrier application has two airspaces, one on either side of the barrier, thus

allowing for both reflection on one side and low emission on the other.

In a roof of a new building, the plywood or oriented strand board roof sheathing

can have a film of aluminum foil bonded to it at the factory. There is no airspace

between the aluminum barrier and the roof above it, so no heat will be radiated

or reflected back toward the outdoors. There must be an air space for this to occur.

Thus the radiant barrier will heat up more than in the example above. Still, of the heat the barrier absorbs, only 5% or so will be radiated into the attic.

One further advantage of radiant barriers in roof assemblies is that the air spaces adjacent to them have higher R-values than air spaces bordering other building materials (R-1.35 verses R-.68). Thus radiant barriers have a slight insulating properties, as well. However, this insulating air film must be relatively calm to be effective - a "dead air" space. If there is air movement in this space, from convective currents, for example, the insulating value is largely lost. For a description of how radiant barriers work in modern windows, see Windows, below.

R-VALUE

This is a measure of the resistance to heat transmission and is used to rate the effectiveness of insulation. It is the inverse of U-value.

SOLAR PHOTOVOLTAIC SYSTEMS

Solar PV systems fall into the realm of energy production rather than energy conservation. These systems are located on or close to the house and generate electricity for the house.

Before installing such a system, the intelligent step is to first reduce your energy consumption. Take an inventory of all house functions that require electricity, quantify how much each function uses, and see if you can reduce this use. For instance, if you have a lot of items that are always on standby, ("phantom loads"), such as audio/video equipment, computers/printers/monitors, etc., that are drawing current even when you are sleeping, plug them into an auto-off surge suppressor. If Uncle Fred left you his retro 1935 Norge refrigerator, which uses 2,000 kWh/yr, consider it having bronzed and replacing it with an Energy Star model.

Not reducing your electrical load by eliminating waste before installing a solar PV system is analogous to running in more and more water to fill your bathtub and ignoring the fact that the stopper is missing. If you reduce your electrical load, then any given size PV system will handle a greater percent of your needs.  Be wary of solar PV companies that do not first do a load calculation and recommend ways you can reduce the load.

• Types of Systems

     Two basic system types are ..

•  Grid-Tied Systems

     These systems have no batteries to store the electricity generated so

     it can be used use at night or when the electric grid goes down. In

     essence, the electric grid is your battery, since whenever you are

     not producing enough electricity to meet your home's needs, the

     extra current comes in from the grid. This is handy, as it avoids the

     cost and hassels of batteries as well as certain system losses. The 

     downside is that when the grid is down, you are too, because these 

     systems have a safety feature that automatically disconnects your  

     inverter,which youneed to convert the DC power generated by the panels

     to AC power used in your house. This "safety feature" is sold as

     protection for line workers from being shocked as they toil away restoring

     electrical service. [It is possible that a civilization capable of putting people

     on celestial objects and then returning them home is also capable

     of guaranteeing that no power can flow to the grid during a power

     outage - and still allow your own generated power to be used by your local house system. I suspect this has more to do with utility

     companies' machinations than with unsophisicated technology.] Many homeowners envision selling the extra power they produce back           to their electricity company,since the power flows both ways. But the utility companies have good lawyers, so it's not that simple. Each             utility has its own net metering agreement with its ratepayers. With many agreements, the utility will pay you (that is, credit you toward           what you owe them) for the electricity you feed back into the grid, but they will do so at a lower cost than what they charge you, often               half as much. Utilities often support home power generation in their PR campaigns, but in the long run, you "empowering" yourself                   threatens their basic business model.

•  Off-Grid Systems

     This type of system is for those who want to be "off the grid." If your home is in

      the middle of the woods, this one's for you. Direct current (DC) power is

      produced in the solar panels and stored in batteries. When the house needs

      power, the DC power is drawn from the batteries, runs through an inverter where

      it is converted to AC power, and then into your house to feed AC appliances.  

     To be more efficient, you can buy appliances that run on DC power.

• Hybrid Systems

     These combine the best of the two systems above, as they are basically grid- tied

     systems with some extra battery storage. Battery-based grid-tied inverters make

     these systems possible, as they can direct power to and from battery banks, as

     well as synchronize with the utility grid. In hybrid systems, fewer batteries are

     needed than in off-grid systems, since the grid itself is your battery most of the

     time. In addition, your electric car (a battery on wheels) can serve as a battery

     too. If it's okay with your utility, you also have power during an outage on the grid.

• System Components

     Different systems have different components (some include automobiles batteries).

     Below are two components common to all solar PV systems.

• Solar Panels

     Solar panels use light energy (photons) from the sun to generate electricity. They are of various physical materials, shapes, sizes, and

     efficiencies and generally produce between 100-320 watts. Multiple panels are grouped in arrays, which are installed on roofs, on                   various raised supports, and even on the ground. Arrays can be stationary or move to track the sun.

• Inverters

    Solar panels produce direct current and your house uses alternating current, so there is an inverter in the system to convert DC to AC.

Given the current level of sophistication of solar photo-voltaic electricity generation, and the fact that efficiencies are going up and prices coming down, it is inevitable that on-site electrical generation will become the dominant technology on earth. Centralized power generation is a dinosaur whose extinction will be a blessing. These huge centralized plants ...

• Burn fossil fuels, often dirty coal, adding both pollutants and greenhouse gasses to the atmosphere. These environmental costs are "externalized," i.e., you pay for them, not the utility.

• Waste energy, since only about 1/3rd of the heat energy consumed is converted to electrical energy. The rest is wasted up the smoke stack. In transmission and distribution to your home, another 10% is lost (10% electricity loss is 30% Btu of original fuel lost).

• Are unreliable, as local or area storms of all kinds can knock them out for days or weeks (try months, as in the case of hurricane Katrina).

• Are ugly to look at, if you consider the aesthetic impact of a cityscape dominated by electric poles and their oppressive cobweb of electric wires running in every direction. This lack of even a vestige of aesthetic consideration, much less artistry, is imposed on us without our input. Upscale subdivisions bury them underground so people don't have to look at them.

U-VALUE (U-FACTOR)

This is a measure of heat transmission, specifically of how much heat passes through a 1 square foot area of a material in one hour, when the temperature difference on the two sides of the material is 1 degree F.  It is the inverse of the R-value.

VENTILATION SYSTEMS

Humans benefit greatly from fresh air in their houses. Most homes in the United States leak in plenty of air from the outdoors (some clean, some not) through infiltration, which is the entry of air from locations we do not control. If a house runs a negative pressure, air will enter it from outside the conditioned space, which might be from the outdoors, from an attic, or from the musty space under a raised house. So, how do you know if your home is leaking sufficient air to maintain reasonable indoor air quality?

• Minimum Ventilation Requirements

     The standard way to calculate the amount of air a house needs is promulgated by the American Society of Heating, Refrigerating, and Air

     Conditioning Engineers (ASHRAE). ASHRAE's Standard 62-1989 recommends that homes have air leakage of at least.35 air changes per

     hour under natural conditions. If the leakage is less than this, mechanical ventilation is recommended. Leakage of .35 natural air

     changes per hour means that all the air in a house would be displaced by new air every three hours. This changing of the air is driven by

     pressure differences in the house created "naturally" (without a fan) by two non-human forces. These natural pressures are called "the n

     factor" and are expressed as a number.     

• Stack Effect

     Warm air is less dense than cool air and this density difference causes warm air to rise up and out through openings in the top of a                  house and cooler air to enter through gaps in the lower part of the house. Thus, in a two story house, the second floor would be under              positive pressure, the ground floor under negative.

• Wind Pressure

     Wind creates a positive pressure on the windward side of the home and negative pressures on the leeward side - in reference to the 

     home's interior. Thus, wind pressure both pushes air into the home and pulls it out of the home (which, in turn, causes even more air to

     come in).

There are a couple of other, human factors that affect home air pressure, including ...

-  Exhaust Pressures

   This is a negative pressure created in a house as air is drawn out by exhaust fans, clothes dryers, kitchen vent hoods, and

   chimneys.

-  HVAC Pressure Differentials

   The powerful fans in heating/air conditioning systems can create pressure imbalances due to ...

>  Differences in air flow, as when conditioned air is supplied to a bedroom that is tightly closed up and an equal amount of  

    air cannot get back to the return air grill. This causes high pressure in the bedroom and low pressure in the room where the

    return grill is located.

>  Differences in duct leakage, for example, when the supply ducts are leaking more than the ducts that return air from the

    rooms back to the A/C equipment. This causes a negative pressure in the house.

• Calculating the Minimum Ventilation Requirement

     There is a spiffy formula for calculating how much air should be coming into a given house - two formulas, actually. One is based on the                      volume of the house; the other, on the number of people living in the house. To be safe, whichever calls for the most air is used.

     Here's how to calculate how much air should be entering a house with a volume of 18,000 cubic feet, with

     three occupants, based on the recommendations of the ventilation scientists.

MVR = .35 air changes per hour x volume of house

60

MVR = .35 x 18,000

60

MVR (expressed in cubic feet per minute) = 105 CFM

     Now we make the calculation based on the number of people living in the house.

MVR = 15 CFM x number of occupants

MVR = 15 CFM x 3 people

MVR = 45 CFM

     To be conservative, the larger requirement is used, so it has been calculated that this

     house should be infiltrating at the rate of 105 CFM in order for it to achieve .35 natural

     air changes per hour, or one complete change of air every three hours. If it is not, mechanical ventilation is recommended.

     We have a problem. How can it be determined if the house is, indeed, sucking in 105 cubic feet of air every minute ? Do we hire a flock of

     mice, armed with tiny flow measuring gauges, to take their stations at the 3,872

     holes in the house through which air is entering ? In fact there is no way to

     measure the precise inflow of air under natural conditions, so we have to use

     something we can measure and try to calculate our way toward the natural

     CFM flow rate we have calculated above.

     This is where the blower door test equipment, with its calibrated fan, comes in

     handy. [see Blower Door, above] The blower door can accurately measure the

     amount of CFM the house is leaking when it is depressurized with a fan to -50

     pascals (a metric unit of pressure). So, what building scientists do is translate the

     minimum ventilation requirement of 105 cfm into a measurable blower door

     number. They do this by multiplying the minimum ventilation number by the

     n- factor, explained above.

     For each climate zone (hot humid, hot dry, marine, etc.), the Department of Energy

     has made a generalized calculation of what the wind pressure and stack pressure

     would be in that zone and ascribed a number to each of these pressures.

     Multiplying the wind pressure number in each climate zone by the stack pressure number yields the n-factor number.

      In New Orleans, which is in zone 3, the n-factor number for a single story house (stack effect) that is normally-well shielded from the wind

      (wind effect) is 21.5. Multiplying the minimum cfm the house needs by the n-factor translates the unmeasurable minimum ventilation rate

      under natural conditions into a measurable blower door number.

105 cfm x n-factor of 21.5 = blower door number of 2,257

     Leakage of 105 CFM natural = leakage of 2,257 CFM at a pressure of 50 pascals

     Presto, there we have it. We turn on our blower door and if the pressure we read is above 2,257 CFM , mechanical ventilation is not

     recommended. If the reading is below 2,257 CFM, the house is so tight that mechanical ventilation is recommended.

• Mechanical Ventilation Systems

     When mechanical ventilation is desired, homeowners have

     three choices.

• Exhaust Ventilation

    This strategy employs a fan or multiple fans to pull

     indoor air out of the house, which is replaced by

    (hopefully) outdoor air infiltration. Spot ventilation

    uses simple fans in bathrooms to accomplish this.

    Whole house exhaust ventilation uses a larger

    central fan to take air from several rooms, often the

    rooms with the most moisture, such as bathrooms

    and kitchen. These systems cannot control the

    quality of the air that enters to replace exhausted air,

    since air comes in, unfiltered, through the myriad holes 

    in the building envelope, sometimes from the attic and

    crawl space underneath the house. The exhaust

    strategy works best in cold climates, where there is

    more moisture in the house than outside it, because it

    prevents moisture accumulation in the house.

• Supply Ventilation

    This strategy uses a fan to bring outdoor air into the

    house, forcing indoor air out through leaks in the

    building envelope. The incoming air often goes

    through a filter and then enters the return side of the

    central A/C system. It is dried and cooled and then

    blown into the rooms through the duct system. This

    strategy is appropriate for hot, humid climates, since

    the air supplied is filtered, heated or cooled as needed

    and dried by the HVAC equipment.

• Balanced Ventilation

    A combination of the exhaust and supply systems is called a balanced system. These systems bring fresh outdoor air in and exhaust an

    equal amount of stale air, thus avoiding pressurizing or depressurizing the house. In very hot and very cold climates, balanced systems           often include a heat recovery ventilator. This is a heat exchanger that tempers the air coming into the house from outdoors. In cold 

    climates, warm indoor air being exhausted transfers some of its heat to the cold air coming in. In hot climates, the cold air conditioned 

    air being exhausted absorbs some of the heat from the hot air coming in, lowering its temperature. In humid climates, energy recovery 

    ventilators are used. These are heat recovery ventilators which also remove some of the humidity coming in.