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76 Expert Q&A

 
 

A. Uniformity is a measure of how evenly or “smoothly“ the lighting level is spread out over an area. It is expressed as a uniformity ratio of average foot-candles divided by the minimum allowable foot-candles. The lower this ratio, the better.

 

A. You can be sure you’re purchasing the right-size ceiling fan by measuring your room area (length times width) and looking for a fan with the appropriate fan diameter:

Room Area (sq. ft.) = Minimum Fan Diameter (inches)
100 sq. feet = 36-inch fan
150 sq. feet = 42–inch fan
225 sq. feet = 48-inch fan
475 sq. feet = 52-inch fan
400+ sq. feet = Two Fans

Some ceiling fans offer reversible operation; they can blow down in summer when the breeze will create a cooling effect, and up in winter to circulate warm air that has risen to the ceiling. This feature is particularly advantageous in rooms with high ceilings that trap warm air during the heating season.

 

A. Perform a tour of your home to determine where it may need insulation. A good rule of thumb is that all heated or cooled areas should be separated from unconditioned areas with insulation. Regardless of your home’s layout, you can use this rule to determine where insulation should be installed. Each area will have its own priority in terms of insulation ease and cost-effectiveness and should be evaluated on the basis of both.

To know if your home currently has enough insulation, contact your local contractor to find out the recommended insulation levels for various parts of a home in your area. They will be able to tell you if your home meets the recommended R-Values for ceilings, walls and floors.

In order of cost-effectiveness for an existing home, it generally pays to insulate first your attic or roof, second your foundation or floor, third your windows, and last, your walls. If you are unsure of where to begin, you may want to take advantage of Georgia Power’s free in-home energy audit or consider having a BPI Assessment performed on your home by one of Georgia Power’s program participating contractors.

 

A. Your team at Georgia Power can run rate analyses that compare your usage against available rates and help you decide the rate that’s best for your home. Contact us for more details.

 

A. A radiant barrier reduces heat transfer. Heat travels from a warm area to a cool area by conduction, convection and radiation. Heat flows by conduction from a hotter material to a colder material when the two materials are in direct physical contact. Heat transfer by natural convection occurs when a liquid or gas is heated, becomes less dense, and rises. Thermal radiation, or radiant heat, travels in a straight line away from a hot surface and heats any object in its path.
When sunshine heats a roof, most of the heat conducts through the exterior roofing materials to the inside surface of the roof sheathing. Heat then transfers by radiation across the attic space to the next material, either the top of the attic insulation or the attic floor. A radiant barrier, properly installed in one of many locations between the roof surface and the attic floor, will significantly reduce radiant heat flow.

Thermal insulation on the attic floor resists the flow of heat through the ceiling into the living space below. The rate at which insulation resists this flow determines the insulation’s R-value. The amount of thermal insulation affects the potential radiant barrier energy savings. For example, installing a radiant barrier in an attic that already has high levels of insulation (R-30 or above) would result in much lower energy savings than an attic insulated at a low level (R-11 or less).

All radiant barriers use reflective foil that blocks radiant heat transfer. In an attic, a radiant barrier that faces an air space can block up to 95% of the heat radiating down from a hot roof. Only a single, thin, reflective surface is necessary to produce this reduction in radiant heat transfer. Additional layers of foil do little more to reduce the remaining radiant heat flow.

Conventional types of insulation consist of fibers or cells that trap air or contain a gas to retard heat conduction. These types of insulation reduce conductive and radiant heat transfer at a rate determined by their R-value. Radiant barriers reduce only radiant heat transfer. There is no current method for assigning an R-value to radiant barriers. The reduction in heat flow achieved by the installation of a radiant barrier depends on a number of factors, such as ventilation rates, ambient air temperatures, geographical location, amount of roof solar gains, and the amount of conventional insulation present.

Several factors affect the cost-effectiveness of installing a radiant barrier. You should examine the performance and cost savings of at least three potential insulation options: adding additional conventional insulation, installing a radiant barrier, and adding both conventional insulation and a radiant barrier.

 
Q. How do you insulate windows?

Posted on August 2012

A. Single pane glass windows are virtually thermal holes in your walls. Having R-Values of roughly 1, they allow 19 times more heat to escape than an R-13 wall surrounding them. If you have lots of windows, insulating them could be one of your best energy improvements. However, keep in perspective how much you can improve them and still see through them. Adding another layer of glass raises their R-Value to just over 2, meaning now they are only losing 9 times as much heat as the insulated wall. Triple glazing can bring a window’s R-Value up to 3, but because of their expense they are only cost justified in severe climates. Storm windows can also be added to existing windows. They add a second layer of glass, halve the energy loss through the windows and often reduce infiltration through cracks in the old window casings. Of course, it would be better to have double-pane windows in the first place. Using double-pane windows to begin with brings three additional comfort advantages which some find more valuable than the energy savings. The first is the reduced noise provided by insulated windows. The second is less infiltration of dust and pollen. And the third is that insulated windows are warmer to the touch, which has a significant effect on body comfort. Because our bodies radiate heat toward cold surfaces even when they are several feet away, a cold window makes one feel colder.

 

A. To properly protect your sensitive electronic equipment you must construct a barrier around it much like you would put a fence around your home. Since you usually can’t prevent the things like lightning that damage your home electronics, you must keep these conditions from getting to your important equipment. Every piece of electrical equipment in your home needs a barrier. Just as it would be silly to dead bolt your front door, then leave the windows wide open, the same is true of your electrical equipment. Every avenue to the outside world must be protected—power, phone, cable, data and control lines must all be protected or your equipment will be vulnerable to damage.
Begin power protection at the main power entrance, the point where your power, cable and phone lines enter the house. By installing a high-energy surge protection device at this location, you can knock down the first wave of high voltage spikes entering your home. Most contractors call these lightning arrestors. But, don’t confuse these devices with a lightning rod. Lightning rods are installed to protect the house from physical damage in case of a direct hit. They won’t protect electrical equipment inside the home. The lightning arrestor is a device that helps divert damaging surges away from your electrical system and out through your ground rod. The cable TV line will probably enter your home near the main power entrance as well. It’s best to have all of your utilities enter your home at one point because it allows you to tie all of their ground rods together to form a single grounding system. This is required by some codes but it’s often overlooked by cable installers. Unless all of your equipment ties into a single ground, protection against surges won’t be as effective.
Moving inside your home, the television, DVD, DVR, CD player and stereo system represent a considerable investment, and they can be easily damaged by spikes. Each should be plugged into a plug-in surge protector. Use a protector that has multiple outlets allowing one device to protect your entire entertainment center. If you have cable service, the lead into the house should be surge-protected as well. Everything should be protected. If you protect your stereo but leave the CD player unprotected, the connection between the two devices provides a path for spikes. Some appliances containing electronic controls (i.e. microwave ovens) may also require surge protection. Make sure you use a surge protector designed for “heavy duty use”. There are surge protectors designed especially for microwaves.
Telephones and answering machines are some of the most commonly damaged devices in the home. A plug-in surge suppressor should be used to protect the power and phone line inputs. A common mistake is protecting only the power line. This does not provide adequate protection. Using a device that contains both protection elements in a single package is best and ensures system compatibility. These devices will have inputs for the phone line and the electric plug. If either line goes directly to the equipment, the equipment is not completely protected.
To prevent the flashing “12:00″ problem, look for clocks and DVD players with built-in battery back-up. Battery back-ups are not designed to keep the unit operating during a power outage, but it will preserve the memory and settings so they will still be there when the power comes back on.

 
Q. How does a heat pump work?

Posted on August 2012

A. A heat pump works like an air conditioner during the summer and reverses to become an air heater during the winter.
In the summer months, refrigerant is piped through the indoor coils, absorbs heat from the room air, and vaporizes. The cooled room air is then re-circulated throughout the house by a blower. The vaporized refrigerant flows into the compressor, which pumps the refrigerant to the outdoor coil, where it condenses back into a liquid by releasing its heat to the outdoor air. Air is circulated through the outside unit by a fan. The cooled refrigerant then flows back to the indoor coil, where the heat transfer cycle is repeated.

In the heating mode, the refrigerant flow is reversed, bringing heat inside from outdoors, essentially working like a conventional air conditioner in reverse. Cold refrigerant is piped through the outdoor coils, absorbing heat from the outside air. The refrigerant vaporizes and flows into the compressor, which pumps it to the indoor coil, where it condenses back into a liquid by releasing its heat to the indoor air. The refrigerant then flows back to the outdoor coils, where the heat transfer cycle starts again.

Like refrigerators, most heat pumps have defrost cycles that minimize frost buildup on the evaporator during the winter heating cycle. Defrost occurs automatically at pre-set time intervals. Defrosting works against the efficiency of the unit when it switches into defrost mode unnecessarily, wasting heating and cooling capacity. Microprocessor controls in some units prevent this from happening. Some controls even determine whether the heat pump or back-up heat is more economical at a particular outdoor air temperature and switch to that heating system.

 
Q. How does an air conditioner work?

Posted on August 2012

A. Refrigeration units, commonly known as air conditioners, are mechanical systems that remove heat and moisture from the air by passing it over a cold surface. When warm, moist inside air is blown across the surface of the unit’s cooling coil, the air temperature drops and the water vapor in it condenses making the air cooler and drier and therefore more comfortable. When the outside air is above 75°F, mechanical refrigeration is usually required to lower the inside temperature and humidity to make people feel comfortable. Refrigerating air for comfort inside the home, called air conditioning, is far more complicated than heating. Instead of using energy to create heat, air conditioners use energy to remove heat. The most common air conditioning systems use what is known as a vapor-compression cycle, similar to the one used by a refrigerator.

The primary difference is a refrigerator moves heat out of its interior and releases it to the surroundings, usually the kitchen, while air conditioners take heat from inside the house and release it to the outside environment.

Home air conditioners have compressors outside containing a fluid refrigerant, usually R-22. This refrigerant fluid can change back and forth between liquid and gas states at temperatures in the 40 to 50°F range. Just like water when it boils, as the refrigerant changes from a liquid to a gas, it absorbs heat, and when it changes back from a gas to a liquid, it releases heat. By changing state, refrigerants move heat from one place to another.

 
Q. How does condensation form?

Posted on August 2012

A. To understand condensation, one must first understand a couple of other concepts. Humidity refers to the amount of water vapor in the air. Relative humidity is a measure of the amount of water vapor in the air compared to the maximum amount possible at a given temperature. Air with a relative humidity of 50% is holding half the total amount of water vapor it is capable of holding at that temperature.

The amount of water vapor that air can hold depends on the temperature of the air. If the air temperature decreases, the maximum amount of water vapor the air can hold is reduced. If air at 70°F and 50% relative humidity is cooled to 52°F, the relative humidity will reach 100% and condensation will begin.

The “dew point” is the temperature at which air saturation occurs, and condensation begins. If air at 100% humidity is cooled, condensation will form as fog in the air or on surfaces at or below this temperature. This phenomenon may be observed on a cold winter day when you “see your breath” in the air; your warm breath is cooled enough to condense part of its water vapor, producing the tiny water droplets as fog.

A similar process occurs when an air-water vapor mixture flows through walls and ceilings of a home. The air is cooled as it moves through the thickness of the building envelope.

When moisture-laden air reaches its dew point, condensation will occur if it is cooled to a lower temperature. The dew point for a given temperature of air from the home varies according to the amount of humidity in that household air.

If the dew point is above 32°F, condensation will form as a liquid. If the dew point is colder than 32°F, the water vapor will condense and immediately form frost or snow.

 

76 Expert Q&A