Model #F-75 MURATA Fax Machines

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Question and Answers

Q:

Why does moisture collect on the inside of my aluminum storm windows?

A:

Information Homeowners Information Technical Information Other Links

RLC Engineering, LLC.

Window Condensation

Craig DeWitt, PhD, PE January 3, 2002

Click here for printer friendly version

Condensation on a window occurs when the surface of the window is cooler than the "dew point" temperature of air in contact with the window. Condensation is a result of a combination of surface temperature and moisture in the air.

Window condensation is usually a wintertime situation, when outside temperatures are very low. Condensation can also happen during the summer, when outside air is very humid and inside temperatures are kept relatively cool. Winter condensation occurs on the inside of windows, while summer condensation occurs on the outside of windows.

Summer condensation problems are mostly visual, whereas winter condensation problems can be destructive. Since outside window and building surfaces often get wet from rain, a little extra liquid water will not be detrimental. The condensation should disappear as outside air temperatures rise. Winter condensation though, can cause decay, mold and paint problems.

Several factors affect heat flow through a window and therefore the surface temperature of the glass, including inside and outside air speed across the glass, sun shine, sky temperature, inside and outside air temperature, and glazing types and treatments.

Energy efficient windows and other window treatments reduce the amount of heat moving through a window system. Double pane glass, low E coatings and inert gas fill help to reduce the flow of heat. This reduced heat flow results in cooler surfaces on the cold side of the window and warmer surfaces on the warm side of the window.

Winter Condensation

Winter condensation occurs when the inside surface of the window is cooler than the dew point temperature of the inside air. The dew point temperature is related to relative humidity. Condensation may occur under high relative humidity at only cool outside temperatures. As the outside temperature drops, the inside surface will also get cooler. Therefore condensation will form at lower relative humidity on cold days.

To prevent winter condensation, either warm the window surface or dry the inside air. Options to warm the window surface include 1) opening drapes, 2) blowing air across the window surface, 3) replacing the window with a more efficient window, 4) adding storm windows, or 5) raising the temperature inside the building. To reduce the relative humidity in the room, control or eliminate moisture sources. People are sensitive to low relative humidity, so in extremely cold weather, the only option to prevent condensation may be to warm the window surface.

Summer Condensation

Summer condensation occurs when the outside window surface is cooler than the dew point temperature of the outside air. In the southeast US, summer dew point temperatures range from about 65F to 75F. When temperatures inside the building are within this range, summer condensation problems can occur.

The outside glass surface in energy efficient windows will be closer to the outside air temperature, while the outside glass of an in-efficient window will be closer to the inside temperature. Low-E coatings help reduce the amount of radiant heat transfer through a window. As the summer sun warms the outside glass, a Low-E coating reduces the amount of this heat that moves inward. (The outer glass can warm significantly in the sunshine. During the winter, the inside glass is warmer because of the reduced radiant heat movement outward, and you don't get that "cold" feeling sitting next to a window.) At night during the summer, heat is radiated from the outside glass to the cold sky and other objects. The Low-E coating reduces the heat transfer from inside, so the outside glass surface can cool significantly below outside air temperatures.

In cases where the inside temperature is below the outside temperature, a Low-E coating will allow the outside glass temperature to drop to about the same as that of an inefficient window. In cases where the outside air is colder than the inside temperature, a Low-E coating allows the outside glass to get even colder. Therefore under the right conditions, windows with Low-E coatings can develop more summer condensation than inefficient windows.

Since we cannot control the outside dew point temperature (or relative humidity), the options for preventing summer window condensation problems are to warm the inside surface of the window as a way to warm the outside surface. Raising the thermostat setting is about the only option. Exterior shutters, shades or even trees can help reduce summer condensation problems as well.

In summary, condensation occurs when a surface falls below the dew point temperature of the air. The outside glass in an energy efficient window will be closer to the outside temperature, and the inside glass will be closer to the inside temperature. The glass in an inefficient window will be more heavily influenced by both inside and outside temperatures. A Low-E coating (that reduces radiant heat transfer) will tend to warm the inside surface in the winter, and the outside surface in summer sunshine. A Low-E coating will also lower the outside surface temperature at night in the summer. Therefore, a low-E coating will reduce the potential for winter condensation, while creating more potential for summer condensation situations (especially if the inside thermostat is set near or below the outside dew point temperature.)

Hope this helps. BB

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B B Garage door -
Sears Technician
November 01, 2009
A:

I think you are talking about double paned windows. If so, I have had this problem in past homes. The windows are sealed when manufactured, and a dessicant is included upon sealing, to remove residual moisture. No water can get in with this seal, therefore it doesn't mist or bead. I believe your seal has been compromised. The windows can be disassembled, cleaned, dried, and resealed. This can be dangerous, however, and the time required to have it done may be equal in cost to simply replace, particularly if the old windows don't track properly when opened or closed, or other excessive vibrations disturb the seal. Ask a local window installer to give you options, some will estimate at little or no charge.

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rjwide1 -
November 03, 2009
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Q:

How do refrigerant lines?

A:

The lines that carry the refrigerant between the evaporator and condenser coils and through the compressor and expansion device are typically copper.

The larger line typically carries a cool gas and is insulated. This is referred to as the suction line. It is also called the return line.

The smaller uninsulated line typically carries a warm liquid. It is most often called the liquid line. Refrigerant line sets sometimes come in precharged standard lengths with fittings on either end. These sets do not have to be field cut or charged.

Where the evaporator coil is higher than the condensing unit, the suction line should slope down toward the condensing unit with a slope of at least one quarter inch per foot.

Extra lines are usually coiled near the evaporator coil. The line should be coiled horizontally rather than vertically. The coils should allow oil to flow down through the coil and back to the condensing unit.



Pressures in the lines may range from 50 psi up to 275 psi. Since Freon is a gas at atmospheric temperature and pressure, leakage through the lines is not like a water leak. The Freon will dissipate as a gas. It may leave an oil residue. Freon 12 has a boiling point of around -20F at atmospheric pressure. At 55 psi, its boiling point is about 30F, and at 75 psi, the boiling point is around 40F.

In some installations, you will find a filter/dryer in the liquid line. Filter/dryers clean and dry the refrigerant. They are often added to a system where the compressor has been replaced. They help remove any contaminants. They are roughly the size and shape of a soft drink can. They may be located in the liquid line near the condenser outlet or near the expansion device.



Frost accumulation just past the filter/dryer indicates a partially plugged unit and service should be recommended.

Supports for refrigerant lines should be every 5 to 6 feet. Bends in refrigerant lines should have a minimum 12-inch radius.

A sight glass may be installed on the liquid line, usually near the condenser. This allows the service person to check refrigerant levels. If bubbling is noted in the sight glass, this indicates possible problems and service should be recommended. The sight glass is about one inch in diameter. Many sight glasses have a colored ring. If the ring color changes, this indicates moisture in the refrigerant. This is a serious condition. About one tablespoon of moisture in the refrigerant system will destroy a compressor in a few months. Sight glasses are more common on commercial systems than on home air conditioning systems.



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expert -
Sears Technician
April 26, 2007