DOUGLAS E. SMITH
        Smith Custom Builders

  Remodeling your home is the perfect time to uprade your existing heating, ventilation and air-conditioning (HVAC) system with new products.
  HVAC is on everyone's mind these days, and is a very hot topic when dIscussing "humidity removal."
  What is the main function of the AC system? It is not just to keep you cool in summer and warm in winter, it is to remove the unwanted moisture in your home during cooling season.
  A way to explain how this works is to think of what happens when a cold front moves into the area. The cool dry air clashes with the warm moist air, condensing the moisture, causing rain.
  The slower the front is moving, the longer it usually rains.
  The larger the temperature differences between the cold front and the warm air, the harder it rains literally wringing the moisture out of the air.
  This same principal works with your AC system; the evaporator coil is approximately 45° to 50° F. When the 76° to 80° air in the home is drawn across the cold coil, it rains in the drain pan and a drain line carries the water out. This is how the humidity is removed from your home.
  When humidity levels are high, like the conditions covering the Gulf Coast region, (more than 60 grains of moisture per pound of dry air) you should run 300 to 350 cubic feet of air per minute of air across the evaporator coil (blower speed) .
  This volume of air across the evaporator coil should give you a "Delta T ," or split, air temperature across the coil of between 18° to 20°, providing the ductwork system has been properly sized to ACCA's manual "D". Check with your AC contractor.
  Given this fact, it is easy to lower the fan speed in small increments to allow the air to stay in contact with the coil surface longer, resulting in more rain (humidity removal) .
 

  There are different types of germicidal lights available on the market today, one of the best that I have seen, can be looked up at www.steril-aire-usa. com. 
  The next upgrade that should be made to your HVAC system is "Fresh Air Make-up" from outside air. These systems are called recovery ventilators.
  This addition to your system does many things, first it will positively pressurize your home, and most homes have a negative pressure, which can be seen by dirt and dust entering the home through baseboards, light switches, plugs, and other openings in the building envelope.
  The big problem is the operation of the kitchen vent hood, bath fans and dryer vent. Every time these fans come on, they remove air from the home, which must be replaced. This removal of air causes outside air to enter the home any way it can, like through the chimney. In the wintertime this can be very dangerous, pulling back into the home carbon monoxide.
  These systems help remove the stagnant air from your home. This type of system will soon be mandatory as per IRC (International Residential Code).
  Another change can be the number and location of return airs throughout the home. A good rule of thumb is one return air per 500 square feet of living space.
  This can be done by the use of a large pleated-type fIlter at the furnace location. Then attached to this filter is a return plenum box allowing all the return pipes to come together as one.
  The goal is to accomplish complete air changes throughout the home. This application of extra returns will add to the overall comfort and help to maintain consistent humidity levels and tem- perature throughout the home.
  Code changes for 2003 include all R-8 ductwork This should be used to reduce the heat gain through the duct liner. In most homes we run the return air ductwork under the blown in R-38 insulation to help efficiency.
  

  One important fact that you must never forget when the fan speed is lowered, design perimeters change, meaning liquid refrigerant (freon) may not all boil off in the evaporator coil and can run the risk of flood back to the compressor. This can result in compressor damage.
  To prevent this from happening, one must install the proper type of expansion valve, which will react quickly and slow down the flow of refrigerant. The use of an expansion valve increases the dehumidification capacity by allowing the full capacity of the coil to be utilized
  Next, we must know what the humidity levels are in our homes. You can buy a digital hygrometer and hang it next to your thermostat. This hygrometer can be purchased through your air-conditioning company, or over the Web at www.inspectortools.com.
  The ideal humidity for the home is between 30 to 50 percent, if possible. Remember the key to "mold control" is moisture control. Mold thrives over 55- to 60- percent humidity.
  Once you know the humidity in the home, you can have the design perimeters changed to achieve proper humidity levels.
  There are new types of equipment on the market today to help with the high humidity levels in the home. Most will adjust the blower speeds to slow the air down over the surface of the evaporator coil.
  The longer the air is in contact with the surface of the evaporator coil, the more moisture that can be removed. Most companies are using humidistats which control blower speeds.
  Also, the use of the "Germicidal Lights" (Ultraviolet) in the supply plenum can help to sterilize most types of mold in the HVAC system.