TASK 2.  RESEARCH

2.1 Moisture and IAQ Research

FSEC conducted moisture and indoor air quality research to help eliminate the most serious problems plaguing HUD Code homes in the Southeast.  To assist the industry, researchers performed diagnostic tests in problem homes, fixed the problems, and evaluated the effectiveness of the problem corrections by conducting pre and postfix short-term tests and related activities.

• Bossier City, Louisiana Experiments

In 2001, the BAIHP team conducted research on two homes to define how tight ducts and a prototype Coleman^® heat pump (proprietary technology) affect energy use and moisture control in a hot, humid climate.  FSEC, in collaboration with Fleetwood Homes, York International Manufactured Housing Division (now Stylecrest Sales), and Coleman^®, monitored two nearly identical side-by-side homes in Bossier City, Louisiana.  The homes contained different air conditioning systems.  House A used a standard split air conditioner, while House B used the Coleman® prototype unit (a more efficient, two-speed split air conditioner).

Figure 48.  Power draw over a 24-hour period,September 2, 2000.

Figure 48 (on left) shows the reduced power draw of the two-speed compressor (green, dotted line) over a 24-hour period on September 2, 2000.  With the unit operating at low-speed for most of the day, the cooling energy savings were 28% when compared to the energy use in House A.  Average daily cooling energy was reduced by about 12% over the monitored period. An added benefit of the two-speed air conditioner was 20% greater moisture removal on days with an outdoor dewpoint above 60°F.

Savings from Duct Repair and POS Ventilation:  In addition to comparing one house to the other, the BAIHP team also compared home performance before and after ductwork and ventilation system changes were made.  

To make the comparison, duct and other leaks were sealed in both houses until the two were equally airtight.  The ventilation method in each home also was changed from exhaust-only to a positive pressure system (POS).  With exhaust-only ventilation, bathroom fans removed stale air from the home which caused fresh air to be pulled in through the building envelope.  To simulate occupant use, two bath exhaust fans were operated by a timer for three hours in the morning and six hours in the evening.

In contrast to exhaust ventilation, the POS system introduced a small amount of fresh air on the return side of the air conditioning cooling coil.  A POS system was installed in each home at the same time the ducts were repaired.  Subsequent monitoring looked at the effects of this alternate ventilation system.  Tightening the ducts and installing a POS ventilation system resulted in an 18% and 37% cooling savings in the two homes. Only about 2% of these savings were attributable to the ventilation system change, the remaining savings are a result of duct repair.

• Building Science and Moisture Problems in Manufactured Housing

Figure 49 shows one-half of a manufactured home recently completed at the factory. These homes have a permanent steel chassis attached below the floor. After production, homes may travel a few hundred miles, hauled by truck, before final setup. The homes are setup by placing blocks under the steel I-beams and anchoring the beams firmly to the ground. A skirting covers the blocks and steel frame in a fully setup home.  (Please see Figure 50.)

Figure 49.  Manufactured home production.	Figure 50.  A fully setup two-section manufactured home with skirting.

Figure 51.  Pressure field and unintentional airflow created by supply duct leaks.

Manufactured homes are typically heated or cooled by a system of ductwork, which delivers hot or cold air from the air handler unit (AHU).  The ductwork can be in the attic or in the belly cavity of the home. The ducts are typically made of aluminum or fiberglass trunk lines which supply air to the floor registers through in-line boots or flex ducts.  The boots or ducts terminate at perimeter registers on the floor.  Supply duct leaks represent one of the biggest causes of moisture in manufactured homes.  (Please see Figures 51, 52, and 53.)  Poor design and construction leave holes at the AHU connection to the main trunk, and where the boots connect to the trunk, supply registers, end caps, cross-over duct connections, and other connection points.  When the AHU blows air, some air leaks into the belly and eventually to the outside through belly board tears.  This loss of air creates a negative pressure inside the house and a positive pressure in the belly.  The negative pressure pulls outside or attic air into the house through cracks and crevices which connect the inside of the house to the outside or to the attic. During northern winters, this outside air is cold and dry and its entry increases occupant discomfort and heating energy use.

During summer in the Southeastern US, the air is consistently at or above the dewpoint of 75°.  If a homeowner keeps their home thermostat set below this 75°F dewpoint, the moisture laden outside air condenses as it comes into contact with the cold inside surfaces. If it condenses behind an impermeable surface such as vinyl flooring or wallpaper, serious mold, mildew, and floor buckling problems can result.

Figure 52.  Cross section showing foundation support, crossover duct, and one type of ventilation system in a manufactured home. (Illustration credit: 1997 Northwest Energy Efficient Manufactured Home Program In-Plant Inspection Manual)

Figure 53.  Floor and belly area with supply ducts. These ducts supply conditioned air to all rooms through floor vents, a common system in manufactured homes.(Illustration credit: 1997 Northwest Energy Efficient Manufactured Home Program In-Plant Inspection Manual)