Ventilation system for reducing the humidity in an attic or roof cavity space

A roof cavity venting system which draws in outside air, mixes it with inside air in the roof cavity to heat the cold outside air and dehumidify the inside air, and expels the mixture into the home living quarters. The system includes exterior and interior ventilation units, a power-driven fan unit mounted in the ceiling between the living quarters and the roof cavity, and a heating element for heating the air which is drawn through the fan unit.

BACKGROUND OF THE INVENTION 
In the maintenance of energy efficient tightly constructed manufactured 
housing a large problem is presented during the cold winter months by the 
accumulation of living area humidity and excessive moisture, in the roof 
cavity above. This problem is caused by the accumulation of warm humid air 
in the living area some of which permeates and accumulates within the roof 
cavity. Moisture condensation and excessive humidity within the roof 
cavity reduces the efficiency of ceiling insulation which in time mats and 
compresses the insulation rendering the insulation ineffective. If cavity 
moisture buildup becomes too great, the ceiling below will sag and become 
water laden and water spotted and the exterior walls of the living areas 
will become wet and warped. Prior solutions to this problem include 
attempting to seal the roof cavity, but this is neither desirable nor 
practically possible due to migration of heat and moisture from the living 
quarters into the attic. Another prior solution has been to vent the attic 
only. This removes some moisture from the attic but does not affect the 
quality of the air in the living quarters. Also, with this system warm air 
is continuously removed from the attic during winter months to create a 
greater temperature gradient between the roof cavity and living quarters 
ceiling thereby increasing living area heating costs. 
SUMMARY OF THE INVENTION 
This invention relates to an attic or roof cavity venting system which 
draws air into the attic space of a modular home from the outside, mixes 
it in the attic with inside living quarters air, heats the mixture, and 
expels the mixture into the living quarters. 
The venting system preferably includes two passive gable ventilation units 
between the outside air and the roof cavity space which open and close in 
response to roof cavity temperature and a plurality of ceiling shutters 
which adjust to control the amount of air passing from the living quarters 
into the roof cavity space. The venting system also includes a 
power-driven fan unit which is mounted in the ceiling in communication 
between the living quarters and the roof cavity and which has a heating 
element for heating the air as it is drawn through the unit. The fan unit 
is normally idle and is activated for a limited period of time in response 
to the humidity level in the roof cavity. Upon activation of the fan unit, 
outside air is drawn into the roof cavity through the passive vents and 
mixed with air from the living quarters drawn into the roof cavity through 
the ceiling shutters. The mixed air is heated to temper the air as it is 
blown into the living quarters. In this manner, the humidity in the roof 
cavity space and living area is reduced and the quality of living area air 
improved. When it is not desirable to operate the fan unit, such as during 
the seasons when the relative humidity of the outside air is high, the fan 
unit may be rendered inoperative for any length of time by a manual 
override switch. Ventilation of the roof cavity space then occurs through 
the gable passive ventilation units. 
Accordingly, it is an object of this invention to provide a novel and 
useful ventilation system for the roof cavity spaces of manufactured and 
modular dwellings such as mobile homes. 
Another object of this invention is to provide a ventilation system which 
improves tne quality of air in the dwelling. 
Another object of this invention is to provide a ventilation system which 
prevents the accumulation of moisture in a roof cavity space. 
Yet another object of this invention is to provide a ventilation system 
which draws outside relatively dry air into the roof cavity space mixes it 
with air from the living area and heats the mixture to temper the air as 
it is blown into the living area. 
Other objects of this invention will become apparent upon a reading of the 
following description.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment illustrated is not intended to be exhaustive or to 
limit the invention to the precise form disclosed. It is chosen and 
described in order to explain the principles of the invention and its 
applicaton and practical use to thereby enable others skilled in the art 
to utilize the invention. 
While the ventilation system of this invention is intended primarily for 
use with modular and mobile homes having generally small roof cavity 
spaces for removing the humidity from the space between the roof 11 and 
ceiling 24 of such a home 12, it may be adapted to use in other types of 
housing having a roof cavity or attic area. The ventilation system shown 
preferably includes a pair of temperature responsive gable vents 14 placed 
in the roof cavity wall 16 to allow communication between the cavity air 
and the outside air. Each temperature responsive vent 14 has a mechanism 
for opening and partially closing the vent in response to ambient 
temperature and may be of the type more fully described in U.S. Pat. No. 
3,528,606. Temperature responsive vents 14 are adjustable and constructed 
to be in a partially open, such as 10-15 percent position, when the 
ambient temperature falls to 40.degree. F. or below, and in a fully opened 
position when the ambient temperature is 70.degree. F. or higher. 
Several ceiling vent registers or shutters 18 are placed in home ceiling 24 
between the living quarters 20 and roof cavity 10 of the home. Each 
ceiling shutter 18 includes adjustable sized openings so as to render the 
ceiling shutter infinitely adjustable between a fully opened and a fully 
closed position. Ceiling registers 18 have been used in conjunction with 
temperature responsive vents 14, to provide cooling of the home and a 
passive system for reducing the humidity in the home roof cavity. 
The ventilation system of this invention also includes a fan unit 22 placed 
in home ceiling 24 with air communication between the unit and shutters 18 
and vents 14. Fan unit 22 includes a cylindrical housing 26 which extends 
above the attic insulation 15. A grill 28 spans the opening at the end of 
housing 26 which extends into living quarters 20. An electric motor driven 
fan 30 is mounted within housing 26. The motor 32 for fan 30 is activated 
in response to a humidistat control 34 electrically connected to the 
motor. Humidistat 34 preferably activates fan motor 32 when the humidity 
level in attic 10 reaches 65% relative humidity, and deactivates the fan 
motor when the humidity level is lowered to 61% relative humidity. Fan 
unit 22 also includes a heating element 36 which is located above fan 30 
and which is similarly activated by humidistat control 34 to heat and 
temper the air which is drawn by the fan and expelled through housing 26 
into the home living quarters 20. 
In the use of the vent system of ths invention, heat and moisture from 
living quarters 20 rises upwardly through ceiling 24 by conduction and 
through ceiling shutters 18 by convection increasing the moisture level in 
the cooler temperatures found in roof cavity 10. As such moisture 
accumulates, the humidity level rises until humidistat control 34 
activates fan motor 32 and heating element 36. Fan 30 draws drier air from 
the outside into roof cavity 10 through temperature responsive vents 14. 
Fan 30 also simultaneously draws warm air from living quarters 20 into 
roof cavity 10 upwardly through ceiling shutters 18. The mixture of air 
drawn into roof cavity 10 is preferably 80% outside air and about 20% air 
from living quarters 20. As the dry outside air is mixed with the air 
already within roof cavity 10 and the warm air from living quarters 20, 
the relative humidity of the air mixture in the roof cavity is lowered to 
reduce condensation. This air mixture is drawn through cylindrical housing 
26 by fan 30, heated by heating element 36, and expelled into the home 
living quarters 20. In this manner the humidity level in living quarters 
and roof cavity 10 is lowered and the air within living quarters 20 is 
freshened with outside air and recirculated throughout the home 12. This 
has beneficial effects upon the health of the occupants of home 12 and may 
supplement the overall home furnace use since the air from the outside is 
heated before being blown into living quarters 20. 
It should be recognized that the venting system will not be operable to 
reduce the humidity level in roof cavity 10 during warm humid weather as 
the outside air would not greatly reduce the humidity level of air 
existing within the roof cavity. For this purpose a switch 38, shown in 
FIG. 5, is provided which has a summer (open) and winter (closed) 
position. The winter or closed position of switch 38 activates the 
humidistat control 34 and the summer or open position deactivates the 
humidistat control. A manual override switch 40 is also provided as 
illustrated in FIG. 5, so that an occupant of home 12 may selectively 
activate fan unit 22 when desired. Such selective activation of fan unit 
22 may be needed to circulate air throughout home 12, or to rid living 
quarters 20 of undesirable odors, fumes, or other annoying substances. 
Although not shown, a second manual switch could be used in conjunction 
with switch 40 to deactivate heating element 36 when summer venting may be 
desired. Switches 38 and 40 are conveniently located within the home 
living quarters. 
It should be understood that the invention is not limited to the terms of 
the above description but may be modified within the scope of the appended 
claims.