Ventilation – Having inlet airway – Pressure regulation
Reexamination Certificate
2003-04-14
2004-07-06
Boles, Derek S. (Department: 3749)
Ventilation
Having inlet airway
Pressure regulation
C454S238000
Reexamination Certificate
active
06758744
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to interior climate control systems and, more particularly, to climate control systems capable of controlling building interior air pressure that is different from the air pressure in external environment (e.g. atmosphere) and the difference can be significantly large.
BACKGROUND OF THE INVENTION
Air pressure is one of fundamental living conditions for human beings. While most of us take a comfortable air pressure (about 1 atmospheric pressure at sea level) as given during our daily lives, in certain circumstances, such as traveling to high altitude regions, people may feel the significance of the variation of surrounding air pressure or have the desire of staying in an area with air pressure much different from the external atmosphere.
In the past years, tremendous efforts have been devoted to control the interior climate within a building construction, such as temperature, humidity, freshness, and air pressure. However, compared to the control over other parameters, the achievements and applications of control over air pressure within building constructions have been quite limited.
Air pressure control, in comparison with other interior climate control mechanisms, is more difficult for the fact that pressure difference is the direct driving force for air to flow. If the internal air pressure is significantly different from external atmospheric pressure, any direct connection between the internal air and external atmosphere, no matter where it is in the building, may quickly lead air to flow from high pressure regions to low pressure regions and thus to reduce the pressure difference between the internal air and the external air.
There are two basic issues in interior air pressure control. The first is sealing the enclosed airway and the second is keeping the internal air refreshed. For the reason discussed above, without sealing the enclosed airway, air will leak through any kinds of interstices of the building, which makes it very difficult to maintain a significant pressure difference between the internal air and external environment. However, since air cannot freely flow in and out of a fully sealed construction we need to take special measures to keep the internal air refreshed.
In the past years, air pressure controls have mainly been applied in special restricted areas such as labs exposed to contaminated environment, patient rooms in hospitals that require special prevention of bacteria and other contaminants, or a manufacturing environment where cleaner air is necessary. For these special interests on special restricted areas, the prior arts of air pressure control have relied on complicated mechanical control systems to modulate the flow rates constantly in response to pressure fluctuations, which would be quite expensive to implement and maintain on a large scale and for significantly large pressure differences. Residential application of those implementations in territories like high altitude regions, where air pressure control is essentially meaningful to many people, could be too much luxury to be a common practice.
With the present invention, the application and maintenance of interior air pressure control systems in building constructions will not be much more expensive than the conventional building ventilation systems. This will make residential usage of air pressure control in need become economically practical.
According to hydrodynamic principles, during an air flow, air pressure is proportional to the square of the flow rate, which means that, as the flow driving force, the difference of pressure is not only proportional to the flow rate, but also proportional to the difference of the flow rate. This dynamic feature favors a rapid diminish of local pressure disturbance in an open air so that the air pressure will quickly reach equilibrium at a short distance from the source of disturbance.
But when air flows through porous media, the dynamic behavior of the flow is quite different from the behavior of air flowing in an open area. In his well known work in hydraulics, Henry Darcy discovered that when underground water flows through soil the hydraulic head drop (equivalent to hydraulic pressure drop) is proportional to the distance the water travels. This important law has been successfully extended to study flows through porous media in various other areas, not only for water flows but also for oil flows as well as gas and air flows.
With this Darcy's law, we realize that instead of using only the conventional construction materials, if we also use permeable porous walls for enclosing an airway, while a stable air pressure difference can be maintained across the porous walls, air can also flow in or out of the enclosed airway through the permeable porous walls. This is the main rationale behind the present invention.
SUMMARY OF THE PRESENT INVENTION
The present invention seeks to provide an interior climate control system to maintain a stable internal air pressure which is different from the air pressure in external environment (e.g. atmosphere) and the difference can be significantly large.
Different from any of the prior arts in building air pressure control, the present invention is defined by the partition of the total internal space into two separate airways by using Permeable Porous Walls. One of said airways is called peculiar airway where the air pressure is different from external environment air pressure (the difference can be significant), and the other of said airways is called normal airway where the air pressure is in equilibrium with the external environment air pressure.
Besides the connection to the normal airway through Permeable Porous Walls, the peculiar airway is connected to the external environment through at least one opening where means for driving air into or out of the airway mechanically are always installed.
In the normal airway, there is at least one free opening to the external environment so that the air pressure in the normal airway is in equilibrium with the external environment. In case that enhancement of air flow in the normal airway is desirable, besides the free openings, the normal airway could also optionally have some openings to the external environment where mechanical air driving means are installed.
Since the air pressure in a peculiar airway can be significantly different from the air pressure of external environment, in case the mechanical driving means, which is the driving force for maintaining the pressure difference, at any opening of said peculiar airway is not in function, the air may flow reversely in the opposite direction. To prevent this kind of reverse air flow, special means are installed in the air path of each said opening to the internal space of said peculiar airway to automatically block reverse air flow whenever said mechanical air driving means is not in function.
In the present invention, with a Permeable Porous Wall of known permeability and geometric sizes, the pressure difference across the porous wall can be maintained at a stable value through the self adjustment of air, and the value of the difference can be determined by the Darcy's law as follows:
P
p
−P
n
=Q·h/A·K,
where P
p
is the air pressure in the peculiar airway, P
n
is the air pressure in the normal airway, h is the thickness of the Permeable Porous Wall, A is the area of the Permeable Porous Wall, K is the permeability of the Permeable Porous Wall, and Q is the air ventilation rate.
For example, if the area of a Permeable Porous Wall is 100 ft
2
, the thickness of said Permeable Porous Wall is 0.6 ft, and the permeability of said Permeable Porous Wall is 0.1 ft
2
/sec·atm, then a 100 ft
3
/min air ventilation rate will result in 0.1 atm (which is about the pressure of 1 meter deep water head) pressure difference across said Permeable Porous Wall.
Since the air pressure in the normal airway is in equilibrium with the external environment air pressure, a constant air pressure difference across the Permeable Porous Wall between the pec
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