EP0292066A2

EP0292066A2 - A method of controlling moisture transport and check valve adapted therefore

Info

Publication number: EP0292066A2
Application number: EP88200984A
Authority: EP
Inventors: Willem Bernard Van Telgen; Gerard Jan Rückert
Original assignee: Ubbink Nederland BV
Current assignee: Ubbink Nederland BV
Priority date: 1987-05-18
Filing date: 1988-05-17
Publication date: 1988-11-23
Also published as: EP0292066A3; NL8701185A

Abstract

The invention lies in the area of controlling, for example countering, transport of moisture from the crawl space located beneath a building to the space inside that building.

The basic cause of moisture transport from the crawl space to the house is the difference in pressure between the crawl space and the house.

The invention proposes a method of the type referred to which comprises the following steps:

(1) ascertaining of the pressure side (i.e. the side on which the wind is directed) of the building, and of the suction side (i.e. the side away from the pressure side),
(2) the arranging of at least one first ventilation opening on the pressure side and at least one second ventilation opening on the suction side, which ventilation openings connect the crawl space with the surrounding air, and
(3) selecting of the (first) passage surface area of the first ventilation opening and the (second) passage surface area of the second ventilation opening such that the second passage surface area is a preselected number of times greater than the first passage surface area.

Description

The invention lies in the area of controlling, for example countering, transport of moisture from the crawl space located beneath a building to the space inside that building.
The realization has begun to grow recently that moisture problems in houses could be partly attributable to a moisture addition from the crawl space. Reference is made in this respect to articles published in the Netherlands trade journal "Bouwwereld".
The trade has reached its own conclusions and brought a great many products onto the market which have in common, certainly in view of the scale on which the problem occurs, that they are very expensive. Worth mentioning here are methods of covering the bottom of the crawl space. What is noticeable here is that attention is focused mainly on possibilities of isolating the moisture source from the house and that the displacement mechanism of the moisture out of the crawl space to the house is not taken into consideration in the solutions offered.
The basic cause of air transport from the crawl space to the house is the pressure difference between the crawl space and the house.
In "Bouwwereld" 1982 the author Schaap rightly points out that an underpressure is created in the house among other factors as a result of thermal draught. Schaap however ignores the fact that with the usual methods of ventilating a crawl space, there is created in the crawl space an overpressure which even exceeds the underpressure in the house for longer periods.
In the terrace houses that are common in the Netherlands, such as those usual in the council housing sector, there is on both sides of the houses generally an equal surface area for ventilating the crawl space.
The pressure in the crawl space can be approximated with the following formula:
wherein:
P_kr = the air pressure in the crawl space in Pa
P_s = air pressure on the pressure side
P_z = air pressure on the suction side in Pa
A_s = ventilation surface area on the pressure side in m²
A_z = ventilation surface area on the suction side in m²
Assumed here are friction-free ventilation openings. Despite this simplifying assumption the formula gives a good illustration of the pressure mechanisms at work in the crawl space.
For a house in an open area and situated at a right angle to the wind direction, the mean values for P_z and P_s can be deduced from the Netherlands norm NEM 3850:
P_z = 15.6 Pa
P_s = -6.2 Pa
Assuming similar ventilation openings on the pressure side and the suction side this would mean an overpressure in the crawl space of 4.7 Pa. Together with an underpressure in the house of circa 4 Pa as a consequence of thermal draught there occurs a resulting pressure difference between house and crawl space of around 8.7 Pa.
Schaap establishes that each cubic metre of air from the crawl space adds 4.5 g of water to the air in the house. In order to obtain an idea of the amounts of moisture which enter the house additionally from the crawl space, an estimate is made of the friction-free surface area of open connections between house and crawl space.
The quantity of air Q flowing into the house from the crawl space can be approximated with formula (2):
The above values are of course disputable because of a number of assumptions. The actual surface area of open connections could thus for example be smaller, the location with respect to the wind could be more favourable and the friction effect in the ventilation openings could have a moderating influence. A number of these factors could however on the other hand be greater than supposed and all these considerations leave essentially intact Schaap's proposition that a moisture addition from the crawl space may result which is in the order of magnitude of the moisture production of a family.
From formula (1) can be seen that the ratio of the ventilation surface areas of the pressure side and the suction side is a determining variable for the pressure in the crawl space. This implies that this pressure can be manipulated by altering this ratio. In order to have no moisture addition from the crawl space the pressure in the crawl space will then have to be lower than or equal to that in the house. By equalizing P_kr and P_w in formula (1), this formula can be defined as formula (3):
After substitution of the previously calculated values:
This means that in the given model three similar ventilation openings must be placed on the suction side and one similar ventilation opening on the pressure side. The air flow out of the crawl space to the house is then hereby reversed.
On the basis of the above analysis the invention proposes a method of the type referred to which comprises the following steps:

(1) ascertaining of the pressure side (i.e. the side on which the wind is directed) of the building, and of the suction side ( i.e. the side away from the pressure side),
(2) the arranging of at least one first ventilation opening on the pressure side and at least one second ventilation opening on the suction side, which ventilation openings connect the crawl space with the outside environment, and
(3) selecting of the first passage surface area of the first ventilation opening and the (second) passage surface area of the section ventilation opening such that the second passage surface area is a preselected number of times greater than the first passage surface area.

Calculated in the preceding as being a sufficient ratio A_s:A_z is 1:3. This is of course only applicable for the given model with the associated assumptions.
Disturbing variables herein are:
- the orientation relative to the mean wind direction.
- the accidented relief of the terrain with respect to the mean wind force.
- the shifting of the wind, which would result in a reversing of the mechanism.
The phenomenon of shifting wind which would precise ly have the effect of causing the moisture entry to the building from the crawl space to increase can be overcome by a following embodiment of the method according to the invention, in which the above specified step (1) and step (3) are replaced by:
(4) the arranging in each ventilation opening of a non-return valve which in closed position has a passage surface area that is a preselected fraction of the passage surface area in open position.
It will be apparent that the relevant non-return valves for use in the ventilation openings preferably require the lowest possible response pressure difference.
This latter embodiment of the method according to the invention can avoid the necessity for an analysis per building of the wind direction and the accidented relief of the terrain. Using this design the occurrence of undesired, reversed moisture transport can in any case be prevented.
The invention further relates to a non-return valve specially intended for use with the above stated method. This non-return valve is characterized by
a housing,
two openings, at least one of which defines a valve seat, and
a valve body present in this housing and co-acting with the valve seat, which body can move under the influence of a pressure difference between the two openings.
Very simple and effective is the embodiment in which the valve body is a plastic ball.
The ball may for instance be a very cheap and light table-tennis ball or consist of expanded polystyrene.
The valve body can also be a hinge suspended plate.
In order to ensure a certain minimum through-flow, also in circumstances where the non-return valve is in its closed position, the non-return valve can display the feature that adjacent to the valve seat opening an additional opening is present.
In an alternative, the embodiment can be chosen such that the valve body can only partially close the valve seat opening.
In order to achieve minimum wind noise through the non-return valve a variant can be characterized by a ventilation channel present between the two openings, the wall of which channel are covered with acoustic damping material.
An inexpensive embodiment is the one in which the housing consists of plastic.
In this latter case the housing may for instance be manufactured by injection moulding.
The invention will now be elucidated with reference to the drawing, in which:

Figure 1 shows a detail cross section through a cavity wall at the level of the transition between the building and the crawl space, with a crawl space ventilation duct;
Figure 2 shows a view similar to figure 1 of another embodiment;
Figure 3 is a partly broken away perspective view of a non-return valve according to the invention;
Figure 4 is a partly broken away perspective view of a variant of the non-return valve;
Figure 5 shows an insert piece for the forming of a non-return valve in a further embodiment;
Figure 6 shows a non-return valve consisting of a duct-shaped housing and the insert piece as in figure 5; and
Figure 7 shows a non-return valve consisting of a housing provided with a grid and of an insert piece as in figure 5.

Figure 1 shows a cavity wall 1 comprising an outer wall 2 and an inner wall 3, the inner wall 3 bearing a floor 4 which separates the inside area 5 of the building from the crawl space 6. The latter communicates with the outside environment 7 via a more or less Z-shaped ventilation duct 8.
Figure 2 differs from the figure 1 through the presence of a ventilation duct 9 which does not have a Z-shape, but a portion 10 protruding through the outer wall 2 and connecting thereto a sloping portion 31 in open communication with the crawl space 6.
Figure 3 shows a non-return valve 11 comprising a housing 12, of which the one side is entirely open while the other has a flat edge 13 which defines a valve seat. Co-acting with this edge 13 is a hinge suspended plate 14, which, depending on the pressure difference over non-return valve 11, can assume the closed position indicated with fully drawn lines or the open position designated with broken lines. The hinged plate 14 has an opening 15 which always ensures a certain through-flow, which is of essential importance for the system according to the invention.
The non-return valve 11 can be accommodated in the ventilation ducts 8, 9 as in the figures 1, 2. In particular the non-return valve 11 can be placed in the portion of the relevant ventilation duct protruding through outer wall 2.
Figure 4 shows a non-return valve 16 in dual and symmetrical form. This non-return valve comprises a rear wall 17 with holes 18 which define valve seats. Two plastic balls 19 can roll over ribs 20 and serve as valve body. The balls 19 can entirely close off holes 18. In addition to the holes 19 in the rear wall 17 also comprises a slotted hole 21, thereby always enabling a certain free passage through non-return valve 16, in accordance with the principle of the invention.
Figure 5 shows an insert piece 22 in a variant of the non-return valve 16 according to figure 4. This insert piece comprises a rear wall 23 with two holes 24 which can be closed off by the plastic balls 19 which are guided by the edges 25 of slot-like openings 26.
Figure 6 shows a ventilation duct 27 in which the insert piece 22 is accommodated. It will be apparent that a free passage remains available inside ventilation duct 27 on either side of insert piece 22, which will result, also in the case the balls 19 close off holes 24 completely, in a certain ventilation through duct 27 being ensured.
Figure 7 shows finally a housing 28 in which is accommodated the insert piece 22. Housing 28 is provided with a grid 29 which displays slotted holes 29 on either side through which free passage is always possible via the free space between insert piece 22 and the inner surface of housing 28.

Claims

1. Method of controlling, for example countering, transport of moisture from the crawl space located beneath a building to the space inside that building, comprising the following steps:

(1) ascertaining of the pressure side (i.e. the side on which the wind is directed) of said building, and of the suction side (i.e. the side away from the pressure side),

(2) the arranging of at least one first ventilation opening on the pressure side and at least one second ventilation opening on the suction side, which ventilation openings connect the crawl space with the outside environment, and

(3) selecting of the (first) passage surface area of the first ventilation opening and the (second) passage surface area of the section ventilation opening such that said second passage surface area is a preselected number of times greater than said first passage surface area.

2. Method as claimed in claim 1, characterized in that step (1) and step (3) are replaced by:
(4) the arranging in each ventilation opening of a non-return valve which in closed position has a passage surface area that is a preselected fraction of the passage surface area in open position.

3. Non-return valve for use with the method as claimed in claim 2, characterized by
a housing,
two openings, at least one of which defines a valve seat, and
a valve body present in this housing and co-acting with said valve seat, which body can move under the influence of a pressure difference between the two openings.

4. Non-return valve as claimed in claim 3, characterized in that the valve body is a plastic ball.

5. Non-return valve as claimed in claim 4, characterized in that the ball is a table-tennis ball.

6. Non-return valve as claimed in claim 4, characterized in that the ball consists of expanded polystyrene.

7. Non-return valve as claimed in claim 3, characterized in that the valve body is a hinge suspended plate.

8. Non-return valve as claimed in claim 3, characterized in that adjacent to the valve seat opening an additional opening is present.

9. Non-return valve as claimed in claim 3, characterized in that the valve body can only partially close the valve seat opening.

10. Non-return valve as claimed in claim 3, characterized by a ventilation channel present between the two openings, the walls of which channel are covered with acoustic damping material.

11. Non-return valve as claimed in claim 3, characterized in that the housing consists of plastic.

12. Non-return valve as claimed in claim 11, characterized in that the housing is manufactured by injection moulding.