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Title:
METHODS AND MEANS FOR ENERGY-EFFICIENT VENTILATION SYSTEMS FOR BUILDINGS
Document Type and Number:
WIPO Patent Application WO/2017/217915
Kind Code:
A1
Abstract:
A ventilation system for a building (1)comprising a stairwell (2);a fire cell (3) separated from said stairwell (2) by a wall (4). Said ventilation system comprises an fresh air intake (5); a stale air exhaust (6);a means for providing air flow (7) in the ventilation system;a heat exchanger (8) arranged to exchange thermal energy between fresh air coming in from the air intake and stale air going out to the exhaust;a ventilation duct (9) arranged for transferring stale air from the fire cell (3) to the stale air exhaust (6) via the heat exchanger (8);a ventilation duct (10) arranged for transferring fresh air from the fresh air intake (5) to the stairwell (2) via the heat exchanger (8);a fire proof air transfer unit (100) arranged as a conduit for transferring air between the stairwell (2) and the fire cell (3). Fire proof air transfer unit suitable for said ventilation system, and uses thereof.

Inventors:
ABRAHAMSSON, Michael (Karlsuddsvägen 36, Vaxholm, 18593, SE)
Application Number:
SE2017/050615
Publication Date:
December 21, 2017
Filing Date:
June 09, 2017
Export Citation:
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Assignee:
ABRAHAMSSONS HANTVERK- & FASTIGHETSSERVICE AB (Åsvägen 8, Upplands Väsby, 19454, SE)
International Classes:
F24F11/00; A62C2/12; A62C2/24; F24F13/14
Foreign References:
DE10033306A12001-05-03
DE19919701A12000-04-27
DE3808424A11989-09-28
DE19533502A11996-03-14
EP0824940A21998-02-25
Other References:
None
Attorney, Agent or Firm:
NOVITAS PATENT AB (P.O. Box, 10204 Stockholm, 10204, SE)
Download PDF:
Claims:
A fire proof air transfer unit (100) comprising: a. inlet terminal (101) comprising a protective vent cover (102); b. outlet terminal (103) comprising a protective vent cover (104); c. an air conduit (105) arranged to provide passage for flowing air from the inlet terminal (101) to the outlet terminal (103); characterized in that the unit (100) comprises a heat-sensitive trigger element (106) configured to trigger a fire proof air flow damper (107) to prevent air flow in case of substantially elevated temperature, arranged in the air conduit (105),

and in that the unit (100) does not comprise powered means for forcing air flow.

The air transfer unit (100) according to claim 1, wherein the unit (100) further comprises a device for preventing back flow (108) from the outlet terminal (103) to the inlet terminal (101).

The air transfer unit (100) according to any of the preceding claims, wherein the device for preventing back flow (108) from the outlet terminal (103) to the inlet terminal (101) comprises a unidirectional valve (109).

The air transfer unit (100) according to any of the preceding claims, wherein the heat-sensitive trigger element (106) is configured to trigger the air flow damper (107) at temperatures exceeding 45°C.

The air transfer unit (100) according to any of the preceding claims, wherein the conduit (105) and/or the vent covers (102, 104) is/are provided with lining (110) comprising a sound dampening material.

The air transfer unit (100) according to any of the preceding claims, wherein the unit (100) is mounted in a wall (4) between two spaces in a building (1).

The air transfer unit (100) according to any of the preceding claims, wherein the unit (100) is fire proof in the sense that it fulfils the requirements of EI60S classification according to EN13501-3 to be able to resist fire for at least 60 minutes in a test according to EN1366-2.

8. A use of an air transfer unit (100) according to any of any of the preceding claims, in a ventilation system where fresh air is provided into a fire cell (3) through a stairwell (2), wherein said unit (100) is arranged in a wall (4) between the stairwell (2) and the fire cell (3).

9. The use of an air transfer unit (100) according to claim 8, in a ventilation system according to any of claims 10-16.

10. A ventilation system for a building (1), wherein a. said building (1) comprises: i. a stairwell (2); ii. a fire cell (3) separated from said stairwell (2) by a wall (4); b. said ventilation system comprises iii. an fresh air intake (5); iv. a stale air exhaust (6); v. a means for providing air flow (7) in the ventilation system; vi. a heat exchanger (8) arranged to exchange thermal energy between fresh air coming in from the air intake and stale air going out to the exhaust; vii. a ventilation duct (9) arranged for transferring stale air from the fire cell (3) to the stale air exhaust (6) via the heat exchanger (8); viii. a ventilation duct (10) arranged for transferring fresh air from the fresh air intake (5) to the stairwell (2) via the heat exchanger (8); ix. a fire proof air transfer unit (100) arranged as a conduit for

transferring air between the stairwell (2) and the fire cell (3); c. wherein said ventilation system is configured such that during operation: x. the air pressure (p2) in the stairwell (2) is at least 1 Pa higher than ambient atmospheric pressure (pO); xi. the air pressure (pi) in the fire cell (3) is at least 1 Pa lower than

ambient atmospheric pressure (pO); xii. a fresh air flow (fl) corresponding to at least 40% of the flow of stale air withdrawn by the ventilation system from the fire cell (3) is provided to the fire cell (3) from the stairwell (2) via the air transfer unit (100).

11. The ventilation system according to claim 10, wherein the fire proof air transfer unit (100) is an air transfer unit (100) the according to any of claims 1-7.

12. The ventilation system according to any of claims 10-11, wherein the fire cell (3) is provided with a passive fresh air inlet (12) for providing flow of fresh air from the ambient outside air to the fire cell (3) without passing the heat exchanger (8).

13. The ventilation system according to any of claims 10-12, wherein the ventilation duct (10) arranged for transferring fresh air from the fresh air intake (5) to the stairwell

(2) via the heat exchanger (8) comprises individual air outlets (13) arranged at more than one floor levels of the stairwell (2) to provide flow of fresh air at said floor levels.

14. The ventilation system according to any of claims 10-13, wherein the ventilation duct (10) arranged for transferring fresh air from the fresh air intake (5) to the stairwell

(2) via the heat exchanger (8) comprises individual air outlets (13) arranged at each floor level of the stairwell (2) to provide flow of fresh air at each floor level.

15. The ventilation system according to any of claims 10-14, wherein the ventilation duct (10) arranged for transferring fresh air from fresh air intake (5) to the stairwell (2) via the heat exchanger (8) is arranged in a repurposed garbage chute.

16. The ventilation system according to any of claims 10-15, wherein the air transfer unit (100) is fire proof in the sense that it fulfils the requirements of EI60S classification according to European Standard EN13501-3 to be able to resist fire for at least 60 minutes in a test according to European Standard EN1366-2.

Description:
METHODS AND MEANS FOR ENERGY-EFFICIENT VENTILATION SYSTEMS FOR

BUILDINGS

TECHNICAL FIELD

The present invention relates to the field of energy efficient ventilation systems for buildings.

BACKGROUND TO THE INVENTION

According to current building regulations in most countries, a larger building shall be divided into different so called fire cells. A fire cell is a room or a group of connected rooms within which a fire may develop but not easily propagate to other fire cells. This means that the structures that surrounds a fire cell, such as walls, framing of joists and so on, must have a certain predetermined resistivity against fire. Examples of fire cells are residential flats, different offices, meeting halls, care departments in hospitals and so on.

To provide surrounding structures, such as walls and framing of joists and also doors with sufficient resistivity against fire is fairly straight-forward. A more common and considerable problem is to prevent fire and fire gas propagation through the ventilation system of the building. Different more or less safe and more or less expensive ways are available to prevent or render more difficult fire and fire gas propagation through the ventilation system.

A safe way is to provide fully separate ventilation systems for each fire cell, but this solution requires a large number of bulky ventilation ducts and expensive air treatment apparatuses. Said solution is thus normally only used for buildings with only a few large fire cells. More typically, the whole or parts of the ventilation system are common for different fire cells.

In many existing buildings, fresh air is provided through vents mounted at or below the windows, whereas the stale air is removed through ventilation ducts that may rely on temperature differences for air flow or may comprise a fan. This arrangement however does not allow for easy recycling of the thermal energy present in the spent air. Therefore, increasing demands for energy-efficiency of existing buildings dictates in many cases that the original design of the ventilation system needs to be replaced by another solution providing higher energy efficiency. Given the high levels of air exchange dictated by building regulations, obtaining the desired level of energy efficiency in practice dictates recycling the thermal energy present in the stale air ventilated out using a heat exchanger.

I n the case of existing buildings that are already in use, it is expensive and unpractical to install new ventilation ducts to allow heat exchange between the fresh air and the stale air. I n case of new buildings, the issue is also present, since installing separate ventilation ducts for both fresh air and stale air adds to building cost and reduces the amount of useful floor space.

Thus, an object of the present invention is the provision of improved ventilation systems for retrofitting in existing buildings as well as for installation in new buildings, means and methods for such purposes, being cost-effective in terms of installation cost, yet providing improved energy efficiency and at the same time providing fire safety that is acceptable from a regulatory perspective.

DEFINITIONS

The term passive in the context of the present disclosure indicates the absence of a powered mechanical or electronic device. In particular, it indicates the absence of a fan or similar device for induction of air flow. It indicates that the operation is entirely dependent on the pressure difference between the inlet and the outlet.

The term inlet means the end of an air conduit intended for air intake. Conversely, the term outlet means the end of an air conduit intended for the air exiting from an air conduit. BRIEF DESCRIPTION OF THE FIGURES

Figure 1: Schematic general representation of a building with a conventional ventilation system.

Figure 2: Schematic representation of a conventional ventilation system, top view of a floor with three separate apartments. Figure 3: Schematic general representation of a building with ventilation system according to the present invention.

Figure 4: Schematic representation of a ventilation system according to the present invention, top view of a floor with three separate apartments. Figure 5a : Fire proof air transfer unit for mounting in a wall (4) between a fire cell (3) and a stairwell (2). Side view.

Figure 5b: A butterfly damper in closed position, axial (front) view. Figure 5c: A butterfly damper in open position, axial (front) view. Figure 5d: A butterfly damper in open position, perspective view. Figure 5e: A butterfly damper in open position, top view. Figure 5f: A butterfly damper in open position, side view.

SUMMARY OF THE INVENTION

The present invention provides an improved ventilation system for retrofitting in existing buildings as well as for installation in new buildings, and a fire proof air transfer unit specifically adapted for use in said system. In particular, the air transfer unit of the present invention represents a solution to the conflicting requirements of the official building code in Sweden and other countries with regard to air turnover rate demands and demands concerning fire prevention/safety. The air transfer unit solves the conflicting demands thus enabling the more cost-efficient and energy-efficient ventilation system, while satisfying all aspects of the building code.

The present invention relates to the following items. The subject matter disclosed in the items below should be regarded disclosed in the same manner as if the subject matter were disclosed in patent claims.

1. A ventilation system for a building (1), wherein

a. said building (1) comprises:

i. a stairwell (2);

ii. a fire cell (3) separated from said stairwell (2) by a wall (4);

b. said ventilation system comprises

iii. an fresh air intake (5);

iv. a stale air exhaust (6);

v. a means for providing air flow (7) in the ventilation system; vi. a heat exchanger (8) arranged to exchange thermal energy between fresh air coming in from the air intake and stale air going out to the exhaust;

vii. a ventilation duct (9) arranged for transferring stale air from the fire cell (3) to the stale air exhaust (6) via the heat exchanger (8);

viii. a ventilation duct (10) arranged for transferring fresh air from the fresh air intake (5) to the stairwell (2) via the heat exchanger (8); ix. a fire proof air transfer unit (100) arranged as a conduit for

transferring air between the stairwell (2) and the fire cell (3);

c. wherein said ventilation system is configured such that during operation: x. the air pressure (p2) in the stairwell (2) is at least 1 Pa higher than ambient atmospheric pressure (pO);

xi. the air pressure (pi) in the fire cell (3) is at least 1 Pa lower than

ambient atmospheric pressure (pO);

xii. a fresh air flow (fl) corresponding to at least 40% of the flow of stale air withdrawn by the ventilation system from the fire cell (3) is provided to the fire cell (3) from the stairwell (2) via the air transfer unit (100). 2. The ventilation system according to item 1, wherein the fire proof air transfer unit

(100) is an air transfer unit (100) the according to any of items 7-12.

3. The ventilation system according to any of the preceding items, wherein the fire cell (3) is provided with a passive fresh air inlet (12) for providing flow of fresh air from the ambient outside air to the fire cell (3) without passing the heat exchanger (8). 4. The ventilation system according to any of the preceding items, wherein the

ventilation duct (10) arranged for transferring fresh air from the fresh air intake (5) to the stairwell (2) via the heat exchanger (8) comprises individual air outlets (13) arranged at more than one floor levels of the stairwell (2) to provide flow of fresh air at said floor levels.

5. The ventilation system according to any of the preceding items, wherein the

ventilation duct (10) arranged for transferring fresh air from the fresh air intake (5) to the stairwell (2) via the heat exchanger (8) comprises individual air outlets (13) arranged at each floor level of the stairwell (2) to provide flow of fresh air at each floor level.

The ventilation system according to any of the preceding items, wherein the ventilation duct (10) arranged for transferring fresh air from fresh air intake (5) to the stairwell (2) via the heat exchanger (8) is arranged in a repurposed garbage chute.

The ventilation system according to any of the preceding items, wherein the air transfer unit (100) is fire proof in the sense that it fulfils the requirements of EI60S classification according to European Standard EN13501-3 to be able to resist fire for at least 60 minutes in a test according to European Standard EN1366-2.

A fire proof air transfer unit (100) comprising: a. inlet terminal (101) comprising a protective vent cover (102); b. outlet terminal (103) comprising a protective vent cover (104); c. an air conduit (105) arranged to provide passage for flowing air from the inlet terminal (101) to the outlet terminal (103); characterized in that the unit (100) comprises a heat-sensitive trigger element (106) configured to trigger a fire proof air flow damper (107) to prevent air flow in case of substantially elevated temperature, arranged in the air conduit (105), and in that the unit (100) does not comprise powered means for forcing air flow. The air transfer unit (100) according to item 8, wherein the unit (100) further comprises a device for preventing back flow (108) from the outlet terminal (103) to the inlet terminal (101). The air transfer unit (100) according to item 9, wherein the device for preventing back flow (108) from the outlet terminal (103) to the inlet terminal (101) comprises a unidirectional valve (109). The air transfer unit (100) according to any of items 8-10, wherein the heat-sensitive trigger element (106) is configured to trigger the air flow damper (107) at temperatures exceeding 45°C. 12. The air transfer unit (100) according to any of items 8-11, wherein the conduit (105) and/or the vent covers (102, 104) is/are provided with lining (110) comprising a sound dampening material.

13. The air transfer unit (100) according to any of items 8-12, wherein the unit (100) is mounted in a wall (4) between two spaces in a building (1).

14. The air transfer unit (100) according to any of items 8-13, wherein the unit (100) is fire proof in the sense that it fulfils the requirements of EI60S classification according to EN13501-3 to be able to resist fire for at least 60 minutes in a test according to EN1366-2.

15. A use of an air transfer unit (100) according to any of items 8-14, in a ventilation system where fresh air is provided into a fire cell (3) through a stairwell (2), wherein said unit (100) is arranged in a wall (4) between the stairwell (2) and the fire cell (3).

16. The use of an air transfer unit (100) according to item 15, in a ventilation system according to any of items 1-6.

DETAILED DESCRIPTION

Ventilation system

In a first aspect, the present invention provides ventilation system for a building, wherein a. said building (1) comprises:

i. a stairwell (2);

ii. a fire cell (3) separated from said stairwell (2) by a wall (4);

b. said ventilation system comprises

iii. an fresh air intake (5);

iv. a stale air exhaust (6);

v. a means for providing air flow (7) in the ventilation system;

vi. a heat exchanger (8) arranged to exchange thermal energy between fresh air coming in from the air intake and stale air going out to the exhaust;

vii. a ventilation duct (9) arranged for transferring stale air from the fire cell (3) to the stale air exhaust (6) via the heat exchanger (8); viii. a ventilation duct (10) arranged for transferring fresh air from the fresh air intake (5) to the stairwell (2) via the heat exchanger (8); ix. a fire proof air transfer unit (100), preferably an air transfer unit according to the second aspect, arranged as a conduit for transferring air between the stairwell (2) and the fire cell (3);

c. wherein said ventilation system is configured such that during operation: x. the air pressure (p2) in the stairwell (2) at least 1 Pa higher than ambient atmospheric pressure (pO);

xi. the air pressure (pi) in the fire cell (3) is at least 1 Pa lower than ambient atmospheric pressure (pO);

xii. a fresh air flow (fl) corresponding to at least 40% of the flow of stale air withdrawn by the ventilation system from the fire cell (3) is provided to the fire cell (3) from the stairwell (2) via the air transfer unit (100). The above system allows for a significant portion of the thermal energy present in the stale air destined to the exhaust (6) to be recovered and reused for heating (or cooling) the fresh air being taken in. Energy savings of 30-40% compared to the conventional solution discussed here can be achieved without any further modifications to the building of the ventilation system. The ventilation system of the invention however allows installation of a geothermal heating with a heat pump to further heat the fresh air, whereby savings up to 80% in energy costs can be achieved.

The building (1) can be any building comprising a stairwell (2) and fire cells (3) adjacent to the stairwell (2), but in preferred cases the building (1) is a residential building and the fire cells (3) are apartments having an entrance via the stairwell (2) (See Figs 3 and 4). The fresh air intake (5) and the stale air exhaust (6) may be arranged in any conventional manner, such as at the rooftop of the building (1).

The means for providing air flow (7) in the ventilation system may be of any conventional type, such as a powered fan. The fresh air flow and the stale air flow may be powered by separate fans. The heat exchanger (8) used in the ventilation system of the invention may be of any type well known in the art to be suitable for the purpose, such as recuperator-type heat exchangers or rotary heat exchangers. Recuperator heat exchangers have an efficiency ranging in 55-90%, depending on design and have the advantage that no contact occurs between the stale air and fresh air, and so the fresh air is not prone to fouling. Rotary heat exchangers can achieve 80% efficiency and has the capability retain air humidity which otherwise can get undesirably low on cold weather conditions. On the other hand, rotary heat exchangers are more prone to fouling.

The fire cell (3) may further be provided with passive (i.e. without powered means for inducing air flow) fresh air inlets (12) for providing flow of fresh air from the ambient outside air to the fire cell (3) without passing the heat exchanger (See Fig 4). This allows for a proportion of the fresh air to enter as ambient air, creating a subjective sensation of freshness in the fire cell (3) air for the occupants. The fresh air inlets (12) further serve to modulate the under-pressure in the fire cells (3) created by the ventilation system thus increasing comfort.

The ventilation duct (9) arranged for transferring stale air from the fire cell (3) to the stale air exhaust (6) via the heat exchanger (8) may be any conventional ventilation duct. In residential spaces, the air is typically removed through outlets in bathrooms and kitchens, since most of the odours and humidity are produced in these spaces. In the Fig 2 illustrating a conventional ventilation system, the ventilation duct for transferring stale air from the fire cell (3) to the stale air exhaust (6) is designated 9b. In contrast to the ventilation system of the present invention, the ventilation duct (9b) of the conventional system does not pass through a heat exchanger.

The ventilation duct (10) arranged for transferring fresh air from the fresh air intake (5) to the stairwell (2) via the heat exchanger (8) may be any conventional ventilation duct.

Preferably, said ventilation duct (10) arranged for transferring fresh air comprises individual air outlets (13) arranged at more than one floor levels of the stairwell (2) to provide flow of fresh air at said floor levels. This allows for a more even distribution of fresh air in the stairwell (2) and counteracts the formation of thermal gradients in the stairwell (2). Most preferably, the ventilation duct (10) arranged for transferring fresh air from the fresh air intake (5) to the stairwell (2) via the heat exchanger (8) comprises individual air outlets (13) arranged at each floor level of the stairwell (2) to provide flow of fresh air at each floor level, providing an ideal solution for even distribution of fresh air (See Fig 3). The ventilation duct (10) arranged for transferring fresh air from fresh air intake (5) to the stairwell (2) via the heat exchanger (8) may be arranged in a repurposed garbage chute (See Fig 4). This allows for the system to be installed in an existing building at a minimum cost, provided that a suitable garbage chute is available.

Air transfer from stairwell to fire cell The fire proof air transfer unit (100) arranged as a conduit for transferring air between the stairwell (2) and the fire cell (3) is typically mounted in the wall (4) separating the fire cell (3) (e.g. apartment) from the adjacent stairwell (2) (See Figs 3 and 4). Preferably, the air transfer unit (100) is an air transfer unit according to the second aspect of the present invention. The air transfer unit (100) is preferably fire proof in the sense that it fulfils the requirements of EI60S classification according to European Standard EN13501-3 to be able to resist fire for at least 60 minutes in a test according to European Standard EN1366-2.

The fire proof air transfer unit (100) is essential for the ventilation system of the present invention to comply with current building regulations from fire safety perspective. As explained in more detail below, the air transfer unit (100) comprises a heat-sensitive trigger element (106) configured to trigger an air flow damper (107) to prevent air flow in case of substantially elevated temperature, arranged in the air conduit (105). In case of fire inside the fire cell (3), the damper (107) will (after being triggered by heat) prevent the spread of smoke and fire gases from the fire cell (3) to the stairwell (2). In the more unlikely scenario of fire in the stairwell (2), the damper (107) will also reduce spread of smoke and fire into the fire cells (3).

Challenges related to compliance with fire regulations have thus far been a major hurdle for cost-effective ventilation system renovations, as well as cost effective ventilation systems for new buildings. The present invention provides a solution to this long-felt need. Operational settings

The operational flows and pressures in ventilation systems are routinely adjusted by skilled operators to provide air flows satisfying regulatory demands. The adjustments are made both at the system level (fan settings and the like) and at local air terminals, and vary depending on the properties of the building and the applicable regulations.

The ventilation system of the present invention is configured such that during operation, the air pressure (p2) in the stairwell (2) is at least 1 Pa higher, preferably 3-12 Pa higher, more preferably 3-8 Pa higher, most preferably 4-6 Pa higher than the ambient atmospheric pressure (pO). The pressure (p2) can be maintained simply by experimentally adjusting the intake flow to an appropriate amount. Alternatively, an optional pressure sensor may be operatively coupled with the intake fan to provide feedback to the fan speed to maintain a set pressure.

The elevated pressure ensures that stale air from the fire cells (3) does not contaminate the fresh air in the stairwell (2). The stale air in the fire cells (3) is often contaminated by smells from e.g. lavatories, cooking or smoking, so it is important for comfort to keep the stale air from spreading within the building (1). In a traditional ventilation system, the stairwell (2) has ambient atmospheric pressure or pressure below the ambient pressure, and the spread of stale air is prevented by having yet lower pressure in the fire cells (3) (e.g. apartments). However, the arrangement may easily be disrupted by the occupants of the fire cell (3) opening a window (or similar), leading to loss of under-pressure in the fire cell (3) allowing stale air and smells to escape to other spaces such as the stairwell (2). In Figure 1, a situation is illustrated where a smoker (human figure) in one of the apartments in a building having conventional ventilation has opened a window, leading to air flows as indicated by the arrows within the same apartment. Some of the smoke contaminates the air in the stairwell. Figure 1 also illustrates the situation (in the apartment immediately above the smoker), where cooking is taking place. There is under-pressure created by a boosted ventilation during cooking illustrated by the walls bulging inwards. If the window were to be opened in the apartment, the under-pressure would be eliminated allowing smells to escape to the stairwell (2). Note that as illustrated in Fig 3, in a building equipped with the inventive ventilation system, the situation with a smoker opening an apartment window would not lead to any airflow to the stairwell, as indicated by arrows. The ventilation system is preferably configured such that during operation, the air pressure (pi) in the fire cell (3) is 5-15 Pa, more preferably 7-13 Pa, yet more preferably 8-12 Pa, most preferably 9-11 Pa below the pressure (p2) in the stairwell (2), to ensure sufficient airflow (fl) from the stairwell (2) through the air transfer unit (100) to the fire cell (3). The ventilation system is configured such that during operation, the air pressure (pi) in the fire cell (3) is at least 1 Pa, preferably at least 2 Pa, most preferably 4-6 Pa lower than ambient atmospheric (pO). This ensures that moist air from the fire cells (3) does not migrate through any gaps, cracks or holes that are unavoidably present in the outer walls, which would carry the risk of condensation within the structures during cold weather, with potential damage to the building including rotting and mold growth. The fire cell (3) pressure (pi) is preferably less than 10 Pa lower than the ambient atmospheric, as too high pressure differentials could lead to undesirable amount of air leakage.

The ventilation system is configured such that during operation, a fresh air flow (fl) corresponding to at least 40%, preferably at least 60%, more preferably at least 70%, most preferably 75-85% of the flow of stale air withdrawn by the ventilation system from the fire cell (3) is provided to the fire cell (3) from the stairwell (2) via the air transfer unit (100). The higher the proportion of air provided by through the air transfer unit (100), the higher the thermal efficiency. However, in practice at least 15% of the air provided should enter through other channels, such as windows, air inlets (13) and the like to create a sensation of freshness in the air thus increasing comfort.

Air transfer unit

In a second aspect of the present invention, there is provided a fire proof air transfer unit (100) comprising (see Fig 5a): a. inlet terminal (101) comprising a protective vent cover (102); b. outlet terminal (103) comprising a protective vent cover (104); c. an air conduit (105) arranged to provide passage for flowing air from the inlet terminal (101) to the outlet terminal (103); characterized in that the unit (100) comprises a heat-sensitive trigger element (106) configured to trigger a fire proof air flow damper (107) to prevent air flow in case of substantially elevated temperature, arranged in the air conduit (105), and in that the unit (100) does not comprise powered means for forcing air flow (such as a fan).

The inlet and outlet terminals (101,103) may be of any conventional design for air transfer units (100).

The conduit (105) may be of any conventional design for ventilation conduits of a size suitable for the application. The length of the conduit is dictated by the thickness of the wall (4) into which the unit is intended to be mounted, preferably 15-50 cm. The conduit (105) may have any shape as long it allows sufficient air flow in the conduit, but is preferably circular having diameter of 10-30 cm or rectangular with a cross-sectional area of 100-400 cm 2 .

By substantially elevated temperature in this context is meant a temperature indicative of a fire, i.e. exceeding 45°C, preferably 50-80°C, most preferably 50-60°C.

The heat sensitive trigger element (106) may be implemented in many ways already known in the art. A preferred implementation is a bimetallic clip (120) that changes shape when the temperature exceeds the designated set-point. The bimetallic clip (120) is set up to hold a pair of fireproof butterfly dampers (121) at an open position. The butterfly dampers (121) are configured to block the airflow once the dampers (121) are released by the shape change in the bimetallic clip brought about by increased temperature. A preferred implementation is a butterfly-configuration illustrated in Figs 5b-5e. The dual butterfly wings of the damper (121) are movably attached to a frame (122) by a hinge mechanism (not shown) comprising a spring (not shown) capable of powering movement of the dual butterfly wings (121) from the open position (Fig 5c, 5d, 5e, 5f) to the closed position (Fig 5c), once the bimetallic clip (120) is released.

The damper (107) is fire proof in the sense that it fulfils the regulatory demands for installation in a ventilation duct between fire cells. The specific manner of determining fire proof ratings varies between jurisdictions and in different applications. It is preferred that the damper fulfils the requirements of EI60S classification according to European Standard EN13501-3 to be able to resist fire for at least 60 minutes in a test according to European Standard EN1366-2. Such components are readily commercially available.

An exemplary suitable damper is ABC-SC60 by ABC Ventilationsprodukter AB, Sweden. Another example is a device designated FDE produced by Halton. Yet another suitable damper is SC+60 from Rf Technologies NV. This type of damper is advantageous in that it works well even in applications where the air pressure differential is low, which is generally the case with a ventilation system of the first aspect. It also requires little to no

maintenance.

The unit (100) may further comprise a device for preventing back flow (108) from the outlet terminal (103) to the inlet terminal (101). As shown in Fig 5a, the device for preventing back flow (108) from the outlet terminal (103) to the inlet terminal (101) may comprise a unidirectional valve (109). In Fig 5a, the device (108) comprises a hinged flap that, in absence of air flow or in case of air flow from the outlet (103) to the inlet (101), tends to return to closed position as illustrated by the thatched arrow by force of gravity. Devices for preventing back flow in a ventilation system are well known and found on the market.

The device for preventing back flow (108) has the added advantage that spread of stale air from the fire cells (3) to the stairwell (2) is prevented in case of ventilation failure, e.g. fan failure or power outage.

The heat-sensitive trigger element (105) may be configured to trigger the air flow damper (107) at temperatures exceeding 45°C, preferably 50°C, more preferably 52°C.

Preferably, the conduit (105) and/or the terminal (101,103) is/are provided with lining (110) comprising a sound dampening material. This will reduce the level of noise travelling between the fire cells and the stairwell. In certain circumstances there are regulatory demands on soundproofing, and in such cases the sound dampening material may be mandatory. The dampening material may be any material commonly used for such purposes, such as rubber or foamed plastics.

The air transfer unit (100) may be mounted in a wall (4) between two spaces in a building, preferably a wall (4) between a fire cell (3) and a stairwell (2). Uses of air transfer unit

In a third aspect, there is provided a use of an air transfer unit (100) according to the second aspect, in a ventilation system where fresh air is provided into a fire cell (3) through a stairwell (2), wherein said unit (100) is arranged in a wall (4) between the stairwell (2) and the fire cell (3). The ventilation system may be according to the first aspect.

General aspects relevant to present disclosure

The term "comprising" is to be interpreted as including, but not being limited to. All references are hereby incorporated by reference. The arrangement of the present disclosure into sections with headings and subheadings is merely to improve legibility and is not to be interpreted limiting in any way, in particular, the division does not in any way preclude or limit combining features under different headings and subheadings with each other.