This invention relates to ventilation systems which provide energy-efficient ventilation for buildings having an internal temperature maintained at a temperature higher than ambient.

In order that a healthy environment may be maintained in buildings where people live and work, adequate ventil¬ ation must be provided. In colder weather heat is lost by the extraction of warm, stale air from buildings and heating of the fresh replacement air is expensive, rep¬ resenting a significant part of the total energy budget of developed countries. Moreover, the high energy consump¬ tion of such countries is a direct cause of environmental damage.

It is an aim of the present invention to reduce the energy consumption incurred by ventilating a building, and thus not only to reduce the cost of operating a ventil¬ ation system, but also to contribute to conservation of the environment. According to the present invention there is provided a ventilation system for recovering heat from stale air extracted from a building having an internal temperature maintained at higher than ambient, the system comprising first air moving means for extracting stale air from the building, second air moving means for intro¬ ducing fresh air into the building, and a heat-exchanger arranged to transfer heat from the extracted stale air to the cooler incoming fresh air.

Preferably the air moving means are constituted by positive displacement bellows arranged to provide a steady air flow, and the heat-exchanger by a counterflow, high pressure drop heat-exchanger.

Preferably again, the air moving means are located between the heat-exchanger and its connections to the interior to be ventilated, such that the enthalpy rise in the air moving means increases the temperature gradient across the heat-exchanger and increases the rate of heat- exchange between the two air flows.

Provision may be made for the removal of condensate from the heat-exchanger via a 'water trap* drain located on the extraction side of the heat-exchanger. If the, or each, drain comprises a water-filled ϋ-tube, the dif¬ ference in pressure of the extraction flow over atmospheric pressure will be compensated by the differential head in the water columns.

The ventilation system according to the present invention thus affords an energy-efficient system which is both silent and compact.

Some embodiments of the invention will now be des¬ cribed, by way of example, with reference to the accompany¬ ing drawings in which

Figure 1 is a side elevation, partly in section, of a ventilation system according to the invention;

Figure 2 is a section on the line II-II of Fig.

1;

Figure 3 is a detail end elevation of part of a bellows plate shown in Fig. 1;

Figure 4 is an elevation, partly in section, of a combined bellows device, which may be substituted for the separate bellows devices of the system of Figs. 1 to 3;

Figure 5 is a section on the line V-V of Fig. 4; and

Figure 6 is a diagrammatic developed perspective view of the cam channel shown in Fig. 4.

As shown in Fig. 1 a heat-exchange ventilation system 10 for use in a room of a house, an office or factory comprises a stale air interior exhaust duct 12, an exhaust air bellows device 14, an exhaust connection duct 16, heat exchanger 18, external exhaust duct 20, fresh air intake duct 22, fresh air connection duct 24, intake bellows device 26 and internal fresh air output duct 28.

The exhaust air bellows device 14 will now be des¬ cribed as typical of both the exhaust and intake devices 14 and 26, and comprises a casing 30 connected to the ducts 12,16 and housing an electric motor 32 arranged to drive, through a worm gear, a camshaft 34 on which is mounted a cam plate 36 having a profiled periphery. Spring-loaded cam-following rollers 38 are each mounted on the distal end of a stem 40 which is loosely held in a guide arm 42 and pivotally-connected at its proximal end to an angle arm 44, pivotally mounted on the floor of the casing 30 and having at its free end a flange 44a to which is secured a perforated bellows plate 46 and, on the left hand side as seen in Fig. 1, a perforated overlying flexible elastomer sheet 48. As shown in Fig. 3 circular perforations 46a in the plate 46 are out of register with circular perfor¬ ations 48a in the sheet 48, thus constituting a one-way valve. The angle arm 44 is connected by bellows 52 to the free end of a second, similar bellows plate 54 mounted on the roof of the casing 30, the free end of the second plate 54 being connected by further bellows 56 to the end wall of the casing 30. The bellows arrangement at the roof of the casing 30 is generally similar except that the fixed end of the bellows 52 is secured to a flange 58.

As the cam wheel 36 is rotated by operation of the motor 32 the upper roller 38 and stem 40 are raised, pivoting the angle arm 44 such that the bellows plate 54

is moved towards the chain-dot limit position and pressing the sheet 48 against its left-hand surface. Air between the plates 46 and 54 thus tends to the compressed, developing a pressure differential across the plate 46 which causes the membrane 48 to separate from the left hand surface of the plate 46 and air to pass through the plate via aper¬ tures 46a, 48a into the exhaust connection duct 16. Simul¬ taneously, the plate 46 is of course being moved towards its chain-dot limit position. By appropriate profiling of the cam wheels 32 a steady flow of air through the bellows device 14 can be achieved.

The exhaust bellows device 26 is of generally similar construction and operates in a similar way, but the elastomer sheets 48 do, of course, lie on the other (right hand side as seen in Fig. 1) of the bellows plates 46,54.

The heat-exchanger 18 comprises an insulated, elong¬ ate oblong section casing 60 having three lower exhaust flow ducts 62,64,66, each constituted by a series of tri¬ angular section channels formed by a floor 68 and a pleated heat transfer web 70, which forms the lower boundary of three similar upper incoming flow ducts 72,74,76 each having a cover 80. At each end the casing 60 has respective end chambers 82,84 for reversing the flow along the ducts such that the flows each pass along the heat exchanger 18 three times. Exhaust flow thus passes from duct 16, through end chamber 82, exhaust flow duct 62 and into end chamber 84, there to be reversed along duct 64. On reaching end chamber 82 the exhaust flow is again reversed to pass along duct 66 and into the exhaust duct 20.

U-shaped condensate drains 86,88 are provided through the floor of each end chamber 82,84, each drain being connec¬ ted to an inclined pipe 90. The head of water trapped in the drain 88 is smaller than that in the drain 86, re¬ flecting the pressure drop through the heat-exchanger 18.

By the use of the above-described ventilation system 10 a steady flow of warm, stale air is quietly exhausted from the interior of a building and is caused to give up its heat efficiently to a matching incoming flow of cooler, fresh air.

As shown in Fig. 4 an exhaust bellows device 100 and an intake bellows device 102 are each housed within a coaxial casing 104 separated by an oblique plate 106. An exhaust air inlet port 108 and a fresh air inlet port 110 are formed through the casing 104 adjacent to, and on opposite sides of, the dividing plate 106: an exhaust air outlet port 112 and a fresh air outlet 114 are formed through respective end plates 116 otherwise closing the ends of the casing 104.

An axial shaft 118 is supported by the end plates 116 and centrally by the dividing plate 106, the shaft being arranged to be driven through a worm 120 and gear 122 by an electric motor 124.

Solid with the shaft 118 is a face cam comprising a drum 126 supported on spokes 128 (see Fig. 5) and having a cam channel 130 cut into its outer surfaces. Freely mounted on the shaft 118 are two piston-type assemblies 131,132 each comprising a crown 133 and an integral skirt 134, which is connected to the casing 104 by a rolling membrane bellows 136. Each crown 133 is formed with per¬ forations 138 (see Fig. 5) and covered with an elastomeric membrane 140 having non-aligned perforations (not shown) . Extending inwardly from the skirt 134 of bellows assembly 131 is a pair of diametrically-opposed arms 146, each carrying a cam rider 148; and, from the skirt 134 of bellows assembly 132, a pair of arms 142 disposed in an axial plane perpendicular thereto and each carrying a cam rider 144.

The intake bellows device 102 is similarly construc¬ ted but the membranes 140 are, of course, secured over the opposite, right hand faces of the crowns 133.

As shown in Fig. 6 the cam channel 130 follows a path that causes each pair of cam riders 144,148 to perform the same axial movements, the movements of the pairs of cam riders 142,146 being 90° out of phase. The associated bellows assemblies 131,132 thus perform two reciprocations for each revolution of the drum 126. It will be noted that the cam channel 130 does not follow a curved path regularly alternating each side of a central circumferential datum line (not shown) on the drum, but rather a path having two relatively long straight sections (shown occupied by the cam riders 144) connected by two short sections more acutely angled to the datum line (shown occupied by the riders 148) . The undulating cam faces constituted by the side walls of the channel 130 thus cause each bellows assembly 131,132 to perform slow pumping strokes in the left-hand direction of Fig. 4, alternating with quick return strokes. One bellows element 131,132 is thus always starting its pumping stroke before the other finished, thus ensuring a steady flow of air from the inlet port 108 to the exhaust port 112.

Besides affording the advantages of the ventilation system 10, the above-described system 100 affords the further advantages of requiring only a single power source (which is cooled by air flowing through the chamber) and providing excellent mechanical balance in both the axial and radial directions, thus reducing vibration and wear.