A mobile accommodation unit with air exchange system

TECHNICAL FIELD OF THE INVENTION The present invention relates to a mobile accommodation unit in accordance with the preamble of claim 1.

BACKGROUND AND PRIOR ART

An increasing use of mobile accommodation units such as campers, caravans and mobile homes, in terms of either year-round living or the use as semi-permanent homes, also raises the demands for living comfort under various conditions. Several functions such as resting, cooking, personal hygiene and socializing shall be accommodated within a living space the dimensions of which are restricted by the need for moving the accommodation unit in a traffics environment. The serviceability of a mobile accommodation unit is judged inter alia by the number of beds it can provide, and it is realized that the number of persons living therein has direct influence on the quality and temperature of the limited volume of air which can be housed in a caravan, a camper, or a mobile home.

Previous measures for adjusting the temperature and improving air quality in mobile accommodation units include, e.g., the use of openable roof hatches, ventilators with or without motor driven fans, or kitchen hoods with exhaust fans. Examples of motor driven ventilator fans for caravans or campers can be found in DE 2610198 A, DE 3003224 A and CN 201283760 Y.

Fan motors in mobile accommodation units are usually powered by the

accommodation unit’s own electrical accumulator/ batteiy which has a terminal voltage of 12 V, typically. This battery is charged from the electric generator of the towing vehicle or the generator of the camper during driving, or from a battery charger connected to 230 V mains power while the accommodation unit is parked. During halts with no access to 230 V mains power, the battery alone shall provide power to several functions in addition to the ventilator fans such as lighting, media units, hair dryer or shaving apparatuses, etc. This leads to a general need and desire for high power economy in electrical consumers of mobile accommodation units.

In a ventilation system based on a centrally disposed, one-way, suction or blowing fan, sub-pressure and over pressure is compensated passively by airflow through static vents and ventilator openings. In this kind of system, it can be difficult or very difficult to ensure circulation of air to all parts of the accommodation unit.

Heating the living space in a mobile accommodation unit usually involves a medium, such as water, which is heated by liquid-gas or 230 V mains power and circulated through heat convectors or through heat tubes disposed in the floor. Ventilation via roof hatches or static roof ventilators including a suction or blowing fan, if

appropriate, is controlled and regulated for maintaining a comfortable inside temperature. Without heat recovery from the exhaust air flow, which is usually the case, there is a raised risk in cold weather that ventilation is reduced such that sufficient exchange of air required for an optimum air quality is not achieved.

The shell structure of a mobile accommodation unit, substantially lacking

partitioning walls, entails a risk of noise and vibrations from fans being transmitted through the structure and amplified through the open plan architecture. This in turn raises the demand for silent running motors and fans in a mobile accommodation unit with its relatively thin walls made of synthetic material or metal plate, as compared to a villa residence for permanent living which has relatively thick and well insulated walls made of wood, stone or concrete.

The prevailing special conditions applied to a caravan or camper entails that traditional ventilation equipment intended for stationary buildings is less suitable for implementation in mobile accommodation units.

A ventilator apparatus intended for ventilation of buildings is known from EP

2 894 412 Bl . In this ventilator apparatus, as well as in other similar known ventilator apparatuses, a fan with reversible rotation is used to generate air flow in two opposite directions. In other words, the blades of the fan have an angle of attack and shape designed to operate passably in both directions of rotation, which on one hand reduces the efficiency of the fan in either flow direction and on the other hand generates a louder noise from the fan.

Such characteristics may be tolerated in a villa residence with good sound insulation and continuous supply of 230 V mains power, but would of course present drawbacks when encountered in a mobile accommodation unit which, in many cases, has a body shell that is prone to cause resonance and which is frequently used without access to external power.

SUMMARY OF THE INVENTION The overall purpose of the invention is to provide a mobile accommodation unit with a highly efficient air exchange system.

One object of the invention is to provide a mobile accommodation unit comprising an air exchange system which offers, in combination, an efficient air exchange and improvement of air quality. Another object of the invention is to provide a mobile accommodation unit

comprising a silent air exchange system.

Another object of the invention is to provide a mobile accommodation unit

comprising an air exchange system with heat recovery.

Another object of the invention is to provide a mobile accommodation unit

comprising an air exchange system ensuring a draft free and nearest possible laminar supply air flow.

One or several of the above mentioned objects is met in a mobile accommodation unit comprising a towed or motorized chassis on wheels, the chassis supporting a living space with associated systems for heating, cooking and personal hygiene, wherein the accommodation unit has an air exchange system comprising at least two sets of fan assemblies which can operate on accumulator power provided by the accommodation unit, wherein each fan assembly is individually arranged in a separate vent duct, respectively, each said vent duct extended between a supply air opening which mouths internally in the accommodation unit and an exhaust air opening which mouths on the exterior of the accommodation unit, wherein the fan assemblies are alternatingly operable to generate exhaust air flow and supply air flow simultaneously via the separate ducts.

A technical effect achieved by this solution is that circulation of air through the open architecture of a mobile accommodation unit can be adjusted and controlled through the positioning of the fan assemblies. Another favourable technical effect achieved by the solution is that the simultaneously generated air flows speed up the change of air and reduces the necessary run time and power consumption of the fan

assemblies.

In a preferred embodiment of the invention, it is provided that a first heat exchange element is arranged in a vent duct on an upstream side of the fan assembly, and a second heat exchange element is arranged on a downstream side of the fan assembly, as seen in the current direction of flow through the vent duct.

Besides the obvious advantage of reduced heating costs through heat recovery, the embodiment provides, with a view on heat transfer efficiency, a beneficial location of heat exchange elements on the pressure side of the fan assembly regardless of flow direction.

In one embodiment, flow channels through at least one of the heat exchange elements in a vent duct are formed with a length / diameter ratio larger than 5 to 1.

A technical effect achieved by this embodiment is that turbulence in the air flow can be suppressed to provide a nearest possible laminar supply air flow from the vent duct.

In one embodiment, the heat exchange elements are ceramic.

Ceramic heat exchange elements are often shaped with through channels of square or hexagonal (honeycomb) section. When building space and weight are important factors, as they are with mobile accommodation units, this embodiment provides an advantageous relationship between volume / weight and effective heat transfer area.

One embodiment of the invention provides that each one of the fan assemblies comprises a first fan and a second fan arranged in succession between heat exchange elements in a vent duct, wherein the fans are individually and alternatingly operable, and wherein one fan is specifically designed and configured to generate axial air flow in a first direction, and the other fan is specifically designed and configured to generate axial air flow in a second and opposite direction.

Several technical effects are achieved by this embodiment: i.e., the fans can be designed and optimized for displacement of the largest possible volume of air at a rotational speed that is low enough for operation at the lowest possible level of noise and substantially without vibration/cavitation in both supply and exhaust modes.

In one embodiment the first and second fans are freely rotating in one of said first or second directions of rotation. In other words, the fan which is not driven in the supply or exhaust flow is freewheeling in the air flow that is generated by the driven fan. The technical effect achieved by this embodiment is that the passive fan neither reduces the air flow, nor causes disturbing sounds, in its idling mode.

Other embodiments of the invention include, e.g.: a common control unit controlling the fan assemblies based on measured

temperature and/or based on detected presence of gas, such as CO or CO2 _, inside the accommodation unit; a temperature sensor arranged at the exhaust opening of a vent duct, the output signal of the temperature sensor being computed by the control unit for

determination of flow direction; a sensor for measuring a content of gas in the accommodation unit, wherein a measured value is computed by the control unit to form a basis for regulation of the rotational speed of the fans; one vent duct and fan assembly being installed in the foremost compartment and the other vent duct and fan assembly being installed in the aftermost compartment of the mobile accommodation unit; at least one vent duct arranged substantially in vertical orientation and its exhaust opening, mouthing on the exterior of the accommodation unit, being arranged in the roof or in the floor of the accommodation unit; the supply air opening of one vent duct being located at low level, such as near to floor level, whereas the supply air opening of the other vent duct being located at high level such as at or near roof level.

Advantageous features and technical effects of embodiments of the invention will also be discussed below along with a detailed description of the embodiments.

SHORT DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be more closely explained below with reference made to the accompanying drawings, wherein Fig. 1 shows a mobile accommodation unit, the longer side facing the viewer being removed for displaying the interior of the mobile accommodation unit in a schematic side view,

Fig. 2 is a schematic sectional view through a vent duct and fan assembly

included in the air exchange system of the mobile accommodation unit according to the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a mobile accommodation unit 1 comprising a living space defined by a roof 2, walls 3 and floor 4. In conventional way, the accommodation unit 1 can be subdivided into a bedroom 5, sanitary room 6, kitchen 7 and living room 8. The accommodation unit 1 is supported on a chassis 10 carried on wheels 9. The chassis 10 can be arranged for towing and form part of a caravan, in Fig. 1 outlined through unbroken lines. In the alternative, together with the accommodation unit 1 the chassis 10 can be motorized and form part of a camper as illustrated through a broken outline in Fig. 1. Albeit not particularly shown in drawings, the chassis and accommodation unit can also alternatively form parts of a mobile home.

The mobile accommodation unit 1 is equipped with passive ventilation in the form of at least one roof hatch 11. A kitchen ventilation 12 comprises an exhaust fan 13.

The exhaust fan 13 is driven by an electric accumulator or battery 14 which also supplies power to other electrical consumers in the accommodation unit, such as lights, radio and television sets, computers and WIFI / intranet, as well as temporarily used electrical devices such as shavers, hair dryers, electric mixers etc. A battery charger 15 is arranged for charging the battery from the generator of the towing car or camper, or by connection to 230 V mains power when possible. The battery voltage is usually 12 volts.

Radiators, tap water heaters, stove and oven are usually operated on gas, but since these functionalities are no part of the present invention there is no need for a detailed explanation herein of these parts which are well known per se.

A control centre 16 comprises the regulators and detectors which typically are required to control the operation of electrically- and gas-powered functions of a mobile accommodation unit.

In accordance with the present invention, and with reference made also to Fig. 2, the mobile accommodation unit 1 provides an active air exchange system comprising at least two sets of accumulator-operable fan assemblies which are each individually integrated in a separate vent duct 17 or 18, respectively. Each vent duct 17, 18 connects a supply air opening 19, mouthing inside the accommodation unit, with an exhaust air opening 20 mouthing on the exterior of the accommodation unit. The vent ducts can be arranged in horizontal or vertical orientations, whereby a vertically oriented vent duct 17 or 18 can be mouthing in the roof or the floor of the

accommodation unit. Preferably, the vent ducts 17 and 18 are placed apart in the length direction of the accommodation unit, in order this way to generate a throughout exchange of air, F /T, in the accommodation unit.

Air exchange F/T is generated as the fan assemblies are simultaneously operated in such way that one fan assembly generates an exhaust air flow F whilst the other fan assembly generates a supply air flow T. The fan assemblies are controlled for alternating generation of exhaust and supply air flows respectively, such that air exchange F/T through the accommodation unit changes direction in accordance with the change from exhaust flow to supply flow through the vent ducts. Formation of pockets with stagnating air in the accommodation unit 1 can this way be

counteracted. Fig. 2 shows, in an axial sectional view, a vent duct 17 or 18 having a fan assembly 21 integrated therein. The fan assembly 21 is supported on arms 22 having an aerodynamic sectional profile, the arms reaching towards the centre of the vent duct from the inner side of the vent duct. The vent duct 17, 18 is cylindrical with a circular section, and has a diameter dimension in the range of 8 to 20 cm, preferably, and a length amounting to at least 3 or 4 times the vent duct diameter. The vent duct 17, 18 is mouthing on the exterior of the accommodation unit via an opening 23 in the wall, floor or roof 24 of the accommodation unit.

The fan assembly 21 comprises two fans 25 and 26 driven by electric motors. The motors 27 and 28 can be powered from the batteiy 14 of the accommodation unit. The fans 25 and 26, here only schematically illustrated, comprises fan wings which are designed specifically to generate axial air flow in one direction only and are alternatingly driven one at a time. More exactly, the fan 25 is configured to generate exhaust air flow F and is driven only when the fan 26 is inactive, whereas the fan 26 is configured to generate supply air flow T and is driven only when the fan 25 is inactive.

Advantageously, the fan hubs 29 and 30 can be equipped with a friction clutch or centrifugal coupling by which the fans are disconnected for free rotation on the motor axes 31 or 32 respectively, when the associated motor is de-energized. This way, the fan 25 is rotating freely with the supply air flow T, and the fan 26 is rotating freely with the exhaust air flow F.

Downstream of each fan, i.e. downstream of the fan 25 with respect to the direction of the exhaust air flow F, and downstream of the fan 26 with respect to the direction of the supply air flow T, a heat exchange element 33 and 34 respectively is arranged in the vent duct 17, 18. The heat exchange element 33 or 34 spans over the entire section of the vent duct, and has a multi-channelled section. The heat exchange element 33, 34 can be realized as a cylinder-shaped ceramic body, comprising a checkered section or a honeycomb structure. The heat exchange elements 33 and 34 are effective for absorbing heat from the exhaust air flow and successively for emitting heat to the supply air flow as the flow through the vent duct changes direction. Location of a heat exchange element 34 downstream of the fan 26 in the supply air flow provides a flow control capacity as will be discussed below.

Dust- or particle filter 35 and insects net 36 may be arranged at the vent duct openings 19 and 20. Although not shown in the drawings it serves to mention that a rain cover can be arranged in front of the external opening 20.

The operation of the fan assemblies 21 is controlled based on measurement of temperature and/or based on the presence of carbon monoxide CO or carbon dioxide CO . To this purpose, sensors 37 are installed and electrically coupled to a control unit 38. These sensors may be placed at high and low levels for measuring of temperature or for detecting light or heavy gases as compared to the density of air. The control unit 38 itself can be coupled to the control centre 16 for exchange of pre set default values.

Signals received from the sensors 37 are computed by the control unit 38 and converted into operation commands for the fan assemblies 21.

The change from exhaust air flow F to supply air flow T can be based on

measurement of the temperature of the exhaust air after its passage through the heat exchange elements 33, 34. A temperature sensor 39, arranged near the exit from the vent duct at the exhaust air opening 20, measures the final temperature of the exhaust air after delivering heat to the heat exchange elements 33 and 34. The control unit 38 compares the final temperature of the exhaust air with a threshold value for the inside temperate in the accommodation unit. When the difference between the threshold temperature and the measured final temperature of the exhaust air reaches or exceeds a pre-set difference between the two values the flow direction is switched, through both vent ducts. This is the start of a new time- controlled or temperature-controlled air circulation cycle.

The length of each air circulation cycle can be varied and adapted to prevailing conditions such as the difference between actual outside air temperature and desired inside air temperature. For example, the control unit 38 can be configured to continuously adapt the length of air circulation cycles to changes in flowrate through the vent ducts. The intensity of air exchange, i.e. the flow rate through the vent ducts, can be raised to needs by controlling the rotational speed of motors 27, 28 and fans 25, 26. In this connection it is particularly provided that a detected presence of gas, such as CO or CO2, is computed by the control unit 38 and converted into a command for increasing or decreasing the rotational speed of the motors and fans, and/or for adjusting the length of the air exchange cycle.

Without limiting the invention hereto, the specification given below shall be understood as suggestion only, indicating that a suitable motor for the fan assembly 21 can have a rated power of about 2 to 4 W and a rotational speed adjustable in the range of about 1000 to 4000 rpm. The fans 25 and 26 are preferably configured to deliver, inside the speed range of the motor at normal operation, an hourly air flow in the range of 10 to 40 m ³ , with an option for reaching a maximum air flow in the order of 100 m ³ per hour in forced ventilation mode.

It further serves to underline the importance of arranging the fan assemblies and vent ducts for providing a near as possible laminar supply air flow T from the supply air openings 19. This property is particularly desirable in the comparatively compact living space of a mobile accommodation unit, since a turbulent air flow might feel like draft close to the vent duct openings. To this purpose it is provided that the fan assemblies 21 can be equipped with fan wings having a changing angle of attack or pitch from the fan hub towards the fan wing tip, this way compensating for the higher rotational speed at the periphery of the fan, and this way also avoiding shear and turbulence between adjacent layers of moving air as viewed over the sectional profile of the vent duct.

An important contribution to a draft free air flow from the supply air openings 19 is provided by the location of the heat exchange element 34 as disclosed, wherein the flow channels 40 through the heat exchange element, if given a length / diameter ratio larger than 5 to 1, can create a laminar or low-turbulent flow through the channels.

As a guide for assessment of the laminar flow capability of the heat exchange element 34, each flow channel 40 can be regarded as a tube with a hexagonal section. The Reynolds number for the flow channel 40 can be calculated using the formula Re = Q · DH/V · A, wherein Q is the flow rate (m ³ /s) through the channel, DH is the hydraulic diameter (m) of the channel, A is the sectional area (m ² ) of the channel, and v is the kinematic viscosity of air which at an air pressure of 1 bar and a temperature of 10 to 20° C amounts to about 15 x lO ¹⁶ . At Reynold numbers lower than 2000 (dimensionless) the air can be assumed to flow out of the flow channel 40 substantially free from turbulence, which effectively contributes to a supply air flow that is free from draft.

Finally, attention is drawn to the location of the vent ducts and fan assemblies in the accommodation unit. An embodiment which is particularly advantageous in respect of air circulation to all compartments of the accommodation unit is the embodiment shown in Fig. 1 , according to which the vent ducts and fan assemblies are spaced apart in the length direction of the accommodation unit. More precisely, it is preferred that one vent duct and fan assembly 18; 21 is located to the foremost compartment 8 and another vent duct and fan assembly 17; 21 is located to the aftermost compartment 5 of the mobile accommodation unit. In order to bring in motion an air volume as large as possible and simultaneously avoiding a formation of pockets of stagnating air, it may be particularly advantageous if the vent ducts are placed such that one supply air opening 19 is located at a low level, such as close to floor level, and another supply air opening 19 is located at a high level, such as at or close to the roof level.

The mobile accommodation unit and air exchange system disclosed hereinabove and in drawings solves the problem of preserving good air quality in the living space of a camper or caravan, without this being achieved at the dispense of low noise level and power economy thanks to an efficient fan assembly arrangement and design and through a distributed heat recovery. The disclosed details and features of the invention can be combined in several ways to form advantageous embodiments under the scope of independent claim 1.