Housing apparatus

Noise attenuating apparatus for housing, inter alia, a compressor and/or condenser unit, the apparatus comprises a substantially box-shaped outer shell and an inner shell which houses the unit. The outer shell is formed with a primary air inlet to receive air into the apparatus and a primary air outlet for discharge of spent air from the apparatus. The inner shell includes an inner chamber and is formed with a secondary air inlet to receive air supplied via the primary air inlet means into the inner chamber to supply air to the unit. The inner shell is also formed with a secondary air outlet opening for flow of spent air from the inner chamber. The space between the inner and outer shells defines a tortuous flow path for the removal of spent air from the apparatus through the primary air outlet means.

The present invention provides housing apparatus for machinery and more
 especially, but not exclusively, to apparatus for housing refrigerator
 condenser and compressor units.
 As is known, in refrigeration systems a compressor circulates a refrigerant
 from an evaporator through a condenser and expansion valve and back to the
 evaporator. A refrigerator essentially contains a compressor to move
 refrigerant (volatile liquid) around a pipe. Refrigerant leaves the
 expansion valve at low pressure causing it to evaporate inside the pipe
 within the evaporator and thereby lose heat. The refrigerant leaves the
 compressor at high pressure. As it flows through the condenser, the high
 pressure causes the vapour to condense back to liquid, giving out heat as
 it does so. Thus, heat flows into the air around the condenser.
 Combined compressor and condenser units are used to provide a cooling
 capacity for refrigerators and freezers within commercial premises for
 example supermarkets. Typically such compressor and condenser units are
 situated in a location remote from commercial premises as they are
 generally large and for this reason are space consuming. Moreover, the
 units are inherently noisy. Noise pollution has become a major social
 issue as it has been shown to be detrimental to living and working
 environments and can have an adverse effect on health.
 The noise problem associated with compressor and condenser units can be
 partially solved by housing such units in sound-proofed constructions.
 Such constructions are commonly built on the "box within a box" principle,
 whereby the inner box is completely isolated from the outer in order to
 provide a high degree of sound insulation. For example, sound-proofing
 apparatus for housing machinery typically comprise a rigid outer shell
 lined with an insulating layer such as plastic foam and an inner shape
 inserted into the outer shell to form a space between the outer and inner
 shell which is also filled with insulating material. One such
 sound-proofing apparatus is disclosed in European patent application EP
 0062166.
 In addition to apparatus which eliminates noise through sound insulation
 and/or sound absorption, there are systems which actively eliminate noise
 by generating sound waves having the same amplitude but an opposite phase
 to the waveforms of the noise thereby cancelling the noise produced. One
 such active noise control system is disclosed in European patent
 application EP0612057.
 In situations where the sound-proofing apparatus is required to house
 machinery such as compressor and condenser units, overheating within the
 internal environment of the apparatus is a problem. Overheating in the
 environment surrounding the machines is generally sensed by a thermostat
 causing operation of the machinery to cease. Once sufficient cooling has
 occurred the machines may restart; however, periods in which the machinery
 is idle can be extremely costful to business. For example, in the United
 Kingdom refrigerated food displayed in a supermarket must be maintained at
 a constant temperature not exceeding 4.degree. C. In situations where the
 temperature of the food has exceeded this limit, the food is considered
 unfit for sale for human consumption and should be removed and destroyed.
 Attempts have been made to overcome this problem of overheating by housing
 the machinery in very large ventilated units, in order to provide a large
 internal area for airflow and heat dissipation from the condenser radiator
 and compressor components. However, such housing units inefficiently
 utilise space, a feature which is disadvantageous in commercial premises
 where optimisation of the use of free space is both cost effective and
 desirable. The desirable aspect associated with reducing the size of
 housing units is because such units are, in addition to being large,
 typically heavy and unsightly. Moreover such unnecessarily large units
 will suffer from difficulties associated with the mobilisation and
 transport thereof.
 It is an object of this invention to provide apparatus for and a method of
 efficiently controlling both of the aforementioned problems of noise and
 overheating generally associated with housing machinery such as
 compressors and condensers, whilst at the same time limiting the size of
 such apparatus to a workable minimum.
 According to the present invention there is provided noise attenuating
 apparatus for housing, inter alia, a compressor and/or condenser unit, the
 apparatus comprising a substantially box-shaped outer shell and an inner
 shell which houses the unit, the outer shell being formed with a primary
 air inlet means to receive air into the apparatus and a primary air outlet
 means for discharge of spent air from the apparatus, the inner shell
 including an inner chamber and being formed with a secondary air inlet
 means to receive air supplied via the primary air inlet means into the
 inner chamber to supply air to the unit, the inner shell also being formed
 with a secondary air outlet opening for flow of spent air from the inner
 chamber; the space between the inner and outer shells defining a tortuous
 flow path for the removal of spent air from the apparatus through the
 primary air outlet means.
 The unit of the invention is typically a noise generating piece of
 apparatus or equipment such as electrical home appliances, computer
 systems or compressor and condenser units for refrigerators, freezers and
 air-conditioning equipment. In a preferred aspect of the invention the
 unit is a combined condenser/compressor.
 The apparatus of the invention may house more than one unit, for example
 two or three units. Preferably, these units will be positioned side by
 side in the inner shell such that cool air supplied by the inner chamber
 is drawn into the units and warm air is discharged for removal from the
 apparatus. In this way a continuous flow of air through the apparatus is
 maintained.
 The housing apparatus is typically a modular construction comprising at
 least two enclosures separated by an air space. Preferably the housing
 apparatus will comprise only two enclosures namely an outer and an inner
 shell.
 The outer shell of the housing apparatus is typically formed of three
 panels secured together to define a box. In order to achieve optimum sound
 insulation all joints must be secured to provide an airtight seal. The
 materials of the panels may be metallic for example stainless or
 galvanised steel. Other materials may of course be used. Preferably, the
 materials of the outer shell are reflective in order to reflect sunlight
 and maintain a cool environment in the apparatus. Moreover, it is possible
 to achieve good sound insulation using multi-layered constructions for
 example combinations of steel and plasterboard. The panels are typically
 lined on their inner surfaces with sound absorptive material such as foam
 or mineral wool, for example Open Cell Foam (Barafire) and Mineral Wool
 Slab (Rockseal). Preferably, the panel lining is a non-flammable material.
 The inner shell of the housing apparatus is typically formed from at least
 three panels secured together to provide an airtight acoustic seal.
 Preferably, the inner shell will comprise four panels including two
 longitudinal side panels, a front panel and a back panel secured to form a
 box. Preferably, the back panel is removable to allow for servicing of the
 unit whilst housed in the apparatus. The width of the inner shell will
 depend upon the dimensions of the unit(s) housed therein. The preferred
 unit of the invention will ideally be positioned in the inner shell such
 that the compressor is disposed adjacent to the inner chamber and the
 condenser is disposed in front of the compressor toward the front panel of
 the inner shell. In this preferred arrangement the width of the unit will
 be such that the outer edges of the unit contact inner surfaces of the
 inner shell thus serving to limit airflow along the sides of the unit and
 ensure optimum airflow through the unit. The materials of the inner shell
 may be sound insulating materials as described for the outer shell.
 The housing apparatus may be manufactured by inserting the inner shell into
 the outer shell and filling all or part of the space therebetween with
 loose acoustic quilting, for example, fibreglass or mineral wool to damp
 out any cavity resonances. Typically a removable lid will be mounted on
 the outer shell such that the undersurface of the lid is flush with the
 uppermost edges of the panels of the outer shell.
 The primary air inlet means of the invention is typically a tubular
 construction which may be formed in a support member for the unit.
 Moreover, the apparatus may comprise a plurality of tubular constructions
 all of which provide air to the inner chamber of the inner shell. The air
 inlet means may be provided at any location in the apparatus. In a
 preferred aspect of the invention the apparatus comprises two air inlet
 means supplying air to the upper and lower regions of the inner chamber.
 The inner chamber of the invention is supplied with air from the primary
 air inlet means. The inner chamber is typically a plenum which
 continuously draws in air from outside via the primary air inlet means.
 The invention may further include a fan located in the space between the
 inner and outer shells, preferably mounted in front of the secondary air
 outlet opening. A thermostat may be located within the inner shell to
 actuate the fan when the temperature within the apparatus rises above a
 predetermined level. Operation of the fan will promote airflow and cooling
 within the housing apparatus.
 The primary air inlet and primary air outlet means of the apparatus
 comprise openings in the outer shell which are preferably located in
 different panels of the outer shell, for example in opposite panels.
 The tortuous channel is typically U-shaped but may be sinuous or take the
 form of any other convoluted arrangement. The tortuous channel provides an
 attenuation route for eliminating low frequency noise. The degree of
 attenuation will depend upon the length of the channels. Typically, the
 channel will be at least 1000 mm in length for example between 1500 mm and
 3000 mm.
 The housing apparatus of the invention provides a method for the control of
 overheating of units as a result of such units being housed in apparatus
 to insulate the noise generated therefrom. In order to provide the
 required free flow of air necessary to prevent overheating in the
 apparatus of the invention the dimensions of the housing apparatus should
 be carefully calculated. The dimensions of the housing apparatus will
 depend upon the dimensions of the unit housed therein. In this respect the
 following empirical formulae may be employed: Assuming that the velocity
 of air within the housing apparatus is less than 6 metres per second
 (m.sup.-1) and the rate of diffusion through the apparatus, measured as
 m.sup.3 s.sup.-1, is less than the figure of 0.00144 (or an approximation
 thereof) multiplied by the width of the unit, the dimensions of the
 housing apparatus can be calculated as follows:
 Length of housing apparatus=length of unit+750 mm, where the length of the
 unit is less than 900 mm
 Width of housing apparatus=width of unit+390 mm, where the width of the
 unit is less than 900 mm
 Height of housing apparatus=height of unit+390 mm, where the height of the
 unit is less than 800 mm
 Where the length of the unit is greater than 900 mm and the width and/or
 height of the unit are greater than 800 mm, the figures of 750 mm and 390
 mm will be greater by the same difference with respect to the dimension to
 which they refer.

The housing apparatus illustrated in FIGS. 1 and 2 comprises a box-shaped
 outer shell 2, a box-shaped inner shell 3 which houses a combined
 condenser/compressor unit 4, and a base panel element 5 provided with
 pipes and/or ducts 6 which link the inner chamber of the apparatus to the
 outside for the passage of wires or cables from the unit.
 The outer shell of the apparatus has side panels 13, 14 and a front panel
 15 attached to the ends of the side panels. The joint between the panels
 13, 14 and the panel 15 of the outer shell are sealed to improve the sound
 insulating properties of the apparatus.
 The unit 4 is supported on a tubular support member 9 in which is provided
 a tunnel 8 for the passage of air from the ambient into the apparatus. An
 alternative housing apparatus provided with two air inlet tunnels 8
 orientated at the top and bottom of the outer shell respectively, is
 illustrated in FIG. 3. More than two air inlet tunnels can of course be
 provided.
 The inner shell 3 which encloses an inner chamber 20 has side panels 16,
 17, a front panel 18 and a removable back panel 19. As with the outer
 shell 2 each side panel of the inner shell is sealed to the adjoining
 panel to provide a good acoustic seal.
 The panels of the inner and outer shells are constructed from steel and the
 internal surfaces thereof are lined with sound absorptive material.
 The inner chamber 20 is enclosed by the removable back panel 19 of the
 inner shell, the side panels 16, 17 and the unit 4 and receives air from
 the air inlet tunnel 8. The unit 4 abuts the inner surfaces of the side
 panels 16, 17 to limit airflow along the sides of the unit.
 Typically, the dimensions of the unit 4 are 900 mm length .times.800 mm
 width .times.800 mm height. Therefore, the total volume of the unit is in
 the order of 0.576 m.sup.3. An air outlet opening 10 is provided in the
 front panel 18 of the inner shell 3. Mounted on the support member 9 is a
 plate fan (not shown) which in use draws air from inside the inner shell
 3, through the opening 10 and out of the unit through outlets 11 (see FIG.
 5). The fan is operatively connected to a thermostat (not shown)
 positioned inside the inner shell 3 which records the temperature of the
 air therein. When the thermostat senses that the temperature of the air
 has risen above a predetermined level, the fan will be actuated.
 The space between the inner shell 3 and outer shell 2 is fitted with loose
 acoustic quilting including mineral wool to damp out any cavity
 resonances.
 A channel is defined between the inner shell 3 and outer shell 2 and
 provides a flow path for the discharge of spent air from the apparatus. As
 will be seen from FIG. 4 the channel is U-shaped and comprises two
 longitudinal channels 26, 27 and a connecting channel 28. One of the
 channels 26 is provided by the space between the panel 13 of the outer
 shell and the panel 16 of the inner shell. The other channel 27 runs
 parallel to channel 26 and is provided by the space between the panel 14
 of the outer shell and the panel 17 of the inner shell. The connecting
 channel 28 connects the parallel channels 26 and 27 and is provided by the
 space between the front panel of the outer shell 15 and the front panel of
 the inner shell 18.
 The outlets 11 formed at the rear of the apparatus between the outer shell
 and inner shell is covered with netting to provide a barrier to the entry
 of rodents, debris and the like.
 A removable lid (not shown), mounted on the outer shell 2 provides an
 enclosure wherein the dimensions of the enclosure can be, for example,
 1650 mm length .times.1190 mm width 1190 mm height, therefore the total
 volume of the enclosure is in the order of 2.377 m.sup.3.
 Air from the outside of the apparatus is fed to the inner chamber 20 via
 the air inlet tunnel 8. Air in the inner chamber is drawn into the unit 4
 at a relatively high pressure. In this way the inner chamber 20 serves as
 a plenum to draw air into the apparatus via the air inlet 8. The flow path
 for air through the inner shell 3 is generally parallel to the flow of air
 through the air inlet tunnel 8. Warm air discharged from the unit 4 is
 drawn through the opening 10 in the inner shell 3 and into the channel 28
 provided between the inner and outer shells. At the point of entry into
 channel 28 the airflow diverges and flows between two L-shaped flow paths.
 Air flows through the parallel channels 26, 27 provided between the inner
 and outer shells and out of the apparatus via the outlets 11 provided at
 the rear of the apparatus.
 During operation the airflow through each channel can be, for example,
 0.00144 times the width of the channel.
 The degree of noise attenuation typically provided by airflow through the
 channels 26, 27 and 28 is recorded in Table 1.
 TABLE 1
 Octave Band Frequency
 (Hz) 63 125 250 500 1000 2000 4000
 Dynamic Insertion Loss 14 21 40 49 50 50 50
 (dB)
 In another embodiment of the invention, the panels of the outer shell of
 the housing apparatus are sealed to a box-shaped frame to provide added
 strength to the apparatus which is desirable where the apparatus is to be
 lifted and moved.
 In a further embodiment of the invention the housing apparatus provides a
 slideable support member for mounting the unit(s) to allow removal of the
 unit(s) from the apparatus with ease.
 It will readily be apparent that numerous modifications and alterations may
 be made to the housing apparatus shown in the accompanying drawings
 without departing from the principles underlying this invention, and all
 such modifications and alterations are intended to be embraced by this
 Application.