Air conditioning unit

Abstract

An acoustic enclosure comprising three parallel ducts. The enclosure has an air inlet formed in a first side wall leading to an opening duct. Part of a second side wall, which opposes the first side w

Description

The present invention relates to an air conditioning unit. More especially the invention relates to an improved air conditioning and refrigeration unit with sound cancelling and attenuation. Background Information Typically, air conditioning and refrigeration condensing units use fan technology to provide cooling air and in conjunction with internal operational compressors create noise emissions which can if untreated can be problematic acoustically. This can result in environmental noise as many of these units are located close to residential and noise sensitive uses. Manufacturers of this type of equipment have been challenged to achieve low noise emission levels but find improving internal operating mechanism technology often inadequate to meet stringent environmental noise level demands. Technically, despite advances in machine and cooling fan technology making interactions in such machines more efficient fan blade air movement and compressor noise remain. Such noise can be exhibited as low frequency noise i.e. 63 to 250 Hz (tonal noise) or as a general noise emission. Traditionally as these are generally small units, solutions have been limited in their ability to control such noise and often result in large acoustic options and designs in comparison to the unit size. Notwithstanding the noise control limitations such design often cause visual non-compliance with planning requirements. In addition to the noise control aspect, ensuring adequate air flow to the condenser face if the air conditioning unit, refrigeration units or power compressor is essential and cannot be compromised. This is often a bigger challenge to engineers than noise control. There are many theories relating to the effect of turning air in relatively low velocity systems. It was accepted that air travels in straight lines unless acted upon by another force. When a change in direction i.e. a 90° (radius) bend is approached one such theory was that the air tended to continue moving in a straight line until sufficient quantity had moved over the outer wall to generate the necessary pressure gradient to force the air around the respective turning point / position. This often leads to high velocities at the bend itself and as a result aerodynamic losses, air and noise pressure increases occur. The movement of air for cooling and ventilation via this method has a tendency to create vortex eddies which are localised turbulent flow patterns. These high pressure zones are not helpful to the smooth flow of air. Use of plain mitred 90° bends with turning vanes do provide a smoother transition for air flow but could creates elevated high frequency noise issues in return. Prior Art Prior to acoustic attenuation was difficult and large by comparison to the unit being treated. The prior art introduced a new compact approach to providing limited acoustic controls to smaller air conditioning units, and refrigeration units, whilst maintaining air ventilation properties. This improvement allows higher levels of sound control and air ventilation protection improving on the prior art. Prior to this innovation the issue of providing high levels of sound attenuation in conjunction with maintaining adequate cooling air movement in a small enclosure the was not considered viable. The existing models provide for long air way runs which endeavour to minimise air flow resistance. The Invention The challenge has always been to balance the input of cooling air to this type of equipment in a compact enclosure devise and yet maintain noise control techniques. Sound control has 2 main elements: 1. Use of an acoustic absorptive medium to control reverberation responses; and 2. An insulation material which ultimately filters the incident broad band sound from one side of the medium to the other side. The above techniques have been used for many years to control noise of operational equipment in various formats, but have limitations in size of the control measures, acoustic performance, air flow requirements and practical use. The invention proposes a compact method using a third route: 3. Allowing input and output air travelling through a designated space / channel / duct to turn 180° turning function through a gap equivalent to the ratio of 1:1.3, the width of the entry and exit space / channel / ducts. The principle is also used to secure the edges oof door and access panels in an enclosure devise associated with the invention. Using initial empirical formula: SWL = SPL - (1 OLogVI + 10LogTI) - (10LogV2 + 10LogT2) Where: SWL = Sound Power Level SOL = Sound Pressure Level V = Volume of space T = duration 4. Anti-vibration technology to the newly designed support base. 5. Acoustically secure pepe access to serve the enclosed unit. Use of an angles non direct route of similar design as above. The invention is a compact attenuation devise that contends that air moved through 180° in a prescribed and controlled space / duct can create conditions for maintaining the cooling and discharge air flow patterns, pressures and the additional beneficial feature of sound cancelling of the sound created by the operation of an internally located machine such as an air conditioning or refrigeration unit. The air velocity should be no higher than 8 metres per second. The favoured velocities, which do not exclude higher velocities for the airflow, are less than 1m per second per second to no more than 8m per second per second. The invention means that forced air travelling along the tubular member of the narrow duct design impacts with the end plate or turning wall or flat panel forming the first part of the 180° turn. It has been discovered that instead of moving in organised lines around a bend, the air moves in a linear format randomly impacting on the rectangular bend surfaces until the turn is navigated. This results from the velocity and pressure of the airflow itself maintaining a thrust in the direction of forced air movement. This apparently chaotic movement in fact smooths the air flow by minimising pressure variations across the width of the moving stream and creating micro high and low pressure zones. This random movement assists greatly in maintaining the air pressure uniformly across the tubular member cross section. This assists in moving the airflow through the 180° direction without any significant loss in pressure or velocity. No supplementary turning vanes or other turning devises are needed. This was proven by applying lightweight steel long turning vanes to such a bend. No movement or vibrations were noted through the described velocity ranges. The random linear movement of the air flow pattern coincidentally, as well as creating variable pressure zones, offers similar conditions for sound cancelling particularly in the low frequency ranges. Albeit that sound travels at 343 metres per second2 in air, the dimensions, directions and reflections created by the 180° format enables the necessary high-pressure zones to form. These nodal points are discrete, but create the sound cancelling conditions necessary to reduce the acoustic energy found emanating from inside the unit. The angular shape offered by the 180° bend / turn creates the right conditions for the multiple reflections and subsequent sound cancellation. In conjunction with this a ratio for the opening distance of the access point to the inlet and outlet ducts. This ratio is in the order of 1.3 to 1.0, where the 1.3 represents the depth of the opening relative to the 1.0 which represents the width of the input (intake) duct(s). Beneficially the sound reduction particularly at the lower frequencies ie 63Hz octave centre band to 250Hz octave centre band as seen in the enclosure type design is generally an increase over traditional attenuation methods. The main advantage is the effective attenuation length is reduced over that seen in traditional splitter type attenuators. Air moves from a fan or air moving devise or an air flow system via a ducted system entering the entry chamber. Air travels to the first turn and turns through 180 degrees travelling along the second chamber to the second turn and turns 180 degrees. Air enters the final chamber to be discharged to atmosphere. These routes can be seen in the drawing A. The 180° bend / turn is beneficial to acoustic attenuation and protects air flow movement to control cooling of the enclosed operational unit. It reduces the length of existing methods of silencer design whilst retaining air flow characteristics. Support casings can be made from galvanised steel or plastic. The 180° bend / turn in the ratio approximately 1.3 to 1.0, where the 1.3 represents the depth of the opening relative to the 1.0 which represents the width of the duct gives significantly greater attenuation than traditional acoustic methods. The invention enables compact acoustic enclosures to provide suitable and adequate attenuation for air conditioning and refrigeration units. Typically, such attenuation i.e. sound reduction is in the order of LAeq 20 to 25dB free field reference 2 x 10-5 Pascal. Uses 1. Acoustic enclosures as seen in the Environ Air Conditioning and Refrigeration Enclosure Systems. 2. Exhaust Silencers whereby the technology claims to act as above for the exhaust gases and significantly reduces low and mid frequency emissions. 3. Acoustic attenuators i.e. silencers for air flow ventilation systems, fans and in- door air conditioning room units. 18 09 24

Claims

1. An acoustic enclosure comprising a housing having first and second opposing side walls and:5 an air inlet formed in the first side wall leading to an openingduct, part of the second side wall forming an end wall orthogonal to the opening duct;an intake duct orientated parallel the opening duct, part of the first side wall forming an end wall orthogonal to the intake duct; and10 a third outlet duct orientated parallel to the opening and intakeducts, the outlet duct leading to an air outlet formed in the second side wall.

2. An enclosure according to claim 1, wherein the ratio of the depth of the 15 opening duct and the width of the intake duct is 1: 1.

33. An air flow system comprising an acoustic enclosure for housing an air conditioning unit or refrigeration unit, the system comprising at least three parallel orientated ducts through which air flows to create high 20 pressure nodal point as the air flow turns 180 degrees to flow from oneduct into another thereby creating sound cancellation conditions to reduce acoustic energy emanating from inside the enclosure.

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