This invention relates to air mixers for mixing together two different air flows, particular air mixers for an air distribution system suitable for a building or other similar structure.
In air handling systems designed for large buildings such as office towers and other large structures, there has been a need to mix together at least two different air flows before distributing the mixed air flow throughout the air ducts of the building by means of a fan. Although various air mixers have been developed for bringing together and mixing two different air streams, these known air mixers tend to be inefficient or else they require a substantial amount of space in the building in order to operate in the intended manner. The most common types of air streams to be mixed in an air handling system are return air flow that is coming back from the interior of the building and a fresh outside air flow. It will be appreciated that in cold weather, the return air would normally be relatively warm, for example room temperature, while the outside air can be quite cold.
In these air handling systems for buildings, air stratification that results from a momentum inherent in moving air streams can keep air streams of different temperatures from mixing for quite some distance. This in turn can cause the air handling system to operate poorly or inefficiently and can also result in poor indoor air quality. Also during the winter time, lack of proper mixing of the incoming air streams can result in freezing or damage of heating coils that are part of the heating system and can generate control sensor errors. In the summer, lack of proper mixing of the air streams can result in poor indoor air temperature control and can increase the energy consumption of the air conditioning system. It should be appreciated that the heat transfer capacities at the cooling coils are based on air flow at uniform temperature and velocity across the coils. Thus a non-uniform temperature distribution for the entering air can cause reduced heat transfer of the coils and the desired temperature in the building may not be maintained.
These mixing problems can become more serious as the amount of outdoor air is increased in the air distribution system. Both government regulations and building users are now often requiring a greater amount of outdoor air.
Recent U.S. Pat. No. 5,463,967 issued Nov. 7, 1995 to Airflow Sciences Corporation describes a static mixer designed for use with a power plant. This mixer has a series of parallel walls arranged in side-by-side spaced apart relationship to form a series of rectangular spaces. The perimeters of these spaces are selectively closed to define respective first and second inlets located on two sides and an outlet located on a third side of the air mixer. This mixer creates interleaving of the two air streams and thus promotes increased homogeneity some distance downstream of the confluence of these streams.
In commonly assigned U.S. patent application Ser. No. 09/298,377 filed Apr. 23, 1999 now U.S. Pat. No. 6,139,425, there is described another static mixer which is capable of properly mixing two different air streams within the mixer itself. This known air mixer employs a set of fixed, parallel partitions arranged in spaced apart, side-by-side manner, these partitions forming alternating primary and secondary air passageways. The primary passageways are open ended and extend from a front side of the mixer to a rear side thereof. There is a side wall located on one side of the air mixer that closes the air passageways on this side and that extends from the front side of the mixer to the rear side. Front end plates extend longitudinally across the front side of the air mixer and extend transversely and respectively across sides of the secondary air passageways. These end plates have elongate edge portions extending along longitudinal edges thereof with each edge portion projecting in a transverse direction beyond the plane defined by an adjacent one of the partitions. Air gaps are formed between the elongate edge portions and front edges of the partitions to enable the air flow in the secondary air passageways to exit therefrom and be mixed in the primary air passageways with air flow passing through the latter passageways. This air mixer can also be equipped with a series of turbulence creating plates mounted within the primary air passageway and distributed across the width of their respective primary air passageways.
Although the aforementioned static air mixer works quite well for air system applications where the outside air ratio as a percentage of total air flow is less than 60 percent, this known air mixer does not work as well in conditions where it is desirable to have all or substantially all of the downstream air flow comprised of outside air. This known mixer may cause a high pressure drop when there is a high volume of outside or secondary air passing through the secondary airflow passages. This situation could for example be encountered where the outside air temperature is the same as or close to the temperature required within the building itself. Under such conditions where 100% outside air is desired, the aforementioned known air mixer generally requires the use of outside air bypass dampers to allow for outside air to enter the air distribution system without passing through the static air mixer.
It is an object of the present invention to provide an improved air mixer that can help avoid undesirable air stratification in an air distribution system and at the same time has low pressure drop whatever the ratio of or percentage of primary airflow and secondary airflow may be.
It is a further object of the present invention to provide a novel air mixer for an air distribution system that employs fixed air mixing devices in the outlet side of the air mixer and that can be manufactured at a reasonable cost.
According to one aspect of the present invention, an air mixer for an air distribution system for a building or similar structure includes a set of fixed, substantially parallel partitions arranged in a spaced-apart manner with one above another. These partitions form alternating primary and secondary air passageways that are capable of conveying first and second air flows respectively. These air passageways are substantially open ended at both inlet and outlet ends. The primary air passageways extend from a first side of the air mixer to a third, outlet side while the secondary air passageways extend at a substantial angle to the primary air passageways and from a second side of the air mixer to the third, outlet side. This apparatus also has fixed air mixing devices arranged at at least a substantial portion of the outlet ends of at least one of the primary air passageways and the secondary air passageways. These air mixing devices are adapted and arranged to mix together the first and second air flows. The air mixer has a substantially triangular shape in plan view, this shape being defined by the aforementioned first, second and third sides.
In a preferred embodiment, the air mixing devices are a plurality of spaced-apart vanes mounted at the outlet ends of the secondary air passageways.
According to another aspect of the invention, an air mixer for a distribution system for a building or similar structure includes a first set of air ducts forming air flow passageways for a first airflow, this first set forming two or more spaced-apart levels of air ducts that extend from a first intake side of the air mixer to an outlet side thereof. A second set of air ducts forms air flow passageways for a second air flow, the second set forming two or more spaced-apart levels of air ducts that alternate with the levels of the first set. The second set of air ducts extend from a second intake side of the air mixer to the outlet side and extend at a substantial angle of up to about 90 degrees to the first set. This air mixer includes fixed air flow mixing devices for mixing the first and second air flows rigidly mounted at outlet ends of at least a substantial portion of the air ducts of the first set or the second set.
In a preferred embodiment the mixing devices comprise a series of curved vanes arranged at each level of the first set or the second set, these vanes acting to redirect the air flow exiting from the outlet ends of at least said substantial portion of the air ducts.
According to a further aspect of the invention, an air mixer for an air distribution system for a building or similar structure includes two adjacent sets of air ducts forming air flow passageways for first and second air flows. One of these sets is oriented at a substantial angle, that is less than 180 degrees, to the other of the sets and each air duct has an inlet end and an outlet end. The inlet ends of one set of air ducts are located on a first side of the air mixer, which has a triangular shape when viewed from above. The inlet ends of the other set are located on a second side of the air mixer while the outlet ends of both sets are located on a third side of the air mixer. Air deflecting vanes for the mixing of the first and second air flows are mounted at at least a portion of the outlet ends on the third side. These deflecting vanes in use act to redirect at least a portion of one of the first and second air flows towards the other of the first and second air flows at the third side of the air mixer.
Further features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.