Mixing section for supply air and return air in an air-condition

Details Mixing section for supply air and return air in an air-condition Mixing section for supply air and return air in an air-condition

1996-01-16

1997-05-27

Joyce, Harold

Ventilation

Having inlet airway

Including structure for mixing plural air streams together

454229, 454236, 454263, F24F 1304

Patent

active

056326750

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a mixing section for supply air and return air in an air-conditioning apparatus comprising
a supply device supplying outdoor air into a room and comprising a supply duct between outdoor air and the room for an outdoor air flow, and means for adjusting the outdoor air flow;
an exhaust device passing exhaust air from the room and comprising an exhaust duct from the room for an exhaust air flow, and means for adjusting the exhaust air flow; and
a return device for returning exhaust air into the room and comprising a return duct between the exhaust duct and the supply duct for a return air flow, and means for adjusting the exhaust air flow;
the supply device and the return device having a common mixing space for mixing the outdoor air and return air flows.
The need for air-conditioning in buildings depends on the number of people staying in the building at a specific time, the amount of impurities entering the air, the heat load, etc. The air-conditioning system, especially the flow of air, has to be designed according to the maximum load. As the heat load is very often the factor determining the design values, the air-conditioning system often has to be operated at an unnecessarily high power, especially in winter, if the power cannot be adjusted. This would require a very high amount of energy, especially thermal energy, as whatever the way cold outdoor air is introduced into the building, the air has to be heated.
To avoid unnecessary consumption of energy, different ways of adjusting the power of the air-conditioning apparatus have been developed. The most natural way is to decrease the supply and exhaust air flows of the air-conditioning system simultaneously when full power is not needed. This may take place e.g. by adjusting the rotation speed of the blowers, by varying the performance curves of the blowers by adjusting the blade angle, or by bringing the air entering the blower into a rotation movement by so-called leading-blade adjusters or simply by increasing the air resistance of the system by dampers.
However, reduction in the air flow causes problems in the distribution of air into rooms. The properties of conventional air distribution means, especially the throw length, change as the air flow is reduced so that the air flow emerging from the air distribution means will not reach everywhere in the room, and so the air will not change at all in some part of the room.
In addition to this common problem, all of the above-mentioned ways of adjustment have their own special problems.
So-called return air operation has been developed mainly to avoid air distribution problems. In the return air operation the flow of outdoor air into the building and the flow of so-called exhaust air from the building are reduced by dampers while passing a portion of the exhaust air flow after the exhaust blower to the suction side of the supply air blower, where it is mixed with outdoor air sucked by the blowers. The exhaust air portion to be passed back into the building is to be kept equal to the reduction of the outdoor and/or exhaust air flow caused by the dampers. The supply and exhaust air blowers and the air distribution means thereby operate all the time at the designed air flow rate.
In principle, the return air system seems to be simple, but once the return air damper is opened to admit exhaust air into the supply air blower, the fully separate exhaust and supply air systems become a single extremely complicated system difficult to control; experiences from apparatus implementations show that air flows in particular are impossible to control. The problems associated with return air operation are so complex that a comprehensive description of great complexity would be required to explain them thoroughly. Therefore it may suffice to refer to Finnish Patent Application 931 848 "An air-conditioning apparatus and a method of controlling its operation" having the same filing date as the present invention.
The manufacturers of air-conditioning apparatuses supply standardized mixing sections,

REFERENCES:
patent: 2400617 (1946-05-01), Wheller
patent: 2987982 (1961-06-01), Wilson
patent: 3212424 (1965-10-01), Davis
patent: 3387649 (1968-06-01), Mullins et al.
patent: 3610522 (1971-10-01), Tutt
patent: 4350100 (1982-09-01), Stephenson
patent: 5127878 (1992-07-01), Meckler
patent: 5413530 (1995-05-01), Montaz

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