AIR-CONDITIONING APPARATUS

Abstract: An air-conditioning unit with a recuperative heat exchanger (24), preferably a plate heat exchanger, in which exhaust-air passages (23) are disposed in cross-flow relation to supply-air passages (20) over a portion of the length of the passages, namely at the inlets and outlets of the passages, and in counterflow relation over the remaining portion of the length of the passages. Control of the supply-air temperature is effected by controlled bypassing of the supply air and/or the exhaust air over the heat exchanger (34) by means of dampers (26, 27).

Description: Air conditioning apparatus This invention relates to an air-conditioning unit of the kind which comprises a recuperative heat exchanger having a system of parallel supply-air passages and a system of exhaust-air passages which are disposed in heat-exchanging re¬ lation to the supply-air passages. More particularly, the in¬ vention relates to an air-conditioning unit of the kind de¬ fined in the precharacterising part of claim 1. Moreover, the invention relates to a method for controlling the supply air temperature in air-conditioning units of this kind. Air-conditioning units of the kind the invention is con¬ cerned with are common in ventilating or air-conditioning systems for general or comfort ventilation of dwellings, com¬ mercial premises in a broad sense, such as offices, schools, hospitals, assembly halls etc., and industry and crafts pre¬ mises. Among the several requirements to be met by air-condi¬ tioning units of this kind are low operating costs and high temperature efficiency of the unit and possibility to con- trol the temperature of the supply air by simple means. The air-conditioning unit according to the invention combines in a favourable way these requirements with other important requirements. This is achieved through the con¬ struction set forth in claim 1. The invention is described in greater detail below with reference to the accompanying drawing, which is a diagrammat¬ ic vertical longitudinal sectional view of an air-condition¬ ing unit embodying the invention. As illustrated, the air-conditioning unit comprises a substantially parallelepipedal, heat-insulating enclosure 11 having an intake 12 for outside air to be converted to supply air, an outlet 13 for supply air, an intake 14 for exhaust air and an outlet 15 for the exhaust air (extract air) . Between the outside-air intake 12, which includes a damper 16 and a supply-air filter 17, both of a conventional kind, and the exhaust-air outlet a supply-air duct extends which is formed by a horizontal lower duct section 18, an overlying, likewise horizontal upper duct section 19 and a system of supply-air passages 20 connecting these duct sec¬ tions. Similarly, between the exhaust-air intake 14 and the exhaust-air outlet 15 extends an exhaust-air duct formed by a horizontal upper duct section 21, an underlying, likewise hor¬ izontal lower duct section 22 and a system of exhaust-air passages 23 interconnecting these duct sections. The supply-air passages 20 and the exhaust-air passages 23 form part of a recuperative heat exchanger 24 which will be described in greater detail below, namely a plate heat ex¬ changer, the plates of which are parallel to the plane of the drawing figure. Accordingly, the supply-air duct and the exhaust-air duct are disposed in heat-exchanging relation to one another in the heat exchanger 24 through the intermediary of the plates which separate the alternately disposed supply- air and exhaust-air passages from one another, but the passa¬ ges are isolated from one another in air-tight fashion. A heat-insulated horizontal partition 25 separates the two lower, substantially aligned duct sections 18 and 22 from the two upper, likewise substantially aligned duct sections 19 and 21. On opposite sides of the heat exchanger 24, the partition includes respectively a bypass damper 26 for supply air and a bypass damper 27 for exhaust air. By means of these dampers, a controlled portion of the supply air and the ex- haust air, respectively, can be bypassed around the heat ex¬ changer. In the upper section, namely the downstream section 19 of the supply-air duct there are provided a supply-air fan 28 disposed at the outlet 13 and a supply-air cooler 29, which preferably includes a separate fan. In the upper, upstream section 21, the exhaust-air duct has an exhaust-air heater 30 (likewise preferably comprising a separate fan) , and in the lower, downstream section 22, the exhaust-air duct, comprises an exhaust-air fan 31 disposed at the exhaust-air outlet. The supply-air cooler 29 and the exhaust-air heater 30 may be of any suitable type, and, besides, may be dispensed with or positioned in a place other than in the air-condi¬ tioning unit proper. Preferably, the supply-air fan 28 and the exhaust-air fan 31 include an electric motor having or being connected with equipment for electronic rotational-speed control. The heat exchanger 24 is adapted for single-stage in- 5 direct evaporative cooling of the exhaust air in accordance with the principles described in EP-A-0 363 340. It thereby embodies the possibility of cooling, when necessary, the supply air in the heat exchanger by cooling the exhaust air and of keeping the surfaces of the exhaust-air passages clean 10 in a simple and efficient manner, so that an exhaust-air filter on the upstream side of the heat exchanger can be dis¬ pensed with. In accordance with the invention, the heat exchanger 24 is also designed such that the exhaust-air passages 20 over a 15 portion of their length as measured in the direction of flow, namely in an upstream region and a downstream region, are disposed in cross-flow relation to the exhaust-air passages 23, and over an intermediate section are disposed in parallel/antiparallel-flow relation, namely counterflow rela- 0 tion, to the exhaust-air passages. To this end, the heat exchanger comprises three super¬ posed sections, a bottom section 24A, a top section 24B and an intermediate section 24C, in which sections the supply-air • • passages 20 are disposed differently. 5 In the bottom section 24A, the supply air entering the duct section 18 is deflected from horizontal flow direction to a vertical flow direction which is maintained in the in¬ termediate section 24C, whereupon in the duct section 19 it is deflected back to horizontal flow in the direction oppo- 0 site to the flow direction in the lower duct section. As is indicated in the figure, the supply-air passages 20 are subdivided into a large number of subpassages 20A dis¬ posed side by side, this subdivision being effected by corru¬ gation of the heat exchanger plates or in some other suitable 5 way, such as by means of fins. The supply-air passages 23, which are also subdivided into a large number of subpassages 23A disposed side by side, are straight and extend vertically all the way from the exhaust-air inlet 23B of the heat exchanger to the exhaust- air outlet 23C thereof. The surfaces which define the exhaust-air passages 23 are smooth throughout their length in order that deposition of dirt may be counteracted and rinsing-away of accumulated dirt may be facilitated. In order that the exhaust air may easily flow from the upper duct section 21 into the exhaust-air passages 23 and from the latter into the lower duct section 22, the inlet ends and the outlet ends of the exhaust-air passages are positioned along surfaces which are inclined to the hori¬ zontal direction in the manner shown in the drawing figure. While the inlet and outlet ends of the supply-air pas¬ sages are disposed in a vertical plane at one side of the heat exchanger, i.e., the side facing the supply-air duct sections 18 and 19, the inlet and outlet ends of the exhaust- air passages are thus disposed along slanting or inclined surfaces at the opposite side of the heat exchanger, i.e., the side facing the exhaust-air duct sections 21 and 22, these surfaces ascending in the direction of flow. The surface area of the horizontal projection of these ascending surfaces is not critical but suitably is 35-65% of the surface area of the vertical projection of the surface, and should preferably not be less than about 25%. When choosing the inclination, it should be kept in mind that the parallel/antiparallel-flow relation of the supply-air pas¬ sages to the exhaust-air passages should encompass as large a portion of the total flow path as can be accepted without un¬ due restriction of the effective inlet and outlet cross- sections for the air. To provide for the evaporative cooling of the exhaust air and for the cleaning of the exhaust-air passages 23, the heat exchanger 24 is equipped at its exhaust-air inlet 23B with a water supply device for supplying water to the sur¬ faces of the exhaust-air passages 23 so that when desired or required these surfaces can be covered with a water film which runs from the inlet to the outlet and is spread over the entire or almost the entire heat transfer surface. This device comprises a number of horizontal open water troughs 32 which extends transversely of the planes of the heat exchanger plates (the plane of the figure) and which are uniformly distributed over and positioned adjacent the in- clined surface in which the inlet ends of the exhaust-air passages are disposed. The longitudinal lateral walls of the troughs are serrated to form water overflow edges which distribute the water in the troughs throughout the heat exchanger trans- versely of the aforesaid plane as is explained in EP-A-0 363 340. Water is fed to the troughs 32 through a distributor tube 33 which is connected to a pump 34. The inlet of this pump is positioned in a water collecting sump 35 beneath the heat exchanger 24. Excess water from the exhaust-air passages is collected by the sump 35 which is also provided with a wa¬ ter feed mechanism (not shown) , preferably controlled by a swimmer, by means of which a constant water level is main¬ tained in the sump. If additional cooling of the supply air is required, the sump can be continuously supplied with cold water, such as direct from the water mains, from a ground water supply or from a water cooler. Excess water can be disposed of -in a suitable manner, e.g., by spreading it over the roof of the building which is provided with the air-conditioning unit. When the air-conditioning unit is being used for re¬ covering heat from the exhaust air, that is, for heating the supply air while utilizing the heat content in the exhaust air, the water supply to the exhaust-air passages 23 of the heat exchanger is intermittent with long off intervals. In this mode of operation, the water supply substantially only serves to keeping the surfaces of the exhaust-air passages clean. As a result of the above-described design of the heat exchanger 24 with countercurrent heat exchange over the larger portion of the flow path through the heat exchanger, the heat recovery can take place at a very high temperature efficiency, 80% or more, although only a single heat ex- changer unit is provided; temperature efficiencies of the just-mentioned magnitude normally require two heat exchanger units connected in series. Primarily, the temperature of the supply air leaving the air-conditioning unit is controlled by adjusting the bypass dampers 26 and 27 by means of a control system which is not shown in detail. This system comprises a temperature trans¬ ducer 35 at the supply-air outlet 13 or at some other suit¬ able place, a control device 36, which is controlled by the temperature transducer and acts on damper actuators 37 and 38 and preferably also on rotational speed controls 39 and 40 for the electric motors of the fans 28 and 31. The control device 36 also controls the water pump 34. Preferably, the two dampers 26 and 27 are actuated si- multaneously, so that both are operated in the same direction substantially synchronously, but it is within the scope of the invention to control the dampers individually. Preferably, the motors of the fans 28, 31 are controlled such that the pressure at the air connections to the unit 11 is kept substantially constant. If additional heating of the supply air is required, the exhaust-air heater 30 can be switched on to heat the exhaust air before it passes through the heat exchanger 24. As has been indicated above, such additional heating, which is nor- ally required only during a very short period of the year, can also take place outside the air-conditioning unit. The bypassing of the supply air and/or the exhaust air around the heat exchanger 24 by means of the dampers 26 and 27, respectively, results in a reduced pressure drop across the heat exchanger and thereby results in a reduced energy consumption in the fans 28, 31. When cooling of the supply air is required, the exhaust air is cooled in the exhaust-air passages 24 by means of the above-described evaporative cooling system. The water film which is formed by the water fed by gravity from the troughs 32 and which is spread over the entire or almost the entire surface of the exhaust-air passages, then both effects the cooling and rinses the surfaces to clean them. If the just-mentioned cooling should be insufficient, as may occasionally be the case during certain warm periods, especially in southern countries, the supply-air cooler 29 may be switched on. As indicated above, this cooling may also take place outside the air-conditioning unit. Switching the supply-air cooler 29 and the exhaust-air heater 30 on and off is normally is effected by means of the control device 36. Over a large portion of a normal annual cycle in count- ries having a temperate climate the requirement for heating and cooling of the supply air is rather limited. Accordingly, over a large portion of. the annual cycle, a substantial por¬ tion of the supply air and exhaust air can be bypassed over the heat exchanger by means of the dampers 26 and 27, re- spectively, resulting in a reduced pressure drop over the supply-air duct and the exhaust-air duct and thereby reduced energy consumption and operating costs. The possibility for the above-described simple control is realized through the provision by which starting the water pump 34 of the watering system results in discontinuation of the heat recovery to the supply air which is instead cooled. The pump is put into operation when the dampers 26 and 27 are fully open. Both the cooling of the supply air and the heat recovery to the supply air are increased with increasing degree of closing of the dampers 26, 27. Consequently, maximum cooling and heat recovery is achieved with fully closed dampers. During the coldest and warmest periods of the year, con¬ trol power is supplied in the form of conventional heating or cooling energy; the required amounts of energy are very s a11, however. All control is effected from a single temperature trans¬ ducer, the temperature transducer 35, in the supply air, and the control takes place sequentially.

Claims: Claims 1. Air-conditioning unit with a recuperative heat ex¬ changer (24) which comprises an inlet (14) and an outlet (15) for exhaust air, an inlet (12) and an outlet (13) for supply air, a system of parallel exhaust-air passages (23) , a system of parallel supply-air passages (20) which are disposed alternatingly with and in heat-exchanging relation to the supply-air passages (23) , characterised in that the exhaust-air passages (23) are essentially straight between the exhaust-air inlet (23B) and the exhaust-air out¬ let (23C) , and the exhaust-air passages (23) are disposed in cross-flow relation to the supply-air passages (20) at passage sections adjacent the inlets (20A, 23B) and the outlets (20B, 23C) and in parallel/antiparallel-flow relation, preferably counter¬ flow relation, to the supply-air passages (20) at an inter¬ mediate section (20C) . 2. Air-conditioning unit according to claim 1, characterised in that the inlet (23B) and the outlet (23C) for exhaust air are open at the same side of the heat ex¬ changer (24) towards respectively a horizontal upstream sec- tion (21) and an underlying horizontal downstream section (22) of an exhaust-air duct. 3. Air-conditioning unit according to claim 2, characterised in that the inlet (20A) and the outlet (20B) for supply air are open towards respectively a horizontal up¬ stream section (18) and an overlying horizontal downstream section of a supply-air duct and are disposed at the other, opposite side of the heat exchanger (24) . 4. Air-conditioning unit according to claim 3, characterised in that a bypass passage including a control damper (27) is provided at the first-mentioned side of the heat exchanger, between the upstream section (21) and the downstream section (22) of the exhaust-air duct, and at the other side of the heat exchanger, between the upstream sec- tion (18) and the downstream section (19) of the supply-air duct. 5. Air-conditioning unit according to any one of claims 1-3, characterised by means for forming a water film which flows from the exhaust-air inlet (23B) of the heat ex¬ changer (24) to the exhaust-air outlet (23C) thereof and which is spread over substantially the entire surface of the exhaust-air passages (23) . 6. Air-conditioning unit according to claim 5, characterised in that the said means includes means for grav¬ ity supply of water to the exhaust-air inlet (23) from water distribution members (32) . 7. Air-conditioning unit according to any one of claims 1-6, characterised by a control device (36, 26, 27) for controlling the supply-air temperature at the supply-air inlet (13) by bypassing a controlled portion of the supply air and/or the exhaust air around the heat exchanger (24) . 8. Air-conditioning unit according to claim 8, characterised in that the control device (36) includes means for controlling the rotational speed of a supply-air fan (28) and/or an exhaust-air fan (31) , preferably for the purpose of keeping the air pressure in supply-air and/or exhaust-air connections of the unit constant. 9. Air-conditioning unit according to any one of claims 1-8, characterised by an exhaust-air heater (30) which is provided at the exhaust-air inlet (14) and/or a supply-air cooler (29) which is provided at the supply-air outlet (13) . 10. A method for controlling the supply-air temperature in an air-conditioning unit, preferably an air-conditioning unit according to any one of claims 1-9, in which supply air is transported in a supply-air duct while undergoing heat ex¬ change in a regenerative heat exchanger with exhaust-air transported in an exhaust-air duct, characterised in that by¬ passing of exhaust air from an exhaust-air duct section (21) upstream of the heat exchanger (24) to an exhaust-air duct section (22) downstream of the heat exchanger and/or by¬ passing of supply air from a supply-air section (18) upstream of the heat exchanger to a supply-air section downstream of the heat exchanger is controlled in dependence of the desired supply air temperature, preferably while holding the pressure in the supply-air and exhaust-air connections (12-15) of the unit constant.

Inventors: PERSSON SIXTEN, PERSSON, SIXTEN
Applicants: PERSSON SIXTEN, PERSSON, SIXTEN
Application year: 1993
Main classification: F24F12
IPC codes: F24F1, F24F12