EP0269634B1

EP0269634B1 - Apparatus for indirect evaporative cooling

Info

Publication number: EP0269634B1
Application number: EP86905456A
Authority: EP
Inventors: Per Norbäck
Original assignee: Carl Munters AB
Current assignee: Carl Munters AB
Priority date: 1985-08-16
Filing date: 1986-08-14
Publication date: 1990-12-27
Anticipated expiration: 2006-08-14
Also published as: SE8503854L; WO1987001188A1; SE8503854D0; SE460151B; AU6333486A; EP0269634A1; DE3676707D1

Abstract

Apparatus for indirect, evaporative cooling of an useful air current, including a contact body (10) made up in layers, with duct systems between the layers. There are two separate duct systems, useful air for cooling passing through one system (16), while a cooling air current passes through the other system (18). Cooling takes place by evaporation of water in the other duct system (18). The duct-forming means (16, 18) in both systems are disposed such that the useful and cooling air currents flow horizontally, while water supply means (24) supplying water to the other duct system (18) are disposed at the top of the contact body (10), allowing the water to flow vertically downwards in this system (18).

Description

The present invention relates to an apparatus for indirect evaporative cooling of a supply air flow including a heat exchange unit made up from layers with ducts between the layers, the ducts being divided into two separate duct systems, where one system has the supply air flow passing through it and the other the cooling air flow, cooling being substantially achieved by evaporation of water in the other duct system, whereby means supplying water to the second duct system are disposed on the upper side of the heat exchange unit, so that the water flows vertically downwards in this duct system.
In SE-B-383 777 an apparatus of this kind is disclosed, in which means supplying water to the second duct system are disposed on the upper side of the unit, so that the water flows vertically downwards in this duct system.
In the known apparatus, however, the supply air flow and the cooling air flow stream in crossflow with regard to each other, which diminishes the cooling effect and makes the apparatus more complicated to build.
In US-A-3 305 010 is disclosed a plate type heat exchanger apparatus in which two fluids of different temperatures are introduced at opposite ends of the apparatus to flow counter to one another between superposed stacked plate and fin elements. However, this apparatus has no means for supplying water to one of the duct systems in order to provide cooling.
Starting from the state of art as known from SE-B-383777 the invention has for the main object to provide an apparatus of the kind mentioned in the introduction with a configuration such that good heat transfer and favourable flow conditions are afforded in its use as an evaporative heat exchanger, the configuration especially enabling the supply air flow to have a horizontal flow direction for the apparatus readily to be incorporated in ventilation plants, where the normal duct system is horizontal.
This object is solved in accordance with the invention by the features as claimed in the characterizing part of claim 1.
Further particulars of the invention are claimed in the dependent claims.
The invention will now be described in detail with reference to the appended drawings, on which there are illustrated preferred embodiments of the invention.

Figure 1 is a side view of an apparatus for indirect evaporative cooling.
Figure 2 is a horizontal section along the line 11-11 in Figure 1.
Figure 3 illustrates the flow of the cooling air in an apparatus according to Figure 1 without intermediate walls.
Figure 4 is a view similar to the one in Figure 3, but with intermediate walls according to the invention.
Figures 5a-5c are cross sections of the layer structure.
Figure 6 is a side view of a plate or panel of the kind required for making up the structure of the apparatus illustrated in Figure 1.
Figure 7 is a side view of a heat exchanger unit built in modules.

The heat exchanger unit 10 illustrated in Figure 1 is used as an indirect heat exchanger for a supply air flow flowing substantially horizontally through the unit which air is to be cooled and is supplied to the inclined end wall surface 28 illustrated in Figure 1 constituting the inlet to a first duct system in the unit 10 the supply air flow flowing through this duct system in the longitudinal direction of said ducts or gaps, which are separate from adjacent ducts or gaps in a second duct system passed through by a cooling airflow.
By way of example it may be said that the unit 10 may be made up from a plurality of flat plates 11-15, these being put together with flange-like stiffening and surface magnifying means therebetween, as illustrated in Figure 5, these means being in the embodiment shown corrugated metal sheets or foils 16. The corrugations in the sheets 16 constitute the ducts for the supply air which is to be cooled in the contact body 10, the sheets 16 being oriented with their corrugations extending in the flow direction of the air. The corrugated foil or sheet 16 thus defines the width of the ducts or gaps in the contact body through which the supply air passes. The corrugations of the sheet 16 must be in good heat conductive contact with the surfaces of the flat plates 11-15. When there are several layers, the crests of the corrugations shall be immediately opposite each other which increases the stability of the body and gives a shorter path for heat conduction.
The plates 11-15 and corrugated sheets 16 are of a thin material with good heat conductivity, e.g. aluminum and are joined to each other by heating, gluing or other suitable method. They may, for example, be made as intrinsically stiff sandwich elements. As will be seen from Figure 5, a desired number of such elements are joined to each other with an intermediate space determined by spacers 32 (Figure 6) arranged between them. The spacers thus also define the width of the gaps 18 in the second duct system in the contact body, through which the cooling air flow shall pass.
For achieving the evaporative cooling effect the walls of the gaps 18 are wetted in a manner known per se. The surface of the plates or foils 11-15 facing towards the gaps 18 is provided with a coating 20 of a water-absorbing and/or soaking material. During the passage of the cooling air through the gaps 18 there will be evaporation of water into the cooling air, so that an intensive transference of heat is obtained from the supply air in the first duct system to the cooling air in the gaps 18, thus reducing the temperature of the supply air to a low value. The walls are normally only kept moistened to the extent necessary for evaporation. The gaps passed through by the cooling air can be made considerably narrower, due to the evaporative cooling effect, than the gaps passed through by the supply air, this being readily enabled by the inventive configuration, where the sandwich elements 12, 14, 16 and the gaps (spacers) 18 can be made to any desired width and mutually independently. The amount of cooling air is also normally less than that of the supply air, due to the evaporative effect.
The flanges of the stiffening means or corrugated sheets 16, included in the sandwich element 12-16 constitutes a large heat transfer surface which is brushed over by the passing supply air flow.
In the embodiment illustrated in Figure 5c the intrinsically stiff panels are fabricated from five flat plates or foils 11-15 with intermediate corrugated sheets or foils 16, but they may of course be made up of only two flat plates or foils 11, 15 with one intermediate corrugated sheet or foil 16 (Figure 5a) or three flat plates (foils) and corrugated sheets (foils) 16 (Figure 5b) depending on the desired stiffness and heat transfer surface desired. The configuration in several layers has the advantage that the wet gap can be made wider and will be less sensitive to variations in the gap width. There will also be fewer panels to handle and they will also be stronger.
The described apparatus 10 is coupled into a ventilation system such that the supply air is drawn in through the ducts formed by the sheets 16 into the first duct system with the aid of a fan 22 (Figure 1). ). A part of the air flow, e.g. 10-50%, of this cooled supply air flow is returned as a cooling air flow in counterflow to the supply air flow through the second duct system 18, where the supply air is moistened by water supplied through jets 24 on the upper part of the apparatus 10, whereat the described, evaporative cooling takes place. The cooling air flow through the apparatus 10 is provided by a second fan 23, which takes the cooling air to an outlet or to an exhaust air duct. The supply air flow is passed to the supply air duct in the ventilation system, or directly to a space that is to be air conditioned.
Figure 2 shows how the major part of the supply air flow leaves the ducts 16 as cooled air to flow out into a room or a fresh air duct in a ventilation system, while a partial flow is turned to enter the ducts 18 to form the cooling air flow, as described above.
As illustrated in Figures 1, 3 and 6 the plates 11-15 are preferably made rectangular, but at one vertical end, the left one in the Figures, they are given the shape preferably of an unequal sided triangle to form a connection part where the shorter side 26 constitutes the outlet from the second duct system 18, while the longer side 28 constitutes the inlet to the duct system 16. In order to seal the duct system 18 from the duct system 16 at this triangular end, a sealing strip 30 is disposed between the plates 11, 15 contiguous to the ducts 18, as illustrated in Figure 6. In this figure which illustrates the plate 11 or 15 as seen from the inside of a duct 18, there may also be seen the spacers 32 that determine the width of the ducts 18. It will also be seen that the sealing strip 30 forms a spacer too. The more or less dot- shaped spacers 32 can also be replaced by corrugated strips at the upper and lower edges of the sheets 11, 15 as well as the right-hand end thereof. The corrugations in the strips then follow the respective directions of the water or the cooling air current.
The flow of the cooling air flow in a duct 18 is depicted in Figure 3, showing that the cooling air flow flows from the right side of the body to the outlet 26. When the other duct system includes ducts 18 extending over the entire surface of the sheet and which are not divided by intermediate walls or corrugations, it may happen that upwardly the cooling air flow has a tendency to deviate upwards where the ducts are open towards the water supply jets 24, such as indicated by the upper dashed line in Figure 3. To reduce this deviation tendency intermediate walls 34 are arranged between the jets 24, as seen in Figure 4. It will also be seen from Figure 3 that the body is provided with a collection trough 36 for excess water. If so desired, recirculation of water from the trough to the jets 24 can be arranged.
To prevent the cooling air deviating from the lower part of the horizontal flow path also, in the same way as at the upper part, intermediate walls 35 are arranged in the trough 36 to extend down to the normal level of the water in the trough, thus to obstruct downward deviation of the air. In this way the cooling air in the contact body both upwardly and downwardly will flow substantially horizontally in heat exchanging association with the supply air flows in the ducts 16.
It is of great importance for the desired cooling effect to be achieved that the cooling air flow is retained within the duct system 18. A leakage therefrom due to portions of the cooling air passing by outside the active heat transferring surface has a doubly negative effect on the cooling. The cooling is namely dependent on both amount and temperature of the cooling air. If the amount decreases due to bypassing, the decreased amount of air has a reduced capacity for attracting from the air flows in the ducts 16, which leads to their leaving the ducts 16 at a raised temperature. This raised temperature results in that the cooling air flows also get an increased temperature, which further enfeebles their capacity to attract energy. The negative effects on cooling thus combine very deleteriously and with this background it will be understood why it is so important to prevent the mentioned bypassing tendency.
The triangular inlet part of the duct system 16, which also constitutes the outlet 28 for the ducts 16 is disposed such that a substantially lower flow resistance is obtained than in the pack itself. This may be achieved by the corrugated sheets being replaced here by a sheet with deeper corrugations or by a plurality of strips which stiffen up the inlet part without exercising any substantial resistance to the air flow. Examples of such strips are illustrated at 27 in Figure 1. It will be seen from the Figure that the inlet and outlet parts 26, 28 are unequally sided, i.e. the inlet for the supply air flow will be greater than the outlet 26 for the cooling air flow. This difference in size can vary and is dependent on the size of the air flows. The outlet for the moist cooling air current is also suitably directed upwards to prevent any unnecessary entrainment of water from the moist ducts 18. Of course, the inlet 28 to the supply air flow duct system 16 could comprise the entire vertical side with the cooling air flow being taken out vertically upwards. The illustrated triangular implementation gives other advantages, however, and these are described below.
As illustrated in Figure 7, a plurality of modules or contact bodies 10 can be built on to each other into a larger unit. In such a pack the supply air can be supplied to the contact bodies 10 via the inlets 28 and the cooling air flow taken away from the bodies via the outlets 26 in a very simple way due to the triangular implementation of the inlet/ outlet part. Another advantage with this implementation is that water can be commonly supplied to all the contact bodies 10 at the upper side of the pack via the jets 24 and be collected at the bottom of the pack in the trough 36. The same water thus runs through all the modules 10 via their duct systems 18. The illustrated combination of several contact bodies or modules 10 does not cause any change in the thermodynamics either.

Claims

1. Apparatus for indirect, evaporative cooling of a supply air flow, including a heat exchange unit (10) made up from layers with ducts (16, 18) between the layers, the ducts being divided into two separate duct systems, where one system (16) has the supply air flow passing through it and the other the cooling air flow, cooling being substantially achieved by evaporation of water in the other duct system (18), whereby means (24) supplying water to the second duct system are disposed on the upper side of the heat exchange unit, so that the water flows vertically downwards in this duct system (18), characterized in that the duct-forming means (16, 32) in both duct systems (16, 18) are adapted such that both supply and cooling air flows move horizontally and that the inlets and outlets of the two duct systems (16,18) are disposed such that the supply air and cooling air flows are in mutual counter flow and that intermediate walls (34,35) are disposed at the top and bottom of the unit such as to prevent cooling air from deviating towards the water supply means (24) or water collection means (36) at the bottom side of the unit.

2. Apparatus as claimed in claim 1, characterized in that the outlet of the first duct system (16) and the inlet of the other duct system (18) are disposed contiguous to and in communication with each other, such that the cooling air flow to the other duct system is branched off as a part of the air leaving the first duct system.

3. Apparatus as claimed in any one of the preceding claims, characterized in that one vertical side (26, 28) of the unit (10) is shaped with an apex, as in a triangle, the sides leading to the apex being formed as respective inlet (28) to the first duct system (16) and outlet (26) from the other duct system (18).

4. Apparatus as claimed in claim 3, characterized in that the adjacent sides (26, 28) of the apex are of different lengths and that the longer side (28) is the opening for the fresh air flow.

5. Apparatus as claimed in any one of the preceding claims, characterized in that the unit is made up of a plurality of flat sheets (12, 13) with intermediate flange-like stiffening and surface- extending means (16) together forming a plurality of intrinsically stiff panels, which are combined with the aid of spacers (32) to form the unit (10), the spacers (32) defining the other duct system (18) while the panels include the first duct system (16).

6. Apparatus as claimed in any one of the preceding claims, characterized in that the triangular inlet part (28) of the first duct system (16) is implemented with a lower flow resistance than the rest of the system.

7. Apparatus as claimed in any one of the preceding claims, characterized in that the outlet (26) from the other duct system (18) is directed upwards.

8. Apparatus as claimed in claim 5, characterized in that the spacers (32) are formed such that the cooling air and water flow substantially unobstructedly in the other duct system, e.g. they are dot-like.

9. Apparatus as claimed in claim 5, characterized in that stiffening means are formed by corrugated sheets (16) between the flat plates (12, 13) and that the corrugated sheets are arranged with the crests of the corrugations in the same horizontal plane.

10. Apparatus as claimed in any one of the preceding claims, characterized in that a plurality of units (10) are stacked one on top of the other, the water supply (24) at the top of the stack to the other duct system and the collection (36) of water at the bottom of the stack being common to all the units (10) in the stack.