US20160252262A1

US20160252262A1 - System and method for air handling and air conditioning

Info

Publication number: US20160252262A1
Application number: US15/027,197
Authority: US
Inventors: Mathieu Mariotto; Stephane Colasson
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2013-10-09
Filing date: 2014-10-07
Publication date: 2016-09-01
Also published as: EP3039353A2; JP6454334B2; EP3039353B1; WO2015052151A3; JP2016532843A; FR3011624B1; CN105612392A; FR3011624A1; WO2015052151A2

Abstract

A system for air handling and air conditioning to supply cool air inside a volume, the system including at least one enthalpy exchanger module including a dual airflow, enabling a heat transfer and a water vapor transfer between both airflows, the system configured to operate according to a cooling mode of the volume in which both airflows are respectively made of an outside airflow to be introduced into the volume, and a cooler dryer foul airflow, coming from inside of the volume. The system further includes: a mechanism enabling relative humidity of the outside airflow at an inlet of the enthalpy exchanger module to be determined; and a controller configured to command a heat supply to the outside airflow before it enters the module, when the relative humidity thereof exceeds a predetermined value.

Description

The invention relates to the field of systems and methods for air handling and air conditioning, for example for buildings exposed to hot humid climates of the type faced in South-East Asia. Nevertheless, other applications are possible. For example, the invention can also be applied to air volumes involved in industrial applications and comprising air drying issues, such as in the paper, food and micro-electronics industry.
The invention more precisely relates to such systems fitted with dual airflow exchangers, of the type enabling a heat transfer as well as a humidity/water vapour transfer between both airflows passing through the exchanger. Such an exchanger providing this dual transfer is also commonly referred to as a “total heat exchanger” or “enthalpy heat exchanger”.
The invention therefore applies to air handling and air conditioning for buildings, preferably for housing and service industries. The exchanger thus not only ensures a heat transfer between the foul airflow and the outside airflow, but also a water vapour transfer between both flows, from the most humid environment to the driest environment.
In hot humid climates, the outside airflow, also referred to as fresh airflow, can have a high temperature, for example around 30 to 35° C., and a strong relative humidity, for example around 90 to 95%. Under these conditions, water vapour transfer therefore occurs from the outside airflow to the foul airflow. Nevertheless, when the relative humidity of the outside airflow is very high, there is a risk of condensation within the exchanger, which is detrimental to its proper operation, its reliability and health security of the process. Indeed, even if the water vapour transfer between both flows passing through the exchanger contributes to reducing the absolute humidity of the outside airflow, the relative humidity is on the other hand increased by cooling this same outside airflow in the exchanger. In this connection, it is reminded that the absolute humidity corresponds to the water vapour concentration per kilogram of dry air, whereas the relative humidity corresponds to the ratio of partial vapour pressure to the saturation vapour pressure (pressure from which air can no longer contain more vapour, otherwise the latter condenses).
In prior art, there are several solutions implementing enthalpy exchangers, which can for example be installed upstream of a vapour compression refrigerating unit. By way of indication, these solutions are alternatives to the use of dehydrating wheels also known from prior art, but belonging to a field far removed from the one of the invention.
Regarding the enthalpy exchanger solutions, few of them resolve the issue of the condensation risk inside the exchanger. A solution is however provided in EP 2 498 013, which discloses the possibility of bypassing the enthalpy exchanger in case of an outside airflow having a too high relative humidity. Nevertheless, by denying the passage thereof through the exchanger, the system undergoes a significant efficiency loss, since the energy associated with the foul airflow remains unused.
So, there is a need for optimizing these systems for air handling and air conditioning with enthalpy exchangers, especially in order to deal with the condensation risks of the highly humid outside airflow.
To address this issue, the object of the invention is first a system for air handling and air conditioning comprising at least one dual airflow enthalpy exchanger module enabling a heat transfer and a water vapour transfer between both airflows, respectively made of a first airflow and a second airflow having a temperature and an absolute humidity lower than those of the first airflow.
According to the invention, the system further includes:

- means for determining the relative humidity of the first airflow at the inlet of said enthalpy exchanger module; and
- control means configured to command a heat supply to the first airflow before it enters said enthalpy exchanger module, when the relative humidity exceeds a predetermined value.

The originality of the invention thus consists in heating, if need be, the first airflow which would be in a condition too close to the saturation curve. It is therefore cleverly performed a rising of the hottest airflow temperature. By a simple rise of its temperature, this first airflow has its relative humidity decreased, and therefore becomes less subject to the condensation risk in the exchanger module. This solution is advantageous on the one hand in that it avoids the bypass of the exchanger as suggested in prior art, and on the other hand in that the heat supply, required for maintaining the airflow at a relative humidity lower than a predetermined value, can be small.
Preferably, the system further includes a vapour compression refrigerating unit fitted with an evaporator and a condenser through which the first airflow after it leaves said enthalpy exchanger module is intended to pass, and the system is designed so that said heat supply comes from said heating unit, and preferably from part of a refrigerant fluid passing through this unit. Alternatively, the heat supply could come from the heat generated by said condenser of the refrigerating unit in operation. The heat supply would then be performed from a refrigerant fluid of the condenser, this fluid being usually air.
Other solutions are worth considering to provide this heat supply, preferably from renewable energies. Typically, it can be solar collectors, or even resistive elements. The above-described solutions aiming at drawing energy at the refrigerating unit is particularly advantageous in that it enables all or part of the unavoidable energies of the thermodynamic cycle to be recovered within such a refrigerating unit.
Preferably, the system comprises a secondary exchanger designed to provide said heat supply to the first airflow, preferably an outside airflow.
To make this secondary exchanger, any technology is possible as a function of the fluid used, namely a liquid, gas fluid or a mixture of both, and as a function of the type of energy, namely a sensible, latent or joule effect energy. In a possible embodiment, said first airflow and part of the refrigerant fluid which flows in the unit pass through the secondary exchanger, this heated fluid leaving the compressor actually enabling the necessary calories to be brought to the first airflow. Nevertheless, without departing from the scope of the invention, any other way of extracting the heat generated within the refrigerating unit is possible, in order to bring it towards the first airflow to be heated.
Preferably, the system comprises a plurality of enthalpy exchanger modules arranged in series through which said first airflow and said second airflow successively pass.
Preferably, the system is then designed so that determining the relative humidity can be performed for at least one enthalpy exchanger module, and so that the first airflow can be heated at least before it enters one of said enthalpy exchanger modules.
Even more preferentially, said control means are designed to command a heat supply to the first airflow before it enters each of said enthalpy exchanger modules, for which the relative humidity determined at the inlet of the module exceeds a predetermined value.
In this instance, the relative humidity is therefore determined at the inlet of each of the modules forming together the enthalpy exchanger. The heat supply is then individually controlled module by module, by comparison with the predetermined value which is preferentially identical for all the exchanger modules, but which could nevertheless differ as a function of the modules.
Other alternatives are possible and covered by the present invention. For example, determining the relative humidity could only be made for a restricted number n of modules, greater than or equal to one, whereas the heat supply could be applied at the inlet of a number m of modules greater than or equal to number n. By way of example, only by determining the relative humidity of the first airflow at the inlet of the first enthalpy exchanger module, the heat supply could be commanded at the inlet of one or several of the modules forming the enthalpy exchanger.
In every case, the heat supply can be regulated, for example stopped only when the relative humidity reaches the predetermined value, or the command can simply lead to the supply of a determined amount of heat, possibly as a function of the determined value of relative humidity.
In every case, multiplying the exchanger modules, and heating the outside airflow successively when it enters different exchanger modules, contributes to rationalizing the use of heat supplied to the outside airflow and to increase the maximum value of relative humidity allowed within the modules. In this connection, it is noted that with generally variable inlet conditions in the different modules, the cascade configuration enables a finer adjustment of the amounts of heat to be used, a minimum safety margin having to be taken into account, hence the notion of rationalizing the used energy. This contrasts with the single module configuration where a more significant safety margin would have to be used to be able to adapt to every possible case.
In this system which enables the energy to be used rationally while avoiding pernicious occurrences of condensation in the enthalpy exchanger, it is preferentially provided to recirculate the outside airflow and the foul airflow countercurrently in the enthalpy exchanger module. Even if a cocurrent solution is possible, the countercurrent solution is preferred for an even more rational use of the drawn energy so as to heat the outside airflow.
Preferably, each enthalpy exchanger module is a module of the waterproof-breathable membrane type, that is liquid water and air tight and water vapour permeable, whether it is a plate, tubular or other exchanger.
Preferably, the system comprises several enthalpy exchanger modules successively arranged along a stacking direction, any two directly consecutive modules having a contact area on either side of which two intermediate passage chambers of airflow are respectively arranged, each being in part delimited by an airflow outlet of one of both modules and an airflow inlet of the other of both modules.
Preferably, the system for air handling and air conditioning is preferentially intended to supply cool air inside a volume, preferably a building, said first airflow is an airflow intended to be introduced into the volume, preferably an outside airflow, and the second airflow is an airflow coming from the inside of said volume, corresponding to a foul airflow in the case where the volume is a building.
The object of the invention is also a method for air handling and air conditioning, the method being implemented using a system such as described above and including a step for determining the relative humidity of the first airflow at the inlet of said enthalpy exchanger module, and then, when the relative humidity exceeds a predetermined value, a step for commanding a heat supply to the first airflow before it enters said enthalpy exchanger module.

Further advantages and features of the invention will appear in the non-limiting detailed description thereafter.

This description will be made with reference to the accompanying drawings among which:

FIG. 1 shows a schematic view of a system for air handling and air conditioning according to a preferred embodiment of the invention;

FIG. 2 shows a view similar to that of FIG. 1, in which the enthalpy exchanger has a different design with several modules;

FIG. 3 shows a chart schematizing the control logic provided by the control means fitting the system for air handling and air conditioning shown in FIG. 2;

FIG. 4 is a schematic view similar to that of FIG. 1, in which the enthalpy exchanger comprises four modules placed in series;

FIG. 5 shows a psychrometric chart on which alphabetic references have been inscribed, these references corresponding to those indicated in the view of FIG. 4; and

FIG. 6 shows a more detailed perspective view of an enthalpy exchanger embodiment, intended to fit a system for air handling and air conditioning according to the invention.

First with reference to FIG. 1, it is shown a system for air handling and air conditioning 100, intended to supply cool air inside a building 200, preferably intended to be exposed to a hot humid climate, such as the one faced in South-East Asia. The system 100 first comprises an enthalpy exchanger 2 as well as a vapour compression refrigerating unit 4, interposed between this exchanger 2 and the building 200. Control means are associated with the enthalpy exchanger 2, and also possibly with the vapour compression refrigerating unit 4.
The enthalpy exchanger 2 is of the conventional type, that is a first outside airflow F1 and a second foul airflow F2 coming from the inside of the building 200 are advantageously intended to pass through it countercurrently, and having a temperature and an absolute humidity lower than those of the first outside airflow F1. Here, the exchanger 2 therefore guarantees a heat transfer between the foul airflow F2 and the outside airflow F1. In other words, the exchanger is provided to use the coolness contained in the foul airflow F2 in order to cool the hot outside airflow F1. It is of course noted that to transfer sensible heat from the flow F1 to the cooler flow F2, the consequence is a lowering of the temperature of the hot airflow F1 coming from the outside.
In parallel, the enthalpy exchanger 2 is provided to transfer part of the water vapour contained in the outside airflow F1 towards the foul airflow F2 having a lower water vapour concentration per kilogram of dry air (absolute humidity) when it leaves the building 200.

- In this operating mode of the system 100, corresponding to a cooling mode of the building 200, the outside airflow F1 leaving the enthalpy exchanger 2 successively passes through the evaporator 10 and the condenser 12 of the vapour compression refrigerating unit 4. In a conventional manner known from those skilled in the art, this unit 4 comprises a coolant/refrigerant fluid 14 which successively flows in a compressor 16, the condenser 12, an expansion valve 18 and the evaporator 10, before being redirected towards the compressor 16.

The outside airflow F1 first passes through the evaporator 10 in order to be cooled, humidity saturated, condensed and in order to reach the appropriate absolute humidity level for air handling, before passing through the condenser 12 in order to undergo therein a temperature increase accompanied with a relative humidity decrease, its absolute humidity remaining constant. This enables the outside airflow F1 to be brought under good humidity and temperature conditions inside the building 200.
Still with reference to FIG. 1, it is noted that one of the features of the invention is that the system further includes means 20 enabling the relative humidity of the outside airflow F1 at the inlet of the exchanger 2 to be determined. These means can be of any design considered as appropriate by those skilled in the art, such as a humidity sensor. As a function of this determination which is communicated to the control means 6, the latter are configured to command a heat supply to the outside airflow F1 before it enters the enthalpy exchanger 2, when this predetermined value of relative humidity exceeds a predetermined value.
The predetermined threshold value of relative humidity from which a sensible energy supply is activated, can be defined based on the sizing data of the enthalpy exchanger and on the knowledge of the enthalpy efficiency of the latter. This enthalpy efficiency depends on the operating conditions, the geometric data of the exchanger and the technology used. Thus, in the case of a waterproof-breathable membrane exchanger, it depends on the physical properties of said membrane, specifically those related to the water vapour transfer, such as the fickian diffusion coefficient, the maximum water intake of the membrane, and the sorption constant.
By proceeding this way, it is possible to increase the temperature of the outside airflow F1 before it enters the exchanger 2, so as to limit the condensation risks detrimental to its proper operation.
In the preferred embodiment depicted in FIG. 1, the heat supply comes from the refrigerant fluid part of which is diverted after it leaves the compressor 16. To create this diversion, it is provided a circuit 26 with a tapping 26 a upstream of the condenser 12 enabling part of the refrigerant fluid 14 to be conveyed up to the inlet of a secondary exchanger 22. At the outlet of this exchanger 22, the refrigerant fluid is redirected by the circuit 26 up to a second tapping 26 b downstream of the condenser 12, for being reintroduced in the refrigerating unit 4.
The secondary exchanger 22 has therefore passing through it on the one hand the outside airflow F1, and on the other hand part of the refrigerant fluid 14 drawn downstream of the compressor 16. The flow rate of the refrigerant fluid passing through the circuit 26 is controlled by a valve 28, controlled by the means 6. Of course, any design considered as appropriate is worth considering for the secondary exchanger 22, for example of the finned tube exchanger type.
It is noted that in the case where the energy drawn in the direction of the secondary exchanger 22 does not make it possible to reach the appropriate thermodynamic conditions before expanding the fluid in the expansion valve 18, it is provided, upstream thereof, a unit heater 27 forming an auxiliary condenser. This unit heater 27 is therefore intended to have passing through it on the one hand the refrigerant fluid 14 after it leaves the condenser 12, and on the other hand an outside airflow F3.
The amount of heat brought to the secondary exchanger 22 can be regulated, for example stopped only when the relative humidity value of the flow F1 determined by the sensor 20 reaches the predetermined value, which can possibly be input by an operator as a function of the encountered needs. This value can also take into account the design of the exchanger, according to its sensitivity to humid airflows regarding condensation risks. It is noted that this sensitivity is largely related to the transfer efficiency of water vapour through the membrane.
With reference now to FIG. 2, it is shown an alternative implementation in which the enthalpy exchanger 2 is made by a plurality of enthalpy exchanger modules M1, M2, . . . , Mi, . . . , Mn, these modules being arranged in series and having successively passing through it the outside airflow F1 and the foul airflow F2 always flowing countercurrently in each of the modules. In this example, a secondary exchanger 22 is associated with each module, present upstream of the inlet of the outside airflow F1. These exchangers are controlled by the means 6 via the valves 28, and they are also each associated with a relative humidity sensor 20 delivering the determined values to these same means 6.
The advantage of such a configuration is that it can bring heat to the outside airflow F1 before it enters each module, that is performing successive heat supplies before it passes in each module.
As schematized in FIG. 3 showing the control logic associated with each of the exchanger modules, it is for example provided, for each module Mi, that determining the relative humidity hri at the inlet of the relevant exchanger module Mi is carried out using the sensor 20. If this value hri is greater than a reference value of relative humidity hrr corresponding to the above-mentioned predetermined value, then the outside airflow F1 is heated by the associated secondary exchanger 22. This is made by controlling the valve 28 ensuring the flow of the refrigerant fluid 14 in the secondary exchanger 22. In the opposite case where the value hri remains lower than the value hrr, no operation is undertaken, that is the outside airflow F1 is not heated before it is introduced in the following module.
The reference value of relative humidity hrr can be the same at each exchanger module Mi, or can be different. By way of indicating example, this value is preferentially the same for all the exchanger modules, when the latter have an identical or similar design.
This way of proceeding makes it possible to keep permanently the outside airflow F1 with a relative humidity lower than the reference relative humidity hrr considered as critical for the enthalpy exchanger modules, simply by delivering successive heat supplies, with a small energy amount.
The embodiment of FIG. 4 is similar to that presented in FIG. 2, in that it has an enthalpy exchanger 2 with several successive modules M1, M2, M3, M4 arranged in series.
In this FIG. 4, several reference points of the foul airflow F2 and of the outside airflow F1 have been identified, at different locations along their paths between the enthalpy exchanger 2 and the building 200. These same references have been inscribed on the psychrometric chart of FIG. 5, informing about the air condition at each of these locations.
Also, with reference both to FIGS. 4 and 5, it is indicated that the outside airflow F1 at the point A, corresponding to the inlet of the exchanger 2, has a high temperature and a high relative humidity, expressing the hot humid climatic conditions of the outside air.
Before being introduced in the first module M1, the flow F1 is heated by the secondary exchanger 22 when its relative humidity exceeds the reference relative humidity. This heating is expressed by the line AA′ on the chart, the point A′ corresponding to the inlet of the first exchanger module M1. Within this module, the flow F1 is cooled and also looses its absolute humidity, which urges it to approach the saturation curve depicted in dotted lines in FIG. 5. Point A1 shows the condition of the airflow F1 at the outlet of the first module M1, before it enters the second module M2, and before its potential heating prior to its introduction in this same module M2. In a similar way to that described above, the airflow F1 is here again heated before it enters the second module M2, at a point A′1 from which it penetrates this second module M2 in order to be cooled therein and discharged from part of its humidity, until it gets out at the point A2 at which it is in a condition close to its saturation curve, as shown in FIG. 5. Analogous phenomena are observed before and during the passage of this flow F1 through the third module M3 and the fourth module M4, which explains the zigzag/cascade chart between the points A and B, respectively corresponding to the inlet points of the flow F1 in the enthalpy exchanger 2, and to the outlet point of this same flow F1 from the exchanger.
When the flow F1 is extracted from this exchanger 2, it therefore passes through the evaporator 10 up to a point C, this passage first leading to a temperature decrease bringing the flow F1 to its saturation curve, which it follows until it reaches its minimum temperature at the point C at which it also has the desired absolute humidity level. Then, the passage of the flow F1 through the condenser 12 causes it to be heated at the desired temperature to enter the building 200, and to be positioned at a relative humidity level also corresponding to the desired needs for the volume of air to be conditioned (relative to the thermal comfort specifications).
By way of indicative example, with this operating mode, the outside air can arrive at a temperature of 35° C. and a relative humidity of 90% before entering the enthalpy exchanger 2, whereas the foul airflow leaving the building 200 at the point E can have a temperature in the order of 22° C. and a relative humidity of about 50%. Also, on the psychrometric chart of FIG. 5, the line segment between points D and E may symbolize the evolution of air during its passage in the building 200, with an increase of its temperature as well as an increase of its absolute humidity level. These values related to the foul airflow F2 continue to increase between points E and F, corresponding to the passage of this flow F2 through the enthalpy exchanger 2, countercurrently with the outside airflow F1.
With reference now to FIG. 6, it is shown an exemplary implementation of an enthalpy exchanger 2 having a clever design, and comprising 5 modules placed in series, referenced M1 to M5. As in the other above-described embodiments, the exchanger modules M1 to M5 have a design with plates and waterproof-breathable membranes, known from those skilled in the art. Such exchangers are for example described in FR 2 965 897.
Indeed, this design relies on the stacking of plates along a direction 31 orthogonal to a direction 30 along which the modules succeed each other. In this embodiment, the modules are in contact in twos along the direction of their stacking 30. Also, two directly consecutive modules define together, at their median part, a contact area 34 on either side of which two intermediate passage chambers of airflow are arranged. There are first an intermediate passage chamber of the airflow F1, referenced 36, and also an intermediate passage chamber of the airflow F2, referenced 38.
As can be seen in FIG. 6, the chambers 36 are arranged staggered to each other, and the chambers 38 are also arranged staggered to each other. Each chamber 36 houses a secondary exchanger 22, which has pipes 40 for feeding and draining the refrigerant fluid, which passes through the exchanger 2 to go towards the condenser fitting the refrigerating unit of the system. Here, each enthalpy exchanger module is in the general shape of a straight prism with a hexagonal base or a diamond shaped base. Consequently, each intermediate chamber 36, 38 is in the general shape of a triangular section, a leg of the triangle being defined by an inlet of airflow of one of the modules, another leg of the triangle being defined by an outlet of airflow of the other of the modules, and the third leg corresponding to a casing 44 laterally running along the exchanger along the direction 30. Preferably, several casings 44 are formed by a same and single plate.
On the other hand, although not represented, upper and lower casings also cover the modules M1 to M5, especially making it possible to make the intermediate chambers 36, 38 independent of one another. Of course, various modifications can be brought by those skilled in the art to the invention which has just been described, only by way of non-limiting examples. In particular, the above-described application relates to the cool air supply of any building, but the invention can more generally apply to the supply of volumes of air to be handled in the field of industrial processes, such as the paper, food or micro-electronics industry.

Claims

1-10. (canceled)

11. A system for air handling and air conditioning comprising:

at least one enthalpy exchanger module including a dual airflow enabling a heat transfer and a water vapor transfer between two airflows, respectively made of a first airflow and a second airflow having a temperature and an absolute humidity lower than those of the first flow;

means for determining relative humidity of the first airflow at an inlet of the enthalpy exchanger module;

control means configured to command a heat supply to the first airflow before the first airflow enters the enthalpy exchanger module, when the relative humidity exceeds a predetermined value;

a vapor compression refrigerating unit including an evaporator and a condenser through which the first airflow can pass after it leaves the enthalpy exchanger module; and

wherein the system is configured so that the heat supply comes from the heating unit, or from part of a refrigerant fluid passing through the heating unit.

12. The system for air handling and air conditioning according to claim 11, further comprising a secondary exchanger configured to provide the heat supply to the first airflow.

13. The system for air handling and air conditioning according to claim 11, comprising a plurality of enthalpy exchanger modules arranged in series and through which the first airflow and the second airflow successively pass.

14. The system for air handling and air conditioning according to claim 13, configured so that determining the relative humidity can be performed for at least one enthalpy exchanger module, and so that the first airflow can be heated at least before the first airflow enters one of the enthalpy exchanger modules.

15. The system for air handling and air conditioning according to claim 13, wherein the control means is configured to command a heat supply to the first airflow before the first airflow enters each of the enthalpy exchanger modules, for which the relative humidity determined at the inlet of the module exceeds a predetermined value.

16. The system for air handling and air conditioning according to claim 11, configured to circulate the first airflow and the second airflow countercurrently in the enthalpy exchanger module.

17. The system for air handling and air conditioning according to claim 11, wherein each enthalpy exchanger module is a module of a waterproof-breathable membrane.

18. The system for air handling and air conditioning according to claim 11, comprising plural enthalpy exchanger modules successively arranged along a stacking direction, any two directly consecutive modules having a contact area on either side of which two intermediate passage chambers of the airflows are respectively arranged, each being partly delimited by an airflow outlet of one of both modules and an airflow inlet of the other of both modules.

19. The system for air handling and air conditioning according to claim 11, configured to supply cool air inside a volume or a building, wherein the first airflow is an airflow to be introduced into the volume or an outside airflow, and wherein the second airflow is an airflow coming from inside of the volume, or to a foul airflow in the case the volume is a building.

20. A method for air handling and air conditioning, the method being implemented using a system according to claim 11, and including determining the relative humidity of the first airflow at the inlet of the enthalpy exchanger module, and then, when the relative humidity exceeds a predetermined value, commanding a heat supply to the first airflow before the first airflow enters the enthalpy exchanger module.