The present invention relates to an arrangement in connection with an air conditioning unit, comprising means for conveying exhaust and supply air through the air conditioning unit, a heat recovery unit having at least two stages and means for introducing additional heat or cooling power into the supply air.

Arrangements of this kind are nowadays common in air conditioning solutions for buildings. Energy is transferred from air to air mainly indirectly through heat exchangers. Ventilating installations are today almost without exception provided with heat recovery units. Also indirect evaporative cooling has increas- ingly been introduced into the market. In such cooling, exhaust air is cooled by humidification, whereafter the temperature effect will be transferred through a heat recovery stage to the supply air, which is cooled. The heat recovery unit may be a plate heat exchanger, a rotor, a radiator combination operating with a fluid, or a heat pump, depending on the requirements on hygiene, technical requirements and space solutions.

Despite the good efficiency of heat recovery units, additional heat is normally needed in ventilation installations in order for the temperature of the supply air not to be too low, in particular if the amount of energy transmitted from the exhaust air must be limited on account of frosting of the exhaust air. The additional heat has conventionally been introduced into the supply air after the heat recovery unit with a water radiator or an electric heater. The use of electricity for heating of air is, however, questionable, and this will be a growing trend in the future. The exhaust air side of heat recovery units becomes frosted when the humidity in the exhaust air is condensed onto the

surface of the heat recovery unit if the surface temperature of the heat recovery unit is below zero. Depending on the relative humidity of the exhaust air, this will take place when the outdoor temperature is - 15°C or lower. The defrosting of a plate heat exchanger, for example, takes place in such a way that part of the supply air is conveyed past the plate heat exchanger, or the entry of supply air to various sections of the heat exchanger in turn is prevented, which will make the warm exhaust air defrost the frosted areas. During the defrosting step, the efficiency of heat recovery will be impaired. The operation of the frosting step and anti- freezing of the additional heating radiator requires special automatics and also electro-mechanical devices in order that the operation may be realized.

It is an object of the invention to provide an arrangement wherewith the drawbacks of the prior art can be eliminated. This has been achieved with the arrange¬ ment of the invention, which is characterized in that the means for introducing additional heat or cooling power into the supply air comprise at least one heating device or/and cooling device disposed between the stages of the heat recovery unit in the exhaust air flow or separate air flow or a combined heating-cooling device adapted to change the temperature of the exhaust air and thereby to influence the temperature of the supply air indirectly through the heat recovery unit.

An advantage of the invention is first of all its good basic heat recovery efficiency and very high community thermal energy efficiency in the heating and/or cooling stage. Furthermore, the overall solution is inexpensive and easy and reliable in operation and has a low consumption of electricity. The good thermal energy efficiency in the heating stage is based on the possibility to use low-grade thermal energy, such as

waste heat or condensation heat, which may even be free of cost if it is not reclaimable in any other manner. The low consumption of electricity is based on the fact that the radiator surfaces are effectively utilized in all stages, and thus the air flow includes no components causing extra air resistance. The plate heat exchanger is not provided with a liquid pump consuming elec¬ tricity. The conventional components provided in the supply and exhaust air flows can advantageously supplement the outcome. In winter, the supply air flow passes through the first stage of the heat exchanger and is heated by the exhaust air, whereafter it is trans¬ ferred to the following stages of heat recovery, in which the temperature reaches a basic level that may be sufficient as such. If this is not enough in the case of air heating, for example, the supply air passes through an additional heating radiator. Since the additional heating radiator is connected in series with the exhaust air heating radiator, these may have a control circuit in common.

In summer, the supply air flow may by-pass heat exchangers through a by-pass route, for example, if no change of state is desired. If the system is provided with humidifying cooling of the exhaust air, the supply air is cooled stepwise in passing through the heat recovery stages. If the temperature is not low enough, it is possible to provide the supply air flow with a cooling radiator.

In winter, the exhaust air flow first passes through the last heat recovery stage on the supply air side, which will decrease the temperature of the exhaust air. Thereafter the radiator in the exhaust air flow will heat the exhaust air before it is passed to the next heat recovery stage, delivering its additional thermal energy and possibly the thermal energy remaining

from the preceding stage or part of it to the supply air through the heat recovery unit.

In summer, it is possible to cool the exhaust air flow by humidifying either in one stage in connec- tion with the heat recovery stages or in separate humidifiers in the flow direction of the exhaust air prior to the heat recovery stages. If this is not suf¬ ficient, the heating radiator provided in the exhaust air flow can be used as a cooling radiator. Additional power can be achieved by furnishing the supply air flow either with a separate cooling radiator or a combined heating and cooling radiator connected in series with the radiator in the exhaust air flow.

The essential difference to conventional oper- a ion is that the temperature of the additional energy may be at a lower level, since in normal operation there is no risk of freezing, while the temperature difference of the heated medium and the heat-delivering medium can still be advantageous. With the conventional arrange- ment, the temperature of the heating medium in the inlet pipe cannot be lower than 30-40°C, which is the normal temperature of water when ventilation is stopped. As a rule, the design temperature for normal use is +60° in and +40° out. With the invention, an energy source may well be used having a temperature of +25°C, for example, in which case the corresponding temperatures may be +25°C in and +20°C out, since the purpose is to heat exhaust air having a temperature above 0°C, yet lower than the temperature of the air exiting the room. At the same time, the automatics can be simplified as regards anti-freezing, anti-frosting and possibly temperature control. Also varying water flows can be passed through the additional heating radiator(s) without any risk of the water becoming frozen. In the following the invention will be explained

in greater detail by means of preferred embodiments shown in the accompanying drawing, in which

Figure 1 is a schematic side view of a preferred embodiment of an arrangement of the invention, Figure 2 is a schematic side view of a second embodiment of the arrangement of the invention,

Figure 3 is a schematic side view of a third embodiment of the arrangement of the invention,

Figure 4 is a schematic side view of a fourth embodiment of the arrangement of the invention,

Figure 5 is a schematic side view of a fifth em¬ bodiment of the arrangement of the invention,

Figure 6 is a schematic side view of a sixth em¬ bodiment of the arrangement of the invention, Figure 7 is a schematic side view of a seventh embodiment of the arrangement of the invention,

Figure 8 is a schematic side view of an eighth embodiment of the arrangement of the invention,

Figure 9 is a schematic side view of an altern- ative implementation of the embodiment of Figure 8,

Figure 10 is a schematic side view of a second alternative implementation of the embodiment of Figure 8, and

Figure 11 is a schematic side view of an altern- ative implementation of a detail of the arrangement of the invention.

In Figure 1, reference numeral 1 denotes the first stage and reference 2 the second stage of a heat recovery arrangement in the flow direction of supply air. These stages are plate heat exchangers. Reference 3 denotes an additional heating device located between the heat recovery stages, e.g. an additional heating radiator, operating if desired at a low temperature level, for example with waste heat or condensation heat that is supplied to the radiator through service pipes

8. It is to be noted that Figure 1 is simplified over against the actual construction, wherefore the figure is to be understood only as a symbolic representation.

Reference 14 in Figure 1 denotes the jacket of an air conditioning unit, reference 15 a supply air fan and reference 16 an exhaust air fan or separate air fan. In this context, separate air denotes other air than exhaust air from the ventilation, which delivers energy to the supply air or in which a change of state indirectly affects the state of the supply air. An example of separate air could be outdoor air or a mixture of outdoor air and indoor air. Reference 17 denotes a possible supply air filter and reference 18 a possible exhaust air filter, respectively. Reference 19 denotes a possible damper for supply air and reference 20 a possible damper for exhaust air. In addition to these details, the apparatus can be provided with conventional components, such as an air mixing unit, electrical outfit, etc. Figure 1 clearly shows the main idea of the invention, i.e. that the means for introducing addi¬ tional heat or cooling power into the supply air com¬ prise at least one heating device or cooling device 3 disposed between the stages 1, 2 of the heat recovery unit in the exhaust air flow or separate air flow, adapted to change the temperature of the exhaust air and thereby to influence the temperature of the supply air indirectly through the heat recovery unit.

Figure 1 additionally shows one possible embodi- ment. Reference 27 denotes a device consuming thermal energy and reference 28 a heat-delivering device, respectively. The device 27 consuming thermal energy or/and the heat-delivering device 28 is/are preferably connected to the same liquid circuit in series with the heating or cooling device 3, and further at a point up-

stream of the heating or cooling device 3 in the liquid flow direction.

The embodiment of Figure 2 shows a heat recovery arrangement in which references 1 and 2 denote the stages of the heat recovery unit, reference 3 an addi¬ tional heating radiator and reference 8 service pipes. Reference 13 denotes an air flow by-pass duct system wherein damper 12 controls the air flow. The damper 12 can be used in summer conditions, for instance, when it is not desired to transfer thermal energy to the supply air.

Figure 3 illustrates by references 1 and 2 the stages of the heat recovery unit and by means of reference 3 a heating air radiator that is located between the heat recovery stages in the exhaust air flow. Reference 4 denotes a heating radiator in the supply air flow; the piping of the liquid side of this radiator is connected in series with the heating radi¬ ator 3 indirectly affecting the temperature of the supply air. Both radiators can be controlled with a single common automatic control circuit, for instance. In this embodiment, the radiator 3 indirectly affects the supply air flow through the heat recovery unit, and radiator 4 affects it directly on account of being located in the supply air flow.

Figure 4 shows an arrangement in accordance with Figure 1, to which an exhaust air humidifier denoted by reference 5 has been incorporated. This humidifier may be a separate humidifier, a humidifying nozzle or a heat recovery unit provided with a humidification arrange¬ ment. It is possible to duplicate the solution in connection with each stage of the heat recovery unit, or upstream of the heat recovery unit in the flow direction of the exhaust air. It is evident that devices 27 and 28 can also be

incorporated into the embodiments of Figures 2-4 as shown in Figure 1.

Figure 5 shows an arrangement in accordance with Figure 4, in which the additional heating radiator 6 has two functions, i.e. heating and cooling. These functions can be performed with the same radiator 6.

Figure 6 shows two stages 1 and 2 of the heat recovery unit and a humidifier 5. A combined radiator 6 enabling heating and cooling is operationally - i.e. on the liquid side - connected with pipes 11 in series with a second combined radiator 7 provided in the supply air flow. By this arrangement, it is possible to enhance the effect of the heating and cooling stages. In this embodiment, radiator 6 indirectly affects the supply air flow through the heat recovery unit, and radiator 7 affects it directly on account of being located in the supply air flow.

Figure 7 shows the basic idea of the solution of Figure 1 implemented with rotary recovery cells illus- trated by references 21 and 22. Other operational alternatives can be implemented in a corresponding way. Radiator 3 is located in the exhaust air flow.

Figure 8 correspondingly shows the basic idea of the solution of Figure 1 implemented with a radiator solution employing some medium. Radiators provided in the supply air flow are denoted by references 23 and 24 and radiators provided in the exhaust air flow by references 25 and 26, respectively.

With regard to the solution of Figure 8, it can be stated that a particularly preferred embodiment is achieved by connecting radiators 23-26 in series in the same flow circuit on the counter-current principle, as shown in Figure 9. Furthermore, for example radiators 23 and 24 can be combined into radiator 234 and radiators 25 and 26 can be separate, as shown in Figure 10. It is

naturally also possible to implement this constructional alternative vice versa.

The heating device and/or cooling device 3 can also be fitted in a by-pass duct 110 as shown in Figure 11. Figure 11 is based on Figure 8. Figure 11 shows only the radiators 25, 26 on the exhaust air side, in other respects the embodiment of Figure 11 corresponds to the embodiment of Figure 8. In this embodiment, the air flow can be directed with baffle 111 to pass via by-pass duct 110 through the heating device 3, or alternatively directly in such a way that the air does not flow into by-pass duct 110, but past the heating device 3. It is also possible to make the construction such that one of the radiators of the heat recovery unit can be by- passed. Also this detail is shown in Figure 11, wherein reference 112 denotes a second baffle that can be turned into the positions shown in the figure, thus enabling the air flow to be directed in the desired manner. Figure 11 shows various possibilities for air flow by means of arrows.

Devices 27 and 28 in accordance with Figure 1 can also be incorporated into the embodiments of Figures

5-8, as has been explained in connection with Figure 1.

The above exemplary embodiments are not to be construed as limiting the invention, but the invention can be modified with complete freedom within the purview of the claims. It will be appreciated that the arrangement of the invention or its details need not necessarily be exactly as shown in the figures, but other kinds of solutions are possible as well. It is to be noted, for example, that even though the figures present solutions in which one radiator located between the heat recovery stages and one radiator fitted in the supply air flow, this is not the only possibility, but it is possible to use more radiators at these points,

etc. Even though the figures primarily illustrate embodiments with a plate heat exchanger, the invention is well suitable for other equipment stated above, or combinations of such equipment.