JP4010354B2 - Thermal storage air conditioning equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat storage air-conditioning facility having an air conditioner and a heat storage tank as main components.
[0002]
[Prior art]
As a conventional heat storage air conditioner, there is one of Japanese Patent Application No. 2000-2752 filed earlier. This is provided with three types of ducts that connect the air conditioning device, the heat storage tank, and the air conditioning target (in the room) in communication with each other, and each of these ducts is provided with an open / close valve that can be driven to open / close and a control device. The combination of ON / OFF of the device and the opening / closing operation of the three on-off valves, (b) a heat storage mode in which the air conditioner is operated to store heat in the heat storage tank, and (b) air conditioning in which the air conditioner is operated by operating the air conditioner (C) The air conditioner is operated to store heat in the heat storage tank, and a plurality of operation modes such as a heat storage air conditioning mode for air-conditioning the air-conditioning target can be performed.
[0003]
[Problems to be solved by the invention]
In the heat storage air-conditioning equipment according to the prior art, in order to be able to perform the various operation modes (A) to (C), a total of three drive type opening / closing valves provided for each duct are used. There are many moving parts, the control is relatively complicated, and it is necessary to carry out inspection and maintenance to make the valve open and close normally without malfunction. It was something that never happened.
[0004]
An object of the present invention is to provide a heat storage air conditioner capable of various operation modes, and to simplify the structure such as reducing the number of on-off valves, and to have excellent reliability with less risk of malfunction. In the point.
[0005]
[Means for Solving the Problems]
As shown in FIG. 1, in the heat storage air conditioning system, the structure of claim 1 includes a blower path 3 for supplying air to the plurality of rooms r and a return path 11 for taking in return air from the plurality of rooms r. A pair of air supply / exhaust ports 1a and 1b of the heat storage tank 1 and an air discharge port 2a of the air conditioner 2 are connected to the air passage 3 and a pair of the heat storage tank 1 are connected in parallel. The other 1b of the air supply / exhaust ports 1a and 1b and the air suction port 2b of the air conditioner 2 are connected to the return path 11, and the air conditioner 2 is provided with an output fan 2c that can variably set the discharge air volume per unit time. A plurality of blower fans 12 for forcibly transferring the air in the air passage 3 to each of the plurality of living rooms r in correspondence with each of the plurality of living rooms r.
A first state in which the air suction port 2b or the air discharge port 2a is closed and the air blowing path 3 is opened; and a second state in which the air suction port 2b, the air discharge port 2a and the air blowing path 3 are all opened. The air switching port 7 is provided with a path switching means 7 that can be switched between a third state where the air suction port 2b and the air discharge port 2a are opened and the air passage 3 is closed,
When the blower fan 12 forcibly transferring the air in the blower passage 3 toward the air conditioning target R is provided in the blower passage 3 and the route switching means 7 is switched to the second state, the unit time of the plurality of blower fans 12 is set. The present invention is characterized in that an air volume control means 8 is provided which can control the magnitude relationship between the total amount of blown air and the discharge air volume per unit time of the output fan 2c .
[0006]
According to the configuration of claim 1, the heat stored in the heat storage tank by switching the path switching means to the first state and operating the blower fan will be described in detail in the section of the embodiment. It is possible to perform a heat dissipation mode in which the conditioned air is supplied to the air conditioning target. The air flow at this time forms an open heat storage path of return path → heat storage tank → blower path (blower fan) → air conditioning target → return path. Next, it is possible to perform a heat storage mode in which the air storage device stores heat in the heat storage tank by switching the route switching means to the third state and stopping the blower fan and air-conditioning the air-conditioning device. The air flow at this time becomes a closed circulation path of air conditioner → air blowing path → heat storage tank → return path → air conditioner.
[0007]
Then, the route switching means is switched to the second state, and the air blower is operated and the air conditioner is air-conditioned, that is, by the air volume control means, the air flow per unit time of the blower fan and the air conditioning By controlling the magnitude relationship with the discharge air volume per unit time of the apparatus, the following three operation modes are possible.
[0008]
First, when the discharge air volume per unit time of the air conditioner is larger than the air flow volume per unit time of the blower fan, the heat storage air conditioner is supplied to both the heat storage tank and the blower fan, that is, the air conditioning target. The mode can be done. The air flow at this time is a closed circulation path of return path → air conditioner → blower path → heat storage tank → return path, and an open air conditioning path of return path → air conditioner → blower path (fan fan) → air conditioning target → return path Both exist.
[0009]
Next, when the discharge air volume per unit time of the air conditioner is the same as the air flow rate per unit time of the blower fan, all of the air conditioned air is supplied to the blower fan, that is, the air conditioning target and does not go to the heat storage tank. Mode is performed. The air flow at this time becomes an open air conditioning path of return path → air conditioner → air blowing path (fan) → air conditioning target → return path. When the air flow per unit time of the blower fan is larger than the amount of air discharged per unit time of the air conditioner, both the heat stored in the heat storage tank and the air conditioned air from the air conditioner are subject to air conditioning by the blower fan. The heat radiation air-conditioning mode supplied to is performed. The air flow at this time includes both the above-described open heat storage path and the open air conditioning path.
[0010]
1, 4, 5, and 6, the air volume control means 8 is configured such that the air volume control means 8 is the sum of the air flow per unit time of the plurality of air fans 12. However, the heat radiation air-conditioning control state in which the discharge air volume per unit time of the output fan 2c is larger and the air flow volume per unit time of the plurality of blower fans 12 are smaller than the discharge air volume per unit time of the output fan 2c. The heat storage air-conditioning control state, and the air-conditioning control state in which the total amount of airflow per unit time of the plurality of blower fans 12 and the amount of discharge airflow per unit time of the output fan 2c are configured to be selectable. It is characterized by being.
[0011]
According to the configuration of claim 2, in the second state in which the air suction port, the air discharge port, and the air passage are all open, the magnitude relationship between the discharge air of the air conditioner and the air volume of the blower fan is positively controlled. By doing so, a desired operation mode state can be set and maintained. That is, if it is in the heat dissipation air-conditioning control state in which the air flow rate per unit time of the blower fan is larger than the air discharge rate per unit time of the air conditioner, the airflow by the air conditioner and the heat dissipation due to passing through the heat storage tank It is possible to obtain a heat radiating air-conditioning mode in which the air-conditioning target is air-conditioned by both winds. Moreover, if the heat storage air-conditioning control state in which the air flow rate per unit time of the blower fan is smaller than the air discharge rate per unit time of the air conditioner, the air conditioner air from the air conditioner is supplied to both the air conditioning target and the heat storage tank. It is possible to obtain a heat storage air conditioning mode to be supplied to the vehicle. Moreover, the air-conditioning mode in which all of the air-conditioning air is just supplied to the air-conditioning target can be obtained by matching the air-flow rate per unit time of the blower fan with the discharge air amount per unit time of the air-conditioning apparatus. That is, it becomes possible to reveal an air conditioning operation state by a general air conditioner having no heat storage tank.
[0014]
In addition, as mentioned above, although the code | symbol was written in order to make contrast with drawing convenient, this invention is not limited to the structure of an accompanying drawing by this entry.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 show a heat storage air conditioner A applied to a private house. The heat storage air conditioning equipment A includes a heat storage tank 1 disposed in a part of a living space such as a close-in, an air conditioner 2 disposed immediately above the heat storage tank 1, and a main duct (air blower) for sending conditioned air to the room R. An example of a path) 3. Individual ducts 4 and 5 which are the front end portions of the main duct 3 arranged behind the ceiling in order to branch the conditioned air sent from the main duct 3 and send it to the respective rooms r1 and r2. An air blowing mechanism 6 provided for each of the ducts 4 and 5, a path switching means 7 provided mainly on the air discharge side of the air conditioner 2, an air volume control means 8, and the like are provided.
[0016]
The operation mode of the heat storage air conditioning equipment A is the air conditioner operation state in each of the rooms r1 and r2, that is, the heat stored in the heat storage layer 1 by the ON / OFF of the air blowing mechanisms 6 and 6, the operation of the air volume control means 8, etc. Supplying conditioned air from each room r1 and r2 to be air-conditioned (1) Heat radiation mode, heat storage layer 1 is stored by the air conditioner 2, and neither room r1 or r2 is air-conditioned (2) The heat storage mode and the air discharged from the air conditioner 2 are supplied to both the heat storage tank 1 and the blower mechanism 6 (ie, the rooms r1 and r2). (3) The heat storage air conditioning mode and the heat of the heat storage tank 1 are not used. The air conditioner 2 alone is used for air conditioning. (4) The air conditioning mode and the heat stored in the heat storage layer 1 and the air discharged from the air conditioner 2 are used to air-condition the rooms r1 and r2. Five types of operation modes can be performed.
[0017]
Next, the structure of each part will be outlined.
The heat storage tank 1 and the air conditioner 2 are arranged in the closet s on the first floor or the second floor, and face the air supply / exhaust ports 1a, 1b of the heat storage tank 1, and the air supply / discharge space 10, 11 is formed. One air supply / exhaust port 1a is connected to the base end side of the main duct 3 through one air supply / exhaust space 10 and the other air supply / exhaust space 11 facing the other air supply / exhaust port 1b. Is connected to the air return port 9 facing the first room r1.
[0018]
The air conditioner 2 includes an air discharge port 2a communicating with the main duct 3 and one air supply / discharge space 10, an air return port 2b communicating with the other air supply / discharge space 11 (an example of a return path), and an output fan 2c. And is configured. The drive motor (not shown) of the output fan 2c has a variable rotational speed by inverter control or the like, and is configured to be able to variably set the discharge air volume per unit time as the air conditioner 2.
[0019]
The blower mechanism 6 includes a blower fan 12 disposed in each individual duct 4, 5 and a damper 13. The damper 13 is composed of a guide plate that is swingable at a fulcrum x provided at the upper end in the individual ducts 4, 5. The damper 13 is lifted and swung by the wind pressure driven by the blower fan 12 to open the individual ducts 4, 5. The fan 12 is configured to be a non-driving type in which the individual ducts 4 and 5 are closed by dropping their own weight when the fan 12 stops.
[0020]
The main part of the path switching means 7 is configured at a location where the main duct 3 is connected to the air discharge port 2a, and part of the path switching means 7 is also configured in each of the air blowing mechanisms 6 and 6. Specifically, a guide plate 14 that is swingable at a fulcrum P provided at a corner portion on the upper side of the intersection of the main duct 3 and the air discharge port 2a, and the guide plate 14 can be driven to swing and maintain freely. The path switching means 7 is constituted by the simple drive motor 15 and the aforementioned dampers 13 and 13.
[0021]
The action of the path switching means 7 is that the air discharge port 2a is closed by operating to the first position t1 where the guide plate 14 is suspended, and the one air supply / discharge space 10 and the main duct 3 are opened. In the first state, the guide plate 14 is operated to the second position t2 that is inclined so that the front end of the guide plate 14 is located in the middle in the width direction of the main duct 3 (one air supply / discharge space 10). Any of the passages 3 can appear in the second state where the passage 3 is opened to the one air supply / discharge space 10.
[0022]
Then, in a state where the guide plate 14 is maintained at the second position t2, any of the air blowing mechanisms 6 and 6 is stopped and both the guide plates 13 and 13 are suspended (both the individual ducts 4 and 5 are closed). The main duct 3 can be closed, and the air discharge port 2a can appear in the third state where the air supply / discharge space 10 is opened. Although not used in this embodiment, the main duct 3 is closed regardless of the air blowing mechanisms 6 and 6 by moving the guide plate 14 upward and swinging into a recumbent posture, and the air discharge port. 2a can also appear in the third state opened to one air supply / discharge space 10.
[0023]
As shown in FIG. 1, drive motors 12 a and 12 a for each blower fan 12, drive motor 15 for the guide plate 14, air conditioner 2, and mode switch 16 are connected to a control device 17 to drive control circuit L. Is configured. The air volume control means 8 is provided as a part of the control device 17 as one control form in various controls. Next, various operation modes of the heat storage air-conditioning equipment A that are mainly generated by the function of the air volume control means 8 will be described.
[0024]
As a precondition, the amount of air flow per unit time in the steady operation state in the air blowing mechanism 6 of the first living room r1 is f1, and the amount of air flow per unit time in the steady operation state of the air blowing mechanism 6 in the second living room r2 is set. It is assumed that f1 + f2 = F, where F2 is the discharge air volume per unit time in the steady operation state in the air conditioner 2. In the drawing, the air conditioner 2 and each blower fan 12 are painted black in the activated state and outlined in the stopped state.
[0025]
(1) The heat radiation mode is obtained by switching the changeover switch 16 to the first operation position (1) as shown in FIG. That is, in the state where the guide plate 14 is operated to the first position t1 and the air conditioner 2 is stopped, one of the air blowing mechanisms 6 is driven (in FIG. 2, both the air blowing mechanisms 6 are driven). Have been). The air flow in this heat radiation mode is such that the air sucked from the air return port 9 passes through the other air supply / exhaust space 11 and the heat storage tank 1 due to the negative pressure generated by the rotation of the air blowing fan 12. The air sent from the air duct 10 to the main duct 3 and the individual duct 4 (5) and sent out by the blower fan 12 passes through the blowout gallery 18 (see FIG. 1) mounted on the ceiling to the intended room r1 (r2). It becomes an open heat storage path to be supplied. Heating is performed when the heat storage in the heat storage tank 1 is hot, and cooling is performed when the heat storage is cold.
[0026]
(2) The heat storage mode is obtained by switching the changeover switch 16 to the second operation position (2) as shown in FIG. That is, this is an operation mode in which the guide plate 14 is operated to the second position t2, the air conditioner 2 is air-conditioned, and all the air blowing mechanisms 6 and 6 are stopped. In this heat storage mode, the air flow is such that the conditioned air blown from the discharge port 2a of the air conditioner 2 passes through one air supply / discharge space 10, the heat storage tank 1, and the other air supply / discharge space 11 in this order. It forms in the closed circulation path | route which returns to the air conditioner 2 from the opening 2b. In this heat storage mode, the air return port 9 communicates with the outside in the closed circulation path, but since there are no other places communicating with the outside, the air return is substantially impossible. Air circulation from the mouth 9 does not occur.
[0027]
(3) The heat storage air conditioning mode can be obtained by switching the changeover switch 16 to the third operation position (3) as shown in FIG. That is, this is an operation mode in which the guide plate 14 is operated to the second position t2, the air conditioner 2 is air-conditioned, and, for example, the air blowing mechanism 6 only in the first room r1 is operated. In this case, the required air volume per unit time of the air conditioning target R is f1, the discharge air volume per unit time of the air conditioner 2 is F, and f1 <F is satisfied.
[0028]
Therefore, the air flow in this heat storage air-conditioning mode is that the air-conditioning wind emitted from the discharge port 2a of the air conditioner 2 is one air supply / discharge space 10, the heat storage tank 1, the other air supply / discharge space 11, and the air return port 2b. The closed circulation path returning to the air conditioner 2 in this order, and the conditioned air from the discharge port 2a of the air conditioner 2 pass through the main duct 3, the individual duct 4, and the air blowing mechanism 6 in a desired room (r1 etc.) Both the open air-conditioning path sent to the are formed. That is, both the heat storage operation to the heat storage tank 1 and the air conditioning operation of the air conditioning target R are performed.
[0029]
In addition, when the air blowing mechanisms 6 and 6 of both the rooms r1 and r2 are operating, the required air volume as the air conditioning target R and the discharge air volume of the air conditioner 2 coincide (f1 + f2 = F). Control is performed to increase the rotational speed of the output fan 2c so that the output of the device 2 is increased and f1 + f2 <F is established. As described above, the air volume control means 8 is configured such that when any operation mode is selected by operating the changeover switch 16, the selected operation mode appears regardless of the operation state at that time. A function of adjusting and controlling each part is provided.
[0030]
(4) The air conditioning mode is obtained by switching the changeover switch 16 to the fourth operation position (4) as shown in FIG. That is, this is an operation mode when the guide plate 14 is operated to the second position t2, for example, the air conditioner 2 is air-conditioned and both the air blowing mechanisms 6 and 6 are activated. In this case, since f1 + f2 = F is established as described above, all the discharge air from the air conditioner 2 is supplied from the main duct 3 to the living rooms r1 and r2, and is not supplied to the heat storage tank 1. In short, this is an operation mode in which the same state as the air-conditioning state by a general air conditioner can be obtained.
[0031]
However, if the air conditioning of one of the first living rooms r1 is turned off in the above state and the operation state is switched to only one of the air blowing mechanisms 6, f2 <F (or f1 <F) is established and the heat storage air conditioning mode is set. Therefore, in that case, the air volume control means 8 controls the air conditioner 2 so that the rotational speed of the output fan 2c is decreased to satisfy f2 = F (or f1 = F). In addition, when f1 = f2 = F is a precondition, when only one of the living rooms r1 or r2 is operating, the air conditioner 2 is steadily operated, and the air blowing mechanisms 6 of both the living rooms r1 and r2 are operated. When No. 6 is activated, the air volume control means 8 performs control so as to increase the rotational speed of the output fan 2c so that f1 + f2 = F is established.
[0032]
(5) The heat radiation air conditioning mode is obtained by switching the changeover switch 16 to the fifth operation position (5) as shown in FIG. That is, when the guide plate 14 is operated to the second position t2, for example, when both the air blowing mechanisms 6 and 6 are operating, the rotational speed of the output fan 2c is slower than that during steady operation by the air volume control means 8. To be controlled.
[0033]
As a result, the air-conditioning air discharged from the discharge port 2a passes through the main duct 3, the individual ducts 4 and 5, the air blowing mechanisms 6 and 6, and is supplied to the two-sided rooms r1 and r2, and the air return port 9 The air sucked from the other air supply / discharge space 11, the heat storage tank 1, the one air supply / discharge space 10, the main duct 3, the individual ducts 4, 5, and the air blowing mechanisms 6, 6, the living room r 1, Both the open heat storage path supplied to r2 are formed.
[0034]
When the air blowing mechanism 6 of only one room r1 or r2 is operated, the air flow rate control means 8 controls so that the rotational speed of the output fan 2c is greatly reduced and f1> F or f2> F is established. It is done.
[0035]
As described above, in (1) heat dissipation mode in which the air conditioner 2 is stopped and (2) heat storage mode in which both the air blowing mechanisms 6 and 6 are stopped, the operation mode at that time is determined, but (3) The heat storage air-conditioning mode, (4) air-conditioning mode, and (5) heat-dissipating air-conditioning mode are determined for the first time by determining the air volume relationship between the blower mechanism 6 and the air-conditioning device 2, but the air volume control means 8 having the changeover switch 16. Therefore, if one of these five types of operation modes is selected, the selected operation mode state is maintained as a convenient and convenient heat storage air conditioning facility A.
[0036]
[Another embodiment]
<< 1 >> As shown in FIG. 7, the path switching means 7 includes a first position t <b> 1 that blocks the air discharge port 2 a, a second position t <b> 2 that blocks neither the air discharge port 2 a nor the main duct 3, and the main duct 3. A guide plate 19 having a three-position switching structure with the third position t3 to be closed and its drive motor 20 may be provided. That is, if the guide plate 14 is operated to the first position t1, the first state is obtained, if operated to the second position t2, the second state is obtained, and if operated to the third position t3, the third state is obtained. It is.
[0037]
<< 2 >> As shown in FIG. 8, the air discharge port 2a is replaced with a freely openable / closable guide plate 14, and can be oscillated and switched between a fourth position t4 for closing the air return port 2b and a fifth position for opening. A two-position switching type guide mechanism comprising an oscillating plate 21 and its drive motor 22 is provided, and the path switching means 7 is constituted by the oscillating plate 21 that is driven and oscillated and the pair of dampers 13 and 13. May be. That is, when any one of the dampers 13 is opened and the swing plate 21 is operated to the fourth position t4 to close the air return port 2b, the first state appears, and any of the dampers 13 and 13 is also closed. In addition, the second state is obtained by operating the swing plate 21 to the fifth position t5 to open the air return port 2b, one of the dampers 13 and 13 is opened, and the swing plate 21 is opened. Is operated to the fifth position t5 to open the air return port 2b, whereby the third state is obtained.
[0038]
<< 3 >> The air-conditioning target R may have three or more living rooms r. In short, the air volume control unit 8 is configured so that the air volume control unit 8 per unit time of the air-conditioning apparatus 2 and the unit time actually sent to the air-conditioning target R What is necessary is just to control the relationship with the blast volume.
[0039]
【The invention's effect】
In the heat storage air-conditioning equipment according to claim 1, path switching means for switching between opening and closing of a pair of air supply / exhaust spaces related to the heat storage tank via the air conditioner and opening / closing states of the air passages for sending the air-conditioned air to the air-conditioning target When the path switching means is in the second state, by providing an air volume control means capable of controlling the magnitude relationship between the air volume per unit time of the blower fan and the discharge air volume per unit time of the air conditioner, A heat dissipation mode that air-conditions the air-conditioning target by storing heat in the heat-storage tank, a heat-storage mode that stores heat in the heat-storage tank with the air-conditioning device, a heat-storage air-conditioning mode that stores heat in the heat-storage tank with the air-conditioning device, and air-conditions the air-conditioning target. It was possible to provide a reasonable operation mode that allows one operation mode to be selected from various operation modes such as an air conditioning mode and a heat radiation air conditioning mode.
[0040]
In the heat storage air-conditioning facility according to claim 2, the air-conditioning air-conditioning system that achieves the above-described effect by the configuration of claim 1 and that the air blowing amount per unit time of the blower fan is larger than the discharge air amount per unit time of the air conditioner. The air volume control means controls the control state and the heat storage air-conditioning control state in which the air flow rate per unit time of the blower fan is smaller than the discharge air volume per unit time of the air conditioner, that is, the heat dissipation air conditioning mode and the heat storage air conditioning mode. Selectable and configurable, making it practical and convenient.
[0041]
In the heat storage air-conditioning facility according to claim 3, the effect of the configuration according to claim 2 is achieved, and the air volume control unit is configured to perform the function of the air volume control unit and the air volume per unit time of the blower fan and the unit of the air conditioner. An air-conditioning control state in which the discharge air volume per hour coincides, that is, an air-conditioning mode, can be realized, and an advantage of improving practical convenience is obtained.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a heat storage air conditioner and its control system. FIG. 2 is an operation diagram of the heat storage air conditioner showing a heat release mode state. FIG. 3 is an action diagram of the heat storage air conditioner showing a heat storage mode state. FIG. 5 is an operation diagram of the heat storage air-conditioning equipment showing the air-conditioning mode state. FIG. 6 is an operation diagram of the heat-storage air-conditioning equipment showing the heat-radiation air-conditioning mode state. FIG. 8 is a schematic diagram showing another structure of the path switching means.
DESCRIPTION OF SYMBOLS 1 Heat storage tank 1a, 1b Air supply / exhaust port 2 Air conditioner 2a Air discharge port 2b Air suction port 3 Air supply path 7 Path switching means 8 Air volume control means 11 Return path 12 Blower fan R Air-conditioning object

Claims (2)

Between a ventilation path for supplying air to a plurality of rooms and a return path for taking in return air from the plurality of rooms,
In order to connect in parallel, one of the pair of air supply / exhaust ports of the heat storage tank and the air discharge port of the air conditioner are connected to the air flow path, and the other of the pair of air supply / discharge ports of the heat storage tank, Connect the air inlet of the air conditioner to the return path,
The air conditioner is equipped with an output fan that can variably set the discharge air volume per unit time,
A plurality of blowing fans for forcibly transferring the air in the ventilation path to each of the plurality of living rooms is provided in the ventilation path so as to correspond to each of the plurality of living rooms,
A first state in which the air suction port or air discharge port is closed and the air passage is opened; a second state in which the air suction port, the air discharge port, and the air passage are all opened; A path switching means is provided that is capable of switching between a third state in which the air suction port and the air discharge port are opened and the air blowing path is closed;
When the path switching means is switched to the second state, the magnitude relationship between the total amount of airflow per unit time of the plurality of blower fans and the amount of discharge airflow per unit time of the output fan can be controlled. Heat storage air conditioning equipment with a simple air flow control means. The air volume control means includes a heat dissipating air-conditioning control state in which a total air flow per unit time of the plurality of blow fans is larger than a discharge air flow per unit time of the output fan, and a unit of the plurality of blow fans. The heat storage air-conditioning control state in which the total air flow per hour is smaller than the discharge air flow per unit time of the output fan , the total air flow per unit time of the plurality of air fans, and the output fan The heat storage air-conditioning equipment according to claim 1, wherein the air-conditioning control state in which the amount of discharge air per unit time coincides is freely selectable.

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