JP2002115939A - Heat pump system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid danger such as explosion, etc., due to leakage of a combustible refrigerant in a heat pump system using the refrigerant. SOLUTION: The heat pump system 100 comprises a sensor 5 for detecting the leakage of a refrigerant in a frame 1 of an outdoor machine, a damper 7 openable only at the outside of the frame to exhaust a leaking refrigerant, a reversible blower fan 2 for an air heat exchanger and a controller for controlling them. The system reversely rotates the fan motor 3 to a regular operation to suck air outside the frame in the event of a combustible refrigerant leakage and the pressure in the frame then rises to open the damper 7, thereby quickly exhausting the refrigerant leaking in the frame of the outdoor machine to outside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat pump system, and more particularly to a heat pump system suitable for using a flammable substance as a refrigerant.

[0002]

2. Description of the Related Art In recent years, tightening of power supply and demand in summer due to an increase in cooling demand has become a serious problem. In particular, in August, when the power consumption peaks, about 40% of the power is used for cooling. And this proportion is expected to remain the same. In order to solve this problem, it is effective to use an absorption-type cooling system with low power consumption as a home air conditioner or an office air conditioner. In addition, absorption chillers that can be driven by a heat source are effective for effective use of industrial waste heat and cogeneration by hybridizing energy devices.

[0003] As an absorption refrigerator, those using an aqueous solution of lithium bromide as an absorption solution and water as a refrigerant are widely used. Other examples include a method using ammonia-water as a working refrigerant, a method using hydrocarbon or HFC as a refrigerant and a vinyl ether compound as an absorbent disclosed in JP-A-9-296966, and JP-A-9-104862. Trifluoroethanol (TFE), which is one of the fluorinated alcohols disclosed in US Pat. here,
TFE is obtained by replacing hydrogen of HFC used as a refrigerant in a compression heat pump with a hydroxyl group OH.
M1 is a high boiling polar solvent.

[0004]

In the conventional absorption refrigerator described above, the one using an aqueous solution of lithium bromide as the absorption solution and water as the refrigerant has a low vapor pressure of water of several hundred Pa in the operating state. Therefore, it was difficult to remove the non-condensable gas. In addition, since lithium bromide has corrosiveness, it was necessary to periodically maintain the absorption refrigerator.
Further, even when performing the heat pump operation, the pure water as the refrigerant may freeze in winter, so that the heat pump operation cannot be performed and the heating operation efficiency is deteriorated.

[0005] In order to solve this problem, an ammonia-water absorption refrigerator capable of operating a heat pump,
Ammonia is of concern for toxicity and that no suitable inhibitors are currently being developed to avoid corrosion, increasing the operating pressure of absorption chillers.
There are problems such as difficulty in achieving heavy utility. Further, when the refrigerant is HFC or TFE, the global warming potential increases. In addition, vinyl ether compounds and D
When MI is used, there is a possibility that corrosion may occur in a high-temperature portion, and there is a problem that measures must be taken.

[0006] Therefore, hydrocarbons such as dimethyl ether are known as refrigerants for heat pumps having a low global warming potential and minimizing maintenance.
'98 (B. Adamson, M. AIRAH, Australia, ”Dimethyl
Ether as an R-12 Replacement ”, Natural Working, F
luids '98, IIR-Gustav Lorentzen Conference, pp.569
-575 (1998)). According to this document,
Hydrocarbons have advantages such as high energy density per unit volume, low viscosity, and low global warming potential.

[0007] Even in a compression heat pump using a compressor in the refrigerating cycle, a flammable substance such as natural refrigerant (propane, isobutane, dimethyl ether, HFC32, etc.) is used as a refrigerant in order to protect the ozone layer and prevent global warming. It has also been tried to use as. Any of these natural refrigerants may burn or explode if leaked. Therefore, when using these refrigerants, it is necessary to provide a heat pump system with a security device.

Therefore, methods for safely using a natural refrigerant are disclosed in JP-A-4-369370 and JP-A-6-18.
0166 and JP-A-8-327195. However, Japanese Patent Application Laid-Open Nos. 4-369370 and 6-180166 describe that the amount of refrigerant leakage is reduced by detecting refrigerant leakage and changing the operation mode of the compression cycle. However, sufficient consideration has not been given to avoiding the occurrence of an explosion due to stagnation of the leaking refrigerant. Japanese Patent Application Laid-Open No. 8-327195 describes that refrigerant leakage is sensed and the leaked refrigerant is diffused, but this is not sufficiently considered in terms of avoiding explosion due to the leaked refrigerant.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned disadvantages of the related art, and has as its object to provide a heat pump system using a flammable refrigerant as a working refrigerant. It is to realize a safe heat pump system which avoids the problem.

[0010]

A first feature of the present invention to achieve the above object is to have an outdoor unit and an indoor unit, connect the outdoor unit and the indoor unit with a pipe, and make the refrigerant flammable. In a heat pump system using a conductive refrigerant, a contact-combustion gas sensor that detects refrigerant leakage, a refrigerant discharge damper that operates when the gas sensor detects refrigerant leakage, and a gas sensor are installed inside the outdoor unit. There is provided a blower fan that rotates in a direction opposite to the normal operation when the leakage of the refrigerant is detected, and a controller that controls the refrigerant discharge damper and the blower fan based on the output of the gas sensor.

Preferably, a baffle plate is provided in the vicinity of the damper to obstruct the flow of air flowing out of the housing, or the outdoor unit has a combustor of an absorption refrigerator, and an intake port of the combustor is provided. The exhaust port of the damper is arranged on the formed side.

A second feature of the present invention to achieve the above object is that a heat pump having an outdoor unit and an indoor unit, connecting the outdoor unit and the indoor unit with a pipe, and using a flammable refrigerant as a refrigerant. In the system, inside the outdoor unit, a contact combustion type gas sensor that detects refrigerant leakage, an emergency refrigerant discharge valve that operates when this gas sensor detects refrigerant leakage, and when the gas sensor detects refrigerant leakage It is provided with a blower fan that rotates in the direction opposite to the normal operation, and a controller that controls the emergency refrigerant discharge valve and the blower fan based on the output of the gas sensor.

[0013] Preferably, an igniter for burning the refrigerant discharged from the emergency refrigerant discharge valve and the combustion chamber are provided in at least one of the inside of the housing of the outdoor unit, adjacent to the housing, or near the housing. Things. In any of the above features, the flammable refrigerant may be guided from the outdoor unit to the indoor unit.

A third feature of the present invention to achieve the above object is that a heat pump having an indoor unit and an outdoor unit, connecting the indoor unit and the outdoor unit with a pipe, and using a flammable refrigerant as a refrigerant. In the system, a gas sensor that detects leakage of the refrigerant is provided on the indoor side where the indoor unit is disposed, and a shutoff valve that shuts off the pipe when the gas sensor detects the leakage of the refrigerant is included in the indoor side pipe. And a refrigerant discharge valve for discharging the refrigerant to the outside of the room.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings. When a refrigerant made of a flammable substance is used for an absorption refrigerator or a compression refrigerator, a gas detecting means is provided in consideration of a gas leak. As a method of detecting the gas leakage, a catalytic combustion type, a semiconductor type, a heat conduction type, a galvanic cell type, a constant potential electrolysis type and a ratio separation type infrared type are known. Table 1 shows a comparison of each of these methods.

[0016]

[Table 1]

Most flammable refrigerants explode when mixed with air when the gas concentration falls within a certain range. For example, in the heat pump system to which the present invention is applied, dimethyl ether or isobutane is used for the refrigerant, and the lower limit of the explosive concentration limit is 2 to 3%. FIG. 1 shows the explosion concentration range of each method. FIG. 1 shows that the catalytic combustion method is suitable for detecting a gas having an explosive concentration limit of 2 to 3%. However, even with this catalytic combustion method, it is difficult to measure at a location near the lower limit of the explosive concentration limit (concentration 0.5% or more). Then, the present inventors experimented to what concentration the catalytic combustion method can be applied to detect the leakage of the flammable refrigerant. The result is shown in FIG. As is clear from FIG. 2, it was found that the dimethyl ether concentration can be practically used by applying the correction formula up to about 1.2%.

Semiconductor gas sensors, which are other types of gas sensors, are capable of detecting low-concentration gases and are widely used as portable gas detectors with higher safety. Since the semiconductor gas sensor detects the leakage even if the refrigerant leakage amount is small, it is easy to avoid the danger of explosion. However, when the refrigerant concentration is high, it takes a lot of time to determine whether to avoid the danger of explosion.

The thermal conductivity type gas sensor is not suitable for detecting low concentration gas. Therefore, when the amount of refrigerant leakage is small, it is difficult to prevent leakage.However, since high-concentration refrigerant concentration can be detected, the explosion can be easily detected because it is detected early in the vicinity of the concentration that causes explosion. Can be avoided.

FIG. 3 shows an embodiment of the heat pump system having the leak detector used in FIG. FIG.
It is a system diagram of a heat pump system. The heat pump is an absorption heat pump, and uses a secondary heat medium such as water to exchange heat with the indoor heat exchanger. The absorption heat pump 100 includes a regenerator 12, a condenser 13, a pressure reducing expansion valve 14, an evaporator 8, an absorber 9, a mixer 10 for mixing a refrigerant and an absorbing liquid, an absorbing solution pump 11, an outdoor unit housing 1, air A blower fan 2 for a heat exchanger and a fan motor 3 are provided. The operation of each of these parts is as follows.

The refrigerant vapor generated in the regenerator 12 is cooled by the ambient air in the condenser 13 and condenses. The condensed and liquefied refrigerant flows into the evaporator 8 via the pressure reducing expansion valve 14. The refrigerant flowing into the evaporator 8 exchanges heat with cold water flowing inside the heat transfer surface via the heat transfer surface. Thereby, the cold water is cooled. On the other hand, the refrigerant rises in temperature due to heat exchange and evaporates to become refrigerant vapor. The refrigerant vapor is mixed in the mixer 10 with the cooled absorption solution flowing out of the absorber 9. The mixed absorption solution flows into the regenerator 12 again through the absorption solution pump 11. The refrigerant heated by the regenerator is concentrated by the condenser 13. Hereinafter, this cycle is repeated.

The secondary heat medium (cold water) heat-exchanged by the evaporator 8 provided in the heat pump system is sent into the building 26 by the secondary heat medium pump 21 arranged in the secondary heat medium pipe. And after exchanging heat with the indoor side heat exchanger 23,
It is sent to the evaporator 8 again. Here, even if the heat pump system uses a flammable refrigerant, the flammable refrigerant does not leak because only the secondary heat medium flows in the building 26.

In the heat pump system shown in FIG. 3, a sensor 5 for detecting a refrigerant leak is provided in the housing 1 of the outdoor unit of the heat pump. Further, a damper 7 for discharging the leaked refrigerant which is easily opened and closed only outside the housing 1 is attached to a lower portion of the housing 1. In addition, at the top inside the housing,
A fan 2 with a motor 3 for an air heat exchanger that can rotate in the reverse direction is provided, and a damper 7 and a controller 6 for controlling the motor 3 are provided at a lower portion in the housing.

When the sensor 5 detects the leakage of the refrigerant, the controller 2 rotates the fan 2 in the reverse direction to draw air from outside the housing 1 into the housing. When the external air is sucked into the housing 1, the pressure inside the housing 1 increases, the damper 7 opens, and the refrigerant leaking into the housing 1 is quickly discharged out of the housing. The combustible gas discharged out of the housing is rapidly diffused and diluted with external air so that the refrigerant concentration in the housing 1 does not rise to the explosion range. Thereby, danger such as explosion can be avoided. When the damper 7 is opened, the emergency refrigerant shut-off valves 15 to 20 installed in the heat pump cycle
To shut off. Thereby, the leakage amount of the refrigerant can also be reduced.

Next, the details of the security device of the heat pump system configured as described above will be described with reference to FIGS. In the air heat exchange type heat pump, the flow velocity of the air passing through the air heat exchanger 13 is reduced in order to improve the heat exchange performance and reduce the noise. Specifically, the fan 2 is rotated so that the inside of the housing 1 has a negative pressure. At this time, the air passing through the air heat exchanger 13 flows from the outside of the housing 1 to the inside. Damper 7 is attached to housing 1
When the fan 2 is normally opened and closed, the external pressure is higher at the time of normal rotation of the fan 2, so that the damper 7 is pressed against the housing 1 and is closed. Therefore, even if the damper 7 is provided, the performance of the air heat exchanger 13 does not decrease.

When the sensor 5 detects the leakage of the refrigerant, the controller 3 rotates the motor 3 in the reverse direction. When the motor 3 rotates in the reverse direction, the fan 2 draws air from outside the housing 1 and the internal pressure of the housing 1 increases. When the fan 2 rotates in the reverse direction, the direction of the air flowing through the air heat exchanger is also reversed. When air flows in the air heat exchanger in the reverse direction, a large resistance or pressure loss occurs as compared with the case where air flows in the forward direction (see FIG. 4). Does not drop.

Here, since the damper 7 is set so as to open even with a slight pressure difference, the damper 7 opens as the pressure in the housing 1 rises. Then, the refrigerant leaked into the housing 1 is pushed out together with the air, and is quickly discharged. FIG. 6
As shown in (1), if a baffle plate 28 that blocks the air flowing out of the damper 7 is provided at a lower portion in the housing 1 and near the damper 7, the effect of diffusing the refrigerant can be further enhanced.

In the above embodiment, the air heat exchanger 13 is provided on the building 26 side, and the fan 2 is arranged on the opposite side of the building 26. Thereby, the damper 7 can be installed on the same housing surface as the fan 2 as shown in FIG. 7, and the diffusion efficiency of the leaked refrigerant is improved. However, when a plurality of heat pumps are installed, or when the installation directions with respect to the building are different, as shown in FIG. 8, if the damper 30 is installed on a housing surface different from the housing surface on which the fan 2 is installed, the leaked refrigerant is removed. Can be easily spread.

FIG. 9 shows an example in which the outdoor unit of the heat pump system has a combustor 36. In the absorption heat pump system shown in FIG. 9, the outlet of the damper 33 for discharging the leaked refrigerant is directed to the combustor 36 side. When a sensor (not shown) detects the leakage of the refrigerant,
The fan 2 is rotated in reverse by an instruction from a controller (not shown). Then, as shown in FIG.
Open to the 6 side. Further, the air containing a large amount of combustible refrigerant that has passed through the damper 33 is guided to a combustor 36 together with the air sucked from the intake port 35 and burned. As a result, the outflowing gas is discharged as harmless carbon dioxide and water vapor out of the heat pump system, so that danger such as explosion can be avoided.

FIGS. 11 and 12 show examples in which emergency refrigerant discharge valves 38 and 40 for forcibly discharging the leaked refrigerant out of the housing 1 are provided. Inside the housing 1, a sensor 5 for detecting refrigerant leakage, and an emergency refrigerant discharge valve 3 for discharging the refrigerant out of the housing.
8, 41 and a controller 6 for controlling them are provided. When the sensor 5 detects the leakage of the refrigerant,
The controller 6 forcibly discharges the refrigerant out of the housing 1.
As a result, the amount of the refrigerant leaking into the housing 1 and staying in the housing 1 can be reduced, and the refrigerant concentration in the housing 1 can be prevented from entering the explosion range. Here, as shown in FIG. 12, the refrigerant discharge unit 4 provided on the downstream side of the emergency refrigerant discharge valve 41
If 0 is installed near the fan 2, the effect of refrigerant diffusion is enhanced.

FIG. 13 shows an example in which a combustion device is provided for burning the refrigerant leaking into the housing 1. The refrigerant discharged from the emergency refrigerant discharge valve 42 is guided into a combustion chamber 57 provided in the upper part of the housing 1. An ignition device 44 is disposed in the combustion chamber 57, and ignites the refrigerant guided into the combustion chamber 57 through the refrigerant discharge section 43 and burns the refrigerant in the combustion chamber 57. Thus, the combustible refrigerant gas is discharged out of the heat pump system in the form of carbon dioxide and water vapor, so that an explosion or the like can be avoided.

In the absorption heat pump, an absorbent is used as a working refrigerant in addition to the refrigerant. The refrigerant evaporates easily, but the absorbent hardly evaporates, and if a pipe leaks, it flows out in a liquid state. In order to prevent the outflow and diffusion of the absorbing solution, a receiving tray 45 for the absorbing solution is provided at the lower part of the housing 1 as shown in FIG.

FIG. 14 shows an example of a direct expansion type heat pump system in which a flammable refrigerant is introduced into the indoor unit 24 as well. FIG.
, The indoor unit 24 includes a sensor 46 that detects leakage of the refrigerant. Inside and outside the housing 1, an emergency refrigerant shut-off valve 5 for shutting off a pipe 56 connecting the indoor unit 24 and the outdoor unit.
3, 54, an emergency refrigerant discharge valve 55 for forcibly discharging the refrigerant to the outside of the housing 1, and a controller 47 for controlling these valves are arranged. When the sensor 46 detects that the refrigerant has leaked into the room 26, the controller 47 closes the emergency refrigerant cutoff valves 53 and 54, and discharges the refrigerant from the emergency refrigerant discharge valve 55 to the outside of the housing 1. Thereby, the amount of refrigerant that leaks and stays inside the room can be reduced.

In each of the embodiments of the present invention described above, a sensor for detecting leakage of the refrigerant is provided in the housing of the outdoor unit of the heat pump system using the flammable refrigerant, and the forward / reverse rotation direction is changed according to the output of the sensor. A fan and a damper that opens and closes according to the output of the sensor are provided. Therefore, when the sensor detects the leakage of the flammable refrigerant, the fan motor rotates in the reverse direction to suck in the air outside the housing, raise the pressure inside the housing, and quickly remove the refrigerant leaking from the damper provided at the lower part of the housing. Since the refrigerant is discharged outside the housing, the refrigerant concentration in the housing can be prevented from entering the explosion range, and the danger of explosion and the like can be avoided.

When the outdoor unit of the heat pump system is an absorption heat pump having a combustor, the air containing the leaked combustible refrigerant is guided to the combustor and burned, so that the gas after combustion is converted into carbon dioxide and water vapor. Dangers such as explosions can be avoided. Further, in the embodiment in which the valve capable of forcibly discharging the refrigerant is provided in the housing itself or in the vicinity thereof, when the leakage of the refrigerant is detected by the sensor, the refrigerant can be forcibly discharged to the outside of the housing, so that the refrigerant stays in the housing. The amount of refrigerant can be reduced. As a result, it is possible to prevent the concentration of the refrigerant in the housing from being in the explosion range. Furthermore, if means for burning the refrigerant discharged from the emergency refrigerant discharge valve is provided,
The exhaust gas becomes completely harmless carbon dioxide and water vapor, and the danger can be avoided.

Further, in the embodiment of the direct expansion type heat pump system for introducing the flammable refrigerant to the indoor unit, an emergency shutoff valve is provided in a pipe connecting the indoor unit and the outdoor unit. Even if there is leakage, the amount of flammable refrigerant sent to the indoor unit can be limited by the emergency shut-off valve, and the indoor refrigerant concentration can be prevented from reaching the explosion range.

[0037]

As described above, according to the present invention, in a heat pump system using a flammable gas as a refrigerant,
Since the leaked refrigerant is immediately guided to the outside of the housing of the outdoor unit or burned inside and outside the housing, the explosion of the flammable gas can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an applicable range of a gas sensor.

FIG. 2 is a graph illustrating the sensitivity of a contact combustion type gas sensor to the concentration.

FIG. 3 is a system diagram of one embodiment of a heat pump system according to the present invention.

FIG. 4 is a view for explaining the operation of the outdoor unit shown in FIG. 3;

FIG. 5 is a view for explaining the operation of the outdoor unit shown in FIG. 3;

FIG. 6 is a schematic view of an embodiment of an outdoor unit provided in the heat pump system according to the present invention.

FIG. 7 is a perspective view of an embodiment of an outdoor unit provided in the heat pump system according to the present invention.

FIG. 8 is a perspective view of another embodiment of the outdoor unit provided in the heat pump system according to the present invention.

FIG. 9 is a perspective view of still another embodiment of the outdoor unit provided in the heat pump system according to the present invention.

FIG. 10 is a schematic view of still another embodiment of the outdoor unit provided in the heat pump system according to the present invention.

FIG. 11 is a schematic view of still another embodiment of the outdoor unit provided in the heat pump system according to the present invention.

FIG. 12 is a schematic view of still another embodiment of the outdoor unit provided in the heat pump system according to the present invention.

FIG. 13 is a schematic view of still another embodiment of the outdoor unit provided in the heat pump system according to the present invention.

FIG. 14 is a schematic view of still another embodiment of the heat pump system according to the present invention.

[Explanation of symbols]

1 ... Outdoor unit housing, 2 ... Fan, 3 ... Fan motor, 4 ...
Fan cover, 5… Sensor to detect refrigerant leakage, 6…
Controller, 7… Damper, 8… Evaporator, 9… Absorber, 10
… Mixer, 11… absorption solution pump, 12… regenerator, 13… air heat exchanger (condenser), 14… pressure reducing expansion valve, 15, 16, 17, 1
8, 19, 20 ... emergency refrigerant shut-off valve, 21 ... pump for secondary heat medium, 22 ... pipe for secondary heat medium, 23 ... indoor heat exchanger, 24 ...
Indoor unit housing, 25… Fan for indoor heat exchanger, 26… Building,
27 ... Basic, 28 ... Baffle plate, 29 ... Damper fixture, 30 ... Damper, 31 ... Damper fixture, 32 ... Partition, 33 ... Damper, 34 ... Damper fixture, 35 ... Inlet, 36 ... Combustor, 37 ... the chimney, 38 ...
Emergency refrigerant discharge valve, 39: refrigerant discharge section, 40: emergency refrigerant discharge valve, 41: refrigerant discharge section, 42: emergency refrigerant discharge valve, 43: refrigerant discharge section, 44: ignition device, 45: absorption liquid receiving tray, 46: Controller, 47: Sensor for detecting leakage of refrigerant, 48: Compressor, 49: Four-way valve, 50: Air heat exchanger, 51: Decompression expansion valve, 52: Indoor heat exchanger, 53, 54: Emergency refrigerant shut-off valve, 55 ...
Emergency refrigerant discharge valve, 56 ... refrigerant pipe, 57 ... combustion chamber, 100 ... heat pump system.

Claims (7)

[Claims] 1. A heat pump system comprising an outdoor unit and an indoor unit, wherein the outdoor unit and the indoor unit are connected by pipes and a flammable refrigerant is used as a refrigerant. A gas sensor to detect, and a refrigerant discharge damper that operates when the gas sensor detects leakage of the refrigerant,
When the gas sensor detects refrigerant leakage, a blower fan that rotates in a direction opposite to the normal operation and a controller that controls the refrigerant discharge damper and the blower fan based on the output of the gas sensor are provided. A heat pump system. 2. The heat pump system according to claim 1, wherein a baffle plate is provided near the damper to obstruct the flow of air flowing out of the housing. 3. The outdoor unit according to claim 1, wherein the outdoor unit has a combustor of an absorption refrigerator, and an exhaust port of the damper is arranged on a side of the combustor where an intake port is formed. Heat pump system. 4. A heat pump system comprising an outdoor unit and an indoor unit, wherein the outdoor unit and the indoor unit are connected by pipes and a flammable refrigerant is used as a refrigerant. A contact-combustion gas sensor for detecting, an emergency refrigerant discharge valve that operates when the gas sensor detects a refrigerant leak, and a blower fan that rotates in a direction opposite to the normal operation when the gas sensor detects a refrigerant leak. And a controller for controlling the emergency refrigerant discharge valve and the blower fan based on an output of the gas sensor. 5. An ignition device for burning refrigerant discharged from the emergency refrigerant discharge valve and a combustion chamber are provided in at least one of the inside of the outdoor unit, adjacent to the housing, or near the housing. The heat pump system according to claim 4, wherein 6. The heat pump system according to claim 1, wherein a flammable refrigerant is guided from the outdoor unit to the indoor unit. 7. A heat pump system comprising an indoor unit and an outdoor unit, wherein the indoor unit and the outdoor unit are connected by piping, and a flammable refrigerant is used as a refrigerant. Providing a gas sensor that detects the leakage of, a shutoff valve that shuts off the piping when the gas sensor detects leakage of the refrigerant and a refrigerant discharge valve that discharges the refrigerant contained in the indoor-side piping to the outside, A heat pump system, both of which are provided outside the room.