JP2000319647A - Air-conditioning refrigerant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide air-conditioning refrigerants which allow humans to sense carbon dioxide as the refrigerant in its early stages when the carbon dioxide leaks and minimize its adverse effect on human bodies. SOLUTION: Air-conditioning refrigerants contain carbon dioxide and an odorant. As the odorant, at least one member selected from the group consisting of tert-butylmercaptan(TBM), dimethyle sulfide(DMS), tetrahydrothiophene(THT), hydrogen sulfide(H2S), mercaptans, and ester/terpenes can be mentioned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air conditioning refrigerant, and more particularly to an air conditioning refrigerant used for cooling a closed space such as an automobile.

[0002]

2. Description of the Related Art
Refrigerants such as chlorofluorocarbons (hereinafter, referred to as CFCs), hydrochlorofluorocarbons (hereinafter, referred to as HCFCs), and hydrofluorocarbons (hereinafter, referred to as HFCs) have been used for cooling means such as refrigeration systems and air conditioners. However, it has become clear that these refrigerants have a large effect on the global environment such as destruction of the ozone layer and global warming. On the other hand, awareness of the global environment has been increasing year by year, and in recent years, alternative refrigerants for these refrigerants have been actively developed. For example, CFC,
As an alternative refrigerant to HFC, hydrocarbon (hereinafter, referred to as HFC)
HC).

[0003] However, HC is a flammable refrigerant. If flammable refrigerant leaks out due to damage to the welded part of the refrigerant circuit, etc., if there is a burning device near the flammable refrigerant that has leaked out, the flammable refrigerant may become an ignition source and cause an explosion was there. As a means to detect such danger beforehand, phosphorus-containing organic substances such as dibutyl acid phosphate are mixed with HC refrigerant used in household refrigerators and the like, and aliphatic esters such as n-butyl acetate are used. (Japanese Patent Application Laid-Open No. 8-296909) is known.
Also, a mixture of an HC-refrigerant used in home refrigerators and a sulfur-containing organic substance such as methyl mercaptan or a nitrogen-containing organic substance (Japanese Patent Application Laid-Open No. Hei 8-14675) is known. When methyl mercaptan or the like is mixed with the HC refrigerant and used, the lubricating property of the HC refrigerant can be improved, and the leakage of the refrigerant can be easily detected due to the generation of odor of methyl mercaptan. However, since HC refrigerant is still a flammable substance, it is difficult to completely prevent the danger of explosion even if HC refrigerant leakage is detected. Therefore, development of a non-flammable refrigerant has been desired.

As a result of the development of a nonflammable refrigerant, carbon dioxide can be mentioned. Carbon dioxide
Since there is no flammability like the above-mentioned HC refrigerant, there is no possibility of becoming an ignition source. Carbon dioxide is basically harmless (non-toxic, non-flammable) to the human body. Therefore, when using an air conditioner having a carbon dioxide refrigerant in a large space or open space such as an office or home, it is almost unnecessary to detect refrigerant leakage. For this reason, means for detecting leakage of carbon dioxide as an air conditioning refrigerant has not been studied.

[0005] The present inventors have studied the application of carbon dioxide as a refrigerant for air conditioning of automobiles, and have obtained certain results. However, if a carbon dioxide refrigerant is used for air conditioning in a closed narrow space such as an automobile, and if carbon dioxide leaks due to any accident, etc., depending on the situation of the accident, the air conditioning used in the passenger compartment There is a possibility that the refrigerant inside may diffuse into the vehicle interior. However, carbon dioxide is basically harmless to humans as described above (non-toxic, non-flammable)
Therefore, there is little awareness of the safety of facilities that use carbon dioxide, and there is currently little interest in the effects of high concentrations of carbon dioxide on the human body. Here, carbon dioxide concentration (%) and its effect on the human body
(Cited Document ¹⁾ Kent, AD: Occupational Health Review, Vo
l.21 No.1-21970, p.1 CANADA, cited reference ²⁾ Hazardous C
chemicals Data Book, 2.ed. NoyesData Corporation 1
986) is shown in Table 1.

[0006]

[Table 1]

In view of Table 1, when the refrigerant diffuses into the passenger compartment, an increase in the concentration of carbon dioxide may adversely affect the human body, such as nervous disorders and dyspnea. However, no means has been known so far for humans to sense the diffused carbon dioxide.

Accordingly, an object of the present invention is to provide an air-conditioning refrigerant capable of detecting the leakage of carbon dioxide as a refrigerant to a human at an early stage and minimizing the influence on the human body. is there.

[0009]

The refrigerant for air conditioning according to the present invention comprises:
It is characterized by containing carbon dioxide and an odorant.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The refrigerant for air conditioning of the present invention contains carbon dioxide and an odorant. The refrigeration cycle of the present invention in which the refrigerant containing carbon dioxide as a main component is used has the following characteristics. Operating pressure is very high compared to CFC. Specifically, the pressure is 10 to 15 MPa at a high pressure and 3.5 to 4 MPa at a low pressure. The high pressure side is a transcritical cycle, which exceeds the critical point. Since the refrigeration cycle using carbon dioxide as a refrigerant has the same vapor compression system as chlorofluorocarbon, the cycle configuration is similar to that of a refrigeration cycle using chlorofluorocarbon as a refrigerant. However, since the high pressure side becomes transcritical and there is no liquid, an accumulator is required as a reservoir for absorbing load fluctuations.

The odorant contained in the refrigerant for air conditioning according to the present invention has an object to promptly recognize a person when a part of the carbon dioxide refrigerant cycle is broken due to an accident or a failure. Such an odorant may be appropriately set in consideration of the characteristics of the refrigeration cycle of the air conditioner using the above-described carbon dioxide refrigerant, ease of mixing with carbon dioxide, and safety to the human body. it can. The odorant is tertiary butyl mechabutane from the viewpoint of general availability.
(TBM), dimethyl sulfide (DMS), tetrahydrothiophene (THT), hydrogen sulfide (H ₂ S), mercaptans (eg, methyl mercaptan), and esters / terpenes (CP). Species can be mentioned. These odorants can be used alone or in combination.

The concentration of the odorant in the refrigerant for air conditioning of the present invention is as follows:
It is appropriate to set the concentration so that the concentration of carbon dioxide leaked into the vehicle can be perceived by a person in the vehicle when it exceeds 0.5% (TLV) (the long-term safety limit shown in Table 1). In addition, the concentration of the odorant perceived by a person varies depending on the type of the odorant, but may be detected by a person when the odor intensity is 2.5 or more depending on the type of the odorant. Therefore, it is appropriate to determine the concentration of the odorant in the refrigerant for air conditioning of the present invention based on the long-term safety limit concentration of carbon dioxide and the concentration at which the odor intensity of the odorant becomes 2.5. Table 2 shows a list of representative odorants and concentrations (ppm) at which the odor intensity becomes 2.5. In the present invention, the concentration at which the odor intensity becomes 2.5 is 0.001 to 1 ppm.
It is preferred to use substances in the range of as odorants.

[0013]

[Table 2]

For example, when the odorant is methyl mercaptan, the concentration at which the odor intensity becomes 2.5 is 0.002 ppm.
Assuming that the volume of the space inside the vehicle (occupant of the vehicle) is 4 m ³ , this space contains 0.002 ppm of methyl mercaptan.
Requires 9.28 × 10 ⁻⁶ g. The leakage of the refrigerant causes the carbon dioxide concentration in the in-vehicle (vehicle occupant) space to become 0.5% when the leakage amount of the refrigerant is 23.7 g. Therefore, if 9.28 × 10 ⁻⁶ g is contained in 23.7 g of refrigerant, that is, if about 2 ppm of methyl mercaptan is contained in carbon dioxide, carbon dioxide having a concentration exceeding the long-term safe limit concentration is obtained. At the concentration, the person in the car can feel the odor of methyl mercaptan. The odorant preferably used in the present invention has a concentration at which the odor intensity becomes 2.5 or more is in the range of about 0.001 to 1 ppm, and therefore depends on the type of the odorant (the concentration of the odor intensity becomes 2.5). It is preferable that carbon dioxide contains an odorant in the range of 1 to 1000 ppm. Although the air conditioning refrigerant of the present invention is mainly used for air conditioning for vehicles, it can be used for other air conditioning as well.

[0015]

The present invention will be further described below with reference to examples. Example 1 As shown in Table 3, tertiary butyl mechabutane (TBM) in the range of 0.1 to 50 ppm was mixed with carbon dioxide to prepare six types of air conditioning refrigerants. Then, the degree of odor was tested for each of the air conditioning refrigerants. Specifically, carbon dioxide gas containing a predetermined amount of tertiary butyl mechabutane (TBM) was prepared. This gas was flown into the cabin and tested to see if the odor could be sensed in the cabin without informing the four subjects. The results are shown in Table 3.

[0016]

[Table 3]

From the results shown in Table 3, it can be seen that when the content of tertiary butyl mechabutane (TBM) is 1 ppm or more, human beings can be sensed without great variation. As a result, even when odorless and colorless carbon dioxide leaks, it is possible to quickly take measures for ensuring safety, and therefore, high safety in operation of the air conditioner is ensured.

[0018]

According to the present invention, it is possible to provide an air-conditioning refrigerant which can ensure safety in a closed space. Further, since no explosive refrigerant is used, there is no fear of explosion due to leakage of the refrigerant.
Further, according to the present invention, even in the event that a carbon dioxide refrigerant leaks, it is possible for a person to quickly detect a refrigerant leak. In addition, if the air-conditioning refrigerant containing carbon dioxide and odorant of the present invention is used, safety in an easily enclosed space can be easily achieved without having to provide an expensive leak sensor and equipment such as a forced exhaust device. Can be secured.

Claims (3)

[Claims] An air conditioning refrigerant comprising carbon dioxide and an odorant. 2. The odorant is tertiary butyl mechabutane.
(1) at least one selected from the group consisting of (TBM), dimethyl sulfide (DMS), tetrahydrothiophene (THT), hydrogen sulfide (H ₂ S), mercaptans, and esters / terpenes (CP). A refrigerant for air conditioning as described in 1 above. 3. The air conditioning refrigerant according to claim 1, wherein the concentration of the odorant in the refrigerant is in a range of 1 to 1000 ppm.