METHOD FOR REFRIGERATION SYSTEMS

Abstract: A method for a refrigerant system having a circulation circuit comprising a screw compressor (1), a condenser (4), an expansion valve (5) and an evaporator (6). In a refrigerant process, in which an oil injected compressor is connected it is impossible to prevent oil from flowing together with the refrigerant out into the circulation circuit, which among others impairs the operation of the evaporator. According to the invention a drastic reduction of the amount of circulating oil has been obtained together with an improved cooling of the compressor by supplying the low pressure side of the compressor with refrigerant liquid with a pressure and temperature lower than the pressure and temperature of the refrigerant in the condenser in such amounts per unit of time that the required cooling and sealing of the compressor is obtained, the effect of the circulating oil being restricted merely to lubricating.

Description: METHOD FOR REFRIGERATION SYSTEMS This invention relates to a method for a refrigeration system for cooling, sealing and lubrication of the working chamber of a screw compressor forming a part of the system, which screw compressor together with a condenser, an expan- sion valve and an evaporator forms a circulation circuit, in which a refrigerant and a small amount of oil are circu¬ lating. In a refrigeration system of this or a similar type, in which oil for lubrication of the compressor's working cha - ber can flow out into the circulation system via an oil se¬ parator situated on the compressor's high pressure side, the oil will sooner or later end up in the evaporator. Be¬ cause the refrigerant evaporates from the liquid surface, an enrichment of the oil will occur in liquid form. This impairs the evaporators efficiency, partly through the shifting boiling point, partly through the impaired coeffi¬ cient of heat transfer. In practice this is handled today through different sys¬ tems of oil returning, for example, pumping to a closed thread in a screw compressor. In an oil injected compres¬ sor, this flood must, however, not be so large that the compressor's discharge temperature begins to come close to the condensing temperature with the ensuing risk for con¬ densation of the refrigerant in the oil separator and dilu- tion of the oil. The object of the invention is to completely or partly eliminate these drawbacks in a simple way. This has, accor¬ ding to the invention, been achieved in that the outlet of the compressor is connected directly to the inlet of the condenser for supplying the refrigerant and the total amount of oil from the compressor to the condenser and re¬ frigerant liquid containing oil with a pressure and tempe¬ rature lower than the pressure and temperature of the re¬ frigerant and oil in the condenser, preferably close to or the same pressure and temperature as in the evaporator, is supplied to the low pressure side of the compressor with such amounts per unit of time, that essentially all of the intended cooling and sealing is secured by means of the re¬ frigerant liquid, the amount of oil present being restric- ted to a value which is required for proper lubrication of the rotors. A collection of refrigerant liquid containing oil takes place, preferably, in a pipe between the expan¬ sion valve and the evaporator, or from the evaporator, af¬ ter which the refrigerant liquid and oil is transported to the compressor's low pressure side through a particular pipe, preferably to a thread with reduced pressure in rela¬ tion to the inlet pressure, which can be achieved by delay¬ ing the opening of the thread towards the inlet. ' The idea of the invention is consequently to have a thorough reduction of the oil flow passing through the compressor and also a thorough increase of the amount of refrigerant injected into the compressor. By means of the reduced oil flood, the oil separator can be dispensed with and, consequently, a meaningfully lower discharge temperature can therefore be allowed. A larger amount of refrigerant liquid can therefore be injected in the compressor for sealing and temperature control. This liquid is undercooled. in relation to the inlet temperature and can therefore be injected into the compressor's low pressure side without risk worsening of the volumeter. The result of this is an improved efficiency because of ^ better sealing and. cooling than what is normally achieved during oil injection for the same goal. Besides a controll- ed low discharge temperature is achieved which gives a smaller difference in thermal deformation between inlet and outlet and even improved lifetime for the oil and refrige¬ rant. An improved efficiency for the evaporator which coun¬ teracts the oil enrichment can even be achieved. The invention is further clarified in the following with reference to the attached drawing, which schematically shows a refrigeration system, with which an example of the method according to the invention is applied. The drawing shows a screw compressor 1 with inlet 2 and outlet 3 which later is directly connected to a condenser 4 which, together with an expansion valve 5 and an evaporator 6 connected to the compressor's inlet, forms a cooling cir¬ cuit containing a refrigerant with a small amount of oil which is required for lubrication of the compressor's work- ing chamber and the rotors located therein. According to the invention there is also a pipe 7 , which connects a collection container 8 by the evaporators inlet side with the compressor's inlet 2 or, when necessary, with a thread 9 with lower pressure than the inlet pressure. ' The ref igeration system dif ers from conventional re¬ frigeration systems, partly because of the absence of an oil separator and a feed back of cooling and sealing oil from the oil separator to the compressor, and partly through the transporting of cold refrigerant liquid con- taining a small amount of oil from the container 8 past the evaporator 6 through the pipe 7 to the compressor 1. As mentioned previously, the amount of oil is sufficient for lubrication of the compressor, but not more, and the re¬ frigerant liquid is sufficient for cooling and sealing the compressor during boiling off. The expansion valve 5 is designed, as known per se, to control the cooling cycle such that refrigerant liquid is always available in the container 8. The requirements for the pressure and temperature of the refrigerant liquid can be satisfied in other ways than those described. The refrigerant can thus be diverted from the pipe between the condenser 4 and the expansion valve 5 and after pressure reduction and proper cooling supplied to the compressor's 1 low pressure side in a suitable way.

Claims: CLAIMS 1. A method for a refrigeration system for cooling, sealing and lubrication of the working chamber of a screw compres¬ sor (1) forming a part of the system, which screw compres¬ sor together with a condenser (4), an expansion valve (5) 5 and an evaporator (6) forms a circulation circuit in which a refrigerant and a small amount of oil are circulating, characterized in that the outlet of the compressor (1) is connected directly to the inlet of the condenser (4) for supplying the refrigerant and the total amount of oil from 10 the compressor (1) to the condenser (4) and refrigerant liquid containing oil with a pressure and temperature lower than the pressure and temperature of the refrigerant and oil in the condenser (4), preferably close to or the same pressure and temperature as in the evaporator (6), is 15 supplied to the low pressure side of the compressor (1) with such amounts per unit of time that essentially all of the intended cooling and sealing is achieved by means of the refrigerant liquid, the amount of oil present in the refrigerant liquid being restricted to a value which is 20 just required for proper lubrication of the rotors. 2. A method according to claim 1, characterized in that refrigerant liquid containing oil in a pipe between the expansion valve (5) and the evaporator (6) or from the 25 evaporator is collected and supplied through a particular pipe (7) to the low pressure side (2, 9) of the compressor, preferably to a thread (9) with reduced pressure.

Inventors: PAMLIN ROLAND, SJOEHOLM LARS, PAMLIN, ROLAND, SJOEHOLM, LARS
Applicants: SVENSKA ROTOR MASKINER AB
Application year: 1986
Main classification: F25B1
IPC codes: F04C29, F25B1