Test chamber and method for its control having cooling circuit accommodating small volume test chamber

A method for conditioning air in a temperature-insulated test space of a test chamber, in particular a climate chamber, the test space being closable to an environment and serving for receiving test material, a temperature ranging from −20° C. to +180° C. being generated within the test space by a cooling device having a cooling circuit using carbon dioxide (CO2) as a refrigerant, a heat exchanger in the test space, a low-pressure compressor and a high-pressure compressor, which is disposed downstream of the low-pressure compressor in a flow direction of the refrigerant, a gas cooler and an expansion valve, the method comprising controlling and/or regulating the temperature in the test space,

• wherein
• the cooling circuit has an internal heat exchanger, which is connected on a high-pressure side of the cooling circuit downstream of the gas cooler and upstream of the expansion valve, the internal heat exchanger being coupled with a medium-pressure bypass of the cooling circuit, the medium-pressure bypass being connected downstream of the internal heat exchanger and upstream of the expansion valve on the high-pressure side as well as upstream of the high-pressure compressor and downstream of the low-pressure compressor on a medium-pressure side of the cooling circuit, refrigerant being dosed in the medium-pressure side from the high-pressure side via the internal heat exchanger by a second expansion valve;
• wherein
• a second bypass is formed in the cooling circuit so as to have a third expansion valve, the second bypass being connected downstream of the internal heat exchanger and upstream of the expansion valve on the high-pressure side as well as downstream of the heat exchanger and upstream of the low-pressure compressor on the low-pressure side, a suction gas temperature and/or a suction gas pressure of the refrigerant being regulated in such a manner upstream of the low-pressure compressor on the low-pressure side of the cooling circuit that refrigerant is dosed as a liquid to the low-pressure side via the third expansion valve;
• and
• wherein
• another bypass is formed in the cooling circuit so as to have another valve, the other bypass being connected downstream of the high-pressure compressor and upstream of the gas cooler on the high-pressure side as well as downstream of the heat exchanger and upstream of the low-pressure compressor on the low-pressure side, a suction gas temperature and/or a suction gas pressure of the refrigerant being regulated in such a manner upstream of the low-pressure compressor on the low-pressure side of the cooling circuit and/or a pressure difference between the high-pressure side and the low-pressure side of the cooling circuit is compensated in such a manner that refrigerant is dosed in the low-pressure side via the other valve.