Transcritical carbon dioxide single-stage and double-stage compression hot water system and control method thereof

Abstract

The invention discloses a transcritical carbon dioxide single-stage and double-stage compression hot water system and a control method thereof. The system comprises a first-stage compressor, a first heat exchanger used for exchanging heat with user side cooling water, a second-stage compressor, a second heat exchanger used for exchanging heat with user side cooling water, a third heat exchanger used for exchanging heat with a liquid-phase refrigerant and a gas-phase refrigerant, an expansion valve, a fourth heat exchanger used for exchanging heat with ambient air, a buffer water tank and a first proportional valve. A first proportional valve, a second proportional valve, a third proportional valve, a fourth proportional valve, a defrosting valve, a refrigerant path bypass valve and the like; the system realizes intelligent switching of single-stage and double-stage transcritical operation under variable working conditions, has outstanding heating capacity and energy efficiency ratio under all working conditions, remarkably improves the comprehensive performance of preparing high-temperature hot water under a low-temperature environment, and also solves the defrosting problem and the oil return problem of a double-stage compression hot water system.

Description

technical field [0001] The invention relates to the technical field of a transcritical carbon dioxide heat pump, in particular to a hot water system with single and double-stage compression of transcritical carbon dioxide and a control method thereof. Background technique [0002] Carbon dioxide has good environmental properties with an ODP value of 0 and a GWP of 1. As a natural working fluid, carbon dioxide also has good physical properties at low temperatures. Transcritical carbon dioxide heat pump system, as an environmentally friendly, efficient, stable and reliable thermal energy comprehensive utilization system, is often used as a building air conditioner to meet the winter heating and summer cooling needs of large buildings in the commercial and public service fields. Studies have shown that the maximum temperature in the gas cooler of a transcritical carbon dioxide heat pump system can reach 140°C. Therefore, a transcritical carbon dioxide heat pump system can provi...

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Problems solved by technology

[0003] However, when the carbon dioxide heat pump water heater produces high-temperature water at low temperature, it faces a series of problems such as serious attenuation of unit energy efficiency ratio and heating capacity, and rise in exhaust temperature. At the same time, the intermediate stage and the The high-pressure pressure control and outlet water temperature control are not perfect enough, neither single-stage nor double-stage compression switching can be realized, resulting in the unit not being able to work normally in high-temperature weather, and there may be false defrosting actions

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