Oil return system of straight expanding ground-source heat pump system with double injectors and oil return method thereof

Abstract

The invention relates to the technical field of ground-source heat pumps and discloses an oil return system of a straight expanding ground-source heat pump system with double injectors and an oil return method thereof. The oil return device of the system comprises a compressor, an oil separator, a condenser / gas cooler, an intermediate heat exchanger, a first injector, a gas-liquid separator, a first electromagnetic valve, a second injector, a second electromagnetic valve, a throttling valve, a downhole heat exchanger, an oil return pipe, an oil level sensor and a controller. By applying the injectors to the straight expanding ground-source heat pump system, a high pressure refrigerant working medium at the outlet of the intermediate heat exchanger in an oil return working condition is injected by the second injector to be collected in liquid state lubricating oil in a U-shaped bend of the oil return pipe. Under the circumstance of no external input power, the lubricating oil returns tothe compressor smoothly, so that the problem of oil return of the compressor of the straight expanding ground-source heat pump system in a heat supply working condition can be solved, and the throttling loss can be also reduce and the input power of the compressor is saved. The system is suitable for all refrigerant working media.

Description

technical field [0001] The invention relates to the technical field of ground source heat pumps, and more specifically relates to an oil return device and an oil return method of a direct expansion ground source heat pump system. Background technique [0002] In northern China, urban heating energy consumption in winter accounts for 40% of the national urban building energy consumption, which is the main component of building energy consumption. In terms of heating methods, central heating and combined heat and power generation are mainly used, and the fuel used in both is mainly coal. The coal-based heating method not only consumes a large amount of coal resources, but also causes serious environmental pollution. Therefore, it is particularly important to develop clean, efficient, and energy-saving renewable energy heating technologies. As a new type of inter-seasonal energy storage and utilization technology for geological bodies, the direct expansion ground source heat ...

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Problems solved by technology

However, when the system runs continuously under low load, the flow rate of refrigerant in the downhole heat exchanger is low, and the oil return problem of the compressor still cannot be solved

In addition, when the length of the standpipe of the downhole heat exchanger in the direct expansion ground source heat pump system reaches hundreds of meters, the setting of multiple oil return traps will inevitably bring inconvenience to the manufacturing process of the downhole heat exchanger;

[0006] 2) Install an oil separator at the outlet of the compressor to reduce the amount of lubricating oil entering the downhole heat exchanger, but this method can only delay the accumulation of lubricating oil at the bottom of the downhole heat exchanger, and cannot fundamentally solve the problem of oil return

This method has certain feasibility, but the throttling loss is relatively large, and the system efficiency is not high, especially not suitable for carbon dioxide direct expansion ground source heat pump systems

[0008] It can be seen that the oil return device of the above-mentioned existing direct expansion ground source heat pump system still has defects and limitations in structure, method and service conditions, so a new type of oil return device for direct expansion ground source heat pump system is developed. The device and its oil return method not only solve the oil return problem of the compressor of the direct expansion ground source heat pump system under the heating condition, but also reduce the throttling loss, save the input work of the compressor, and are not affected by the refrigerant Type restrictions have become the primary task in the field of direct expansion ground source heat pumps

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