Heat pump

Abstract

A heat pump of the present invention has a compressor and an expander coupled with a common axis of rotation, a first throttling device disposed in a circulation passage of refrigerant, and a second throttling device disposed in a bypass passage diverted from the expander. A control device controls the openings of these throttling devices. The control device executes a first controlling in which the opening of the first throttling device is adjusted in order to bring a high pressure PH in a refrigeration cycle close to a predetermined value determined based on a value at which the coefficient of performance (COP) of the heat pump is optimized, and after the first controlling is completed, it executes a second controlling in which the opening of the second throttling device is adjusted in order to bring a degree of superheat SH close to a predetermined positive value. This ensures smooth and stable operations of the heat pump.

Description

[0001] This application is a continuation of prior pending International Application Number PCT / JP2005 / 022655, filed on Dec. 9, 2005, which designated the United States.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to heat pumps useful for hot water heaters, air-conditioners, and the like, and more particularly to a heat pump furnished with a mechanism for recovering energy with an expander. [0004] 2. Description of the Related Art [0005] A heat pump employing an expander in place of an expansion valve can recover the expansion energy of refrigerant as electric power or mechanical power. As the expander, in many cases a positive displacement expander is used that has a space with a variable capacity for introducing and expanding the refrigerant therein. The energy recovery with the expander has a significant value, particularly in the transcritical cycle of carbon dioxide in which the high pressure reaches a supercritical state of ...

AI Technical Summary

Benefits of technology

[0019] It is therefore an object of the present invention to enable efficient operations in a heat pump in which the expander and the compressor are coupled directly, and at the same time ensure the reliability of the compressor.

[0021] Further, in the heat pump of the present invention, the control device executes a first controlling in which, when the difference between a high pressure PH of the refrigerant circulating in the circulation passage and a predetermined value PHT determined based on a value at which the coefficient of performance of the heat pump is optimized is outside a predetermined range PHDR, the opening of the second throttling device is varied so that the absolute value of the difference between the pressure PH and the predetermined value PHT becomes smaller. After completing the first controlling, the control device executes a second controlling in which, when the difference between a degree of superheat SH of the refrigerant flowing into the compressor and a predetermined positive value SHT is outside a predetermined range SHDR, the opening of the first throttling device is varied so that the absolute value of the difference between the degree of superheat SH and the predetermined value SHT becomes smaller.

[0022] In the present invention, when the second throttling is adjusted to attempt an improvement in the coefficient of performance while ensuring smooth cycling operations, the first throttling device subsequently is adjusted to control the degree of superheat of the refrigerant. This controlling allows even the heat pump in which the compressor and the expander are coupled directly to perform smooth and efficient operations according to operation conditions while ensuring the reliability of the compressor.

Problems solved by technology

Because of its structure, the expander cannot recover energy unless the refrigerant passes through it in a predetermined direction.

In the heat pump in which the expander and the compressor are directly coupled, the expander and the compressor operate at the same rotational speed and therefore it is impossible to vary the ratio between the displacement of the expander and the displacement of the compressor according to operation conditions.

For that reason, the heat pump in which the expander and the compressor are coupled directly has difficulty in performing a smooth operation according to operation conditions, although it has good efficiency in energy recovery.

For example, if the expander is designed based on the standard condition in a cooling operation, the displacement of the expander will be too large in a heating operation with respect to the required value.

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