US-12624868-B2 - Transcritical carbon dioxide single-stage and double-stage compression hot water system and control method therefor

US12624868B2US 12624868 B2US12624868 B2US 12624868B2US-12624868-B2

Abstract

A hot water system with transcritical carbon dioxide single-stage or double-stage compression and a control method therefor is provided. The hot water system includes a first-stage compressor, a first heat exchanger for exchanging heat with cooling water on user side, a second-stage compressor, a second heat exchanger for exchanging heat with the cooling water on user side, a third heat exchanger for exchanging heat between a liquid phase refrigerant and a gas phase refrigerant, an expansion valve, a fourth heat exchanger for exchanging heat with ambient air, a buffer water tank, a first proportional valve, a second proportional valve, a third proportional valve, a fourth proportional valve, a defrosting valve, and a refrigerant circuit bypass valve. The hot water system can switch between the single-stage compression ad the double-stage compression in high-temperature and low-temperature weather, ensuring that the system has good heating capacity and energy efficiency ratio.

Inventors

Hao Pan
Dan Xiong
Xiaoliang Tang
Jun You
QIANG KANG
Xiaofei Song

Assignees

JIANGSU SUJING GROUP CO., LTD.

Dates

Publication Date: 20260512
Application Date: 20220526
Priority Date: 20211228

Claims (17)

1 . A control method for a hot water system with transcritical carbon dioxide compression, wherein the hot water system with transcritical carbon dioxide compression comprises: a first-stage compressor, a first heat exchanger for exchanging heat with cooling water on a user side, a second-stage compressor, a second heat exchanger for exchanging heat with the cooling water on the user side, a third heat exchanger for exchanging heat between a liquid phase refrigerant and a gas phase refrigerant, an expansion valve, a fourth heat exchanger for exchanging heat with ambient air, a buffer water tank, a first proportional valve, a second proportional valve, a third proportional valve, a fourth proportional valve, a defrosting valve, and a refrigerant circuit bypass valve; wherein the first-stage compressor, the first heat exchanger, the second-stage compressor, the second heat exchanger, a liquid phase refrigerant flow side of the third heat exchanger, the expansion valve, the fourth heat exchanger, and a gas phase refrigerant flow side of the third heat exchanger are sequentially circularly connected; two ends of the refrigerant circuit bypass valve are respectively connected to the gas phase refrigerant flow side of the third heat exchanger and an air suction inlet of the second-stage compressor, and two ends of the defrosting valve are respectively connected to an exhaust vent of the second-stage compressor and a refrigerant inlet of the fourth heat exchanger; the buffer water tank, the first proportional valve, the first heat exchanger, the third proportional valve, and the second heat exchanger are sequentially connected, an inlet of the second proportional valve is connected to the buffer water tank, an outlet of the second proportional valve is respectively connected to an inlet of the third proportional valve and an inlet of the fourth proportional valve, the inlet of the fourth proportional valve is further connected to the first heat exchanger, and an outlet of the fourth proportional valve is connected to the buffer water tank; the control method comprising: detecting an evaporation pressure P 0 of the hot water system, a temperature t gout of the refrigerant at the outlet of the second heat exchanger, and a surface temperature t e of the fourth heat exchanger, respectively; recording a target exhaust pressure of the first-stage compressor as P 1,o ; and recording a target exhaust pressure of the second-stage compressor as P 2,o ; controlling a first controlling operation if the hot water system is in a mode of double-stage compression, the first controlling operation comprises: making the refrigerant circuit bypass valve in a closed state, solving the following formulas simultaneously: P 1 , o = P 0 · P 2 , o + Δ ⁢ P ⁢ P 2 , 0 = f 1 ( t gout , P 1 , 0 , t e ) ⁢ f 1 ( t gout , P 1 , 0 , t e ) = ( 3.896 - 0.0223 * t e ) × t gout + ( 0.496 * t e - 10.55 ) + 1.032 × P 1 , 0 0.13 wherein ΔP is the pressure correction value and ranges from −5 bar to 10 bar, using obtained P 1,o and P 2,o as target values and comparing the target values with an actual exhaust pressure P 1 of the first-stage compressor and an actual exhaust pressure P 2 of the second-stage compressor which are detected, and according to a difference between P 1 and P 1,o and a difference between P 2 and P 2,o , adjusting an opening of the expansion valve and an operating frequency of the first-stage compressor to make P 1 close to P 1,o , and P 2 close to P 2,o ; controlling a second controlling operation if the hot water system is in a mode of single-stage compression, the second controlling operation comprises: making the refrigerant circuit bypass valve in an open state, shutting down the first-stage compressor, adjusting an opening of the first proportional valve to 0 and an opening of the second proportional valve to 100%, solving the following formulas: P 2 , 0 = f 2 ( t gout , P 0 , t e ) ⁢ f 2 ( t gout , P 0 , t e ) = ( 3.896 - 0.0223 * t e ) × t gout + ( 0.496 * t e - 10.55 ) + 1.032 × P 0 0.13 wherein ΔP is the pressure correction value and ranges from −5 bar to 10 bar, using an obtained P 2,o as a target value and comparing it with the actual exhaust pressure P 2 of the second-stage compressor actually detected, and according to the difference between P 2 and P 2,o , adjusting the opening of the expansion valve to make P 2 close to P 2,o ; wherein the control method further comprises controlling an outlet temperature of the second heat exchanger, including: adjusting the openings of the first proportional valve and the second proportional valve respectively to control a degree of suction superheat Δts2 to be 5 K-10 K; adjusting openings of the third proportional valve and the fourth proportional valve respectively, recording the opening of the first proportional valve as EXP 1 , the opening of the second proportional valve as EXP 2 , the opening of the third proportional valve as EXP 3 , and the opening of the fourth proportional valve as EXP 4 , and controlling EXP 1 +EXP 2 =EXP 3 +EXP 4 +ΔEXP, wherein ΔEXP is an opening compensation for hydraulic loss and is 3%-6%; wherein the control method further comprises controlling defrosting, including: if the surface temperature t e of the fourth heat exchanger is lower than a setting temperature t 1 within a duration T 1 , the suction pressure P 1 of the second-stage compressor is lower than a setting pressure P 1s within a duration T 2 , and T 1 a * T 2 1 - a = T , starting defrosting, wherein, a = 0.104 - 0.014 * t a + 2.78 * 10 - 4 * t a 2 + 4.04 * 10 - 6 * t a 3 + 2.35 * 10 - 7 * t a 4 , is 30 min to 60 min; and when starting defrosting, closing the expansion valve, shutting down the fan, closing the first proportional valve, opening the defrosting valve, making the first-stage compressor runs to the frequency Hz 1 , which is an operational frequency of the first-stage compressor and is 50 Hz to 65 Hz, and making the second-stage compressor does not shutdown.
2 . The control method for a hot water system with transcritical carbon dioxide compression according to claim 1 , wherein the hot water system with transcritical carbon dioxide compression further comprises a compressor oil separator, the compressor oil separator comprises an oil separator refrigerant inlet, an oil separator refrigerant outlet, and an oil separator lubricating oil outlet, wherein the oil separator refrigerant inlet is connected to the exhaust vent of the second-stage compressor, and the oil separator refrigerant outlet is respectively connected to the second heat exchanger and the defrosting valve, and the oil separator lubricating oil outlet is respectively connected to an oil return opening of the first-stage compressor and an oil return opening of the second-stage compressor.
3 . The control method for a hot water system with transcritical carbon dioxide compression according to claim 2 , wherein the hot water system with transcritical carbon dioxide compression further comprises a first oil circuit solenoid valve and a second oil circuit solenoid valve, two ends of the first oil circuit solenoid valve is respectively connected to the oil separator lubricating oil outlet and the oil return opening of the second-stage compressor, and two ends of the second oil circuit solenoid valve is respectively connected to the oil separator lubricating oil outlet and the oil return opening of the first-stage compressor.
4 . The control method for a hot water system with transcritical carbon dioxide compression according to claim 1 , wherein the hot water system with transcritical carbon dioxide compression further comprises a reservoir, which is respectively connected to a refrigerant outlet of the second heat exchanger and the liquid phase refrigerant flow side of the third heat exchanger; and/or, the hot water system with transcritical carbon dioxide single-stage or double stage compression further comprises a gas-liquid separator, which is respectively connected to the fourth heat exchanger and the gas phase refrigerant flow side of the third heat exchanger.
5 . The control method for a hot water system with transcritical carbon dioxide compression according to claim 1 , wherein the hot water system with transcritical carbon dioxide compression further comprises a water pump, which is respectively connected to the buffer water tank, the first proportional valve and the second proportional valve; and/or, the hot water system with transcritical carbon dioxide compression further comprises a fan for blowing ambient air to the fourth heat exchanger and directly facing the fourth heat exchanger.
6 . The control method for a hot water system with transcritical carbon dioxide compression according to claim 1 , wherein the first-stage compressor is a variable frequency compressor, the second-stage compressor is a fixed frequency compressor, and the fourth heat exchanger is a finned tube evaporator.
7 . The control method for a hot water system with transcritical carbon dioxide compression according to claim 1 , wherein the hot water system with transcritical carbon dioxide compression further comprises an environmental temperature sensor, a buffer water tank outlet temperature sensor, a first heat exchanger outlet temperature sensor, a second heat exchanger outlet temperature sensor, a first-stage compressor exhaust pressure sensor, a first-stage compressor exhaust temperature sensor, a first-stage compressor suction pressure sensor, a first-stage compressor suction temperature sensor, a second-stage compressor exhaust pressure sensor, a second-stage compressor exhaust temperature sensor, a second-stage compressor suction pressure sensor, a second-stage compressor suction temperature sensor, a second heat exchanger refrigerant outlet temperature sensor, a fourth heat exchanger surface temperature sensor, and a fourth heat exchanger refrigerant evaporation pressure sensor; wherein the buffer water tank outlet temperature sensor is arranged at an outlet of the buffer water tank, the first heat exchanger outlet temperature sensor is arranged at an outlet of the first heat exchanger, the second heat exchanger outlet temperature sensor is arranged at the outlet of the second heat exchanger, the first-stage compressor exhaust pressure sensor and the first-stage compressor exhaust temperature sensor are respectively arranged at an exhaust vent of the first-stage compressor, the first-stage compressor suction pressure sensor and the first-stage compressor suction temperature sensor are respectively arranged at an air suction inlet of the first-stage compressor, the second-stage compressor exhaust pressure sensor and the second-stage compressor exhaust temperature sensor are respectively arranged at the exhaust vent of the second-stage compressor, the second-stage compressor suction pressure sensor and the second-stage compressor suction temperature sensor are respectively arranged at the air suction inlet of the second-stage compressor, the second heat exchanger refrigerant outlet temperature sensor is arranged at an refrigerant outlet of the second heat exchanger, and the fourth heat exchanger surface temperature sensor and the fourth heat exchanger refrigerant evaporation pressure sensor are arranged on the fourth heat exchanger.
8 . A hot water system with transcritical carbon dioxide compression, comprising: a first-stage compressor, a first heat exchanger for exchanging heat with cooling water on user side, a second-stage compressor, a second heat exchanger for exchanging heat with the cooling water on user side, a third heat exchanger for exchanging heat between a liquid phase refrigerant and a gas phase refrigerant, an expansion valve, a fourth heat exchanger for exchanging heat with ambient air, a buffer water tank, a first proportional valve, a second proportional valve, a third proportional valve, a fourth proportional valve, a defrosting valve, and a refrigerant circuit bypass valve; wherein the first-stage compressor, the first heat exchanger, the second-stage compressor, the second heat exchanger, a liquid phase refrigerant flow side of the third heat exchanger, the expansion valve, the fourth heat exchanger, and a gas phase refrigerant flow side of the third heat exchanger are sequentially circularly connected; two ends of the refrigerant circuit bypass valve are respectively connected to the gas phase refrigerant flow side of the third heat exchanger and an air suction inlet of the second-stage compressor, and two ends of the defrosting valve are respectively connected to an exhaust vent of the second-stage compressor and a refrigerant inlet of the fourth heat exchanger; the buffer water tank, the first proportional valve, the first heat exchanger, the third proportional valve, and the second heat exchanger are sequentially connected, an inlet of the second proportional valve is connected to the buffer water tank, an outlet of the second proportional valve is respectively connected to an inlet of the third proportional valve and an inlet of the fourth proportional valve, the inlet of the fourth proportional valve is further connected to the first heat exchanger, and an outlet of the fourth proportional valve is connected to the buffer water tank.
9 . The hot water system with transcritical carbon dioxide compression according to claim 8 , further comprising a compressor oil separator, the compressor oil separator comprises an oil separator refrigerant inlet, an oil separator refrigerant outlet, and an oil separator lubricating oil outlet, wherein the oil separator refrigerant inlet is connected to the exhaust vent of the second-stage compressor, and the oil separator refrigerant outlet is respectively connected to the second heat exchanger and the defrosting valve, and the oil separator lubricating oil outlet is respectively connected to an oil return opening of the first-stage compressor and an oil return opening of the second-stage compressor.
10 . The hot water system with transcritical carbon dioxide compression according to claim 9 , further comprising a first oil circuit solenoid valve and a second oil circuit solenoid valve, two ends of the first oil circuit solenoid valve is respectively connected to the oil separator lubricating oil outlet and the oil return opening of the second-stage compressor, and two ends of the second oil circuit solenoid valve is respectively connected to the oil separator lubricating oil outlet and the oil return opening of the first-stage compressor.
11 . The hot water system with transcritical carbon dioxide compression according to claim 8 , further comprising a reservoir, which is respectively connected to a refrigerant outlet of the second heat exchanger and the liquid phase refrigerant flow side of the third heat exchanger; and/or, the hot water system with transcritical carbon dioxide compression further comprises a gas-liquid separator, which is respectively connected to the fourth heat exchanger and the gas phase refrigerant flow side of the third heat exchanger.
12 . The hot water system with transcritical carbon dioxide compression according to claim 8 , further comprising a water pump, which is respectively connected to the buffer water tank, the first proportional valve and the second proportional valve; and/or, the hot water system with transcritical carbon dioxide compression further comprises a fan for blowing ambient air to the fourth heat exchanger and directly facing the fourth heat exchanger.
13 . The hot water system with transcritical carbon dioxide compression according to claim 8 , wherein the first-stage compressor is a variable frequency compressor, the second-stage compressor is a fixed frequency compressor, and the fourth heat exchanger is a finned tube evaporator.
14 . The hot water system with transcritical carbon dioxide compression according to claim 8 , further comprising an environmental temperature sensor, a buffer water tank outlet temperature sensor, a first heat exchanger outlet temperature sensor, a second heat exchanger outlet temperature sensor, a first-stage compressor exhaust pressure sensor, a first-stage compressor exhaust temperature sensor, a first-stage compressor suction pressure sensor, a first-stage compressor suction temperature sensor, a second-stage compressor exhaust pressure sensor, a second-stage compressor exhaust temperature sensor, a second-stage compressor suction pressure sensor, a second-stage compressor suction temperature sensor, a second heat exchanger refrigerant outlet temperature sensor, a fourth heat exchanger surface temperature sensor, and a fourth heat exchanger refrigerant evaporation pressure sensor; wherein the buffer water tank outlet temperature sensor is arranged at an outlet of the buffer water tank, the first heat exchanger outlet temperature sensor is arranged at an outlet of the first heat exchanger, the second heat exchanger outlet temperature sensor is arranged at the outlet of the second heat exchanger, the first-stage compressor exhaust pressure sensor and the first-stage compressor exhaust temperature sensor are respectively arranged at an exhaust vent of the first-stage compressor, the first-stage compressor suction pressure sensor and the first-stage compressor suction temperature sensor are respectively arranged at an air suction inlet of the first-stage compressor, the second-stage compressor exhaust pressure sensor and the second-stage compressor exhaust temperature sensor are respectively arranged at the exhaust vent of the second-stage compressor, the second-stage compressor suction pressure sensor and the second-stage compressor suction temperature sensor are respectively arranged at the air suction inlet of the second-stage compressor, the second heat exchanger refrigerant outlet temperature sensor is arranged at an refrigerant outlet of the second heat exchanger, and the fourth heat exchanger surface temperature sensor and the fourth heat exchanger refrigerant evaporation pressure sensor are arranged on the fourth heat exchanger.
15 . A control method for a hot water system with transcritical carbon dioxide compression according to claim 1 , comprising detecting an evaporation pressure P 0 of the hot water system, a temperature t gout of the refrigerant at the outlet of the second heat exchanger, and a surface temperature t e of the fourth heat exchanger, respectively, recording a target exhaust pressure of the first-stage compressor as P 1,o , and recording a target exhaust pressure of the second-stage compressor as P 2,o ; controlling the first controlling operation if the hot water system is in a mode of double-stage compression, the first controlling operation comprises: making the refrigerant circuit bypass valve is in a closed state, solving the following formulas simultaneously: P 1 , o = P 0 · P 2 , o + Δ ⁢ P ⁢ P 2 , 0 = f 1 ( t gout , P 1 , 0 , t e ) ⁢ f 1 ( t gout , P 1 , 0 , t e ) = ( 3.896 - 0.0223 * t e ) × t gout + ( 0.496 * t e - 10.55 ) + 1.032 × P 1 , 0 0.13 wherein ΔP is the pressure correction value and ranges from −5 bar to 10 bar, using obtained P 1,o and P 2,o as target values and comparing them with an actual exhaust pressure P 1 of the first-stage compressor and an actual exhaust pressure P 2 of the second-stage compressor which are actually detected, and according to a difference between P 1 and P 1,o and a difference between P 2 and P 2,o , adjusting an opening of the expansion valve and an operating frequency of the first-stage compressor to make P 1 close to P 1,o , and P 2 close to P 2,o ; controlling the second controlling operation if the hot water system is in a mode of single-stage compression, the second controlling operation comprises: making the refrigerant circuit bypass valve in an open state, shutting down the first-stage compressor, adjusting an opening of the first proportional valve to 0 and an opening of the second proportional valve to 100%, solving the following formulas: P 2 , 0 = f 2 ( t gout , P 0 , t e ) ⁢ f 2 ( t gout , P 0 , t e ) = ( 3.896 - 0.0223 * t e ) × t gout + ( 0.496 * t e - 10.55 ) + 1.032 × P 0 0.13 wherein ΔP is the pressure correction value and ranges from −5 bar to 10 bar, using an obtained P 2,o as a target value and comparing it with the actual exhaust pressure P 2 of the second-stage compressor actually detected, and according to the difference between P 2 and P 2,o , adjusting the opening of the expansion valve 6 to make P 2 close to P 2,o .
16 . The control method for a hot water system with transcritical carbon dioxide compression according to claim 15 , further comprising controlling an outlet temperature of the second heat exchanger, including: adjusting the openings of the first proportional valve and the second proportional valve respectively to control a degree of suction superheat Δt s2 to be 5 K-10 K; adjusting openings of the third proportional valve and the fourth proportional valve respectively, recording the opening of the first proportional valve as EXP 1 , the opening of the second proportional valve as EXP 2 , the opening of the third proportional valve as EXP 3 , and the opening of the fourth proportional valve as EXP 4 , and controlling EXP 1 +EXP 2 =EXP 3 +EXP 4 +ΔEXP, wherein ΔEXP is an opening compensation for hydraulic loss and is 3%-6%.
17 . The control method for a hot water system with transcritical carbon dioxide compression according to claim 15 , further comprising controlling defrosting comprising: if the surface temperature t e of the fourth heat exchanger is lower than a setting temperature t 1 within a duration T 1 , the suction pressure P 1 of the second-stage compressor is lower than a setting pressure P 1s within a duration T 2 , and T 1 a * T 2 1 - a = T starting defrosting, wherein, a = 0.104 - 0.014 * t a + 2.78 * 10 - 4 * t a 2 + 4.04 * 10 - 6 * t a 3 + 2.35 * 10 - 7 * t a 4 , T is 30 min to 60 min; and when starting defrosting work, closing the expansion valve, shutting down the fan stops, closing the first proportional valve, opening the defrosting valve, making the first-stage compressor runs to the frequency Hz 1 , which is an operational frequency of the first-stage compressor and is 50 Hz to 65 Hz, and making the second-stage compressor does not shutdown.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to PCT/CN2022/095094, filed on May 26, 2022, which claims priority to Chinese Application No. 202111623041.2, filed on Dec. 28, 2021, the entire contents both of which are hereby incorporated by reference. FIELD OF TECHNOLOGY The following relates to the field of transcritical carbon dioxide heat pump technology, and specifically relates to a hot water system for transcritical carbon dioxide single-stage or double-stage compression and a control method therefor. BACKGROUND Carbon dioxide has good environmental properties with an ODP (Ozone depletion potential) value of 0 and a GWP (Global warming potential) value of 1. As a natural working medium, carbon dioxide also has good physical properties at low temperatures. The transcritical carbon dioxide heat pump system, as an environmentally friendly, efficient, stable, and reliable comprehensive utilization system of thermal energy, is often used as building air conditioner to meet the needs of winter heating and summer cooling in large buildings in the commercial and public service fields. Research has shown that the maximum temperature inside the gas cooler of a transcritical carbon dioxide heat pump system can reach 140° C., therefore the transcritical carbon dioxide heat pump system can provide hot water at higher temperatures. However, when producing high-temperature water at low temperatures, the water heater of the carbon dioxide heat pump currently faces a series of problems such as severe attenuation of energy efficiency ratio and heat generation of the system, as well as an increase in exhaust temperature. At the same time, the pressure control of intermediate stage and high-pressure, as well as the control of outlet water temperature of the current transcritical carbon dioxide double-stage compression system, are not improved enough to achieve the switching between single-stage and double-stage compression, resulting in the system being unable to operate normally in high-temperature weather, and may also have false defrosting actions. SUMMARY An aspect relates to an improved hot water system for transcritical carbon dioxide single-stage or double-stage compression, which can switch between the single-stage compression and the double-stage compression in high-temperature and low-temperature weather, ensuring that the system has good heating capacity and energy efficiency ratio when producing high-temperature water in both high-temperature and low-temperature weather, and which, at the same time, also solves the control problem of outlet temperature and defrosting problem in the transcritical carbon dioxide single-stage or double-stage compression system. A hot water system with transcritical carbon dioxide single-stage or double-stage compression is provided, comprising: a first-stage compressor, a first heat exchanger for heat exchange with user side cooling water, a second-stage compressor, a second heat exchanger for exchanging heat with cooling water on user side, a third heat exchanger for exchanging heat between a liquid phase refrigerant and a gas phase refrigerant, an expansion valve, a fourth heat exchanger for exchanging heat with ambient air, a buffer water tank, a first proportional valve, a second proportional valve, a third proportional valve, a fourth proportional valve, a defrosting valve, and a refrigerant circuit bypass valve. Wherein, the first-stage compressor, the first heat exchanger, the second-stage compressor, the second heat exchanger, a liquid phase refrigerant flow side of the third heat exchanger, the expansion valve, the fourth heat exchanger, and a gas phase refrigerant flow side of the third heat exchanger are sequentially circularly connected. Two ends of the refrigerant circuit bypass valve are respectively connected to the gas phase refrigerant flow side of the third heat exchanger and an air suction inlet of the second-stage compressor, and two ends of the defrosting valve are respectively connected to an exhaust vent of the second-stage compressor and a refrigerant inlet of the fourth heat exchanger. The buffer water tank, the first proportional valve, the first heat exchanger, the third proportional valve, and the second heat exchanger are sequentially connected, an inlet of the second proportional valve is connected to the buffer water tank, an outlet of the second proportional valve is respectively connected to an inlet of the third proportional valve and an inlet of the fourth proportional valve, the inlet of the fourth proportional valve is further connected to the first heat exchanger, and an outlet of the fourth proportional valve is connected to the buffer water tank. In some embodiments, the hot water system with transcritical carbon dioxide single-stage or double-stage compression further comprises a compressor oil separator, the compressor oil separator comprises an oil separator refrigerant inlet, an oil separator refrigerant outl