Building domestic hot water storage system adapted to low-temperature heat supply pipe network

Abstract

The application discloses a building domestic hot water storage system suitable for low-temperature heat supply pipe network, which comprises a main temperature-raising heat pump, a circulating temperature-raising heat pump, a gravity stratified heat accumulator, a plate heat exchanger, a condensation side electromagnetic valve, a low-temperature heat medium circulating pump, a heat accumulator heat release circulating pump, a variable frequency water supplement pump, a domestic hot water pipeline circulating pump, a confluence electric three-way valve, a low-temperature primary network water supply pipe, a low-temperature primary network return pipe, a domestic hot water system water supply pipe, a domestic hot water system water supplement pipe, a domestic hot water system circulating pipe, a heat exchanger temperature supply sensor, a heat pump temperature supply sensor, a water supply pipe pressure sensor, a primary network anti-freezing electromagnetic valve, a return pipe temperature return sensor, an evaporation side electromagnetic valve, a heat accumulator heat release branch, a primary network heat supplement branch and a main temperature-raising heat pump heating branch. The application effectively meets the domestic hot water demand of terminal heating buildings, and further reduces the return water temperature of a low-temperature area heat supply system.

Description

Technical Field

[0001] This invention relates to the field of low-temperature heating in buildings, specifically a building domestic hot water storage system adapted to low-temperature heating pipe networks. Background Technology

[0002] Accelerating the construction of a new energy system is the only way to achieve carbon peaking and carbon neutrality goals and promote green and low-carbon development. From a macro perspective, building a new generation of urban centralized heating systems characterized by low-temperature / ultra-low-temperature water supply is an effective path to significantly reduce heat loss in the heat transfer and distribution process, efficiently utilize low-grade waste heat on the supply side, and promote carbon neutrality in the building heating sector. In low-temperature / ultra-low-temperature district heating systems, the primary network's water supply temperature is too low to directly supply domestic hot water to end-user buildings. Electric heat pumps and thermal storage equipment are needed to improve heat quality and manage the total supply. Meanwhile, the gradual improvement of the electricity spot market and the promotion and implementation of real-time electricity pricing pose new challenges to the operation and control of electric heat pumps. The time mismatch between cheap electricity supply and the domestic hot water demand of building users is prominent. The existence of thermal storage equipment can alleviate the time mismatch problem, match the "supply side" and the "heat demand side," and mitigate the serious energy and economic waste caused by the high return water temperature of the primary network.

[0003] In summary, for low-temperature / ultra-low-temperature district heating systems that simultaneously provide heating for the space and domestic hot water, there is currently a lack of a building domestic hot water storage system and control method adapted to low-temperature heating networks to reduce the return water temperature. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a building domestic hot water storage system and control method adapted to low-temperature heating networks.

[0005] The technical solution of this invention to solve the aforementioned technical problem is to provide a building domestic hot water storage system adapted to a low-temperature heating network. The system comprises a main heating heat pump, a circulating heating heat pump, a gravity-driven stratified heat accumulator, a plate heat exchanger, a condenser-side solenoid valve, a low-temperature heat medium circulation pump, a heat accumulator heat release circulation pump, a variable frequency water supply pump, a domestic hot water pipeline circulation pump, a combined electric three-way valve, a low-temperature primary network supply pipe, a low-temperature primary network return pipe, a domestic hot water system supply pipe, a domestic hot water system makeup pipe, a domestic hot water system circulation pipe, a heat exchanger temperature sensor, a heat pump temperature sensor, a supply pipe pressure sensor, a primary network antifreeze solenoid valve, a return pipe temperature sensor, an evaporator-side solenoid valve, a heat accumulator heat release branch, a primary network heat replenishment branch, and a main heating heat pump heating branch. One end of the low-temperature primary network water supply pipe is connected to the primary network, and the other end is divided into two primary branches. The first primary branch is equipped with a primary network antifreeze solenoid valve. The second primary branch is divided into two secondary branches, namely a primary network heat replenishment branch and a main heating heat pump heating branch. The main heating heat pump heating branch is equipped with a condenser-side solenoid valve, and its end is connected to the condenser inlet of the main heating heat pump. The primary network heat replenishment branch is divided into two branches. One branch is equipped with an evaporator-side solenoid valve and its end is connected to the evaporator inlet of the main heating heat pump. The other branch is connected to one inlet end of a combined electric three-way valve. The bottom side interface of the gravity stratified heat accumulator is connected to one end of the heat release branch of the heat accumulator. A low-temperature heat medium circulation pump is installed on the heat release branch of the heat accumulator. The other end of the heat release branch of the heat accumulator is connected to the other inlet end of the combined electric three-way valve. The outlet end of the combined electric three-way valve is connected to the evaporator inlet of the circulating heating heat pump through a pipeline. The condenser outlet of the main heating heat pump is connected to the top heat storage interface of the gravity stratified heat accumulator via a pipeline; the top heat release interface of the gravity stratified heat accumulator is connected to the heat inlet of the plate heat exchanger via a pipeline; a heat exchanger temperature sensor is installed on the heat outlet pipeline of the plate heat exchanger; a heat pump temperature sensor is installed on the condenser outlet pipeline of the circulating heating heat pump; the end of the heat outlet pipeline of the plate heat exchanger and the end of the condenser outlet pipeline of the circulating heating heat pump merge and are connected to one end of the domestic hot water system supply pipe; a supply pipe pressure sensor is installed on the domestic hot water system supply pipe; the other end of the domestic hot water system supply pipe is connected to the domestic hot water terminal equipment. The domestic hot water system circulation pipe is equipped with a domestic hot water circulation pump, one end of which is connected to the domestic hot water circulation equipment and the other end of which is connected to the condenser inlet of the circulating heating heat pump; the domestic hot water system makeup water pipe is equipped with a variable frequency makeup water pump, one end of which is connected to the cold water and the other end of which is connected to the cold inlet of the plate heat exchanger. A heat accumulator heat release circulation pump is installed on the cold outlet pipe of the plate heat exchanger, and the end of the pump is divided into two branches. The end of one branch is connected to the bottom heat storage and release interface of the gravity stratified heat accumulator, and the end of the other branch is connected to the end of the evaporator outlet pipe of the circulating heating heat pump, then to the end of the evaporator outlet pipe of the main heating heat pump, then to the end of the first primary branch of the low temperature primary network water supply pipe, and finally connected to one end of the low temperature primary network return water pipe. A return water pipe temperature sensor is installed on the low temperature primary network return water pipe, and the other end of the low temperature primary network return water pipe is connected to the primary network.

[0006] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention utilizes a main heating heat pump, a circulating heating heat pump and a gravity stratified heat storage device to enhance the heating capacity of the heating system, effectively meet the domestic hot water demand of the terminal heating buildings, and further reduce the return water temperature of the low-temperature area heating system, improve the recovery and utilization rate of low-grade waste heat at the heat source, increase the heat transmission and distribution capacity of the heating network and reduce the heat dissipation along the return water network.

[0007] (2) This invention utilizes a gravity-layered heat storage device to achieve distributed heat storage at the building level, solves the time mismatch problem between fluctuating electricity prices and intermittent domestic hot water load, utilizes more low-priced electricity to complete the heat storage of the heat storage device, and minimizes the system operating cost of domestic hot water supply; at the same time, the gravity-layered heat storage device serves as a backup heat source for the circulating heating heat pump, improving equipment performance and system economy.

[0008] (3) This invention does not include a domestic hot water storage tank. The water temperature at any point in the domestic hot water distribution system is above 50℃ (or below 15℃) and flows continuously, effectively preventing Legionella proliferation and ensuring the hygiene of the domestic hot water. At the same time, the opening and closing state switching of the primary network antifreeze solenoid valve maintains the minimum circulation flow of the low-temperature primary network, avoiding pipe freezing and cracking accidents. Attached Figure Description

[0009] Figure 1 This is an overall structural diagram of the present invention; Figure 2 This is a structural diagram of the gravity stratified heat storage device of the present invention; Figure 3 This is a graph showing the temperature and pressure detected by sensors at different locations in this invention; Figure 4 This is a diagram illustrating the interlocking control logic framework of the cryogenic heat medium circulating pump and the confluence electric three-way valve of the present invention. Figure 5 This is a logic framework diagram of the interlocking control of the main heating heat pump, the condenser-side solenoid valve, and the evaporator-side solenoid valve in the device of the present invention. Figure 6 This is a temperature distribution diagram of the system operating conditions in Embodiment 1 of the present invention.

[0010] In the diagram, the components are: 1. Main heating heat pump; 2. Circulating heating heat pump; 3. Gravity stratified heat storage tank; 4. Plate heat exchanger; 5. Condensing side solenoid valve; 6. Low-temperature heat medium circulation pump; 7. Heat storage tank heat release circulation pump; 8. Variable frequency water supply pump; 9. Domestic hot water pipeline circulation pump; 10. Combined flow electric three-way valve; 11. Low-temperature primary network water supply pipe; 12. Low-temperature primary network return pipe; 13. Domestic hot water system water supply pipe; 14. Domestic hot water system water supply pipe; 15. Domestic hot water system circulation pipe; 16. Heat exchanger temperature sensor; 17. Heat pump temperature sensor; 18. Water supply pipe pressure sensor; 19. Primary network antifreeze solenoid valve; 20. Return water pipe temperature sensor; 21. Evaporator side solenoid valve; 22. Heat storage tank heat release branch; 23. Primary network heat replenishment branch; 24. Main heating heat pump heating branch. Top heat storage interface 3-1, top heat release interface 3-2, bottom heat storage and release interface 3-3, bottom side interface 3-4, top water distributor 3-5, bottom water distributor 3-6, first temperature sensor 3-7, second temperature sensor 3-8, third temperature sensor 3-9, fourth temperature sensor 3-10. Detailed Implementation

[0011] Specific embodiments of the present invention are given below. These specific embodiments are only used to further illustrate the present invention in detail and do not limit the scope of protection of the present invention.

[0012] This invention provides a building domestic hot water storage system (hereinafter referred to as the system) adapted to a low-temperature heating network. The system comprises a main heating heat pump 1, a circulating heating heat pump 2, a gravity stratified heat accumulator 3, a plate heat exchanger 4, a condenser-side solenoid valve 5, a low-temperature heat medium circulation pump 6, a heat accumulator heat release circulation pump 7, a variable frequency water supply pump 8, a domestic hot water pipeline circulation pump 9, a combined electric three-way valve 10, a low-temperature primary network water supply pipe 11, a low-temperature primary network return pipe 12, a domestic hot water system water supply pipe 13, a domestic hot water system water supply pipe 14, a domestic hot water system circulation pipe 15, a heat exchanger temperature sensor 16, a heat pump temperature sensor 17, a water supply pipe pressure sensor 18, a primary network antifreeze solenoid valve 19, a return pipe temperature sensor 20, an evaporator-side solenoid valve 21, a heat accumulator heat release branch 22, a primary network heat replenishment branch 23, and a main heating heat pump heating branch 24. One end of the low-temperature primary network water supply pipe 11 is connected to the primary network, and the other end is divided into two primary branches. The first primary branch is equipped with a primary network antifreeze solenoid valve 19. The second primary branch is divided into two secondary branches, namely the primary network heat supplement branch 23 and the main heating heat pump heating branch 24. The main heating heat pump heating branch 24 is equipped with a condenser-side solenoid valve 5, and its end is connected to the condenser inlet of the main heating heat pump 1. The primary network heat supplement branch 23 is divided into two branches. One branch is equipped with an evaporator-side solenoid valve 21 and its end is connected to the evaporator inlet of the main heating heat pump 1. The other branch is connected to one inlet end of the combined electric three-way valve 10. The bottom side interface 3-4 of the gravity stratified heat accumulator 3 is connected to one end of the heat accumulator heat release branch 22. A low-temperature heat medium circulation pump 6 is installed on the heat accumulator heat release branch 22. The other end of the heat accumulator heat release branch 22 is connected to the other inlet end of the confluence electric three-way valve 10. The outlet end of the confluence electric three-way valve 10 is connected to the evaporator inlet of the circulating heating heat pump 2 through a pipeline. The condenser outlet of the main heating heat pump 1 is connected to the top heat storage interface 3-1 of the gravity stratified heat accumulator 3 via a pipeline; the top heat release interface 3-2 of the gravity stratified heat accumulator 3 is connected to the heat inlet of the plate heat exchanger 4 via a pipeline; a heat exchanger temperature sensor 16 is installed on the heat outlet pipeline of the plate heat exchanger 4; a heat pump temperature sensor 17 is installed on the condenser outlet pipeline of the circulating heating heat pump 2; the end of the heat outlet pipeline of the plate heat exchanger 4 and the end of the condenser outlet pipeline of the circulating heating heat pump 2 converge and are connected to one end of the domestic hot water system supply pipe 13; a supply pipe pressure sensor 18 is installed on the domestic hot water system supply pipe 13; the other end of the domestic hot water system supply pipe 13 is connected to the domestic hot water terminal equipment. A domestic hot water circulation pump 9 is installed on the domestic hot water system circulation pipe 15, one end of which is connected to the domestic hot water circulation equipment and the other end is connected to the condenser inlet of the circulating heating heat pump 2; a variable frequency water supply pump 8 is installed on the domestic hot water system makeup water pipe 14, one end of which is connected to the cold water and the other end is connected to the cold inlet end of the plate heat exchanger 4. A heat storage circulation pump 7 is installed on the cold outlet pipe of the plate heat exchanger 4, and the end is divided into two branches. The end of one branch is connected to the bottom heat storage and release interface 3-3 of the gravity stratified heat storage accumulator 3. The end of the other branch is connected to the end of the evaporator outlet pipe of the circulating heating heat pump 2, and then to the end of the evaporator outlet pipe of the main heating heat pump 1. After that, it is connected to the end of the first primary branch of the low temperature primary network water supply pipe 11, and then to one end of the low temperature primary network return water pipe 12. A return water pipe temperature sensor 20 is installed on the low temperature primary network return water pipe 12, and the other end of the low temperature primary network return water pipe 12 is connected to the primary network.

[0013] Preferably, the gravity stratified heat storage device 3 includes a top heat storage interface 3-1, a top heat release interface 3-2, a bottom heat storage and release interface 3-3, a bottom lateral interface 3-4, a top water distributor 3-5, a bottom water distributor 3-6, a first temperature sensor 3-7, a second temperature sensor 3-8, a third temperature sensor 3-9, and a fourth temperature sensor 3-10. The top water distributor 3-5 has an upward-facing opening and is installed at a height of 15 / 16 inside the gravity stratified thermal accumulator 3; the bottom water distributor 3-6 has a downward-facing opening and is installed at a height of 1 / 16 inside the gravity stratified thermal accumulator 3; the top heat storage interface 3-1 and the top heat release interface 3-2 are located at the top of the gravity stratified thermal accumulator 3; the bottom heat storage / release interface 3-3 is located at the bottom of the gravity stratified thermal accumulator 3; the bottom side interface 3-4 is located on the side of the gravity stratified thermal accumulator 3, at a height of 1 / 4 inside the gravity stratified thermal accumulator 3; the first temperature sensor 3-7 is installed at a height of 7 / 8 inside the gravity stratified thermal accumulator 3; the second temperature sensor 3-8 is installed at a height of 3 / 4 inside the gravity stratified thermal accumulator 3; the third temperature sensor 3-9 is installed at a height of 1 / 4 inside the gravity stratified thermal accumulator 3; and the fourth temperature sensor 3-10 is installed at a height of 1 / 8 inside the gravity stratified thermal accumulator 3.

[0014] This invention also provides a control method (hereinafter referred to as the method) for a building domestic hot water storage system adapted to a low-temperature heating network, characterized in that the method includes the following steps: Step 1, System Status Division; When there is a demand for domestic hot water and the primary network is supplying heat normally, the condenser-side solenoid valve 5 and the evaporator-side solenoid valve 21 are opened, the domestic hot water pipeline circulation pump 9 operates at a fixed frequency, the heat storage heat release circulation pump 7 and the variable frequency makeup water pump 8 operate at a variable frequency; the circulating heating heat pump 2 uses the heat storage heat release branch 22 or the primary network makeup heat branch 23 as the heat source; when the circulating heating heat pump 2 uses the heat storage heat release branch 22 as the heat source, the low temperature heat medium circulation pump 6 is turned on; Inside the gravity stratified thermal accumulator 3: the first temperature sensor 3-7 measures the temperature T at 7 / 8 of the height of the gravity stratified thermal accumulator 3. 3a (abbreviated as T) 3a The second temperature sensor 3-8 measures the temperature T at 3 / 4 of the height of the gravity stratified thermal accumulator 3. 3b (abbreviated as T) 3b The third temperature sensor 3-9 measures the temperature T at 1 / 4 of the height of the gravity stratified thermal accumulator 3. 3c (abbreviated as T) 3c The fourth temperature sensor 3-10 measures the temperature T at 1 / 8 of the height of the gravity stratified thermal accumulator 3. 3d (abbreviated as T) 3d ); for T 3a T 3b T 3c and T 3d Each is given a set value T 3a，set T 3b，set T 3c，set and T 3d，set ; The heat exchanger temperature sensor 16 measures the supply water temperature T1 (hereinafter referred to as T1) of the domestic hot water system supply pipe 13; the heat pump temperature sensor 17 measures the inlet temperature T2 (hereinafter referred to as T2) of the water flowing from the circulating heating heat pump 2 to the domestic hot water system supply pipe 13; the supply pipe pressure sensor 18 measures the supply water pressure P (hereinafter referred to as P) of the domestic hot water system supply pipe 13; and the return water temperature sensor 20 measures the return water temperature T1 of the low-temperature primary network return pipe 12. H (abbreviated as T) H ); for T1, T2, P and T H Each is given a set value T 1，set T 2，set P set and T H，set ; State 1: T 3a <T 3a，set At this time, the top water temperature of the gravity stratified heat storage unit 3 cannot reach the set outlet water temperature, and the main heating heat pump 1 needs to be turned on to store energy for the gravity stratified heat storage unit 3. At this time, the demand on the domestic hot water side is not considered. State 2: T 3a ≥T 3a，set At this point, the top water temperature of the gravity stratified heat storage unit 3 reaches the set outlet water temperature, and there is no need to turn on the main heating heat pump 1 to store energy for the gravity stratified heat storage unit 3. At this point, the demand for domestic hot water is not considered. State 3: T 3a ≥T 3a，set And T 3b <T 3b，set At this time, the top water temperature of the gravity stratified heat storage unit 3 reaches the set outlet water temperature. In order to ensure that the gravity stratified heat storage unit 3 can continue to work stably, the main heating heat pump 1 still needs to be turned on to store energy for the gravity stratified heat storage unit 3. At this time, the demand on the domestic hot water side is not considered. State 4: T 3a ≥T 3a，set And T 3b ≥T 3b，set At this time, the top water temperature of the gravity stratified heat storage unit 3 reaches the set outlet water temperature, which also ensures that the gravity stratified heat storage unit 3 can work continuously and stably. There is no need to turn on the main heating heat pump 1 to store energy for the gravity stratified heat storage unit 3. At this time, we do not consider whether there is demand on the domestic hot water side. State 5: T 3c <T 3c，set At this time, the heating capacity of gravity stratified heat storage device 3 is lower than that of the low-temperature primary network; State 6: T 3c ≥T 3c，set At this time, the heating capacity of gravity stratified heat storage device 3 is not lower than that of the low temperature primary network; State 7: At this time, the electricity price is low and T3d ≥T 3d，set At this time, the bottom temperature of the gravity stratified heat storage unit 3 is higher than the set value, so there is no need to turn on the main heating heat pump 1 to store energy for the gravity stratified heat storage unit 3. State 8: At this time, the electricity price is low and T 3d <T 3d，set At this time, the bottom temperature of the gravity stratified heat storage device 3 is lower than the set value, and the heating capacity of the gravity stratified heat storage device 3 is insufficient. It is necessary to turn on the main heating heat pump 1 to store energy for the gravity stratified heat storage device 3. State 9: When T H ≤T H，set At this time, there is a probability that the low-temperature primary network return water pipe 12 will freeze. At this time, the primary network antifreeze solenoid valve 19 will open, and hot water and cold water will mix to prevent the low-temperature primary network return water pipe 12 from freezing. Step 2: System operation begins, control measures commence; Step 2.1, Determine T 3a With T 3a，set The relationship; if T 3a ≥T 3a，set The system is in state 2, proceed to step 2.2; if T 3a <T 3a，set The system is in state 1, proceed to step 2.6; Step 2.2: Determine if the current electricity price is in a high-price phase; if not, proceed to Step 2.3; if it is in a high-price phase, determine T. 3b With T 3b，set The relationship; if T 3b ≥T 3b，set The system is in state 4, proceeding to step 2.7; if T 3b <T 3b，set The system is in state 3, proceed to step 2.6; Step 2.3: Determine if there is a demand for domestic hot water; when there is no demand for domestic hot water, the circulating heating heat pump 2, plate heat exchanger 4, low-temperature heat medium circulation pump 6, heat storage heat release circulation pump 7, variable frequency water supply pump 8, and domestic hot water pipeline circulation pump 9 all stop working, ending all control and completing all steps; when there is a demand for domestic hot water, proceed to step 2.4. Step 2.4: The domestic hot water pipeline circulation pump 9 operates at a fixed frequency. Calculate T1 and T. 1，set The deviation is adjusted by changing the frequency of the heat storage heat circulation pump 7, and the discrete PI control algorithm shown in equation (1) is used for regulation: (1) In equation (1), U7(k) represents the operating frequency of the DDC (Direct Digital Control) output to the heat storage heat circulation pump 7 at time k; U7(k-1) represents the operating frequency of the DDC output to the heat storage heat circulation pump 7 at time k-1; K p,7 The proportional gain represents the control algorithm; T0 represents the discrete sampling period; T I,7 The integral time of the control algorithm is represented by eT1(k); eT1(k) represents the time difference between T1 and Tk at time k. 1,set The deviation; eT1(k-1) represents the difference between T1 and T at time k-1. 1,set Deviation; Calculate T2 and T 2，set The deviation is adjusted by changing the frequency of the circulating heating heat pump 2, and the discrete PI control algorithm shown in equation (2) is used for regulation: (2) In equation (2), U2(k) represents the operating frequency of the DDC output to the circulating heating heat pump 2 at time k; U2(k-1) represents the operating frequency of the DDC output to the circulating heating heat pump 2 at time k-1; K p,2 The proportional gain represents the control algorithm; T0 represents the discrete sampling period; T I,2 The integral time of the control algorithm is represented by eT2(k); eT2(k) represents the time difference between T2 and T at time k. 2,set The deviation; eT2(k-1) represents the difference between T2 and T at time k-1. 2,set Deviation; Calculate P and P set The deviation is adjusted by changing the frequency of the variable frequency water supply pump 8, and the discrete PI control algorithm shown in equation (3) is used for regulation: (3) In equation (3), U8(k) represents the operating frequency of the DDC output to the variable frequency water supply pump 8 at time k; U8(k-1) represents the operating frequency of the DDC output to the variable frequency water supply pump 8 at time k-1; K p,8 The proportional gain represents the control algorithm; T0 represents the discrete sampling period; T I,8 Indicates the integration time of the control algorithm; e p (k) represents the time interval P and P at time k. set deviation; e p (k-1) represents the time interval P and P at time k-1. set Deviation; Determine T 3c With T 3c，set The relationship; if T 3c <T 3c，set If the system is in state 5, the low-temperature heat medium circulation pump 6 is shut down, the confluence electric three-way valve 10 switches to the primary network heat supplement branch 23, and proceeds to step 2.5; if T 3c ≥T3c，set If the system is in state 6, the low-temperature heat medium circulation pump 6 is turned on, the confluence electric three-way valve 10 is switched to the heat storage heat release branch 22, and the process proceeds to step 2.5. Step 2.5, Determine T 3d With T 3d，set The relationship; if T 3d ≥T 3d，set The system is in state 7, proceed to step 2.7; if T 3d <T 3d，set The system is in state 8, proceed to step 2.6; Step 2.6: Turn on the main heating heat pump 1, and simultaneously turn on the condenser side solenoid valve 5 and the evaporator side solenoid valve 21; Step 2.7: Turn off the main heating heat pump 1, and at the same time turn off the condenser side solenoid valve 5 and the evaporator side solenoid valve 21; Step 3, System Detection: When T H ≤T H，set At this time, the system is in state 9, and the primary network antifreeze solenoid valve 19 is open, mixing hot and cold water to prevent the primary network return pipe from freezing; when T H <T H，set At that time, close the primary network antifreeze solenoid valve 19.

[0015] The working principle of this invention is as follows: Hot water along the low-temperature primary network water supply pipe 11 is diverted at the second confluence point. One diverted stream flows along the main heating heat pump branch 24, enters the main heating heat pump 1 through the condenser inlet, then flows out through the condenser outlet of the main heating heat pump 1, and flows into the gravity stratified heat storage 3 through the top heat storage interface 3-1. When there is no demand for domestic hot water, the water along the primary network supplementary heating branch 23 is not diverted, but enters the main heating heat pump 1 through the evaporator inlet, then flows out through the evaporator outlet of the main heating heat pump 1, and then flows out after merging with the low-temperature primary network return water pipe 12. Water flowing out from the bottom heat storage and release interface 3-3 of the gravity stratified heat storage 3 merges with the low-temperature primary network return water pipe 12 and flows out. When there is a demand for domestic hot water: determine T 3c With T 3c，setThe relationship is as follows: When the system is in state 5, the primary network heat supply branch 23 is split again. One branch enters the main heating heat pump 1 through the evaporator inlet, then flows out through the evaporator outlet of the main heating heat pump 1, and then merges with the low-temperature primary network return water pipe 12 before flowing out. The other branch enters the circulating heating heat pump 2 through the evaporator inlet of the circulating heating heat pump 2 through the merging electric three-way valve 10, then flows out through the evaporator outlet of the circulating heating heat pump 2, and then merges with the low-temperature primary network return water pipe 12 before flowing out. The cold water from the heat storage heat release circulation pump 7 is not split, but merges with the cold water flowing out from the evaporator outlet of the circulating heating heat pump 2, and then merges with the cold water flowing out from the evaporator outlet of the main heating heat pump 1, flowing along the low-temperature primary network return water pipe 12. Water flows out of the pipe; when the system is in state 6, the primary network heat supplement branch 23 does not need to be split. The hot water flowing out from the bottom side interface 3-4 of the gravity stratified heat storage 3 passes through the confluence electric three-way valve 10, enters the circulating heating heat pump 2 through the evaporator inlet, and then flows out through the evaporator outlet of the circulating heating heat pump 2, and flows out after merging with the low temperature primary network return water pipe 12; the cold water of the heat storage circulation pump 7 is split, one branch flows into the gravity stratified heat storage 3 through the bottom heat storage and release interface 3-3 of the gravity stratified heat storage 3; the other branch merges with the cold water flowing out from the evaporator outlet of the circulating heating heat pump 2, and then merges with the cold water flowing out from the evaporator outlet of the main heating heat pump 1, and flows out along the low temperature primary network return water pipe; Hot water flowing out from the top heat release port 3-2 of the gravity stratified heat storage 3 enters the plate heat exchanger 4 through the hot inlet end of the plate heat exchanger 4, and then flows out through the hot outlet end of the plate heat exchanger 4; domestic hot water circulation water enters the circulating heating heat pump 2 through the condenser inlet of the circulating heating heat pump 2 through the circulating hot water system circulation pipe 15, and then flows out through the condenser outlet of the circulating heating heat pump 2, and merges with the hot water flowing out through the hot outlet end of the plate heat exchanger 4 and flows out through the domestic hot water system supply pipe 13; cold water enters the plate heat exchanger 4 through the cold inlet end of the plate heat exchanger 4 through the domestic hot water system makeup water pipe 14, and then flows out through the cold outlet end of the plate heat exchanger 4. To prevent the primary return water pipe 12 from freezing at low temperatures, determine T H With T H，set The relationship is as follows: When the system is in state 9, the hot water along the low-temperature primary network water supply pipe 11 is split at the first confluence point. One branch enters the main heating heat pump through the heating branch 2 of the main heating heat pump, and the subsequent flow direction is the same as above. The other branch is connected to the low-temperature primary network return water pipe 12 through the primary network antifreeze solenoid valve 19, and flows out along the low-temperature primary network return water pipe 12 after merging with the cold water.

[0016] Example 1: Quantitative calculation of operating costs: setting T 3a，set =55℃, T 3b，set =50℃, T3c，set =40℃, T 3d，set =50℃, the power of the main heating heat pump 1 is 30kW, the power of the circulating heating heat pump 2 is 15kW, the total length of the low-temperature primary network return water pipe 12 is 1000m, the ambient temperature is 5℃, and the heat transfer coefficient K of the low-temperature primary network return water pipe 12 is 1.2W / (m) 2 (℃), the outer diameter of the insulation pipe D=0.2m, the domestic hot water demand occurs from 8:00-10:00 in the morning, 13:00-15:00, and 17:00-19:00, the gravity stratified heat storage unit 3 has sufficient heat storage capacity, the specific design temperature is as follows Figure 6 The reference peak-valley electricity prices are shown in Table 1.

[0017] Table 1

[0018] In traditional district heating systems, when there is a demand for domestic hot water, the main heating heat pump 1 is activated to charge the gravity stratified heat storage tank 3, and the circulating heating heat pump 2 is also activated. At this time, the electricity consumption is calculated based on a 150-day heating season.

[0019] The system is in state 8, and can activate the main heating heat pump 1 to charge the gravity stratified heat storage unit 3 when electricity prices are low. At this time, the electricity price is calculated based on the electricity consumption over a 150-day heating season.

[0020] Therefore, the electricity cost can be saved by approximately (31368-19992.45) / 31368=36.7%.

[0021] Example 2: Calculate the heat loss along the return pipe: In a traditional district heating system, the return water temperature is 25℃. The heat loss along the pipe at this temperature is:

[0022] The return water temperature is 15℃, and the heat loss along the flow path is:

[0023] Therefore, the heat loss along the path is reduced by approximately (15072-7536) / 15072=50%.

[0024] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A building domestic hot water storage system adapted to low-temperature heating networks, characterized in that, The system includes a main heating heat pump (1), a circulating heating heat pump (2), a gravity stratified heat storage device (3), a plate heat exchanger (4), a condenser-side solenoid valve (5), a low-temperature heat medium circulation pump (6), a heat storage device heat release circulation pump (7), a variable frequency water supply pump (8), a domestic hot water pipeline circulation pump (9), a combined electric three-way valve (10), a low-temperature primary network water supply pipe (11), a low-temperature primary network return water pipe (12), a domestic hot water system water supply pipe (13), a domestic hot water system water supply pipe (14), a domestic hot water system circulation pipe (15), a heat exchanger temperature sensor (16), a heat pump temperature sensor (17), a water supply pipe pressure sensor (18), a primary network antifreeze solenoid valve (19), a return water pipe temperature sensor (20), an evaporator-side solenoid valve (21), a heat storage device heat release branch (22), a primary network heat replenishment branch (23), and a main heating heat pump heating branch (24). One end of the low-temperature primary network water supply pipe (11) is connected to the primary network, and the other end is divided into two primary branches; the first primary branch is equipped with a primary network antifreeze solenoid valve (19); the second primary branch is divided into two secondary branches, namely the primary network heat supplement branch (23) and the main heating heat pump heating branch (24); the main heating heat pump heating branch (24) is equipped with a condenser side solenoid valve (5), and its end is connected to the condenser inlet of the main heating heat pump (1); the primary network heat supplement branch (23) is divided into two branches, one branch is equipped with an evaporator side solenoid valve (21) and its end is connected to the evaporator inlet of the main heating heat pump (1), and the other branch is connected to one inlet end of the combined electric three-way valve (10); The bottom side interface (3-4) of the gravity stratified heat accumulator (3) is connected to one end of the heat accumulator heat release branch (22). A low-temperature heat medium circulation pump (6) is installed on the heat accumulator heat release branch (22). The other end of the heat accumulator heat release branch (22) is connected to the other inlet end of the combined electric three-way valve (10). The outlet end of the combined electric three-way valve (10) is connected to the evaporator inlet of the circulating heating heat pump (2) through a pipeline. The condenser outlet of the main heating heat pump (1) is connected to the top heat storage interface (3-1) of the gravity stratified heat storage tank (3) through a pipeline; the top heat release interface (3-2) of the gravity stratified heat storage tank (3) is connected to the heat inlet of the plate heat exchanger (4) through a pipeline; a heat exchanger temperature sensor (16) is installed on the heat outlet pipeline of the plate heat exchanger (4); a heat pump temperature sensor (17) is installed on the condenser outlet pipeline of the circulating heating heat pump (2); the end of the heat outlet pipeline of the plate heat exchanger (4) and the end of the condenser outlet pipeline of the circulating heating heat pump (2) are connected to one end of the domestic hot water system supply pipe (13); a supply pipe pressure sensor (18) is installed on the domestic hot water system supply pipe (13); the other end of the domestic hot water system supply pipe (13) is connected to the domestic hot water terminal equipment. A domestic hot water circulation pump (9) is installed on the domestic hot water system circulation pipe (15), one end of which is connected to the domestic hot water circulation equipment and the other end is connected to the condenser inlet of the circulating heating heat pump (2); a variable frequency water supply pump (8) is installed on the domestic hot water system water supply pipe (14), one end of which is connected to the cold water and the other end is connected to the cold inlet of the plate heat exchanger (4). A heat storage heat release circulation pump (7) is installed on the cold outlet pipe of the plate heat exchanger (4), and the end is divided into two branches; the end of one branch is connected to the bottom heat storage and release interface (3-3) of the gravity stratified heat storage (3), and the end of the other branch is connected to the end of the evaporator outlet pipe of the circulating heating heat pump (2), and then connected to the end of the evaporator outlet pipe of the main heating heat pump (1), and then connected to the end of the first primary branch of the low temperature primary network water supply pipe (11), and then connected to one end of the low temperature primary network return water pipe (12); a return water pipe temperature sensor (20) is installed on the low temperature primary network return water pipe (12), and the other end of the low temperature primary network return water pipe (12) is connected to the primary network.

2. The building domestic hot water storage system adapted to low-temperature heating networks according to claim 1, characterized in that, The gravity stratified heat storage device (3) includes a top heat storage interface (3-1), a top heat release interface (3-2), a bottom heat storage and release interface (3-3), a bottom side interface (3-4), a top water distributor (3-5), a bottom water distributor (3-6), a first temperature sensor (3-7), a second temperature sensor (3-8), a third temperature sensor (3-9), and a fourth temperature sensor (3-10). The top water distributor (3-5) has an opening facing upwards and is installed at a height of 15 / 16 inside the gravity stratified heat accumulator (3); the bottom water distributor (3-6) has an opening facing downwards and is installed at a height of 1 / 16 inside the gravity stratified heat accumulator (3); the top heat storage interface (3-1) and the top heat release interface (3-2) are located at the top of the gravity stratified heat accumulator (3); the bottom heat storage and release interface (3-3) is located at the bottom of the gravity stratified heat accumulator (3); and the bottom side interface (3-4) is located at the bottom of the gravity stratified heat accumulator. (3) is located on the side of the gravity stratified heat storage device (3) at 1 / 4 of its height; the first temperature sensor (3-7) is installed at 7 / 8 of its height inside the gravity stratified heat storage device (3); the second temperature sensor (3-8) is installed at 3 / 4 of its height inside the gravity stratified heat storage device (3); the third temperature sensor (3-9) is installed at 1 / 4 of its height inside the gravity stratified heat storage device (3); and the fourth temperature sensor (3-10) is installed at 1 / 8 of its height inside the gravity stratified heat storage device (3).

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