CN106440404B - A kind of solar water heat pump system - Google Patents

Abstract

A solar hot water heat pump system, which can use the heat pump to combine solar heating with the return water of the secondary heat network in the central heating system. The system includes: a solar heating subsystem, a hot water tank, valves, Water pumps, heat pumps, temperature sensors, pressure sensors, and control devices; the system is used to provide domestic hot water, use solar energy to heat tap water, and then use heat network return water and heat pumps to further increase the temperature of domestic hot water. This solar energy combined with heat pump method can ensure the hot water heating temperature when solar energy fluctuates or is insufficient on the basis of utilizing solar energy, and at the same time reduces the return water temperature of the heating network; it not only ensures the stability of solar heating but also takes into account the improvement The economy of central heating.

Description

A solar hot water heat pump system

technical field

A new solar hot water heat pump system is used to provide domestic hot water. The system uses solar energy to heat tap water, and then uses the return water from the heating network and heat pump to further increase the temperature of domestic hot water. This solar energy combined with heat pump method can ensure the hot water heating temperature when solar energy fluctuates or is insufficient on the basis of utilizing solar energy, and at the same time reduces the return water temperature of the heating network. It not only ensures the stability of solar heating, but also improves the economy of central heating.

Background technique

In areas rich in solar energy, my country has generally begun to promote household solar water heaters to provide hot water. The performance of domestic solar water heaters fluctuates and intermittently with the solar energy supply period. In continuous rainy weather or at night, the stored water capacity of domestic water heaters often cannot fully meet the domestic hot water demand. On the other hand, district heating systems are commonly used in towns and cities in northern China. In the central heating system, the return water temperature of the secondary heating network is generally between 40 and 60°C, which is very suitable for combining with a heat pump to increase the temperature of domestic domestic hot water. Combining solar heating with heat pumps and heat network return water can ensure the hot water heating temperature when solar energy fluctuates or is insufficient on the basis of utilizing solar energy, while reducing the heat network return water temperature and improving heating economy.

Contents of the invention

In order to solve the above problems in the prior art, the present invention proposes a solar hot water heat pump system, which is characterized in that the system can use the heat pump to combine solar heating with the return water of the secondary heat network in the central heating system , the system includes: including solar heating subsystems, hot water tanks, valves, water pumps, heat pumps, temperature sensors, pressure sensors, and control devices;

The solar heating subsystem includes a hot water side and a cold water side. The equipment on the hot water side includes solar hot water collectors, circulating water pumps, and hot water pipes for heat exchangers; the equipment on the cold water side includes water pumps, valves and exchangers. Heater cold water pipeline;

The system integrates solar heating, heat pump and heating network return water together to provide domestic hot water while reducing the temperature of the heating network return water; after processing by this system, when the local solar energy is insufficient, the temperature of the domestic hot water provided can also be stabilized at 50-60°C;

The hot water of multiple solar heating subsystems shares a hot water tank; the capacity of the hot water tank is determined according to the design of the hot water produced by solar hot water; the hot water tank is covered with insulation materials; Near the water pipe; the set pressure in the hot water tank adopts atmospheric pressure

The solar collector receives sunlight radiation on the roof of the building to obtain heat. The temperature of the circulating water in the solar collector rises after being heated and enters the heat exchanger. In the heat exchanger, the circulating water on the hot water side is cooled by the living Cooled with water, the cooled circulating water is pressurized by the circulating water pump and then enters the solar collector again, and the circulating water flows back and forth to transfer the solar heat to the domestic water supply;

The water pump extracts the external domestic water, and the domestic water enters the cold water side of the heat exchanger of the solar heating subsystem. The domestic water is heated by the high-temperature circulating water in the heat exchanger, and then enters the hot water tank. The water pump is placed downstream of the heat exchanger , to prevent the pressure of the heat exchanger pipeline from being too high; place a switching valve upstream of the heat exchanger, and shut off the valve when it stops working;

The hot water tank is connected to multiple pumping pipelines, and the domestic water in each pumping pipeline enters the hot water tank through the pump, and the water outlet of the hot water tank is connected to a booster pump, and the booster pump is connected to the hot water tank and the heat pump. Condenser inlet and bypass pipe, exhaust valve installed on the top of the hot water tank, temperature sensor, water level sensor and pressure sensor installed in the hot water tank, when the water temperature in the hot water tank reaches the set value, the booster pump will The hot water is pumped into the heat pump condenser or bypass pipe. When the water level in the hot water tank is lower than the warning water level, the booster pump stops working. When the water level in the hot water tank is higher than the warning water level, open the drain valve to lower the water level. When the pressure in the hot water tank is greater than the set value, open the exhaust valve;

The heat source of the heat pump is the return water of the heating network, and the cold source of the heat pump is the domestic water supply provided by the hot water tank. When the solar energy is sufficient, if the temperature of the domestic water in the hot water tank has reached the temperature required for domestic hot water, the bypass pipe will be opened The valve directly provides domestic hot water; when the solar energy is insufficient, the temperature of domestic water in the hot water tank does not reach the temperature required for domestic hot water, then the valve of the heat pump condenser is opened to introduce domestic water into the heat pump condenser as The cold source of the heat pump; use the booster pump to introduce the return water in the heat supply return pipe into the evaporator of the heat pump as the heat source of the heat pump; the function of the heat pump is to transfer the heat of the return water in the heat network to the domestic water, so Heating water into domestic hot water;

When the solar energy is insufficient, the water temperature in the hot water tank is low; the temperature T _1,in of the domestic water supply is also low; in order to ensure that it is not infected by Legionella, the set temperature T _{1,out of} the domestic hot water is generally at 50 ~60°C;

Further, when there are multiple buildings in the heating area, solar collectors can be placed on the roof of each building to form a set of solar heating subsystems, and several sets of solar heating subsystems can form a large solar energy supply system. heat system.

Furthermore, the heat pump can adopt the types of electric heat pump and steam heat pump commonly used in the heating industry; the energy efficiency index of the heat pump is generally measured according to its COP (coefficient of performance); according to the general definition in the heat pump machinery industry, COP can be Expressed as the ratio of the heat _Q1 obtained by domestic hot water to the power consumption W of the compressor;

COP＝Q ₁ /W (1)

If the environmental heat dissipation loss is not considered, the heat Q ₁ obtained by domestic hot water is the sum of the heat Q ₂ extracted from the return water of the heating network and the power consumption W of the compressor;

Q ₁ =Q ₂ +W (2)

The heat Q ₁ obtained by the domestic hot water is a function of the temperature T _1,in of the domestic water supply entering the heat pump condenser and the temperature T _1,out of the domestic hot water leaving the heat pump condenser;

in, is the mass flow rate of domestic water supply in the heat pump condenser, kg/s; C _p is the specific heat capacity of water, J/kg; ΔT ₁ is the temperature difference between outlet and inlet water temperature, °C;

The heat Q ₂ extracted from the return water of the heat network is a function of the temperature T _2,in of the heat network return water entering the heat pump evaporator and the temperature T _{2,out of} the heat pump evaporator;

in, is the mass flow rate of heat network return water in the heat pump evaporator, kg/s; C _p is the specific heat capacity of water, J/kg; ΔT ₁ is the temperature difference between inlet and outlet water temperatures, °C;

The COP value of the heat pump cannot exceed the COP value of the theoretical reverse Carnot cycle; the COP value of the theoretical reverse Carnot cycle is shown in formula (5); therefore, under the condition of a certain compressor power consumption W, a higher temperature T _2,in or a lower temperature T _1,in can increase the COP value of the heat pump;

Among them, COP _c is the COP value of the theoretical reverse Carnot cycle; T ₁ is the temperature of the heat source; T ₂ is the temperature of the heat sink.

Further, in order to further save energy and reduce the power consumption of the compressor; the return water of the heating network can be used as the cold source of the heat pump to provide sufficient heat; since the return water temperature of the heating supply is relatively high, which is close to the set temperature of domestic hot water, Set the COP value of the heat pump to 5.0; the heat pump evaporator uses water as the medium.

Further, a temperature sensor is installed at the outlet of the solar collector; when the outlet water temperature of the collector is higher than the set temperature, increase the circulating water volume of the circulating water pump; when the outlet water temperature of the heat collector is lower than the set temperature, reduce the circulating water pump Install the sensor at the outlet of the cold water side of the heat exchanger; when the temperature of the domestic water at the outlet of the cold water side is higher than the set temperature, increase the circulating water volume of the pump; when the temperature of the domestic water at the outlet of the cold water side is lower than the set temperature, Reduce the circulating water volume of the pump; when the solar heating subsystem stops working, close the valve on the pumping pipeline; multiple sets of pumping pipelines are connected to the hot water tank; the water level control method is adopted for the hot water tank; according to the water level set by the water tank, Control the flow of the pump, and control the flow of the booster pump before the inlet of the heat pump condenser according to the demand for domestic hot water; control the start and stop of the heat pump equipment and the power of the compressor according to the set temperature of the domestic hot water.

Further, when installing solar thermal collectors on the roofs of multiple buildings; there will be multiple sets of solar heating subsystems to form a set of solar heating subsystems to form the heating subsystem of the solar hot water heat pump system, and multiple sets of solar heating subsystems The thermal subsystems share a hot water tank; multiple sets of solar heating subsystems operate in parallel.

Further, a solar thermal collector is arranged on the roof of a building; the area of the solar thermal collector is 500m ² .

Further, in the solar collector, circulating water with a lower temperature enters the collector, and after being heated by sunlight radiation, the circulating water with a higher temperature leaves the collector; the temperature sensor T1 monitors the circulating water at the outlet of the collector Temperature; the circulating water enters the hot water side of the heat exchanger after leaving the heat collector; after heat exchange, the temperature of the circulating water decreases; the circulating water enters the circulating water pump Pump1 to pressurize after leaving the heat exchanger; the pressurized circulating water flows into the solar energy In collector No. 1; at the temperature sensor T1, if the water temperature at the outlet of the collector is lower than the set temperature, the circulating water volume is reduced by adjusting the operating frequency of the circulating pump Pump1; if it is higher than the set temperature, the circulating water is increased Water volume; use the T1 temperature value to adjust the circulating water volume; in the pumping pipeline, the temperature of domestic water is relatively low, often from tap water; during the heating period in northern China in winter, the temperature of domestic water is set at 5°C.

Furthermore, when ignoring the heat dissipation loss, according to the law of energy conservation, the heat provided by the solar collector to the circulating water is equal to the heat obtained by pumping water; then the formula is:

in, is the circulating water flow rate of the solar heating subsystem, kg/s; is the circulating water average specific heat capacity of the solar heating subsystem, J/kg; The water temperature at the collector outlet of the circulating water of the solar heating subsystem, °C; The water temperature at the inlet of the collector for the circulating water of the solar heating subsystem, °C; is the domestic water flow rate of the pumping pipeline, kg/s; is the average specific heat capacity of domestic water in the pumping pipeline, J/kg; is the outlet water temperature of the pumping pipeline, °C; is the inlet water temperature of the pumping pipeline, °C; Heat _s is the heat from the solar collector.

Further, if the solar radiation absorbed by the solar collector is 800W/m ² , the solar energy obtained by the solar collector is 400kW; when the following parameters are taken,

From formula (6), it can be known that the circulating water flow rate of the solar collector and domestic water flow of pumping line No. 1 respectively,

When setting different domestic water outlet water temperature That is, the temperature value monitored by the sensor T1 can obtain different domestic water flow rates; when the user's domestic hot water consumption is small, the water temperature can be increased Like this, solar energy can be utilized to the greatest extent to increase the temperature of domestic water.

The beneficial effects of the invention include: being able to use solar energy to heat domestic water supply and generate domestic hot water. When solar energy is insufficient, the heat pump is used as an auxiliary heat source to heat domestic water supply. And use the central heating return water as the cooling source of the heat pump, which greatly reduces the power consumption of the heat pump, and at the same time reduces the temperature of the heating return water.

Description of drawings

Figure 1 is a diagram of a solar hot water heat pump system;

Figure 2 is a diagram of a solar heating system composed of multiple sets of solar heating subsystems;

Fig. 3 structure diagram of hot water tank;

Fig. 4 flow chart of hot water tank control;

Figure 5 booster pump control flow chart;

Figure 6 heat pump control flow chart;

Detailed ways

Embodiment 1: A solar hot water heat pump system and its control method. The system combines solar heating with return water from a secondary heating network in a district heating system using a heat pump. It is characterized in that the system includes: solar collectors, heat exchangers, hot water tanks, valves, water pumps, heat pumps, temperature sensors, pressure sensors, and control devices;

The solar heating subsystem includes a hot water side and a cold water side. Among them, the equipment on the hot water side includes solar hot water collectors, circulating water pumps and hot water pipelines of heat exchangers. As shown in Figure 1, the solar collector, the circulating water pump Pump1 and the hot water pipeline of the heat exchanger form the hot water side. The equipment on the cold water side includes suction water pumps, valves and heat exchanger cold water pipelines. As shown in Figure 1, the water pump Pump2, the valve Valve1 and the cold water pipeline of the heat exchanger form the cold water side.

When there are multiple buildings in the heating area, solar collectors can be placed on the roof of each building to form a set of solar heating subsystems. Several sets of solar heating subsystems can form a large solar heating system. As shown in Figure 2, the solar heating system proposed by the present invention is composed of solar heating subsystems No. 1 to No. n, and multiple subsystems share one hot water tank.

This system integrates solar heating, heat pump and heat network return water to provide domestic hot water while reducing the temperature of heat network return water. After being processed by this system, when the local solar energy is insufficient, the temperature of the domestic hot water provided can also be stabilized at 50-60°C.

The hot water of multiple solar heating subsystems shares a hot water tank. The capacity of the hot water tank is determined according to the design of solar hot water production. The hot water tank is covered with insulation. The hot water tank should be placed as close as possible to the return pipe of the heating network. The set pressure in the hot water tank adopts atmospheric pressure

Solar collectors receive heat from sunlight on the roof of a building. The circulating water in the solar collector is heated and the temperature rises, and then enters the heat exchanger. In the heat exchanger, the circulating water on the hot water side is cooled by the domestic water on the cold water side. The cooled circulating water is pressurized by the circulating water pump and then enters the solar collector again. In this way, the circulating water circulates back and forth to transfer the solar heat to the domestic water supply.

The water pump extracts domestic water from the outside. Domestic water enters the cold water side of the heat exchanger of the solar heating subsystem. Domestic water is heated by high-temperature circulating water in the heat exchanger, and then enters the hot water tank. The water pump is placed downstream of the heat exchanger to prevent the pressure of the heat exchanger pipe from being too high. An on-off valve is placed upstream of the heat exchanger to shut off the valve when it stops working.

The hot water tank is connected with a plurality of pumping pipelines, and the domestic water in each water pumping pipeline enters the hot water tank through the water pump. The water outlet of the hot water tank is connected with a booster pump. The booster pump is connected to the hot water tank and the condenser inlet and bypass pipe of the heat pump. An exhaust valve is installed on the top of the hot water tank. A temperature sensor, a water level sensor and a pressure sensor are installed in the hot water tank. When the water temperature in the hot water tank reaches the set value, the booster pump pumps the hot water in the water tank into the heat pump condenser or bypass pipe. When the water level in the hot water tank is lower than the warning water level, the booster pump stops working. When the water level in the hot water tank is higher than the warning water level, open the drain valve to lower the water level. When the pressure in the hot water tank is greater than the set value, the exhaust valve is opened.

The heat source of the heat pump is the return water of the heat network. The cold source of the heat pump is the domestic water supply provided by the hot water tank. When the solar energy is sufficient, if the domestic water temperature in the hot water tank has reached the required temperature of domestic hot water, the valve of the bypass pipe is opened to directly provide domestic hot water. When the solar energy is insufficient, the domestic water temperature in the hot water tank does not reach the required temperature of the domestic hot water, then the valve of the heat pump condenser is opened, and the domestic water is introduced into the heat pump condenser as a cold source of the heat pump. Use the booster pump to introduce the return water in the heat supply return pipe into the evaporator of the heat pump as the heat source of the heat pump. The function of the heat pump is to transfer the heat of the return water in the heating network to the domestic water, and heat the domestic water into domestic hot water. Heat pumps can be electric heat pumps, steam heat pumps and other types commonly used in the heating industry. The energy efficiency index of a heat pump is generally measured according to its COP (coefficient of performance). According to the general definition in the heat pump machinery industry, COP can be expressed as the ratio of the heat _Q1 obtained by domestic hot water to the power consumption W of the compressor.

COP＝Q ₁ /W (1)

If the environmental heat dissipation loss is not considered, the heat _Q1 obtained by domestic hot water is the sum of the heat _Q2 extracted from the return water of the heating network and the power consumption W of the compressor.

Q ₁ =Q ₂ +W (2)

The heat Q ₁ obtained by the domestic hot water is a function of the temperature T _1,in of the domestic supply water entering the heat pump condenser and the temperature T _{1,out of} the domestic hot water leaving the heat pump condenser.

in, is the mass flow rate of domestic water in the heat pump condenser, kg/s; C _p is the specific heat capacity of water, J/kg; ΔT ₁ is the temperature difference between outlet and inlet water temperature, °C.

The heat Q ₂ extracted from the heat network return water is a function of the temperature T _2,in of the heat network return water entering the heat pump evaporator and the temperature T _2,out leaving the heat pump evaporator.

in, is the mass flow rate of heat network return water in the heat pump evaporator, kg/s; C _p is the specific heat capacity of water, J/kg; ΔT ₁ is the temperature difference between inlet and outlet water temperatures, °C.

According to the second law of thermodynamics, the COP value of the heat pump cannot exceed the COP value of the theoretical reverse Carnot cycle. The COP value of the theoretical reverse Carnot cycle is shown in formula (5). Therefore, under a certain compressor power consumption W condition, a higher temperature T _2,in or a lower temperature T _1,in can increase the COP value of the heat pump.

Among them, COP _c is the COP value of the theoretical reverse Carnot cycle; T ₁ is the temperature of the heat source; T ₂ is the temperature of the heat sink.

When the solar energy is insufficient, the water temperature in the hot water tank is low. The temperature T _1,in of domestic water supply is also lower. In order to ensure that it is not infected by Legionella, etc., the set temperature T _1,out of domestic hot water is generally 50-60°C. To achieve such a set temperature, according to formula (3), a larger heating capacity Q ₁ of the heat pump is required. For further energy saving, reduce the power consumption of the compressor. The return water of the heat network can be used as the cold source of the heat pump to provide sufficient heat. In northern China, central heating projects are commonly used in winter. The return water temperature in central heating projects is generally high, generally above 40 °C. On the other hand, in the central heating project, it is hoped to reduce the return water temperature and increase the temperature difference between supply and return water. Therefore, when the solar energy is insufficient, it is very appropriate to use the heating return water as the cold source of the heat pump. Due to the high temperature of the heating and return water, which is close to the set temperature of domestic hot water, the COP value of the heat pump is generally around 5.0. At this time, the heat pump becomes an effective auxiliary heat source for heating domestic hot water. In addition, the heat pump evaporator uses water as the medium, which has good heat exchange performance. The volume of the evaporator can be greatly reduced, saving the occupied area of the heat pump.

Install a temperature sensor at the outlet of the solar collector. When the outlet water temperature of the collector is higher than the set temperature, increase the circulating water volume of the circulating water pump. When the water temperature at the collector outlet is lower than the set temperature, reduce the circulating water volume of the circulating water pump. Install the sensor at the outlet of the cold water side of the heat exchanger. When the domestic water temperature at the outlet of the cold water side is higher than the set temperature, increase the circulating water volume of the pump. When the domestic water temperature at the outlet of the cold water side is lower than the set temperature, reduce the circulating water volume of the pump. When the solar heating subsystem stops working, close the valve on the pumping pipeline. Multiple sets of pumping lines are connected to the hot water tank. The hot water tank adopts the water level control method. According to the water level set by the water tank, the flow rate of the water pump is controlled, and the control process is shown in Figure 4. According to the demand for domestic hot water, the flow rate of the booster pump before the inlet of the heat pump condenser is controlled. The control process is shown in Figure 5. According to the set temperature of domestic hot water, the start and stop of the heat pump equipment and the power of the compressor are controlled. The control process is shown in Figure 6.

The system can use solar energy to heat domestic water supply and generate domestic hot water. When solar energy is insufficient, the heat pump is used as an auxiliary heat source to heat domestic water supply. And use the central heating return water as the cooling source of the heat pump, which greatly reduces the power consumption of the heat pump, and at the same time reduces the temperature of the heating return water.

Embodiment 2: In the system of this embodiment, only one solar heating subsystem is installed, as shown in FIG. 1 . Additionally, there is a shared hot water tank. In general engineering, solar collectors can be installed on the roofs of multiple buildings. At this time, there will be multiple sets of solar heating subsystems to form a solar heating system and share a hot water tank. Multiple sets of solar heating subsystems operate in parallel. Therefore, it is only necessary to analyze the working conditions of one of the solar heating subsystems to representatively clarify the characteristics of the solar hot water heat pump system and its control system proposed by the present invention.

This system places solar collectors on the roof of a building. The area of the solar collector is 500m ² .

The solar heat collector, the circulating water pump Pump1, the heat exchanger, the valve Valve1 and the water pump Pump2 form the solar heating subsystem. Among them, the valve Valve1, the cold water side of the heat exchanger and the pump Pump2 form a pumping pipeline.

Domestic water is generally preferred to use local tap water. The temperature of tap water varies with local air temperature.

In a solar collector, circulating water with a lower temperature enters the collector, and after being heated by solar radiation, circulating water with a higher temperature leaves the collector. The temperature sensor T1 monitors the circulating water temperature at the outlet of the collector. The circulating water enters the hot water side of the heat exchanger after leaving the collector. After heat exchange, the temperature of circulating water decreases. After the circulating water leaves the heat exchanger, it enters the circulating water pump Pump1 for pressurization. The pressurized circulating water flows into the No. 1 solar collector. At the temperature sensor T1, if the water temperature at the outlet of the heat collector is lower than the set temperature (preferably 40-60°C), the circulating water volume is reduced by adjusting the operating frequency of the circulating pump Pump1. If it is higher than the set temperature, increase the amount of circulating water. Use the T1 temperature value to adjust the circulating water volume. In the pumping pipeline, the temperature of domestic water is relatively low, and it often comes from tap water. During the heating period in northern China in winter, the temperature of domestic water is assumed to be 5°C.

When ignoring heat loss, according to the law of energy conservation, the heat provided by the solar collector to the circulating water is equal to the heat obtained by pumping water. Then the formula is:

in, is the circulating water flow rate of the solar heating subsystem, kg/s; is the circulating water average specific heat capacity of the solar heating subsystem, J/kg; The water temperature at the collector outlet of the circulating water of the solar heating subsystem, °C; The water temperature at the inlet of the collector for the circulating water of the solar heating subsystem, °C; is the domestic water flow rate of the pumping pipeline, kg/s; is the average specific heat capacity of domestic water in the pumping pipeline, J/kg; is the outlet water temperature of the pumping pipeline, °C; is the inlet water temperature of the pumping pipeline, °C; Heat _s is the heat from the solar collector, w.

If the amount of solar radiation absorbed by the solar thermal collector is 800W/m ² , the solar energy obtained by the solar thermal collector is 400kW. When taking the following parameters,

From formula (6), it can be known that the circulating water flow rate of the solar collector and domestic water flow of pumping line No. 1 respectively,

When setting different domestic water outlet water temperature That is, the temperature value monitored by the sensor T1 can obtain different domestic water flow rates; when the user's domestic hot water consumption is small, the water temperature can be increased Like this, solar energy can be utilized to the greatest extent to increase the temperature of domestic water.

In the hot water tank, domestic water heated by solar energy is kept. In engineering application, the domestic water outlet water temperature of each pumping pipeline The same set temperature value is preferred. Otherwise, the temperature mixing phenomenon of various domestic water in the hot water tank will occur, resulting in uneven water temperature in various places in the water tank. Uneven water temperature is not conducive to the stable supply of domestic hot water. The hot water tank is wrapped with an outer insulation layer to isolate the heat from the hot water and the external environment. Each pumping pipeline is connected to the bottom of the hot water tank. The outlet of the water supply pipe of the water tank is installed at a position slightly higher than the bottom. The water supply pipe of the water tank is connected with a booster pump Pump3. A booster pump is connected to the hot water tank and heat pump. The booster pump pumps the hot water in the hot water tank into the heat pump condenser. The shape of the hot water tank can be cube or cylinder etc. Open the observation hole on the top of the water tank. The large water tank has a manhole. A temperature sensor, a water level sensor and a pressure sensor are installed in the hot water tank. When the water temperature in the hot water tank reaches the set value and the water level in the water tank is lower than the warning water level, the booster pump Pump3 pumps the hot water in the water tank into the heat pump condenser. When the water level in the hot water tank was lower than the warning water level (preferably 10% of the full water level in the casing), the booster pump Pump3 stopped working. When the water level in the hot water tank is higher than the warning water level, the drain valve Valve4 is opened to reduce the water level. When the pressure sensor in the hot water tank detects that the pressure in the tank is greater than the pressure setting value, the exhaust valve is opened to reduce the pressure in the tank. The pressure setting value is preferably a gauge pressure of 5KPa.

When the temperature of the hot water tank is higher than the set temperature of domestic hot water (such as 55°C), the valve Valve2 is opened, and the domestic hot water passes through the bypass pipe to directly provide domestic hot water.

When the temperature of the hot water tank is lower than the set temperature of domestic hot water (such as 55°C), the valve Valve3 is opened, and the domestic hot water passes through the heat pump to provide domestic hot water after raising the water temperature.

The heat pump is a water source heat pump based on further recovery of heating return water. The cold source of this heat pump is neither the outside air nor the surface water in rivers and lakes. This heat pump is only intended for integration in a central heating network. Since the temperature of the heating and return water can often reach above 40°C, it is much higher than the ambient temperature in cold winter. Therefore, the evaporator that can be used in the heat pump is small in size and high in heat exchange efficiency. Assume that the temperature difference from the cold source (40°C) to the heat source (55°C) is only 15°C. Preliminary experimental studies have shown that for heat pumps using electric compressors, the heating efficiency (COP) can exceed 5.0. Significantly reduces the production energy consumption of domestic hot water. On the other hand, from the point of view of the central heating system, this kind of heat pump reduces the return water temperature and improves the efficiency of the heating system. The heat pump proposed by the present invention is also a good energy-saving measure for central heating systems.

However, the heat pumps used can only be used in heating network applications with a winter heating season. For non-heating periods, the heat pump is out of service. The domestic water can be heated by the solar heating system of this system, and then the domestic water bypasses the heat pump through the bypass pipe. Then use other auxiliary heating means to heat the domestic water.

Claims (10)

1. A solar thermal water heat pump system capable of combining solar heating with return water from a secondary heat network in a central heating system using a heat pump, the system comprising: the solar water heater comprises a solar heat supply subsystem, a hot water tank, a valve, a water pump, a heat pump, a temperature sensor, a pressure sensor and a control device;

the solar heating subsystem comprises a hot water side and a cold water side, wherein equipment on the hot water side comprises a solar hot water collector, a circulating water pump and a heat exchanger hot water pipeline; the equipment on the cold water side comprises a water pump, a valve and a heat exchanger cold water pipeline;

the system integrates solar heat supply, a heat pump and heat supply network return water, provides domestic hot water and reduces the temperature of the heat supply network return water; after the treatment of the system, when the local solar energy is insufficient, the temperature of the provided domestic hot water can be stabilized at 50-60 ℃;

hot water of a plurality of solar heating subsystems shares a hot water tank; the capacity of the hot water tank is determined according to the design of the hot water quantity of the solar hot water; the hot water tank is covered by a heat insulation material; the hot water tank is placed near a return water pipe of the heat supply network as much as possible; the pressure in the hot water tank is set to be atmospheric pressure;

the solar heat collector receives sunlight radiation on the roof of a building to obtain heat, circulating water in the solar heat collector is heated to increase the temperature and enters the heat exchanger, the circulating water on the hot water side is cooled by domestic water on the cold water side in the heat exchanger, the cooled circulating water is pressurized by the circulating water pump and then enters the solar heat collector again, the circulating water flows in a reciprocating circulating manner, and the solar heat is transferred to the domestic water for supplying water;

the water pump extracts outside domestic water, the domestic water enters the cold water side of the heat exchanger of the solar heating subsystem, the domestic water is heated by high-temperature circulating water in the heat exchanger and then enters the hot water tank, and the water pump is placed at the downstream of the heat exchanger to prevent the pipeline pressure of the heat exchanger from being too high; a switch valve is arranged at the upstream of the heat exchanger, and the valve is closed when the heat exchanger stops working;

the hot water tank is connected with a plurality of water pumping pipelines, domestic water in each water pumping pipeline enters the hot water tank through a water suction pump, a water outlet of the hot water tank is connected with a booster pump, the booster pump is connected with a condenser inlet and a bypass pipe of the hot water tank and a heat pump, an exhaust valve is arranged at the top of the hot water tank, a temperature sensor, a water level sensor and a pressure sensor are arranged in the hot water tank, when the water temperature in the hot water tank reaches a set value, the booster pump pumps hot water in the water tank into the heat pump condenser or the bypass pipe, when the water level in the hot water tank is lower than an early warning water level, the booster pump stops working, when the water level in the hot water tank is higher than the early warning water level, a drain valve is opened;

the heat source of the heat pump is heat supply network backwater, the cold source of the heat pump is domestic water supply provided by the hot water tank, and when solar energy is sufficient, if the temperature of the domestic water in the hot water tank reaches the temperature required by the domestic hot water, the bypass pipe valve is opened to directly provide the domestic hot water; when solar energy is insufficient and the temperature of domestic water in the hot water tank does not reach the temperature required by the domestic hot water, a valve of the heat pump condenser is opened, and the domestic water is introduced into the heat pump condenser to serve as a cold source of the heat pump; the booster pump is utilized to introduce the return water in the heat supply return water pipe into the evaporator of the heat pump to be used as a heat source of the heat pump; the heat pump is used for transferring the return water heat in the heat supply network to the domestic water and heating the domestic water into domestic hot water;

when the solar energy is insufficient, the water temperature in the hot water tank is low; temperature T of domestic water supply_1,inIs also lower; in order to ensure that the domestic hot water is not infected by legionella, the set temperature T of the domestic hot water_1,outGenerally 50 to 60 ℃.

2. A solar thermal water heat pump system according to claim 1, wherein: when a plurality of buildings are arranged in the heat supply area, a solar heat collector is arranged on the roof of each building to respectively form a set of solar heat supply subsystem, and a plurality of sets of solar heat supply subsystems form a large-scale solar heat supply system.

3. A solar thermal water heat pump system according to claim 1, wherein: the heat pump can adopt an electric heat pump and a steam type heat pump which are commonly adopted in the heat supply industry; the energy efficiency index of a heat pump is generally measured according to its cop (coeffient of performance); according to a common definition within the mechanical industry of heat pumps, COP expresses the heat Q obtained for domestic hot water₁The ratio to the compressor power consumption W;

COP＝Q₁/W (1)

if the environmental heat dissipation loss is not considered, the heat Q obtained by the domestic hot water₁Is the heat Q extracted from the return water of the heat supply network₂The sum of the compressor power consumption W; q₁＝Q₂+W (2)

Heat quantity Q obtained from domestic hot water₁Is the temperature T of domestic water supply entering the condenser of the heat pump_1,inAnd the temperature T of domestic hot water leaving the condenser of the heat pump_1,outA function of (a);

wherein,the mass flow of domestic water in a heat pump condenser is kg/s; c_pIs the specific heat capacity of water, J/kg; delta T₁Is the temperature difference of the water temperature at the inlet and the outlet, DEG C;

heat Q extracted from return water of heat supply network₂The temperature T of the return water of the heat supply network entering the evaporator of the heat pump_2,inAnd the temperature T leaving the heat pump evaporator_2,outA function of (a);

wherein,the mass flow of the return water of the heat supply network in the heat pump evaporator is kg/s; c_pIs the specific heat capacity of water, J/kg; delta T₁Is the temperature difference of the inlet and outlet water temperatures, DEG C;

the COP value of the heat pump cannot exceed the COP value of the theoretical reverse Carnot cycle; the COP value of the theoretical reverse Carnot cycle is shown as the formula (5); therefore, under the condition of a certain compressor power consumption W, the temperature T is higher_2,inOr a lower temperature T_1,inThe COP value of the heat pump can be improved;

wherein the COP_cIs the COP value of the theoretical reverse Carnot cycle; t is₁Is the temperature of the heat source; t is₂Is the temperature of a cold source。

4. A solar thermal water heat pump system according to claim 1, wherein: in order to further save energy, the power consumption of the compressor is reduced; the return water of the heat supply network is used as a cold source of the heat pump to provide sufficient heat; because the temperature of the heat supply return water is higher and is close to the set temperature of the domestic hot water, the COP value of the heat pump is set to be 5.0; the heat pump evaporator uses water as a medium.

5. A solar thermal water heat pump system according to claim 1, wherein: a temperature sensor is arranged at the outlet of the solar heat collector; when the water temperature at the outlet of the heat collector is higher than the set temperature, the circulating water quantity of the circulating water pump is increased; when the water temperature at the outlet of the heat collector is lower than the set temperature, the circulating water quantity of the circulating water pump is reduced; a sensor is arranged at the outlet of the cold water side of the heat exchanger; when the temperature of the domestic water at the cold water side outlet is higher than the set temperature, increasing the circulating water quantity of the water pump; when the temperature of the domestic water at the cold water side outlet is lower than the set temperature, the circulating water quantity of the water pump is reduced; when the solar heating subsystem stops working, a valve on the water pumping pipeline is closed; a plurality of sets of water pumping pipelines are connected to the hot water tank; the hot water tank adopts a water level control method; controlling the flow of a water pump according to the water level set by the water tank, and controlling the flow of a booster pump in front of an inlet of a condenser of the heat pump according to the demand of domestic hot water; and controlling the start and stop of the heat pump equipment and the power of the compressor according to the set temperature of the domestic hot water.

6. A solar thermal water heat pump system according to claim 1, wherein: when solar collectors are installed on roofs of a plurality of buildings; a plurality of solar heat supply subsystems form a solar heat supply system to form a heat supply subsystem of a solar hot water heat pump system, and the plurality of solar heat supply subsystems share one hot water tank; the multiple sets of solar heating subsystems run in a parallel mode.

7. A solar thermal water heat pump system according to claim 1, wherein: arranging a solar heat collector on the roof of a building; the area of the solar heat collector is 500m²。

8. A solar thermal water heat pump system according to claim 1, wherein: in the solar heat collector, circulating water with lower temperature enters the heat collector, and after being heated by sunlight radiation, the circulating water with higher temperature leaves the heat collector; a temperature sensor T1 monitors the temperature of the circulating water at the outlet of the heat collector; circulating water enters the hot water side of the heat exchanger after leaving the heat collector; after heat exchange, the temperature of the circulating water is reduced; circulating water enters a circulating water Pump1 to be pressurized after leaving the heat exchanger; the pressurized circulating water flows into a solar heat collector No. 1; at the temperature sensor T1, if the water temperature at the outlet of the heat collector is lower than the set temperature, the circulating water quantity is reduced by adjusting the working frequency of the circulating Pump 1; if the temperature is higher than the set temperature, increasing the circulating water amount; adjusting the circulating water quantity by utilizing a T1 temperature value; in the water pumping pipeline, the temperature of domestic water is low and the domestic water is usually from tap water; during the winter heat supply period in the north of China, the temperature of domestic water is set to be 5 ℃.

9. A solar thermal water heat pump system according to claim 1, wherein: when the heat dissipation loss is neglected, according to the law of energy conservation, the heat provided by the solar heat collector to the circulating water is equal to the heat obtained by pumping water; then there is the formula:

wherein,the flow rate of circulating water of the solar heating subsystem is kg/s;the average specific heat capacity of circulating water of a solar heating subsystem is J/kg;the outlet water temperature, DEG C, of the collector which is the circulating water of the solar heating subsystem;the collector inlet water temperature, DEG C, of the circulating water of the solar heating subsystem;the flow rate of domestic water in the water pumping pipeline is kg/s;the average specific heat capacity of domestic water in a water pumping pipeline is J/kg;the outlet water temperature of the water pumping pipeline is at the temperature of DEG C;the water temperature is the inlet water temperature of the water pumping pipeline; heat_sIs the heat from the solar collector.

10. A solar thermal water heat pump system according to claim 9, wherein: if the solar heat collector absorbs the solar radiation of 800W/m²Then the solar energy obtained by the solar heat collector is 400 kW; when the following parameters are taken in the form of,

solar energy collection can be known from formula (6)Flow rate of circulating water in heaterDomestic water flow rate of No. 1 water pumping pipelineRespectively, are as follows,

when different domestic water outlet water temperatures are setNamely the temperature value monitored by the sensor T1, different domestic water flow rates can be obtained; when the domestic hot water consumption of the user is small, the water temperature can be increasedThus, the temperature of the domestic water can be improved to the maximum extent by utilizing the solar energy.