Method of connecting a low-grade heat source to a hot water supply system

Abstract

The invention relates to the field of thermal engineering and to systems for supplying hot water to buildings. A method of connecting a low-grade source to a water supply system envisages supplying cold water from a water pipe to a primary stage heater where it is heated by a supply of a heat transfer medium from a heat network pipe, or by a supply of heat from a low-grade energy source. Heat from the low-grade energy source is pumped by a heat pump into a storage tank where a heat transfer medium is heated before being pumped into the primary stage heater. Cold heat transfer medium is returned to the storage tank and to the heat pump. Water heated in the primary stage heater is supplied to a secondary stage heater where it is further heated by a heat transfer medium from the heat network, after which cold heat transfer medium is sent to a heat network pipe and the heated water is supplied to the water supply system, with water from the system being returned in part to the secondary stage heater and mixed with water from the primary stage heater. The technical result consists in enhancing the potential of individual heating substations having dual-stage heating systems by connection to energy-efficient low-grade heat sources, and in reducing the load on the heat network.

Description

[0001] METHOD OF CONNECTING A LOW-POTENTIAL HEAT SOURCE TO A HOT WATER SYSTEM

[0002] The invention relates to the field of thermal power engineering and can be used in hot water supply systems (hereinafter referred to as DHW) of residential and public buildings and residential microdistricts.

[0003] District heating networks for heating and hot water supply of houses and other buildings are well known, particularly in certain countries. In district heating networks, the heat carrier (usually water and / or steam with some additives) is heated in a boiler room / combined heat and power plant (CHP). From there, the heat carrier is distributed through pipes and sometimes through intermediate heat exchangers or mixing circuits to many buildings. The buildings contain individual heating points where the tap water is heated for hot water supply purposes, and the heat carrier is used for general heating and hot water supply purposes.

[0004] Currently, a two-stage connection scheme for DHW heaters is widely used for heat supply of buildings of various purposes. The connection scheme for DHW heaters in closed heat supply systems is selected depending on the ratio of the maximum heat flow for hot water supply Qhmax and the maximum heat flow for heating Qomax (see, for example, the Code of Practice SP 510.1325800.2022 "Heating points and internal heat supply systems"):

[0005] 0.2 > Qhmax / Qomax >1 ,2 - single-stage parallel circuit;

[0006] 0.2 < Qhmax / Qomax <1 .2 - Two-stage SHvME.

[0007] A common recommendation (see, for example, No. 261-FZ Federal Law of the Russian Federation "On Energy Saving and Improving Energy Efficiency and Amending Certain Legislative Acts of the Russian Federation") is to use low-potential heat sources for DHW systems. However, when using heat pumps, the temperature of the heated medium significantly affects their performance coefficient COP (abbr. Coefficient of Performance), equal to the ratio of total heat output to total energy consumption. Heating the coolant to a temperature of 65-70 °C, necessary to ensure the sanitary standard of hot water temperature, leads to a significant increase in the energy consumed by the heat pump and a decrease in the economic efficiency of using the heat pump.On the other hand, in a two-stage connection scheme of DHW heaters, water heating is divided into two parts, in the first stage up to 35-40 °C, in the second up to 65 °C, which is convenient for using heat pumps as a heat source for the first stage of heating.

[0008] A heating, air conditioning and hot water supply system based on renewable energy sources is known from the prior art (see Efimov N.N. Heating, air conditioning and hot water supply system based on renewable energy sources for the Southern Federal District / / Technical sciences. News of higher education institutions. North Caucasian region. - 2012. - No. 1. - Pp. 62-65 / [Electronic resource]. - Access mode: URL: https: / / cyberleninka.ru / article / n / sistema-otopleniva-konditsionirovaniya-i-qoryacheqo-vodosnabzheniva-na-baze-vozobnoylyaemyh-istochnikov-enerqii-dlya-yuzhnoqo / viewer), operating in heating and hot water supply modes; passive air conditioning and hot water supply. Switching from one operating mode to another is carried out by switching flows with three-way valves using servo drives. The control signal to the servo drives comes from the room thermostat located in the heating point room. In the heating and DHW mode, the three-way valves switch according to the thermostat signal.In this case, the heat pump operates in the nominal mode, providing both heating and hot water supply to the consumer. In the passive air conditioning and hot water supply mode, at the thermostat signal, the three-way valves disconnect the heat pump from the heating and connect the ground heat exchanger directly to the fan coils, which provide air cooling in the room. Hot water supply is still provided by the heat pump, which in this case operates at a reduced load.

[0009] A hot water supply system is known (see patent CN206300246U, published 04.07.2017), including: a tank for heat supply water, the inlet from the side of the low-temperature receiver is connected to a water supply pipe, and the outlet from the side of the low-temperature receiver is connected to a hot water pipeline; a photovoltaic and one photothermal solar subsystem is connected through a first heat exchanger to an inlet / outlet port of the tank for supplying water on the side of the first heat source; an external heat exchange subsystem with a ground heat pump is connected through a second heat exchanger to the photovoltaic and photothermal solar heat exchanger of the subsystem, and the generated thermal energy is intended for simultaneous heating of a shallow soil layer during the conversion of solar energy into electrical energy using a group of valves in the spring and autumn operating mode;It is also connected with the ground source heat pump room heat exchange subsystem to pass through the valve group in winter operating mode by transmitting the energy of shallow soil to the geothermal heat pump room heat exchange subsystem; The geothermal heat pump room heat exchange subsystem is connected through the 3rd heat exchanger to the input / output port of the heat supply tank from the secondary heat source side, and the heat supply tank is provided by transmitting the energy of shallow soil by the valve group in winter operating mode.

[0010] The closest solution to the claimed one is a hot water supply system (see Russian patent for invention No. 2793831, published on June 29, 2022), containing supply and return pipelines of the heating network, a building heating system used as a low-potential heat source, a heat pump, and a circulation pump. The system additionally comprises a hot water storage tank, a recuperative heat exchanger, a three-way valve and pipes for supplying and discharging the make-up heat carrier, wherein the hot water storage tank is connected to the heat pump via the heating medium, the recuperative heat exchanger is installed in front of the hot water storage tank via the heated medium, the three-way valve is included in the heating system circuit and is connected via the pipe for supplying the make-up heat carrier to the supply pipeline of the heating network, the pipe for discharging the make-up heat carrier is included in the low-potential circuit of the heating system in front of the three-way valve and is connected to the return pipeline of the heating network.

[0011] The disadvantages of known analogues are that they do not assume connection to two-stage heating, which is widely used, for example, in the Russian Federation. That is, various existing schemes for connecting heat pumps to DHW heating require significant improvement of the heating scheme.

[0012] The task, which the claimed invention is aimed at solving, is the development of a scheme for connecting heaters from a heat pump to a two-stage scheme for connecting DHW heaters for residential and public buildings, residential microdistricts.

[0013] The technical result of the invention consists in expanding the functional capabilities of individual heating point devices with two-stage heating systems by providing the possibility of connecting energy-efficient low-potential heat sources to them, as well as reducing the load on the heating network and increasing the economic efficiency of its use.

[0014] The technical result is achieved by a method of connecting a low-potential heat source to a hot water supply system, which includes stages in which cold water from a water supply system is supplied to at least one first-stage heater, where it is heated by supplying a heat carrier from a return pipeline of a heating network or by supplying heat from a low-potential energy source. In this case, the heat carrier from the low-potential energy source is pumped through at least one heat pump into an accumulator tank, in which the heat carrier circulating in it is heated. The heat carrier in the accumulator tank, having displaced the cold water, is pumped by a pump into the first-stage heater, where it heats the water intended for hot water supply, and the cooled heat carrier from the first-stage heater returns back to the accumulator tank and is then supplied to the said heat pump.The tap water heated in the first stage heater is fed to at least one second stage heater, where it is heated with a heat carrier from the heating network, after which the cooled heat carrier is sent to the return pipeline of the heating network, and the heated water is supplied for the needs of the DHW, the water in the DHW system of the building partially returns through the circulation pipeline to the second stage heater, mixing with the water received from the first stage heater. A low-potential energy source within the framework of the described invention is understood to be a secondary or renewable energy source, for example, the heat of exhaust air, the heat of ground or waste water, or another low-potential energy source.

[0015] The heat carrier is understood to be the entire volume of heated water moving through pipelines into the heating system or into the hot water supply system, as well as steam and condensate.

[0016] The essence of the claimed invention is explained by figures. Figure 1 shows a diagram of connecting a low-potential heat source in the form of a heat pump to a hot water supply system with heating from the return pipeline of the heating network, and Figure 2 shows a diagram of connecting a low-potential heat source in the form of a heat pump to a hot water supply system with heating from a heat pump. The following is indicated by numbers:

[0017] 1 - first stage heater,

[0018] 2 - second stage heater,

[0019] 3-7 - pipeline shut-off valves,

[0020] 8 - make-up pump,

[0021] 9 - circulation pump for the circuit with the first stage heater,

[0022] 10 - circulation pump for the circuit with heat pumps,

[0023] 11 — pressure limiting regulator “to itself”,

[0024] 12 - storage tank,

[0025] 13 - heat pump,

[0026] 14-16 - pipeline shut-off valves.

[0027] The DHW system implementing the claimed invention has two heating stages: up to a temperature of 35°-40°C (implemented by at least one first stage heater 1) and in the range from 35°-40°C to the sanitary standard of 65-70°C (implemented by at least one second stage heater 2). In this case, heating can be performed in two ways: from the return pipeline of the heating network or from the heat pump 13. The first stage heaters 1 and the second stage 2 have the design and operating principle of heat exchangers: one of the water flows is the heating coolant, the other is the heated hot water for sanitary needs. In this case, heat from the more heated coolant is transferred through the surface of the heater walls to the less heated coolant. The first stage heater 1 is connected to the return pipeline of the heating network through pipelines with shut-off valves (gate valves) 3 and 4.Also, the first stage heater 1 is connected to at least one heat pump 13 through pipelines with shut-off valves (gate valves) 5, 6 and an accumulator tank 12. The number of heat pumps 13 depends on the nature of the low-potential energy source. The heat pump 13 is connected to the low-potential heat energy source on the evaporator side, and is connected to the accumulator tank 12 and the first stage heater 1 on the condenser side by a system of pipelines. The presence of the accumulator tank 12 is due to the uneven operation of the DHW system - there are peak load hours, there are minimum load hours, and the accumulator tank allows smoothing out the peaks.The circulation of the heat carrier between the storage tank 12 and the first stage heater 1 is performed by the circulation pump 9 for the circuit with the first stage heater, designed to ensure the heat consumption through the first heating stage at the maximum consumption of heated tap water (maximum hourly water consumption for DHW). The circulation of the heat carrier between the storage tank 12 and the heat pump 13 is performed by the circulation pump 10 for the circuit with heat pumps, designed to ensure the heat carrier consumption at the maximum power of all heat pumps 13, if there is more than one. The total thermal power of heat pumps 13 must be no less than the average hourly heat consumption for heating the first stage of DHW. The feed pump 8 is designed to feed the storage tank 12 in emergency situations when it becomes necessary to feed the coolant circuit of the heat pump 13 from the return pipeline of the heating network (see Fig.1) or from the water supply system (see Fig. 2). The pressure limiting regulator "to itself" 11 for the heat pump 13 is installed on the pipeline between the heat pump 13 and the storage tank 12, provides the required pressure in the heat pump 13 and reduces its value to the permissible value in the storage tank 12 and the first-stage heater 1. The second-stage heater 2 is connected to the DHW circulation circuit through pipelines with shut-off valves (valves) 14-16.

[0028] The method of connecting a low-potential heat source to the DHW system is carried out as follows. Water intended for DHW from a cold water supply is fed to at least one first-stage heater 1 in a known manner, where it is heated from an initial temperature to a temperature of +35 - +40 °C. Heating of sanitary water in the first-stage heater 1 is carried out by feeding a heat carrier from the return pipeline of the heating network or from at least one heat pump 13.

[0029] When the first stage heater 1 is operating with heating from the return pipeline of the heating network, shut-off valves 5-7 are closed, and 3-4 are opened.

[0030] When the first stage heater 1 is operating from the heat pump 13, shut-off valves 3-4 are closed and 5-7 are opened.

[0031] Heat pump 13 transfers heat from the low-potential energy source to storage tank 12, heating the coolant to approximately 45 °C for the purpose of heating the DHW in the first-stage heater 1. When warming up to peak load hours, hot water in storage tank 12 displaces cold water. The operating mode of circulation pump 10, filling storage tank 12 with heat, is calculated and set in advance in accordance with information on peak hours and hours with minimum load. Pump 9 pumps out the heated coolant from the upper part of the storage tank 12 and transfers it to the first stage heater 1, then the cooled coolant returns to the lower part of the storage tank 12. The cooled coolant in the lower part of the storage tank 12, by means of the circulation pump 10, enters the heat pump 13 through the pipelines. In the case of heating the sanitary hot water in the first stage heater 1 from the return pipeline of the heating network, pump 9 is switched off.If it becomes necessary to replenish the heat carrier circuit of the heat pump 13, the feed pump 8 is switched on and water is pumped in from the return pipeline of the heating network (see Fig. 1) or from the water supply (see Fig. 2). If the required pressure at the entry point of the heated heat carrier from the heat pump 13 into the storage tank 12 is exceeded, the pressure limiting valve 11 reduces its value to the permissible value in the storage tank 12 and the first stage heater 1.

[0032] Water intended for DHW, heated in at least one first-stage heater 1, enters through a pipeline through an open valve 14 into at least one second-stage heater 2, where it is heated to a temperature of +65... +70 °C in accordance with sanitary standards by a heat carrier entering the second-stage heater 2 from the heating network (temperature of about +90... +150 °C), after which the cooled heat carrier is directed into the return pipeline of the heating system, and the heated water is fed through an open valve 16 into the circulation circuit for DHW needs. Water in the building's DHW system partially returns through the circulation to the second-stage heater 2, mixing with water coming from the first-stage heater 1. If necessary (for example, when performing repair work), it is possible to turn off the second-stage heater 2. In this case, shut-off valves 14 and 16 are closed, and 15 is opened.

Claims

CLAUSES OF THE INVENTION A method for connecting a low-potential heat source to a hot water supply system, comprising the steps of feeding cold water from a water supply system into at least one first-stage heater, where it is heated by feeding a heat carrier from a return pipeline of a heating network or by feeding heat from a low-potential energy source, wherein the heat from the low-potential energy source is pumped through at least one heat pump into an accumulator tank, in which the heat carrier circulating in it is heated, the heat carrier in the accumulator tank, having displaced the cold water, is pumped by a circulation pump into the first-stage heater, where it heats water intended for hot water supply, and the cooled heat carrier is fed back into the accumulator tank and is then fed into the said heat pump, the water heated in the first-stage heater is fed into at least one second-stage heater,where it is heated with a coolant from the heating network, after which the cooled coolant is sent to the return pipeline of the heating network, and the heated water is supplied for hot water supply needs, the water in the building's hot water supply system is partially returned through the circulation pipeline to the second-stage heater, mixing with the water coming from the first-stage heater.

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