RU2464500C1 - Two-stage heat regenerator for hot water supply system - Google Patents

Abstract

FIELD: power engineering.

SUBSTANCE: invention is related to hot water supply systems, namely, to heat regenerators. A two-stage heat regenerator for a hot water supply system makes it possible to usefully spend heat of waste water to heat water supplying the hot water supply system. The regenerator comprises two recuperative heat exchangers designed to transfer heat from waste water to water supplying to water heaters. The hot supply system comprises a conventional heater for hot water (60-90°C) and a heater for cold water, which differs only by the fact that it heats water to low temperature (20÷25°C). In the first heater water is heated, which supplies to the hot heater, in the second one - water supplying to the cold heater. Due to original design of a device it may be possible to achieve a much larger saving of energy compared to available analogues with the same area of heat exchange surfaces.

EFFECT: energy saving during water heating due to achievement of synergetic effect during serial connection of two recuperative heat exchangers.

3 cl, 2 dwg

Description

A two-stage heat regenerator can be used in centralized and autonomous hot water systems for residential and public buildings.

A device for the regeneration of heat of wastewater, containing one recuperative heat exchanger, is designed to transfer heat from wastewater to tap water, the input of which is connected to a cold water network, and the output is connected to the input of a heater for hot water [1].

The possibilities of heat recovery in such a device are limited by the heat capacity of the water supplying the hot water heater, since due to the heat of the waste water it is possible to heat only the water supplying the hot water heater and only to a temperature lower than the temperature of the waste water.

A device for the regeneration of heat of wastewater, containing one recuperative heat exchanger, designed to transfer heat from wastewater to tap water, the input of which is connected to a cold water network, and the output is connected to the heater inlet, in which the water is heated to the desired temperature [2] .

Such a device allows to obtain significant energy savings for heating water, but has other limitations. Such a heat recovery system, unlike the others, can be used with only one set of water fittings.

A device for the regeneration of heat of wastewater, containing one recuperative heat exchanger, is designed to transfer heat from wastewater to tap water, the input of which is connected to a cold water network, and the output is connected to a cold water supply line to a water pipe [3].

The possibilities of heat recovery in such a device are also limited by the heat capacity of the water entering the cold water supply line to the valves, since due to the heat of the wastewater it is possible to heat only the water entering the cold water supply line to the valves, and only to a temperature lower than the waste temperature water. However, such a device has another, much more significant drawback, which requires detailed consideration.

The temperature of heating the water in the heat exchanger is highly dependent on the temperature of the water used by the user, which creates serious problems when regulating the temperature of the water by the user. Figure 2 shows an exemplary dependence of the temperature of the heating of tap water in the heat exchanger from the temperature of the water used by the user (see Figure 2, dependence 10). For example, if the user, acting on the regulating body of the water fittings, changes the water temperature by 14 ° C (from 33 ° C to 47 ° C), then the temperature of the water heating will change by 11 ° C, which will lead to an increase in the temperature of the water used by the user, approximately 8 ° C. Then the process is repeated and as a result, after some time, the temperature of the water used by the user will increase by about 16 ° C and will be equal to 63 ° C.

As a result, when using such a system, the user will be forced to periodically act on the regulator of the valves to adjust the temperature of the water.

It should also be noted that when using such a system, this problem cannot be effectively solved by installing a heater. Suppose, after a heat exchanger, we install a cold water heater that will automatically heat the water to a predetermined temperature before releasing water to the cold water supply line to the taps, so that the water temperature in the cold water supply line to the taps is constant. The set temperature in the cold water supply line cannot be higher than 25 ° C, because the temperature control range will be inconvenient for the user. Obviously, even when the heater is installed, it will not be possible to use the system (see Figure 2, dependence 10), since it is necessary that the temperature of water heating in the heat exchanger be less than the set temperature (for example, 22 ° C) over the entire range of the temperature of the water used (22 ÷ 57 ° С). If you change the heat transfer conditions (for example, reduce the heating surface area of the heat exchanger) so that at the maximum water temperature (about 57 ° C) the temperature of the water heating in the heat exchanger does not exceed 22 ° C (see Figure 2, dependence 11), then in the main mode (at a temperature of the used water of 37 ° C) the energy savings will be very small - about 6% of the total energy consumption for heating water.

As the closest analogue of the invention, the last device [3] was selected.

Figure 1 schematically shows a heat regenerator for a hot water system, consisting of two recuperative heat exchangers connected in series to a sewage removal line 1 to which wastewater receivers 2 are connected. The first heat exchanger 3 is designed to transfer heat from wastewater to tap water, supply heater for hot water 4. The second heat exchanger 5 is designed to transfer heat from wastewater to tap water supplying the heater for cold water 6. The output of the heater for hot minutes of hot water is connected to the water supply line to water fittings 7, and a heater outlet for cold water connected to a cold water supply line to water fittings 8. At line removal wastewater strainer installed baffle 9 before the first heat exchanger in the course of the waste water.

Figure 2 shows several approximate dependencies in order to illustrate the differences of the claimed invention from the closest analogue [3].

The abscissa is the temperature of the water used (t _in , ° C).

Dependence 10 - temperature of heating tap water in the heat exchanger when using the device [3]. When calculating the curve, the heat transfer conditions are selected so that at a temperature of the used water of 37 ° C, the temperature of water heating in the heat exchanger reaches 22 ° C.

Dependence 11 is also the temperature of heating tap water in the heat exchanger when using the device [3], but in other conditions. In this case, the heat transfer conditions when calculating the curve are selected in such a way that at a temperature of the used water of 57 ° С, the temperature of water heating in the heat exchanger was equal to 22 ° С.

Dependence 12 - the temperature of the heating of tap water in the second heat exchanger of the claimed invention under heat transfer conditions, selected in such a way that when the temperature of the water used is 37 ° C, the temperature of water heating in the heat exchanger reaches 22 ° C.

Dependence 13 is also the temperature of the water used by the consumer (for illustration purposes only).

Dependence 14 - temperature of tap water in a cold water network (for illustration purposes only).

The proposed heat regenerator for the hot water supply system (see Figure 1) consists of two recuperative heat exchangers connected in series to the wastewater removal line 1, to which at least one wastewater receiver 2 is connected, and designed to transfer heat from the wastewater to tap water, and the inlet of the second heat exchanger 5, which is located last along the waste water, is connected to the cold water network, and the output of this heat exchanger is connected to the inlet of the cold water heater 6, which automatically heats the water to a predetermined temperature, which is higher than in the cold water network, before releasing water to the cold water supply line to the water draw fitting 8, the inlet of the first heat exchanger 3, which is located first along the waste water, is connected to the cold water network, and the outlet connected to the inlet of the hot water heater 4, which automatically heats the water to a predetermined temperature, which is higher than in the cold water heater, before releasing water to the hot water supply line to the tapping fitting 7.

The proposed device operates as follows:

When the user opens the faucet, water is poured into the wastewater receiver and through the spillway into the wastewater line and washes the heating surface first of the first and then the second heat exchanger. At the same time, tap water moves on the other side of the heating surfaces, which is heated by the heat of the waste water. Heated water from the first heat exchanger enters the hot water heater, where it is automatically heated to a predetermined temperature (60 ÷ 90 ° C). Heated water from the second heat exchanger enters the cold water heater, where it is automatically heated to a predetermined temperature (20-25 ° C). By increasing the temperature of the water supplying the heaters, the energy consumption for heating the water is reduced.

You can get a similar technical result if you connect the input of the first heat exchanger not with the cold water network, but with the output of the second heat exchanger. In this case, tap water, before entering the first heat exchanger, will be heated in the second heat exchanger. The water flow through the second heat exchanger and its heat output will increase, but the technical result will remain the same.

To prevent clogging of the pipes or contamination of the heating surfaces in front of the first heat exchanger along the waste water can be installed mesh filtering partition 9 (see Figure 1).

The temperature of the water used by users when taking a shower, washing their hands and other water procedures is on average about 37 ° C, and directly during use, the water temperature decreases slightly. Thus, wastewater carries a large amount of thermal energy of low potential, which is not beneficially used.

By heating the water supplying the hot water heater with wastewater, a reduction in energy consumption for heating the water can be achieved. The temperature in the cold water network is too low. Water with such a low temperature is not required by the user, the user requires water with a temperature of 22 ° C to 55 ° C and, therefore, it is possible to heat cold water with wastewater. By heating the cold water, it is possible to reduce the consumption of hot water and, consequently, reduce the energy consumption for heating the water.

The main technical result is energy saving for heating water.

To achieve a technical result, it is necessary that two recuperative heat exchangers are connected in series to the wastewater removal line, the input of the first heat exchanger is connected to the cold water network or to the output of the second heat exchanger, and the output to the hot water heater, the input of the second heat exchanger is connected to the network cold water, and the outlet - to the cold water supply line to the fittings, and the wastewater removal line must be connected to at least one wastewater receiver (wash basin, shower tray, bathtub).

The heat exchangers must be connected in series, with the first heat exchanger must be switched on first along the waste water.

This arrangement of heat exchangers allows you to solve the main problem inherent in the closest analogue [3]. This issue requires a more detailed consideration.

For example, if the user sets the average temperature of the water (about 37 ° C), then part of the flow of used water (about 30%) will be provided by the heater for hot water and tap water will wash the heating surfaces of the first heat exchanger, cooling the waste water. The higher the temperature of the water used will be set, the greater the flow rate of water through the first heat exchanger and the stronger the waste water will be cooled in the first heat exchanger, and vice versa. Due to this effect, a decrease in the dependence of the temperature of water heating in the second heat exchanger on the temperature of the water used is achieved. The dependence of the temperature of water heating in the second heat exchanger on the temperature of the water used (see Figure 2, dependence 12) will be significantly less than that of the nearest analogue [3] (see Figure 2, dependence 10).

The heater for hot water can be either flowing or storage type. An energy source for heating water does not affect the achievement of a technical result. The only condition is that the heater must fulfill its function, namely, to automatically heat the water to a predetermined temperature, which is higher than in the cold water network, before releasing water to the hot water supply line to the valves.

The above signs are enough to obtain the main technical result - saving energy on heating water. From the closest analogue [3], the device is distinguished by the presence of another recuperative heat exchanger, switched on first along the waste water, the input of which is connected to a cold water network, and the output is connected to a hot water heater.

In addition to saving energy, the productivity of the heating system will increase significantly, since now with the same power of the energy source, the system is capable of releasing a greater flow rate of water of a given temperature.

However, in this case, the temperature in the cold water supply line to the valves will depend on the temperature of the water used, and the water heating system can only be considered functional if the system is able to provide a stable temperature of cold and hot water in the water lines to the valves, therefore, the output the second heat exchanger must be connected to the cold water supply line to the water fittings through the cold water heater.

The dependence of the temperature of water heating in the second heat exchanger on the temperature of the water used (see Figure 2, dependence 12) allows to obtain significant energy savings. For example, if the set temperature in the cold water heater is equal to 22 ° C, then in the entire temperature range of the used water, the temperature of the water heating in the second heat exchanger will vary within small limits (22 ÷ 24 ° C, see Figure 2, dependence 12 ), and in the main mode (at a temperature of the used water of 37 ° C) energy saving will be the maximum possible. Obviously, it is impossible to achieve such an effect when using the closest analogue [3] (see FIG. 2, dependence 10, 11) for reasons already described in the description of the closest analogue.

The heater for cold water can be either flowing or storage type. An energy source for heating water does not affect the achievement of a technical result. The only condition is that the heater must fulfill its function, namely, to automatically heat the water to a predetermined temperature, which is higher than in the cold water network, but lower than in the hot water heater, before releasing water to the cold water supply line to the valves.

The difference between the set temperatures of the hot water heater and the cold water heater determines the range of regulation of the water temperature.

It should be noted that when using the claimed invention, large energy savings can be obtained in the main mode (at a temperature of used water of 37 ° C) in comparison with analogues [1] and [3] with the same heat exchange surface area due to the greater consumption of tap water cooling waste water. Suppose that the thermal power would remain the same, then with an increase in the flow rate of tap water cooling the wastewater, the water should heat less when passing heating surfaces, which will lead to an increase in temperature head. Since heat transfer should occur more intensively with an increase in the temperature head, it means that the thermal power of the heating surfaces cannot remain the same and should increase.

Bibliography

1. Patent US 2010139579 A1 (Water heater special for bathroom), inventors - SU SHAOHUA, TAN QING, publication date - 06/10/2010.

2. Patent CN 1686037 A (Energy saving bath room capable of self heating water), inventors - CHEN FEI, HE BO, LI FENGQUAN, publication date - 10.26.2005.

3. Patent US 4372372 A (Shower bath economizer), inventors - RAYMOND HUNTER, date of publication - 08.02.1983.

Claims (3)

1. The heat recovery system for the hot water system, consisting of two recuperative heat exchangers connected in series to the wastewater removal line to which at least one wastewater receiver is connected, and designed to transfer heat from the wastewater to tap water, the second heat exchanger input , which is located last along the waste water, is connected to the cold water network, and the output of the second heat exchanger is connected to the cold water supply line to the water fittings, the input of the first heat the exchanger, which is located first along the wastewater, is connected to the cold water network or to the outlet of the second heat exchanger, and the output of the first heat exchanger is connected to the inlet of the hot water heater, which automatically heats the water to a predetermined temperature, which is higher than in the cold water network before releasing water to the hot water supply line to the taps. 2. The heat recovery system for the hot water supply system according to claim 1, characterized in that the output of the second heat exchanger is connected to the cold water supply line to the taps through a cold water heater that automatically heats the water to a predetermined temperature that is higher than cold water networks, but lower than in a hot water heater. 3. The heat recovery system for the hot water supply system according to any one of claims 1 or 2, characterized in that a strainer screen is installed on the sewage removal line in front of the first heat exchanger along the waste water.

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