Balancing fittings in a water heating system

Energy conservation and improving energy efficiency are priority areas for the development of the global economy. The need to increase the energy efficiency of the engineering equipment of buildings is due to both the requirements to reduce the energy consumption of buildings in general, and the increase in the proportion of energy-consuming climate systems used in modern construction. In large modern office, hotel and residential complexes to achieve the greatest energy efficiency it is necessary to use various technical solutions. The main element of an energy-efficient heating system is regulation. Balancing devices allow to not only balance and tune the system at any time of operational period but also serve as stop valves during reparation and diagnostics. Determination of energy savings bases on the average value heat consumption before and after modernization, depending on the type of installed valves or their combination. The focus of the work is hydraulic calculation of the heating system the authors conduct research on the effect of differently balancing fittings on the hydraulics of the heating system.


Introduction
According to the Federal Law "About energy saving and increasing energy efficiency and on making changes certain legislative acts of the Russian Federation" dated November 23, 2009 № 261-FZ (latest edition), there is a need to increase energy efficiency based on modernization, technological development and transition to a rational and environmentally responsible use of energy resources.
The energy efficiency of the heating system consists of the effective use of the source fuel energy potential, i.e. the heating system must use the maximum amount of energy from the source fuel, while the rooms should not overheat or cool. In decentralized heating (for example, a small cottage) it is possible to achieve a comfortable microclimate much easier in view of its size. However, as in large modern office, hotel and residential complexes, to achieve the greatest energy efficiency of the system, it is necessary to use various technical solutions to achieve the greatest energy efficiency of the system [1].
The main element of an energy-efficient heating system is its regulation, that allows to supply the heat carrier to the heating devices in sufficient quantities to ensure the heat balance of the rooms with a changing outdoor temperature and an indoor air temperature set by a room user (within the normalized range). For this functional purpose of the room). Balancing devices are used to perform the regulation of heating system, they allow not only to balance and tune the system at any time of its installation but also serve as stop valves during repairment and diagnostics [2,3].
In this paper, three types of balancing devices are considered: a throttling orifice, a manual balancing valve, and an automatic balancing valve [4,5].

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The throttling orifice is a steel disc with a hole in the middle. The flow is regulated by changing the diameter of the inner hole.

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Manual balancing valve -the changes in the position of the spindle drives the working cone, that reduces or increases the diameter of the coolant section.

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The automatic balancing valve is set to the maximum water flow rate. The pressure will increase as a coolant consumption decrease with changes on radiator thermostat. At that moment the capillary tube comes into effect. It uses an automatic valve that instantly analyzes the differential pressure. Balancing valves should be installed to divide the system into modules that can be balanced independently of the rest of the system, i.e. each branch, each riser and each source must be equipped with a balancing valve.
The purpose of the study is to develop a methodology for choosing a technical solution for balancing heating systems based on energy efficiency indicators of the system.

General data
The object of study is a two-pipe heating system with a lower wiring of the main pipelines in the residential three-story two-entrance house with unheated basement and attic. There is water as a heat carrier with a temperature in the supply pipe of 80 °C and a return of 60 °C is taken as a heat carrier. Types of pipes -ordinary steel water-gas piping according to GOST 3262-75 PN 1.0 MPa, Tmax 150 °C. calculation of hydraulic pressure losses in system sections; − hydraulic linkage of parallel instrument and other branches of the system, using control valves for dynamic balancing during unsteady thermal and hydraulic modes of the heating system; − determination of pressure loss and flow rate in the heating system. The heat load of the design section is equal to the heat flux that must transfer (on the supply pipelines) or transferred (on the return pipelines) the coolant that is transported on the site. The flow rate of the coolant in the area is determined by the formula (1): where c = 4.2 kJ/(kg·°C) is the specific heat capacity of water; t γ -rated temperature of the hot fluid in the heating system, °C; 0 t -rated temperature of the cooled coolant in the heating system, °C.
The internal diameter of the pipeline is determined according to the table, knowing the flow rate of the coolant in this section and the temperature difference of the supply and return pipes.
Pressure loss on an arbitrary section of the system is the sum of two components: pressure loss on hydraulic friction during transportation of the coolant in the pipe and pressure loss in local resistances.
where G -mass flow rate of the coolant of the section, kg/h; S -the hydraulic resistance characteristic of the system section, Pa/(kg/h)², calculated by the formula (3): where A -specific dynamic pressure, Pa/(kg/h)²; ξadj -adjusted coefficient of local resistance of the section.
The determination of the coefficient of hydraulic friction is carried out according to the formula (4) where Re -Reynolds number; ke -equivalent pipe roughness, mm. The specific dynamic pressure in the pipeline with fixed diameter is the dynamic pressure created by the flowing coolant at a mass flow rate of 1 kg/h determines by the manufacturer of the pipeline, or by the formula (5): The hydrodynamic characteristics of the pipes can be determined from the table provided by the manufacturer.
The hydraulic resistance of the heating system is defined as the sum of the pressure losses in the sections.
The diameter of the throttling orifice hole is determined by the formula (7): where G -mass flow rate of the coolant of the section, kg/h; ∆PHS -pressure loss in the regulation section, MPa.

Hydraulic calculation in the program
Hydraulic calculation of the heating system can be done manually, as well as using software that performs hydraulic calculation, selection of the diameters of the fittings, as well as heating devices, for example, AUDITOR CO 6.0, AUDITOR CO 3.8, KAN CO 3.8, HERZ CO 3.8, DAFFOSS CO 3.8, Rehau CO3.8 etc.
In this work, the hydraulic calculation is performed in the program Rehau CO 3.8. Before starting the calculation, general data and a detailed flat diagram of the heating system of the entire building with heat losses and temperatures in each room, pipe lengths and necessary fittings should be entered.

Results
The calculation in the program was carried out with various variations of balancing reinforcement (Table 1): 1. Without any balancing and shutoff valves; 2. Automatic balancing fittings on risers of the system -as reinforcement selected AB-PM -differential pressure and direct flow control; 3. Manual balancing valve and globe valve on risers, as reinforcement selected USV-I, shut off valve with smooth presetting, female thread; 4. Balancing fittings in front of the heating devicesdirect thermostatic valve with presetting, RTR-N, as well as a direct shut-off valve with the possibility of connecting a drain valve, designed to turn off a separate heating device for dismantling or maintenance without draining the entire system; 5. The combination of balancing valves № 1: automatic adjustment on risers and manual in front of heating appliances; 6. The combination of balancing valves №2: manual adjustment on risers and manual adjustment in front of radiators; 7. Throttling orifice on the risers of the system. Table 1 presents the summary calculation results.   As we can see from the results obtained, the installation of balancing valves increases the hydraulic resistance of the system. The software calculation does not consider the resistance caused by the installation of throttling orifice.

Comparison of the results
The percentage of calculations in relation to manual is: 8 1 17703 17400 1.7% 17703 The discrepancy between manual hydraulic calculation and hydraulic calculation without reinforcement is due to roundings that were used in manual calculations.

Fig. 3. A histogram of the results of calculations for overheating of premises
As we can see from the results obtained, the system overheats the most in the absence of any balancing valves. The heating system is not energy efficient. The least hydraulic resistance and overheating of the system is observed when the installation of throttling orifice in each riser of the heating system. But with this design option, users of the heating system cannot control the heat transfer of the heater.  Energy savings with balancing with throttling orifice prevail over calculation option № 1 without the use of fittings by 6.2%.
Also, an energy efficient option is the calculation with balancing on risers and radiators. In this calculation, we observe the greatest hydraulic losses, but the smallest overheating of the system and the ability of users to adjust the comfortable temperature in the rooms by adjusting the pre-setting of the heating devices.

Discussion
In [4][5][6], field studies of the energy efficiency of heating systems using balancing valves of various types were carried out. According to the research results, energy savings were determined based on the average heat consumption before and after modernization, depending on the type of installed valves or their combination. In [7], the results of an experimental study are presented showing that the use of manual balancing valves reduces the energy efficiency of the system. This circumstance is caused by the fact that the comfort temperature is not maintained inside that leads to overheating and excessive fuel consumption. Works [8][9][10][11][12] show the positive use of thermostatic valves on heating radiators. And the article [13] gives the analysis of the control quality of a thermostatic valve. In [14], studies were conducted on the effect of balancing valves on the flow shape and conclusions were drawn that the changes in the flow shape are insignificant.
The problem of energy efficiency of the heating system is also considered in [15][16][17][18].
In [19,20], show the example is given of using automatic balancing fittings, which reduced the energy consumption by pumps of the heating system by 14%.
In [21,22], the authors conduct research on the effect of balancing fittings on the hydraulics of the heating system. In this article, a similar conclusion is obtained that shut-off and control valves increase the hydraulic losses of the system, but at the same time increase its energy efficiency.
The energy efficiency of the building will heal not only from the energy efficiency of engineering systems, but also from the building envelope. Comparison of materials and proposals for improving the energy efficiency of the entire building are considered in [23][24][25].
Article [26] says that it is necessary to increase the energy efficiency of not only new buildings under construction, but also to invest in improving the energy efficiency of already constructed buildings. And the work [27] analyzes the development of regulatory and legislative support for the energy efficiency of buildings in the Russian Federation.

Conclusion
In this paper, the main attention is paid to the hydraulic calculation of the heating system.
1. According to the results of the calculations, the smallest hydraulic resistance is possessed by a system that is balanced by throttling orifice.
2. The most energy-efficient is the system that is regulated by throttling orifices set on the risers.
3. From the comfort of use as well as high energy efficiency point of view designed systems № 4, 5, 6 that have adjustments on the risers and radiators are the best.
Balancing valves add additional resistance to the pipeline, but at the same time regulates the coolant, making the system more energy efficient. Thus, the use of a balanced heating system will allow people living in large residential complexes to set their own comfortable indoor temperature by adjusting the thermostatic valve on the heating radiator. In the future, when the meter is installed on the radiator it will allow to save finances.
Also, the installation of throttling orifice regulates the system in the way that the coolant with the specified temperature parameters comes to the most remote riser, without cooling down.