Return Water Research Articles

A novel concept for energy-efficient floor heating systems with minimal hot water return temperatures

The study proposed and investigated a new concept for hydronic floor heating in dwellings with the aim of reducing hot water temperatures toward a more robust and energy efficient operation. Modern heating systems often rely on low return temperatures to improve operation efficiencies through reduced heat losses from return pipes, greater utilisation of condensation heat from boiler flue gases or from the increased COP of heat pumps. Our study investigated the potential of using an apartment heating substation (or ‘flat station’) to supply space heating through two mixing loops using hot water supply temperatures of 30°C to bathrooms and 24°C to all non-bathrooms. The concept sought to minimise hot water supply temperatures to utilise a self-regulating effect while ensuring low return temperatures. In the first iteration of the concept, the high-temperature return water from the bathrooms was cascaded to the non-bathrooms to heat these rooms and provide further cooling of the hot water. The calculated energy-weighted return temperature under this original concept was 25.6 °C for the example case of a new energy-efficient apartment building. However, there was limited potential to utilise the cascaded coupling, so considering the complexity of its configuration and controls, the authors simplified the proposed concept to two mixing loops without a cascaded coupling. The calculated return temperature with the updated concept was 25.7 °C. The control of the floor heating included some aspect of self-regulation because the heat transfer strongly depended on the indoor temperature. Based on the results of this preliminary investigation, the concept may provide a robust and energy-efficient option for configuring floor-heating systems in situations that rely on low hot-water return temperatures.

Research of cascade averaging control in hydraulic equilibrium regulation of heating pipe network

Abstract The heating pipe network system with such dynamic characteristics as nonlinearity and large time lag may cause hydraulic disorder. To solve this problem, this paper proposes a unit control-based hydraulic equilibrium control strategy, which constructs an equilibrium regulation system for heating pipe networks by optimising the inlet device of each unit and using a novel control theory. By developing a cascade control system to control the return water temperature and the pressure difference between supply and return water of the branches at each unit of the pipe network, we were able to stabilise the pressure and control the temperature. Then, we used the averaging control theory to set the parameters of regulation systems between each unit. The research results indicate that, compared to the traditional single-loop negative-feedback return water temperature control system, the cascade averaging controller has a better control effect than the single-loop PID controller. This is because it has a smaller overshoot and can cope with system interference factors quickly. Therefore, the temperature of return water between each unit can be coordinated and fluctuation is within a smaller range. This effectively eliminates the influence of static and dynamic hydraulic disorder on entire system stability.

Quantitative and qualitative indicators of natural and waste waters in the Dnipro basin

Analysis of the state of water resources in Ukraine provides an opportunity to improve the ecological situation on the basis of hydrographic and water management zoning using the latest methodological approaches and technologies for constructing the water balance of the basin areas. The aim of the research is to establish patterns of change in the quality indicators of the country's water resources in the largest basin of the Dnipro River. The study was carried out on the basis of an assessment of indicators for monitoring changes in the quantitative and qualitative indicators of water resources in the Dnipro basin in 2016-2021.A decrease in the Dnipro runoff was recorded: the average long-term natural runoff at the mouth is 53.3 km3, and the actual runoff is about 11 km3 (20%) less than the natural runoff. A decrease in the quantitative indicators of water intake from the Dnipro basin in 7365 million m3, a decrease in the quantity (up to 547.1 million m3) and a deterioration in the quality of return water and the general state of water resources in the basin from the northwest to the southeast. The measurements’ results of the indicators of the waters’ qualitative state in the reservoirs and the main watercourses of the basin at the locations of the monitoring points indicate that the norms are exceeded by a multiplicity of more than 5 times, including in terms of BOD and COD, which reflect the intensity of pollution of water bodies with easily oxidizing and difficult oxidizing organic compounds. The screening of pollutants revealed the content of pesticides, drugs, antidepressants, heavy metals-carcinogens in the Dnipro water, which makes it possible to investigate the problems with water resources, taking into account the specifics of the river basin. Such an assessment shows that climate change and industrial enterprises, as notable anthropogenic component, are significant factors affecting water resources. This indicates the importance of the direction of the policy of state regulation on water monitoring, the introduction of an irrigation and drainage strategy, the construction of centralized water supply and sanitation systems and strict control over the indicators of wastewater discharge.

Feasibility of a booster for DHW circulation in apartment buildings

With increasing focus on the performance of district heating systems, a concept is developed to obtain low district heating return temperatures from domestic hot water systems with a high share of circulation loss. For these systems, it is challenging to realize a low district heating return temperature by direct heat exchange only, due to the high flow of circulation return water at 50 °C. The concept is termed Circulation Booster. The purpose of the Circulation Booster is to boost the domestic hot water circulation temperature and at the same time secure a low district heating return temperature from this part of the service. The domestic hot water circulation temperature is heated in two steps: direct heat exchange and a heat pump. The heat source for the Circulation Booster is district heating, and the heat pump itself is driven by electricity. The paper includes the field experiences from a 1-year test period, concluding that the concept is operating as intended. Further, the performance results regarding electric consumption and district heating return temperatures and an economic feasibility study are presented. The current tariff structure in Denmark related to the district heating return temperature and electric costs gives a feasible economic case for the Circulation Booster concept with a direct payback time of 5,1 years. An increasingly progressive tariff scheme for low district heating return temperature or lower electric costs could further improve the economic feasibility of the Circulation Booster concept.

Energy, exergy and exergoeconomic evaluation of the air source transcritical CO2 heat pump with internal heat exchanger for space heating

• The system performance of CO 2 heat pump with internal heat exchanger is compared. • The system performance is evaluated with energy, exergy and exergoeconomic analysis. • The COP and exergy efficiency is significantly enhanced with the proposed system. • The cost per unit of exergy production is obviously reduced with the proposed system. • The internal heat exchanger effectiveness and sensitivity analysis are conducted. Currently, the air source heat pump is widely used for space heating. Although the CO 2 has great potential in the refrigeration system, the basic transcritical CO 2 heat pump performance is restricted by the huge throttling irreversibility caused by the higher gas cooler outlet temperature. The internal heat exchanger has been investigated extensively from the energetic perspective. However, little information is available about the exergy analysis, let alone the exergoeconomic analysis. In this paper, the transcritical CO 2 heat pump with/without the internal heat exchanger is studied with the energy, exergy, and exergoeconomic analysis. Results show that the optimal coefficient of performance can be increased to 2.96 and 2.17 in the different heating terminals. The enlarged internal heat exchanger effectiveness is also beneficial to reduce the optimal discharge pressure and increased the system coefficient of performance. The throttling valve irreversibility is decreased from 0.067 to 0.145 kW·kW −1 to 0.040–0.071 kW·kW −1 . With total irreversibility decrement, the exergy efficiency can be effectively improved, resulting in the 55.65%-73.42% reduction of the throttle valve cost rate. Considering the CO 2 compressor investment, its total exergy cost rate increment is reached up to 34.06%-50.21%, leading to the higher exergoeconomic factor. However, the sensitivity analysis results show that the cost per unit of exergy production is more sensitive to the electricity price. Moreover, the optimal cost per unit of exergy production reduction is declined by 58.71% with the return water temperature of 30 °C.

Sand production and building of borehole storage facilities in Russia’s Far North

The environmental problems that arise in the course of gas–condensate and oil field development in the conditions of the Russian Far North are discussed. It is urgent to boost theoretical advancement in the area of design as well as structural and process decision-making when justifying parameters for building underground storage facilities for liquid and solid waste of drilling. Building of borehole storage facilities belongs in the class of physicochemical geotechnologies, which supposes that a part of natural rock mass is removed via a borehole drilled from ground surface (borehole hydraulic technology). The main processes involved in the building are thermal destruction of permafrost sandy and clay rocks and the lift of sand and return water from bottomhole to ground surface. The lifting parameters should ensure removal of sand and water from boreholes at the preset flow rate and at the controlled water–air interface position in compliance with the underground storage facility building program. It is found that the average washout capacity in permafrost sandy rocks during construction of an underground storage facility is linearly dependent on the product of average reduced rate of thermal destruction and average temperature of water in borehole, which proves the accepted washout design procedure. In the zone of a future underground storage facility in permafrost sandy rocks, it is typical that rock properties are highly variable both along and across sand strata. The air-lift parameters depend on the air-lift capacity and on the density of fluid to be lifted. The stable air-lift of sandy slurry is possible when the slurry density is not higher than 1.4 g/cm3, which conforms to the water content round 54 %.

Non-linear grey-box modelling for heat dynamics of buildings

This paper introduces a non-linear grey-box (GB) model based on stochastic differential equations that describes the heat dynamics of a school building in Denmark, equipped with a water-based heating system. The building is connected to a local district heating network through a heat exchanger. The heat is delivered to the rooms mainly through radiators and partially through a ventilation system. A monitoring system based on IoT sensors provides data on indoor climate in the rooms and on the heat load of the building. Using this data, we estimate unknown states and parameters of a model of the building’s heating system using the maximum likelihood method. Important novelties of this paper include models of the water flow in the circuit and the state of the valves in the radiator thermostats. The non-linear model accurately predicts the indoor air temperature, return water temperature and heat load. The ideas behind the model lay a foundation for GB models of buildings that use different kinds of water-based heating systems such as air-to-water/water-to-water heat pumps. Such GB models enable model predictive control to control e.g. the indoor air climate or provide flexibility services.

Покращення технології забору дренажних вод, які фільтруються з водосховищ, та їх використання

Goal. To offer the improved technology of water intake by systems of anti-filtration protection of territories against flooding from reservoirs and preparation of drainage waters for water use. Methods. Analytical-synthetic — for the analysis of modern scientific research and development of measures to improve the technology of water intake by anti-filtration curtains from flooding from reservoirs; statistical — for the analysis of parameters of a technological process; calculation — to create a simulation model of the anti-filtration curtain with vacuum siphon technology of water intake. Results. To improve the ecological condition of the territories located in the zones of influence of the Dnieper reservoirs, it is proposed to improve the design and technological parameters for vertical drainage systems. The main attention is paid to anti-filtration systems with airlift drainage from drainage wells, in particular the protection of the territory of Kamianskyi pod (area 6400 ha), located on the left bank of the Kakhovka reservoir. It is proposed to improve the anti-filtration systems by replacing the airlift technology of water intake from wells with a vacuum siphon to avoid clogging of the filters. According to the results of modeling according to the author’s method of calculation of vertical drainages with siphon drainage of filtration waters from wells, 3 different variants of anti-filtration curtains for hydrogeological conditions of Kamianskyi pod are presented. It is also proposed to use the drainage water, after proper preparation, to meet local water needs to avoid losses associated with its transportation over long distances. The ratio of daily human water use for sanitary, household, and drinking needs is considered. Conclusions. For rational water use, they proposed the use of groundwater, which causes flooding of areas adjacent to reservoirs, and pumped back to reservoirs, to use to meet different water needs. That is, use anti-filtration curtains as infiltration water intakes and return water after use and treatment to reservoirs.

Energy, exergy, economic (3E) analysis, optimization and comparison of different ORC based CHP systems for waste heat recovery

ORC-CHP (combined heat and power based on organic Rankine cycle) systems have been widely adopted to recover low-grade heat. Economy, one of the advantages of ORC-CHP system, is optimized and compared in this paper. Three ORC-CHP systems are simulated and compared, including SS (serial system), the CS (the condensation system) and SS/CS (serial/condensation system). Energy-exergy-economic (3E) models for these cycles are developed, by using the genetic algorithm, the system performances are optimized with respect to the maximum profit ratio of investment (PRI). The result shows that the SS/CS has the highest PRI value under the considered working conditions. According to the results of economic analysis, the cost of the heat exchangers occupies the largest share in the three systems, all above 70%. When operated under optimal working conditions, most of the energy in the heat source is used to heat return water, leading to all three systems showing low electrical efficiency (less than 0.7%) and high thermal efficiency (more than 92%). Exergy analysis shows that most of the exergy destruction to the SS and the SS/CS occurs in hot water heaters, while for CS, it mainly occurs in the evaporator (67.48%) and then the condenser (31.35%).

A theoretical study of the effects of different heating loads on the exergy performance of water-based and air-based space heating systems in buildings

The present study investigated theoretically the exergy performance of floor heating, radiators, and air heating under three different space heating loads of 10, 30 and 50 W/m2. The effects of different supply and return water temperatures were studied for the radiators, and the effects of different supply air temperatures were studied for the air heating system. All systems were assumed to be connected to a boiler. The floor heating system was further analyzed assuming an air-to-water heat pump, and a ground-source heat pump.Floor heating was the optimal heating system due to its low exergy demand. The separation of thermal environmental conditioning and ventilation was an efficient solution. The results prove thermodynamically that renewables (i.e., ground source heat in the present study) and low temperature heating systems (i.e., floor heating in the present study) are a resource- and exergy-efficient combination proven by their exergy efficiencies up to 10.5%. The critical COP concept was validated (2.57 in this study).The power use of auxiliary components might seem negligible in terms of energy; however, it is critical in terms of exergy as it affects the exergy performance drastically. The relative importance of auxiliary power becomes more critical at low space heating loads.

Control strategy for energy saving of refrigerating station systems in public buildings

In this work, a global energy saving optimal control strategy is proposed to address the high energy consumption of chilled water pumps caused by the small temperature difference between supply and return water, and the low efficiency of the chillers. The developed control strategy consists of two parts: the group control scheme and an optimal controller for variable water temperature/volume control. The group control scheme coordinates each chiller's operating time based on its running time and the chiller load rate. The optimal controller regulates the chilled water pump frequency according to the chilled water temperature difference and the valve opening at important terminal air conditioning units, and calculates the chilled water supply temperature under optimal comprehensive energy consumption of chillers and pumps. The proposed control strategy is easy to be embedded into the existing control systems of refrigerating stations. This scheme is then applied to the air conditioning system of a large public building in Beijing, China. Experimental results show that the proposed strategy can save up to 63% of energy consumption from the chilled water pumps and 6% from the chillers compared to the original control scheme.

Research on Water Quality Monitoring and Evaluation System under Agricultural Irrigation Automation

In order to timely grasp the status and change trend of the irrigated agricultural water environment, we refer to the farmland irrigation water quality evaluation standards, and select 11 monitoring items in different basins to monitor the agricultural irrigation water quality for 2 consecutive years. The article uses the pollution index method to evaluate the monitoring results. The results show that the comprehensive pollution index of surface irrigation water and underground irrigation water quality is less than 1, but there is a rising trend; the concentration of some pollutants in the irrigation return water is higher than that of the irrigation water, and some individual indicators exceed the standard, but they do not constitute comprehensive pollution. Finally, through the design of the remote sensing image water quality monitoring and evaluation system (RWQMES), the unified management of the three functions of water quality remote sensing image analysis and processing, water quality prediction and evaluation is realized.

Hybrid Carbon Dioxide Heat Pump for the Multifamily Residential Buildings in the Heat Supply System Based on CHP

The work is devoted to centralized heat supply systems based on CHP plants and the use with them heat pumps (HP) on carbon dioxide as refrigerant. Heat pumps are used in heat supply systems for buildings and use the heat of the outside air and, at the same time, the heat of the return network water (WWR) as a source of low-grade heat (LHP). The aim of the study is to develop a structural diagram of such a heat pump, where the outside air is heated by a heat exchanger installed in the return water line of the heating system, to develop a hydraulic circuit of a heat pump taking into account the law of regulation of the building heating system, to develop an algorithm for controlling the operating modes of the so-called balancing heat exchanger installed after gas cooler and internal heat exchanger of the heat pump. The most significant results were the hydraulic circuit of the heat pump, the aerodynamic circuit of the air supply path to the heat pump evaporator, the balancing heat exchanger control system, taking into account the requirement to ensure the operation of the control valve in a single-phase flow. The significance of the results obtained consisted in obtaining the dependences between the CO temperature graph and the parameters of the thermodynamic cycle of the heat pump, which ensured the operation of the control valve of the heat pump in a single-phase environment.

Collaborative optimization method and operation performances for a novel integrated energy system containing adiabatic compressed air energy storage and organic Rankine cycle

Integrated energy system (IES) coupled with advanced adiabatic compressed air energy storage (AA-CAES) and organic Rankine cycle (ORC) has the superiority to peak-load regulation and improve system performance. Therefore, a novel IES-ORC-CAES system, which includes AA-CAES, ORC and ICE, is proposed in this paper. In this system, the user return water is used to recover the compression heat generated by AA-CAES. The ICE exhaust smoke flows through three parts successively, the heat exchangers of AA-CAES energy release side, the ORC and absorption heat pump arranged in parallel and the tail heat exchanger, realizing the cascade utilization of energy and meeting the diversified energy demand of users. Considering the time of use electricity price and aiming at economy, environmental protection and energy efficiency, a collaborative optimization method that can dynamically adjust the energy output of the system is proposed. The results indicate that compared with the IES-ORC system (without AA-CAES), the annual operation cost, CO2 emission and primary energy consumption of the IES ORC-CAES system can be reduced by 14.84%, 13.06% and 11.69% under the economic, environmental and energy efficiency objectives. Furthermore, by coordinating the regulation of ICE, AA-CAES and ORC, the flexibility of the system energy supply is realized, and the matching of the electric-heat ratio on the source and load side is improved. Finally, the thermodynamic analysis of the IES-ORC-CAES system is carried out through parameter analysis. The research results can provide the reference for the operation optimization of the complex IES.

Examining a Non-Mixing Concept for Hydronic Heating Systems: A Simulation Study

While buffer tanks are common to address the short-cycling concern of hydronic heating systems, they involve water mixing, where the boiler’s hot water is mixed with the system’s return water. This water mixing condition brings concerns of the performance of the boilers and the in-space heating equipment (e.g., radiant floors and terminal units) due to the reduced temperature differences (ΔT) through these devices. Then, a non-mixing concept is introduced by putting a movable separation plate in a buffer tank, which can store supply hot water and return cold water separately. To examine this non-mixing concept, a simulation study is conducted by developing two hydronic system models with mixing and non-mixing concepts. After simulating these models under continuous heating loads, it is observed that the non-mixing model can achieve better system efficiency (e.g., 86.7% versus 82.0% for low heating loads) due to better boiler’s efficiency and less system cycles. In addition, it is noted that the non-mixing concept allows better control of supply water temperature, which can better support the outdoor reset control of boilers.

Fast simulation and high-fidelity reduced-order model of the multi-zone radiant floor system for efficient application to model predictive control

Model predictive control, as the most popular intelligent advanced control technology in recent years, is increasingly applied to building air conditioning systems to achieve adaptive and energy-efficient operation of the system, however, model predictive control imposes higher requirements on the computational efforts of the model. In this research, a complex coupled heat transfer model of the increasingly popular radiant floor system is analyzed and a full-order model of the radiant floor is developed. Then, after controllability and observability analysis, a fast high-fidelity reduced-order model that can accurately characterize the dynamic thermal performance of the original model is proposed applying the balanced truncation method. The accuracy of the reduced-order model was verified by comparing the radiant floor surface temperature, return water temperature, zone air temperature, and unheated average internal surface temperature with experimental test results, the TRNSYS model, and the full-order model. The computation time of the reduced-order model for open-loop simulation was reduced by 86% to 98% compared to the TRNSYS model. More importantly, the reduced-order model can effectively reduce the complexity of the model predictive control, resulting in a 38% to 78% saving in computation time compared to the full-order model, significantly improving computational efficiency and enhancing the robustness of the model predictive control.

Statistical modelling and climate variability of compound surge and precipitation events in a managed water system: a case study in the Netherlands

Abstract. The co-occurrence of (not necessarily extreme) precipitation and surge can lead to extreme inland water levels in coastal areas. In a previous work the positive dependence between the two meteorological drivers was demonstrated in a managed water system in the Netherlands by empirically investigating an 800-year time series of water levels, which were simulated via a physical-based hydrological model driven by a regional climate model large ensemble. In this study, we present an impact-focused multivariate statistical framework to model the dependence between these flooding drivers and the resulting return periods of inland water levels. This framework is applied to the same managed water system using the aforementioned large ensemble. Composite analysis is used to guide the selection of suitable predictors and to obtain an impact function that optimally describes the relationship between high inland water levels (the impact) and the explanatory predictors. This is complex due to the high degree of human management affecting the dynamics of the water level. Training the impact function with subsets of data uniformly distributed along the range of water levels plays a major role in obtaining an unbiased performance. The dependence structure between the defined predictors is modelled using two- and three-dimensional copulas. These are used to generate paired synthetic precipitation and surge events, transformed into inland water levels via the impact function. The compounding effects of surge and precipitation and the return water level estimates fairly well reproduce the earlier results from the empirical analysis of the same regional climate model ensemble. Regarding the return levels, this is quantified by a root-mean-square deviation of 0.02 m. The proposed framework is able to produce robust estimates of compound extreme water levels for a highly managed hydrological system. Even though the framework has only been applied and validated in one study area, it shows great potential to be transferred to other areas. In addition, we present a unique assessment of the uncertainty when using only 50 years of data (what is typically available from observations). Training the impact function with short records leads to a general underestimation of the return levels as water level extremes are not well sampled. Also, the marginal distributions of the 50-year time series of the surge show high variability. Moreover, compounding effects tend to be underestimated when using 50-year slices to estimate the dependence pattern between predictors. Overall, the internal variability of the climate system is identified as a major source of uncertainty in the multivariate statistical model.

Development of Crop Geometry for Drip Irrigated Rice Cultivation

Aims: To determine the effectiveness of the selected dripper spacing and dripper discharge rate on crop growth and yield parameters of rice crop and to determine the suitable variety and crop geometry for higher productivity and use efficiency of drip irrigations system.
 Study design: Experiment was conducted in strip plot design, method of establishment as main plot treatment viz., Direct seeded under raised bed (M1) and Transplanting under raised bed, varieties as sub-plot treatment viz., ‘ADT 54’, ‘TKM 13’ and‘ CR 1009 sub-1’(medium and long duration variety)and spacing as sub- sub-plot treatment viz., 20 x 10 cm , 20 x 20 cm , 25 x 25 cm and 20 x 40 x 10 cm (Paired row) .
 Place and duration of the study: Agricultural Engineering College and Research Institute, Kumulur, Tiruchirapalli district of Tamil Nadu during 2019-2021(two years) in sandy clay loam soil during Samba season
 Methodology: The growth and yield parameters viz., plant height, number of tillers and productivity tillers, number of filled grains, test weight and grain and straw yield was observed and economics on cost of cultivation, gross return, net return and BCR were calculated and water use efficiency and water productivity were calculated.
 Results: Studies showed that 90 cm lateral and 60 cm dripper spacing with 4lph is the optimum for rice cultivation under sandy clay loam soil. Combination of direct seeded rice in raised bed with medium duration variety ‘TKM 13’ in the spacing of 20x40x10 cm(paired row)was recorded higher grain yield(7075 kg/ha) and net return(Rs. 82526/ha), BCR (2.76 )and higher water use efficiency (7.69 kg./ha-mm) in drip irrigated paddy cultivation during Samba season.
 Conclusion: Direct seeding in raised bed with medium duration variety at the spacing of 20x40x10 cm along with other agronomic practices is the best for getting higher yield parameters, yield, net return, higher water use efficiency and water productivity in Samba (Rabi) season under drip irrigated rice cultivation.

Low carbon district heating in China in 2025- a district heating mode with low grade waste heat as heat source

Clean district heating systems are needed in large cities, especially in Northern China. This paper presents a low carbon district heating system that features a low return water temperature, use of low grade waste heat as the main heat source, long distance heat transmission with a large temperature difference, distributed peak heating load addition by natural gas and heat-power decoupling with heat pump and thermal storage. This Low carbon district heating 2025 system is suitable for large cities, large waste heat sources, high heating densities and the utilization of using existing large heating networks in almost all the cities of Northern China. These clean heating systems in Chinese cities have great potential to reduce energy use, reduce emissions and improve the district heating system economics.

Impact of Water Temperature Changes on Water Loss Monitoring in Large District Heating Systems

This paper explores how water temperature changes in a district heating system (DHS) impact the monitoring of water losses. Water volume in DHS is constantly monitored, recorded, and replenished. The leakage and failure status of the DHS is often monitored through measuring the make-up water flow rate. In this paper, we present the methodology and a simplified model of the dynamics of the heating system operation, which was used to determine the profile of changes in the average temperature and density of water in the system. The mathematical model of the district heating network (DHN) was verified by comparing the results of simulation calculations, i.e., calculated values of the temperature of water returning to the heat source, with the measured values. Fluctuations in water temperature cause changes in the density and volume of water in the DHN, which affect the amount of water supplementing the system. This is particularly noticeable in a DHN with a large water volume. The study reports an analysis of measurement results of operating parameters of a major DHS in Poland (city of Szczecin). Hourly measurements were made of supply and return water temperature, water flow rate, and pressure throughout the whole of 2019. The water volume of the analyzed DHN is almost 42,000 m3 and the changes in water volume per hour are as high as 5 m3/h, representing 20–30% of the value of the make-up water flow rate. The analysis showed that systems for monitoring the tightness of the DHS and detecting failures, on the basis of measurements of the make-up water flow rate, should take into account the dynamics of water volume changes in the DHN.