Distribution Heat Losses Research Articles

AbSolut - Integration of Absorption Technologies in District Heating and Cooling Systems for Enhanced Economic and Ecological Impact

District heating (DH) systems play a crucial role in meeting heating demands across the European Union (EU) and Austria, with significant potential for energy efficiency improvements and decarbonization. However, the transition towards climate neutrality by 2040 poses significant challenges, particularly in decarbonizing existing DH systems and integrating renewable energy sources. This work explores the application of absorption technologies, specifically absorption heat exchangers (AHX), absorption chillers (AC), and absorption heat pumps (AHP), in optimizing DH systems. The study investigates the utilization of AHX as transfer substations to increase heat capacity within existing grids by up to 30%, facilitating the integration of renewables and reducing distribution heat losses. Additionally, AC implementation for cooling supply demonstrates efficiency improvements through dynamic operation modes, renewable energy integration, and reduced electricity demand. Furthermore, AHP for waste heat utilization in DH power plants showcases environmental benefits, cost savings, and enhanced energy security. Through detailed techno-economic analyses and case studies, the paper evaluates the viability and economic feasibility of absorption technologies in DH applications. Challenges such as system integration, spatial requirements, and driving energy optimization are addressed, offering insights into overcoming barriers to adoption. Overall, the research highlights the transformative potential of absorption technologies in enhancing the efficiency, sustainability, and resilience of DH systems. By leveraging these technologies, DH operators and stakeholders can navigate the transition towards climate neutrality, while ensuring reliable and cost-effective heating and cooling solutions for urban areas.

Data-driven assessment for the supervision of District Heating Networks

There is an ongoing trend towards temperature reduction in District Heating Networks, allowing for the reduction of distribution heat loss and enabling the integration of low exergy heat production systems. There is a clear scientific consensus on the improved sustainability of such systems. However, there is not sufficient knowledge on how to deliver a successful transition to a low temperature District Heating system, while ensuring the operational levels of the existing system. This paper presents the experience on the progressive temperature reduction of a district heating subnetwork over the 2018–2021 period in Tartu, Estonia. Data from heat meters is extensively used to assess the capacity of substations and network branches to deliver the required heat and quality levels. Faulty substations are identified for targeted assessment and improvement works. Several substations have been identified as missing some of the performance criteria. This has led to further analysis, closer supervision and interventions in the operational conditions of the network. This is an ongoing process, expected to remain in the established procedures of the DH network operator. At the end of the process, a temperature reduction of 7 ºC has shown an improvement of 4.8% in network heat loss.

Direct absorption nanofluid-based solar collectors for low and medium temperatures. A review

Solar energy is expected to play an important role in the decarbonization of the energy and industrial sectors. Low and medium temperature (<400 °C) solar thermal collectors have proved to be a reliable solution to supply heat and decarbonize the industrial sector, with over 800 Solar Heat for Industrial Processes (SHIP) plants put in operation in the last decade. Governmental support policy is a key factor for solar thermal energy to play a major role in CO2 emission reduction, which require improving the efficiency of solar collectors and reducing costs. Recent studies have demonstrated the potential of nanoparticles to enhance the optical properties of heat transfer fluids for direct absorption solar collectors (DASC). In a DASC the transfer fluid absorbs volumetrically the incident radiation, resulting in a more homogeneous temperature distribution and less heat losses than in conventional surface collectors. In this paper, the current state-of-the-art of SHIP installations and conventional surface collectors is presented, and a critical literature review dedicated to nanofluid-based DASC for both concentrating and non-concentrating collectors is provided. The key findings and the challenges to be overcome toward promoting the development of nanofluid-based DASC for SHIP applications are discussed.

Involving 4th generation district heating technologies: residential buildings in remote areas of Russia

This study aims to justify the possibility of expanding the energy and economic efficiency of a district heating [DH] system. The case study territory is a remote area of the Omsk region (Russia); the method is electric heating. To address this issue, we (1) considered the potential of modernizing these DH systems, (2) analyzed available options, (3) designed the main and auxiliary heat generation equipment, and (4) committed a feasibility study. The design heat consumption was 0.24 MW. To achieve this goal, we suggested two heat pumps; their capacity was 280 kW, and the investment required to install two heat pumps of 150 kW was 2.6 billion rubles. The total capital cost was 4.0 billion rubles. The annual effect after the heat pumps were installed was 0.7 billion rubles. The payback period was 5.6 years; to decrease it, one should install multiple heat pumps on the consumer side. The reason is to avoid heat distribution losses. Replacing traditional DH plants with electric boilers is feasible only if the cost of heat is 6,600 rubles per MWh or above. This cost has already been achieved for several DH plants. Ground source heat pumps are viable at lower prices, approximately 4,100 rubles per MWh. This option is especially helpful in remote areas of the Omsk region where the billing tariff is already high. When modernizing the heat supply infrastructure of the northern areas of the Omsk region, one can increase annual electricity consumption by 6%, decrease tariffs, and become more ecologically friendly at the same time.

Economic Analysis of Heat Distribution Concepts for a Small Solar District Heating System

One challenge in today’s district heating systems is the relatively high distribution heat loss. Lowering distribution temperatures is one way to reduce operational costs resulting from high heat losses, while changing the distribution system from steel pipes to plastic pipes and changing the heat distribution concept can reduce investment costs. The result is that the overall life cycle cost of the district heating system is reduced, leading to the improved cost competitiveness of district heating versus individual heating options. The main aim of this study was to determine the most cost-efficient distribution system for a theoretical solar district heating system, by comparing the marginal life cycle cost of two different distribution systems. A secondary aim was to determine the influence of the employed pipe type and insulation level on the marginal life cycle cost by comparing detailed economic calculations, including differences in pipe installation costs and construction costs, among others. A small solar-assisted district heating system has been modeled in TRNSYS based on a real system, and this “hybrid” model is used as a basis for a second model where a novel distribution system is employed and the heating network operating temperature is changed. Results indicate that a novel distribution concept with lower network temperatures and central domestic hot water preparation is most efficient both from an energy and cost perspective. The total life cycle costs vary less than 2% for a given distribution concept when using different pipe types and insulation classes, indicating that the investment costs are more significant than operational costs in reducing life cycle costs. The largest difference in life cycle cost is observed by changing the distribution concept, the novel concept having approximately 24% lower marginal life cycle cost than the “hybrid” system.

Heliostat field aiming strategy optimization with post-installation calibration

Heliostat field aiming strategy significantly affects the safety and operational efficiency of the Solar Power Tower (SPT) system. Heliostats installed in fields are likely to show deviations of optical properties from design specification to some extent. Such deviations generally reflect in the surface curvatures and normal directions of heliostat facets. These differences can give rise to the inevitable degradation of optical performance, impacting the execution effect of the pre-designed aiming strategy. Focusing spot distortion with an inappropriate aiming strategy possibly leads to overheated local areas or component damages. To cope with this error and to improve the light concentration performance, an aiming strategy optimization approach with post-installation calibration was proposed in this paper. An equivalent parameter model was developed based on heliostat parameters, producing a more accurate description of optical performance. The adopted heliostat parameters were obtained by the parameter identification method. The parameter identification was formulated by photographed solar flux images and simulated flux distributions. The aiming strategy optimization model of heliostat field was built with obtained identification parameters, and the optimization goal considers utilized solar power absorbed by the heat transfer fluid and flux distribution uniformity. The simulation results showed substantial improvement from the proposed aiming strategy. • A novel approach to heliostat field aiming strategy optimization is developed. • Effective heliostat optical parameters are obtained by parameter identification. • Identified parameters calibrate heliostat deviations in aiming strategy optimization. • Flux distribution uniformity and heat loss are considered in the optimization goal.

Electrified district heating networks: a thermo-economic optimisation based on exergy and energy analyses

This paper presents a thermo-economic optimisation of an electrified district heating network consisting of wind power plant, gas-fired combined heat and power plant and heat pumps. The load flow problem of the resulting multi-energy system is formulated by considering all physical and operating parameters in both of the electricity and heat distribution networks. First, energy and exergy analyses are applied to identify and isolate lossy branches of a meshed heating network. This is followed by the optimal placement of heat pumps. Finally, supply and return temperatures are optimised. Particle swarm optimisation technique is implemented in order to find the best place of heat pumps, their economical dispatch and optimal temperature profile of the district heating network. Results show that up to 59.12% of the distribution heat loss and 9.37% of the operating cost can be saved by following a step-by-step methodology discussed in this paper.

Enabling smart control by optimally managing the State of Charge of district heating networks

Digitalization and smart control of district heating networks are emerging as key features to make these systems flexible and optimal. However, since effective and scalable methods for large-scale systems are currently unavailable, the implementation of smart controllers can be challenging and time-consuming. This is addressed herein by proposing a novel approach to include the thermal capacity of the connected buildings in the optimal control of large-scale heating networks. A reduced-order model of the aggregated communities supplied by a large-scale network is used to define their State of Charge, which is exploited to store or retrieve energy when convenient, while maintaining indoor comfort. This concept is included in a Model Predictive Controller that optimizes power plant management and heat distribution. The results show that the controller successfully shaves heat supply peaks to different regions up to 16% and reduces the difference between distribution and soil temperature up to 20%. At the same time, the return temperature is kept close to the set-point of 35 °C, which is lower than the historical operation and further reduces distribution heat losses. The procedure can be easily replicated to optimize systems of different sizes and to support their transition to efficient, smart district heating networks.

Double Loop Network for Combined Heating and Cooling in Low Heat Density Areas

This study investigated a double loop network operated with ultra-low supply/return temperatures of 45/25 °C as a novel solution for low heat-density areas in Denmark and compared the proposed concept with a typical tree network and with individual heat pumps to each end-users rather than district networks. It is a pump-driven system, where the separate circulation of supply and return flow increased the flexibility of the system to integrate and displace heating and cooling energy along the network. Despite the increased use of central and local water pumps to operate and control the system, the simulated overall pump energy consumption was 0.9% of the total energy consumption. This was also an advantage at the design stage as the larger pressure gradient, up to 570 Pa/m, allowed minimal pipe diameters. In addition, the authors proposed the installation of electrically heated vacuum-insulated micro tanks of 10 L on the primary side of each building substation as a supplementary heating solution to meet the comfort and hygiene requirements for domestic hot water (DHW). This, combined with supply water circulation in the loop network, served as a technical solution to remove the need for bypass valves during summer periods with no load in the network. The proposed double loop system reduced distribution heat losses from 19% to 12% of the total energy consumption and decreased average return temperatures from 33 °C to 23 °C compared to the tree network. While excess heat recovery can be limited due to hydraulic issues in tree networks, the study investigated the double loop concept for scenarios with heat source temperatures of 30 °C and 45 °C. The double loop network was cost-competitive when considering the required capital and operating costs. Furthermore, district networks outperformed individual heat pump solutions for low-heat density areas when waste heat was available locally. Finally, although few in Denmark envisage residential cooling as a priority, this study investigated the potential of embedding heating and cooling in the same infrastructure. It found that the return line could deliver cold water to the end-users and that the maximum cooling power was 1.4 kW to each end-user, which corresponded to 47% of the total peak heat demand used to dimension the double loop network.

District heating load profiles for domestic hot water preparation with realistic simultaneity using DHWcalc and TRNSYS

To reach the goal of decarbonizing energy systems, newly constructed buildings must adhere to higher efficiency standards. In new residential developments, this results in a higher share and significance of the energy demand for domestic hot water preparation. In order to generate realistic load profiles for domestic hot water preparation, which can help with dimensioning district heating systems, four substation types were modeled in TRNSYS. Two instantaneous and two storage systems were considered for single family and multi family houses. 11 fictitious buildings were defined, for which the systems were dimensioned. Yearly simulations were conducted, using DHWcalc draw-off profiles as input. The impact of domestic hot water preparation system design on energy balances, return temperatures and simultaneity factors was investigated. Distribution heat losses amount to approximately the same energy demand as the useful energy demand for domestic hot water. In single family houses, storage heat losses also account for a significant energy demand, but in larger multi family houses the storage heat losses are negligible. The yearly weighted average return temperatures of the investigated buildings vary from 25 to 54 °C. Instantaneous DHW preparation result in 8–9 K lower return temperatures for the district heating system than storage systems. An important influencing factor on the return temperature is the relation of energy used by the circulation system to the useful energy demand, resulting in lower return temperatures in more densely inhabited buildings. Load duration curves for superposed profiles were calculated and compared to literature values. The results show, that DHWcalc draw-off profiles provide a suitable basis with realistic simultaneity for district heating load profiles. It is shown, that the time interval for which simultaneity factors are calculated must always be considered. Also, the importance of the underlying probability distributions for draw-off profiles was shown by comparing different approaches.

Low Temperature District Heating: An Expert Opinion Survey

Among the available solutions for building heating and cooling, district heating (DH) and district cooling (DC) systems are considered some of the best options since they can ensure a better control of pollutant emissions and greater efficiency than individual systems. Nevertheless, improvements are needed to increase their sustainability and reliability. The so-called “low temperature district heating” (LTDH) concept has been introduced in recent years in an attempt (i) to reduce the distribution heat losses through a temperature decrease in the DH network, (ii) to favor the integration with renewable energy sources, and (iii) to create the conditions required for the development of future smart energy systems. However, many concerns have been raised about its implementation in both existing and new systems. For this reason, this paper aims to identify the stakeholders’ ranking of the barriers against LTDH system development and implementation over the next few years. Aiming to this, a questionnaire was designed, including an analysis of current gaps and strengths, and then submitted to more than 50 Italian and international experts in the field of DH. An in-depth analysis of the received answers was performed, focusing in particular on the Italian experts’ answers. Comments and suggestions on how to promote the transition to the new LTDH approach are reported.

Implications of supplying district heat to a new urban residential area in Sweden

Here we analyze the cost, primary energy and CO2 implications of supplying district heat, considering different supply and return temperatures, to a new residential area in Växjö, Sweden. We explore four land exploitation alternatives consisting different types of buildings with various heated floor areas as well as occupancy densities and two levels of building energy efficiency, based on the Swedish building code and passive house criteria. The analysis shows that energy performance of the buildings and land exploitation alternatives strongly influence the annual heat demand and its profile, which steers the design of the local heat distribution network. Additionally, supply and return temperatures of district heat somewhat influence the design of the network. The distribution heat losses could be reduced by 25% and 50% if district heating systems of 65/30 °C and 50/20 °C, respectively, are used instead of a conventional 80/40 °C system. However, for the same land exploitation alternative, the local distribution heat losses are about the same whether or not the buildings are designed to meet the Swedish building code or passive house criteria, since the same pipe distance is required and the variation of pipe diameters is small. A 50/20 °C system increases electricity use to boost hot water temperature to avoid the risk of legionella bacteria, and this influences quantity of district heat supply, primary energy use and costs. Therefore, a 65/30 °C system appears to be more primary energy and cost efficient than a 50/20 °C system. Increased insulation of district heating network reduces heat losses but this is not cost effective due to increased investment cost. The results are similar whether or not the analysis is based on current energy supply or future renewable based energy supply. This study increases understanding of strategies for planning and designing new urban residential areas and their energy supply systems to reduce primary energy use as well as monetary costs, and to minimize the climate impacts of the built environment.

Multi-mode control method for the existing domestic hot water storage tanks with district heating supply

The hot water tank is widely used for domestic hot water (DHW) preparation. When supplied by district heating (DH), the operation of DHW tanks directly influences the DH return temperature, thereby affecting the DH system efficiency, supply capacity and the realization of the low temperature district heating. However, the conventional charging method often results in high DH return temperature. This study develops a new charging method aiming at reducing the DH return temperature without violating the comfort or hygiene requirements. The concept uses the multi-mode charging method considering the periodical characteristics of the load pattern. Multi scenarios are simulated by dynamic models using the practical DHW load profiles from a case study. Moreover, the impacts of the tank configuration, the location of the temperature sensor, and the distribution heat loss are investigated. The results show that the new control method can reduce the primary return temperature by 5–8 °C compared to the conventional control method. The distribution heat loss imposes great impact on the DH return temperature. In addition, the tank with the external heat exchanger performs better than the tank with the internal heating coil if the circulation heat loss is less than 50% of the DHW demand.

Energy consumption for domestic hot water use in Norwegian hotels and nursing homes

Domestic Hot Water (DHW) production constitutes a significant proportion of the energy demand of modern buildings, and as the building envelope is improved the share increases. This article discusses the results from a measurement campaign in Norwegian hotels and nursing homes. The energy demand for DHW and distribution heat losses for 3 hotels and 3 nursing homes are shown. The results show that number of bedrooms is a better parameter for describing DHW consumption than sqm of heated floor area. There are large variations in the measured distribution losses, mainly due to malfunctioning of the hot water circulation system. For nursing homes, the measured energy consumption is significantly lower than the normative profiles, which can have large impact on the requirements for the design of the building heating system. For hotels, the measured energy consumption is in the range of the normative profiles.

Triple function substation and high-efficiency micro booster heat pump for Ultra Low Temperature District Heating

District-Heating (DH) covers around the 9% of the total heat demand in the EU, with a proven highperformance levels and low operational costs. DH may suffer adaptations in order to maintain competitiveness with individual heating systems. The most important one is the reduction of supply temperatures up to 50°C, emerging the concept of Ultra Low Temperature (ULT) DH. ULT DH allows the transmission and distribution heat losses minimization, since heat losses are proportional to the temperature-gradient between supply line the ambient, increasing overall system performance. Furthermore, enables the integration of low-grade energy sources with low marginal costs, such as solar thermal energy or waste heat from industrial and commercial buildings. This study presents the combination of a novel 3 function-scheme (3FS) substation and a micro booster heat pump for domestic hot water. The novel design of the substation allows different operation modes between the grid and the building according to the temperature level and demand range every moment. Regarding the microbooster, this unit is used directly to lift the temperature of the domestic hot water (DHW), so that risk of legionella is avoided and that the required comfort temperature is reached. Preliminary test for the energy performance of the booster heat pump was measured on serially produced units according to tapping profiles and methodologies of standard EN16147. DHW coefficients of performance of 5.2 and 8.5 were measured for heat source supply temperatures respectively of 25 and 40 °C and return temperatures of 22 and 30 °C. This paper explores the possible operational modes of a 3FS in combination with a Building Integrated Solar Thermal System (BISTS) and a Microbooster heat pump.

The influence of wind speed, aperture ratio and tilt angle on the heat losses from a finely controlled heated cavity for a solar receiver

The first systematic experimental study of the combined influences of wind speed (0–9 m/s), aperture ratio (0.33–1) and tilt angle (15°–45°) on the mixed (free and forced) convective heat losses from a heated cavity, is presented. The cylindrical cavity is heated by 16 individually temperature-controlled heating elements in the open section of a wind tunnel. Heat flux distribution and total heat losses from the cavity were measured. A complex inter-dependence was found between aperture ratio, wind speed and convective heat losses. In particular, the total heat losses can vary by up to ∼75% by varying the aperture ratio from 0.33 to 0.75, for no wind condition, but the effect of aperture ratio is decreased as wind speed is increased. The tilt angle was found to have a small effect on the heat losses relative to the aperture ratio and wind speed. Nevertheless, the average minimum mixed heat loss for various wind speeds occurs for a tilt angle of between 15° and 30° for a downward tilting solar tower system.

Final and primary energy use for heating new residential area with varied exploitation levels, building energy performance and district heat temperatures

Abstract There is great potential to build new energy-efficient building blocks in combination with efficient energy supply systems. Such a development will contribute to achieve national energy and climate goals as well as the overall aim for a sustainable development. Here, we analyze final and primary energy use for heating a new residential area by using district-heating. The area, located in Vaxjo, in south Sweden has potentially varied land exploitation levels, energy performance of buildings and district heat supply/return temperatures. The results show that the district heating demand will be reduced by about 52-56% if buildings in the area meet the Swedish passive house criteria instead of the Swedish building code. The exploitation levels of construction in the area strongly influence the total heating demands. A dense instead of a low exploitation will increase the area’s heating demand more than four times. But, the heat demand density of the residential area has quite a small impact on the total heat losses of the distribution network in contrast to changed supply and return temperatures. The distribution heat losses could be reduced by up to 50% with lower supply/return temperatures. However, a reduction of district heat supply/return temperatures to 50/20oC increases electricity use for boosting hot water temperature to avoid the risk of legionella bacteria. This causes a shift from district heat production to electricity production and increases the primary energy use. The results of this study can be used for further considerations of costs and benefits of energy supply options for new residential areas.

Improved efficiency for distribution and use of district heating: A simulation study of retrofitting a Swedish apartment complex from the 1970's

Important features of the next generation of district heating systems are low distribution heat losses and low distribution temperatures. The purpose of this transition is to compensate for reduced heat demand densities caused by increased energy efficiency in buildings. In Sweden a majority of multi-family residential buildings are connected to district heating networks that are up to 50 years old. This study investigates the possibility to improve building energy efficiency and simultaneously reduce distribution temperatures and losses for a Swedish apartment complex built in the 1970's. The results show that a combination of better insulated building envelopes and ventilation heat recovery can reduce the heat demand in the studied apartment complex by 53%. The improved building energy performance significantly reduces the required supply temperatures for space heating and reduces heat distribution losses to some extent. The heat distribution losses can be reduced further (up to 49%) by replacing central hot water preparation with apartment based heat exchangers. This eliminates heat losses from pipes for domestic hot water supply and hot water circulation. The study concludes that a potential cost-synergy occurs when a holistic strategy is adopted and conventional energy efficiency measures are combined with reduced distribution losses.

Impact of Different Design Guidelines on the Total Distribution Costs of 4th Generation District Heating Networks

When it comes to the design of new district heating networks, different design guidelines of different countries and pipe manufactures occur. All guidelines are aiming to restrict the specific pressure drop per meter pipe length to avoid uneconomic network operation. This paper evaluates the impact of different design guidelines from Sweden, Germany and Austria, as well as pipe manufacture recommendations on the total distribution costs. The analysis was conducted for a 4th generation district heating network for a new housing development (3 km trench length). The resulting district heating networks were compared in terms of total distribution costs. The results state that designing small networks at maximum heat load by allowing high specific pressure drops of 300 Pa/m shows the most economic results in terms of capital costs and variable costs. Compared to 70 to 100 Pa/m recommendations, 6 – 8 % investment costs for transportation pipes can be saved designing the network with 300 Pa/m pressure drops of short duration. Regarding distribution heat loss costs, the smaller the average diameter of the network the lower the heat distribution losses. Optimal network design leads to a 7 % heat loss reduction for the whole network. Furthermore, the paper compares total costs of the networks designed for two different design temperatures: 70°C supply with 40 °C return and 40°C supply temperature with 25 °C return. In terms of total distribution costs, both networks are very similar, which shows that ultra-low temperature networks have no economic disadvantages compared to state of the art 70°C networks, as often believed.

Ultra-low temperature district heating system with central heat pump and local boosters for low-heat-density area: Analyses on a real case in Denmark

Low temperature district heating (DH) system gives easier access to the renewable energy as heat sources and improves the heat distribution efficiency. From the exergy point of view, low DH supply temperature also better matches the exergy demand of space heating and domestic hot water. It is more beneficial to operate district heating system under lower temperature level for the heat-sparse area where the distribution losses accounts for a large proportion in the total heat supply. In this study, the actual performance of a case ultra-low temperature district heating (ULTDH) system in Denmark was investigated based on long-term measurements. The system combines the central heat pump and local boosters, while the impact of such configuration on the overall system performance was analysed. The energy, exergy and economy performances of the case system were compared to medium temperature district heating system (MTDH) and low-temperature district heating system (LTDH). The results show that the LTDH system without supplementary heating has the highest energy and exergy efficiency. While the ULTDH system has better performance compared to the MTDH system in energy, exergy and economy due to substantial savings from the distribution heat loss.