Efficient District Heating Research Articles

Modelling Hourly Thermal Energy Demand: A Machine Learning Approach of Residential District Heating Substations in Turin

This paper explores the application of the XGBoost machine learning model for forecasting the hourly thermal demand in District Heating Systems, aligning with the European Union’s ambitious sustainability targets as outlined in the Renewable Energy Directive (RED) and the Energy Efficiency Directive (EED). Accurate forecasts of thermal demand are crucial for enhancing the efficiency of district heating systems through the integration of renewable energy sources and the adoption of waste heat recovery, thereby contributing significantly to achieving climate neutrality by the year 2050. This study presents a dual approach to forecasting: at the individual building level, and at an aggregated level by considering the average characteristics of the served building stock. Through a comprehensive case study of the Turin district heating system (Italy), which comprises hourly data from approximately 200 heat exchange substations across nine heating seasons, this research evaluates the comparative effectiveness of different forecasting approaches in terms of prediction accuracy and computational efficiency. The findings aim to guide district heating operators and planners in selecting the most suitable forecasting approach based on available input information, desired accuracy, and computational constraints, contributing to the strategic planning and development of sustainable and efficient district heating systems.

The bidirectional substation for district heating users: experimental performance assessment with operational profiles of prosumer loads and distributed generation

The regulatory European and national policies outline the role of efficient district heating in achieving mid and long-term decarbonization targets. Prosumers could be equipped with bidirectional exchange substations to increase the local production contribution. The present paper evaluates the contribution of a bidirectional substation in maximizing the use of thermal energy produced locally by renewable sources or waste heat in a densely populated area, considering the limitation due to the non-contemporaneity of production and consumption and possibilities to overcome them. The substation prototype and the control system were tested in operational conditions, assuming the district heating network operating at two temperature levels (80 °C/50 °C and 60 °C/30 °C for supply and return) and applying the hardware-in-the-loop technique for coupling the substation in real-time with data-driven thermal loads (multi-family residential building) and production (solar panels and waste heat) profiles. The various energy flows in the substation are presented for representative days, resulting in a district heating contribution to the user’s load ranging between 99.8 % (winter day) and 21.8 % (summer day). The net-metering mechanism was considered, and the assessment extended to the entire year. The local production contribution to the user’s load ranges between 24 % and 100 %, depending on the system configuration considered.

Sustainable deployment of energy efficient district heating: city business model

Heating and cooling account for 50% of the European Union's energy consumption and, therefore, reducing its impact is essential to minimise dependency on energy imports (particularly fossil fuel), which are bound to geopolitical conflicts. District heating arises as a critical player in this transition towards a more efficient energy framework. Despite its numerous advantages, implementation is still hindered by inadequate District Heating business models and incentives. This study conducts a holistic examination on the feasibility, effectiveness and, ultimately, the efficiency of establishing a publicly owned and public-privately managed District Heating infrastructure network via a pilot intervention in the city of San Sebastian in the north of Spain. A Value Proposition Canvas, Value Creation Ecosystem and City Model Canvas analysis provides insight into fundamental patterns and relevant recommendations for other municipalities trying to find a business model in which all the involved stakeholders can capture value while addressing at the same time the energy challenges of cities.

Intelligent Approaches to Fault Detection and Diagnosis in District Heating: Current Trends, Challenges, and Opportunities

This paper presents a comprehensive survey of state-of-the-art intelligent fault detection and diagnosis in district heating systems. Maintaining an efficient district heating system is crucial, as faults can lead to increased heat loss, customer discomfort, and operational cost. Intelligent fault detection and diagnosis can help to identify and diagnose faulty behavior automatically by utilizing artificial intelligence or machine learning. In our survey, we review and discuss 57 papers published in the last 12 years, highlight the recent trends, identify current research gaps, discuss the limitations of current techniques, and provide recommendations for future studies in this area. While there is an increasing interest in the topic, and the past five years have shown much advancement, the absence of open-source high-quality labeled data severely hinders progress. Future research should aim to explore transfer learning, domain adaptation, and semi-supervised learning to improve current performance. Additionally, a researcher should increase knowledge of district heating data using data-centric approaches to establish a solid foundation for future fault detection and diagnosis in district heating.

Optimization of district heating system considering carbon taxes and subsidies based on energy policy stage goals

Climate change is one of the main issues that humanity will face in the upcoming decades. Low-carbon district heating is an important alternative for decarbonizing the heating sector against unsustainable higher carbon emission heating methods. Most available studies have concentrated on fixed or predetermined policies instead of attempting a numerical optimization of carbon taxes and subsidies in district heating. This study proposes the optimization of a district heating system in Northeast China considering carbon taxes and subsidies based on energy policy stage goals. Research shows that carbon taxes and subsidies have a certain impact on the change in district heating sources. With the increase in carbon taxes, heating from non-fossil energy sources is increasing, an area that can also be promoted with subsidies for non-fossil energy. Considering the total cost of heating enterprises, it is appropriate to set the carbon tax for district heating at $86. Similarly, considering government expenditure, it is suggested that construction subsidies be set at 10.5$/m2, 3.5$/m2, and36.5 $/m2 for air source heat pumps, biomass boilers, and ground source heat pumps. In addition, the obtained results can be used as guidelines for the heating industry to design more efficient district heating and focus research and development efforts on the most promising non-fossil energy heating technologies.

REHABILITATING J. L. ROMANY’S SOCIAL HOUSING IN THE 21ST CENTURY

Introduction: The modern heritage of 20th century Spanish architecture, particularly in the city of Madrid, includes an extensive range of high-quality social housing that, due to its peripheral location and economic restrictions, can be lost without public policies to preserve it. Updating this housing to meet the current habitability requirements, as well as enhancing and transforming it into high-quality 21st century residential buildings, is a task that cannot be postponed. Purpose of the study: The issues of energy efficiency, habitability and accessibility are very salient today, so it seems pertinent to recover relevant examples of 20th century architecture and investigate to what extent the parameters with which they were designed are still valid. Methods: This paper reviews housing case studies in two neighborhoods, Poblado Dirigido de Fuencarral and Colonia Juan XXIII de Carabanchel, comprehensively analyzing the original buildings and their current rehabilitation. This includes comparing the buildings’ energy efficiency before and after the intervention carried out. Approach: This study verified that in both cases, an attempt was made to recover several elements of the original design during rehabilitation. Results: We found that both projects were originally committed to creating an open, pedestrian-friendly city with abundant vegetation, which is still a valid value today. Despite the economic restrictions at the time of construction, both projects used advanced energy strategies, such as the passive design offered by cross ventilation, the unusual thermal insulation envelope, or the efficient district heating. Novelty: In addition, this paper aims to incorporate the heritage of the great mid-20th century architect José Luis Romany, author of both projects, into modern Spanish architecture.

The economic potential of district heating under climate neutrality: The case of Austria

This paper focuses on the requirement of the Energy Efficiency Directive for assessing the potential of efficient heating and cooling. The paper describes the method for calculating the economic potential of efficient district heating (DH) in Austria under different scenarios, assuming the full decarbonisation of the heating sector by 2050. A spatially explicit approach is used to derive heat demand density maps, heat distribution costs and potential DH areas. The obtained areas are clustered, and depending on their potential spreads, up to four supply portfolios on the installed generation capacities are assessed in each cluster. While this method maintains the level of detail, it significantly reduces the number of required sensitivity analyses. Finally, the least cost portfolios of DH supply in each cluster are identified and compared with the costs of individual heat supply. The economic potential of DH by 2050 is calculated accordingly. The analyses revealed that the DH market share within DH areas is the main driver of DH competitiveness. Depending on the scenario, the economic DH potential varies between 13% and 50% of space and water heating demand in Austria. The extensive application of renewable gases in this sector was not economically feasible under any scenario.

Greening of the District Heating Systems—Case Study of Local Systems

The integration of renewable energy resources into district heating systems is gaining momentum across Europe, as heat producers are expected to work towards the EU Directive of Efficient District Heating and Cooling to achieve carbon neutrality by 2050. This paper studies the techno-economic implications of transforming conventional district heating systems of six locations in Poland, generating 8.5 PJ of heat annually, into sustainable and efficient district heating systems. These new systems consist of flat solar collectors integrated with seasonal pit thermal energy storages and gas heating plants, acting as flexible heat sources, covering residual heat demand and/or increasing the parameters of the working medium in the network. Using the IEA-TIMES software, two scenarios were considered, namely STAT and DYN. The results show that reaching a 20% share of heat production by solar thermal would demand extra construction of seasonal heat storage facilities with a total capacity of 197 TJ, which is approximately 4.5 times bigger than the largest seasonal heat storage located in Vojens, Denmark. The projected increase in the prices of natural gas and CO2 emission allowances accelerates the transformation of systems towards greater use of solar heating plants. In the period 2025–2050 the heat generation costs increase by ca. 65%. The contribution of the CAPEX and OPEX costs components are presented.

Efficient District Heating in a Decarbonisation Perspective: A Case Study in Italy

The European and national regulations in the decarbonisation path towards 2050 promote district heating in achieving the goals of efficiency, energy sustainability, use of renewables, and reduction of fossil fuel use. Improved management and optimisation, use of RES, and waste heat/cold sources decrease the overall demand for primary energy, a condition that is further supported by building renovations and new construction of under (almost) zero energy buildings, with a foreseeable decrease in the temperature of domestic heating systems. Models for the simulation of efficient thermal networks were implemented and described in this paper, together with results from a real case study in Italy, i.e., University Campus of Parma. Activities include the creation and validation of calculation codes and specific models in the Modelica language (Dymola software), aimed at investigating stationary regimes and dynamic behaviour as well. An indirect heat exchange substation was coupled with a resistive-capacitive model, which describes the building behaviour and the thermal exchanges by the use of thermos-physical parameters. To optimise indoor comfort conditions and minimise consumption, dynamic simulations were carried out for different operating sets: modulating the supply temperature in the plant depending on external conditions (Scenario 4) decreases the supplied thermal energy (−2.34%) and heat losses (−8.91%), even if a lower temperature level results in higher electricity consumption for pumping (+12.96%), the total energy consumption is reduced by 1.41%. A simulation of the entire heating season was performed for the optimised scenario, combining benefits from turning off the supply in the case of no thermal demand (Scenario 3) and from the modulation of the supply temperature (Scenario 4), resulting in lower energy consumption (the thermal energy supplied by the power plant −3.54%, pumping +7.76%), operating costs (−2.40), and emissions (−3.02%). The energy balance ex-ante and ex-post deep renovation in a single user was then assessed, showing how lowering the network operating temperature at 55 °C decreases the supplied thermal energy (−22.38%) and heat losses (−22.11%) with a slightly higher pumping consumption (+3.28%), while maintaining good comfort conditions. These promising results are useful for evaluating the application of low-temperature operations to the existing district heating networks, especially for large interventions of building renovation, and confirm their potential contribution to the energy efficiency targets.

Promoting efficient district heating in Estonia

The Estonian Power and Heat Association (EPHA), in cooperation with Tallinn University of Technology (TalTech), has developed a methodological approach to calculating and awarding the Efficient District Heating Label (Label) that recognises and certifies the efficiency of the district heating (DH) system or certifies that the DH system mainly uses renewable energy and cogenerated heat. The Label informs the consumer about the efficiency of the DH system and highlights DH as an efficient, environmentally friendly, inexpensive, and convenient heating method.The presence of the label serves as the basis for determining a lower primary energy factor (PEF) when calculating the energy performance of buildings that consume or will consume heat from a labeled DH system. Prior to this, a fixed DH PEF was used in Estonia.It is important to note that using the EU Energy Performance Directive definition of efficient DH networks for PEF differentiation is a novel approach. According to the information available, such differentiation solutions have never been used before.This study describes the main methodological approaches to Label assignment and calculation, as well as the most critical aspects of the system implementation in Estonia.

PROSPECTS FOR DECARBONIZATION OF DISTRICT HEATING IN UKRAINE

The purpose of the work is to determine promising areas for decarbonization of district heating in Ukraine, as well as measures necessary for their practical implementation. State of the development of bioenergy in the world and in the EU is presented, and considerable contribution of bioenergy to the production of renewable heat is emphasized. In Ukraine, the existing problems of long-term planning at the state and regional levels in the heat supply sector need to be addressed. Recommendations for solving these problems have been developed. One of them is the elaboration of the Heat Supply Strategy until 2035, built on the principle of the Energy Strategy of Ukraine, as well as the Action Plan for its implementation. It is recommended to introduce the term “efficient district heating” in the legislation of Ukraine, which corresponds to Directive 2012/27/EU on energy efficiency, and to declare the purpose of increasing the share of such systems in district heating. The role of bioenergy in the process of decarbonization of district heating of Ukraine is analyzed. It is shown that one of the ways that can significantly improve the situation in heat supply is the wide involvement of biomass and solid biofuels in this sector. For the effective implementation of this task it is necessary to launch an electronic trade system for solid biofuels (biofuel exchange), introduce competition in district heating systems, as well as perform a set of additional actions and measures. This will allow not only to stabilize the situation with heat supply in Ukraine, but also to reduce the heat tariff for end users by 15-20%.

Experimental characterization of a prototype of bidirectional substation for district heating with thermal prosumers

The prosumer, already widespread in the electrical sector, is still uncommon in the district heating (DH) sector. Nevertheless, this figure can potentially provide a relevant contribution to increase the renewable fraction of heat and to decrease the fossil fuel consumption, hence enhancing sustainable and efficient district heating. Moreover, prosumers are more informed and responsible towards energy production and energy savings. In order to enable the two-way heat exchange, the thermal substation at the interface between the prosumer and the DH network must be properly upgraded.The present paper aims at providing a comprehensive contribution to the design and testing of an innovative bidirectional substation for active district heating, focusing on the hydraulic configuration and on the control strategies. The realized substation primarily fulfils the prosumer’s heat demand and supplies the excess heat to the DH network only if it is available at the temperature contractually defined with the DH operator, while it uses the network as a source if the local production is not sufficient to cover the user’s heat demand. The prototype, with a technology readiness level TRL 4, can be connected to a generic micro-generation system, e.g. solar thermal or heat recovery units. An extensive test campaign has been carried out in order to evaluate its dynamic behavior both from energetic and hydraulic points of view. Test confirmed the reliable operation of the substation, which is able to handle simultaneous heat exchanges with the user’s heating system and the DH network at pressure loss lower than 0.2 bar and at temperatures within ±0.6 °C of the prescribed setpoint after transients shorter than 5 min, even with ±10 °C step changes in the inlet fluid temperatures.

Cost and Energy Reduction of a New nZEB Wooden Building

The current study demonstrates the possibilities of reducing energy use and construction costs and provides evidence that wooden nearly-zero-energy buildings (nZEB) are technically possible at affordable construction costs by using novel design processes and procurement models that enable scalable and modular production. The energy efficiency solutions were derived by increasing/decreasing the insulation value of the building envelope in successive steps. Financial calculations were based on the investment needed to achieve the nearly-zero-energy levels. Overall, many opportunities exist to decrease the cost and energy use compared to the current (pre-nZEB) practice because the net present value can change up to 150 €/m² on the same energy performance indicator (EPI) level. The EPI in the cost-even range was reached by combining a ground-source heat pump (between 115 and 128 kWh/(m2·a)) and efficient district heating (between 106 and 124 kWh/(m2·a)). As energy efficiency decreases, improving energy efficiency becomes more expensive by insulation measures. Throughout the EPI range the most cost efficient was investment in the improvement of the thermal transmittance of windows (3–13 €/(kWh/(m2·a))) while investments in other building envelope parts were less effective (4–80 €/(kWh/(m2·a))). If these were possible to install, photovoltaic (PV) panels installed to the roof would be the cheapest solution to improve the energy performance. Integrated project delivery procurement (design and construction together) and the use of prefabricated wooden structures reduced the constructing cost by half (from ~2700 €/net m2 to 1390 €/net m2) and helped to keep the budget within limits.

Economic and environmental potential for solar assisted central heating plants in the EU residential sector: Contribution to the 2030 climate and energy EU agenda

Aligning with the ambitious EU 2030 climate and energy package for cutting the greenhouse emissions and replacing conventional heat sources through the presence of renewable energy share inside efficient district heating fields, central solar heating plants coupled with seasonal storage (CSHPSS) can have a viable contribution to this goal. However, the technical performance variation combined with inadequate financial assessment and insufficient environmental impact data associated with the deployment of those innovative district heating systems represents a big challenge for the broad implementation of CSHPSS in Europe. In this context, our paper presents a comprehensive evaluation for the possibility of integrating CSHPSS in the residential sector in various EU member states through the formulation of a multi-objective optimization framework. This framework comprises the life cycle cost analysis for the economic evaluation and the life cycle assessment for the environmental impact estimation simultaneously. The technical performance is also considered by satisfying both the space heating demand and the domestic hot water services. The methodological framework is applied to a residential neighborhood community of 1120 apartments in various EU climate zones with Madrid, Athens, Berlin, and Helsinki acting as a proxy for the Mediterranean continental, Mediterranean, central European, and Nordic climates, respectively. The optimization results regarding the energy performance show that the CSHPSS can achieve a renewable energy fraction above 90% for the investigated climate zones. At the same time, the environmental assessment shows significant improvement when using the CSHPSS in comparison to a natural gas heating system, in those cases the environmental impact is reduced up to 82.1–86.5%. On the other hand, substantial economic improvement is limited, especially in the Mediterranean climate zone (Athens) due to low heating demands and the prices of the non-renewable resources. There the total economic cost of the CSHPSS plants can increase up to 50.8% compared to a natural gas heating system. However, considering the incremental tendency in natural gas prices all over EU nowadays, the study of future plant costs confirms its favorable long-term economic feasibility.

Mapping energy and exergy flows of district heating in Sweden

District heating has been available in Sweden since the 1950s and used more than half of the total energy use in dwelling and no-residential premises in 2013. Energy and exergy efficient conversion and energy resources are key factors to reduce the environmental impact. It is important to understand energy and exergy flows from both the supply and demand sides. The exergy method is also a useful tool for exploring the goal of more efficient energy-resource use. Sankey diagrams together with energy and exergy analyses are presented to help policy/decision makers and others to better understand energy and exergy flows from primary energy resource to end use. The results show the most efficient heating method in current district heating systems, and the use of renewable energy resources in Sweden. It is exergy inefficient to use fossil fuels to generate low quality heat. However, renewable energies, such as geothermal and solar heating with relative low quality, make it more exergy efficient. Currently, about 90% of the energy sources in the Swedish district heating sector have an origin from non-fossil fuels. Combined heat and power is an efficient simultaneous generator of electricity and heat as well as heat pump with considering electricity production. Higher temperature distribution networks give more distribution losses, especially in exergy content. An outlook for future efficient district heating systems is also presented.

Heat demand mapping and district heating grid expansion analysis: Case study of Velika Gorica

Highly efficient cogeneration and district heating systems have a significant potential for primary energy savings and the reduction of greenhouse gas emissions through the utilization of a waste heat and renewable energy sources. These potentials are still highly underutilized in most European countries. They also play a key role in the planning of future energy systems due to their positive impact on the increase of integration of intermittent renewable energy sources, for example wind and solar in a combination with power to heat technologies. In order to ensure optimal levels of district heating penetration into an energy system, a comprehensive analysis is necessary to determine the actual demands and the potential energy supply. Economical analysis of the grid expansion by using the GIS based mapping methods hasn’t been demonstrated so far. This paper presents a heat demand mapping methodology and the use of its output for the district heating network expansion analysis. The result are showing that more than 59% of the heat demand could be covered by the district heating in the city of Velika Gorica, which is two times more than the present share. The most important reason of the district heating's unfulfilled potential is already existing natural gas infrastructure.

Evaluation of Energy Consumption of Municipal Buildings by Heat Energy Demand Mapping

The work is based on the EU Directive 2012/27/EU concerning energy efficiency. One of the objectives for energy efficient solutions is improvement of existing district heating systems. Compared to individual boilers, district heating ensures a low-carbon and cost-effective way to heat buildings. In order to determine what would make significant improvement in the existing heating system and to identify what specific energy efficiency measures can be applied, it is necessary to evaluate the current situation. The study identified the potential heat consumers in the Salaspils municipality through a software of geographical information systems. With the help of a created heat map it is possible to determine the areas where it would be beneficial to extend the existing district heating network or vice versa. During the study, the comprehensive assessment of the efficient district heating potential for exploitation is made based on the data of consumer location and building characterization. The methodology for assessment of heat consumption that has been developed in this study is based on the European Commission's methodology for determining the comprehensive national heating potential. The study emphasizes identification of consumers and methods for their mapping and assessing possibilities of district heating potential in the respective region.

Optimal integration of solar energy in a district heating network

The implementation of European Directive 2012/27 calls for the presence of a renewable share inside efficient district heating and cooling. Solar thermal energy can be a viable contribution to this aim but particular attention must be put into its integration inside the district heating systems. In fact, the variable and non-controllable nature of renewable heating must be handled by fulfilling users demand and coordinating its output with other controllable sources. Thermal energy storage is often necessary for exploiting the renewable sources at their best. An optimisation procedure has been developed to find the dispatching strategy for the different power sources present in the network. The optimisation procedure can be used at the planning level to find out the best sizing proportions of solar and conventional sources and for defining the optimal capacity of storage. After a brief description of the optimisation procedure and of its simulation modules, one test case is presented and results about advantages due to solar heating are discussed.

Achieving low return temperatures from district heating substations

District heating systems contribute with low primary energy supply in the energy system by providing heat from heat assets like combined heat and power, waste incineration, geothermal heat, wood waste, and industrial excess heat. These heat assets would otherwise be wasted or not used. Still, there are several reasons to use these assets as efficiently as possible, i.e., ability to compete, further reduced use of primary energy resources, and less environmental impact. Low supply and return temperatures in the distribution networks are important operational factors for obtaining an efficient district heating system. In order to achieve low return temperatures, customer substations and secondary heating systems must perform without temperature faults. In future fourth generation district heating systems, lower distribution temperatures will be required. To be able to have well-performing substations and customer secondary systems, continuous commissioning will be necessary to be able to detect temperature faults without any delays. It is also of great importance to be able to have quality control of eliminated faults. Automatic meter reading systems, recently introduced into district heating systems, have paved the way for developing new methods to be used in continuous commissioning of substations. This paper presents a novel method using the temperature difference signature for temperature difference fault detection and quality assurance of eliminated faults. Annual hourly datasets from 140 substations have been analysed for temperature difference faults. From these 140 substations, 14 were identified with temperature difference appearing or eliminated during the analysed year. Nine appeared during the year, indicating an annual temperature difference fault frequency of more than 6%.

Wood would burn

Absract In view of the world-wide problem of energy sustainability and greenhouse gas production (carbon dioxide), it is timely to review the issues involved in generating heat and power from all fuels and especially new (to the UK) solid fuels, including high moisture fuels such as wood, SRF, oil shale, tar sands and brown coal, which will become major international fuels as oil and gas become depleted. The combustion properties of some of these materials are significantly different from traditional coal, oil and gas fuels, however the technology proposed herein is also applicable to these conventional fuels. This paper presents some innovative combustion system options and the associated technical factors that must be considered for their implementation. For clarity of understanding, the novel concepts will be largely presented in terms of a currently developing solid fuel market; biomass wood chips. One of the most important characteristics of many solid fuels to be used in the future (including oil shale and brown coal) is their high moisture content of up to 60%. This could be removed by utilising low grade waste heat that is widely available in industry to dry the fuel and thus reduce transport costs. Burning such dried wood for power generation also increases the energy available from combustion and thus acts as a thermal transformer by upgrading the low grade heat to heat available at combustion temperatures. The alternative approach presented here is to recover the latent heat by condensing the extrinsic moisture and the water formed during combustion. For atmospheric combustion, the temperature of the condensed combustion products is below the dew point at about 55–65 °C and is only suitable for recovery in an efficient district heating system. However, in order to generate power from the latent heat, the condensation temperature must be increased to the level where the heat can be used in the thermodynamic power cycle. This can be achieved by increasing the combustion pressure to above 80 bar, resulting in the recovered latent heat being available at more than 200 °C. It can then be used to increase the cycle efficiency by about 15% by pre-heating the boiler water and/or combustion air etc. A further advantage is that the high pressure of the combustion gases also reduces the superheater tube stress since it can balance the steam pressure. The key advantage of this high pressure flue gas is that it is above the pressure at which carbon dioxide ‘condenses’ to a liquid or supercritical gas at atmospheric temperature. Thus when used with oxy-fuel combustion, the carbon dioxide flue gas from which the moisture has been condensed can be cooled to atmospheric temperature and the supercritical CO2 can be fed directly into the pipes leading to the sequestration site. An important consideration of these strategies is to ensure that non-condensable gases in the exhaust, including oxygen and nitrogen, do not adversely affect the ‘condensation’ processes. When oxy-fuel combustion is used, the flame temperature must be moderated by a cool diluent. Recycled carbon dioxide is often proposed for this duty. However, since the latent heat is recovered, the moisture or even additional water can fulfil this role. This latter option may be advantageous since it is more efficient to pump wood chip fuel in water into the high pressure zone rather than feed solid wood particles. Surplus water can be simply drained and the wet wood chips are a good fuel when the latent heat of the moisture in the fuel gases is recovered into the power cycle. Bearing in mind that it is much more efficient to pump a liquid to high pressure than to compress the same material as a gas, indicates that cryogenic oxygen is a suitable material to use for an efficient power station that generates energy from biomass (or other fuels such as coal etc). Finally, combustion of the hydrogen from the water–gas reaction with oxygen allows the steam temperature in the turbine to be increased to the “gas-turbine engine” range of 1000–1400 °C and hence the biomass and/or fossil fuel cycle efficiency can be well over 60%!