Low-temperature Heating System Research Articles

Exergy analysis of the performance of low-temperature district heating system with geothermal heat pump

Abstract Exergy analysis of low temperature geothermal heat plant with compressor and absorption heat pump was carried out. In these two concepts heat pumps are using geothermal water at 19.5 oC with spontaneous outflow 24 m3/h as a heat source. The research compares exergy efficiency and exergy destruction of considered systems and its components as well. For the purpose of analysis, the heating system was divided into five components: geothermal heat exchanger, heat pump, heat distribution, heat exchanger and electricity production and transportation. For considered systems the primary exergy consumption from renewable and non-renewable sources was estimated. The analysis was carried out for heat network temperature at 50/40 oC, and the quality regulation was assumed. The results of exergy analysis of the system with electrical and absorption heat pump show that exergy destruction during the whole heating season is lower for the system with electrical heat pump. The exergy efficiencies of total system are 12.8% and 11.2% for the system with electrical heat pump and absorption heat pump, respectively.

Minewater 2.0 Project in Heerlen the Netherlands: Transformation of a Geothermal Mine Water Pilot Project into a Full Scale Hybrid Sustainable Energy Infrastructure for Heating and Cooling

In the last 10 years numerous research and commercial initiatives have been undertaken in Europe to develop abandoned coal mining fields into low-temperature resources. One of the most successful is the Minewater project of the municipality of Heerlen, the Netherlands, where a low-temperature district heating system was launched in operation in October 2008, under the European Interreg IIIB NWE programme and the 6th Framework Program project EC-REMINING-lowex. The Minewater project is now being upgraded from a straight forward pilot system to a full-scale hybrid sustainable energy structure called Minewater 2.0. A totally new concept which becomes an essential part of the Sustainable Energy Structure Plan of Heerlen and has the following landmarks:•Energy exchange instead of energy supply: cluster grids for energy exchange between buildings and the existing mine water grid for energy exchange between cluster grids.•Energy storage and regeneration in mine water reservoirs instead of depletion.•Addition of poly-generation: bio-CHP, solar energy, feed in of waste heat (data centres and industry), cooling towers for peak cold demands.•Enlargement hydraulic and thermal capacity mine water grid through improving well pumps, pressure boosting systems and reuse of the existing mine water return pipe for additional supply and disposal of hot mine water.•Fully automatic and demand-driven supply of hot and cold mine water through usage of pressurized buffer systems at the extraction wells and sophisticated injections valves at the injection wells.•All geographically dispersed mine water installations at buildings, clusters and wells are equipped with sophisticated process control units that communicate with a Central Monitoring System (CMS) through the internet. A very new application in the build environment.The first phase of the Minewater 2.0 project is in operation since June 2013. In November 2013 at the congress we will be able to share the first experiences.

Development of an Evaluation Methodology for the Potential of Solar-thermal Energy Use in the Food Industry

The research project ‘Solar Heat in the Liquid Food Industry’ (part of the FORETA Research Network [1]) focused on the development and optimisation of low-temperature heating systems for the liquid food industry. Its main objectives are in energy efficiency, waste heat recovery and the feasibility of a solar-thermal process heating system. Based on the particular simulation results the overall solar-thermal potentials for German breweries and dairies were determined. In this connection a literature review indicated that most of the potential studies on solar-thermal energy use in the industry or related to specific industrial sectors are based on the total use of low-temperature heat. In opposition to these results, the available and mainly limited roof area was found to be a more important aspect for the solar-thermal potential. Hence, the development of a methodology for a site- specific analysis was necessary. The interconnection of only a few defined evaluation criteria resulted in a more realistic estimation of the potential for a solar-thermal heat supply.

Combined simulation of a deep ground source heat exchanger and an office building

It is analyzed, if and to which share the deep borehole heat exchanger (BHE) at RWTH Aachen University in its current state is capable of heating an office building located at its top, called SuperC. Furthermore, possible modifications to the BHE and to the hydraulic connection to the building's heating system are discussed.Models of the BHE and of the building are each validated with measurement data and than connected to each other to carry out system simulations for one heating period. It is found that the BHE in its current state can support the heating system by a notable share of the annual heating demand by supplying the low temperature heating systems of the building. An alternative system configuration and a different inner BHE pipe provide the opportunity of higher supply temperatures leading to a higher fraction of geothermal heating.

Low temperature radiator heating distribution and emission efficiency in residential buildings

Low and nearly zero energy buildings with decreased heating need can utilize low temperature heating systems for energy efficient heating. Distribution and emission losses for low temperature radiator heating cannot be found from European standards or scientific literature. The use of the losses of conventional systems can result in significant overestimation of heating energy use. In this paper, distribution and emission losses of low temperature and conventional radiator heating system were determined in North and Central Europe climates for low energy detached houses and apartment buildings. Detailed dynamic components of heating system in the whole building energy simulation model allowed to quantify these losses. Main findings of the study show that distribution losses can be controlled with low temperature heating curves and emission losses with PI type thermostats. For conventional systems the losses higher than 50% of heating need were calculated in the apartment building. With low temperature heating curve, PI thermostats and limited heating period distribution and emission losses were possible to keep below 1% in detached houses in both climates. In apartment buildings the minimal achievable losses were significantly higher, between 6 and 12% in North and Central European climates, respectively. Proportional thermostats add 2 to 6% to these losses. Based on results, heating curve of 45/35°C can be recommended for detached houses and even 40/30°C for apartment buildings. Insulating distribution and connection pipes in heated spaces proved to have no practical effect on heat losses. Compared to EN 15316-2-1:2007, the losses were significantly lower especially for low temperature heating curves. A new set of tabulated values is proposed for the revision of the standard. It was possible to explain the mechanism of losses, but still it was not possible to calculate losses from hourly energy need data with the correlation equation leading to overestimation by factor of about 10 compared to dynamic simulation.

Recycled Water Reuse and Rainwater Utilization Project of Jilin Jianzhu University

As a heating system of energy saving, environmental protection, comfortable, safe and new-type, low-temperature radiation ground electric heating system has many advantages that other heating ways can not be on a par with such as long service life and free from maintenance within 50 years and has been gradually accepted by broad developers and residents. It has been broadly applied in heat supply in residence, industrial workshop, classrooms and hospitals; warm preservation in pipeline and warming in high tunnel and snow melting in slope road.

Energy performance of low temperature heating systems in five new-built Swedish dwellings: A case study using simulations and on-site measurements

In Europe, high energy consumption in built environments has raised the need for developing low energy heating systems both in new building and in retrofitting of existing buildings. This paper aims to contribute by presenting annual results of calculated and measured energy consumption in five new-built semi-detached dwellings in Stockholm, Sweden. All buildings were equipped with similar low temperature heating systems combining under-floor heating and ventilation radiators. Exhaust ventilation heat pumps supported the low temperature heating system. Buildings were modeled using the energy simulation tool IDA Indoor Climate and Energy (ICE) 4, and energy consumption of the heat pumps was measured. Results showed that calculated and measured results were generally in agreement for all five dwellings, and that the buildings not only met energy requirements of the Swedish building regulations but also provided good thermal comfort.

Feasibility Analysis of Application of Low-Temperature Radiation Electric Heating System

As a heating system of energy saving, environmental protection, comfortable, safe and new-type, low-temperature radiation ground electric heating system has many advantages that other heating ways can not be on a par with such as long service life and free from maintenance within 50 years and has been gradually accepted by broad developers and residents. It has been broadly applied in heat supply in residence, industrial workshop, classrooms and hospitals; warm preservation in pipeline and warming in high tunnel and snow melting in slope road. Take 16 classic users in certain community as research target in analysis of energy saving potentiality of low-temperature radiation electric heat supply.

The Feasibility Study on Utilization of the Industrial Gas Waste Heat and Low-Temperature Floor Radiant Heating System in Resident Sub-District Based on the Heat Exchangers

We used the industrial gas waste heat as the heat source of low-temperature floor radiant heating system to save energy and protect our environment, which is the thing that predecessors didn’t do. So we designed heat exchangers, which are the key parts of them, and accurately calculated their heat transfer area by using the method of ε-NTU. Through temperature drop and pressure of the gas changed, we compared their variable quantity, and draw the conclusion that improving the temperature and pressure can reduce it effectively. Using this technology, we can save 30000 tons of anthracite into a heating season , which is worth ￥24,000,000 or so, in the resident sub-district ,whose heating building area of 10000 m2, so the practical application of it has very well prospect, and the research based on it has strong economic significance and social significance.

Current state of the art of geothermal heat pumps as applied to buildings

This paper summarizes the current state of the art of geothermal heat pumps as applies to buildings. Geothermal or ground source heat pump (GSHP) systems provide heating, cooling as well as domestic hot water, by the use of the underground or bodies of surface water as heat source or sink. More specifically, a GSHP system comprises a heat pump (usually water-to-water) and a ground source system (ground heat exchanger or groundwater well) in order to provide heating and cooling to the building through a low-temperature heating system and domestic hot water as well. The main concept of a GSHP system is the maximization of the heat pump efficiency i.e. minimization of electricity consumption mostly due to underground temperature which is almost invariant throughout the year. So, it is clear that GSHP systems have contribution to the environmental protection and reduction of greenhouse gas emissions. GSHPs are a mature industry, with a continuous trend of development and due to their increasing energy efficiency due to recent advances of the technology (described in the following chapters) are attractive and are more and more considered as an excellent substitute of conventional heating/cooling sources including air source heat pumps and variable refrigerant volume. Due to these advances in several cases the high efficiency of GSHP compared to the initial capital cost minimizes the need for subsidies.

Evaluation of Working Parameters of Radiant Heating Systems

The basic benefit of low-temperature radiant heating systems is thermal comfort. Additional sound insulation and high inertia factor that provide heating of the surfaces, even without initial phase of energy consumption, can be regarded as an advantage. This paper discusses benefits of low temperature systems installed under the floor or wall surfaces. This study is aimed to demonstrate the influence of heating system elements on indoor air parameters especially on internal surface of building envelope. The model described in this paper offers to optimize building energy performance with low temperature pipes built in the construction.

A New Heat Transfer Model for Floor Configuration Layer of the Low-Temperature Water Floor Radiant Heating System

The floor configuration layer and the floor radiant heat transferred by heat transferred configuration layer exterior with other walls are taken into account in this paper, then physical and mathematics models are developed. Simulation results as well as testing results are compared and analyzed to prove that the models and the calculation methods are right.

A MULTIFUNCTION DEHUMIDIFYING HEAT PUMP FOR GREENHOUSES

mprovements in greenhouse structure and equipment with the aim of saving energy (double walls, thermal screens) have led to better insulation and airtightness but have also induced microclimatic changes, especially on nighttime humidity levels. During the last decade, dynamic climate procedures such as temperature integration have been frequently implemented to save energy in greenhouses. Temperatures may reach low levels and the greenhouse ventilation may remain particularly weak when using these types of systems, but the humidity level is always high. Consequently, the occurrence of fungal diseases and physiological disorders increases and greenhouse air dehumidification is required. In order to cope with this problem, a multifunction compression heat was developed, first, for dehumidifying the greenhouse during the night and, second, for heating the greenhouse in the same way as that of a conventional air-source heat pump, in addition to the boiler. To reach these objectives, a second evaporator is added to draw the heat from the outside to the inside (air-air). A water condenser (air-water) may also be added to provide a low-temperature heating system. The activation of the heating mode depends on the coefficient of performance (COP) and on the economic viability (bi-energy system: depending on the main energy source used). The dehumidification heat pump is designed for use at night as a function of the vapour pressure deficit (VPD) set point. A dynamic model of water vapour exchanges was developed to evaluate during the night the water vapour transfer between the different sub-systems (heat pump evaporator, crop, inside air, roof, outside air) considered as sources and sinks of water vapour. This model makes it possible to determine the power of the dehumidification systems according to the characteristic parameters of the greenhouse, the crop and the outside climate. This device is being implemented in a glasshouse in the west of France. Adjustments are, however, still necessary to validate the model and to optimise energy efficiency.

Low-temperature baseboard heaters with integrated air supply – An analytical and numerical investigation

The functioning of a hydronic baseboard heating system with integrated air supply was analyzed. The aim was to investigate thermal performance of the system when cold outdoor (ventilation) airflow was forced through the baseboard heater. The performance of the system was evaluated for different ventilation rates at typical outdoor temperatures during the Swedish winter season. Three different analytical models and Computational Fluid Dynamics (CFD) were used to predict the temperature rise of the airflow inside the baseboard heater. Good agreement between numerical (CFD) and analytical calculations was obtained. Calculations showed that it was fully possible to pre-heat the incoming airflow to the indoor temperature and to cover transmission losses, using 45 °C supply water flow. The analytical calculations also showed that the airflow per supply opening in the baseboard heater needed to be limited to 7.0 l/s due to pressure losses inside the channel. At this ventilation rate, the integrated system with one air supply gave about 2.1 more heat output than a conventional baseboard heating system. CFD simulations also showed that the integrated system was capable of countering downdraught created by 2.0 m high glazed areas and a cold outdoor environment. Draught discomfort in the case with the conventional system was slightly above the recommended upper limit, but heat distribution across whole analyzed office space was uniform for both heating systems. It was concluded that low-temperature baseboard heating systems with integrated air supply can meet both international comfort requirements, and lead to energy savings in cold climates.

Flow patterns and thermal comfort in a room with panel, floor and wall heating

Thermal comfort aspects in a room vary with different space heating methods. The main focus in this study was how different heating systems and their position affect the indoor climate in an exhaust-ventilated office under Swedish winter conditions. The heat emitters used were a high and a medium–high temperature radiator, a floor heating system and large wall heating surfaces at low temperature. Computational fluid dynamics (CFD) simulations were used to investigate possible cold draught problems, differences in vertical temperature gradients, air speed levels and energy consumption. Two office rooms with different ventilation systems and heating needs were evaluated. Both systems had high air exchange rates and cold infiltration air. The general conclusions from this study were that low temperature heating systems may improve indoor climate, giving lower air speeds and lower temperature differences in the room than a conventional high temperature radiator system. The disadvantage with low temperature systems is a weakness in counteracting cold down-flow from ventilation supply units. For that reason the location of heat emitters and the design of ventilation systems proved to be of particular importance. Measurements performed in a test chamber were used to validate the results from the CFD simulations.

Development of a Small-Capacity Adsorption System for Heating and Cooling Applications

This paper describes the prototype of a small adsorption heat pump working on the adsorption pair silica gel-water. The developed system consists of two modules, each containing an adsorption reactor and a second heat exchanger for evaporation and condensation of the working fluid. The two modules are operated periodically in order to obtain a quasi-continuous heating or cooling output. A reliable control unit has been developed and implemented in the machine. Hot water provided at temperatures of 80°C to 95°C is used to drive the machine, and heat from the low-temperature heat source (10°C to 20°C) is upgraded to the intermediate temperature level of about 35°C to 45°C, which is suitable for low-temperature heating systems such as wall or floor heating installations. For cooling applications, chilled water of 10°C to 15°C is produced in an almost continuous mode. The first prototypes have been tested. Heating coefficients of performance (COPs) of more than 1.3 and cooling COPs for air-conditioning purposes (12°C to 15°C) of 0.5 have been achieved. The machine provided a mean heating power of up to 15 kW and a cooling power of up to 8 kW.

Investigating control strategies for a domestic low-temperature heat pump heating system

Despite energy conservation regulations and efforts for improving HVAC operations, numerous domestic buildings do not perform energy efficiently and many times the indoor environment is far away from specified comfort levels. Especially in houses served from low-temperature heating systems the low ability of the heating system to respond to fast changing thermal loads is common. In such cases, the implementation of new, sophisticated controls is an important issue. In this study, we use a reference model of a domestic low temperature heat pump heating system developed in TRNSYS–EES and analyse its operation. Several methods of control strategies have been applied for specified time periods in order to keep the comfort within reasonable ranges. Prognostic climatic control and increased ventilation rates when required are some of these methods. The results depict the influence of the control method on the indoor temperature and the comfort indexes of PMV and PPD. The highest indoor temperature difference for a chosen day reaches 4 °C when there is no shading and when there is internal shading with the option of applying prognostic climatic control. Generally, the findings highlight the importance of dynamics in controlling functions and the difficulty of incorporating in models unpredictable factors as the solar radiation.

Seasonal Thermal Energy Storage in Germany

Since 1993 German research work has been made in the Research and Development programs, “Solarthermie-2000” and “Solarthermie2000plus”. One aim of the programs is to improve and demonstrate the technical and economic feasibility of different seasonal thermal energy storage concepts and technologies. The research work comprises basic Research and Development on storage concepts, design, construction, and long term monitoring and evaluation of (so far) eight large scale demonstration plants. The demonstration plants are designed to cover between 35 and 60% of the annual heat demand of new housing areas by solar energy. The first plants of the program are in operation since 1996. The data and experiences show that all investigated storage concepts are working without major technical problems. The annual heat output of the stores strongly depends on the return temperature of the connected district heating net which is determined by the heating systems of the connected consumers. Obviously a low temperature heating system in buildings is necessary to optimize the thermal output of the seasonal heat storage systems.

Exergy analysis of a low temperature radiant heating system

The purpose of this study is to gain insight into the process of heating a room with a low-temperature radiant heating system and solar energy, considering energy conversion and heat transfer steps in the building (where heat is required), in the incident solar radiation (which supplies part of the heat required) and in the heating system (which provides for the additional heating needs, by using electricity from a gas-fired power plant to drive a heat pump). We applied a theoretical framework developed by Shukuya et al., to a dynamic simulation model and did numerical calculations for a room with an exterior wall, with and without a south-facing window, during a heating season in the Netherlands. The exergy analysis allows direct comparison between different energy types (e.g., heat, electricity, fuel) on a common basis, and the concept of exergy consumption is useful for expressing how and where energy is dispersed in the course of energy conversion and heat transfer steps. The results show that exergy consumption in the room (demand side) is relatively small compared to the supply side (fuel burned at the power plant and the sun reaching the ground and facade). The calculations also show that the total amount of exergy consumed during the heating season can be larger than the total amount of exergy supplied during the same period, as a result of heat storage in the building mass, and of changes in the outdoor temperature between the moment of heat storage and heat release.

04/02065 Energy analysis of a low-temperature heat pump heating system in a single-family house: Sakellari, D. and Lundqvist, P. International Journal of Energy Research, 2004, 28, (1), 1–12

04/02065 Energy analysis of a low-temperature heat pump heating system in a single-family house: Sakellari, D. and Lundqvist, P. International Journal of Energy Research, 2004, 28, (1), 1–12