Search

Focuses on a study which investigated the influence of domestic hot water (DHW) load profiles with a constant total yearly heat demand for a solar combisystem. Realistic load profiles for DHW; Definition of the fraction energy savings; Relations of the thermosyphon loop; Distribution of the solar energy gain.

A solar-assisted liquid desiccant demonstration plant was built and experimentally evaluated. Humidity of the air, density of the desiccant, and all relevant mass flow rates and temperatures were measured at each inlet and outlet position. Adiabatic dehumidification experiments were performed in different seasons of the year under various ambient air conditions. The moisture removal rate mv, the mass balance factor κm, and the absorber effectiveness, εabs, were evaluated. An aqueous solution of LiCl was used as liquid desiccant with an initial mass fraction of about 0.4 kgLiCl/kgsol. The mass flow rate of the air through the absorber was about 1100 kg/h. The experimental results showed a reduction in the air humidity ratio in the range of 1.3-4.3 g/kg accompanied with an increase in the air temperature in the range of 3-8.5 K, depending on the inlet and operating conditions. For the air to desiccant mass flow ratio of 82, a mass fraction spread of 5.7% points in the desiccant and a volumetric energy storage capacity of 430 MJ/m³ were achieved. By operating the desiccant pump in an intermittent mode, a mass fraction spread of about 13% points in the desiccant and an energy storage capacity of about 900 MJ/m³ were reached. In addition, the experimental results were compared with results from a numerical model. The numerical model overestimates the heat and mass transfer because it assumes ideal surface wetting and uniform distribution of the circulated fluids. [ABSTRACT FROM AUTHOR]

Highlights • A process heat comparison methodology is developed for solar thermal and heat pumps. • The methodology determines an upper limit for specific solar turn-key investment. • Only a few key inputs are required for its use, obtainable with an energy audit. • Nomograms quickly show the lower cost process heat technology, applicable worldwide. • Results are primarily dependent on heat pump operating hours and solar thermal yield. Abstract Low carbon heat generation is now a major concern for many industries to achieve sustainability targets, however, it is not always clear which renewable or low carbon process heat technology is the most economical. This article develops a techno-economic assessment methodology to compare the cost effectiveness of solar thermal and electricity powered vapor compression heat pumps for process heat generation. Using key investment and performance indicators, it clearly elucidates the lower cost renewable or low carbon heat technology under most conditions found in low temperature industries. The analysis also calculates the maximum turn-key specific investment, inclusive of all material, labor, and financial costs, for solar thermal to remain financially competitive against heat pumps, serving as a target for the solar thermal industry. The methodology, which is independent of plant size, process temperature, and technology, reveals key results when applied to three cities in Europe of varying solar irradiation and current electricity costs. In Seville, the maximum turn-key specific solar investment is typically greater than 500 €/m2 ap , meaning that solar thermal will most likely provide lower cost heat than heat pumps. The case for Stockholm is the opposite, with the maximum investment being primarily less than 300 €/m2 ap , a challenging turn-key solar plant investment target that leads to the superiority of heat pumps in this region. There is a wide range (230–1000 €/m2 ap) of maximum turn-key solar thermal investment figures for a central German location (Würzburg), indicating that either technology could be selected, but this is highly dependent on the process and other boundary conditions. Therefore, at any time now or in the future, the developed methodology can flexibly compare solar thermal and heat pumps so that the lower cost process heat technology can quickly be selected, while also providing a plant investment target for the solar thermal industry. [ABSTRACT FROM AUTHOR]

Solar energy is an important measure to reduce fossil fuel use and carbon emissions from the energy supply in industries requiring heat below 150 °C. A robust methodology was developed to compare two solar conversion technologies (solar thermal and photovoltaics via resistance heating) to determine which provided lower cost heat, highly flexible for various plant sizes, investments, currencies, locations, and process temperatures. At current PV investments, solar thermal plants must be installed turn-key below 400 €/m 2 ap in northern European climates and 500 €/m 2 ap in southern to remain economically competitive. Photovoltaic heat is already the lower cost heat provider for many applications in northern latitudes above 100 °C. In future PV cost scenarios, solar thermal must reduce investments below 250 €/m 2 ap to remain competitive in Europe and 400 €/m 2 ap in higher solar resource regions. When opportunity costs are considered, photovoltaics are better utilized to offset local electrical, not thermal, demand. Despite this fact, future efforts must be given to solar thermal cost reduction in order to remain competitive against all other renewable heat producers. [ABSTRACT FROM AUTHOR]

In conventional air-conditioning systems with vapour compression cycles the dehumidification is realised by cooling the air below the dew point of the supply air. One possibility to avoid cooling the air below the dew point and thus to reduce the electric energy demand of air-conditioning systems is hybrid liquid desiccant air-conditioning systems (HLDACS) which use an open absorption cycle for dehumidification of the air. This conceptual study examines four different HLDACS with respect to their electric energy demand and shows energy saving potentials compared to a conventional air-conditioning system for three different climatic design conditions. All considered systems consist of an open absorption system in combination with either a vapour compression system (VCS) or an indirect evaporative cooling system. The results show that electric energy savings of 30–60% depending on the HLDACS and climates are possible. [ABSTRACT FROM AUTHOR]

The decarbonisation of urban district heating (DH) systems requires increased heating grid flexibility. Therefore, this article examines the optimised operation of a tank thermal energy storage (TTES) on the secondary side of a new DH substation for an industrial site in a German city, in order to shave the peaks of the whole DH system and thus reduce the need for heat-only boilers (HOB). The accuracy of heat load and return temperature forecasts for both the industrial consumer and the DH grid is critical to the performance of the optimisation-based operating strategy of the TTES. Therefore, long short-term memory neural networks are used in combination with continuous model updates through incremental learning to create two forecasting scenarios, one using only preceding data for the forecasts and the other including future weather data. The results show that high forecasting accuracy is most relevant for reducing the annual maximum peak, with a reduction of 2.8% in the preceding data scenario, 4% with future weather data and 7% in a benchmark with perfect forecasts. The economic viability of the storage through HOB heat savings is primarily affected by lower forecasting accuracy when the additional cost of HOB heat is less than 60 €/MWh. • Optimised operation of thermal storage at large district heating substations can shift heat supply from HOB to CHP. • Incremental learning improves heat load forecasts generated by deep learning models. • Forecasting accuracy has a significant impact on district heating peak shaving. • Short optimisation intervals and weather forecasts are required to reduce annual maximum peaks. [ABSTRACT FROM AUTHOR]

Highlights: [•] A simulation-based fault detection approach for solar thermal systems was developed. [•] Faults are detected by comparing simulated and measured energy yields. [•] Faults causing an energy loss of ca 25% can be detected. [•] A field test with three systems between 15 and 1290m2 was carried out. [•] Several faults were detected, identification of faults is more difficult. [Copyright &y& Elsevier]

Abstract: To increase the fractional energy savings achieved with solar thermal combisystems the store volume may be increased. Installation of large stores in single-family houses is, however, often limited by space constraints. In this article the influence of the store dimensions, as well as internal and external auxiliary volume configurations, are investigated for large solar water stores by annual dynamic TRNSYS simulations. The results show that store sizes up to 4m3 may be used in solar heating systems with 30m2 collector area. It is further shown that well-insulated stores are rather insensitive to the geometry. Stores deviating from the conventional dimensions still yield high fractional energy savings. Furthermore, the simulations show that the performance of an internal auxiliary volume configuration in most cases exceeds that of a solution with an external auxiliary unit. The practical limitations of very thin auxiliary volumes must, however, be further investigated. [Copyright &y& Elsevier]

Heat pumps powered by renewable electricity have a significant potential to become a critical technology to disruptively decarbonize industry. An essential step towards this goal is the development of an accurate understanding and model of how heat pumps in large-scale implementations perform in terms of economics, energy, and the environment. In this study, the influence of system design and operating conditions on the coefficient of performance (COP) of large-scale (>50 kW th) electric driven mechanical compression heat pumps is reviewed. The review underscores the knowledge gap on the capabilities of large-scale heat pumps, especially the lack of simple mathematical COP-models based on real-world data. Developing and transferring a reliable COP-model and a comprehensive overview on capabilities of market available heat pumps to academics and practitioners (e.g. research engineers, energy-managers and consultants) can close this knowledge gap. Therefore, this study assembles a comprehensive dataset for the system configuration and performance of 33 large-scale heat pumps from 11 different manufacturers and addresses three main objectives: (1) Classifying and evaluating the capabilities of market available heat pumps. (2) Modelling the correlation between the COP and the operating conditions. (3) Developing an economic and ecological evaluation method for a heat pump project. Applying the developed models to accurately assess real-world performance and build a sound business case for large-scale heat pumps has the potential to accelerate the uptake of renewable energy and help improve overall environmental sustainability. • Summaries the potential and capabilities of market available heat pumps. • Examines the influence of system configuration on heat pump efficiency. • Develops accurate models for estimating the COP depending on operating conditions. • Presents a short-cut method for economic and ecological feasibility assessment. [ABSTRACT FROM AUTHOR]

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. • Dynamic simulations of different DHW preparation systems in TRNSYS. • Generation of DH load profiles for DHW for instantaneous and storage systems. • Instantaneous DHW systems yield lower return temperatures than storage systems. • Simultaneity factors were calculated for different systems and time scales. • Time scale and probability distributions for DHW draw-offs influence peak loads. [ABSTRACT FROM AUTHOR]

Heat load profiles of new residential developments in rural, sub-urban, and urban context were generated by means of a generic model and dynamic simulations. The combined effect of district building density, building energy efficiency standard, and hot water preparation system on the heat load is discussed in detail. Hundred residential districts representing medium sized developments were defined by varying the distribution of building types. Therefore, a simplified building typology of 13 fictitious buildings was developed. The presented methodology allows to quickly estimate the total heat demand of new residential developments based on the plot ratio and buildings' energy efficiency standard only. The investigations reveal that the building density as well as the hot water preparation system have a significant impact on the yearly district heating return temperatures. Instantaneous domestic hot water preparation results in up to 14 K lower annual average district heating return temperatures. However, the building density also has a significant influence on the return temperature, resulting in important differences between urban and rural districts. • Heat load profiles of rural, sub-urban, and urban districts were generated. • The German energy efficiency standards for new buildings were considered. • The impact of building systems engineering on the return temperature was assessed. • Instantaneous DHW preparation achieves significant lower DH return temperatures. • Districts of plot ratio greater than 0.3 show beneficial linear heat densities. [ABSTRACT FROM AUTHOR]