Solar Space Heating System Research Articles

Modeling and comparative assessment of solar thermal systems for space and water heating: Liquid water versus air-based systems

This work pertains to the transient modeling and comparative study of active solar thermal space and water heating systems using liquid and air-type solar thermal collectors as the main energy source. The study utilizes TRNSYS to simulate the two systems in the context of Taxila's weather data (located at 33.74°N, 72.83°E), with the goal of meeting peak space and domestic water heating demands of 20 kW and 200 lit/day, respectively. The liquid water-based system (S-1) is primarily composed of a liquid solar collector, thermal storage, an auxiliary heater, connections to the hot water supply, and the space heating load through a water–air heat exchanger. In contrast, the air-based system (S-2), employs a pebble bed storage to store heat extracted from the solar thermal air collector. The heated air is subsequently used directly for space heating and passed through an air–water heat exchanger for water heating. Dynamic simulations of both systems span the entire winter season, and various performance metrics, including solar fraction, primary energy savings, and solar collector thermal efficiency, are computed. The results revealed that at the same collector area, the liquid water-based system (S-1) shows a higher solar fraction than the air-based systems (S-2) while the primary energy savings of the S-1 resulted in lower values than S-2 at smaller collector areas (< ∼30 m2) but surpasses the S-2 with increasing collector size. The optimal collector tilt for both systems is determined to be 50°, while specific storage volumes corresponding to maximum primary energy savings are estimated to be 100 and 40 L/m2 for S-1 and S-2, respectively.

Experimental development, techno-economic and environmental analysis of a hybrid solar space heating system in a subtropical climate

Conventional modes of space heating are expensive and cause greenhouse gas emissions resulting in global warming. In this paper, an experimental analysis of a hybrid solar space heating system consisting of flat plate collectors (FPC) and evacuated tube collectors (ETC) along with a convective radiator is presented. Techno-economic and environmental analysis of the system is performed under real winter conditions in a subtropical climate. The experimental setup is designed such that flat plate collectors and evacuated tube collectors can also be operated separately for comparative analysis with the hybrid system (HC). The experimental results show that ETC achieved a maximum average energy efficiency of 72 % followed by the hybrid collector (HC) and FPC with energy efficiencies of 61 % and 57 %, respectively. The maximum exergy efficiency for ETC, HC and FPC are 54 %, 42 % and 33 % respectively in the month of December with low ambient temperatures. The corresponding maximum sustainability index achieved by ETC, HC and FPC, is 1.76, 1.52 and 1.39 respectively. In addition, the panel radiator achieved a maximum heat gain of 1484 W with an average room temperature in the range of 16.4–24.3 ℃. The economic analysis shows that the benefit-to-cost ratio for the hybrid varies from 0.82 to 1.6 and the payback period varies from 8.9 to 7.41 years compared to the electric heater for an inflation rate of 6–13 %. About 38 % more life cycle cost is observed for electric heater as compared to HSSHS. Environmental analysis reveals that 99 % and 78 % more greenhouse gas emissions are caused by conventional heaters compared to hybrid systems. Thus, a hybrid arrangement of FPC and ETC can be more beneficial for space heating compared to individual installations of these low-temperature solar collectors.

Investigation of a novel space heating scheme based on evacuated flat-plate solar collector and virtual energy storage

Solar space heating is an effective method to solve the high energy consumption problem of buildings. However, traditional solar space heating systems usually suffer from spacious land occupation problems that hamper their development. In this paper, a solar space heating system based on a novel type of evacuated flat-plate solar collector (EFPC) is proposed. An experimental study and district energy system demonstration are carried out to prove its feasibility and superiority. The results denote that this system can enormously upgrade solar energy efficiency and curtail land occupation by 66.98%. Moreover, the solar energy resource and the heating demand profile usually have an opposite variation tendency during the whole day, which results in a giant energy storage scale and land occupation. A solar space heating scheme based on EFPC and virtual energy storage is proposed to cope with this daily solar energy mismatch issue and the results manifest that the peak load can be shifted by more than 50%. Therefore, this solar space heating scheme can immensely reduce the land occupation of solar plants and it has a humongous prospect for achieving solar energy penetration and carbon emission reduction goals.

Investigation of a Solar Space Heating System Based on an Evacuated Tube Collector for Baghdad Climatic Conditions

The current work aims at evaluating the overall experimental performance of the solar space heating system regarding the local meteorological conditions of Baghdad. Two types of systems have been considered, namely, the thermal radiator with and without a fan. Indeed, a thermal radiator is connected to evacuate the tube solar collector through a circulating pump to distribute the heat into a room with dimensions of (3×3 m2). The experimental measurements for the current research were carried out during a period of six days in February and March, i.e., under mild conditions where the weather ranged between sunny and cloudy during the day. In order to find out the system performance, the solar radiation intensity, wind speed, inlet and outlet temperatures from solar collectors, inlet and outlet temperatures from thermal radiators, room temperature, and ambient temperature have been measured using specific instruments. The results revealed that, under sunny conditions, the room temperature of the system without a fan changes from 16.2 oC to 23.9 oC with a temperature difference of 7.7 oC. However, when a fan is used, the temperature difference reaches 10 oC. Such an improvement in the performance of the solar heating system that characterized the current work in comparison with its counterpart research is a direct result of the adoption of two main ideas. The first of them is the use of a modern metal heat exchanger that contains vertical and horizontal tubes. In addition to that, it is equipped with a fan that helps to increase the heat exchange between the heat radiator and the room space due to forced convection. Furthermore, the fan works to distribute the heat homogeneously inside the room, thus increasing the efficiency of the system. The second idea, however, is the use of a modern system represented by software that analyzes the results and evaluates the values of solar radiation and wind speed.

Technical assessment, economic viability, and environmental impact of a solar-driven integrated space and water heating system in various configurations

The use of solar heaters for space and water heating applications in energy efficient buildings is one of the most promising applications of solar energy, particularly in heating-dominated areas. In this paper, six different cases have been compared for an integrated solar space and water heating system, according to results based on the variation in terms of predicted solar fraction and collector efficiency. These models are developed from the combination of two simulation models (configuration 1 and configuration 2) based on different operational strategies and control schemes within the load-side loop and six methods of implementing the properties of different solar collectors, varying thermal energy storage systems (sensible and latent), and selecting optimum PCMs within latent thermal energy storage (LTES). A system operating under configuration 2 (C-2) energized with an evacuated tube collector (ETC) can offer more than 12 % higher solar fraction than a system operating under configuration 1 (C-1) energized with a flat plate collector (FPC). Furthermore, it is anticipated that incorporating optimum PCMs can significantly enhance the thermal energy storage capacity and significantly further enhance the solar fraction depending upon the working schedules and heating requirements. The detailed financial feasibility analysis concludes that the payback period of such a system is up to 5.9 years without considering financial incentives. Moreover, a 60 % reduction in greenhouse gas (GHG) emissions is achieved compared to a base system powered by electricity.

Optimization of the solar space heating system with thermal energy storage using data-driven approach

The employment of solar space heating is a significant measure to achieve carbon neutrality. However, the design of the solar space heating system usually leads to the dilemma of a trade-off between the economic benefit and environmental protection, which cannot be solved by single-objective optimization. In this work, in order to design a solar space heating system of a bungalow equipped with radiant floor heating, multi-objective optimization of the solar collector area and the volume of the water thermal energy storage (TES) tank is performed by coupling TRNSYS simulation, machine learning and genetic algorithm (GA). Simulation for the entire winter operation of the solar space heating system is conducted in TRNSYS, and a database with various combinations of the design variables are generated, based on which an artificial neural network (ANN) is constructed to capture the mapping of the design variables and the system performance indicators. After proper training and validation, the ANN model with satisfactory forecasting precision is utilized as the objective function for optimizing the system. GA is employed for searching the solutions of the multi-objective optimizations. This data-driven approach combining ANN and GA is helpful to achieve the optimal solutions. For the solar space heating system, the CO2 emission reduction can benefit most from the enlargement of the solar collector area and the TES tank volume, while the payback period reaches its minimum when both the solar collector area and the TES tank volume are small. By comparing single-objective with multi-objective optimizations, it is found that the single-objective optimization cannot reveal the interactions among the CO2 emission reduction, annualized life cycle cost (ALCC) and payback period (PBP) and that the optimization focusing on a single objective probably leads to apparent defects and inapplicability in reality. Better balance among the CO2 emission reduction, ALCC and PBP can be achieved from the Pareto optimums of the multi-objective optimization rather than the single-objective optimization. According to the TOPSIS evaluation, the most appropriate design scheme is obtained from the multi-objective optimization and has the potential to reduce the carbon emission by 5480.6 kgCO2eq/year while the ALCC and payback period are only 33.40 ¥/(m2·year) and 3.70 years, respectively.

Simulation and optimisation study on a solar space heating system in Baotou, China

Dual-water tank energy storage has been adopted in some solar heating systems to mitigate solar energy randomness and instability. Two types of dual-water tank solar heating (DWTSH) system are introduced and analysed in this paper, one is the traditional DWTSH system and the other has a thermal buffer and is named TB-DWTSH. Analysis software called TRNSYS was used for the simulation, the tank water temperatures and solar guarantee of two systems were measured and compared. A new thermal comfort evaluation criterion for the solar heating system is briefly introduced. The TRNSYS model was verified by a pilot project of a traditional DWTSH system. The heating systems were assessed based on the solar guarantee rate of the heating system and the thermal comfort index. The outcome showed that the simulation results are generally consistent with the experimental results. Compared with the traditional DWTSH system, the comfort index could be greatly improved in the TB-DWTSH system between 8 a.m. and 9 a.m. local time. Furthermore, compared with the traditional DWTSH system, the energy consumption of the auxiliary heat source is reduced by 30%. This study provides a good foundation for future research on DWTSH systems.

Experimental results of a solar space heating system with PCM: Small-scale setup and real-scale setup

Northern India receives considerable solar energy, while at the same time has a large demand for space heating. Solar space heating, combined with a thermal energy storage using PCM, could play a very important role in maintaining comfort conditions i.e. 15 ℃ to 20 ℃ in the cold regions where the temperature goes down to −15 ℃ to −20 ℃. This paper presents experimental results for using PCMs with transition temperature 22 ℃, 29 ℃, and 34 ℃, used for maintaining the comfort conditions, tested in a small-scale setup and a real-scale setup. The results show stabilization of the temperature of the test room, PCM type, and required PCM quantity.

Proposal and assessment of a new solar space heating system by integrating an absorption-compression heat pump

In cold regions, solar space heating is a clean and promising method that can be used to reduce the consumption of fossil fuels and electricity; however, the heat supply cost is extremely high because of the high investment, low energy efficiency, and short operating time. In this paper, a new system is proposed to improve the thermodynamic and economic performance of solar space heating in this paper. An absorption-compression heat pump is integrated with a conventional solar heating system in which the temperature of the collected heat is decreased by 20 °C to 30 °C, to increase the solar collection efficiency. The low-temperature heat collected by the solar collector is upgraded through the absorption-compression heat pump to generate high-temperature heat for space heating in winter and low-pressure process steam for industrial applications in other seasons. The thermodynamic performance of the proposed system is investigated through a numerical simulation. The results show that the efficiency of the solar collector increased by 39.50%, its annual effective operating time reached 2682 h, which is approximately four times that of a conventional solar heating system, and the annual solar energy utilization ratio increased from 4.82% to 43.74%. The payback period of the proposed system decreases to 5.69 years when the natural gas price equals 7.25 cents/kWh, which is 9.35 years shorter than that of the reference system. Furthermore, parameter optimization is performed on the solar collector area, storage tank volume and heat pump capacity. A minimum payback period of 5.44 years is obtained when the solar collector area, storage tank volume and heat pump capacity equal 170 m2, 11.17 m3 and 18.35 kW, respectively. This work provides a new way to utilize solar energy more efficiently and economically.

Validated TRNSYS Model for Solar Assisted Space Heating System

The present study involves a validated TRNSYS model for solar assisted space heating system as applied to a residential building in Jordan using new detailed radiation models of the TRNSYS 17.1 and geometric building model Trnsys3d for the Google SketchUp 3D drawing program. The annual heating load for a building (Solar House) which is located at the Royal Scienti?c Society (RS5) in Jordan is estimated under climatological conditions of Amman. The aim of this Paper is to compare measured thermal performance of the Solar House with that modeled using TRNSYS. The results showed that the annual measured space heating load for the building was 6,188 kWh while the heati.ng load for the modeled building was 6,391 kWh. Moreover, the measured solar fraction for the solar system was 50% while the modeled solar fraction was 55%. A comparison of modeled and measured data resulted in percentage mean absolute errors for solar energy for space heating, auxiliary heating and solar fraction of 13%, 7% and 10%, respectively. The validated model will be useful for long-term performance simulation under different weather and operating conditions.

Experimental and numerical investigations of a solar space heating system based on design of experiments method

In this paper, a solar water heating system (SWHS) based on 4 m2 flat plate collectors is integrated to an office building to ensure the heat demand. The SWHS is equipped with Labview software and a multichannel digital card that makes the system control and data acquisition automatic. A TRNSYS model is developed and validated against experimental data and then used for optimization purposes. A sensitivity approach based on the Design of Experiments method and dynamic simulations is proposed to optimize the solar fraction. For this purpose, 134 simulations have been carried out. Metamodels of the solar fraction have been then established for three ranges of the collector area; namely, [2–10] m2; [10–20] m2 and [20–30] m2. The results have shown that the solar fraction is highly dependent on the collectors’ area and the storage volume. Furthermore, the impact of the pump control strategy on the solar fraction has increased with larger systems. Finally, optimum design parameters have been obtained using the fitted models to achieve the targeted solar fraction of 60%. The proposed approach could be used for the optimization of solar heating systems design.

Reviewing the Exergy Analysis of Solar Thermal Systems Integrated with Phase Change Materials

The application of thermal storage materials in solar systems involves materials that utilize sensible heat energy, thermo-chemical reactions or phase change materials, such as hydrated salts, fatty acids paraffin and non-paraffin like glycerol. This article reviews the various exergy approaches that were applied for several solar systems including hybrid solar water heating, solar still, solar space heating, solar dryers/heaters and solar cooking systems. In fact, exergy balance was applied for the different components of the studied system with a particular attention given to the determination of the exergy efficiency and the calculation of the exergy during charging and discharging periods. The influence of the system configuration and heat transfer fluid was also emphasized. This review shows that not always the second law of thermodynamics was applied appropriately during modeling, such as how to consider heat charging and discharging periods of the tested phase change material. Accordingly, the possibility of providing with inappropriate or not complete results, was pointed.

Experimental analysis of a solar assisted desiccant-based space heating and humidification system for cold and dry climates

In the current work, an experimental analysis of a solar-assisted desiccant based heating and humidification system is performed for winter season under actual cold and dry conditions of Taxila, Pakistan. The installed setup consists of a silica-gel based desiccant wheel, a heat wheel, dual collector field of flat plate and evacuated tube collectors, and insulated storage tank. The day long measurements and assessments are reported during the months of December to February. The selected months represent wide range of cold and dry weather conditions which are applicable to different climate zones. The experimental results revealed that on average the system heating capacity, COPth, COPe, and auxiliary thermal power requirements for heating are around 5.9 kW, 1.48, 2.14 and 2.75 kW, respectively. Moreover, the solar fraction and the thermal efficiency of collector arrays are observed to be 64.75% and 40%, respectively. The uncertainties associated with humidification effectiveness, heating capacity and COPth are ±2.1%, ±5.5%, and ±7%, respectively. Finally, heating seasonal performance factor of 5 Btu/Wh is achieved. Based on the assessments, it is noted that the solar-assisted heating and humidification system is a viable solution for operation in cold and dry conditions.

Using PSO-GA algorithm for training artificial neural network to forecast solar space heating system parameters

An Artificial Neural Network (ANN) model based on PSO-GA optimization algorithm is applied to predict a Solar Space Heating System (SSHS) performance. An experimental research is conducted into the SSHS equipped with a Parabolic Through Collector (PTC). A number of influential factors such as I, Ta, T2c and Tw are considered to validate the ANN results. The proposed PSO-GA algorithm is used to identify a complex non-linear relationship between input and output parameters of the SSHS, and to obtain the optimized estimating ANN model. To show the accuracy of the PSO-GA model in training ANN, its results are compared with those of two highly powerful optimization algorithms, namely High Exploration Particle Swarm Optimization (HEPSO) and Team Game Algorithm (TGA), based on some evaluating criteria such as Mean Absolute Percentage Error (MAPE), Variance Accounted For (VAF), the coefficient of determination (R2) and Root Mean Square Error (RMSE). Results show the reliability of PSO-GA-ANN with highest R2 and RMSE. Afterwards, testing phases of the PSO-GA algorithm are done based on its parameters to obtain the best model of the neural network. Eventually, comparing the proposed model to Multi-Layer Perception Artificial Neural Network (MLPANN) exhibits its higher ability to estimate outputs when more accurate results are required.

Clear-days operational performance of a hybrid experimental space heating system employing the novel mini-channel solar thermal & PV/T panels and a heat pump

The paper investigated a hybrid experimental space heating system that comprises the novel mini-channel solar thermal and PV/T panels, as well as a heat pump. The major advantage of the system lies in the multiple functions of providing energy for space heating in winter and domestic hot water in other seasons, and generating electricity annually to balance the electricity demand of the system. Compared to traditional flat-plate solar collectors, the mini-channel solar thermal and PV/T panels have the smaller cross-sectional area, higher fluid flow velocity and thus higher heat transfer rate between the heat-carrying fluid and panel walls, thus leading to enhanced solar thermal and electrical efficiencies. It is found that during the typical-day testing, the mini-channel thermal panels had average solar efficiency of 50.8%; while the mini-channel PV/T panels had average solar efficiency of 45.0% and the whole system had average Coefficient of Performance (COP) of 4.9. The system made use of solar and gas sources with the fractional solar consumption of 44%, while its operation was under the pre-set time schedule, i.e., solar panels on from 9:00 to 6:00, heat pump on from 18:00 and 20:00, and gas heater on from 22:00 to 9:00. Throughout the testing period, the room temperature was maintained at above 18 °C, thus enabling achieving the required thermal comfort. Concerning the complexity of such a system, a simplified system comprising the mini-channel thermal and PV/T panels and a heat pump was suggested. In brief, the research has produced fundamental data for the mini-channel-based solar thermal and PV/T panels and established a foundation for designing a simple and low-cost mini-channel based solar space heating system for rural houses in cold climatic regions of China, which will subsequently contribute to significant fossil fuel saving and carbon emission reduction in the global extent.

Volume design of the heat storage tank of solar assisted water-source heat pump space heating system

The paper presents a method to design the volume of the heat storage tank of the solar assisted water-source heat pump space heating (SAWHPSH) system. With the area of the solar thermal collector calculated according to the China national design code for solar heating system, the space heating load and the solar radiation are considered simultaneously in this method. The design method of the volume of the solar heat storage tank is elaborated afterwards. In order to show the advantage of this design method, TRNSYS software was used to simulate the same SAWHPSH case project with the volume of the heat storage tank designed by both the method brought out in the paper and the one described in the China national design code. Performances of the system designed by the two different methods are investigated and the results show that the SAWHPSH system with the heat storage tank volume designed by the method presented in the paper has a higher average system COP.

Efficiency of a Solar Hydronic Space Heating System under the Algerian Climate

Hydronic heating systems supplied by renewable energy sources are one of the main solutions for substituting fossil fuel and natural gas consumption. This paper presents the development of modeling and analysis of a solar hydronic heating system in an existing single-family house built in 1990’s heated by low-temperature radiators. The simulation has been used to study the potential of using this system under climatic conditions in Algeria. And for this purpose, a component based on the simulation model for the thermal behavior of each component of the system are carried out in order to evaluate the economic performance for this system. The system is compared, with a conventional high-temperature boiler system. The results indicated that single-family houses could be heated with solar hydronic heating and provided an acceptable level of thermal comfort in the room with 22°C, according to the results of the analysis, the solar energy covers only 20.8% of the total energy consumption in a single-family house. Furthermore, the thermal performance of the heating conventional system can be largely improved up to 15%.

Efficiency of a Solar Hydronic Space Heating System under the Algerian Climate

Efficiency of a Solar Hydronic Space Heating System under the Algerian Climate

Energy and exergy evaluation of an integrated solar heat pipe wall system for space heating

In this paper, an integrated solar heat pipe wall space heating system, employing double glazed heat pipe evacuated tube solar collector and forced convective heat transfer condenser, is introduced. Thermal performance of the heat pipe solar collector is studied and a numerical model is developed to investigate the thermal efficiency of the system, the inlet and outlet air temperatures and heat pipe temperature. Furthermore, the system performance is evaluated based on exergy efficiency. In order to verify the precision of the developed model, the numerical results are compared with experimental data. Parametric sensitivity for design features and material associated with the heat pipe, collector cover and insulation is evaluated to provide a combination with higher thermal performance. Simulation results show that applying a solar collector with more than 30 heat pipes is not efficient. The rate of increasing in temperature of air becomes negligible after 30 heat pipes and the trend of the thermal efficiency is descending with increasing heat pipes. The results also indicate that at a cold winter day of January, the proposed system with a 20 heat pipe collector shows maximum energy and exergy efficiency of 56.8% and 7.2%, which can afford warm air up to 30°C. At the end, the capability of the proposed system to meet the heating demand of a building is investigated. It is concluded that the best method to reach a higher thermal covered area is to apply parallel collectors.

Simulation and optimization study on a solar space heating system combined with a low temperature ASHP for single family rural residential houses in Beijing

A pilot project of the solar water heating system combined with a low temperature air source heat pump (ASHP) unit was established in 2014 in a detached residential house in the rural region of Beijing, in order to investigate the system application prospect for single family houses via system optimization design and economic analysis. The established system was comprised of the glass heat-pipe based evacuated tube solar collectors with a gross area of 18.8m2 and an ASHP with a stated heating power of 8kW for the space heating of a single family rural house of 81.4m2. The dynamic thermal performance of the pilot system was measured for continuous 20days under typical cold climate conditions and the test data was used to validate the TRNSYS simulation model established. On the basis of model validation, system optimizations of both the existing pilot household and the typical rural house with good building insulation were undertaken to figure out the system economical efficiency in the rural regions of Beijing. The results show that the payback periods of the solar space heating system combined with the ASHP with the collector areas 15.04–22.56m2 are 17.3–22.4 years for the established pilot household on the current electricity price level of 0.5RMB/kWh, comparing with the reference condition of the fully ASHP space heating. It is further found that the equivalent solar heat price per kWh is too high under the current solar market cost price and collector technology. To put forward the integrated solar space heating for reducing carbon emission, it is suggested that the Beijing municipal government should offer some financial subsidy to compensate the equivalent solar heat price per kWh.