Combisystem Research Articles

Preliminary study for solar combisystem potential in Canadian houses

Solar combisystems that are capable of providing space heating and cooling as well as domestic hot water heating present a promising alternative to conventional systems to achieve net zero energy status in residential buildings. To determine whether or not the performance of such systems would be suitable in the northerly Canadian context, a preliminary study was conducted to evaluate the thermal performance of a solar combisystem with space heating, cooling, domestic hot water heating and thermal storage capability for houses in the four climate regions of Canada (Atlantic, Central, Prairies and Pacific) based on simulations conducted using models developed within the TRNSYS 17.1 energy simulation software. For days without sufficient sunshine, auxiliary heating and cooling systems are included. The operation of the solar combisystem and the auxiliary systems is controlled using a realistic control algorithm. Sensitivity analysis is conducted to determine effects of solar collector area and storage capacity on solar combisystem performance. The results show that solar combisystems can provide a substantial fraction of the space heating, cooling and domestic hot water heating energy requirement of a simple house in all major climatic regions of Canada. As to be expected, climatic conditions have an important impact on solar combisystem performance. The results also show that increasing solar collector area enhances solar fraction, and the solar fraction curve peaks at a specific storage capacity. Based on the favorable results found in this study, it is clear that further and more detailed studies are warranted on solar combisystem applications in Canada. The next step in this work will be a much more detailed evaluation using the Canadian Hybrid Residential Energy End-use and Emissions Model.

Energy and exergy analysis of solar combisystems

Solar combisystem is a hot-topic since 1998 by the help of broad participation TASK-26 project in Europa and USA. The aim of this study is to determine energetic and exergetic analysis results of implemented solar combisystem in Turkey. Experimental system is built up and internal working parameters, external system parameters are measured between 1 and 31 January 2011. Totally, 544 Wh/day electrical energy is consumed to provide comfort conditions, 86% energy saving is achieved and maximum instantaneous collector efficiency is observed as 52%. The system, is supplied the energy demand that is needed to provide comfort conditions of the space and reached the values of overall system exergy efficiency between 1% and 16%. The values of inlet vertical temperature distribution are found between (20 ± 2°C).

Solar Assisted Heat Pump Systems with Ground Heat Exchanger – Simulation Studies

Different concepts of solar assisted heat pump systems with ground heat exchanger are simulated according to IEA SHC Task44/HPP Annex38 reference conditions. Two aspects of the concepts are investigated using TRNSYS simulations. First, the solar impact on system efficiency is assessed by the seasonal performance factor. Second, the solar impact on the possible shortening of the ground heat exchanger is evaluated by the minimum temperature at the ground heat exchanger inlet.The simulation results reveal diverging optimums for the concepts. The direct use of solar energy clearly achieves the best effect on the efficiency improvement. A simple domestic hot water system reaches a seasonal performance factor of 4.5 and solar combi-systems seasonal performance factors up to 6. In contrast, the use of solar energy on the cold side of the heat pump achieves the best effects on the shortening of the ground heat exchanger of up to 20%.Two highly sensitive influences are investigated with the developed transient system model. First, the minimum allowed heat source temperature is varied. Here 1K equals a variation of 0.25 in the seasonal performance or of around 10% ground heat exchanger length. Second, the ground heat exchanger model is simulated without and with a pre-pipe that improves the transient model behavior. The influence of this pre-pipe on the SPF is small for conventionally designed ground heat exchangers, but of around 2K for the minimum inlet temperature. Therefore, the dynamic model quality reveals potential to reduce the size of the ground heat exchanger corresponding to investment costs.

Energetic Performance Analysis of a Solar Combisystem. Application to a Rural House in Chlef Region (Algeria)

During the last decade, housing construction has become a priority axis in the development policy in Chlef district (north-west of Algeria). However, the construction of these homes surely leads to a significant increase in energy consumption of this region. This makes the reduction of energy consumption in buildings is a major challenge. Space heating and cooling loads are the most post energy consumer. These loads can be reduced through many means; notable among them is the thermal insulation of the building envelope and use of solar energy.In this paper, the energetic performances of a solar combisystem providing both space heating and domestic hot water for a typical rural house located in Chlef district are analyzed. Two cases are investigated and their performances are compared. The first case considers the house in its current condition and the second case considers that the envelope house is well thermally insulated and single glazing windows are replaced by double glazing windows. Energy balances are established using Trnsys software.

Optimization of a residential solar combisystem for minimum life cycle cost, energy use and exergy destroyed

This paper presents the optimization of a model of a solar combisystem in an energy efficient house in Montreal (Qc), Canada. A hybrid particle swarm and Hook–Jeeves generalized pattern search algorithm is used to minimize the life cycle cost, energy use and exergy destroyed of the combisystem. The results presented include four different optimal configurations depending on the objective function used. The optimizations were able to reduce, compared with the base case combisystem, the life cycle cost of the combisystem by 19%, the life cycle energy use by 34%, the life cycle exergy destroyed by 33% and 24% using the technical boundary and physical boundary, respectively. Due to the high cost of the solar collector technologies and the low price of electricity in Quebec, none of the optimal configurations have acceptable financial payback periods. However, they all have energy payback times between 5.8 and 6.6years. The use of technical boundary in the exergy analysis favors the use of electricity over solar energy due to the low exergy efficiency of the solar collectors. The use of the physical boundary, on the other hand, favors the use of solar energy over electricity, and all of the combisystem configurations have exergy payback times between 4.2 and 6.3years.

Performance optimization and analysis of solar combi-system with carbon dioxide heat pump

In this paper, a solar combi-system which consists of solar collectors and a carbon dioxide heat pump is proposed and investigated through simulation and optimization. Performance analysis and comparison are primarily conducted to show the feasibility and reasonability of using a CO2 heat pump as an auxiliary heater under local weather conditions. Then, a system model with a test building in TRNSYS is developed for performance optimization. The most influential variables are identified using influence and sensitivity analyzes of single parameters. Subsequently, a multi-parameter optimization using the high-weight parameters is carried out to obtain a final design result. The simulated results of the optimized case show that the average coefficient of performance of the CO2 heat pump is 2.38, and the solar fraction of the system is 69.0% for the entire heating season. The time when a comfortable temperature level can be achieved in the indoor environment accounts for 81.6% of the entire heating season. Furthermore, the performance characteristics of the proposed system are evaluated in terms of the thermal balance, fraction of the thermal energy saving, feasibility of net zero energy, economic factor, and CO2 emissions reduction.

Thermoeconomic analysis of storage systems for solar heating and cooling systems: A comparison between variable-volume and fixed-volume tanks

The paper investigates different control strategies for the thermal storage management in SHC (Solar Heating and Cooling) systems. The SHC system under investigation is based on a field of evacuated solar collectors coupled with a single-stage LiBr–H2O absorption chiller; auxiliary thermal energy is supplied by a gas-fired boiler. The SHC is also equipped with a novel thermal storage system, consisting in a variable volume storage tank. It includes three separate tanks and a number of mixers and diverters managed by novel control strategies, based on combinations of series/parallel charging and discharging approaches. The aim of this component is to vary the thermal storage capacity as a function of the combinations of solar radiation availability and user thermal/cooling energy demands. The system allows one to increase the number of active tanks when the time shift between solar energy and user demand is high. Conversely, when this time shift is low, the number of active tanks is automatically reduced. In addition, when the solar energy in excess cannot be stored in such tanks, a heat exchanger is also used in the solar loop for producing DHW (Domestic Hot Water).The analysis is carried out by means of a zero-dimensional transient simulation model, developed by using the TRNSYS software. In order to assess the operating and capital costs of the systems under analysis, an economic model is also proposed. In addition, in order to determine the set of the synthesis/design variables which maximize the system profitability, a parametric analysis was implemented. The novel variable-volume storage system, in both the proposed configurations, was also compared with a constant-volume storage system from the energy and economic points of view. The results showed that the presented storage system allows one to save up to 20% of the natural gas used by the auxiliary boiler only for very high solar fractions. In all the other cases, marginal savings are achieved by the variable-volume storage tanks system.

Performance of a combined solar heating system for residential applications in Greece

Combined solar heating is an emerging technology that offers the potential for realising more efficient use of solar thermal energy in order to cover space heating and domestic hot-water loads. This paper is focused on small-scale applications of single-family residential dwellings in Greece. A system-level model was developed and validated. The model was exercised to evaluate strategies for optimal design and operation of solar combisystems (SCSs), using a range of performance criteria as objective functions for optimisation. The effect of SCS design and operating variables on steady-state system performance has been investigated. System design and operation optimisation has been performed through the integration and synthesis of system-level modelling with system optimal design, optimisation, and annual simulation studies to provide a comprehensive assessment.

Dynamic simulation of a novel high-temperature solar trigeneration system based on concentrating photovoltaic/thermal collectors

The paper is focused on the dynamic simulation of a Photovoltaic/Thermal collector (PVT) integrated in a high-temperature Solar Heating and Cooling (SHC) system. The system is based on the following main components: concentrating parabolic PVT (photovoltaic thermal) collectors, a double-stage LiBr-H2O absorption chiller, storage tanks, auxiliary heaters, balance of plant devices. The PVT is made-up by a parabolic dish concentrator and a triple-junction receiver. The polygeneration system provides electricity, space heating and cooling and domestic hot water for a given building, whose simulation is also included in the model. In particular, PVT produces electric energy, which is in part consumed by the building loads (lights and equipments), in part by the system parasitic loads, whereas the eventual excess is sold to the public grid. Simultaneously, the PVT provides the heat required to drive the absorption chiller. The system was simulated by means of a zero-dimensional transient model, that allows the evaluation of temperature profiles and also heat/electrical energy flows for whatever period of the year. It is also possible to evaluate the overall energetic and economic performance on whatever time basis (day, week, month, year, etc.). The economic results show that the system under investigation can be profitable, if a proper funding policy is available. The paper also includes an extensive parametric analysis aiming at evaluating the set of design and operating parameters (solar field area, tank volumes, set point temperatures, etc.) that maximize the energetic and/or economic performance of the system.

Residential Solar-Based Seasonal Thermal Storage Systems in Cold Climates: Building Envelope and Thermal Storage

The reduction of electricity use for heating and domestic hot water in cold climates can be achieved by: (1) reducing the heating loads through the improvement of the thermal performance of house envelopes, and (2) using solar energy through a residential solar-based thermal storage system. First, this paper presents the life cycle energy and cost analysis of a typical one-storey detached house, located in Montreal, Canada. Simulation of annual energy use is performed using the TRNSYS software. Second, several design alternatives with improved thermal resistance for walls, ceiling and windows, increased overall air tightness, and increased window-to-wall ratio of South facing windows are evaluated with respect to the life cycle energy use, life cycle emissions and life cycle cost. The solution that minimizes the energy demand is chosen as a reference house for the study of long-term thermal storage. Third, the computer simulation of a solar heating system with solar thermal collectors and long-term thermal storage capacity is presented. Finally, the life cycle cost and life cycle energy use of the solar combisystem are estimated for flat-plate solar collectors and evacuated tube solar collectors, respectively, for the economic and climatic conditions of this study.

Energy analysis of Solar Combisystems in Turkey

IEA has done an organization with the attendance of USA, Germany, Italy, Norway etc. to innovate the solar space heating systems. These countries lay the foundations of “Solar Combisystems” by presenting the extent of TASK 26.In this paper, an experimental study has done to improve the existing solar space heating systems in Turkey. Experimental system has built up by devising thermal stratified boiler and internal working parameters, external system parameters have been measured between December 2010 and May 2011. The system includes two closed flow cycle. There are three control units to control flow cycles which are placed into the system. Also system presents new approach on floor heating method by using copper finned-copper flow tubes for space heating. The new approach in design and application state has a positive impact on the energy flow of the system. The results show that energy saving ratio is performed between 59% and 89% monthly.The system, supplies the energy demand of the space that is needed to provide comfort conditions. Also fractional solar consumption (FSC) change is investigated daily, monthly and annually. Annual FSC value of the established system is approximately 83%.

Solar and pellet combisystem for apartment buildings: Heat losses and efficiency improvements of the pellet boiler

This paper is based on the analysis of the solar combisystem installed in a 4-storey apartment building in Sigulda, Latvia. The combisystem consists of: 42m2 of flat plate solar collectors, a 2.35m3 accumulation tank and a 100kW pellet boiler as the auxiliary heater. This paper focuses on the optimisation of the thermal performance of the pellet boiler.During laboratory tests on the 25kW pellet boiler, the influence of the supply ratio of the combustion air, the chemical and heat losses in the flue gases on the performance of the boiler was established. The results demonstrate the optimum thermal performance, CO emissions, chemical and heat losses, which are related to the amount of free oxygen (O2) in the flue gases.The results of the laboratory tests were then applied to optimise the operation of the 100kW pellet boiler. The flue gas measurements for the 100kW boiler were performed in order to identify the O2 concentration, CO emissions and flue gas temperature. The results showed that what is required to optimise performance is to reduce the amount of air supplied to the boiler’s combustion chamber. Changes were made to the boiler’s control algorithms to achieve the desired result.Additionally, boiler performance was improved by changing the location of the air intake point. Decreasing temperatures in the heat accumulation tank were achieved by making modifications to the boiler’s control algorithms.

Global approach test improvement using a neural network model identification to characterise solar combisystem performances

Solar CombiSystems (SCSs) are very efficient systems for reducing conventional energy consumption of building but their thermal performances are strongly dependent on the environment where they are installed (type of climate and thermal quality of the building). Currently it is impossible to predict the energy savings generated by a SCS as there is no standard test to characterise SCS performances.Currently, the Short Cycle System Performance Test (SCSPT), based on a 12days test of the complete SCS on a semi-virtual test bench, is able to predict annual energy savings with a good accuracy, but the performance prediction is limited to only one environment (the building and the climate corresponding with the test).Based on the SCSPT procedure, this paper proposes an improvement of the method by identifying a global SCS model from the test data. Then, the identified model would be able to simulate the tested SCS in any environment and thus to characterise its performances.The proposed model to identify is a “grey box” model, mixing a “White Box” model composed of known physical equations and a “Black Box” model, which is an Artificial Neural Network (ANN). A complete process is developed to train and select a relevant global SCS model from such a test.This approach has been validated through numerical simulations of three detailed SCS models. Compared to those annual results, “Grey Box” SCS models trained from a twelve days sequence are able to predict energy consumption with a good accuracy for 27 different environments. An experimental application of this procedure has been used to characterise a real system.

Comparative Studies on Solar Combisystem by Different Auxiliary Heat Sources

This paper proposes a solar combisystem model with biomass boiler as its auxiliary heat source. Taking specific constructions of towns into consideration, solar combisystems with four different auxiliary heat sources——gas boiler, electric boiler, coal boiler and biomass boiler are compared from the aspects of comprehensive energy price, CO2 emissions and social benefits. The results show that, compared with the solar combisystems with conventional energy boilers as their auxiliary heat sources, the system with biomass boiler as its auxiliary heat source has favorable economic, social and environmental benefits.

Theoretical study of solar combisystems based on bikini tanks and tank‐in‐tank stores

PurposeLow flow bikini solar combisystems and high flow tank‐in‐tank solar combisystems have been studied theoretically. The aim of this paper is to study which of these two solar combisystem designs is suitable for different houses. The thermal performance of solar combisystems based on the two different heat storage types is compared.Design/methodology/approachThe thermal performance of Low flow bikini solar combisystems and high flow tank‐in‐tank solar combisystems is calculated with the simulation program TRNSYS. Two different TRNSYS models based on measurements were developed and used.FindingsBased on the calculations it is concluded that low flow solar combisystems based on bikini tanks are promising for low energy buildings, while solar combisystems based on tank‐in‐tank stores are attractive for the houses with medium heating demand and old houses with high heating demand.Originality/valueMany different Solar Combisystem designs have been commercialized over the years. In the IEA‐SHC Task 26, twenty one solar combisystems have been described and analyzed. Maybe the mantle tank approach also for solar combisystems can be used with advantage? This might be possible if the solar heating system is based on a so‐called bikini tank. Therefore, the new developed solar combisystems based on bikini tanks is compared to the tank‐in‐tank solar combisystems to elucidate which one is suitable for three different houses with low energy heating demand, medium and high heating demand.

Design and dynamic simulation of a novel solar trigeneration system based on hybrid photovoltaic/thermal collectors (PVT)

In this paper, a Solar Heating and Cooling (SHC) system including photovoltaic/thermal (PVT) collectors is considered, implementing a novel polygeneration system producing electricity, space heating and cooling and domestic hot water. In particular, PVT collectors operating up to 80°C are considered. A case study for a university building located in Naples (Italy) is developed and discussed. The system is mainly composed by: PVT collectors, a single-stage LiBr–H2O absorption chiller, storage tanks and auxiliary heaters. The system also includes additional balance-of-plant devices: heat exchangers, pumps, controllers, cooling tower, etc. The PVT produces electricity which is utilized in part by the building lights and equipments and in part by the system parasitic loads; the rest is eventually sold to the grid. Simultaneously, the PVT system provides the heat required to drive the absorption chiller. The system performance is analyzed from both energetic and economic points of view by means of a zero-dimensional transient simulation model, developed with TRNSYS. The economic results show that the system under investigation can be profitable, provided that an appropriate funding policy is available. In addition, the overall energetic and economic results are comparable to those reported in literature for similar systems.

Solar Combisystem Characterization with a Global Approach Test and a Neural Network Based Model Identification

The market for small Solar CombiSystems (SCSs) is penalized by its lack of common performance test method. The methodology proposed in this paper is based on the SCSPT procedure which tests each combisystem as a whole system on a semi-virtual test bench. Test results are used to identify a “Gray Box” model of the tested SCS, which includes an Artificial Neural Network. This model can then simulate the behavior of the system for any climate and any building. Results of all those simulations are finally used according to the FSC procedure in order to characterize the tested SCS performances with a simple curve. An experimental study of this methodology with two real SCS is presented in this paper.

Thermal Performance Analysis of Solar Collectors Installed for Combisystem in the Apartment Building

Thermal Performance Analysis of Solar Collectors Installed for Combisystem in the Apartment Building The paper focuses on the application of wood pellet and solar combisystem for space heating and hot water preparation at apartment buildings under the climate of Northern Europe. A pilot project has been implemented in the city of Sigulda (N 57° 09.410 E 024° 52.194), Latvia. The system was designed and optimised using TRNSYS - a dynamic simulation tool. The pilot project was continuously monitored. To the analysis the heat transfer fluid flow rate and the influence of the inlet temperature on the performance of solar collectors were subjected. The thermal performance of a solar collector loop was studied using a direct method. A multiple regression analysis was carried out using STATGRAPHICS Centurion 16.1.15 with the aim to identify the operational and weather parameters of the system which cause the strongest influence on the collector's performance. The parameters to be used for the system's optimisation have been evaluated.

The Influence of Energy Conservation on the Performance of Solar Thermal Systems – A Cold Country Case Study

The European Union has set a goal that the energy use in the built environment shall be reduced by 41% to the year 2050 compared to 2005-2006. This could introduce new opportunities for solar thermal systems in cold countries. In such countries, like Sweden and Canada, the economy in solar thermal collector installation projects is often spoiled by the fact that most of heating energy demand of the building occurs during periods when the available solar energy is low.The present paper investigates the performance of solar thermal systems subjected to different quota between space heating and domestic hot water demand (DHW). This study investigates the performance of a solar thermal system integrated to four different buildings with varying heating loads in two different locations, Sweden and Canada. Models of single family houses are created which are able to simulate the total heating demand with different heating demand profiles but the same DHW demand. Simulations are performed in TRNSYS, an advanced tool used to simulate transient systems. Results indicate that solar combisystems tend to generate more useful energy and therefore be more cost effective when installed in buildings with higher heating demands.

Simulation and Evaluation of Different Boiler Implementations and Configurations in Solar Thermal Combi Systems

This simulation study investigates both different boiler specifications and various kinds of boiler integration in solar thermal combi systems with the help of a new developed fossil fuel boiler model. For each variant, the simulation outcomes to be discussed are the annual boiler efficiency, the cycling rate and, as the main indicator, the primary energy savings of the complete system. The results indicate that the effects of a solar thermal system on the annual boiler efficiency are small. Besides the system layout the annual amounts of hot water and space heating demand and their temperature levels affect the impact of the solar thermal system. Each additional storage tank, which is heated by conventional energy, should be analyzed critically due to their additional heat losses, which reduce the system efficiency. The latter is particularly true for a boiler buffer storage. This study points out that the savings of primary and final energy are the most important indicators for the assessment of solar thermal combi systems. Subsystem indicators like the annual values of collector yield and boiler efficiency give additional information, but they are not sufficient for a full evaluation of a complete system.