G. Oliveti, N. Arcuri, M. De Simone, R. Bruno,

Department of Mechanical Engineering — University of Calabria
87036 — P. Bucci 44/ C — Rende (CS) — ITALY
M. De Simone, marilena. desimone@unical. it

Abstract

A critical analysis of the calculation procedure of solar gain in buildings with reference to an attached sunspace bordering air conditioned environments was developed. The EN ISO 13790:2008 Standard provides a simplified calculation method for the estimation of solar gain based upon the monthly energy balance in a stationary regime, to be applied both during winter heating and summer cooling. Moreover, the Standard hypothesises possible simplifications to be evaluated in relation to climatic conditions and the type of greenhouse-environment system. The direct, indirect and total solar contribution evaluated by means of the Standard are compared with those obtained with a dynamic calculation code, with the aim of highlighting the limits of the schematization adopted by the Standard. Furthermore, the gain in an airconditioned environment obtained by means of a windowed wall is compared with that produced by the use of a sunspace opposite the same wall.

Keywords: Energy balance, solar heat gain, Standard, sunspace.

1. Introduction

The use of solar radiation in buildings is of particular interest in the case of the use of glazed systems such as glazed balconies and sunspaces. Sunny spaces adjacent to air conditioned volumes are passive solar systems, usable in order to reduce the thermal energy requirement of adjacent spaces in winter and to control solar gain in the summer months.

For solar contribution we are refering to the energy that, in a determined time interval, reaches the airconditioned environment by means of the separating walls of the lodge or the greenhouse. Such a gain is produced by solar radiation which directly penetrates the environment through the glass surfaces, and the energy transmitted by conduction through the dividing walls consequent to the absorption of solar radiation. The energy absorbed by the greenhouse shell is in part given to the adjacent rooms, in part transferred to the outside, in part removed by the ventilation flow and in part remains accumulated within the opaque walls [1].

The EN ISO 13790:2008 Standard [2] in Annex E provides a calculation method of solar gain obtainable with specific elements including unconditioned sunspace attached to buildings; it confirms the UNI EN 832:2001 calculation method [3] based upon the monthly energy balances in a stationary regime and also extends its validity to the summer. Furthermore, the EN ISO 13790 suggests conservative simplifications in calculating the monthly energy requirements of the adjacent environment whose validity requires checking in different national realities.

The Standard method distinguishes between direct solar contribution which reaches the airconditioned environment through the glazed and opaque surfaces which separate the sunspace from the environment, and indirect solar contribution deriving from heating of the air in the sunspace. For the evaluation of direct contribution, consider the energy entering through the glass separation surface of the sunspace-environment completely absorbed by the environment (black cavity hypothesis), and the energy absorbed by the opaque separation components, which is conducted in the walls, evaluated by a simplified model that does not consider the effects of thermal capacity.

The estimation of indirect solar contribution is obtained considering the solar energy absorbed by only the opaque components of the sunspace, after the conductive transfers in the conditioned environments, which one is supposed to be transferred to the greenhouse air.

In this article, by means of the DEROB-LTH (Dynamic Energy Response of Buildings) dynamic simulation code [4], a critical analysis was developed of the procedures used by the EN ISO 13790 Standard for the calculation of direct and indirect solar contribution, and furthermore, with reference to the Italian climate, verifies the possibility of adopting some simplifications proposed by the same Standard relating to the heating and the cooling. The system considered is an attached sunspace separated from an adjacent airconditioned environment by a mixed opaque-glazed wall, and bordering by means of the flooring with a second airconditioned space. The DEROB-LTH code resolves the transmission of solar radiation through the glazed surfaces taking into consideration the directional aspects, and the absorption in the greenhouse and the adjacent environment considering the directly irradiated portions of the surfaces and the redistribution of solar radiation consequent on reflection phenomena. Moreover, the code resolves the thermal field in the glazed and opaque walls of the sunspace taking into consideration the effective surrounding conditions that act upon both the internal and external surfaces [5].

The comparison of monthly energy was carried out in the same application conditions of the Standard, that is to say considering only solar power as an agent on the sunspace. This was obtained in the simulations by eliminating the other powers, or rather by imposing the same temperature constant as the aircondtioned environment for the external air and the sky. The simulations were conducted on an hourly basis using both direct and diffuse radiation values relative to the average monthly day [6].

1.1. Principal menu

The SIGA SOL 1.0 ( Geographic Information System Applied to Solar Energy) is made up of three principal blocks: management, planning, and updating of data bank., according to what can be seen in Fig. 1. Management and planning occur at two levels: macro-spatial (state) and local (municipal). The updating of data bank can be done by rectification, exclusion or inclusion of information to data banks that are associated to already installed energy systems.

1.2. Functionalities

The use of a GIS tool requires the formulation of questions, whose answers are products of crossing one or more data banks and or maps. The result is not normally completely conclusive (closed) and the product is a group of spatial information and/or reports that almost always still require the interpretation of who made the question. The SIGA SOL 1.0 was constructed to give the user answers to questions, of general and simple character, that in the majority of times corresponds to one layer of information or complex questions whose answers are products of crossing of diverse layers of information. The answer to questions of simple general character are denominated default functionality and are recorded as sub-menus in the menus of management and planning at macro-spatial and local level. The non default functionalities generated by complex questions by the users can be printed or recorded and can be transformed into default functionalities. Other default functionalities associated to the tasks of updating the data bank and dimensioning renewable energy systems are in the sub-menus of the updating and planning menu.

It is of major importance to determine the influence of the fluid medium and the fluid dynamics inside the collector on the heat transfer. The heat transfer through a surface depends not only on the thickness and the heat conductivity of the material but also — and in some cases even predominantly — on the heat transfer coefficient between the fluid and the wall which is determined by the fluid dynamics in the vicinity of the surface. Thus one of the main objectives of this work was to study in detail the behaviour and the characteristics of the fluid flow by means of numerical simulations. By using computational fluid dynamics methods (CFD) it was possible to calculate the fluid flow in the absorber, the heat distribution in the solid materials and the radiation interaction between the internal and external surfaces.

In order to develop a systematic way to compare the mechanisms and the performance of different collector types, calculations for a simple flat plate collector were first made and the influence of various parameters was examined.

For symmetry reasons, the numerical model was reduced to a stripe of 1cm width and symmetric boundary conditions were set for both sides. The model consists of approx. 100’000 finite volumes (Fig. 1). CFD simulations were performed in order to quantify how the heat transfer depends on

• the length of the collector.

• the position of the absorber (above, in between or below the carrier fluid).

• the height of the fluid channel.

• the mass flow rate.

Through series of systematic calculations the following dependencies were discovered:

The temperature difference between inlet and outlet is proportional to the length (Fig. 2).

The pressure drop in the fluid channel is proportional to the length.

The temperature difference increases if the height d of the channel decreases.

The pressure drop increases reciprocally with the channel height d.

AT is constant if the mass flow rate Фщ is held constant for different collector geometries.

The pressure drop is proportional to the mass flow rate.

Furthermore, the simulations showed that the position of the absorber does not influence the outlet temperature of the carrier fluid. However the temperature of the surrounding solid materials depends on the position of the absorber. Thus this parameter is of relevance for the design of the absorber for material or stability reasons. This topic is discussed in Section 4.

In order to carry out investigations and to describe an established collector we developed an input mask in which all relevant geometrical and material data can be entered. A macro is generated from this information that completely describes the collector and that can be executed by OptiCAD.

For instance, different types of CPC-reflectors can be easily generated just by entering the designated half acceptance angle and the reflector arc length in such a parametrical model. Every other parameter of the reflector geometry such as angle of truncation, concentration ratio and height of the reflector are automatically determined. For more information on CPC-collectors, see [2] and [3].

The next step after fixing the geometrical and optical properties of the different collector components is to define the simulation mode. Simulations in the transversal or longitudinal plane are possible or also for all other angles (3D-IAM).

Two different alternatives exist for the determination of the IAM-values over the hemisphere (3D — IAM):

Either, the simulation can be carried out in polar coordinates (0 — theta, ф — phi) or in the projections of the incident angle (0t — theta_t, 0l — theta_l). The latter are used e. g. in different solar simulation programs such as TRNSYS. Figure 3 shows the angle conventions for the projected incidence angles theta_t and theta_l of solar radiation incident from an optional direction.

Transversal

Longitudinal

Direction

When OptiCAD is started, the macro which also contains the description of the ray-tracing calculation is imported and executed. The interpretation of results (e. g. plot of 3D-IAM) happens automatically within the file of the input mask. Thus, it is assured that simulation settings and the output of a simulation as well as the analysis of results are documented together in one file.

To describe the temperature field in a tube’s coating we choose a system of polar coordinates with O as the initial point and write Laplace’s equation in the polar coordinates assuming that the process is stationary [7]:

(12)

(13) (14) (15) (16) (17)

d© 2jf>1,pP = Q (p <ф<п-ф1); dp d©2d(/?1,p) = 0 {n + p1 <p< 2п-ф1); dp

Applying the Fourier method of separation of variables [8] one obtains:

where k is a positive integer.

The time-use data is only available for one weekday and one weekend day per household, and therefore the model only generate average profiles for one day of each type, not depending on season

or day of the week. To enable further model development the time dependent variations in load measured in the 24 apartments are investigated below.

The energy use for hot water for different months, expressed as average daily demand per average household member, is found in Figure 3. The lowest hot water consumption is found during the summer months and the highest consumption during winter. The average daily energy use for hot water is 5.4 and 4.4 kWh/person for 2005 and 2006 respectively, with a variation of the maximum and minimum consumption of ±17-26 % around the average. The results correspond well to the monthly relative variations found in [9].

The half-year including summer is investigated more in detail in Figure 4, showing the weekly variations in hot water demand in April to October. A clear minimum is found in July and August, which is the usual vacation period in Sweden.

A more fair and uniform approach is being proposed by Horta et al.(2008 a, b), to be applied independently of the underlying optics. This approach allows using the test data currently collected on trials and is based on absorber irradiance values, Gabs = B cos 0 K(0) + Kd D + Kr D (where Kd and Kr are computed assuming an isotropic diffuse field) and a certain a posteriori correction of the efficiency, that includes an estimate of the diffuse fraction of the radiation during performance trials, fD — unknown but by norm in the range 10% to 30%.

The work examined how these new algorithms can be implemented in practice and what is their influence on thermal solar system (not just collector) performance, using a solar simulation software with quasi-stationary thermal balances, SolTerm 5.

Results with a typical DHW system for Lisbon can be found at Table 1, using data for three flat-plate and one 2D commercial collectors (flat, CPC), coupled to an oversized storage (to ignore dissipation and other effects in a first phase). The energy supplied by the system ES (kWh/year) and the respective solar fraction fS, computed with the previous and proposed approaches (ref, new) are compared.

Conclusions

For the range of climates and collector types surveyed, the new approach to the incidence angle modifier meant a 2% to 4% rise in estimated performance for flat plate type collectors and a 6% to 8% rise for a CPC type collector.

This is very significant, and justifies that further results for realistic storage sizes, other climates, collectors, load profiles, and ranges of solar fraction must be obtained, aiming the elaboration of recommendations for the use of the new algorithms.

References

Horta, P., M. J. Carvalho, M. Collares-Pereira and W. Carbajal (2008a). “Incidence angle modifiers for beam, diffuse and reflected radiation: a general approach for energy calculations”, submitted to Solar Energy, May 2007.

Horta, P., M. J. Carvalho, M. Collares-Pereira, and W. Carbajal (2008b). Long term performance calculations based on steady state efficiency test results: analysis of optical effects affecting beam, diffuse and reflected radiation”, submitted to Solar Energy, May 2007.

Christoph Brunner 1, Hans Schnitzer 1 2, Bettina Slawitsch 1,

Hans Schweiger 3, Claudia Vannoni 4

1JOANNEUM RESEARCH Forschungsgesellschaft mbH — Institut fur Nachhaltige Techniken und Systeme

Elisabethstrasse 16, A-8010 Graz
Tel.: +43-316 / 876 2413, Fax: +43-316 / 8769 2413
E-Mail: christoph. brunner@joanneum. at

2Institute fur Ressourcenschonende und Nachhaltige Systeme, Technische Universitat Graz

Inffeldgasse 21, A-8010 Graz

3energyXperts. BCN

Creu dels Molers 15, 2-1, Barcelona, Spain
4Dipartimento di Meccanica e Aeronautica, Univerity of Rome, Sapienza

Abstract

Thermal energy (heat and cold) demand in industry constitutes about 20 % of the total final energy demand and produces about 21 % of the CO2 emissions in Europe. Even if energy efficiency in industry in Europe has improved the last decades, there remains a large unexploited potential for reducing energy demand that could be achieved by the intelligent combination of existing solutions and technologies.

The present project aims at contributing to a widespread implementation of integral energy- efficient solutions for thermal energy supply in the industrial sectors with a high fraction of low and medium temperature heat demand, especially the food, wood processing and metal treatment sectors that will be first addressed within this project.

For optimising thermal energy supply, a holistic integral approach is required that includes possibilities of demand reduction by heat recovery and process integration, and by an intelligent combination of existing affordable heat (and cold) supply technologies, under the given economic constraints. The presented Intelligent Energy Europe — IEE project uses as a basis available methods and tools that address some parts of these topics, adds missing elements and brings them together into a complete EINSTEIN tool kit for thermal energy auditing, which is used in all the project’s activities.

Most of the tools have been developed within the IEA Task 33/IV “Solar heating for industrial processes (SHIP)”. The proposed methodology focuses at first on the optimization of the given process to reduce the absolute energy demand before further integrating solar heat in the technical and economical most suitable way.

The optimization of the process is achieved by the integration of energy efficiency measures and heat exchange. The analysis for this optimization is done with the mathematical model of the Pinch Analysis. With the help of the Pinch Analysis the minimal heat and minimal cooling demand of a process can be calculated and the theoretical possibilities of heat recovery are shown.

After having gained a proposed solution for optimizing the given process in terms of energy efficiency, a strong information tool is used that allows for further optimization that might lead to changes of the process, changes of the energy distribution system or changes of the energy supply system. This developed tool, the so called “matrix of indicators” will be described in the following. It was designed as a decision support tool for solar experts and facilitates work with industry and the identification of suitable solar applications.

With the help of the “Matrix of Indicators” the ideal solution to implement energy efficiency measures and integrate solar process heat can be found. The final steps prior to implementation include the solar simulation, the economical evaluation and the analysis of the practicability of the proposed solution.

The realisation of the methodology in form of a complete auditing tool-kit including an expert system software tool makes it easy to use, easily distributable, and helps reducing time (and therefore cost) and increasing standardisation (and therefore quality) of energy audits. The EINSTEIN tool-kit will be available in Czech, English, German, Italian, Polish, Spanish and Slovenian language. Within the project, 90 industrial companies will be audited, starting from autumn 2008. It is assumed that in addition to the thermal audits carried out within this project; at least 100 companies will have used this self-assessment at the end of the project and 100 reports to be available. Energy auditors and consultants are trained in training courses. At least about 200 trained auditors (of the 240 people attending the training courses) will be available at the end of this project as multipliers, who in their everyday practice are working in the field of energy auditing and therefore in the future will induce further improvements in energy efficiency. A Europe-wide training-of-trainers course will complete the training program and help to expand its impact also to countries not directly involved into the project’s activities.

1. Introduction

Thermal energy (heat and cold) demand in industry constitutes about 20 % of the total final energy demand and produces about 21 % of the CO2 emissions in Europe. Even if energy efficiency in industry in Europe has improved the last decades, there remains a large unexploited potential for reducing energy demand that could be achieved by the intelligent combination of existing solutions and technologies.

The present project aims at contributing to a widespread implementation of integral energy — efficient solutions for thermal energy supply in the industrial sectors with a high fraction of low and medium temperature heat demand, especially the food, wood processing and metal treatment sectors that will be first addressed within this project.

2. Methodology

The present project aims at overcoming the barriers mentioned above (and described in details in b) and at contributing to a widespread implementation of integral energy-efficient solutions for thermal energy supply, especially in SMEs and in general in all industrial companies where the really used energy supply systems are still far from best practice. The project focuses on the food, wood processing and metal treatment sectors but can be easily extended to other industrial sectors

with high fraction of low and medium temperature heat demand such as chemical, textile industry, pulp and paper industry.

The specific objectives in order to achieve this are:

• the reduction of the time and cost required for thermal energy audits and the development of a self-assessment tool for thermal energy supply, in order to reach a wider market penetration of energy-efficient technologies

• a wider diffusion of knowledge on integral energy-efficient solutions for thermal energy supply in industry among the actors who can act as future driving forces for improving energy efficiency

• the execution of a thermal energy auditing campaign in industrial companies and the creation of best practice examples for an efficient heat and cold supply

• the improvement of the technical skill of the relevant actors (auditors, industrial technical staff, etc.) by means of training activities and of an assisted thermal energy auditing campaign

• the improvement of quality and reliability of thermal energy audits by means of the standardisation of the procedure and decision support tools

EINSTEIN contributes to the IEE priorities and in particular answers to the need of setting “tools to help industries, in particular SMEs, to develop an intelligent energy approach, including training of energy auditors”. The project is structured into the main blocks below:

• Standardized Audit — the EINSTEIN Expert System: methodology that works out energy efficient solutions for your production process based on energy saving and renewable energy sources

• Audit Campaign: A limited number of energy audits

• Self-Assessment Tool: Check your Performance

• High Quality Training: Training workshops for energy managers, technicians and consultants

• Information Workshops for decision makers

The EINSTEIN methodology can be divided into 4 main steps. During the pre-audit the important data for the future calculation will be collected and a preliminary evaluation will be done. If a potential will be identified the analysis of the status quo will form the main step during the audit phase. By using the EINSTEIN tool kit the conceptual design of saving options and preliminary energy targets will be defined. At the end an economical feasible solution will be proposed.

.

Most of the tools of the EINSTEIN audit tool kit have been developed within the IEA Task 33/IV “Solar heating for industrial processes (SHIP)”. The proposed methodology focuses at first on the optimization of the given process to reduce the absolute energy demand before further integrating solar heat in the technical and economical most suitable way.

The complete thermal auditing tool kit is formed by a software tool (expert system), questionnaires for data acquisition and thermal auditing and system design guidelines. The EINSTEIN tool kit for the day-by-day auditing practice is based on the information on current auditing practices, tools and user needs.

The optimization of the process is achieved by the integration of energy efficiency measures and heat exchange. The analysis for this optimization is done with the mathematical model of the Pinch Analysis. With the help of the Pinch Analysis the minimal heat and minimal cooling demand of a process can be calculated and the theoretical possibilities of heat recovery are shown.

After having gained a proposed solution for optimizing the given process in terms of energy efficiency, a strong information tool is used that allows for further optimization that might lead to changes of the process, changes of the energy distribution system or changes of the energy supply system. This developed tool, the so called “matrix of indicators” will be described in the following. It was designed as a decision support tool for solar experts and facilitates work with industry and the identification of suitable solar applications.

With the help of the “Matrix of Indicators” the ideal solution to implement energy efficiency measures and integrate solar process heat can be found. The final steps prior to implementation include the solar simulation, the economical evaluation and the analysis of the practicability of the proposed solution.

As stated above the Matrix of Indicators was developed as decision support system for solar experts, to facilitate the ideal integration of solar process heat into industrial processes.

On the ordinate for solar application relevant industry sectors are listed. Although the above discussed processes occur in practically all industry sectors, some distinguish themselves by a greater potential than others. On the abscissa different unit operations, which have been identified as relevant for solar applications are listed.

Further on the ordinate there is a button for general information about the unit operations, about competitive technologies for this unit operations and a column for possible solar integration schemes.

The unit operation is generally described by the functioning of the unit operation, the implementation possibilities and the area in which it can be used.

Following information will be found in the description:

• general objectives

• influencing parameters (temp, pressure, humidity, medium)

• temperature levels

• fields of application

• descriptions of techniques, methods and equipment

• environmental issues

The idea of the competitive technologies is described generally and an overview of alternative technologies and possible application fields is given. Competitive technologies are technologies that might constitute an alternative option for the specific requirements. Solutions how else the required problem could be solved and how (dis)advantageous other options are compared to the proposed unit operation are shown.

The solar integration schemes give a general overview of the solar installations for different applications. Additionally, specific integration schemes are proposed for each problem, as solar integration is possible in several ways and the ideal methods depend on the industrial processes which are sector — and plant-specific.

The availability of a new methodology that allows for realising more energy audits in future at a lower cost, delivering at the same time high quality and innovative recommendations will be the main outcome of the present project, even more important as the impact of the directly induced improvements of energy efficiency in industry described below.

The realisation of the methodology in form of a complete auditing tool-kit including an expert system software tool makes it easy to use, easily distributable, and helps reducing time (and therefore cost) and increasing standardisation (and therefore quality) of energy audits. The EINSTEIN tool-kit will be available in Czech, English, German, Italian, Polish, Spanish and

Slovenian language. With the available EINSTEIN tool-kit it will be possible to realise high quality fast-audits including company visit, proposal and approximate energetic and economical evaluation of an alternative system within about 24 to 40 hours of a trained auditor. The alternative proposals will include all the available technological options including cogeneration and polygeneration, process integration technology, heat pumps, solar thermal energy and biomass.

There will be also a simplified version of the software tool for web-based self-assessment of the companies, so that even a larger number of companies can be reached by the proposal, especially those companies who are not willing to spend money for energy-auditing due to other priorities. This web-page for self-assessment will be widely disseminated via the different dissemination activities foreseen in the project. It is assumed that in addition to the thermal audits carried out within this project, at least 100 companies will have used this self-assessment at the end of the project and 100 reports to be available.

Energy auditors and consultants will be trained in training courses. At least about 200 trained auditors (of the 300 people attending the training courses) will be available at the end of this project as multipliers, who in their every day practice are working in the field of energy auditing and therefore in the future will induce further improvements in energy efficiency. A Europe-wide training-of-trainers course will complete the training program and help to expand its impact also to countries not directly involved into the project’s activities. This training and the guidance towards proposals generated by the EINSTEIN expert system decision support tools will induce that energy auditors increase their horizon towards innovative, non-conventional solutions using the holistic approach of EINSTEIN. At the same time they will have the appropriate tool in order to correctly evaluate these options. Some of these auditors at the end of the project will be able to act as future trainers using the EINSTEIN training material.

From the dissemination activities, that range from workshops and conferences oriented to specific target groups, to distribution of the methodology and software tool via internet, further public will be reached. It is expected, that at least 10,000 persons (technicians and decision makers in industry, energy auditors, consultants, policy makers and local authorities) will be reached and 1,000 persons will assist to these activities while 2,500 copies of the EINSTEIN tool-kit will be distributed all over Europe by the end of the project.

Standardisation of the auditing methodology and comparability of energy supply alternatives also will help public bodies and energy agencies to evaluate the present state (situation with respect to current best practice) and the achieved improvements by energy efficiency measures, and therefore lead to a better control of the real impact of energy policies. The tool could become a reference for public support programmes in the field of industrial energy efficiency.

Within the project, 90 industrial companies will be audited. For all these industrial companies a proposal for improvement of energy efficiency and use of renewable energy for heating and cooling will be available and several best practice examples will be selected. Energy demand for heating and cooling in industrial companies may vary from 50 MWh/year for small enterprises up to several 100,000 MWh for big companies

Assuming a mean primary energy demand for heating and cooling of 5000 MWh/year for the studied companies, and a mean potential for saving of 30 %, a total saving potential of 150.000 MWh/year (about 2.5 M€/year in terms of energy costs based on natural gas prices) will be identified. It is expected that decisions for realisation of at least 10% of this savings potential will

be taken during the project and another 20% during the first year after the project leading to a real energy saving of 45,000 MWh/year (0.7 M€/year in terms of energy costs).

Furthermore it is assumed that this direct impact of the project is at least multiplied by a factor of two by energy efficiency measures and renewable energy projects indirectly induced by the project and while the project is ongoing, due to the training and dissemination activities.

3. Conclusions

Energy efficiency measures often have benefits that extend beyond energy savings and include pollution prevention, process efficiency, and increased productivity. Total benefits for industrial companies are therefore on the focus of the proposed action. Among such benefits, the implementation of the recommended measures for energy saving will lead to a reduction in the energy bill and therefore to an increased competitiveness of the companies. Apart from the economic savings on a short term, due to reduced demand and the use of renewable energy sources (RES) the companies will have a higher security of supply and more stable and foreseeable energy costs on the long term.

Moreover the thermal energy auditors will benefit directly from the project by improving their qualification, by learning about innovative technological options and by therefore being able to offer a better service.

The EINSTEIN tool will form a very innovative and strong tool which will change the energy audit methodology radically in order to identify the maximum of energy saving and the ideal integration of renewable energy into industrial processes in a very short time.

References

[1] Muller T., Begander U., Schnitzer H., Brunner Ch., Weiss W. (2003), PROMISE — Produzieren mit Sonnenenergie — Potenzialstudie zur thermischen Solarenergienutzung in Gewerbe — und Industriebetrieben in Abhangigkeit der Produktionsprozesse,

[2] Energieverwertungsagentur, www. eva. ac. at/enz/efluss. htm vom 8.6.2004

[3] Brunner CH. Schweiger H. Vannoni C. IEA Task 33 — Solar heating for industrial Processes — SHIP

[4] Faninger G. (2004), Entwicklung des Solarmarktes in Osterreich 1975 — 2003, Verband AUSTRIA SOLAR und Dachverband Energie-Klima, Marz 2004

[5] Schnitzer H., Brunner C., Gwehenberger G. (2006): Minimizing greenhouse gas emissions through the application of solar thermal energy in industrial processes. Journal of Cleaner Production,

doi: 10.106/j. jclepro.2006.07.023

The following HPS system concept has been selected for the investigations. It may be described by the characteristics given below:

• Unglazed Collectors: Inexpensive, uncritical operation mode (no stagnation, no steam generation), uncomplicated opportunities for building integration

• In order to realize an uncomplex system: Solar heat only directed to the evaporator side of the heat pump and: No option for direct use of solar heat for domestic hot water or space heating foreseen.

• Limitation of the investigations: Heating systems for small buildings (< 30 MWh/a heating demand)

• Thermal soil regeneration as the main target: A permanent increase of the yearly mean HPS source temperature if compared to a non-solar BHE system is the aim, but a significant seasonal storage effect is not planned. Thus, even with SC the ground is mainly serving as a heat source.

All these characteristics and restrictions form a reasonable unit. As for small buildings the seasonal storage effect may not be achieved due to the high thermal losses, the solar heat is mainly used for the regeneration of the soil. This leads to lower source temperatures in winter. Under these condi­tions unglazed SC find an ideal application temperature level, due to the fact that they are operated nearby or even below ambient air temperature.

1. BH discharging ►

2. BH charging

…………………………. ►

3. Serial-operation

The system (Fig. 1) is operated in three modes: Charging, discharging and serial operation. While operating in the discharging mode the BHE delivers with its own ground heat to the heat pump, whereas in the serial-operation mode the BHE is supported by the SC as additional heat source. In the operation mode “charging”, the collector is heating up and thus regenerating the soil around the BHE, while the HP is turned off. This concept realizes a simple hydraulic connection of the com­ponents and therefore allows different volume flow rates in the collector and BHE circuit.

After finishing the code, the storage model was validated in two steps. In a first step, the simulation behaviour was compared to measured data from previous system tests using measured hot water draw off curves and storage heat loss curves from several different testing days (Figure 3).

In a second step, the thermal behaviour of the double mantle heat exchanger store was compared with CARNOT’s existing simple water store model — insulated cylindrical hot water storage without any additional heat exchangers — validated by Hafner et al [4]. In order to compare both storage types, the gap between the inner and outer mantle of the double mantle storage model was assumed to be zero.

Both types of validation tests showed a deviation between simulation and measurements of less then 5%.

3. System Simulation

In the next step a complete thermosiphon system composed of solar collector, the necessary piping, the so-called thermosiphon pump (a block setting the thermosiphonic flow rate according to pressure differences in the system) and the newly developed double mantle heat exchanger storage was built up (Figure 4). The implemented technical data is identical to a system which was tested according to ISO 9459-2 at the CENTRE OF EXCELLENCE FOR SOLAR ENGINEERING in Ingolstadt (Table 1).

All blocks in the system are connected via data vectors according to their position in the system. The most important vector is the so called thermo hydraulic vector (THV), in which all relevant values are bundled. It includes the fluid identity, e. g. water or water-glycol mixture, fluid pressure, pressure drop (calculated in the block before), fluid temperature and density. Due to this THV, a realistic system behaviour can be achieved.

In the following, two different thermosiphon systems were simulated according to data measured at Ingolstadt University, using irradiation on the collector plane, the thermosiphonic flow rate and temperatures at collector / storage in — and outlet. The corresponding simulation runs show a good correlation between measured and simulated data, as can be seen in Figure 5 showing the flow rate and the accumulated flow through collector and storage over a whole day.

Fig. 5. Measured and simulated flow rate in a thermosiphon solar hot water heater