Solar Domestic Hot Water Research Articles

CORRELATION OF EXPERIMENTAL AND THEORETICAL HEAT TRANSFER IN MANTLE TANKS USED IN LOW FLOW SDHW SYSTEMS

Experimental and theoretical investigations of vertical mantle tanks for solar domestic hot water systems have been carried out. Differently designed mantle tanks have been evaluated in a laboratory test facility and a transient three-dimensional CFD-model of one of the mantle tanks is developed in the CFD-program CFX 4.1. The model is validated against the experimental tests and good agreement between measured and calculated results are achieved. The results from the CFD-calculations are used to illustrate the thermal behaviour and the fluid dynamics in the mantle and in the inner tank. The CFD-calculations are used to carry out a detailed analysis of the heat transfer from the solar collector fluid to the wall of the inner tank. The analysis has resulted in a local Nusselt-Rayleigh correlation for the heat transfer between the solar collector fluid and the wall of the inner tank.

A REVIEW OF LARGE-SCALE SOLAR HEATING SYSTEMS IN EUROPE

Large-scale solar applications benefit from the effect of scale. Compared to small solar domestic hot water (DHW) systems for single-family houses, the solar heat cost can be cut at least in third. The most interesting projects for replacing fossil fuels and the reduction of CO 2-emissions are solar systems with seasonal storage in combination with gas or biomass boilers. In the framework of the EU–APAS project “Large-scale Solar Heating Systems”, thirteen existing plants in six European countries have been evaluated. The yearly solar gains of the systems are between 300 and 550 kWh per m 2 collector area. The investment cost of solar plants with short-term storage varies from 300 up to 600 ECU per m 2. Systems with seasonal storage show investment costs twice as high. Results of studies concerning the market potential for solar heating plants, taking new collector concepts and industrial production into account, are presented. Site specific studies and predesign of large-scale solar heating plants in six European countries for housing developments show a 50% cost reduction compared to existing projects. The cost–benefit-ratio for the planned systems with long-term storage is between 0.7 and 1.5 ECU per kWh per year.

Analysis of a Load-Side Heat Exchanger for a Solar Domestic Hot Water Heating System

Testing is done of an unpressurized drainback system with a load-side heat exchanger. Analytical calculations for the heat exchanger effectiveness and three models for convective heat transfer coefficients from correlations are compared against the experimental data. TRNSYS simulations were performed using the average effectiveness of 0.78 (the calculated effectiveness varies from 0.68 to 0.95); the results compare favorably with experimental results, indicating that a constant effectiveness is an adequate model for the system.

Modelling and simulation aspects of a solar hot water system

The paper deals with the modelling and simulation aspects of the main components of a solar hot water system. Mathematical model was developed to describe the thermal behaviour and energy balance of different solar collectors and hot water storage tanks. Block-oriented simulation technique was used to obtain the solution of the dynamic model. For the identification of the model a laboratory scale measurement was carried out. The results of the simulation could support the selection of appropriate components and sizing of a solar domestic hot water system to be built.

In situ characterization of solar flat plate collectors under intermittent operation

The Bayerisches Zentrum für angewandte Energieforschung Bayern (ZAE) performs an in situ test of eight different solar domestic hot water systems in Oberpfalz, Bayern. We present results of the evaluation of the collector loop from one system. This system has been chosen because due to the relatively low load the variability of the collector loop temperature is expected to be insufficient for testing purposes. The system under test consisted of the collector field and the piping from the cellar to the roof. First, we use a dynamic collector model which ignores the extra pipes and thus implicitly takes into account the pipes by modified parameter values. It is shown that this model can be inaccurate if the input data such as the irradiance and the inlet temperature do not vary sufficiently and independently from each other. Second, we use a model which explicitly takes into account the pipes, using the overall loss coefficient and the total specific heat capacity of the pipes as new parameters. It is shown that it is possible to identify the values of these additional parameters. The overall accuracy improves with the extended model. The models without and with pipes differ mainly in dynamic effects associated with the energy stored in the pipes during stops of the collector loop pump.

CSHPSS systems in Greece: Test of simulation software and analysis of typical systems

Actual energy and environmental problems call for an increase of the use of solar energy. In Greece, though solar domestic hot water (DHW) systems are very popular, active solar space heating remains marginal, mainly because of the lack of experience of building professionals. Central solar heating plants with seasonal storage (CSHPSS) are promising systems. In this article, the design data of an interseasonal storage system in Greece are compared with the results of two CSHPSS simulation software codes, MINSUN and SOLCHIPS. The comparison showed good agreement and therefore these user-friendly tools can be used with confidence for the design of CSHPSS under Greek weather conditions. SOLCHIPS was used in order to assess the technical and economic feasibility of three generic types of CSHPSS under four climatically different Greek locations. The results show that CSHPSS, mainly used until now in northern countries, is also an interesting solution for southern climates. With the high solar fractions that CSHPSS achieve, their use can further reduce not only the conventional energy consumption of buildings, but also the associated CO 2 emissions that contribute significantly to the already heavy pollution of Greek urban areas.

Introducing advanced testing methods for domestic hot water storage tanks in Jordan

In Solar Domestic Hot Water (SDHW) systems the usage of hot water storage tanks is absolutely essential, and, the thermal behaviour of these tanks has a large influence on the efficiency of the entire system. To assess this influence, as well as to improve the quality of the storage tanks, it is very important to determine its parameters. Through a technical co-operation project between the Royal Scientific Society (RSS) in Amman and the Technical University of Munich (TU) (sponsored by the Forschungszentrum Karlsruhe), work was carried out: • — to apply a new development in storage testing to the existing facility at the RSS • — to examine its applicability • — to examine its reproducibility to local storage tanks made in Jordan. This paper presents the above referenced work including a description of the storage test facility and the applied ‘dynamic system testing’ procedure, which is based on the transient system simulation TRNSYS and the program for dynamic fitting DF. Through the testing of two storage tanks, it became evident that another test sequence was needed to determine the thermal vertical conductivity in the storage tanks. A new test sequence was proposed and tested to determine this parameter, which has a profound influence on the determination of certain other parameters.

Active solar space heating of residential buildings in northern Hellas—a case study

The final energy consumption in Hellenic residential and tertiary sector buildings represents almost one-third of the total energy budget. From this, space and water heating represents 70% of the total. Space heating and electricity generation in Hellas are based on fossil fuels, with a serious environmental impact. Despite the popularity of simple solar domestic hot water systems, active solar space heating remains, for various reasons, marginal. The aim of this paper is to demonstrate the potential of combined active space and domestic hot water solar systems, both technically and economically. An assessment of the reduction of the environmental impact is also included. The results confirm that modern solar technology constitutes a viable option for energy retrofit in the building sector in Hellas.

Use of expert systems for the selection and the design of solar domestic hot water systems

The aim of this article is the study of the application of expert systems to a mechanical engineering research domain with practical and commercial interest, such as design and manufacturing of Solar Domestic Hot Water (SDHW) Systems. The issues studied were the selection and the design of SDHW systems. The application of an expert system was explored. Frame and class formalism was used for knowledge representation together with forward and backward chaining techniques for drawing conclusions and utilizing the accumulated information present. The appropriate computer program was developed to yield the selection of SDHW systems using the software tool LEONARDO 3.0 (1989), an integrated environment for the development of expert systems. The developed program was tested with data according to the Greek standard ELOT corresponding to the ISO/DIS 9459-2 and it performed successfully for 21 SDHW systems available on the Greek market. Apart from the possibility of selection of a SDHW system, the program also supports the facility for updating its knowledge base with new data so that it can be adapted to changes appearing on the market. The program proved to be functional and user friendly to a high degree.

The Oxford Solar House

This paper presents preliminary results from the first nine months of monitoring the Oxford Solar House (OSH) which was built, in particular, to evaluate the potential for photovoltaics to contribute cost effectively to domestic energy supply in the UK. The house was built in a south facing site with good solar access. It has a 4kW PV system integrated into the roof structure and a 5m 2 solar thermal domestic hot water pre-heat. The house was designed to require a minimum of energy for heating, cooling and lighting, therefore optimizing the significance of the contribution of the solar electric supply. The performance of the PV system is presented, as well as an analysis of the whole design strategy to minimize energy loads.

Potential of solar domestic hot water systems in rural areas for greenhouse gas emission reduction in Poland

Application of solar energy for preparing domestic hot water is one of the easiest methods of utilization of this energy. At least part of the needs for warm tap water could be covered by solar systems. At present, mainly coal is used for water heating at dwellings in rural areas in Poland. Warm tap water consumption will increase significantly in the future as standards of living are improved. This can result in the growth of electricity use and an increase in primary fuel consumption. Present and future methods of warm sanitary water generation in rural areas in Poland is discussed, and associated greenhouse gas (GHG) emissions are estimated. It is predicted that the emission of CO2 and NOx will increase. The emission of CO and CH4 will decrease because of changes in the structure of the final energy carriers used. The economic and market potentials of solar energy for preparing warm water in rural areas are discussed. It is estimated that solar systems can meet 30%–45% of the energy demand for warm water generation in rural areas at a reasonable cost, with a corresponding CO2 emission reduction. The rate of realization of the economic potential of solar water heaters depends on subsidies for the installation of equipment.

An empirical model for natural convection heat exchangers in SDHW systems

Natural convection heat exchangers are valuable devices in solar domestic hot water systems, but they are difficult to model. The output pressures and temperatures they develop are complex functions of the flow and temperatures that they are subjected to, and these latter quantities—which vary over each hour in the year—are themselves dependent on the exchanger outputs. Yet to optimize the exchanger and to be truly confident of its performance, one needs good models which can be embedded into total simulation codes, like WATSUN or TRNSYS. This paper gives a suitable exchanger model and outlines how it can be used to model a total system. The model calls for a set of steady state experiments to be carried out on the exchanger in question, characterizing the exchanger. The experiments produce curves of collector effectiveness and shear pressure drop, both plotted against flow rate. A suitable experimental apparatus is described, and the results obtained for a particular exchanger are reported. Also reported are transient experiments that verify the applicability of the steady state experiments to real, time-varying conditions.

An empirical model for natural convection heat exchangers in SDHW systems

Natural convection heat exchangers are valuable devices in solar domestic hot water systems, but they are difficult to model. The output pressures and temperatures they develop are complex functions of the flow and temperatures that they are subjected to, and these latter quantities—which vary over each hour in the year—are themselves dependent on the exchanger outputs. Yet to optimize the exchanger and to be truly confident of its performance, one needs good models which can be embedded into total simulation codes, like WATSUN or TRNSYS. This paper gives a suitable exchanger model and outlines how it can be used to model a total system. The model calls for a set of steady state experiments to be carried out on the exchanger in question, characterizing the exchanger. The experiments produce curves of collector effectiveness and shear pressure drop, both plotted against flow rate. A suitable experimental apparatus is described, and the results obtained for a particular exchanger are reported. Also reported are transient experiments that verify the applicability of the steady state experiments to real, time-varying conditions.

95/03803 Technology for sustainable development: A case study of solar domestic hot water heating in Ontarlo

95/03803 Technology for sustainable development: A case study of solar domestic hot water heating in Ontarlo

Technology for sustainable development: A case study of solar domestic hot water heating in Ontario

In Ontario, potential contributions of solar domestic hot-water (SDHW) heating to air-emission mitigation have been identified. The provincial utility Ontario Hydro does not include solar heating in its current demand-side management plans because of the capital cost barrier. We present results of life-cycle cost analyses for installing a typical solar system in single-family dwellings in Toronto. For high hot-water load, the generated societal benefits make solar domestic hot-water heating an economically viable option.

Estimation of the effects of an intensive solar intervention in the historical centre of jaén (Spain)

AbstractThis paper is directed at evaluating the theoretical potential of an intensive solar intervention in the historical centre of the city of Jaén (Spain). Using the outputs of a solar intervention proposal comprising biomass, photovoltaics and solar thermal domestic hot water (DHW) over a 50‐building sample (in which those suitable for solar measures have been selected by evaluating each one over a collection of parameters), energy savings, environmental benefits and economic aspects of the envisaged actions are extrapolated over the entire historical centre. A saving of about 70% of conventional source energy annual consumption and a decrease of some 70% and 73% of CO2 and SOx annual releases, respectively, could be reached with respect to the present situation. Besides, an amount of conventionally generated electricity equivalent to the yearly photovoltaic‐generated electricity would require 131500 m3 of water a year, which is a rather significant feature for a dry climate like that of the city. the unitary cost of energy in the new scenario would be 60.7 pta kWh‐1 for photovoltaics, 329.9 pta m‐3 for DHW using solar thermal installations and 4.6 Pta kWh‐1 for biomass heating (1 US$ = 132.7 pta; 1 ECU = 160.9 pta).

Computational evaluation of solar heating systems using concrete solar collectors

This paper uses the F-chart technique to evaluate three types of solar heating systems, namely; space solar heating and domestic hot water system (SHDHW), domestic hot water system (DHW) and solar swimming pool heating system (SPHS), using three types of concrete solar collectors, models A, B, and C, and one conventional metallic solar collector. The economical analysis of SHDHW system revealed that the concrete collectors provided about 49 and 63% of the annual load when the collecting area of the solar panel increased from 55 to 88 M 2 (25 to 40% of the building roof area). The corresponding solar contributions when conventional metallic collectors were used are 41 and 53%, respectively. This represents an improvement of the annual solar fraction of about 19% when concrete collectors are used instead of the metallic collectors. It was found that solar heating systems with concrete solar collector models gave higher solar fractions and total life cycle savings than the conventional solar metallic collector.

Control problems in solar domestic hot water systems

The settings on the controller for a solar domestic hot water system can have major impact on the “ratings” obtained from a 1-day test or simulation. The settings become more critical as the effectiveness of any freeze protection heat exchanger decreases. This paper develops equations for optimal controller settings that will maximize the simulated performance. The practice of using solar radiation that is constant over hourly periods in both experimental- and simulation-based rating procedures is shown to cause problems. Recommendations are made for controller settings that yield a “fair” rating comparison.

Case study. Five year operation of a solar heating and domestic hot water installation in Madrid (Spain). Statistical study

This case study shows the performance of a solar installation providing space heating and domestic hot water to a single-family house. Experimental thermal analogy was used to dimension the equipment, thus taking into account the building's high thermal inertia.

Comparison of Experimental and Simulated Thermal Ratings of Drain-Back Solar Water Heaters

Short-term experimental tests of drain-back solar water heaters are compared to ratings obtained using TRNSYS to determine if computer simulations can effectively replace laboratory thermal ratings of solar domestic hot water heating systems. The effectiveness of TRNSYS in predicting changes in rating due to limited changes in collector area, collector flow rate, recirculation flow rate, storage tank volume, and storage tank design is validated to within ±10 percent. Storage tank design is varied by using a stratification manifold in place of the standard drop tube. Variations in other component sizes and operating factors are based on current industry standards.