Energy savings for solar heating systems

In this paper the realistic behaviour and efficiency of heating systems were analysed, based on long term monitoring projects. Based on the measurements a boiler model used to calculate the boiler efficiency on a monthly basis was evaluated. Comparisons of measured and calculated fuel consumptions showed a good degree of similarity. With the boiler model, various simulations of solar domestic hot water heating systems were done for different hot water demands and collector sizes. The result shows that the potential of fuel reduction can be much higher than the solar gain of the solar thermal system. For some conditions the fuel reduction can be up to the double of the solar gain due to a strong increase of the system efficiency. As the monitored boilers were not older than 3 years, it can be assumed that the saving potential with older boilers could be even higher than calculated in this paper.     

Energy flow through the flat-plate solar water heating system

A simulation model of the flat-plate solar water heating system is used to trace the flow of energy through the system from the collector to storage and load for a system operating under idealised sunlight conditions.     

The impacts of solar water heating in low-income households on the distribution utility’s active, reactive and apparent power demands

In Brazilian low-income households, water-heating requirements are typically met by electrical showerheads. On average, 73.1% of all residential units in the country are equipped with these resistance-heating devices, with nominal powers ranging from 3 to 8 kW. This situation imposes a considerable burden on the electricity utility companies, since electrical showerheads typically represent the highest load but the lowest utilization (load factor) in a residential consumer unit. Furthermore, typical utilization times coincide with, and contribute to, the electrical power demand peaks in Brazil, rendering these low-cost, high-power electrical devices a high-cost consumer for the electrical system to cater for. For low-income residential consumers, electricity tariffs are subsidized, and utilities must therefore make a considerable investment in infrastructure for a limited return. In this paper we analyze the impacts of solar water heating in low-income households on the distribution utility active, reactive and apparent power demands. We have monitored a statistically representative group of low-income residences equipped with a compact domestic solar water heater in Florianopolis - Brazil for 1 year. We show that in comparison with identical residential units using electrical showerheads, with the adoption of solar water heating the reductions in the active, reactive and apparent power demands on the distribution utility were 49%, 29% and 49% respectively.     

Evaluation of retrofitting gas-fired cooling and heating systems into BCHP using design optimization

The influence of energy prices on the feasibility of a retrofit is investigated. The retrofit describes the conversion of a system from HVAC to BCHP for energy-saving. This includes two optimal retrofit design models, of which the exergetic efficiency and annual costs (AC) are the separate objective functions. The retrofit scheme is planned to insert gas engines as prime movers into the original system, which have adopted gas-fired absorption chillers. The solutions of the optimizations show that such a retrofit can result in a remarkable rise in exergetic efficiency but is not viable with current energy prices. The contradictory solutions reveal a gap between the current energy prices system of the country and the present energy situation. Further investigation gives the critical lines of which each divides the coordinate plane of natural gas–electric prices into two parts of benefit and deficit. If the electric price rises to a certain extent, the retrofit will be advantageous both in benefit and energy-saving. So it is really an urgent task to reform the energy prices system in China. Conclusions may be helpful for other similar retrofit projects, and for legislators and the government which are responsible for improving the energy market in China.     

Performance of collector/storage solar water heaters: Arbitrary demand pattern

This paper presents a simple transient model for predicting the thermal performance of two novel water heaters which combine both collection and storage of solar energy in a single configuration. The proposed model is applicable for demand patterns, characteristic of various domestic and industrial applications. The model takes into account the appropriate heat transfer processes during sunshine and off-sunshine hours and predicts, for a particular case, the time dependence of water temperature which is in close agreement with experimental observations. The model also predicts the variation of water temperature for the withdrawal of hot water at constant flow rate. Furthermore, it determines the time dependence of flow rate corresponding to extraction of hot water at constant temperature; this is a desirable situation in process heating and other applications.     

Solar potential for water heating explored by GIS

A method is presented for the estimation of solar energy and market potential for water heating in the residential sector. The model was developed under a Geographical Information System and provides the tools to handle the spatial and time discrepancies of solar radiation and energy demand. A geographic database with climatic data is used for estimating efficiencies and monthly/annual coverage of water heating load. Financial analysis is conducted on the basis of the energy production cost and the Net Present Value of the investment. Different financial scenarios are considered and the expected energy yields from a large-scale deployment of solar thermal systems in the residential sector of Greece are assessed.     

A parametric study of the small-scale solar pond (SSSP)

A parametric study of salt-gradient solar ponds of size less than 100 m² is presented. The study is based on a dynamic model of the pond which takes into account the variation of solar radiation, ambient temperature and the amount of heat extracted with time. Furthermore3 it considers a small-scale pond whose top is covered by a transparent cover, thus considerably reducing the thickness of the top convective zone. The parameters investigated include: pond dimensions, depths of the different layers, starting dates for pond operation and load application, pond insulation and the value of the thermal load.     

Analyzing variables for district heating collaborations between energy utilities and industries

One vital means of raising energy efficiency is to introduce district heating in industry. The aim of this paper is to study factors which promote and inhibit district heating collaborations between industries and utilities. The human factors involved showed to affect district heating collaborations more than anything else does. Particularly risk, imperfect and asymmetric information, credibility and trust, inertia and values are adequate variables when explaining the establishment or failure of industry-energy utility collaborations, while heterogeneity, access to capital and hidden costs appear to be of lower importance. A key conclusion from this study is that in an industry-energy utility collaboration, it is essential to nurture the business relationship. In summary, successful collaboration depends more on the individuals and organizations involved in the relationship between the two parties than on the technology used in the collaboration.     

太阳能加热输送原油系统集热器的选择

为了减少原油输送所需的加热能耗，可以采用太阳能集热器加热原油。目前常用的3种集热器中热管式集热器的热效率高、抗冻能力强、保温好、启动快、技术综合经济性好，最适合我国北方的气候和原油加热的工况条件，是最佳的选择。     

Determination of design space and optimization of solar water heating systems

In this paper, a methodology is proposed to determine the design space for synthesis, analysis, and optimization of solar water heating systems. The proposed methodology incorporates different design constraints to identify all possible designs or a design space on a collector area vs. storage volume diagram. The design space is represented by tracing constant solar fraction lines on a collector area vs. storage volume diagram. It has been observed that there exists a minimum as well as a maximum storage volume for a given solar fraction and collector area. Similarly existence of a minimum and a maximum collector area is also observed for a fixed solar fraction and storage volume. For multi-objective optimization, a Pareto optimal region is also identified. Based on the identified design space, the solar water heating system is optimized by minimizing annual life cycle cost. Due to uncertainty in solar insolation, system parameters and cost data, global optimization may not be utilized to represent a meaningful design. To overcome this, a region of possible design configurations is also identified in this paper.     

The passive solar heated school in wallasey. IV. An observational study of the thermal response of a passive school building

An observational study on the Wallasey School has demonstrated its ability to maintain in most conditions of climate an equitable indoor climate both in regard to daily mean temperatures and daily variations, through use of solar gain and heat from the lights, and the appropriate control of ventilation. During occupied periods, air temperatures are usually between 17°C in winter and 23°C in sunny summer periods. The room provides a mainly ‘cold wall’ environment. The observational data and a series of model estimates have been compared. The general level of temperature within the building is known to depend strongly on ventilation rate, but since ventilation rate was not measured, steady-state comparisons as such are not possible. The observed and estimated temperature profiles for air and various surfaces including that of the furnishings during a very sunny period are in broad agreement. Analyses of the transient response of the structure in winter conditions has demonstrated a long response time (several days) describing the response of the enclosure, and a shorter response time of about half a day which describes the rate of settlement of internal temperature differences which may be initially present. Evidence is presented indicating low values for the convective heat transfer coefficient. An autocorrelational technique demonstrates that the thermal ‘memory’ of the classroom is much longer in winter than in summer. The response of the room during occupied and unoccupied periods is broadly similar, but conditions are rather more variable during occupation.     

Thermal modelling of a few novel solar collector-cum-storage units for passive heating

Analytical models have been put forward to predict the thermal performance of passive heating systems, which have previously been suggested. The systems consist of a water vessel for heat storage and a structure positioned on its outside wall, which act as a solar collector and a thermal insulation for the storage, respectively. Four different variations of structures have been considered and numerical calculations performed corresponding to the physical parameters of an earlier reported experimental study. The analysis is able to predict the experimental results fairly satisfactorily.     

The passive solar heated school in Wallasey. V. Energy requirements for A passive school building

The near-south-facing glazed wall of the Wallasey School admits large solar gains in sunny weather, sufficient to meet in full the heat need in cold weather. It permits large heat losses, however, and during dull weather, and during the long winter nights there is little or no compensating solar gain. The net effect of such glazing over a season might be either to save, or to waste energy as compared with a windowless building, according to the sunniness and coldness of the climate and the window characteristics. To examine the action of the glazing, use was made of 50 years of daily mean ambient temperature, and contemporary sunshine hours, in conjunction with the solar gain factor for the translucent and pinboarded areas of the solar wall, and for certain values of design temperature and ventilation rate. It is concluded that such glazing leads to modest savings, of around 5 to 10 W/m² daily average. Most of the saving appears to be achievable by around 30 per cent glazing; further glazed area tends to supply unwanted solar gain in sunny periods while increasing the losses in sunless conditions. The annual electricity consumptions are noted for the 20 year life of the building. Their costs suggest that the building has been economical to heat.     

The passive solar heated school in wallasey. III model studies of the thermal response of a passive school building

Using information on the dimensions and materials of a room in the Wallasey School, estimates are presented of its response to heat inputs due to the lighting system and the sun. The daily variation due to these influences is calculated using transient and harmonic approaches.     

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 CO₂-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 m² collector area. The investment cost of solar plants with short-term storage varies from 300 up to 600 ECU per m². 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.     

太阳能热水系统的节能效益分析

以呼和浩特北方宾馆为例，计算分析了该系统相关的节能效益指标，并列出了其他一些工程实例的节能效益指标，初步分析研究了太阳能热水工程的节能效益。给出了太阳能热水系统的增投资的回收期算法。