Economic optimization of low-flow solar domestic hot water plants

A solar plant for hot-water production was investigated by the dynamic simulation code (TRNSYS). A typical daily home consumption for a 4 persons family was considered. The hot-water demand temperature (53 °C) is controlled by a conventional fuel auxiliary heater and a tempering valve. A heat-exchanger is considered between collector and storage tank. The fluids circulate by pumps activated by photovoltaic panels. This simplifies plant control systems and allows for stand-alone utilization of the plant. Annual energy performance, in terms of solar fraction, was calculated for three Italian localities. The economic viability of such a plant was evaluated with the life cycle savings (LCS) method, considering three conventional fuels (Gas-Oil, LPG and Electricity). Italian Government incentives show an economic viability only in comparison with electrical energy.     

Structure of domestic hot water consumption

We analyse the time and volume distributions for hot water consumption using data acquired from seven New Zealand households. This shows that there is a high proportion of low volume draws, 50 per cent yielding less than 2–31, depending on the household. In addition draws tend to be separated by relatively short intervals, 50 per cent following the previous draw by not more than 10–20 min. By use of a dynamic model of the hot water piping we estimate that thermal losses in the piping exceed 20 per cent of the heat energy supplied by the hot water cylinder for average households. We show that the use of pipe insulation may reduce these losses by 5–7 per cent.     

Domestic hot water and solar energy in Ireland

Two systems are discussed which involve the use of solar energy to supply domestic hot-water requirements and their usefulness in Ireland is examined. the systems are evaluated for thermal performance and cost-effectiveness but the use of a computer simulation model of a system involving a typical commercially available solar panel. It is shown that such systems may be economically justified when compared with electricity, but only if the water supply is directly heated by solar panels and only if the installed cost of such panels is low. Further, it appears that the system performance is relatively insensitive to the panel orientation and consequently that retro-fit installations on existing houses are unlikely to cause difficulties.     

Enhancement of natural circulation type domestic solar hot water system performance by using a wind turbine

Performance improvement of existing 200 litres capacity natural convection type domestic solar hot water system is attempted.A two-stage centrifugal pump driven by a vertical axis windmill having Savonius type rotor is added to the fluid loop.The windmill driven pump circulates the water through the collector.The system with necessary instrumentation is tested over a day.Tests on Natural Circulation System(NCS)mode and Wind Assisted System(WAS)mode are carried out during January,April,July and October,2009.Test results of a clear day are reported.Daily average efficiency of 25-28% during NCS mode and 33-37% during WAS mode are obtained.With higher wind velocities,higher collector flow rates and hence higher efficiencies are obtained.In general,WAS mode provides improvements in efficiency when compared to NCS mode.     

An experimental study on a modified air conditioner with a domestic hot water supply (ACDHWS)

The recovery of condenser heat in air conditioners is attractive because of its great economy and environmental value. This work experimentally studies a modified air conditioner with a domestic hot water supply (ACDHWS) that operates in the space-cooling and water-heating mode. The working principles and the basic features of the ACDHWS are introduced in this paper. This is followed by an experimental study on dynamic operation characteristics, hot water supply performance, energy efficiency and the temperature distribution of hot water in the storage tank of the unit. The results show that the ACDHWS can reliably be used to heat domestic hot water without losing its cooling capacity when it is controlled well in different operation conditions. Comparatively, the coefficient of comprehensive energy performance (COP₂) of the ACDHWS is about 38.6% higher than that of the original unit. Furthermore, it is proved that the ACDHWS can continuously supply hot water for householders if a suitable hot water storage tank is installed. All these may be much helpful to develop a perfect ACDHWS product.     

Experimental study of a domestic boiler using hydrogen methane blend and fuel-rich staged combustion

Storing excess wind and solar energy in the form of hydrogen injected into the natural gas grid is one of the main ingredients of the energy transition. This hydrogen injection has an impact on emissions and the performance of user equipment. The present work reports on an experimental study of the combustion of methane-hydrogen mixture with fuel rich transverse staggered injection. The 15 kW domestic boiler used was equipped with 16 burners (2 × 8). The aim of this work is to better understand the simultaneous effects of fuel rich staged combustion (Ø = 2.0 ÷ 4.0), hydrogen blending of methane (0 ÷ 45%) on pollutant emissions and efficiency while maintaining a compromise between high power, fuel economy and low emissions. The results show that NO_x, CO₂ emissions decrease, CO and C_xH_y emission values increase and thermal efficiency values decrease with increasing hydrogen percentage and fuel rich staggering combustion.     

Fossil fuels substitution by the solar energy utilization for the hot water production in the heating plant “Cerak” in Belgrade

The main objective of this paper is to evaluate energy and environmental benefits of the large-scale solar heating system connection with district heating system. The assessment of fossil fuels substitution by the solar energy for the hot water production for domestic use, during the summer period, is done. Hot water for district heating and domestic use is produced in heating plant “Cerak” placed in the suburb of Belgrade. The existing production and distribution system are based on fossil fuel energy, mainly on the natural gas. In the first phase of the project plan was to install about 10,000 m² of solar collectors to substitute nearly 25% of natural gas consumption. During the summer period, the saving of natural gas calculated for presented system is approximately 430,000 m³ and in this way 900 t of the CO₂ emissions would be reduced.     

Measurements of household electricity and domestic hot water use in dwellings and the effect of different monitoring time resolution

The use of household electricity and domestic hot water has been measured for 72 apartments in an apartment building located in the south of Sweden. The measurements were carried out with samples every 6 s, a tenfold increase in resolution compared to available published data, during a measurement period of five days, in the winter season, including a weekend. The influence of the time resolution on the distribution of data was analysed by integrating the 6 s data to represent longer logging intervals. Extreme values, especially the high values, are shown to be reduced if the time interval is increased. The maximum household electric power was 50% higher at a 6 s resolution compared to 60 s and the corresponding difference for domestic hot water flow was 40%. Daily variations has to be considered for photovoltaic installations and solar thermal collectors, energy simulations of buildings need at least hourly data and all kind of power design in a building or its services benefits from much more resolved data.     

Domestic hot water storage: Balancing thermal and sanitary performance

Thermal stratification within hot water tanks maximises the availability of stored energy and facilitates optimal use of both conventional and renewable energy sources. However, stratified tanks are also associated with the proliferation of pathogenic bacteria, such as Legionella, due to the hospitable temperatures that arise during operation. Sanitary measures, aimed at homogenising the temperature distribution throughout the tank, have been proposed; such measures reduce the effective energy storage capability that is otherwise available. Here we quantify the conflict that arises between thermodynamic performance and bacterial sterilisation within 10 real world systems. Whilst perfect stratification enhances the recovery of hot water and reduces heat losses, water samples revealed significant bacterial growth attributable to stratification (P<0.01). Temperature measurements indicated that users were exposed to potentially unsanitary water as a result. De-stratifying a system to sterilise bacteria led to a 19% reduction in effective hot water storage capability. Increasing the tank size to compensate for this loss would lead to an 11% increase in energy consumed through standing heat losses. Policymakers, seeking to utilise hot water tanks as demand response assets, should consider monitoring and control systems that prevent exposures to unsanitary hot water.     

Experimental and numerical study of thermal stratification in a mantle tank of a solar domestic hot water system

The simulation and the optimisation of the mantle tank of solar domestic hot water systems needs dynamic simulation over long periods of time (e.g. 1 year). A model for such a mantle tank was developed by using the zonal approach. The dimensions of the zones are determined based on physical considerations. A mixing coefficient is identified to model the water flow in the mantle heat exchanger. Comparisons of the results of temperatures distribution of the model and of experiments show a difference <7% for three positions of the inlet water flow in the mantle heat exchanger.     

Experimental study of a domestic thermoelectric cogeneration system

Thermoelectric application for power generation does not appear to be appealing due to the low conversion efficiency given by the current commercially available thermoelectric module. This drawback inhibits its wide application because of the overall low thermal efficiency delivered by typical thermoelectric applications. This paper presents an innovative domestic thermoelectric cogeneration system (TCS) which overcomes this barrier by using available heat sources in domestic environment to generate electricity and produce preheated water for home use. This system design integrates the thermoelectric cogeneration to the existing domestic boiler using a thermal cycle and enables the system to utilise the unconverted heat, which represents over 95% of the total absorbed heat, to preheat feed water for domestic boiler. The experimental study, based on a model scale prototype which consists of oriented designs of heat exchangers and system construction configurations. An introduction to the design and performance of heat exchangers has been given. A theoretical modelling for analysing the system performance has been established for a good understanding of the system performance at both the practical and theoretical level. Insight has also been shed onto the measurements of the parameters that characterise the system performance under steady heat input. Finally, the system performance including electric performance, thermal energy performance, hydraulic performance and dynamic thermal response are introduced.     

关于常压热水锅炉的系统设置和节能

常压热水锅炉在国内已有广泛的应用,但常压热水锅炉房目前尚无权威的设计布置方法,而导致安全事故常有发生。在这种锅炉的布置中必须有通大气管和锅炉热水箱。循环热水泵应设于锅炉的出口。在循环热水泵选型时,其压头应为热用户与锅炉房的高程差及管网阻力之和,回水管路上必须设启闭网和阻力调节阀。常压锅炉的节能特性应视热水管网的构成情况具体分析。这种锅炉大体上用在低层、低参数、小容量的场合较为合适。     

中水源热泵用于生活热水系统方案设计

结合工程实例,详细介绍了利用水源热泵进行学校浴室废水热能回收的方案设计,并对该系统和传统燃气锅炉系统的年运行费用进行比较。结果表明该系统具有很好的节能潜力。     

Efficient single glazed flat plate photovoltaic-thermal hybrid collector for domestic hot water system

This paper deals with the design of a single glazed flat plate Photovoltaic-Thermal (PV-T) solar collector. First, the thermal and electrical performances of several single glazed flat plate PV-T concepts based on water circulation are investigated, using a simple 2D thermal model, then different ways of improvement are presented. It mainly consists in focusing on the heat transfer between PV cells and fluid, and also on the optical properties of materials. Thus, the most appropriate concept configuration has been identified and suitable material properties have been selected. A prototype collector has been designed, built and tested. A high thermal efficiency was reached at zero reduced temperature. For this level of thermal efficiency, the corresponding electrical efficiency has is lower than efficiency of a standard PV panel using the same technology. However, this solar PV-T collector is reaching, in these standard conditions, the highest efficiency level reported in the literature.     

热水采暖系统改造的启示

供暖系统普遍存在用户冷热不均,燃料耗量高,电力消耗量大的问题,已经到了必须认真解决的时候了。本文通过工程实例说明,解决这个“老大难”部下的基本途径和方法。     

地源热泵复合系统热水机组实验研究

通过实验系统模拟复合系统中制热水机组的各个特定工况,分别进行静态实验测试,分析机组的性能和输入功率在三种不同工况下的变化情况,指出复合系统中制热水机组具有很高的节能效果。     

Life cycle environmental impact of a thermosyphonic domestic solar hot water system in comparison with electrical and gas water heating

A methodology for the environmental impact evaluation over the life span of a Domestic Solar Hot Water System (DSHWS) is presented. The results are compared to the environmental consequences of the conventional energy form substituted and the total environmental gain is calculated. For the purposes of this analysis, the “Eco-indicator ’99” Life Cycle Impact Assessment methodology was adopted and the materials and procedures of the DSHWS production and utilization are evaluated.     

染色工艺清洁热水的回收与利用

染色过程中需用大量的间接冷却水，高温冷却水的排放，不仅浪费了大量能源，而且给污水生化处理带来了困难，采用变频控制技术，建设热水回收系统，在节能，环保，提高产量等方面取得了一举多得的效果。     

变容量家庭能源中心单独制热水模式的实验研究

提出了可全年供应空调和热水需要的变容量家庭能源中心系统,并提出单独制热水模式下的性能系数计算方法。通过对该模式瞬时动态特性的研究,指出变容量压缩机可以有效地保证机组的安全可靠运行。实验研究了单独制热水模式在不同环境温度、不同压缩机负荷条件下的性能。结果表明,在同一压缩机负荷条件下,热水性能系数均随环境温度的升高而升高,与传统热泵热水器的变化趋势相同。而压缩机负荷变化对机组热水性能系数的影响在不同的环境温度下呈现不同的规律,因此,可根据不同的环境温度优化控制压缩机负荷,以提高制热水效率,节约能源。     

An integrated domestic refrigerator and hot water system

This paper presents a new design of a prototype refrigeration-cum-hot water heating system for domestic use. The system uses the heat energy rejected from the compressor and condenser of a vapour-compression refrigerator by storing it in a heat sink. This energy is then transferred to mains water entering the hot water cylinder, where the water temperature is boosted by an electric resistance heater to a preset temperature for domestic usage. A prototype system of such a configuration was assembled as an integrated unit with the refrigerator adjacent to the water tank. The system is called the Home Energy Centre (HEC). Power consumption and temperature distribution were measured for standing and draw off tests using the unit as a conventional hot water cylinder, refrigerator or as the combined system. A new parameter, ϕ, is defined to compare the system performance as the HEC prototype against its performance when working only as a refrigerator or a water heater. The system performed better as the prototype than it did as a hot water heater, but needs to be improved further to fully explore its expected potential. © 1998 John Wiley & Sons, Ltd.