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.     

Technical and economic performance of residential solar water heating in the United States

This paper examines the regional, technical, and economic performance of residential rooftop solar water heating (SWH) technology in the U.S. It focuses on the application of SWH to consumers in the U.S. currently using electricity for water heating, which currently uses over 120 billion kWh per year. The variation in electrical energy savings due to water heating use, inlet water temperature and solar resource is estimated and applied to determine the regional “break-even” cost of SWH where the life-cycle cost of SWH is equal the life-cycle energy savings. For a typical residential consumer, a SWH system will reduce water heating energy demand by 50–85%, or a savings of 1600–2600 kWh per year. For the largest 1000 electric utilities serving residential customers in the United States as of 2008, this corresponds to an annual electric bill savings range of about $100 to over $300, reflecting the large range in residential electricity prices. This range in electricity prices, along with a variety of incentives programs corresponds to a break-even cost of SWH in the United States varying by more than a factor of five (from less than $2250/system to over $10,000/system excluding Hawaii and Alaska), despite a much smaller variation in the amount of energy saved by the systems (a factor of approximately one and a half). We also consider the relationships between collector area and technical performance, SWH price and solar fraction (percent of daily energy requirements supplied by the SWH system) and examine the key drivers behind break-even costs.     

Hybrid photovoltaic-thermosyphon water heating system for residential application

In order to improve the energy performance of the photovoltaic system, much effort has been spent on the research and development of hybrid PVT (photovoltaic-thermal) technology using water as the coolant. The fin performance of the thermal absorber is known to be one crucial factor in achieving a high overall energy yield of the collector. Accordingly, an aluminum-alloy flat-box type PVT collector was constructed, with its fin efficiency approaching unity. Its design is primarily for natural circulation and for domestic water heating purpose. Our test results showed that a high final hot water temperature in the collector system can be achieved after a one-day exposure. A numerical model of this photovoltaic-thermosyphon collector system was also developed and the model accuracy was verified by comparison with measured data. The energy performance of the collector system was then examined first, through reduced-temperature analysis, and second, as applying in the “hot summer and cold winter” climate zone of China. The numerical results are found very encouraging, and the equipment is capable of extending the PV application potential in the domestic sector.     

On the potential trade-offs between energy supply and end-use technologies for residential heating

In Sweden, where district heating accounts for a significant share of residential heating, it has been argued that improvements in end-use energy efficiency may be counter-productive since such measures reduce the potential of energy efficient combined heat and power production. In this paper we model how the potential trade-offs between energy supply and end-use technologies depend on climate policy and energy prices. The model optimizes a combination of energy efficiency measures, technologies and fuels for heat supply and district heating extensions over a 50 year period. We ask under what circumstances improved end-use efficiency may be cost-effective in buildings connected to district heating? The answer hinges on the available technologies for electricity production. In a scenario with no alternatives to basic condensing electricity production, high CO₂ prices result in very high electricity prices, high profitability of combined heat and power production, and little incentive to reduce heat demand in buildings with district heating. In contrast, in a scenario where electricity production alternatives with low CO₂ emissions are available, the electricity price will level out at high CO₂ prices. This gives heat prices that increase with the CO₂ price and make end-use efficiency cost-effective also in buildings with district heating.     

Energy conservation options for residential water heaters

Current designs of gas-fired and electric water heaters present a substantial opportunity for energy conservation through reductions in jacket losses, pilot losses and flue-gas losses. A systematic analysis and comparison of alternative energy-conserving designs has been carried out. Promising options for gas-fired water heaters include increased insulation, thermostat setback, forced-draft burners with intermittent ignition and flue closure, and instantaneous (low storage) designs. High efficiency electric water heaters incorporate increased insulation, thermostat setback, solar preheat, and heat pump operation. The evolution and market penetration of these alternative designs, some of which are commercially available at this writing, can reduce the energy usage for residential water heating in the U.S. by approx. 0.3 quads in the near-term, and up to 1.0 quads in the long-term as advanced designs achieve widespread saturation.     

住宅太阳能热水系统评价

介绍太阳能热水系统的评价指标。结合实例,对承德某太阳能热水系统的节能费用、投资回收期、环保效益进行计算,并与常规热水系统进行了比较。     

Energy savings in the combustion based process heating in industrial sector

Energy efficiency and savings strategies in the combustion based industrial process heating has been reviewed comprehensively and presented in this paper. This work compiles latest literatures in terms of thesis, journal articles, conference proceedings, web materials, reports, books, handbooks on industrial process heating systems in the industrial sector. Different types of equipment used (i.e., recuperator, regenerators, heat wheels, heat pipes, economizers, etc.) and energy savings are reviewed in various industrial processes heating. Based on the review results, it is found that significant amounts of energy could be saved by using heat recovery system in the industrial process heating. By using recuperator up to 25% energy can be saved in the furnace. In the case of boiler, by using economizers 10% to 20% energy can be saved. Economic analysis shows that the payback period of recuperator and economizer are normally less than 2 years. It is also found that the payback period is lower when operating hour is comparatively high.     

Energy savings potential from improved building controls for the US commercial building sector

The US Department of Energy (DOE) sponsored a study to determine the national savings achievable in the commercial buildings through widespread deployment of controls, elimination of faults, and use of better sensing. The study estimated savings from 34 measures in 9 building types and across 16 climates. These buildings are responsible for almost 57% of the US commercial building sector energy consumption. In addition to the individual measures, three packages of measures were created to estimate savings: (1) efficient building, (2) typical building, and (3) inefficient building. The results showed significant potential for energy savings across all building types and climates. The total site potential savings by building type aggregated across all climates for each measure varied between 0 and 16%. The total site potential savings aggregated across all building types and climates for each measure varied between 0 and 11%. The national potential site energy savings across all building types studied is 29%. Across all building types, the savings represent approximately 1393 PJ (1.32 quads) of site energy savings or 2912 PJ (2.76 quads) of primary (or source) energy savings. Extrapolating the results for other building types not analyzed as part of this study, the primary energy savings could be in the range of 4220 to 5275 PJ. For comparison, the total US primary energy consumption across all sectors of energy use was 102,762 PJ (97.4 quads) in 2015. This makes commercial building control improvements strategically important to sustained reductions in national energy consumption. To realize most of this potential savings, many gaps can be addressed through research development and deployment (RD&D), as recommended in this paper.     

Passive and active residential solar heating: A comparative economic analysis of select designs

This paper compares four passive solar heating concepts to a conventional air collector/rock storage system. Masonry (Trombe) and water walls are considered in the presence and absence of night insulation. The performance of optimally sized systems is evaluated on a state-by-state basis. The effects of low interest loans and National Energy Act (NBA) income tax credits are examined. With natural gas as the alternative fuel, the passive designs evaluated here offer more promise than the active system. This is true with or without inclusion of incentives, although either incentive option enhances economic performance. The passive designs evaluated in this paper are economically competitive against the electric resistance alternative in all but a few states. Moreover, on a life cycle cost basis, these designs are feasible today. Although the optimal solar fractions are generally low, passive designs offer the opportunity to incorporate solar heating into a new home at costs much less than their active counterparts. This is because there are no discernible fixed costs, thereby allowing a simple movement from zero to 100% solar when evaluating economic feasibility. When both active and passive design are shown to be cost competitive against alternative fuels, higher solar fractions will be associated with the active systems. This is principally due to the substantial fixed cost component of active systems, which forces one to achieve a given solar fraction before economic feasibility can be shown.     

Determinants of electricity use for residential water heating: The hood river conservation project

Because 85% of the homes in the Pacific Northwest have electric water heaters, water heating is the second most important residential electricity end-use in the region (second to space heating). This paper analyses the determinants of water-heating electricity use, using end-use load data and responses to a detailed home interview. These data are available for 142 homes in Hood River, Oregon.On average, these homes used 5000 kWh/yr for water heating. Almost 60% of the household-to-household variation in electricity use was explained with eight variables in a simple regression model. The number and ages of household members are the strongest determinants of electricity use: use increases by roughly 1000 kWh/yr with each additional household member. Other statistically significant determinants of water-heating electricity use are hot-water temperature, water-heater location, number of showers in the home and house type.Electricity use varies considerably throughout the year (as well as across households). Weekly usage was 50% higher in mid-winter than in summer. About half of this temporal variation is due to changes in outdoor temperatures and half is due to seasonal changes in behavior (i.e. increased use of hot water in winter).     

The demand function for residential heat through district heating system and its consumption benefits in Korea

The demand for residential heat (RH) through a district heating system (DHS) has been and will be expanded in Korea due to its better performance in energy efficiency and the abatement of greenhouse gas emissions than decentralized boilers. The purposes of this paper are two-fold. The first is to obtain the demand function for DHS-based RH in Korea and investigate the price and income elasticities of the demand employing the quarterly data covering the period 1988–2013. The short-run price and income elasticities are estimated as −0.700 and 0.918, respectively. Moreover, the long-run elasticities are −1.253 and 1.642, respectively. The second purpose is to measure the consumption benefits of DHS-based-RH employing the economic theory that they are the sum of the actual payment and consumer surplus for the consumption. Considering that the average price and estimated consumer surplus of the DHS-based RH use in 2013 are computed to be KRW 87,870 (USD 84.1) and KRW 62,764 (USD 60.1) per Gcal, the consumption benefits of the DHS-based RH are calculated to be KRW 150,634 (USD 144.2) per Gcal. This information can be beneficially utilized to conduct an economic feasibility study for a new DHS project related to RH supply.     

Energy savings of a house with solar heating, earth cooling and air circulation

A new type of residence with solar heating, earth cooling and air circulation(the SEA House) has been proposed by the authors. In winter, the house is heated by solar energy. Thermal insulation, heat storage and air circulation are used to maintain the room temperature at a comfortable level and to reduce the energy demands for air-conditioning. In summer, the cooling tubes are used for the purpose of cooling the proposed house. In this paper, the energy savings of the SEA House are analyzed quantitatively. Comparing to the energy used for the air-conditioning of the existing residential houses in Hokkaido, Sendai, Tokyo and Kagoshima, it is estimated that only 19%, 18%, 14% and 24% of energy are needed for the airconditioning of the SEA House respectively.     

Energy and exergy performance of residential heating systems with separate mechanical ventilation

The paper brings new evidence on the impact of separate mechanical ventilation system on the annual energy and exergy performance of several design alternatives of residential heating systems, when they are designed for a house in Montreal. Mathematical models of residential heating, ventilation and domestic hot water (HVAC–DHW) systems, which are needed for this purpose, are developed and furthermore implemented in the Engineering Equation Solver (EES) environment. The Coefficient of Performance and the exergy efficiency are estimated as well as the entropy generation and exergy destruction of the overall system. The equivalent greenhouse gas emissions due to the on-site and off-site use of primary energy sources are also estimated. The addition of a mechanical ventilation system with heat recovery to any HVAC–DHW system discussed in the paper increases the energy efficiency; however, it decreases the exergy efficiency, which indicates a potential long-term damaging impact on the natural environment. Therefore, the use of a separate mechanical ventilation system in a house should be considered with caution, and recommended only when other means for controlling the indoor air quality cannot be applied.     

Ordinal benefits vs economic benefits as a reference guide for policy decision making. The case of hydrogen technologies

The paper presents an Investment Evaluation Method in Energetic–Economic–Environmental field which is particularly indicated for Hydrogen Technologies because it enables us to account not only for the traditional economic return and the possible negative externalities (damages), but also for: i) the induced economic benefits at a social level; ii) those positive (and negative) externalities usually considered as being estimable in economic terms as “proxies”; iii) and, finally, Ordinal Benefits. That is those Benefits which are never ever reducible to a simple monetary value, nonetheless they can always be object of a possible estimation, still in economic terms, by means of values understood as a “cipher”.     

Energy efficiency and energy savings

Technical energy conservation, in which energy is saved by producing the same goods and services at higher efficiency, is contrasted with energy savings produced by shifting end uses from more to less energy intensive activities. It is shown that the former is considerably more effective in saving energy. The general theory is confirmed by the use of concrete examples.     

Energy demand and conservation in US residential and commercial buildings Impact of the US national energy plan

This paper evaluates the impact of the US National Energy Plan on energy demand in US commercial and residential buildings. Following a brief historical review of energy use patterns in US buildings, estimates are presented of how the National Energy Plan would affect the sector in terms of fuel expenditures and investment in energy using equipment and structures. The analysis is based on economic-engineering models of energy demand which are currently being used by the US Department of Energy to evaluate conservation programmes. The demand models incorporate behavioural as well as technological determinants and are sufficiently disaggregated to allow consideration of individual components of the National Energy Plan.     

Energy, economic and environmental analysis on RET-hydrogen systems in residential buildings

The aim of this study was to analyze energy, economic and environmental performances of a set of scenarios dealing with the production and the use of hydrogen as energy carriers in residential applications in combination with renewable energy (RE).The authors also made an investigation into the required economic conditions necessary for making H₂–RE residential systems competitive with conventional ones, which are based on the use of grid electricity and natural gas.A case study was enacted in a small residential district in Palermo (Italy) made by five multi-storey buildings.Many energy systems have been considered according to several fuel-device combinations (electric grid, fuel cell, PV panels, wind turbines, boiler etc.).The software HOMER (hybrid optimization model for electric renewables), developed by NREL and Midwest Research Institute (USA), was used, in order to study the energy balance of the system and its components. Moreover, it was possible to simulate the hourly operation of each system and to calculate technical, economic and environmental performance parameters.The net present cost and the cost of energy are the two main parameters used to compare economic performances of the systems with both actual and expected costs in the medium term.A sensitivity analysis was carried out in order to appreciate the most important parameters influencing the economic performances of the systems and to define possible future scenarios of competitiveness between technologies.Emissions of CO₂ (the most important greenhouse gas) and other pollutants have been considered for an environmental benefits analysis.     

Analytical performance and economic evaluation of residential wind or wind and solar powered heating systems

A performance and cost model for a variety of wind powered space and water heating systems for single family residences is presented. In addition to wind powered systems, combined wind and solar systems are modeled and compared to conventional and solar only heating systems. Analytical results are presented for a site in Amherst, Massachusetts. System capital economic details include an itemized cost breakdown of the wind heating system components. The results demonstrate that wind powered systems are presently competitive with electric based heating systems and will be competitive with oil or gas systems in the future.     

Alternative power sources for residential air-conditioning systems

An integrated system which utilise three sources of energy for the purpose of airconditioning (i.e. heating and cooling) a residential building is considered. The system includes a control unit which determines (according to a built-in programmed logic) which energy source is to be used. The system's three power provisions are: (a) line electricity, (b) electric power generated by an appropriate wind turbine and (c) a hot water system heated by solar collectors. System requirements and operation were simulated by a computer program which calculated the air-conditioning load and the energy provisions throughout a twenty-four hour period. In winter operation, about 68 per cent of the required heating was supplied by solar heating and 32 per cent by wind-generated power and in summer operation, in a typical day, all the required cooling energy was provided by wind-generated power.