Similar Energy Savings Research Articles

Energy assessment of advanced and switchable windows for less energy-hungry buildings in the UK

Globally, greenhouse gas emissions from the operational phase of buildings are significantly contributing towards climate change. Global and national efforts, through the Sustainable Development Goals and the UK's 2050 targets, aim to reduce these emissions with net zero energy buildings (NZEBs). A building's glazing plays a significant role in overall building energy consumption due to their traditionally ‘leaky’ nature. This study utilises experimental data from test cells and the International Glazing Database to evaluate the performance of advanced and smart/switchable windows on an existing low energy building (LEB) situated in north Wales, UK, as a step towards making the modelled building a NZEB. A number of glazing constructions were considered in this work; advanced window – vacuum, aerogel, vacuum-aerogel and smart window – PDLC, PDLC-aerogel and PDLC-vacuum, in their fixed and switching states. Results revealed that PDLC-vacuum offered the greatest reduction in building energy, yielding a theoretical U-value of 0.810–0.831 W/m2K and a G-value of 0.257–0.455. Despite its successes, it was notably susceptible to window orientation and window-to-wall ratio. Vacuum and aerogel glazing both offered similar energy savings, with the latter prone to overheating, stressing cooling loads. These advanced windows offered differing daylighting potential with vacuum able to meet 78% of useful daylight illuminance compared to aerogel's 60%. Given the prioritisation trilemma between heating, lighting and cooling needs of a building, PDLC-vacuum presents the best step towards a NZEB. As such, further efforts should concentrate on the development of a PDLC-vacuum window, maintaining smart window functionality and achieving low U-value for cold climates.

A machine-learning-based event-triggered model predictive control for building energy management

Model predictive control (MPC) for building energy management has exhibited a huge potential for largely cutting down energy use and improving human comfort. However, the high demand for computational power for solving the optimization is challenging the widespread deployment of MPC in real buildings. Typical MPC employs a time-triggered mechanism (TTM) that runs optimization recurrently at each time step without considering the necessity, which could cause excessive computation resource usage. This paper proposes an event-triggered mechanism (ETM) that only runs optimization when triggering events occur. Contrary to conventional ETMs that only considers the current information (e.g., room conditions), the ETM proposed is based on a cost function that covers the past, current, and future information. Based on the proposed ETM, a machine-learning-based event-triggered model predictive control (ETMPC) system that optimizes both building energy efficiency and thermal comfort is developed. The developed ETMPC system is then employed for air-conditioning control for performance evaluation through simulations. The control performance of the proposed ETMPC is compared to an MPC employing TTM and a common thermostat. Compared to the MPC employing TTM, the proposed ETMPC reduced the computational load in terms of the number of optimization runs by 77.6%–88.2%, meanwhile, achieving similar energy savings (more than 9.3% energy saving over the thermostat) as the MPC employing TTM does (9% energy saving over the thermostat). With the significant reduction of computational load, the ETMPC achieves similar thermal comfort performance as the MPC employing TTM does, and it is significantly better over the thermostat.

Computationally Efficient Hierarchical Model Predictive Control Via Koopman Operator

Abstract Combined powertrain and velocity optimization can achieve significant energy efficiency improvements. However, due to the multitime scales in the system, the optimization is performed hierarchically and by separating time scales. To enforce state constraints, iteration between controller is introduced, for example, using Lagrange multipliers as metric for constraint violation. In this paper, an extension of the Koopman operator theory is presented with to obtain a data-driven approximation of the multipliers' behavior hence eliminating the need for iterations. Because the evolution of the Lagrange multipliers is the result of a fast dynamics optimization problem, and not the response of a nonlinear dynamical system, a novel technique in which the Lagrange multipliers are interpreted as a dynamic system is presented here. The approximate Koopman linear system is then derived using extended dynamic mode decomposition and it is integrated with the slow dynamic optimization. Results show that the Koopman augmented controller, which is solved as one single optimization, meets state and input constraints and achieves similar energy savings compared to an iterative approach.

Impact of energy efficiency and decarbonisation policies for buildings: A comparative assessment of Austria and Switzerland

Reducing heat demand and decarbonising heat supply are essential if countries have to meet net zero emission targets. This paper presents a comparative assessment of the impact of energy efficiency polices for heat demand reduction and heat decarbonisation in the buildings sector (2000–2017) in Austria (AT) and Switzerland (CH). It assesses the heat demand, heat supply, effect of different factors on changes in total heat consumption, impact of energy policies that provide public subsidies for heating and compares the effectiveness of different policies and measures. The assessment shows that renewable heat supply in residential buildings has to be increased by about 150 PJ (130% increase from 2017) in AT by 2040 and by 120 PJ (210%) in CH by 2050, which is challenging. Energy savings from improvements in energy efficiency from 2000 to 2017 are 83 PJ in AT and 97 PJ in CH, but these are largely offset by increase in activity and wealth effects thereby resulting in small changes in final heat consumption. The average (2014–2017) annual public subsidies for heating were about 2500 million Euros and 310 million CHF and contributed to 51% and 36% share of energy saving in AT and CH respectively. Both countries achieved similar energy savings, albeit following different policy approaches. Public subsidies for heating are an important policy instrument in AT but have lower cost effectiveness. On the other hand, CH minimised the use of public spending by deploying other policies and funding measures that leveraged private investment to achieve similar energy savings.

Energy and cost savings with continuous low temperature heating versus intermittent heating of an office building with district heating

Future low-temperature district heating systems (LTDH) require supply and return temperatures as low as 55 °C and 25 °C, respectively. In this direction, the use of night setbacks in heating of office buildings is a problem. This article investigated in a typical office building with large distribution system by tests and simulations the energy and cost savings by changing the control of the heating system from a continuous high-temperature operation either to a high-temperature intermittent heating or to a continuous low-temperature operation. Both strategies secured thermal comfort and resulted in similar energy savings of approximately 11% in the specific building. The reduction of the return temperature was higher under continuous low-temperature operation, resulting in additional cost savings due to a motivation tariff for low-temperature operation used in Denmark. As a result continuous low-temperature operation can achieve the highest total cost reduction for heating of 23.1%. Even if the results refer to the specific building, continuous low-temperature heating may result in significant energy savings in other buildings with large distribution systems. Moreover, implementing motivation tariffs towards LTDH may provide additional economic incentives. Therefore, it is interesting to investigate continuous low-temperature heating in each building and quantify the cost and energy savings towards LTDH.

On-line motion profile optimization for reciprocating mechanisms

Reciprocating mechanisms are widely used in industry because a complex movement is achieved by a simple rotation of the driven axis. Given the tendency to evolve towards more energy-efficient machines and flexible production, motion profile optimization offers a cost-effective solution as it results in large energy savings without any hardware adaptions. However, the existing optimizers are used off-line because the position-dependent parameters such as load torque and inertia of the system model must be known in advance. When the actual machine differs from the model, or when parameters change during operation due to process flexibility, the off-line determined motion profile is no longer optimal and results in unnecessary energy consumption.This paper therefore presents an on-line approach in which the varying inertia is estimated on the actual machine and used for updating the motion profile. The sliding discrete Fourier transform is proposed for real-time estimation and a gradient-based algorithm combined with Chebyshev polynomials is proposed for on-line optimization. Experimental validation on an industrial pick-and-place unit proves that the presented method leads to similar energy savings as off-line optimizers, but without prior knowledge of the parameters, and is moreover capable of handling mass changes during operation.

Operational feasibility of a hybrid roof insulation system with bamboo and vegetation: An experimental study in tropical climatic conditions

A significant portion of the global energy is consumed for creating thermally comfortable building interiors. Insulating the roof has been identified as an effective measure in addressing the issue. Bamboo-transversed is a novel roof insulation material which has proven to yield significant energy saving. This paper presents the results of an experimental study conducted to compare the Life Cycle Operational Performance of polystyrene insulation, bamboo insulation, rooftop vegetation and hybridizing vegetation with polystyrene and bamboo. Results indicated that Polystyrene is a better thermal insulator than bamboo producing 12% reduction of annual energy consumption in comparison with that of 8% of bamboo. When hybridized with rooftop vegetation, both produce similar energy savings around 13–14%. However, polystyrene produced a reduction of 5% in the 50-year Life Cycle Cost analysis, in which bamboo produced 3% while the vegetated cases producing only 2% saving. Bamboo was proven to be paying back its initial investment in 0.9 years, while the same was 1 year for polystyrene. Hybridized insulated system was proven to take 2–4 years to pay back the initial investment. Hence, it was proven that hybridizing rooftop vegetation with bamboo does not boost the operational performance sufficiently to justify its investment.

Design and Performance Analysis of Segmented Wireless Sensor Networks

This article presents the design and a theoretical performance analysis of a segmented wireless sensor network whose sink node is equipped with a switched-beam smart antenna. We compare the performance of the proposed segmented system against that of a conventional wireless sensor network (WSN) where all the nodes contend to access the medium in order to identify the system's conditions where the use of a smart antenna is justified. Our results show that the segmented network outperforms the WSN by reducing the cluster formation time in up to 25 with similar energy savings.

Building Energy Management Using Increased Thermal Capacitance and Thermal Storage Management

This study simulates an increased thermal capacitance (ITC) and thermal storage management (TSM) system to reduce the energy consumed by air conditioning and heating systems. The ITC/TSM is coupled with phase change materials (PCM), which enable tank volume reduction. The transient energy modeling software, the Transient System Simulation Tool (TRNSYS), is used to simulate the buildings’ thermal response and energy consumption, as well as the ITC/TSM system and controls. Four temperature-controlled operating regimes are used for the tank: building shell circulation, heat exchanger circulation, solar panel circulation, and storage. This study also explores possible energy-saving benefits from tank volume reduction such as losses associated with the environment temperature due to tank location. Three different tank locations are considered in this paper: outdoor, buried, and indoor. The smallest tank size (five gallons) is used for indoor placement, while the large tank (50 gallons) is used either for outdoor placement or buried at a depth of 1 m. Results for Atlanta, Georgia show an average 48% required energy decrease for cold months (October–April) and a 3% decrease for warm months (May–September) for the ITC/TSM system with PCM when compared with the reference case. A system with PCM reduces the tank size by 90% while maintaining similar energy savings.

Effects of intensification on process features and control properties of lignocellulosic bioethanol separation and dehydration systems

Separation and dehydration process is a key step to reduce the total production cost of lignocellulosic bioethanol. In the earlier work (Torres-Ortega and Rong, 2016), we have obtained new intensified systems for lignocellulosic bioethanol separation and dehydration through dividing wall columns, which have considerable reduction to both capital and energy costs. This work presents the analysis of process features and control properties of the intensified systems with similar capital reduction and energy savings. The control properties were based on singular value decomposition (SVD) and dynamic performances under mild disturbances and changes of set point in Aspen Dynamics V8.8. The control properties and dynamic responses of the intensified separation systems were examined against the reference system for their structural changes during intensification by thermal couplings and column section recombination. The simultaneous analysis of process feature changes by intensification and their control properties achieved the intensified systems with both cost savings and competitive control properties.

Enhanced Thermal Performance of Mosques in Qatar

Qatar has an abundance of mosques that significantly contribute to the increasing energy consumption in the country. Little attention has been given to providing mitigation methods that limit the energy demands of mosques without violating the worshippers’ thermal comfort. Most of these researches dealt with enhancing the mosque envelope through the addition of insulation layers. Since most mosque walls in Qatar are mostly already insulated, this study proposes the installation of shading on the mosque roof that is anticipated to yield similar energy savings in comparison with insulated roofs. An actual mosque in Qatar, which is a combination of six different spaces consisting of men and women’s prayer rooms, ablutions and toilets, was simulated and yielded a total annual energy demand of 619.55 kWh/m2. The mosque, whose walls are already insulated, yielded 9.1% energy savings when an insulation layer was added to its roof whereas it produced 6.2% energy savings when a shading layer was added above this roof. As the reconstruction of the roof envelope is practically unrealistic in existing mosques, the addition of shading to the roof was found to produce comparable energy savings. Lastly, it was found that new mosques with thin-roof insulation and shading tend to be more energy-efficient than those with thick-roof insulation.

Quantifying the benefits of a building retrofit using an integrated system approach: A case study

Building retrofits provide a large opportunity to significantly reduce energy consumption in the buildings sector. Traditional building retrofits focus on equipment upgrades, often at the end of equipment life or failure, and result in replacement with marginally improved similar technology and limited energy savings. The Integrated System (IS) retrofit approach enables much greater energy savings by leveraging interactive effects between end use systems, enabling downsized or lower energy technologies. This paper presents a case study in Hawaii quantifying the benefits of an IS retrofit approach compared to two traditional retrofit approaches: a Standard Practice of upgrading equipment to meet minimum code requirements, and an Improved Practice of upgrading equipment to a higher efficiency. The IS approach showed an energy savings of 84% over existing building energy use, much higher than the traditional approaches of 13% and 33%. The IS retrofit also demonstrated the greatest energy cost savings potential. While the degree of savings realized from the IS approach will vary by building and climate, these findings indicate that savings on the order of 50% and greater are not possible without an IS approach. It is therefore recommended that the IS approach be universally adopted to achieve deep energy savings.

Bare-metal reservation for cloud: an analysis of the trade off between reactivity and energy efficiency

In this work, we investigate factors that can impact the elasticity of bare-metal resources. We analyse data from a real bare-metal deployment system to build a deployment time model, then use it to determine how long it takes to deliver requested resources to cloud users. Simulation results show that reservations can help reduce the time to deliver a provisioned cluster to its customer, by enabling machines to be started in advance or be kept powered on when there are impending reservations. Such an approach, when compared to strategies that switch-off idle resources, shows that similar energy savings can be achieved with much smaller impact on the time to deliver the provisioned clusters.

Performance Comparison of Destratification Fans for Large Spaces

Ceiling fan is proven to have a beneficial effect on increasing air velocity and reducing temperature stratification and thus saving energy for high ceiling applications. Studies show that the velocities produced by large diameter, ceiling mounted fans do not produce a negative or positive effect on human comfort. Recently, smaller, high velocity fans have been introduced to the market as an alternative to these large diameter fans that provides similar energy savings due to reduced destratification, while still not moving the air fast enough to cause human discomfort, though these products have been studied less. This study simulates and compares the performance of both large and small diameter fans using a validated computational fluid dynamics (CFD) model. Two different types of destratification fans are investigated for their performance in destratifying the air temperatures in warehouse style retail stores. A portion of a retail store is used as a base to create the test environment. Simulations show that the small diameter high speed fan (SDHSF) is very good at bringing a well-mixed column of air all the way to the floor, but the spaces without a fan directly overhead are hardly affected. The large diameter low speed fans (LDLSF) are able to mix nearly the entire space, though they created uncomfortable drafts near head height. Between these two fans, the LDLSF is more successful at destratifying the entire space, though the SDHSF is better at only destratifying a specific, smaller area. Varying the speed of the LDLSF also allows for successful destratification, while maintaining acceptable draft velocities.

Developing long-term strategies to reduce energy use and CO2 emissions—analysis of three mitigation scenarios for iron and steel production in China

We perform a scenario analysis of three strategies for long-term energy savings and carbon dioxide (CO2) emission reductions in iron and steel production in China, using a linear optimization modeling framework industry sector energy efficiency modeling (ISEEM). The modeling includes annual projections for one base scenario representing business-as-usual (BAU) and three additional scenarios representing different strategies to reduce annual energy use and CO2 emissions from 2010 to 2050. Specifically, the three scenarios for cost-optimization modeling include changing the production share (PS), predefining emission reduction (ER) target, and stipulating carbon emission pricing (CP), respectively. While the three strategies are projected to result in similar annual energy savings by approximately 15 % compared to that of the BAU scenario in year 2050, the carbon emission pricing strategy brings about the highest annual energy savings in the medium term (e.g., 2025). In addition, adopting carbon emission pricing strategy will result in the highest emission reduction from BAU with much higher costs, i.e., by 20 % in 2025 and 41 % in 2050, while adopting either PS or ER strategies will result in a moderate level of emission reduction from BAU, i.e., by approximately 4 % in 2025 and 14 % in 2050. The analysis of China’s national strategies to reduce energy use and emissions provides important implications for global mitigation strategies.

Effect of climatic conditions on energy consumption in direct fresh-air container data centers

To examine the use of fresh-air cooling to reduce energy consumption in container data centers (CDCs) regardless of location, a prototype fresh-air-cooled CDC was constructed in a Tokyo suburb, and a year-long operating test was conducted. Fresh-air cooling of information technology (IT) equipment does not require energy for air conditioning, and can be operated at reduced cost and energy usage. However, the characteristics of fresh-air change throughout the year, which would make it difficult to maintain inside temperature and humidity of a server room at the set points. Also, some geographic locations may be unsuitable for CDCs cooled directly by fresh-air. In addition to fresh-air cooling, CDCs at these locations have been equipped with supplemental air-conditioning units such as air conditioners to control the internal temperature and humidity. To reduce energy usage, it is desirable to use energy conservation methods such as evaporative cooling and waste heat from IT equipment as supplemental air-conditioning because they can be more feasible in compact facilities than conventional air conditioners. Although data centers (DCs) that supplement fresh-air cooling with these air-conditioning methods are currently in operation, it is not clear whether these methods can be applied in any location regardless of the climatic conditions. Depending on the application, in particular, it is necessary to set up CDCs in urban suburbs, because large access latency for users may be required. To examine these issues, a fresh-air-cooled CDC was set up and evaluated for one year in a Tokyo suburb, under different climate conditions of existing fresh-air-cooled DCs. The results confirmed that evaporative cooling and the use of waste heat from IT equipment were sufficient to support direct fresh-air cooling even when the characteristics of fresh-air were outside the range of acceptable server settings. Moreover, this CDC realized an annual energy savings of 20.8% compared with the centers that use conventional air conditioning. Furthermore, the power usage effectiveness of this CDC was found to be 1.058 from the energy usage and was compared with that of existing direct fresh-air-cooled DCs which is located in the urban suburbs. The CDC near Tokyo exhibited similar energy savings to other DCs.

Effect of the roller blinds on heat losses through a double-glazing window during heating season in Central Europe

Heat losses through window glazing are unavoidable but can be significantly suppressed during night hours using roller blinds. Results of calculations of the effect of roller blind on heat losses from central part of double-glazing window during the night in the heating season in Central Europe are presented. The hourly meteorological data for the outdoor air temperature, wind velocity and sky temperature are used. It is demonstrated that internal roller blinds can save about 33% and external roller blinds about 45% of heat losses through a central part of the double-glazing window at the blind to glass pane spacing above 20mm. The similar relative energy savings were obtained for the double-glazing window having low emissivity coatings, i.e. for the emissivity ɛ=0.20 the internal and external roller blind can save about 29% and 44% respectively.

Minimum-Energy Cooperative Routing in Wireless Networks with Channel Variations

This paper considers the problem of finding minimum-energy cooperative routes in a wireless network with variable wireless channels. We assume that each node in the network is equipped with a single omnidirectional antenna and, motivated by the large body of physical layer research indicating its potential utility, that multiple nodes are able to coordinate their transmissions at the physical layer in order to take advantage of spatial diversity. Such coordination, however, is intrinsically intertwined with routing decisions, thus motivating the work. We first formulate the energy cost of forming a cooperative link between two nodes based on a two-stage transmission strategy assuming that only statistical knowledge about channels is available. Utilizing the link cost formulation, we show that optimal static routes in a network can be computed by running Dijkstra's algorithm over an extended network graph created by cooperative links. However, due to the variability of wireless channels, we argue that a many-to-one cooperation model in static routing is suboptimal. Hence, we develop an opportunistic routing algorithm based on many-to-many cooperation, and show that optimal routes in a network can be computed by a stochastic version of the Bellman-Ford algorithm. We use static and opportunistic optimal algorithms as baselines to develop heuristic link selection algorithms that are energy efficient while being computationally simpler than the optimal algorithms. We simulate our algorithms and show that while optimal cooperation and link selection can reduce energy consumption by almost an order of magnitude compared to non-cooperative approaches, our simple heuristics achieve similar energy savings while being computationally efficient as well.

Biomechanical pulping of softwood with enzymes and white-rot fungus Physisporinus rivulosus

Manufacturing of mechanical pulp is a very energy-consuming process. Application of enzymes to wood chips is an attractive alternative to decrease energy demand in the refining process and to introduce novel functional properties on fibers. A variety of enzymes were applied to plug screw compressed chips in order to improve enzyme access onto wood fibers. Consumption of refining energy was examined with a laboratory low-intensity refiner after 6-h enzyme treatments with manganese peroxidase (MnP), laccase-mediator system, pectinase, or a cellulase mixture. The results were compared to biopulping with the white-rot fungus Physisporinus rivulosus. Specific energy consumption resembling the first-stage refining was measured, and chemical modifications on the fibers were evaluated. The specific energy consumption in the refining of Scots pine wood chips treated with MnP decreased about 11% when compared to the untreated reference chips, and in the refining of Norway spruce somewhat less, 6%. Fungal pre-treatment resulted in similar energy savings on spruce as MnP treatment did. Hydrolytic enzyme and MnP treatments on pine resulted in similar energy savings on average, though the hydrolytic enzyme treatments at their best reached to about 15% energy savings. Polyelectrolyte titration indicated increased surface charge in the case of MnP treated pine pulps, which were refined to low freeness values (CSF 85–130 ml). Most laboratory handsheet properties, i.e. strength, light scattering and opacity, were improved at given specific refining energy. Only brightness was slightly decreased. The MnP treatment seems to be a promising concept for energy savings and fiber surface modifications.

Energy performance of wood-burning cookstoves in Michoacan, Mexico

There have been few detailed assessments of the actual impacts of improved stove interventions in rural communities, although many improved stove projects have reported overall efficiencies from tests in simulated kitchens using water-boiling tests (WBTs). This paper presents an integrated energy evaluation of the Patsari cookstove, an efficient wood-burning cookstove developed in Mexico that has recently obtained international recognition, in comparison to traditional cookstoves in rural communities of Michoacan, Mexico. The evaluation uses three standard protocols: the WBT, which quantifies thermal efficiency and firepower; the controlled cooking test (CCT), which measures specific energy consumption associated with local cooking tasks, and the kitchen performance test (KPT), which evaluates the behavior of the stoves in-field conditions and estimates fuel savings. The results showed that the WBT gave little indication of the overall performance of the stove in rural communities. Field testing in rural communities is of critical importance, therefore, in estimating the benefits of improved stoves. In the CCT for tortilla making, the main cooking task in Mexican rural households, Patsari stoves showed fuelwood savings ranging from 44% to 65% in relation to traditional open fires ( n=6; P<0.05). These savings were similar in magnitude to the average energy savings from KPT before and after Patsari adoption of 67% ( n=23; P<0.05) in rural households exclusively using fuelwood. Similar energy savings of 66% for fuelwood and 64% for LPG, respectively, were also observed in households using mixed fuels. With sound technical design, critical input from local users and proper dissemination strategies, therefore, improved stoves can significantly contribute to improvements in the quality of life of rural people with potential benefits to the surrounding environment.