1,720,969 research outputs found
Assessment of Emerging Renewable Energy-based Cogeneration Systems for nZEB Residential Buildings
Full text linkNet Zero Energy Buildings (nZEB) imply reduced consumption by means of good insulation, passive strategies and highly efficient energy supply systems. Among others, micro cogeneration systems are considered as one of the system solutions with the highest potential to enable nZEB.These systems entail production of electricity and usable thermal energy (heat and/or cooling) to cover the energy demands of residential buildings, high energy efficiency levels and proximity of the energy source to the building. The concept of cogeneration is not new but the interest in smallscale cogeneration technologies based on renewable energy sources has increased tremendously in the last decade. A significant amount of experimental and modelling research has recently been presented on emerging technologies. In this paper, four main technologies are assessed: Fuel Cells (FC), Photovoltaic thermal (PV/T), solar thermal reversible heat pump /organic Rankine cycle (HP/ORC) and cogeneration solar Thermoelectric generators (TEG).This paper aims to give an overview of the state-of-the-art developments, discuss the fundamental and technical challenges facing commercial adoption and prospects of these technologies for use in single-family houses. A schematic of each technology, a graph comparing the technical characteristics and a radar chart contrasting the strengths and weaknesses of each technology in market diffusion are provided
Evaluation of the Energy and Comfort Performance of a Plus-Energy House under Scandinavian Summer Conditions
Full text linkThe thermal indoor environment and the energy performance of a plus-energy house are evaluated in the present study. The study case is EMBRACE, a two-storey dwelling of 59 m2 designed to host a single family. The building includes a semi-outdoor space covered by a glazed envelope, where the thermal environment is also investigated. The house is located in Nordborg, Denmark, where it is undergoing a year-round measurement campaign, of which are presented hereafter the results ranging from June to September 2015.The thermal environment proved to be satisfactory, with 58 and 15 hours above 26°C respectively in the first and ground floors. In general, the indoor climate was quantitatively better during the heating period (June and September) than in the cooling period (July and August). Overheating did not result to be an issue, which suggests that the installation of a cooling system could have been avoided. The energy balance proved to be positive, with a total of 1563 kWh of electricity produced by the photovoltaic cells installed on the roof, and 333 kWh used by the mechanical systems of the house during the four studied months. The air temperature in the semi-outdoor space frequently reached 2 to 3°C higher than outdoors, which increases the amount of comfortable occupancy hours in this space. The results suggest that the house could perform effectively as a plus-energy house during the whole year
Structures that Include a Semi-Outdoor Space:Part 2: Thermal Environment
Full text linkThe thermal environment of buildings with a second "skin" and semi-outdoor space is examined in the present study. A literature review was conducted on similar structures and only a few studies were found focusing on the thermal environment. Two different building case studies were chosen with different building and shield geometry, different levels of insulation but same shield material; Dome of Visions (DoV) and EMBRACE. Both buildings were modelled in IDA ICE 4.6.2 simulation software in order to assess the thermal environment of the building and assess how long the semi outdoor space of each building can be used by the occupants. The study was based on weather data for Copenhagen. In addition to the simulations, physical measurements were performed in DoV to assess the thermal environment in the semi-outdoor space. Since existing standards are not applicable for semi-outdoor spaces, an alternative method was followed with adjustable clothing level and three different tolerance levels. The semi-outdoor area of both buildings was found to provide more than double the comfortable occupancy hours compared to outdoors and the semi outdoor spaces can be roughly used for 45% of the year. Finally, the semi-outdoor space’s temperature in DoV was higher than the ambient throughout winter by at least 3ºC
Simulation Study of the Energy Performance of Different Space Heating Methods in Plus-energy Housing
Full text linkDue to a shortage of energy resources, the focus on indoor environment and energy use in buildings is increasing which sets higher standards for the performance of HVAC systems in buildings. The variety of available heating systems for both residential buildings and office buildings is therefore increasing together with the performance of the systems.This paper reports the results of a simulation study carried out using the commercially available building simulation software IDA ICE. The considered house was designed as a plus-energy house and it was located in Denmark. The dynamic building simulation model has been validated and calibrated with measurement data from the house in a previous study. The studied systems were radiant floor heating, warm-air heating through ventilation system and radiator heating. The energy performance of systems for achieving the same thermal comfort was compared.The effects of several parameters on system energy performance for each space heating solution were investigated; floor covering resistance of the floor heating system, having a heat recovery on the exhaust in the ventilation system, and different working temperature levels for the radiator heating. For all cases the heat source was a natural gas fired condensing boiler, and for the floor heating cases also an air-to-water heat pump was used to compare two heat sources. The systems were also compared in terms of auxiliary energy use for pumps and fans.The results show that the investigated floor heating systems had the best performance in terms of energy with a total energy saving of 23% compared to warm-air heating with heat recovery. It can furthermore be coupled to other heat sources than a boiler. The floor covering resistance of the floor heating system should be kept to a minimum to fully benefit from the low temperature heating potential since an increased floor covering requires higher average water temperatures in the floor loops and decreases the COP of the heat pump. The water-based heating systems required significantly less auxiliary energy input compared to the air-based heating system.Furthermore, the results show that low temperature heating systems, as seen in floor heating in this study, can contribute to achieving plus-energy targets by minimizing the energy use for space heating purposes while achieving necessary thermal comfort for the occupants
Energy Performance of Water-based and Air-based Cooling Systems in Plus-energy Housing
Full text linkEnergy use in buildings accounts for a large part of the energy use globally and as a result of this, international building energy performance directives are becoming stricter. This trend has led to the development of zero-energy and plus-energy buildings. Some of these developments have led to certain issues regarding thermal indoor environments, such as overheating.Thermal comfort of occupants should not be sacrificed for energy efficiency but rather, these should be achieved simultaneously. Although the priority should be to minimize the cooling demand during the design, this is not always achieved and cooling might be needed even in residential buildings.This paper focuses on the cooling operation of a detached, single-family house, which was designed as a plus-energy house in Denmark. The simulation model of the house was created in IDA ICE and it was validated with measurement data in a previous study. The effects of the cooling demand (internal vs. external solar shading), the space cooling method (floor cooling vs. air-cooling with ventilation system), and the availability of a nearby natural heat sink (intake air for the ventilation system being outdoor air vs. air from the crawl-space, and air-to-water heat pump vs. ground heat exchanger as cooling source) on the system energy performance were investigated while achieving the same thermal indoor conditions.The results show that the water-based floor cooling system performed better than the air-based cooling system in terms of energy performance and also regarding the energy use of auxiliary components such as pumps and fans. The total reduction in primary energy used was 31% compared to the air-based systems with intake air from outdoors.The integration of natural heat sinks into the cooling system of the house results in significant energy use reductions. The coupling of radiant floor with the ground enables to obtain “free” cooling, although the brine pump power should be kept to a minimum to fully take advantage of this solution. By implementing a ground heat exchanger instead of the heat pump and use the crawl-space air as intake air an improvement of 37% was achieved.The cooling demand should be minimized in the design phase as a priority and then the resulting cooling load should be addressed with the most energy efficient cooling strategy. The floor cooling coupled with a ground heat exchanger was shown to be an effective means to minimize the energy use for cooling purposes, and this can contribute to achieving zero-energy or plus-energy targets in future buildings
Numerical simulation of the effects of hanging sound absorbers on TABS cooling performance
Full text linkRecently there has been a considerable increase in the use of Thermally-ActiveBuilding Systems (TABS) in Europe as an energy-efficient and economical coolingand heating solution for buildings. However, this widespread solution requires large uncovered hard surfaces indoors, which can lead to a degradation of the room acoustic comfort. Therefore, challenges arise when this system has to be combined with acoustic requirements.Soffit-hanging sound absorbers embody a promising solution. This study focuses on quantifying their impact on the cooling performance of TABS, assessed by means of the cooling capacity coefficient of the ceiling deck. The influence of different ceiling coverage ratios (0-30-45-60 and 80%) as well as the influence of the distance at which the absorbers are placed is studied by numerical simulations using a new, specially-developed TRNSYS Type. Tests were performed in a test room simulating a two-person office of 20 m2, with a typical cooling load of 42 W/m2. The results show that covering 60% of the ceiling surface with sound absorbershanging at 300 mm from the ceiling active deck is expected to reduce the coolingcapacity coefficient of TABS by 15.8%. This drops to 25.4% with a coverage of 80%. The presence of acoustic panels also affects the thermal comfort: the operative temperature in the room increases by 0.9°C in the former case and up to 1.6°C in the latter. Results also show that comfort ventilation supplied to the enclosure has a considerable influence on the thermal conditions in the room; if the ventilation is removed, then the operative temperature increases by 1.8°C for a 60%-covered ceiling
Validation of a numerical model of acoustic ceiling combined with TABS
Full text linkThermally-Active Building Systems (TABS) have proven to be an energy-efficientand economical cooling and heating solution for commercial buildings. However,acoustic comfort is often jeopardized in such buildings, due to the thermalrequirements of the system. More knowledge is required to understand to whichextent a layer of hanging sound absorbers will impede the heating and coolingperformance of the system, and how this translates on the thermal comfort for theoccupants.In order to address these issues, this study focuses on validation of a new TRNSYScomponent (Type Ecophon Acoustic Elements) developed to simulate partiallycovered suspended ceilings such as hanging sound absorbers. The tool is validated by numerically modelling a set of similar experiments carried out in full-scale by a previous study. For this, a total of 12 scenarios from two case studies have been modelled, with varying suspended ceiling coverage ratios, type of suspended ceilings, internal heat gains and TABS water supply temperatures.The results obtained from the simulations are very close to the experimental results. The first set of measurements analyzed the effect of the above-mentioned parameters in the heat flow from TABS; the difference between the numerical results and measurements is in the range of -6.9% to +5.2%. The second evaluates the impact on TABS cooling capacity coefficient and room temperatures. The simulated cases led to absolute differences +4.3% higher in average for the cooling capacity coefficient. The operative temperature in the room is particularly well estimated, with a maximum relative difference of +0.3°C in total of five scenarios
Control of Single-room Ventilation with Regenerative Heat Recovery for Indoor Climate and Energy Performance
Full text linkThe Danish government will seek energy-efficiency improvements to meet their targeted aims. Single-room ventilation with heat recovery allows simple installation through the façade and may be broadly deployed in apartments. Danish building regulations require greater than 80% heat recovery in new constructions and will soon require 85%. The development of single-room ventilation units may aim for these requirements as a result. The exhaust temperatures in highly efficient heat exchangers may approach outdoor levels. The cold exhaust cannot contain ample moisture, so vapour will condense on the heat exchanger. Available literature suggests that uncoated rotary heat exchangers transfer this condensate to the supply air, so the drying capacity of the ventilation system may be severely limited. This could raise indoor relative humidities to unsafe levels, which could promote the growth of dust-mites and mould. Controls may increase drying capacity by increasing ventilation airflow, but this may not be sufficient to limit moisture-related risks. This research investigated the added demand-control measure of reducing variable heat recovery to increase drying capacity when using an uncoated rotary heat exchanger in single-room ventilation. Simulations demonstrated that increased airflow sufficiently lowered the relative humidity in living rooms and bedrooms during most hours of the year. Decreased heat recovery was only necessary for a limited number of hours to maintain safe indoor relative humidities in these rooms, and the overall average reduction in heat recovery was less than 3%. The combined measures only succeeded in living rooms and bedrooms, and the results confirmed that rotary heat exchangers should not be used in kitchens or bathrooms, where moisture risks may be unavoidable
Hot water tanks:How to select the optimal modelling approach?
No full textThere is a rising interest for optimal use of thermal energy storages (TES) in buildings for load shifting in demand response programs and to improve energy efficiency. In this context, a state of the art of the different methods for simulating sensible TES is performed. Mathematical equations which describes the processes occurring in the storage are difficult to solve without considerable simplifying equations. That is the reason why a large number of storage models have been developed in the last decades. Few studies compare the different modeling approaches and their respective advantages and limitations. A review of the literature is thus performed and focuses on eight different modeling approaches. The comparison is performed in terms of computational time, accuracy and application. A tree of selection is proposed to select the optimal TES modeling approach for a given application
Analysis of the occupants’ behavior related to natural ventilation
Full text linkThe real energy performance of buildings depends both upon deterministic aspects (building'sphysics and engineering systems) and probabilistic aspects such as weather and occupantbehavior. Occupant behavior is usually not directly considered when calculating the expected energy performance of buildings. In fact, field test studies all over the world have shown discrepancies between expectation and real energy performances of buildings. This gap could be bridged, by embedding stochastic occupants’ behavior models within buildings’ energy performances simulation software. Within this work, an established method to analyze the probability of a state change of the windows, based on logistic regression, was applied to monitored data (measured each minute) from two refurbished residential buildings. The weather as well as the five rooms of each of the 60 apartments located in the buildings were monitored in terms of indoor environmental quality and window operation for four years. The aim of this work is the investigation of the drivers leading occupants to open and close windows.The evaluation of the 300 windows showed: the two most common drivers leading to the opening action were the time of the day and the carbon dioxide concentration in the room. The two most common drivers leading to the closing action were: the daily average outdoor temperature, and the time of the day
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