Evaluation of new active technology for low-energy houses

Using energy at low-quality levels opens up new possibilities for low-energy houses. Low-quality energy can be heat at a temperature that is close to that of its surrounding, and can be used, for example, to pre-heat ventilation air or domestic hot water. Pre-heating the incoming outdoor air reduces the need to heat ventilation and reduces the need for high-quality energy such as electricity or heat from a fire. This thesis investigates two such possible energy utilizations, the PV/T solar window and the hybrid ventilation system. They are very different in how they reduce the need for auxiliary energy in buildings, and they cover different fields of low-energy building technique. However, what they have in common is the concept of low-quality energy. The solar window produces both electricity and hot water. What the photovoltaic cells cannot utilize at the high-quality energy level is instead used to produce hot water. The hybrid ventilation system pre-heats the incoming ventilation air in the heat recovery system, thereby lowering the need for high-quality energy. The PV/T solar window comprises PV cells laminated on solar absorbers placed in a window behind the glazing. To reduce the costs of solar electricity, tiltable refl ectors were included in the design to concentrate solar radiation onto the solar cells. The refl ectors enable control of the amount of solar radiation transmitted into the building. The insulated refl ectors also reduce thermal losses through the window. The effects on the light distribution and the architectural implications are discussed in earlier studies (Fieber, 2005; Fieber et al., 2003; Fieber, Nilsson, & Karlsson, 2004) together with effects on the building when different strategies for controlling the reflectors are used. Long-term measurements were taken of the thermal- and electrical energy output from the solar window. A model was developed to simulate the electricity and hot water production, and the model was calibrated against the measured values from a prototype solar window installed in a laboratory and against a solar window built into a single-family building. The results from the simulation showed that the solar window produces about 35% more electrical energy per unit cell area than a vertical flat PV module. However, PV cells placed on the roof of the building would produce approximately 17% more electricity per unit cell area than the solar window. The simulations carried out on system level showed that installing a 16 m² solar window (glazed area) in a single-family building reduces the annual heating need by approximately 600 kWh. However, if the absorbers (5.06 m²) and PV cells (4 m²) from the solar window are installed separately on the roof instead of in the window, the annual heating need is reduced by a further 1100 kWh. A water-to-air heat exchanger was developed for use in naturally ventilated buildings. This requires that the pressure drop of the air is kept close to zero. The heat exchanger comprises solar collector absorbers soldered onto a manifold. Basic heat transfer equations were used in order to optimize the dimensions of the heat exchanger in terms of heat transfer and pressure drop. A laboratory measurement showed the temperature heat recovery rate to be 80% at component level. At the same time the pressure drop was 1 Pa for the designed air flow rate. System simulations were then carried out in order to investigate the impact for a building equipped with natural/hybrid ventilation with heat recovery. A brine-based heat recovery system enables the utilization of other energy sources such as ground collectors or waste water heat recovery units. A waste water heat recovery system was built into a single-family house, and was designed to supply energy to both domestic hot water and the ventilation system. The simulations showed that a typical single-family house can reduce the heating need by approximately 600-800 kWh annually, i.e. roughly 25% of the annual need for hot water, with waste water heat recovery. The simulations showed that using ground collectors for the ventilation system has limited effects on the heating need, so the main benefit is limited to lowering the risk of frost on the heat exchanger surface. The overall conclusion from an energy perspective is that the solar window performs poorly compared to standard solar energy components. The hybrid ventilation system with the developed heat exchangers has the potential to be an interesting ventilation system when building low-energy houses or when renovating residential buildings to improve energy effi ciency

Integrated Daylight and Energy Evaluation of Passive Solar Shadings in a Nordic Climate

Modern well-insulated and highly glazed buildings experience increased overheating, even in cold climates. The study focused on external and internal passive solar shadings on a south-oriented façade, having predetermined that external and internal shadings’ main function is solar heat gain and glare protection, respectively. A daytime-occupied office space with several external shading geometry variations was simulated using an integrated daylight and energy approach aided by Radiance, Daysim, and EnergyPlus within Grasshopper. The method involved preparation of daylight-driven lighting schedules, and glare-driven internal blinds operation schedules for each design scenario, which were further applied to annual energy simulations. The interdependence of light in visible and thermal form, its impact on the building performance, and the resulting occupant response to the changing indoor conditions are core to this study. The comparative nature of the study allowed to evaluate thermal and visual performance of fixed external shadings in Nordic climates. The chief study findings highlight the gross impact of internal shading operation on overall building performance and indoor comfort, and the holistic benefit of external solar protection that includes reduction of total energy use and improvement of occupants’ thermal and visual comfort

Assessing combined object and mutual shading on the performance of a solar field

To make well-informed decisions on the implementationof solar energy on roofs within the urban environment, anew method was developed and described that couldsupport such decision-making. This method takes both themutual shading and shading from external objects intoaccount. The method consists of the following six steps:1) construction of the scene, 2) performance of annualsolar irradiation analyses, 3) performance of statisticalanalyses, 4) calculation of the energy output, 5)calculation of the parameters payback time and profit, 6)displaying the results. Analysing the data by setting ownpreferences will make more informed decision-makingpossible. The outputs from the method are mapsindicating which locations surrounded by objects that areprofitable for PV installations. Alternatively, the mapscan be used to show payback times for the PV installation

Energy use of buildings in relation to occupancy rates

This paper presents basic data of the energy demand for district heating and plug loads logged by a building management system of an energy-efficient academic building located in Lund, Sweden. The data refers to the years 2019 and 2020 when occupancy varied significantly due to the Corona pandemic. The data shows that the building energy demand adapts poorly to fluctuating occupancy rates. With a possible increase of smart working in the future, building codes should account for more fluctuating occupancy rates in the modelling of the energy demand of buildings

Future possibilities of green walls in a medium sized Hungarian town: A case study of Kecskemét

Reflector edges, sharp acceptance angles and by-pass diodes introduce large variations in the electrical performance of asymmetrical concentrating photovoltaic/thermal modules over a short incidence angle interval. It is therefore important to quantify these impacts precisely. The impact on the electrical performance of the optical properties of an asymmet-rical photovoltaic/thermal CPC-collector was measured in Maputo, Mozambique. The measurements were carried out with the focus on attaining a high resolution incidence angle modifier in both the longitudinal and transversal directions, since large variations were expected over small angle intervals. A detailed analysis of the contribution of the diffuse radiation to the total output was also carried out. The solar cells have an electrical efficiency of 18% while the maxi-mum measured electrical efficiency of the collector was 13.9 % per active glazed area and 20.9 % per active cell area, at 25 °C. Such data make it possible to quantify not only the electrical performance for different climatic and operating conditions but also to determine potential improvements to the collector design. The electrical output can be increased by a number of different measures, e.g. removing the outermost cells, turning the edge cells 90°, dividing each receiver side into three or four parts and directing the tracking, when used, along a north-south axis

A need assessment for designing sustainable solar drying technology in Nepal and Bhutan

publishedVersio

Combined solar and membrane drying technologies for sustainable fruit preservation in low-income countries – prototype development, modelling, and testing

publishedVersionpublishedVersio