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In the present study, a zero-dimensional thermal model has been developed to analyze a novel low concentration photovoltaic-thermal (CPVT) collector. The model has been developed by driving heat transfer and energy balance equations for each part of the collector and then solving all the equations simultaneously. Moreover, a Monte-Carlo ray-tracing software has been used for optical stimulations of the parabolic trough solar collector. The novel CPVT collector has been experimentally tested at Gavle University (Sweden) and the model has been validated against the experimental results. The primary energy saving equivalent to the thermal-electrical power cogeneration of the CPVT collector has been determined. The effect of glass cover removal, heat transfer fluid (HTF) inlet temperature and mass flow rate on the collector performance has been investigated. The optimum HTF mass flow rates of the collector for maximum electrical yield and overall primary energy saving were determined under specified operating conditions by considering the pump consumption. The effect of mean fluid temperature on the thermal and electrical efficiencies has been studied and the characteristic equation of the thermal efficiency has been obtained. The thermal and electrical peak efficiencies of the collector have been found to be 69.6% and 6.1%, respectively.

In this study, the performance of different cooling technologies from energy and economic perspectives were evaluated for six different prototype residential Nearly Zero Energy Buildings (NZEBs) within a planned future city district in central Sweden. This was carried out by assessing the primary energy number and life cycle cost analysis (LCCA) for each building model and cooling technology. Projected future climate file representing the 2050s (mid-term future) was employed. Three cooling technologies (district cooling, compression chillers coupled/uncoupled with photovoltaic (PV) systems, and absorption chillers) were evaluated. Based on the results obtained from primary energy number and LCCA, compression chillers with PV systems appeared to be favorable as this technology depicted the least value for primary energy use and LCCA. Compared to compression chillers alone, the primary energy number and the life cycle cost were reduced by 13%, on average. Moreover, the district cooling system was found to be an agreeable choice for buildings with large floor areas from an economic perspective. Apart from these, absorption chillers, utilizing environmentally sustainable district heating, displayed the highest primary energy use and life cycle cost which made them the least favorable choice. However, the reoccurring operational cost from the LCCA was about 60 and 50% of the total life cycle cost for district cooling and absorption chillers, respectively, while this value corresponds to 80% for the compression chillers, showing the high net present value for this technology but sensitive to future electricity prices.

This chapter investigates the implementation of district cooling systems by exploring several research studies reported in the literature. The topics addressed include typologies and design parameters, benefits and limitations, applications of the system, and the technology readiness level. District cooling systems are generally regarded as cost-efficient and environmentally friendly solutions. One might think that district cooling is only a solution for areas with a very warm climate. However, based on the reported results of the surveyed studies, the number of operating district cooling systems has increased over the years, with the Scandinavian countries taking the lead in this market within European countries. Implementation of these systems concluded reduction in primary energy and electricity use, they also proved to be an environmentally efficient way.

Energy use on heating, ventilation and air conditioning (HVAC) accounts for about 50% of building energy use. To have a sustainable built environment, energy efficient ventilation systems that deliver good indoor environmental quality are needed. This study evaluates the cooling energy saving potential of a newly proposed ventilation system called Intermittent Air Jet Strategy (IAJS) and compares its performance against a mixing ventilation (MV) system in a classroom located in three cities with different climates, Singapore with ‘hot and humid’, Ahvaz with ‘hot and dry’ and Lisbon with “moderate” climate. The results show a significant reduction of cooling energy need and flexibility in control strategies with IAJS as a primary system in hot and humid climates like Singapore. Hot and dry climate with short cool periods like Ahvaz show possible application and considerable energy savings with IAJS as a primary system under optimized variable setpoints, but moderate climates have an increased risk of occupant discomfort likely due to increased draft especially during the cool season. Thus, IAJS as a secondary system that operates only during cooling season may be conducive for moderate climates like Lisbon. Additionally, the results show that supply fan energy savings can also be realized if well implemented.

Temporarily enhanced natural ventilation of indoor environments can be achieved by opening windows and/or doors, i.e. airing. In this study, wind driven airing rate through doors was measured by tr...

The movement of people and other objects indoors may affect airflow patterns and velocities near local exhaust ventilation hoods, and consequently has influence on the hoods’ ability to remove locally emitted contaminants and on ventilation energy requirements. In this study, such disturbance effects have been studied experimentally and numerically, with the movements consisting of a human-sized plate, cylinder and detailed manikin, respectively, making back-and-forth movements near an exhaust hood. In the experimental part of the study, a 3-D sonic anemometer was used to measure air velocity in front of the hood opening. The numerical simulations used dynamic mesh to handle object movements. The numerical results were validated against the experimental ones and yielded supplementary results on the air flow field. The results show that the turbulence produced by the objects movements included marked air velocity peaks – both assisting and impeding the suction flow – in the near field of the exhaust hood. The generated turbulence, and particularly those peaks, proved substantially larger in the case of plate movement than with cylinder and manikin movement. Overall the results indicate that a moving cylinder represents human movement better than a moving plate, and thus that it’s better to use a cylinder in some test standards that now stipulate a plate as moving object. A Percentage of Negative Velocity (PNV) parameter was introduced for assessing the capture efficiency of the local exhaust system. The PNV represents the percentage of time that the air flow is directed away from the exhaust hood in an imagined point of contaminant release. The study includes test cases where the PNV values were significantly above zero, suggesting a strong effect on the capture efficiency of the exhaust hood. Human induced turbulence that cause such reverse air flows and overall impedes hood suction may be counteracted by enhanced exhaust flow rate, but then at higher energy consumption.

In churches, intentional airing may be a measure to evacuate temporarily high levels of contaminants, emitted during services. Crucial contaminants include moisture and other emissions that may deteriorate and/or soil painted surfaces and other precious artefacts. Most old churches do not have any mechanical ventilation system or any purpose provided openings for natural ventilation, but the ventilation is governed by air infiltration. Enhanced airing may be achieved by opening external windows or doors. Thus, models provided in energy simulation programs should predict this kind of airflows correctly, to get a proper estimation of the total energy use. IDA indoor climate and energy (IDA-ICE) simulation program is examined here and its model for airflow through large vertical openings is investigated. Moreover, field measurements were performed for airing rate in a historical church. The simulated single-sided flows were of the same magnitude of the measured ones, but the effect of wind direction was less...

Ventilation through open doors is a simple way to temporarily enhance ventilation of indoor spaces, with the purpose to evacuate indoor air pollutants or to adjust the indoor temperature. In church ...

Validated by wind tunnel data, this study numerically investigates the integrated impacts of wind and thermal buoyancy on urban turbulence, ventilation and pollutant dispersion in full-scale 2D deep street canyons (aspect ratio AR = H/W = 3 and 5, W = 24 m). Isothermal urban airflows for such deep street canyons can be Reynolds-number-independent when reference Reynolds number (Re) exceeds the critical Re (Rec~106,107 when AR = 3, 5), i.e. AR = 5 experiences two main vortices and one-order smaller NEV* (~10−3, the normalized net escape velocity) than AR = 3 with a single main vortex (NEV*~10−2). With sufficiently large Re (Re > Rec) and the same air-wall temperature difference (Ri = 2.62, 4.36 when AR = 3, 5), four uniform wall heating patterns were considered, including leeward-wall heating (L-H), windward-wall heating (W–H), ground heating (G-H), and all-wall heating (A-H). Various indicators were adopted to evaluate street ventilation and pollutant dilution capacity (e.g. age of air (τ,s), NEV*, pollutant transport rates (PTR)). Full-scale wall heating produces a strong upward near-wall buoyancy force, which significantly influences flow patterns and improves street ventilation for most cases. When AR = 3, L-H strengthens the single-vortex airflow. When AR = 5, L-H converts the isothermal double vortices into a single-clockwise vortex. For both ARs, W–H reverses the main clockwise vortex to an enhanced counterclockwise one, moreover G-H and A-H cause a more complicated multi-vortex pattern than isothermal cases. Overall, when AR = 3, L-H and W–H increase NEV* by 68% and 40% than the isothermal case. When AR = 5, four wall heating patterns all raise NEV* considerably (by 150%–556%). For both ARs, the L-H, W–H and A-H amplify the contribution of mean flows on removing pollutants but reduce that by turbulent diffusion compared with isothermal cases.

C and 2.2 L/min flow rate showed that the electrical yield can increase by 25%. On the other hand, by using insulation, the thermal yield increases up to 3% when working at a temperature of 23 &deg, vle University (Sweden) with the ability to measure ambient, cell and HTF temperature, flow rate and solar radiation. The experimental results were validated by means of an in-house developed CFD model. Based on the validated model, the effect of collector tilt angle, HTF, insulation (on the back side of the reflector), receiver material and front glass on the collector performance were considered. The impact of tilt angle is more pronounced on the thermal production than the electrical one. Furthermore, the HTF recirculation with an average temperature of 35.1 &deg, C above ambient., Photovoltaic (PV) panels and thermal collectors are commonly known as mature technologies to capture solar energy. The efficiency of PV cells decreases as operating cell temperature increases. Photovoltaic Thermal Collectors (PVT) offer a way to mitigate this performance reduction by coupling solar cells with a thermal absorber that can actively remove the excess heat from the solar cells to the Heat Transfer Fluid (HTF). In order for PVT collectors to effectively counter the negative effects of increased operating cell temperature, it is fundamental to have an adequate heat transfer from the cells to the HTF. This paper analyzes the operating temperature of the cells in a low concentrating PVT solar collector, by means of both experimental and Computational Fluid Dynamics (CFD) simulation results on the Solarus asymmetric Compound Parabolic Concentrator (CPC) PowerCollector (PC). The PC solar collector features a Compound Parabolic Concentrator (CPC) reflector geometry called the Maximum Reflector Concentration (MaReCo) geometry. This collector is suited for applications such as Domestic Hot Water (DHW). An experimental setup was installed in the outdoor testing laboratory at G&auml

Airing can be a solution to introduce extra ventilation in large single zone buildings, especially where there are large aggregations of people such as churches or atriums. In naturally ventilated ...

Ventilation and infiltration caused by wind are difficult to predict because they are non-local phenomena: driving factors depend on the surrounding terrain and neighbouring buildings and on the building orientation with respect to the wind direction. Wind-driven flow through an opening is complex because wind can flow through the opening or around the building, in contrast to buoyancy driven flow. We explored wind and air infiltration phenomena in terms of pressure distributions on and around buildings, stagnation points, flow along facades, drag forces, and air flow through openings. Field trials were conducted at a 19th-century church, and wind tunnel tests were conducted using a 1:200 scale model of the church and other models with openings. The locations of stagnation points on the church model were determined using particle image velocimetry measurements. Multiple stagnation points occurred. The forces exerted on the church model by winds were measured using a load cell. The projected areas affected by winds in various directions were calculated using a CAD model of the church. A fairly large region of influence on the ground, caused by blockage of the wind, was revealed by testing the scale model in the wind tunnel and recording the static pressure on the ground at many points. The findings of this study are summarized as a number of steps that we suggest to be taken to improve the analysis of wind driven flow in buildings and with these suggestions as a basis for further improvement of prediction methods for wind-driven flows.

Bifacial photovoltaic cells can produce electricity from the incoming solar radiation on both sides. Used in combination with concentrating solar technology, bifacial photovoltaic cells can see its ...

Air infiltration in ancient churches and other historical and monumental buildings is of great importance considering moisture transfer, energy consumption, thermal comfort and air pollutants that induce surface soiling. Two of the most established models for predicting air infiltration rate in buildings are the Lawrence Berkeley Laboratory (LBL) model and the Alberta air Infiltration Model (AIM-2). Being originally developed mainly for dwellings, their applicability to large single zone buildings is evaluated in this study by comparing model predictions with field measurements in three historical stone churches that are naturally ventilated only through infiltration. The somewhat more developed AIM-2 model yielded slightly better predictions than the LBL model. However, an LBL version that allows inclusion of the Neutral Pressure Level (NPL) of the building envelope produced even better predictions and also proved less sensitive to assumptions on air leakage distribution at the building envelopes. All models yielded however significant overpredictions of the air infiltration rate. Since NPL may be difficult to attain in practice, the AIM-2 model was chosen for model modification to improve predictions. Tuning of this model by varying its original coefficients yielded however unrealistic model behaviors and the eventually suggested modification implied introducing a correction factor of 0.8. This reduced the median absolute prediction error from 25% to 11%. Thus, especially when the NPL is not at hand, this modification of the AIM-2 model may suit better for air infiltration assessment of churches and other buildings similar to the tested kind.