| 1. |
- Blomqvist, Claes, 1945-
(author)
-
Distribution of Ventilation Air and Heat by Buoyancy Forces inside Buildings : An Experimental Study
- 2009
-
Doctoral thesis (other academic/artistic)abstract
- The main task of the ventilation system in a building is to maintain the air quality and (together with the heating or cooling system) the thermal climate at an acceptable level within the building. This means that a sufficient amount of ventilation air at the appropriate temperature and quality must be supplied to satisfy thermal comfort and air quality demands and that this air is distributed to the parts of the building where people reside. Air movements caused by buoyancy forces can determine the distribution of ventilation air within buildings. The purpose of this thesis is to advance the state of knowledge of buoyancydriven air movements within buildings and to determine their importance both for ventilation air distribution and the maintenance of thermal comfort and air quality in buildings. The work is focused on studying thermally-driven air movements through large openings, both horizontal and vertical (i.e. doorways). The properties of a special type of thermally-driven currents, so called gravity currents, have also been explored. Large vertical openings like doorways are important for air exchange between rooms within a building. Air movements through doorways separating rooms with different air temperatures are often bidirectional and the buoyancy-driven flow rates are often greater than those caused by the mechanical ventilation system alone. Bidirectional flows through doorways can effectively spread contaminants, for example, from a kitchen or a hospital rooms, yet the results of this study indicate that the conversion of a thermally-driven bidirectional flow to a unidirectional flow via an increase of the mechanically forced flow rate requires forced flows that are more than three times greater than the thermally-driven flows. Experiments conducted in this project indicate that the resistance to buoyancy-driven flows in horizontal openings is significantly greater than that in vertical openings. Model tests have shown, however, that this problem may be mitigated if a simple model of a staircase located in the centre of the room (being ventilated) is linked to the horizontal ventilation opening. Gravity currents in rooms occur in connection with so called displacement ventilation as cool gravity currents propagate along the floor that are driven by the density difference of the ventilation air and the ambient, warmer air within the room. As these gravity currents easily pass obstacles and to a certain extent are self-controlling, they can effectively distribute the cool air within rooms in a building. Likewise, warm gravity currents occur when warmer air introduced in a room rises and spreads along the ceiling plane. One application where warm gravity currents may be used to advantage is when converting buildings from electric heating to district hot water heating thus, avoiding the introduction of an expensive hydronic heating system. This report includes a full-scale laboratory study of the basic properties of thermally-driven warm air gravity currents in a residential building and examines the possibilities of using the resulting air movements for the distribution of ventilation air as well as heat. Results from laboratory tests show that this conversion method may prove effective if certain conditions on the layout of the building are fulfilled.
|
|
| 2. |
- Chiesa, Giacomo, et al.
(author)
-
Remove sensible heat from indoor environments
- 2023
-
In: International Energy Agency - Resilient Cooling of Buildings - State of the Art Review. - Vienna : Institute of Building Research & Innovation. ; , s. 130-189
-
Book chapter (other academic/artistic)abstract
- The world is facing a rapid increase of air conditioning of buildings. It is the motivation of Annex 80 to develop, assess and communicate solutions of resilient cooling and overheating protection. Resilient Cooling is used to denote low energy and low carbon cooling solutions that strengthen the ability of individuals and our community to withstand, and prevent, thermal and other impacts of changes in global and local climates. It encompasses the assessment and Research & Development of both active and passive cooling technologies of the following four groups:Reduce heat loads to people and indoor environments.Remove sensible heat from indoor environments.Enhance personal comfort apart from space cooling.Remove latent heat from indoor environments.The present review sums up the state of the art in cooling solutions which may be regarded as resilient. Its main objective is to systematically describe the available cooling solutions, their physical basis, their benefits and limitations, their technology readiness level, their practical availability, and applicability. Doing so, the State-of-the-Art Review forms the basis for the work of Annex 80.
|
|
| 3. |
- Gu, Zhenhong
(author)
-
Approaches to energy efficient building development : studying under Chinese contexts
- 2007
-
Licentiate thesis (other academic/artistic)abstract
- This thesis presents a general description of approaches to energy efficient building development under Chinese contexts. The purpose of the work is to discuss how Chinese building development can be approved from an energy saving perspective. Building development is a complicated process that relates to many stakeholders’ interests. The developed countries have studied in this field extensively for several decades. Generally, the approaches to energy saving can be set at three levels: administration, construction industry and architectural design. More new strict codes for energy efficient buildings are being issued for enforcement. At the same time, many research institutes have developed Building Environmental Assessment (BEA) methods, where energy efficiency is an important factor in the models. Various technical solutions for energy efficiency are developed as well. The administrative approaches are not the main objective discussed in the thesis, though the importance of them is undeniable. BEA systems are not only assessment methods, but also market-based stimulating approaches for sustainability of construction market. Technical methods have been developed for a long period. Passive House and Low Exergy (LowEx) Systems are two representative examples in European countries. All of these approaches are relatively unfamiliar to Chinese architects and developers, let alone their effect and applicability. The thesis tries to analyse this situation and their applicability within Chinese context. In China to a certain project, the importance of technical issues is relatively recognized. However, a few successful individual cases in technique can not change the reality that most of new building development has failed in energy efficiency in China. This is a serious situation when China is in an enormous expansion phase in building new houses. The thesis tries to discuss the reasons for this phenomenon. One reason could be that the stakeholders in the developing process are not aware of the importance of collaboration which is the only method to get “Both Win” according to Game theory. The thesis discusses a paradigm to replace two traditional linear paradigms in building developing process. Architects should act as coordinators of different stakeholders rather than technical supporters. The thesis tries to discuss the propositional route of developing energy efficient buildings. Technical approaches are basic research, which presents the concepts that have been proved realizable; BEA encourages developers to develop more energy efficient buildings for economic benefit, which will make good demonstrations for whole market; national laws and policies are final approaches, which ensure that every project will have good performance of energy efficiency. When the old standardization and legislation are finished, a new cycle will begin with more advanced techniques. China government has started the progress to enhance energy efficiency. However, this process will be tough and slow. The thesis discusses Chinese special conditions and the problems that cry out for solution in the future.
|
|
| 4. |
- Iqbal, Ahsan, et al.
(author)
-
Discharge coefficient of centre-pivot roof windows
- 2015
-
In: Building and Environment. - : Elsevier BV. - 0360-1323 .- 1873-684X. ; 92, s. 635-643
-
Journal article (peer-reviewed)abstract
- Use of centre-pivot roof windows is very common in single family houses in Nordic Europe. Unfortunately the wind-driven airflow characteristics of this kind of windows are missing in the scientific literature. In the present study, the airflow rate through the window was specified by using the discharge coefficient. Wind tunnel measurements using a modelled centre-pivot roof windowwas used in the present study. For smaller sash opening angles the value of discharge coefficientwas approaching unity and the discharge coefficient decreased with increase in the sash opening angle. The value of 0.6 was only obtained when the window was without sash. Hence, the inclusion of sash improved the airflow characteristics of the window due to increased value of the dischargecoefficient. The discharge coefficient also depended on turbulence in the flow. In the absence of external wind, the turbulence was described by the value of Re. Only for higher values of Re the still-air discharge coefficients became independent of the flow direction and the air velocity. Whereas for wind driven natural ventilation the ratio of average air speed within the opening and the reference wind speed (velocity ratio) was used to define the fully developed turbulent flow. Constant values of wind-driven discharge coefficients were obtained when the average air speed within the opening was equal to or greater than the reference wind speed i.e. the velocity ratio greater than unity. Moreover, when the velocity ratio was greater than unity, the still-air discharge coefficients became identical to the wind-driven discharge coefficients.
|
|
| 5. |
- Iqbal, Ahsan, et al.
(author)
-
Effect of opening the sash of a centre-pivot roof window on wind pressure coefficients
- 2014
-
In: The International Journal of Ventilation. - 1473-3315 .- 2044-4044. ; 13:3, s. 273-284
-
Journal article (peer-reviewed)abstract
- This paper describes the effect of outward opening the sash of a window on local and overall windpressures. Wind tunnel experiments were used for the purpose of evaluation. A centre-pivot roofwindow on a pitched roof in a modelled scaled building was used in the analysis of wind pressures.The wind pressures were defined in terms of wind pressure coefficients. Traditionally, wind pressurecoefficients are extracted from the analysis of a sealed plane surface. These wind pressurecoefficients are used to estimate the natural ventilation rate through windows/openings due to windeffect. Surface averaged wind pressure coefficients do not accurately estimate the airflow rates. Therefore, local wind pressure coefficients are needed, especially for dynamic calculation of airflow rates. From the wind tunnel experiments, it is concluded that outward opening the sash can significantly affect the wind pressure distribution near to the window. The use of wind pressurecoefficients from the analysis of a sealed plane surface may lead to erroneous estimation of airflow rate.
|
|
| 6. |
- Larsson, Ulf, 1966-
(author)
-
On the performance of stratified ventilation
- 2018
-
Doctoral thesis (other academic/artistic)abstract
- People nowadays spend most of their time indoors, for example in their homes, cars, in trains, at work, etc. In Sweden, the energy demand in the built environment is a growing issue. The building sector accounts for 40% of total energy use and 15% of total CO2 emissions, and around one-third of the energy use in the world is related to providing a healthy and good comfort indoors. To achieve acceptable indoor climates new designs for the ventilation systems have been proposed in recent decades, among them stratified ventilation systems.Stratified ventilation is a concept that often allows good performance for both indoor air quality and thermal comfort. Stratified ventilation systems are effective in reducing cross contamination, since there is virtually no mixing in the space; the temperature and the pollutant concentration increase linearly from the heat source with the height of the occupied zone. There are many different ventilation supply devices using the stratified principle, such as displacement supply device (DSD), impinging jet supply device (IJSD) and wall confluent jet supply device (WCJSD).The main aim of this thesis is to analyze and compare different supply devices based on stratified ventilation, with different setups, related to thermal indoor climate, energy efficiency and ventilation efficiency. The ultimate goal is to contribute to an increased understanding of how ventilation systems with stratified supply devices perform.Two scientific methods have mainly been used in this thesis, i.e., experimental and numerical investigations. For numerical experiments the CFD (Computational Fluid Dynamics) code ANSYS and FIDAP have been used. Experimental studies have been performed with thermocouples, Hot-Wire Anemometry (HWA) and Hot-Sphere Anemometry, thermal comfort measurement equipment and tracer gas measurement equipment.This thesis mainly focuses on three research questions: Interaction between a supply device based on stratified ventilation and downdraft from windows; Flow behavior, energy performance and air change effectiveness for different supply devices based on stratified ventilation; and Thermal comfort for different supply devices based on stratified ventilation.Research question one showed that the arrangement of displacement supply device and window in cold climate has significant effect on the flow pattern below the window. Different supply airflow rates have an effect on both the velocity and the temperature of the downdraft. In this case the velocity decreased by approximately 9.5% and the temperature in the downdraft decreased 0.5°C when the flowrate from the supply device increased from 10 to 15 l/s.Research question two showed that airflow patterns between different air supply systems were essentially related to characteristics of air supply devices, such as the type, configuration and position, as well as air supply velocities and momentum. For WCJSD, IJSD and DSD, positions of heat sources (such as occupant, computers, lights and external heat sources) played an important role in formation of the room airflow pattern. One interesting observation is that the temperature in the occupied zone is lower and a more stratified temperature field implies a more efficient heat removal by a stratified air supply device. The results revealed that the lowest temperature in the occupied zone was achieved for DSD, but with IJSD and WCJSD slightly warmer, while the system with a mixing supply device (MSD) showed a much higher temperature. The results confirm that air change effectiveness (ACE) for the DSD, WCJSD and IJSD is close to each other. However, MSD shows lower ACE in all the present papers than IJSD, WCJSD and DSD.Research question three showed that ventilation systems with stratified supply devices in almost all of the studied cases showed an acceptable level for predicted percentage dissatisfied (PPD), predicted mean vote (PMV) and percentage dissatisfied due to draft (DR). If comparing ventilation systems, using IJSD, WCJSD or DSD with MSD always showed thermal comfort better or at the same level.
|
|
| 7. |
- Marszal, Anna Joanna, et al.
(author)
-
North European Understanding of Zero Energy/Emission Buildings
- 2010
-
In: Zero Emission Buildings : proceedings of Renewable Energy Research Conference 2010 : June 7th - 8th 2010 - proceedings of Renewable Energy Research Conference 2010 : June 7th - 8th 2010. - 9788251926232 ; , s. 167-178
-
Conference paper (peer-reviewed)
|
|
| 8. |
- Marszal-Pomianowska, Anna, et al.
(author)
-
Operation of power distribution networks with new and flexible loads : A case of existing residential low voltage network
- 2020
-
In: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 202
-
Journal article (peer-reviewed)abstract
- This paper aims to visualize how the planned electrification of heat demand together with the utilization of energy flexibility in buildings will influence the performance of local electricity network. Thereby, the work contributes to the research on smart energy system in the residential sector. The flexibility service is provided by two demand-side-management strategies a) activation of the thermal mass to modulate load profile of a heat pump, b) control of household appliances' starting times. Three configurations of load mix in the local electricity network are investigated: a) domination of non-renovated houses, b) with equal share of high and low heat demand houses, c) domination of energy efficient houses. The model is soft-coupled and anchored in existing low voltage (LV) network and existing residential buildings. The energy flexible buildings enhance the LV network performance, by decreasing the afternoon peaks, without compromising the occupants' thermal comfort. The highest impact is for the LV network dominated by energy efficient houses. There are also new challenges, namely the newly created peak loads and transformer overloading during night time. It is a consequence of uniform price signal sent to all flexible customers and electrification of heating demand without parallel improvement of energy performance.
|
|
| 9. |
|
|
| 10. |
- Zhang, Chen, et al.
(author)
-
Resilient cooling strategies – A critical review and qualitative assessment
- 2021
-
In: Energy and Buildings. - : Elsevier BV. - 0378-7788 .- 1872-6178. ; 251
-
Journal article (peer-reviewed)abstract
- The global effects of climate change will increase the frequency and intensity of extreme events such as heatwaves and power outages, which have consequences for buildings and their cooling systems. Buildings and their cooling systems should be designed and operated to be resilient under such events to protect occupants from potentially dangerous indoor thermal conditions. This study performed a critical review on the state-of-the-art of cooling strategies, with special attention to their performance under heatwaves and power outages. We proposed a definition of resilient cooling and described four criteria for resilience—absorptive capacity, adaptive capacity, restorative capacity, and recovery speed —and used them to qualitatively evaluate the resilience of each strategy. The literature review and qualitative analyses show that to attain resilient cooling, the four resilience criteria should be considered in the design phase of a building or during the planning of retrofits. The building and relevant cooling system characteristics should be considered simultaneously to withstand extreme events. A combination of strategies with different resilience capacities, such as a passive envelope strategy coupled with a low-energy space-cooling solution, may be needed to obtain resilient cooling. Finally, a further direction for a quantitative assessment approach has been pointed out.
|
|
