| 1. |
- Pieskä, Henrikki
(författare)
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High-Temperature Cooling Systems for Sustainable Buildings Using Geothermal Energy : Holistic Assessment in the Mediterranean Climate
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sustainable development is increasing its significance in both the scientific and political agenda. In light of this development, the United Nations have published 17 Sustainable development goals (SDGs). The SDGs relate to all aspects of sustainable development, the most significant for this thesis being energy decarbonisation and sustainable industry.Space cooling is increasing in significance globally, on the one hand because of a global rise in temperatures due to climate change, on the other hand because of the rising living standards in developing countries mean more people will have access to cooling. Cooling has been linked to all 17 SDGs, and affects not only energy use but also health, well-being and productivity. Radiant cooling is gaining popularity as an alternative for conventional, air-based cooling systems. The main advantages of radiant cooling are lower energy requirement for transportation and the ability to use low-grade renewable energy resources such as geothermal cooling.Building retrofitting is also a significant topic in sustainable development. Currently, while 75% of buildings in European Union (EU) are inefficient according to current building standards, 85-95% of these buildings are still predicted to be in use in 2050. This means retrofitting existing buildings to improve their energy efficiency is vital for reducing the EU's greenhouse gas emissions. Most of the work presented in this thesis relates to a European research project, Geofit, which sought to make retrofitting buildings with geothermal heating and cooling systems viable and cost-effective. Most of the work was done using building energy modelling, and focused on one of the project's pilot sites, in Sant Cugat, Spain. The pilot was selected for showcasing the potential of an innovative high-temperature radiant cooling system, supplied with geothermal energy.The results showed that retrofitting the building with the radiant cooling system would achieve significant benefits in thermal comfort, reducing the highest temperature reached during the cooling season from 32 °C to 27.9 °C. The fraction of the cooling season, when indoor temperature exceeds 26 °C was reduced from 83% to 23%. The results also show that the radiant cooling system can achieve this improvement with higher efficiency and lower environmental impact than a conventional all-air cooling system.It should be noted that in the hot and humid climate of Spain, the radiant cooling system has to contend with the risk of water condensing on the surfaces of the cooling panels. This risk can be mitigated in two ways: limiting the system's cooling capacity or dehumidifying the air entering the building. Limiting the cooling capacity leads to thermal discomfort, while dehumidification approximately doubles the system energy use. Therefore, the needs and requirements of the retrofit case need to be carefully evaluated and balanced when planning a retrofit project.
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| 2. |
- Sadeghian, Parastoo
(författare)
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Computational fluid dynamics application in indoor air quality and health
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Indoor air quality directly affects the comfort, performance, and well-being of occupants. Indoor pollution can cause immediate or long-term health effects and has been responsible for 4.1% of global deaths in recent decades. In operating rooms, providing a high indoor air quality is especially critical as surgical site infection can occur in patients due to air contamination in operating rooms.Surgical site infections due to antibiotic resistant bacteria may threaten the safety and lives of millions of people each year. To moderate and reduce indoor contamination, it is necessary to select a proper ventilation strategy.Improving ventilation system performance requires a deep understanding of airflow patterns and contamination distribution.This thesis adopted computational fluid dynamics to evaluate airflow patterns and the spread of airborne contaminations in indoor environments. Moreover, we sought to provide an approach to facilitate transferring the obtained knowledge to medical experts and decisionmakers to reduce the infection risk after the surgery.The use of warming blankets has raised the concern about surgical site infections. Warming blankets are used to prevent hypothermia in patients during surgery. However, our results showed that these warming blankets reduce the bacteria-carrying particles level at the wound due to warm upward airflows.Surgical lamps can block the airflow and generate a low-velocity area under the lamp that increases the accumulation of contaminants. The simulation results revealed that a novel fan-mounted surgical lamp reduced the contamination level to an acceptable range for infection-prone surgeries. This novel surgical lamp successfully reduced contamination in the operating room supplied with both turbulent mixing and laminar airflow ventilations.In another study, we implemented a protective curtain and showed that this strategy could significantly reduce the exposure level of the medical team to a patient with infectious respiratory disease. This novel protective curtain is located between the patient’s upper body and the lower part during surgery. We found a 57% reduction in bacteria-carrying particle concentration at the wound by adopting this curtain. Thus, using this protective curtain can reduce the exposure level of both patient and surgical team in the operating room.Besides investigating the performance of ventilation systems in hospitals, we investigated the application of diffuse ceilings ventilations in clinics, especially waiting rooms. Diffuse ceiling ventilation systems are common air distribution systems in offices and schools. Based on simulation results, a diffuse ceiling with a central opening and evenly distributed heat loads resulted in the highest cooling capacity and thermal comfort in clinic waiting rooms.We have visualised the airflow field and airborne particles in operating rooms with the help of virtual reality techniques. We found the virtual reality environment more engaging to understand the airflow field and particle movements in operating rooms.
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| 3. |
- Eriksson, Martin
(författare)
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A Statistical Approach to Estimate Thermal Performance and Energy Renovation of Multifamily Buildings : Case study on a Swedish city district
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Several climate and energy goals have been set in the European Union, one of them being to increase energy efficiency. In Sweden, a large potential for increased energy efficiency lies in the residential and service sectors, which account for about 40% of total energy use. A large share of buildings in Sweden were built in the Million Homes Program in the 1960s and ’70s. These buildings are now in need of renovation, which enables renovation with the ambition of reducing energy use. In this thesis, the purpose is to develop an energy signature method, a bottom-up statistical method. This method has been validated using a building energy simulation software called IDA ICE, for two kinds of multifamily buildings from the Million Homes Program. The energy signature method has then been applied to a district located in Gävle, Sweden, containing more than 90 multifamily buildings with similar construction. In addition to characterizing current thermal performance of the buildings, the energy signature method is further developed so that potential for energy renovation of the district can be simulated. Simulated energy renovation is developed to comply with building energy use requirements, according to the most recent Swedish building regulations. Both on building and district level, sensitivity analysis is performed. In both cases the energy signature method is insensitive to changes in internal heat gains and indoor temperature. To investigate the effects of simulated renovation on a local district heating system, results are visualized in a duration diagram, where energy use reduction in different load periods is displayed. Thus, it is demonstrated how the energy signature method can be used as a rapid way of simulating energy renovation on district level and with readily available data.
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| 4. |
- Nourozi, Behrouz, 1986-
(författare)
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Advances in Ventilation Heat Recovery : An assessment of peak loads shaving using renewables
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The building sector accounts for approximately 40% of total global energy usage.In residential buildings located in cold climate countries, 30-60% of this energy isused for space heating, 20–30% is lost by discarded residential wastewater, and therest is devoted to ventilation heat loss.Sweden experienced a construction boom during the so-called Million Programme(MP) in the 1960s and 1970s. A retrofit requirement of buildings constructed duringthis era shifted from pure exhaust ventilation to mechanical ventilation with heatrecovery (MVHR), which peaked in Swedish dwellings between 1990 and 2000. It isestimated that 43% of Swedish multi-family buildings built during this decade wereequipped with MVHR systems. A common problem with efficient MVHR systemsis frost formation during cold winter hours when cold outdoor air and humid, warmreturn air exchange heat in the air handling unit. Outdoor air preheating usinglocally available renewable heat sources has been an alternative solution to preventfrost formation in the heat exchanger.The main objective of this work was to investigate the solutions for improving theperformance of MVHR systems during the coldest periods of the year. The primaryfocus was frosting, a critical problem in MVHR units that operate duringcold periods. The recovered heat from discarded wastewater and the local geothermalenergy were the two investigated renewable heat sources used to preheat theincoming cold outdoor air to the MVHR in order to prevent frost formation on theheat exchanger surface.The performance of the suggested outdoor air preheating systems and the impactof air preheating on the entire system’s thermal efficiency were evaluated by TRNSYSdynamic simulations. Temperature control systems were proposed based onthe identified frost thresholds to efficiently use the limited thermal capacity ofwastewater and maintain a high heat recovery of MVHR. Two outdoor air preheatingsystems configurations with temperature-stratified and -unstratified tanks weredesigned and compared. A life cycle cost analysis was applied to further investigatethe cost-effectiveness of the studied systems.Detailed heat transfer simulation of the ventilation heat exchanger revealed thatwhen condensation occurred in the heat exchanger, the heat transfer rate betweenthe return airflow and the plate increased significantly. This was reflected by asharp increase in the plate temperature, increasing the supply air temperature tothe building. Monitoring the relative humidity of the airflow at the inlet of theheat exchanger and using the onset values of frosting/condensation suggested in this work will allow a more precise and proactive prediction of freezing and moreefficient utilization of outdoor air preheating resources.The results obtained from the simulation of building energy usage indicated thatresidential wastewater had sufficient thermal potential to reduce the defrosting needfor MVHR systems (equipped with a plate heat exchanger) in central Swedish citiesto 25%. For colder regions in northern Sweden, the defrosting time was decreased by50%. The suggested temperature control systems ensured high MVHR temperatureefficiencies above 80% for most of the heating season, while the frosting period wasminimized. LCC analysis revealed that outdoor air preheating systems equippedwith temperature stratified wastewater tank and an unstratified storage tank couldpay off their investment costs in 17 and 8 years, respectively.
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| 5. |
- Sadeghian, Parastoo
(författare)
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A new generation of hospital operating room ventilation
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surgical site infection is responsible for 38 percent of reported infections after surgery. This infection increases mortality and treatment costs, and prolongs the hospitalization of patients. Bacteria-carrying particles are the main cause of surgical site infection and one of the main sources of these particles is skin fragments released from the surgical personnel during an ongoing surgery. Ventilation systems reduce the concentration of bacteria-carrying particles by supplying clean air in the operating room. The performance of operating room ventilation systems is affected by internal disruptions such as medical equipment, surgical lamps, number of staff and their behaviour during the surgery.Using computational fluid dynamics, this thesis investigates the airflow behaviour and distribution of the contamination in the operating room under the presence of various internal disruptions. In this regard, three common ventilation systems are considered: laminar airflow, turbulent mixing and temperature-controlled airflow ventilations. This study tries to overcome the weaknesses of the ventilation systems by providing sustainable solutions and continuously being in contact with design companies.It is common to use warming blankets to prevent reduction in the core body temperature of the patient during major surgeries. However, there is a major concern that these blankets disrupt the supplied airflow, which results in rising contaminant concentration. Most of the studies about warming blankets are clinical works and it is still not clear whether or not these blankets should be used. The results of the present study show that using warming blankets had no impact on increase of contamination level at the surgical zone. However, one common type of warming blanket – a forced-air warming blanket – can considerably increase the concentration of bacteria-carrying particles at the wound area if it becomes contaminated.The simulated results of the airflow field and particle tracking showed that the laminar airflow ventilation system was disturbed more easily by the local heat loads than overall heat loads in the operating room.Surgical lamps are considered as an obstacle in the supplied airflow path. These lamps create a stagnant area above the operating table and increase the contamination level. In this regard, a novel design of surgical lamp, a fan-mounted surgical lamp, was introduced to operating rooms.This device was used in the operating rooms equipped with laminar airflow and mixing ventilation system. The simulated results revealed that this lamp significantly reduced the contamination level at the operating table.Visualization techniques were adopted to teach and improve the understanding of surgical personnel about transmission of contaminated particles in operating rooms. Here, a virtual and augmented reality interface was used to visualize the impact of differences in ventilation principle, surgical staff constellation and work practice.
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| 6. |
- Wang, Cong
(författare)
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Ventilation Performance in Operating Rooms : A Numerical Assessment
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surgical site infections (SSIs) remain one of the most challenging postoperative complicationsof healthcare and threaten the lives of millions of patients each year. Current evidence hasshown a positive relationship between the airborne concentration of bacteria-carryingparticles (BCPs) in the operating room (OR) and the rate of infections. The OR ventilation iscrucial for mitigating the dispersion of airborne bacterial contaminants and thus controllingthe risk of SSIs. A variety of ventilation schemes have been developed for OR use. Each haspros and cons and may be better suited than another for operations under certain conditions.The proper functioning of OR ventilation is also affected by external and internal disruptions.By applying Computational Fluid Dynamics (CFD), the present study investigates the airflowand contaminant distribution in ORs under different conditions.The airflow distribution is of critical importance in removing or diluting airbornecontaminants. The conventional mixing ventilation is not able to reliably create an ultracleanenvironment. The usage of mixing ventilation in infection-prone surgery should be limited,especially when a large surgical team is involved. Laminar airflow (LAF) ventilation demandsa sufficient airflow rate to achieve desired performance. Temperature-controlled airflow(TAF) ventilation represents an effective ventilation scheme that can serve as an energyefficientalternative to LAF.Door openings have a detrimental impact on the microbiological cleanliness of the OR. Thetemperature in the OR and adjacent space should be well controlled to minimize the interzonalcontaminant transfer. Temporarily reducing the OR exhaust flow during door operationforms a directional airflow towards the adjacent space, which is found to be an effectivesolution to ensure the isolation.Surgical lamps serve as physical obstructions in the airflow path and significantly deterioratethe performance of LAF ventilation. It is highly recommended to improve the shape anddesign of the lamps in the LAF ventilation. TAF is found to be less sensitive to the presenceof surgical lamps in the airflow path. The buoyancy-driven airflow used by TAF is morecapable of circumventing obstacles than the inertia-driven flow used by LAF. Thermal plumesdeveloped from the surgical equipment in the OR have the potential to distort the buoyancydrivenairflow in TAF.The thesis conducts a comprehensive literature review of important topics in OR ventilation.The present study enhances the understanding of the strengths and limitations of differentventilation schemes and increases the knowledge of the design and usage of OR ventilation.
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