If we discuss the problems of the thermal and acoustical environment of conventional buildings we can see a huge amount of research, literature and the results of their applications across a vast number of projects. Conventional structures have usually sufficiently thick enclosures where you can tackle with a solution for insulation. By contrast, a tensile membrane skin is extremely thin and lightweight. It, therefore, provides little or no thermal buffering to the interior and reliance cannot be placed upon its thermal mass to dampen the effects of fluctuation in outdoor temperature and radiation \citep*{Forster2004}. The emergency sheltering solutions by far are considering mostly the issues of mass production and cheapness. In this regard, the solutions such as the family tent from the UNHCR core relief items catalogue \cite{supply2011a} are designed to be versatile and are not tailored to specific weather conditions. In this regard, the shelters not only do not provide the appropriate internal comfort in accordance with EN15251 but also in some occasions are cold enough to cause diseases such as hypothermia or even death \citep*{Pepper2013}.
As for the acoustics. The nature of the acoustical behaviour of membrane structures is generally unknown, with many acoustic treatment techniques normally applied to a traditional building being inapplicable to such lightweight structures. \citep*{Forster2004} Several problems are though evident. Such as drumming. The emergency shelters do not possess the multilayered complex roofing and the only enclosure that stands between the occupant and the external agents is the thin layer or a thin composite structure which doesn’t really provide a goodacousticalinsulation. The raindrop sound may even be amplified and cause much discomfort.
In a general discussion about the membrane structures, there are several groups of experts that have been working to get all the bits and pieces of knowledge that were implied across various projects to assemble in a unified guidebook. The fruitful results of such meticulous research works are the European Design Guide for Tensile Surface Structures (2004) \citep*{Forster2004} by TensiNet and the Prospect for European Guidance for the Structural Design of Tensile Membrane Structures (2016) \citep*{Stranghöne2016} by JRC. These two guidebooks are also a big step towards creating standards and regulations for this domain. However, a summarized explanation of thermal and acoustical characteristics for these structures is only present in the first one.
If we narrow down the subject to focus more on the issues of emergency sheltering we can see that only a few institutions and researchers exist that focus on the topic from the thermo-acoustical point of view. One of the major actors in this field is, of course, the UN’s subsidiary UNHCR (United Nations High Commissioner for Refugees) that provided a significant amount of development in this field.DuringMarch 2012 - February 2016 a research was developed named S(P)EEDKITS, that incorporated several parties to improve the current level of development for emergency sheltering. \cite{wwwspeedkitseu}Another initiative that is dealing with housing for displaced people is BetterShelter \cite{shelter} that is cooperating with UNHCR and IKEA to design, prototype, test and implement better solutions for emergency sheltering.InRMIT(Royal Melbourne Institute of Technology) there’s a group of experts called HARB (Humanitarian Architecture Research Bureau) \cite{bureau} Their aim is to bring a multidisciplinary approach and gather different professionals (architects, engineers etc.) to work on sustainable solutions for emergency housing. Global Shelter Cluster \cite{Cluster2017} is a coordination entity that in hand with IFRC and UNHCR assists in emergency housing responses. Each year they publish a case study overview \cite{Cluster2017} that describes the shelters developed across the world. CLUSTEX in Politecnico di Milano \cite{clustex} is dealing with textiles structures with a particular focus for emergency sheltering. Several articles are published in recent years by member experts. The hub also carries out structural tests for textiles.
The Sphere Handbook as a result of numerous knowledge contributions and case studies has composed guiding principles to follow performing the shelter design task. Although they contain no technical details or specifications, they can be useful in the quick understanding of the context and the directions to follow while searching for solutions. The following is an excerpt of scenarios regarding decisions for various climates:
In warm, humid climates, design and orient shelters to maximise ventilation and minimise entry of direct sunlight. A higher ceiling helps air circulation. An attached covered outdoor space helps reduce direct sunlight and protect from rain. Consider the use of adjacent shaded or covered external space for food preparation and cooking, with separate space for other living activities. The roof should be sloped for rainwater drainage with large overhangs, except in locations vulnerable to high winds. The shelter construction material should be lightweight with a low thermal capacity, such as timber. Use raised floors to prevent water entering the covered living area.
In hot, dry climates, heavyweight construction material (such as earth or stone) ensures thermal
comfort despite changes in night and day temperatures. Alternatively, use a lightweight construction with adequate insulation. Pay attention to the structural design of heavyweight construction in seismic risk areas. Provide shaded and ventilated places where possible and appropriate. If only plastic sheeting or tents are available, provide a double-skinned roof with ventilation between the layers to reduce radiant heat gain. Position door and window openings away from the direction of the prevailing hot wind. Internal flooring should meet the external walling without gaps, to prevent dust and disease vectors entering.
In cold climates, a lower ceiling is preferable to minimise the internal volume that requires heating. Shelters occupied throughout the day require heavyweight construction with high thermal capacity. For shelters only occupied at night, lightweight construction with low thermal capacity and substantial insulation is more appropriate. Minimise air flow, particularly around door and window openings, to ensure personal comfort while also providing adequate ventilation for space heaters or cooking stoves.
Adequate ventilation helps maintain a healthy internal environment, prevents condensation and reduces the spread of communicable disease. It reduces the effect of smoke from indoor household stoves, which can cause respiratory infections and eye problems. Consider natural ventilation where possible. \cite{2018}
Below studies are practices of various researchers to examine the topic.
One of the first attempts to assess the internal thermal environment of the emergency shelter is the test by engineers from Cambridge University \citep{Crawford2005} in 2002 among whom was Peter Manfield that has done a significant effort in emergency sheltering research. The physical test was carried out with the external temperature of -20 Co. The internal comfort was registered through a set of sensors that were distributed across the surface and inner volume. Later on the physical model tests were calibrated into a simulation test and further, the tent model was tested with the climatic data of Islamabad, London and Pristina. This was one of the first attempts at using the computer simulation for emergency shelter assessment. In their tests, they revealed one of the dominant problems that occur in emergency textile shelters. As below mentioned:
- The temperature shows a dramatic difference in height.
- Without a proper insulation, it is unlikely to achieve an internal comfort by mere casual thermal gains.
- During peak activities inside the tent, the humidity can get to its maximum
Several other attempts occurred in recent years. In 2013 engineers from University of Rome Tor Vergata, have tried to develop a different solution for the emergency tents in order to improve the internal comfort \citep{Cornaro2015}. Pursuing this, they assembled a tent and tested its performance during May 7-15. Then the received information of the physical test was used in highest details to calibrate a simulation model for the same period. And later on, the calibrated model was tested with different solutions of design and materials in Torino (winter) and Palermo (summer). Their research shows that by adding high insulating material (aerogel pad) and a particular treatment of the floor a better internal environment can be achieved. This will dramatically decrease the energy demand for the tent. A very interesting approach can be seen in the research and implementation project by Clustex/Politecnico di Milano researchers \citep*{Viscuso2016}. Together with S(P)EEDKITS \cite{wwwspeedkitseu} they have developed three different solutions with the use of textiles that were later given scores on various performances. The thermal comfort of the most promising solution was tested with the weather data of Ulaanbaatar (Mongolia), Tabriz (Iran), Damascus (Syria) and Dakar (Senegal). The winner concept was prototyped in ten units and tested by Senegal and Luxembourg Red Cross delegations. Probably one of the most sustainable solutions in this field was proposed by researchers from Politecnico di Milano \citep{Salvalai2017}. The concept was to collect the disposedskis that accumulate in significant quantities each year and are not a subject of recycling and to implement them as a construction element inside an emergency shelter. The designed ski yurt-like structure was enveloped by multilayer composite that was in a double PVC layer, both outside and inside, with thermo-reflective insulation system interposed in between. Later on, the design was simulated for the thermal comfort analysis with the climate data of Palermo. The shelter was assembled in Italy then disassembled and sent to Guinea Bissau. In terms of internal comfort, it was suitable for hot climates. The notable thing here was the chimney effect that due to the opening in the highest point could let the hot air out of the tent and thus not cause the height temperature variance as it usually happens with the vaulted tents without a skylight opening.Oneofthefewresearchworksthat showed a backward approach is the analysisby \citep{Obyn2014} where instead of just doing the simulation for different climatic zones they actually did investigations on the real tents in different climatic zones (Brussels in Belgium, Sag Nioniogo in Burkina Faso and Bertrange in Luxembourg). They used the famous and omnipresent family tent from the UNHCR core relief items catalogue \cite{supply2011a} to see how it actually performs. Afterwards, they made the corresponding computer simulations and the compare results were quite accurate. Also, a good methodology for such kind of assessments is described.Notallthedesignedsheltersareending up in the emergency field. Among the ones that actually are being implemented not all the tents are being monitored to see whether they are performing well or not. Among the ones that are currently under monitoring is the Multipurpose Unit \cite{polilink} by Clustex researchers together with IFRC and Ferrino that have been sent to Burkina and Senegal Burkina to serve \cite{clustex}.