1. Introduction
Temporary housings (THs), as a special type of building, have been widely used for refuging survivors of natural disasters [
1], for sheltering patients during widespread disease, for residency of constructors in large engineering projects or for accommodating people in great public activities. The lifetime of TH is usually from 6 months to 5 years [
2], or even longer depending on its function and quality. THs are generally prefabricated with lightweight structures and easy to be built, dismantled and stored for future reuse [
3,
4]. Compared to constructing permanent buildings, the utilization of THs can not only progress the construction but also improve the energy efficiency and decrease carbon dioxide emission on these special occasions. Container houses (CHs), as a kind of THs, are increasingly and widely used, which originated from the reuse of shipping containers in architecture [
5]. They are manufactured in standard dimensions, which makes them an excellent modular building [
6]. However, some problems with the indoor environment are found for THs including for CHs. Air quality is recognized as an important factor having a major effect on human health and has been studied by many scholars [
7,
8,
9]. For temporary shelters, there are survey results showing that the total concentration of Volatile Organic Compounds (VOCs) and Particulate Matter (PM) in the room is very high [
10]. While more problems are focused on the indoor thermal environment. Chen et al. [
11] found that poor sound and heat insulation are common problems for THs. Some scholars studied the indoor thermal environment of THs in cold regions and hot summer and cold winter zones in China, finding that the natural indoor temperature sometimes was not within the comfort range of the human body [
12,
13,
14]. The occupants’ satisfaction with the thermal insulation performance of CHs is predominantly low [
15]. Thapa et al. [
16,
17] conducted a series of surveys on the indoor thermal environment and thermal comfort in four main earthquake affected districts in Nepal and analyzed the total heat loss coefficient per floor area of five shelters in Lalitpur during winter, which ranged from 11.3 to 15.2 W/(m
2·K), suggesting that thermal insulation was very low.
While the thermal performance of temporary buildings is receiving a lot of attention, the thermal technology is also improving. Honma [
18] introduced that according to the special specification of the Hokkaido government, glass wool insulation of 100 mm should be applied in the wall and ceiling of emergency temporary housing. Soga et al. [
19] mentioned that different solutions on thermal technology of THs had be taken in different regions of Japan, such as increasing the thickness of insulation in Hokkaido. In the Mediterranean area, Cross-Laminated Timber (CLT) technology was applied to THs [
20,
21], which provides high insulation and good air tightness. It enables building structures to avoid thermal bridging and allows achieving remarkable energy savings in the heating season [
22]. For CHs, Grębowski et al. [
23] proposed that the envelope can be internally insulated, using glass wool or insulated with sprayed polyurethane foams. Additionally, Berbesz et al. [
24] also pointed out that proper insulation is an important aspect for container house design.
In cold and severe cold regions, it is important to improve the insulation performance of the envelope of THs. Mario et al. [
25] proposed that increasing the thickness of the insulation was required to achieve the adequate thermal transmittance coefficient that corresponds to the location of the deployment of the troops by comparing the energy efficiency requirements of the tents and containers that were used in military camps and the energy-efficient design requirements that were demanded by the energy efficiency standards for buildings in the civil sector. A simulation study by Liu et al. [
26] on increasing the different thickness of rock wool (RW) to the walls of a TH at a construction site in Tianjin showed that the average indoor temperature increased with increasing insulation thickness. Yang et al. [
27] analyzed the energy performance of portable houses composed of loess and porous materials in different climate zones and showed that the benefits of increased insulation were higher in areas where heating energy was dominant, and an insulation thickness of at least 100 mm is recommended. Furthermore, in Cornaro et al.’s study [
28], the average heating power demand decreased by 59.4% when they incorporated aerogel into the walls and roof as well as used the modular floor consisting of polyethylene grids to enhance the insulation performance of an emergency shelter tent.
In order to reduce energy consumption in buildings, many countries have introduced measures to improve their building energy-efficiency standards and increasingly deployed the zero/low energy buildings. The zero energy container units were investigated based on a variety of energy efficiency technologies, where insulation is always a crucial consideration [
29,
30,
31]. Meanwhile, the heat transfer coefficient (
U-values) of the envelope in these studies is designed to be very low (0.1 or 0.26 W/(m
2·K)), and Vacuum Insulation Panels (VIPs) are mostly used, while considering the interior space of the CH. Yet, both the improvement of energy-efficiency standards and the deployment of low-energy buildings typically focus on reducing the energy use in building operation [
32]. It is also important to consider the contribution of insulation materials to the life cycle environmental impact. Pargana et al. [
33] evaluated the environmental impacts on the production of conventional thermal insulation materials (extruded and expanded polystyrene (XPS and EPS), polyurethane, expanded cork agglomerate and expanded clay lightweight aggregates (LWA)) by means of a cradle to gate LCA methodological approach, and concluded that different materials contribute differently to the environmental impact, with a low contribution in EPS to all impact categories and the largest impact of LWA on global warming potential. Llantoy et al. [
34] developed a comparative life cycle assessment (LCA) of different insulation materials (polyurethane, XPS, and mineral wool) in the Mediterranean continental climate, whose results showed that XPS presented the worst environmental performance, and the best environmental performance was for the mineral wool and the cubicles with three insulation materials achieving an energy saving of 27%, 25%, 23%, respectively, in comparison to the non-insulated cubicle. Tettey et al. [
32] improved the original design of a residential building to achieve reference buildings to different energy-efficiency levels and at the same time varied the insulation materials in different parts of the reference buildings to achieve hypothetical options with similar energy-efficiency levels. Furthermore, they compared the production primary energy and CO
2 emission of the reference and optimum designs of the buildings under the different energy-efficiency standards. The results showed a reduction of approximately 6–7% in primary energy use and 6–8% in CO
2 emission when the insulation material in the reference buildings is changed from RW to cellulose fiber in the optimum versions. On the other hand, economic rationality is also one of the factors that must be considered in the design of energy-saving buildings. With these consideration, both environmental sustainability and cost should be highly concerned in selecting the insulation material of a building. Annibaldi et al. [
35] considered environmental and economic factors to develop a framework to identify the optimal material to be used to achieve the highest level of energy efficiency in building retrofits, and the research was applied to an industrial factory in Italy. The optimal thickness of ten materials with different origin were obtained and their results showed that all materials analyzed displayed economical savings, and three of them showed reductions in the production of emissions from an environmental point of view. Considering that the increase in insulation thickness makes the cost of insulation higher, some studies used life cycle cost (LCC) to evaluate the cost and benefit of the envelope and to find the optimal thickness of insulation material [
36,
37,
38,
39]. However, most researches of the assessment of envelope insulation at present were aimed at permanent buildings, rather than THs.
In this paper, the geometric model was created based on a CH that was used in the Yanqing zone of the Beijing 2022 Olympic and Paralympic Winter Games. We resorted to EnergyPlus to simulate the indoor air temperature and validated the simulation results with the measured values tested in the Yanqing zone. Then, the heating energy consumption of CH with different insulation materials was simulated under the meteorological parameters of the Yanqing zone. In the simulation process, we enhanced the thermal insulation performance of the CH with reference to the limit values of the U-values of the envelope according to energy-efficiency standards of permanent buildings. Environmental and economic benefits were analyzed for the production stage of insulation materials and the operation stage of the building. Furthermore, considering that the service life of the CH variables in the application situation, the economic thickness of the insulation materials with a service life of 1 to 20 years was analyzed using the life cycle cost method.
4. Conclusions
In this study, the insulation of a CH was improved with reference to the requirements of NZEB standard for thermal performance of the envelope, the heating energy consumption of CH with different insulation materials was simulated and their economic and environmental benefits were analyzed. Meanwhile, the economic thickness of different insulation materials was calculated considering the service life of the CH.
Improving the insulation performance of CH has a great energy-saving effect. The annual heating energy consumption of CH is reduced by 32.8% at the altitude of 2177.5 m and 21.4% at the altitude of 950 m compared to the original envelope when the U-values of the envelope meet the NZEB standard. In addition, carbon emissions are reduced as the service lives of CH increase. After reducing the U-values of the envelope to meet NZEB standard, carbon emissions are 18.5% lower at the altitude of 2177.5 m and 29.5% lower at the altitude of 950 m, if the CH is used for 20 years. Therefore, it is evidently seen that HVIP has the longest payback period, up to 31.4 years at the altitude of 950 m, which is less economically beneficial when meeting the NZEB standard.
What is more, the service life of the CH has a great impact on the economic thickness. When the service life is from 1 to 20 years, the economic thickness range is 47–235 mm for RW, 41–197 mm for XPS, 33–149 mm for PU, and 4–18 mm for HVIP at the altitude of 2177.5 m. At the altitude of 950 m, the economic thickness range is 28–158 mm for RW, 26–131 mm for XPS, 25–118 mm for PU, and 2–12 mm for HVIP. The total cost and carbon emission of the economic thickness of HVIP is still higher than that of conventional insulation materials. If HVIP is widely used in the future, the price may be reduced, which is likely to result in the reduction of the total cost and carbon emission reduced.
CHs are now a commonly used prefabricated element in the building industry. The CHs achieved a variety of functional applications during the Beijing 2022 Olympic Winter Games. After the game, as sustainable legacies, the CHs have been recycled and transformed as convenience stores, reading bars, hotel rooms and so on to play an important role in urban comprehensive development and urban renewal. Although the research of this paper is based on the meteorological parameters of Xiaohaituo Mountain, the results are also appropriate for similar climate conditions.