Earth-Sheltered House: a Case Study of Dobraca Village House Near Kragujevac, Serbia

sustainability

Article Earth-Sheltered House: A Case Study of Dobraca Village House near Kragujevac, Serbia

Aleksandar Rudnik Milanović 1,*, Nadja KurtovićFolić 2 and Radomir Folić 2

1 Rudnik Urbanism Design Architecture, 34000 Kragujevac, Serbia 2 Departmant of architecture and urbanism, Faculty of Technical Sciences, University of Novi Sad, 21000 Novi Sad, Serbia; [email protected] (N.K.F.); [email protected] (R.F.) * Correspondence: ofﬁ[email protected]

Received: 14 August 2018; Accepted: 7 October 2018; Published: 11 October 2018

Abstract: This paper presents the case study of the authors’ design of the earth-sheltered house in Village Dobraca near Kragujevac, Serbia, in the context of development and some thermal properties of the underground housing. The historical insight, in brief, provides a better understanding of the reasons for their modern use as energy efficient and sustainable structures. It shows that underground houses even today are more thermally efficient than above ground houses since, besides earth, there is no need for new additional thermal layers. The article also includes a review of the representative physical forms of the underground housing through different periods, with the result of measurement of their main properties. The study of the underground housing structures provides an insight of the relation between the location and typology of underground homes in a contest of climate zones. These structures have an almost constant temperature, which provides the primary “comfort” condition in which the man is determined to live in. The results on property-based monitoring data showed that the earth-sheltered house could provide the thermal comfort that is close to the ideal human needs temperature. Today, the new materials and especially the solar, geothermal, and wind accessories, enables the maximum sustainability of these specific building structures and provides them with an even better energy efficiency.

Keywords: earth-sheltered house; underground housing; historical insight; property-based monitoring data; sustainability

1. Introduction Underground residential architecture is neither a new a concept, nor is its use discontinued; it is noticed that today there is a large number of buildings belonging to a group of subterranean structures bearing different denominations. Traditionally, these structures were built, above all, in the cases where the level of energy consumption for their functioning is reduced to the minimum. Underground housing, began when natural holes and natural or artificial caves were used, or primitive artificial structures were created [1]. Modern underground architecture is particularly developed in the field of housing. One of the main purpose of using this typological form of housing, is the ability to save energy by using the earth as an insulator, as well as other passive systems, such as solar, geothermal or wind energy for generating all the clean energy needed for the functioning of the houses [2]. In theory and practice there are two main types of this specific architecture. The first type is underground earth-sheltered home, built below the level of terrain or completely underground. These types of underground structure provide enough functional needs for living space through the atrium as a central outdoor courtyard. The second type is bermed earth-sheltered homes, which could be built above the terrain, or partially buried in the grade, with earth covering one or more walls. In most cases, these structures have only one facade, with the earth that covers the other sides [3].

Sustainability 2018, 10, 3629; doi:10.3390/su10103629 www.mdpi.com/journal/sustainability Sustainability 2018, 10, 3629 2 of 15

The main objective of this research is to determine correlations between the earth-sheltered house and the soil depth, and to improve their thermal efficiency with some additional energy renewable resources. A critically analysis of the underground main housing types is aimed in order to identify factors that contribute the house performance and their thermal efficiency. To date, the underground houses and their thermal efficiency have been mostly analysed through the relation between their structural and thermal characteristic, and less within the connection between the soil depth, location of the houses, and climate zones. Rob Roy [4], as an advocate of the theory and practice of underground houses, starts his book with defining a profound typology of these structures, based on a very clear description that refers to two different approaches to subsurface dwelling: The bermed house and the chambered house. The bermed house involves construction of the structure at/or close to original grade and “berming” the side walls of the building with earth as well as covering the roof with earth and sod. In the chambered house, the entire structure is below the original grade. The characteristics of underground houses are often used to describe their position and the benefits that these structures have in regard to atmospheric conditions, but also their energy savings properties in their use. In addition to these very positive characteristics of the underground homes according to Ray G. Scott [5], once you are closed 1.2 m or 1.5 m underground, with every exterior exposure, you can expect to find year around temperature stabilizing. The construction of underground houses can be viewed in the context of the structural typological aspect similarity, but thermal characteristics of the earth sheltered houses according to the University of Minnesota studies [6], have resulted primarily from anticipation of substantial energy savings. In typical above ground structures, energy is wasted due to unwanted heating or cooling of the surroundings. Energy efficiency and thermal aspects of an underground structure can also be linked to the present day’s criteria related to the ecological properties of buildings. The development of modern underground architecture has its similarities, with ecologically responsible design since the energy crisis of 1972 [7]. In this paper a global review of the evolutionary development of underground housing is made. The historical periods when this type was especially developed and used are considered also in the relation to their thermal efficiency. The development of underground residential physical structures intensified at the turn of this century, precisely with the emergence of innovations in the area of building technology, the emergence of new materials and energy supply systems. In this sense, underground structures can certainly be viewed through the aspect of long-term potential benefits of earth-covered buildings, which has to do with their substantial independence from temporary power outages [8]. In conclusion, it is recommended that wider use of underground housing could be favorable from the aspect of thermal characteristics.

2. Historical Development Review of Underground Housing The chronological study of underground housing starts with the results of archaeological research of human origin. From the very beginning, people used various forms of shelter, including various forms of caves, holes, pits, or natural recesses cut in the rocks, which were a form of natural underground habitats. During the Neolithic period, people gradually abandoned the woodland, mountainous regions and settled in fertile plains. The mental effort that enabled people to start building, and not to use natural shelters, is a segment of the so-called “Neolithic revolution”. In Iran, one of the cradles of civilization, there are still well-preserved remains of a whole series of underground dwellings. In the area of Maymand, the winter troglodyte houses were carved out of the soft rock, in layers of up to ﬁve houses/apartments in height. The remains of the settlement today consist of 400 identiﬁed houses and 123 units, which are authentic and intact. This settlement represents one of Iran’s oldest surviving villages. It has been continuously inhabited for 2000 or 3000 years, and some archaeologists claim that the village belongs even to the Mesolithic period [9]. The Orkney, the so called “Neolithic Heart”, which was declared a UNESCO World Heritage Site in 1999, includes a group of Neolithic Monuments to the Scottish Archaeology Archipelago and consists of a large tombstone with Maas Hove, two ceremonies of stone circles (Stenness and Brodgar Ring) and settlements. Skara Sustainability 2018, 10, 3629 3 of 15

Brae is a Neolithic settlement with earth sheltered residential buildings built between 3180 and 2500 B.C. The appearance of underground residential architecture can be perceived on all continents. In addition to the physical structures that were built by human hands, still were natural shelters, which were later converted to housing. Mesa Verde National Park in Colorado is the most valuable preserved habitat that represent the apex of architectural sophistication of the Northern San Juan Ancestral Puebloan culture (550 to 1300 A.D.). There are various sizes of structure on the site that were built from sandstone and mud mortar. In the case of Mesa Verde, there is a rare situation of two various underground structures on the site. The first observation is that the whole village was built under the cliff, and the second is that besides masonry-walled villages there is also a pit house settlement on the site [10]. Besides the Mesa Verde, the site of S. Eustachius in Göreme, Cappadocia, Turkey, represents the very unique fragment of the rupestrian culture heritage. These structures were built as subterranean shelters. Located in a zone of volcanic origin, the settlements were made thanks to the natural plasticity of the environment, that enabled the ancient inhabitants to build the space for a living and in the same time as the shelters that could save their lives from the enemy attack. In periods of intensive warfare and destruction, people used the underground structures as living forms of protection from an enemy. The structures carved in vertical slopes of loess like corridors and used for housing, and, the name of the” lagum” is still used in the Vojvodina region, Serbia. Maintaining constant temperature conditions in residential buildings in the 21st century is becoming one of the major aspects that significantly affects the quality of life. The deeper from the surface of the earth the more stable the temperature of the earth. Studies indicate that the relative temperature fluctuation is stabilized at the depth of 0.2 m, while at two m below the surface of the earth the temperature is equal to the average annual temperature [11]. Asia and Africa are certainly continents where the natural environment is used today for these purposes. The new underground residential architecture arises with increased awareness for energy consumption and rests on the experience of anonymous builders of underground facilities, whose concepts today are innovative solutions for the housing problem of the 21st century man.

3. Methodological Approach This paper presents a Case study based on the analysis of the underground housing from different periods and from different locations, with an emphasis on the thermal characteristics that affect the energy efficiency and comfort of life. The analysis was conducted through different historical periods to highlight the advantages and disadvantages of this type of housing. Based on various ways of building underground houses in relation to the terrain, the division into underground buildings integrated into the terrain (buried in rocks and buried in the fields), and true underground buildings built in the ground and bermed earth-sheltered buildings was accepted. Dobraca house near Kragujevac has been shown in a way that very old historical examples can serve as good inspiration for experimental thermal efficient design in 21st century. The method analysis of thermal characteristics, based on external and internal temperature measurements and wind speed in a certain period of time is shown. As a basis for the conclusion and recommendations, a review of the quoted references concerning research at different locations as well as the work of the author is used.

4. The Basic Types of Underground Houses

4.1. Underground Buildings Integrated into the Existing Ambient The Chinese model of underground residential architecture (in addition to the Yaodong of the atrium type construction), as the most prominent model, has elevation type facilities created by the integration of the premises into the terrain. There are two types of underground structures; facilities that were buried in the rocks and those that were buried in the ﬁeld, serving as the inner yard, called yaodong wells or ﬂooded yards. The Loess Plateau, covering 400,000 km2, spreads over the whole of the Shanxi province and great areas of Shaanxi, Ningxia, Gansu, and Henan provinces. The Loess Sustainability 2018, 10, 3629 4 of 15

Plateau, with cave dwellings cut into the friable loess, was inhabited in ancient times [12]. The “troglodytes” still live in the types of housing units that can be found as a group of desert villages in North Africa, such as Matmata in the Bula region of Tunisia. “Troglodytes” housing is made by hollowing the core shafts in the ground and then from those holes, used as small courtyards, the houses interiors were cut in the dry vertical earthen “walls”. This type of underground living is characteristic for its constant temperature that allows adequate functioning of these units, even during the winter period.

4.2. True Underground Buildings One of the rare examples of completely underground facilities is the mining area and the town of Coober Pedy in South Australia. Coober Pady is an underground city in South Australia, located 850 km North of Adelaide. Over a long period of time, isolated and remote, it was experiencing cold nights in winter and heat in summer period. Such conditions forced their inhabitants to live in the caves excavated on the slopes of the hills next to the city. Due to the natural insulation provided by the ground, underground structures are thermally efﬁcient [13]. The temperature varies between 35 ◦C and 45 ◦C in the shade, and in the summer period, more than half of the population of 4000 people lives below, where temperatures remain constant and pleasant. Coober Pedy opal ﬁelds were discovered in 1913 and cover an area of 4.954 km2. The similar type of structure could be found in Kandovan village in the district of Sahand in the central region of the province of Osku East Azerbaijan in Iran. In this unique village, homes are not only built on mountains, but carved into it. This rocky structure, which is compressed and shaped into pile pillars containing pockets ideal for housing, originates from volcanic ash and debris arising from the eruption of Sahand Mountain.

4.3. Bermed Earth Sheltered Buildings of an Elevation Type For the purpose of promoting energy-efﬁcient, socially and spatially acceptable construction structures, the Greater Norfolk City of Great Britain has for the ﬁrst time approved the construction of underground residential architecture as a grant-based construction, with the explanation of the application, that the building would be with net zero energy [14]. This status was obtained thanks to the solar collectors and the typological characteristics of the object, with its three sides made of earth, which minimizes its energy needs.

5. Thermal Efﬁciency of Underground Housing Energy efﬁciency, with the energy spent on heating and ventilation, as well as other forms of communal requirements in buildings, is often more often studied in above ground structures. The problem is also more prominent for public buildings where the number of residents is often higher than in residential buildings. However, because of the similarity between the problems, it is possible to apply software programs that can be adapted both to aboveground housing, and underground dwellings [15].

5.1. Aboveground and Earth-Sheltered Building The monitoring of the energy characteristics of earth sheltered residential buildings by observing their energy supply needs (heating and cooling) was provided by Staniec and Nowak [16], who compared the basic characteristics of the buildings by comparing the results of aboveground buildings with flat roofs covered by the topsoil layer, and the need for subterranean residential buildings depending on of the characteristics of the soil layers and their thickness. The obtained results indicate the specific benefits of underground residential buildings and that they are specifically dependent on the diffusion of soil layers that serve to build up underground housing. A connection between typology of residential buildings and energy parameters of structures was observed in relation to two basic types of structures, such as bermed and truly buried underground housing. In this sense, it is possible to categorize them in relation to the four basic divisions as totally Sustainability 2018, 10, 3629 5 of 15

Sustainability 2018, 10, x FOR PEER REVIEW 5 of 15 underground,Sustainability 2018 at, zero10, x FOR level, PEER above REVIEW zero level, and on the hill-side. By comparing the values 5 of 15 and impactsthat in according the general to context their typology,preference Hassan to thermal and stability Sumiyoshi is given [17 ]to made burial thestructures conclusion that largely that in the generaldependthat contextin theon thegeneral preference climatic context characteristics to thermalpreference stability of to the thermal zones is given stabilityin which to burial is they given structureswere to burialconstructed. that structures largely It is thatsignificant depend largely on the climaticthatdepend such characteristics on objects the climatic have ofan thecharacteristics insufficient zones in degree which of the of theyzones visual were in acceptability which constructed. they ofwere structures It constructed. is signiﬁcant as well It thatasis potentialssignificant such objects haveforthat an room such insufﬁcient lighting. objects have degree an insufficient of visual acceptability degree of visual of structures acceptability as wellof structures as potentials as well for as roompotentials lighting. for room lighting. 5.2.5.2. True True Underground Underground Buildings Buildings 5.2. True Underground Buildings HouseHouse in thein the Town Town Bu Bu Gheilan/Gharyan/Libya Gheilan/ Gharyan/ Libya House in the Town Bu Gheilan/ Gharyan/ Libya TheThe main main characteristic characteristic ofof thethe trulytruly underground atrium atrium house house is that is that in most in most cases cases they theywere were The main characteristic of the truly underground atrium house is that in most cases they were builtfrombuiltfrom the the natural natural material, material, suchsuch as limestone and and clay. clay. Their Their most most advance advance characteristic characteristic is also is also builtfrom the natural material, such as limestone and clay. Their most advance characteristic is also thatthisthatthis type type of of structure structure does does not not pollutepollute the ambient ambient and and the the landscape. landscape. thatthisThe typemain of evidence structure that does document not pollute the the good ambient thermal and performance the landscape. of the underground house in TheThe main main evidence evidence that that documentdocument the the good good thermal thermal performance performance of the of underground the underground house housein Gharyan, is the facts that in the summer (Figure 1) the indoor temperature is 20 °C less◦ than the in Gharyan,Gharyan, isis thethe factsfacts that in the summer summer (Figure (Figure 1)1 )the the indoor indoor temperature temperature is 20 is 20°C lessC lessthan than the the external ambient temperature, and nearly 10 °C◦ above it in winter (Figure 2). externalexternal ambient ambient temperature, temperature, and and nearly nearly 1010 °CC above it it in in winter winter (Figure (Figure 2).2 ).

Figure 1. Temperature data: Gharyan during one day in summer [18]. FigureFigure 1. 1.Temperature Temperature data:data: Gharyan during during one one day day in insummer summer [18]. [18 ].

FigureFigure 2. 2.Temperature Temperature data: Gharyan Gharyan during during one one day day in winter in winter [18]. [ 18]. Figure 2. Temperature data: Gharyan during one day in winter [18]. Sustainability 2018, 10, x FOR PEER REVIEW 6 of 15

Sustainability5.3. Bermed 2018 , 10, x FOR PEER REVIEW 6 of 15 Sustainability 2018, 10, 3629 6 of 15

5.3.Old Bermed Yaodong House in the Yulin Village/ Shaanxi Province/ Republic of China 5.3. BermedThe thermal comfort of old Yaodong cave located at Loess Plateau in Shaaxi Province in OldRepublic Yaodong of China House is unsatisfactoryin the Yulin Village/ if compared Shaanxi with Province/ the modern Republic residences. of China Old Yaodong House in the Yulin Village/Shaanxi Province/Republic of China TheIn summer, thermal thecomfort indoor of temperature old Yaodong raises cave the locate leveld ofat thermalLoess Plateau comfort in whichShaaxi is Provincesustainable in Republic(FigureThe 3) thermalof and China it is comfort isalmost unsatisfactory of10 old °C Yaodongless if thancompared cavethe exte located withrnal the atambient Loessmodern Plateau temperature, residences. in Shaaxi but Province in winter in itRepublic is much belowof ChinaIn the summer, is comfortable unsatisfactory the indoor situation. if comparedtemperature with raises the modern the level residences. of thermal comfort which is sustainable (FigureAccordingIn 3) summer, and it tois the almostthe indoor poor 10 °C temperaturecondition less than of the raisesold exte heating thernal level ambient system of thermal temperature,and insulation, comfort but which in winterwinter is sustainable itdays is much the ◦ belowinterior(Figure the3 thermal) andcomfortable it isenvironment almost situation. 10 isC neither less than good the enou externalgh for ambient modern temperature, standards nor but readily in winter controllable. it is much Thebelow temperatureAccording the comfortable to outside the situation.poor would condition go down of oldto − 18heating °C in systemmost cases and (Figureinsulation, 4). Inin order winter to dayskeep the interiorwarmthAccording thermal inside the toenvironment theyaodong poor condition cave, is neither it should of good old be heating enou completelygh system for modern insulated and insulation, standards from the in nor outside winter readily daysconditions controllable. the interior [19]. Thethermal temperatureproblem environment with outside temperatures is neitherwould goodbelowgo down enough human to −18 forneeds °C modern in are most resolved standards cases in(Figure modern nor readily 4). yaodongIn order controllable. homesto keep with Thethe ◦ warmthnewtemperature thermally inside outside theisolated yaodong would profil gocave,es down for it windowsshould to −18 be and Ccompletely in doors. most cases insulated (Figure from4). In the order outside to keep conditions the warmth [19]. Theinside problem the yaodong with temperatures cave, it should below be completelyhuman needs insulated are resolved from in the modern outside yaodong conditions homes [19]. with The newproblem thermally with temperaturesisolated profil belowes for windows human needs and doors. are resolved in modern yaodong homes with new thermally isolated proﬁles for windows and doors.

Figure 3. Hourly Temperature in Yulin Village during one day in the summer [19].

Figure 3. Hourly Temperature in Yulin Village during one day in the summer [19]. Figure 3. Hourly Temperature in Yulin Village during one day in the summer [19].

Figure 4. Hourly Temperature in Yulin Village during the one of the coldest day in winter [19]. Figure 4. Hourly Temperature in Yulin Village during the one of the coldest day in winter [19]. 6. The Case Study—Dobraca House in Kragujevac, Serbia

TheFigure author 4. Hourly´s experimental Temperature design in Yulin built Village in the during village the one Dobraca, of the coldest near Kragujevac day in winter municipality, [19]. located in the central part of the Republic of Serbia, will be presented in this section.

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6.6. The The Case Case Study—Dobraca Study—Dobraca House House in in Kragujevac, Kragujevac, Serbia Serbia TheThe author´s author´s experimental experimental design design built built in in the the village village Dobraca, Dobraca, near near Kragujevac Kragujevac municipality, municipality, locatedSustainabilitylocated in in the 2018the central, central10, 3629 part part of of the the Republic Republic of of Serbia, Serbia, will will be be presented presented in in this this section. section. 7 of 15

6.1.6.1. Design Design Process Process 6.1. Design Process TheThe bermedbermed undergroundunderground earth-shelteredearth-sheltered houshousee waswas designeddesigned andand inspiredinspired byby thethe earlyearly The bermed underground earth-sheltered house was designed and inspired by the early Neolithic NeolithicNeolithic house house (Figure (Figure 5a) 5a) from from the the archeological archeological site site Lepenski Lepenski Vir Vir in in Serbia. Serbia. The The measurement measurement of of house (Figure5a) from the archeological site Lepenski Vir in Serbia. The measurement of the house thethe house house from from Lepenski Lepenski Vir Vir was was the the same same one one that that we we used used for for design design of of the the earth earth sheltered sheltered house, house, from Lepenski Vir was the same one that we used for design of the earth sheltered house, in the case inin the the case case of of the the Dobraca Dobraca House House in in Serbia Serbia (Figure (Figure 5b). 5b). of the Dobraca House in Serbia (Figure5b).

(a()a ) (b(b) )

FigureFigure 5. 5. (( a())a Lepenski)Lepenski Lepenski Vir:Vir Vir ﬂoor: :floor floor plane plane plane of theof of the housethe house house [20 ];[20]; [20]; (b) ﬂoor( b(b) )floor planefloor plane plane and elevationand and elevation elevation of Dobraca of of Dobraca Dobraca house house(Source:house (Source: (Source: authors). authors). authors).

TheThe terrainterrain terrain waswas was suitable suitable suitable for for for implementing implementing implementing this this kindthis kind kind of structure. of of structure. structure. The house The The house (Figurehouse (Figure 6(Figure) was ﬁnished 6)6) was was finishedinfinished 2008 andin in 2008 the2008 monitoringand and the the monitoring monitoring of average of of temperatureaverage average temperature temperature and wind and and was wind wind taken was was quarterly taken taken quarterly quarterly during the during during 2012 theandthe 2012 2016.2012 and and 2016. 2016.

Figure 6. Dobraca bermed earth-sheltered house (Source: authors). FigureFigure 6. 6. Dobraca Dobraca bermed bermed earth-sheltered earth-sheltered house house (Source: (Source: authors). authors). 6.2. Monitoring Some Parameters

The daily temperature inside and outside the bermed-earth sheltered house in Dobraca was analyzed with special emphasis on the insulation layers and wind speed during 2012 and 2016. According to the presented measurement (Tables1 and2), the temperature inside this bermed-earth sheltered house was in the range from a minimum of 15.8 ◦C to maximum 20.6 ◦C (even on the coldest winter day in 2012), which is close to the ideal human needs temperature [21]. Sustainability 2018, 10, x FOR PEER REVIEW 8 of 15

6.2. Monitoring Some Parameters The daily temperature inside and outside the bermed-earth sheltered house in Dobraca was analyzed with special emphasis on the insulation layers and wind speed during 2012 and 2016. According to the presented measurement (Tables 1 and 2), the temperature inside this Sustainabilitybermed-earth2018, 10sheltered, 3629 house was in the range from a minimum of 15.8 °C to maximum 20.68 °C of 15 (even on the coldest winter day in 2012), which is close to the ideal human needs temperature [21].

TableTable 1. 1.Quarterly Quarterly measuredmeasured ofof dailydaily temperaturetemperature (14 h) during 2012 2012 (Source: (Source: authors). authors).

o Daily temperature 2012 oC 40 30 20 10 0 -10 Jan-12 Apr-12 Jul-12 Oct-12 1234 Temperature inside 15.8 17.66 20.22 19.33 Temperature outside -5 19.8 34 22.4 Wind speed m/sec 1.2 0.8 0.4 2

TableTable 2. 2.Quarterly Quarterly measuredmeasured ofof dailydaily temperaturetemperature (14 h) during 2016 2016 (Source: (Source: authors). authors).

o Daily temperature 2016 oC 40 35 30 25 20 15 10 5 0 Jan-12 Apr-12 Jul-12 Oct-12 1234 Temperature inside 16 18 20.6 19.72 Temperature outside 6 20.3 35.4 22.8 Wind speed m/sec 2.2 2.8 3.2 3.6

InIn addition, addition, somesome authorsauthors concluded that that unde undergroundrground houses houses facing facing eastwards eastwards could could make make a significant heat reduction [22], and we have also noticed that the genuine Lepenski Vir neolithic asignificant significant heat heat reduction reduction [22], [22], and and we we have have also also noticed noticed that that the the genuine genuine Lepenski Lepenski Vir Vir neolithic neolithic house on the Danube River has the same orientation as the Dobraca house in Kragujevac. As was househouse on on the the Danube Danube RiverRiver hashas thethe samesame orientationorientation as the Dobraca house house in in Kragujevac. Kragujevac. As As was was expected, the concrete shell structure, with just bituminous coatings and green roof about 0.4 m expected,expected, thethe concreteconcrete shellshell structure,structure, with just bituminous coatings coatings and and green green roof roof about about 0.4 0.4 m m thickness provides nearly satisfies the temperature for comfortable living inside the house. thickness provides nearly satisfies the temperature for comfortable living inside the house. At the Dobraca house location, the wind reaches the operating speed of the small wind turbine At the Dobraca house location, the wind reaches the operating speed of the small wind turbine as an alternative energy resource. The small wind turbine installed at a height of 10 m above ground as an alternative energy resource. The small wind turbine installed at a height of 10 m above ground could produce around 2406 kWh of wind energy per year [23]. Since the energy consumption of this could produce around 2406 kWh of wind energy per year [23]. Since the energy consumption of this small house in Dobraca with about 50 m2 floor space is below 2000 kWh, the wind turbine could small house in Dobraca with about 50 m2 floor space is below 2000 kWh, the wind turbine could provide all the necessary electric energy for this house in future. Currently, the Dobraca house uses provide all the necessary electric energy for this house in future. Currently, the Dobraca house uses electrical energy from Kragujevac low-voltage energy network as a part of the Serbian high-voltage electrical energy from Kragujevac low-voltage energy network as a part of the Serbian high-voltage electricity transmission system. electricityAccording transmission to the data system. presented in Master plan for mountain Rudnik, the average wind speed in thisAccording area is between to the data 2.6–4 presented m/s (Figure in Master 7). plan for mountain Rudnik, the average wind speed in this area is between 2.6–4 m/s (Figure7). Sustainability 2018, 10, x FOR PEER REVIEW 9 of 15 Sustainability 20182018,, 1010,, 3629x FOR PEER REVIEW 99 of of 15

Figure 7. Wind rose graph of wind speed and direction at Rudnik mountain [24]. Figure 7. Wind rose graph of wind speed and direction at Rudnik mountain [24]. Figure 7. Wind rose graph of wind speed and direction at Rudnik mountain [24]. AverageAverage solarsolar irradiationirradiation atat the the Rudnik Rudnik mountain mountain (Figure (Figure8), based8), based on theon datathe data from from Master Master plan planRudnik RudnikAverage is relatively is solar relatively highirradiation andhigh it and isat about theit is Rudnikabout 1320 kWh1320 mountain [kWh24], which [24], (Figure which has a8), greathas based a potentialgreat on potentialthe for data using forfrom PVusing Master panels PV panelsasplan the Rudnik secondas the issecond alternative relatively alternative energyhigh and energy resource it is about resource in the 1320 case in kWh the of thecase[24], Dobraca ofwhich the Dobraca has house a great (located house potential (located within for anwithin using Rudnik PVan Rudnikmountainpanels asmountain the inﬂuence second influence area). alternative The area). information energy The information resource presented in presentedthe in thiscase section of in the this isDobraca basicsection data house is thatbasic (located could data bethat within used could foran bedetailedRudnik used formountain research detailed of influence theresearch energy area).of consumptionthe Theenergy information consumption for this presented house. for this in house. this section is basic data that could be used for detailed research of the energy consumption for this house.

Figure 8. Average solar irradiation at the Rudnik mountain [24]. Figure 8. Average solar irradiation at the Rudnik mountain [24]. In the last 30 years,Figure the 8. annual Average temperature solar irradiation in Kragujevac, at the Rudnik has mountain been raised [24]. in approximately one In the last 30 years, the annual temperature in Kragujevac, has been raised in approximately one degree ◦C (Figure9). This temperature is almost equal, with the underground temperature over 10 degreeIn °Cthe (Figure last 30 years,9). This the temperature annual temperature is almost in equal, Kragujevac, with the has underground been raised intemperature approximately over one 10 meters depth (Figure 10). metersdegree depth°C (Figure (Figure 9). 10).This temperature is almost equal, with the underground temperature over 10 meters depth (Figure 10). Sustainability 2018, 10, x FOR PEER REVIEW 10 of 15

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Figure 9. Annual temperature in Kragujevac, Serbia in the period 1980–2012 [24]. Figure 9. Annual temperature in Kragujevac, Serbia in the period 1980–2012 [24]. Figure 9. Annual temperature in Kragujevac, Serbia in the period 1980–2012 [24].

Figure 10. Temperature regarding soil depth inin thethe samesame climateclimate zonezone asas CaseCase StudyStudy househouse [[25].25]. It canFigure be 10. concluded Temperature that regarding while monitoring soil depth in monthlythe same climate soil temperature zone as Case at Study four house m depth [25]. in the It can be concluded that while monitoring monthly soil temperature at four m depth in the temperate zone, it is in the range 12–15 ◦C, which is close to the average annual temperature in temperate zone, it is in the range 12–15 °C, which is close to the average annual temperature in Kragujevac,It can be Serbia. concluded that while monitoring monthly soil temperature at four m depth in the Kragujevac, Serbia. temperateFigure zone, 11 shows it is thein the position range of 12–15 the 75 °C, m deepwhic well,h is close located to 50the m averag South-Weste annual of thetemperature house, with in Figure 11 shows the position of the 75 m deep well, located 50 m South-West of the house, with drinkingKragujevac, water, Serbia. but also for non-drinking requirements. drinkingFigure water, 11 shows but also the fo positionr non-drinking of the 75 requirements. m deep well, located 50 m South-West of the house, with drinking water, but also for non-drinking requirements. Sustainability 2018, 10, x FOR PEER REVIEW 11 of 15 Sustainability 2018, 10, x 3629 FOR PEER REVIEW 1111 of of 15

FigureFigure 11. 11.SiteSite plan plan of the of theDobraca Dobraca house house with with all the all theauxiliary auxiliary facilities facilities (Source: (Source: authors). authors). Figure 11. Site plan of the Dobraca house with all the auxiliary facilities (Source: authors). TheThe water water from from the the well well could could also also be used be used as separate as separate open open loop loop VSWC VSWC systems systems with with water water for for heatingheating Theand and water cooling cooling from the thethe house, house,well or could as or an as also anintegrated integratedbe used hybridas hybridseparate system system open connected loop connected VSWC with with systems solar solar PV with PV panels. panels.water In for In future,heatingfuture, there thereand is ancooling is anoption option the for house, forinstalling installing or as the an the waterprintegrated waterproofoof hybrid membrane membrane system on onconnectedthe the roof roof for with forrain rain solarharvesting harvesting PV panels. with with In thefuture,the possibility possibility there to is reuse toan reuse option that that waterfor water installing for for all allnon-drinking the non-drinking waterproof requirements membrane requirements onin inthe the house.roof house. for rain harvesting with theThe possibilityThe Dobraca Dobraca to house reuse house was that was built water built at forthe at all the 12% non-drinking 12% terrain terrain slope slope requirements (Figure (Figure 12). 12 inThat). the That slope house. slope provides provides 3.8 3.8m of m of soilsoil above aboveThe the Dobraca the external external house walls walls was that that built are are atlocated located the 12% at at the terrain the back-side back-side slope of(Figure of the the building, 12). That andand slope 4.054.05 provides mm ofof bermed bermed 3.8 m soil of soilsoillayers layers above on on the thethe left externalleft and and right rightwalls side side that of of are the the located house. house. at the back-side of the building, and 4.05 m of bermed soil layers on the left and right side of the house.

FigureFigure 12. 12.CrossCross section section of Dobraca of Dobraca house house with with the thesoil soil cover cover measure measure (Source: (Source: authors). authors). Figure 12. Cross section of Dobraca house with the soil cover measure (Source: authors). 7. Discussion7. Discussion 7. Discussion TheThe multifunctionality multifunctionality of of undergroundunderground housinghousing structures structures is reﬂectedis reflected in a number in a number of advantages of advantagesthat theseThe thatmultifunctionality facilities these havefacilities in relation haveof underground in to relation aboveground to abovegroundhousing residential structures residential buildings. is reflected Inbuildings. addition in In to aaddition the number landscape to of theadvantagesprotection landscape aspects, thatprotection these the facilities energy aspects, aspect have the inenergy therelation climate aspe to ctaboveground change in the period climate residential becomes change the buildings. period primary becomes In aspect addition relatedthe to the landscape protection aspects, the energy aspect in the climate change period becomes the SustainabilitySustainability2018 2018,,10 10,, 3629x FOR PEER REVIEW 1212 of 15 15

primary aspect related to the implementation of exactly this typological form. In addition, it should tobe thenoted implementation that these structures of exactly are this an typologicalideal typolo form.gical form In addition, when it itcomes should to be combinations noted that thesewith structuresother energy are anefficient ideal typologicalsystems in formorder whento obtain it comes the house to combinations that with withzero otherconsumption. energy efficient Energy systemssavings in orderthese forms to obtain of construction the house that are with mostly zero reflected consumption. in the reduction Energy savings of energy in these consumption forms of constructionfor the needsare of cooling mostly and reflected heating in the[26]. reduction The earth of does energy not consumptionreact as fast to for temperature the needs changes of cooling as andthe air heating does. [This26]. Themeans earth that, does for not instance, react as if fastthe air to temperaturesurface temperature changes ranges as the airfrom does. −15 This °C to means 35 °C ◦ ◦ that,through for instance,the year if(winter the air through surface temperature summer), then ranges three from m below,−15 C the to 35ground´sC through surface the yeartemperature (winter ◦ throughwill vary summer), only between then three10 °C m to below, 15 °C the[27]. ground ´s surface temperature will vary only between 10 C ◦ to 15 InC[ the27 ].search of the ideal typological characteristics of underground residential buildings, CoffeeIn theand search Crier have of the designed ideal typological a courtyard characteristics house in Austin, of underground Texas, USA residential [28]. Their buildings, main task Coffee was andto design Crier havethermal designed efficiency a courtyard buildings, house and in the Austin, building Texas, that USA could [28 survive]. Their the main tornado task was impact. to design The thermalsolar energy efficiency panels buildings, were also and integrated the building on thatthe couldsite, and survive it is theone tornado of the “pionier” impact. The hybrid solar energyenergy panelsefficiency were model also integratedof the house, on thein th site,e late and 1970’s it is one of the of the20th “pionier” century. hybrid energy efficiency model of the house,A step in further the late towards 1970’s of the the thermal 20th century. efficiency of underground housing is in the direction of designingA step a furtherhybrid system towards by the integrating thermal heat efficiency pump of systems underground with PV housing (Figure 13). is in the direction of designing a hybrid system by integrating heat pump systems with PV (Figure 13).

Figure 13. Proposed a full solar water pumping system with monitoring system [29]. Figure 13. Proposed a full solar water pumping system with monitoring system [29]. Efﬁciency of energy consumption in above ground and underground structures can be determined by observingEfficiency the of intervals energy between consumption the established in above initial ground and endand pointsunderground of use of energystructures for heatingcan be anddetermined cooling. by According observing to Roodmanthe intervals & Lenssen between [30 th],e buildingsestablished use initial 35% ofand energy end inpoints the world of use and of areenergy directly for heating responsible and cooling. for 35% According of global emissions.to Roodman Two-thirds & Lenssen of [30], global buildings electricity use 35% production of energy is forin the building world operations.and are directly An important responsible consideration for 35% of global for the emissions. development, Two-thirds design of and global construction electricity ofproduction buildings is with for building low energy operations. requirements, An import asideant from consideration their usage, for are the the development, local, prevailing design climate and conditionsconstruction [31 of]. buildings with low energy requirements, aside from their usage, are the local, prevailingClimate climate zones conditions as a belt shaped [31]. zones in which the underground structures are located should be consideredClimate zones as a prerequisite as a belt shaped for the zones use ofin typologicalwhich the underground models for which structures the provision are located of thermal should comfortbe considered and the as achievementa prerequisite of for the the passive use of typological house effects models are possible, for which but the with provision the provision of thermal of alternativecomfort and energy the achievement sources such of as the solar passive collectors house and effects geothermal are possible, pumps. but with the provision of ◦ alternativeThe achievement energy sources of the such temperature as solar collectors range of and 18–21 geothermalC in any pumps. period of the year represents the ultimateThe goalachievement of using modernof the temperature technologies range in combination of 18–21 °C within any these period typological of the year forms represents of housing the forultimate obtaining goal aof home using thatmodern is energy technologies efﬁcient in but combination also with idealwith thermalthese typological comfort andforms temperature of housing relationshipsfor obtaining thata home allow that its is maximum energy efficient use. Bermed but also earth with sheltered ideal thermal homes comfort are mostly and located temperature at the moderaterelationships (temperate) that allow climate its maximum zone which use. Bermed enjoys more earth precipitationsheltered homes with are warm mostly not located hot weather at the moderate (temperate) climate zone which enjoys more precipitation with warm not hot weather Sustainability 2018, 10, 3629 13 of 15 together with mild winter. The earth shelters in this region are located in the North to South direction and the whole part of the Southern façade is covered with large windows for capturing solar energy [32]. True underground house typology could be found mostly in hot and humid climate, where there is an extremely high temperature during the day with the intensive sun radiation.

8. Conclusions The climate changes intensify the energy consumption of household appliances such as heating and cooling equipment, which requires the launch of new and alternative procedures with a large influence on the reduction of the CO2 emissions in the atmosphere. In that sense, the thermal efficiency characteristic of underground buildings could be one of the main reasons for promoting this type of the buildings in future urban planning documentation. Through the historical development and thermal efficiency review in this paper, it has been concluded that the good thermal comfort is one of the important living space characteristic of humans through the history of making the decision to live in the underground structures. While presenting the case study of Dobraca house, the conclusion should be pointed out that in temperate climatic zones, bermed-earth sheltered underground houses are one of the house types for achieving the optimum temperature inside the building with minor inclusion of the alternative energy resources. The result of the Case study earth-sheltered house shows that, with the soil about four m depth, and additional wind energy resources, such as small wind turbines and hybrid PV panels, could bring positive results in order to provide an adequate thermal comfort for inhabitants during the winter. In this sense, based on the data from this paper, the following conclusions can be drawn:

• The thermal characteristic of the underground housing structures depends on their location and typology and their relations with the climate zone. • At the temperate climate zone, the entrance facing eastwards is one of the inﬂuential factors for keeping the temperature under 21 ◦C during the summer time, even if the outside temperature is above 35 ◦C. • The green roof with just 0.4 m of soil, provides enough thickness for keeping the internal temperature stabile.

Taking into account all the mentioned qualities, thermal efﬁciency is one of the most important ones, and it can be stated that underground earth-sheltered structures, in temperate climate zones with a terrain slope more than 10%, can certainly be recommended as sustainable and desirable habitat models in the 21st century.

Author Contributions: Conceptualization, A.R.M.; Methodology, A.R.M. and N.K.F.; Software, A.R.M.; Validation, N.K.F. and R.F.; Formal Analysis, A.R.M. and N.K.F.; Investigation, A.R.M.; Resources, A.R.M. and N.K.F.; Data Curation, N.K.F.; Writing-Original Draft Preparation, A.R.M.; Writing-Review & Editing, A.R.M. and N.K.F.; Visualization, A.R.M; Supervision, R.F.; Project Administration, A.R.M. Funding: This research received no external funding. Acknowledgments: The paper is written as a part of research project TR 36,042 supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia. This support is gratefully acknowledged. Conﬂicts of Interest: The authors declare no conﬂicts of interest.

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