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Procedia Engineering 165 ( 2016 ) 49 – 57

15th International scientific conference “Underground Urbanisation as a Prerequisite for Sustainable Development” Fighting energy poverty by going underground

a, a b Lefkothea Papada *, Nikolas Katsoulakos , Dimitris Kaliampakos

aMetsovion Interdisciplinary Research Center, National Technical University of Athen, Patission 42, Athens, 10682, Greece bNational Technical University of Athen, Patission 42, Athens, 10682, Greece

Abstract

The inadequate coverage of energy needs in the residential sector, known as energy poverty, is a primary socio-economic problem, worldwide. Especially in Greece, under the pressure of the recent economic crisis, households face serious difficulties in meeting sufficiently their energy needs. We will show that one long-term way to minimize energy consumption, and therefore, tackle energy poverty, is the turn to underground constructions. Although underground built space can offer important benefits in terms of energy demand and consumption, underground residences have been largely regarded as unusual, far from the common residence type. However, in Greece and especially in Greek islands, underground residences have been often used in order to deal with extreme heat, during summer. Moreover, since 2012, underground constructions have been introduced as a special residence type by the Greek building regulation, thus facilitating the expansion of such practice. In this paper, the benefits of an underground residence in terms of energy poverty are being examined. More specifically, energy consumption required to achieve desired energy standards is calculated both for an earth-sheltered and an aboveground residence of similar characteristics in Greece. In this way, an indicative energy poverty ratio is calculated for the two residence types. The different climatic conditions throughout the country have been taken into consideration, by examining different Climatic zones. The findings show lower energy poverty ratios in the case of the underground residence at all climatic zones. In other words, a household living in an underground dwelling can more easily meet its energy needs compared to another one living in an aboveground dwelling. Hence, the analysis shows that modern architecture design should more systematically turn to underground constructions, incorporating the advantages of bioclimatic performance and energy savings. ©© 20162016 The The Authors. Authors. Published Published by Elsevier by Elsevier Ltd. ThisLtd .is an open access article under the CC BY-NC-ND license (Peerhttp://creativecommons.org/licenses/by-nc-nd/4.0/-review under responsibility of the scientific). committee of the 15th International scientific conference “Underground Peer-reviewUrbanisation under as aresponsibility Prerequisite of for the Sustainable scientific committee Development of the .15th International scientific conference “Underground Urbanisation as a Prerequisite for Sustainable Development

* Corresponding author. Tel.: +30-265-140-23-59 E-mail address: [email protected]

1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 15th International scientific conference “Underground Urbanisation as a Prerequisite for Sustainable Development doi: 10.1016/j.proeng.2016.11.734 50 Lefkothea Papada et al. / Procedia Engineering 165 ( 2016 ) 49 – 57

Keywords: energy poverty; underground; aboveground; earth-sheltered; energy consumption; energy poverty ratio; energy savings;

1. Introduction

The inadequate energy coverage emerges as a crucial socio-economic problem of recent years, worldwide. Global energy demand is continually increasing and is expected to increase by nearly 30% from 2013 to 2040, according to the central World Energy Outlook scenario [1]. At the same time, the global economic situation is characterized by great instability, with fuel prices going through constant fluctuations. This trend results in the current energy problem, in which households face difficulties in meeting sufficiently their energy needs (space heating and all other domestic energy needs) and suffer from energy poverty. A practical way to measure energy poverty has been that of UK, which regards a household as energy poor if it is needed to spend more than 10% of its income for domestic energy expenditure, in order to have an adequately warm home [2]. An adequately warm home is the one maintaining 21°C in the living room and 18°C in the rest of the house [2]. Globally, 1.2 billion people have no access to electricity and more than 2.7 billion people keep on cooking with biomass, which causes harmful indoor air pollution [3]. The problem is also severe within Europe as , affecting approximately 10-15% of the European population [4], with Greece, Bulgaria and Cyprus being first on the list of the most energy poor countries. For the case of Greece, the recent economic crisis -since 2009- has deteriorated the energy poverty issue, with substantial variations in fuel prices, numerous arrears in electricity bills and drastic reduction in households’ incomes [5]. The Greek residential sector represents over 29% of the whole final energy consumption (5.04 Mtoe), of which almost 64% is used for space heating, as shown on Table 1 [6].

Table 1. Percentage distribution of the total energy consumption by end-use. End use of energy consumption Percent Space heating 63.7% Domestic hot water 5.7% Cooking 17.3% Space cooling 1.3% Lighting 1.7% Appliances and equipment 10.2% It is noteworthy that 41% of the dwellings are thermally unprotected, as built prior to 1980, when the first Building Thermal Insulation Regulation was enacted in Greece. In fact, the basic thermal regulations approaching the European standards (KENAK Regulation) were introduced just a few years ago, in 2010. It has been reported that Greek households present the highest energy consumption in Europe, while also being significantly higher even from countries with very cold climates, such as the Nordic countries [7].

2. Underground space living

Underground space has been used as a safe haven since ancient times, providing protection to people against enemies and climatic conditions. Through the course of time, energy gains of underground space have turned underground constructions as a good alternative for handling extreme climatic conditions and reducing energy losses. Notable examples of underground dwellings can be seen all over the world. The heritage of “ dwellings” has been preserved in several regions, such as Guyaju (China), Matmata (Tunisia), Cappadocia (Turkey), Kandovan (Iran), (), Guadix and Granada (Spain), Santorini (Greece) and (an underground town in Australia). Apart from the old, traditional cave dwellings, modern earth-sheltered dwellings can be found in certain regions, such as Base Valley (), Oxford Gardens (London), Therme Vals region (Switzerland) etc. Representative examples are shown on Figures 1 and 2. In Greece, several projects including modern earth-sheltered houses in islands (i.e. Kea, Ios, Milos, Crete) are currently under construction, as only in 2012 the Greek state Lefkothea Papada et al. / Procedia Engineering 165 ( 2016 ) 49 – 57 51 included such structures into the Building Regulation, facilitating their construction. More specifically, according to the Building Regulation, earth-sheltered buildings are characterized by the following features: x They are constructed beneath the ground surface. x Their roof is accessible, covered with the material of the natural soil and follows the natural geometry of the ground. x They have only one main façade exposed above the ground surface. Modern underground architecture design addresses the need for bioclimatic residences with low energy demand and consumption, incorporating cost-effective techniques and landscape’s aesthetic qualities. It should be noted, though, that such constructions were and remain pioneering, as underground residence techniques have not gained a wide acceptance yet and are still regarded as “unusual”.

Fig. 1. Cave dwelling in Santorini, Greece. 52 Lefkothea Papada et al. / Procedia Engineering 165 ( 2016 ) 49 – 57

Fig. 2. Modern earth-sheltered dwelling in Therme Vals region (Switzerland).

The main benefits of earth-sheltered dwellings (based on good geological backgrounds), compared to aboveground ones, are the following [8,9]: x Significantly better energy performance, thus achieving energy and cost savings. x Maximization of the available construction space as built in areas of high inclination and taking advantage of space below the ground surface. Moreover, materials derived from the excavation can be used in subsequent stages of the construction. x Minimization of construction materials and maintenance costs, as having limited surface area exposed above the ground surface. x Increased resistance to extreme weather conditions and safer environment against earthquakes and fire. x Ensuring cooling during summer and heat in winter, as temperature remains stable beneath the ground surface. In addition, there is no possibility of frozen pipes. x Minimization of the visual and the environmental footprint of the construction. From the above points, the first and foremost benefit of underground living is energy savings. In this paper, an underground residence vs a typical aboveground one is examined in terms of energy poverty and the possible benefits of going underground are explored.

3. Methodology

The energy poverty status is calculated as follows (DECC, 2015):

Energy poverty ratio (EPR) = (required energy consumption x price) / income (1)

According to Eq.1, a household is regarded as energy poor if ERP exceeds 0.10. Therefore, the higher is the ratio, the higher is the risk of energy poverty. Lefkothea Papada et al. / Procedia Engineering 165 ( 2016 ) 49 – 57 53

The required energy consumption of a household, found in Eq.1, consists of six main end-uses, as shown on Table 1, with space heating representing the main load of it. It has been referred [10] that among the above loads, space heating and cooling are the only ones that can be objectively assessed for different regions, as depending on technical parameters (meteorological conditions and characteristics of the building shell) whereas the rest ones vary depending on individual behavioral and economic characteristics of households. In this paper, the required energy consumption is calculated based on space heating and cooling, providing a good estimate of the final energy consumption, according to the method of degree-days:

Eh = Htot/nh xHDDx 24/1000 (2)

Ec = Htot/nc xCDDx 24/1000 (3)

where, Eh: annual energy consumption for heating (KWh) Ec: annual energy consumption for cooling (KWh) Htot: total heat transfer coefficient of the building due to convection and due to ventilation (W/°C) HDD: heating degree days (°C*days), CDD: cooling degree days (°C*days) nh: the efficiency rate of the heating system nc: the energy efficiency ratio (EER) of the cooling system Using Eqs. 2 and 3, Eq. 1 is transformed as follows:

ౄ౪౥౪ మర ౄ౪౥౪ మర ୶ୌୈୈ୶ ୶୮୰ଵା ୶େୈୈ୶ ୶୮୰ଶ ሺሻ ൌ ౤౞ భబబబ ౤ౙ భబబబ (4) ୍୬ୡ୭୫ୣ where, pr1: price of thermal energy (€/KWh) pr2: price of cooling energy (€/KWh) Income: (before-tax) annual income of the household (€)

Two building models with the same geometrical characteristics and heating/cooling systems have been created (one for the aboveground and one for the underground residence), so that the comparison between the two is possible. More specifically, the main characteristics of the two models are the following: x Detached house built after 2011 x Area of 100 m2 x Thermal insulation to the walls and the roof for the aboveground residence whereas no thermal insulation for the underground one (the soil layer around the building works as insulation). The thermal transmittance coefficient is: 9 Walls: U = 0.40-0.60 W/m2 K for the aboveground and 0.26-0.34 W/m2 K for the underground 9 Roof: U = 0.35-0.50 W/m2 K for the aboveground and 0.11 W/m2 K for the underground 9 Floor: U = 0.38-0.49 W/m2 K for the aboveground and 0.29-0.35 W/m2 K for the underground x Wooden window frames with double glazing (12mm air gap), U = 2.60-3.20 W/m2 K x Oil fired boiler for heating x Air conditioning split units for cooling x Total efficiency rate (nh) of the thermal energy system: 0.90 x Energy Efficiency Ratio (EER) of air conditioning units: 3.00 In order to take into account the different climatic characteristics throughout Greece, 4 different tests have been made, examining the two building models lying at the most representative regions of the 4 Climatic zones of Greece (A and B are the warmer ones while C and D the colder ones). More specifically, the regions selected as representatives of the Climatic zones are (Figure 3): x Chania for Climatic zone A (Lat: 35.33, Long:25.18, Alt: 30 m) x Athens for Climatic zone B (Lat: 37.96, Long:23.67, Alt: 107 m) 54 Lefkothea Papada et al. / Procedia Engineering 165 ( 2016 ) 49 – 57

x Thessaloniki for Climatic zone C (Lat: 40.62, Long:22.97, Alt: 31 m) x Kozani for Climatic zone D (Lat: 40.30, Long:21,78, Alt: 625 m)

Fig. 3. Regions selected as representatives of the Climatic zones of Greece.

Two EPR have been calculated for the 4 regions (4 Climatic zones) selected, one for the aboveground and one for the underground building model, according to Eq. 4. All variables vary depending on the respective region but the only decisive factor differentiating an aboveground from an underground residence is the heat transfer coefficient (Htot), which depends on the technical characteristics of the building shell and on the climatic conditions prevailing. More specifically, the base temperatures selected for the calculation of degree-days are 16°C for HDD and 22°C for CDD, as better approximating the climatic conditions of Greece. The prices of heating oil supply have been obtained by the Ministry of Development, Competitiveness, Infrastructure, Transport and Networks [11] for year 2014. The incomes have been obtained by [5] for year 2014, a research based on a primary survey of households in Greece. For the Htot calculation, a mathematical model has been constructed, calculating Htot based on several parameters, i.e. the area of the building, the year of its construction / the corresponding technical characteristics, the type of the residence and the respective Climatic zone, all based on the Greek legislation [12]. The steps followed are depicted on Figure 4. Lefkothea Papada et al. / Procedia Engineering 165 ( 2016 ) 49 – 57 55

Fig. 4. Steps followed for the “Energy poverty ratio” calculation.

4. Results and Discussion

The results of the total heat transfer coefficient (Htot) are shown on Table 2. The Htot values for the aboveground building model are considerably higher compared to the underground one at all climatic zones. Lower heat transfer coefficients imply lower heat flux and consequently lower energy losses. Thus, at first stage, the Htot values reveal a far better energy performance for the underground model.

Table 2. Total heat transfer coefficient (Htot) for the aboveground and the underground building model. Aboveground Underground Percentage increase for the aboveground Chania (A) 278.724 199.054 +40% Athens (B) 253.924 188.124 +35% Thessaloniki (C) 235.974 179.984 +31% Kozani (D) 221.024 173.344 +28% The annual energy consumption for heating, cooling, as well as the overall energy consumption required to achieve desired energy standards, are shown on Table 3. As indicated by the data, the aboveground building presents significantly higher total energy consumption than the underground one at all cases, with the difference varying between 28% and 40%, depending on the Climatic zone. Actually, the greater energy savings by going underground is observed at Chania, (the warmest Climatic zone), wherein annual energy consumption reaches extremely low levels. Thus, it is confirmed that the soil layer around the plays a crucial role in reducing thermal losses and maintaining air temperature at a constant level. Apparently, moving from the warmer to the colder Climatic zones increases energy consumption, as much in aboveground as in underground dwellings. As an example, a building lying at Kozani (Climatic zone D) presents 175-200% greater total energy consumption (for the aboveground and the underground, respectively), compared to the same building lying at Chania (Climatic zone A). However, in both climatic zones, the underground building model wins by far the aboveground one, in terms of energy savings. 56 Lefkothea Papada et al. / Procedia Engineering 165 ( 2016 ) 49 – 57

Moreover, it is shown that the vast majority of energy consumption consists of thermal loads. The ratio of heating / cooling energy consumption leans steadily towards heating at all regions, varying between 0.76/0.24 at Climatic zone A to 0.98/0.02 at Climatic zone D.

Table 3. Annual heating, cooling and overall energy consumption in (KWh) for the aboveground and the underground building model. Chania (A) Athens (B) Thessaloniki (C) Kozani (D)

Abovegr Undergr Abovegr Undergr Abovegr Undergr Abovegr Undergr

Eh 3585 2560 6274 4648 7558 5765 12695 9957

Ec 1142 816 930 689 1005 767 240 188

Etot 4727 3376 7204 5337 8563 6531 12935 10145

Percentage +40% +35% +31% +28% increase for aboveground The energy poverty ratio results are displayed in Figure 5 and Table 4. As shown, the aboveground building’s ratio is steadily and significantly higher compared to this of the underground building for all Climatic zones, reaching up to an increase of 40%. This fact reflects the greater difficulty of a household living in an aboveground building to sufficiently meet its energy needs. In other words, a typical aboveground building is 28%-40% more vulnerable to energy poverty vs a similar building built underground, thus it should spend approximately 1.5 times more the amount of money spent by the underground building in order to cover its energy needs. This creates an important economic burden, exposing more often aboveground constructions to the risk of energy poverty.

0.09 0.083 Aboveground Underground 0.08 0.065 0.07 0.065 0.06 0.049 0.05 0.039 0.043 0.032 0.04 0.028 EPR 0.03 0.02 0.01 0.00 Chania (A) Athens (B) Thessaloniki Kozani (D) (C)

Fig. 5. Energy poverty ratio for the aboveground and the underground building model.

Table 4. Difference of the Energy poverty ratio between the aboveground and the underground building model. Chania (A) Athens (B) Thessaloniki (C) Kozani (D) Percentage increase for the +40% +35% +31% +28% aboveground

5. Conclusions

The analysis presents the benefits of an underground residence vs the typical aboveground residential model prevailing in Greece. Apart from the smaller environmental impact and the successful integration into the natural environment, the main benefit of an underground residence proves to be the great energy savings potential and the lower risk for energy poverty occurrence. More specifically, total energy consumption of the Lefkothea Papada et al. / Procedia Engineering 165 ( 2016 ) 49 – 57 57 underground building model proves to be 28-40% lower than the aboveground’s. Moreover, domestic energy expenditure with respect to income is drastically reduced, presenting an energy poverty ratio greatly reduced, up to 40%. This figure reveals the major comparative advantage of the underground building model, as providing a far better level of thermal comfort with regard to the respective cost, by only built underground. Such a difference is not easy to be reached by bioclimatic design in typical aboveground structures, which would also affect the construction cost. The findings show that modern architecture design should more systematically turn to underground constructions as residence models, taking advantage of their significant energy gains. This tactic is also consistent with the EU 20/20/20 targets, which aim to reduce greenhouse gas emissions by 20% by 2020 (as compared to 1990), increase the amount of renewable energy of the energy supply by 20% and reduce the overall energy consumption by 20% through energy efficiency.

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