Comparative study between the Passive House Standard in warm climates and Nearly Zero Energy Buildings under Spanish Technical Building Code in a dwelling design in Seville, Spain

Comparative study between the Passive House Standard in warm climates and Nearly Zero Energy Buildings under Spanish Technical Building Code in a dwelling design in Seville, Spain Milagrosa Borrallo-Jiménez a , Maria LopezDeAsiain b, ⇑ , Paula M. Esquivias c , David Delgado-Trujillo a a Departamento de Construcciones Arquitectónicas 1, Escuela Técnica Superior de Arquitectura, Universidad de Sevilla, Avd. Reina Mercedes nº2, 41012 Sevilla, Spain b Instituto Universitario de Arquitectura y Ciencias de la Construcción, Escuela Técnica Superior de Arquitectura, Universidad de Sevilla, Avd. Reina Mercedes nº2, 41012 Sevilla, Spain c GIR Termotecnia, Departamento de Ingeniería Energética y Fluidomecánica, Escuela de Ingenierías Industriales, Universidad de Valladolid, Paseo del Cauce n°59, 47011 Valladolid, Spain article info Article history: Received 29 July 2021 Revised 8 October 2021 Accepted 10 October 2021 Available online 24 October 2021 Keywords: Passive House Standard warm climate Nearly Zero Energy Buildings passive architecture energy efficiency abstract The Passive House Standard is based on the reduction of energy demand and consumption. In Spain, this Passive House concept has become the preferred alternative for achieving nearly Zero Energy Buildings. The necessary criteria were incorporated into Spain’s 2019 Technical Building Code, which considers the passive design of buildings. In fact, it is possible that the design of many Spanish buildings complying with the basic criteria of passive architecture and the current regulatory framework, meet the requirements of the Passive House. On the other hand, the adaptation of the standard to different climates is very general and wideranging. The inflexibility of certain criteria brings into question the effectiveness of the certification in warm climates such as in the south of Spain or Southern Europe. This study compares the application of basic Passive House standards with Spain’s current building regulations to achieve nZEB in a project which applies passive design strategies to a single-family dwelling in Seville, Spain. The results show that the current national regulations render unnecessary the application and/or certification of the Passive House standard as a guarantee of energy efficiency and offer a better solution in terms of building sustainability for a warm climate. Ó2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction The Energy Performance of Buildings Directive 2010/31/EU [1] introduced the concept of nearly Zero-Energy Buildings (nZEB) in order to promote buildings that are more efficient at fulfilling the current minimum energy performance requirements. The definition and requirements must be included in the national plan of each EU Member, including a numerical indicator of primary energy use expressed in kWh/m 2 per year. The first Spanish National Plan [2] derived from this directive, defined the nZEB as one that reached class A in the Energy Efficiency Rating Scheme, as the primary energy consumption of class A buildings is 70 % lower than buildings fulfilling the minimum energy requirements of the Spanish Technical Building Code (hereinafter CTE) approved in 2006 [3]. The update of the CTE in 2013 [4] was more demanding in regards to the minimum energy requirements but the 2014 [5] and 2017 [6] national plans did not include an update in the definition of nZEB. However, they did highlight that the update of the CTE was a step forward to reaching nZEB. The December 2019 update of the CTE [7] introduced a fixed, quantitative threshold to define what Spain classifies as a nZEB and the 2020 National Plan [8] includes measures focused on reaching a high energy efficient and decarbonized building stock before 2050 in line with the Directive 2018/844/EU [9]. An increased wareness of achieving low energy buildings gave rise to several Green Building Rating Systems and Sustainability assessment methods for buildings that include an assessment of energy efficiency. The main Green Building Rating Systems and Sustainability assessment methods for buildings known in Spain are LEED [10], BREEAM [11], and VERDE [12]. Additionally, there are other construction standards such as Passive House (hereinafter PH) [13], Effinergie [14], Casaclima [15] and Minergie-ECO [16]. Among them, the Passive House standard is one of the most internationally recognised [17] and promoted as a guarantee of https://doi.org/10.1016/j.enbuild.2021.111570 0378-7788/Ó2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). ⇑ Corresponding author at: Escuela de Arquitectura, Av. Reina Mercedes 2, 41012 Sevilla, Spain. E-mail addresses: [email protected] (M. Borrallo-Jiménez), [email protected] (M. LopezDeAsiain), [email protected] (P.M. Esquivias), [email protected] (D. Delgado-Trujillo). Energy & Buildings 254 (2022) 111570 Contents lists available at ScienceDirect Energy & Buildings journal homepage: www.elsevier.com/locate/enb nZEB in Spain, despite not being rigourously implemented as an official certification. 1.1. The Passive House standard The PH methodology sets out guidelines for achieving ultra-low energy buildings and the voluntary certification of those that meet its criteria. Until very recently, these guidelines had been one step ahead of energy efficiency regulations in some countries, such as Spain, and were considered a benchmark for high energy efficient buildings [17]. Authors such as Colclough et al. [18] recognise the methodological value of this standard in the reduction of energy consumption in different climates and highlight the main strategy of the PH system which is based on controlling the envelope with high levels of insulation and airtightness. This strategy is currently being adapted [18] through a number of codes and regulations at both national and European levels. For a building to be considered a Passive House, it must meet the following criteria [13]: 1. The space Heating Energy Demand is not to exceed 15 kWh/m 2 - year or 10 W/m 2 (peak demand). 2. The Primary Renewable Energy Demand must not exceed 60 kWh/m 2 year for Passive House Classic certification. 3. The Airtightness must be verified with an onsite pressure test giving a maximum of 0.6 air changes per hour at 50 Pascals pressure (ACH50). 4. Thermal comfort must be met for all living areas during winter as well as in summer, with no>10 % of the hours in a given year over 25 °C. For achieving these criteria, the standard proposes an intelligent building design, incorporating passive strategies to control the heat balance, and the implementation of the 5 Passive House principles: 1. High Thermal insulation 2. High insulated windows 3. Heat recovery ventilation 4. Airtightness of the building 5. Absence of thermal bridges This method requires exhaustive control both of the building design, carried out by a certified Passive House Designer and verified through Passive House’s own software (Passive House Planning Package – PHPP) and of the building execution, including several controls by accredited Passive House certifiers. The obligation to apply nZEB energy efficiency concepts to European public buildings from 2018, and to all buildings from 2020 [1] led to a 2015 update of the general PH standards in place since 1991 (Table 1) so as not to lag behind the nZEBs [18]. 1.2. Adaptation of the Passive House standard to warm climates The Passive House began as a building concept which provided high thermal comfort levels with low energy consumption in the context of Central European homes. The standard is now widely accepted in Central European countries [19], particularly in Germany, the country where it was conceived (505 certified homes), and France (311 certified homes). However, in countries such as Spain, the number of PH certified homes remains very low (101 certified homes) [20]. Of the 101 certified homes in Spain, 3.9 % are in Andalusia, an area classified by Köppen as a warm climate [21,22], while the remaining homes are located in a temperatewarm climate, proving that the number of certified homes decreases dramatically in warm climates. This same trend can been seen in Portugal, the south of Italy and Greece [20]. Central European climate conditions, with harsher winters than the south of Europe (which suffers harsher summers) define the Passive House standard, which is based on passive heating strategies. In Southern European climates, which have higher levels of solar radiation and less severe winters, it may be simpler to reduce heating demand [23]. However, these buildings have a higher cooling demand which means habitability and comfort conditions are linked to passive cooling strategies such as natural crossventilation, night ventilation, night radiative cooling or evaporative cooling [24]. While the basic principles of the Passive House standard are general and can be applied across all countries [25]], numerous studies highlight the need to adapt the criteria of the standard to other climate conditions [18] where there is overheating as a result of high levels of insulation, high levels of humidity and poor interior air quality as a result of airtightness and a lack of air renewal. Some of the basic principles of Passive House in its original environment such as mechanical heat recovery ventilation and thermally broken triple glazed windows can be detrimental strategies in warm climates [26] which has a negative effect on its implementation in other climates. As a consequence, the Passive House standard has been modified to adapt to temperate and warm climates within the framework of the Passive-On Project [23]. It was considered that the unique qualities of climate conditions should be taken into account and as a result, that passive strategies depend on climate zones [17,25]. It was concluded that certain passive strategies could be implemented in the design of buildings in warm climates, adapting the concept of the passive home to these climates. These strategies include: - Natural, mainly night time, ventilation to dissipate internal and solar gains. - High thermal inertia which helps avoid overheating and decreases cooling demand. - Use of solar shading such as awnings, blinds or overhangs, which help with solar control. Table 1 Passive House requirements. 1991 and 2015 versions. Source: the authors, from PH standard. 1991 2015 Heating Energy Demand 15 kWh/m 2 15 kWh/m 2 or Peak demand 10 W/m 2 Cooling Energy Demand 15 kWh/m 2 15 kWh/m 2 and dehumidification or Peak demand 10 W/m 2 Airtightness 1 0.60 h 1 n 50 0.60 h 1 n 50 Primary Energy Demand Non-renewable Energy Demand: 120 kWh/m 2 year Covers heating, cooling, DHW and electrical consumption Renewable Energy Demand: 60/ 45/30 kWh/m 2 year for Classic/ Plus/Premium certification Maximum deviation: ± 15 kWh/ m 2 year Renewable energy generated onsite: 60/120 kWh/m 2 year for Plus/Premium certification Covers heating, cooling, dehumidification, DHW, lighting, auxiliary electricity and electrical appliances Outdoor Air rate 30 m 3 /h person (Residential buildings) 30 m 3 /h person (Residential buildings) Heat recovery unit Compulsory/Needed Compulsory/Needed 1 verified with an onsite blower door test. M. Borrallo-Jiménez, M. LopezDeAsiain, P.M. Esquivias et al. Energy & Buildings 254 (2022) 111570 2 Passive strategies gain importance when adapting to different climates so that glazing quality, insulation levels and installations depend on the climate but also on the building form and orientation [19]. As a result, in warm climates, night ventilation can be fundamental for avoiding overheating [27]. These strategies should be implemented as a priority [28] alongside the 5 principles of the Passive House (insulation and airtightness of the envelope). Furthermore, the project showed that low demand for heating can be achieved using air extraction systems without using heat recovery [23,29]. Table 2 shows the adaptation of Central European (cold climate) PH criteria to the warm and temperate climates characteristic of the south of Europe [30]: As can be observed, criteria for new buildings in warm climates contemplate the justification for indirect heating and cooling energy demand as well as the non-compulsory usage of a heat recovery unit in the air extraction system. Nevertheless, one of the PH standard’s weak points is the lack of rigourous adaptation to the diversity of climate zones with no reference to regional micro and macro climate conditions [31]. 1.3. Implementation of the Passive House standard in Spain Prior to the 2019 update of the Spanish Technical Building Code [7], the absence of a definition for nZEB based on quantitative criteria meant that the PH standard was seen as the only alternative for achieving nZEB in Spain. New build homes achieving Class A energy ratings in Spain, possibly meet all or at least some of the PH criteria, yet never get certified. This could be for a number of reasons: additional cost, difficulty of design or execution, demands of an external certification, lack of adaptation to the diversity of climate zones. With regards to additional costs, adopting the PH standard has implications on the cost of the home [18]. However, this increase is not comparable to that of the rest of Europe: additional costs are around 2.85 % in Seville and 10 % in France [23]. This range reflects the differences in construction costs, traditions and thermal regulations between countries. The initial return on investment period also differs between countries: from 19 years in countries such as the United Kingdom, France or Germany to 4 years in the south of Spain. As the number of countries in which the PH standard has been implemented increases, costs have decreased. In Central Europe costs have been reduced from an intial 12 % to the current 3–5 % which reduces amortisation to 10 years [32]. This additional cost is usually reflected in the design and construction of the envelope, which requires greater insulation and thermal breaks of both facings and glazing [18] than traditional construction. In Spain, traditional construction methods do not make use of triple glazing. Nevertheless, some authors point out that the additional cost associated with complying to the PH standard is the minumum in terms of cost-effectiveness necessary to meet the expectations and restrictions of nZEB buildings [18]. Considering the increased energy efficiency demands of the updated CTE, the aim of this study is to verify whether applying the PH standard in warm climates offers a competitive advantage with regards to the improvement of energy behaviour, building and economic sustainablility, compared to compliance with current Spanish regulations through passive design criteria. 2. Materials and methods This study evaluates the use of passive strategies in the design process of a dwelling in the south of Spain, a warm interior climate, as a necessary method to achieve the nZEB requirements set out in the 2019 CTE. It also compares the energy behaviour of the dwelling with the requirements set out by the PH standard for certification. 2.1. Case study description and location The case study is a terraced single-family dwelling on a 210 m 2 plot of mostly flat land. The dwelling is NE-SW facing and has a front and back patio. Other adjoining dwellings sit to the left and right hand side. The two-storey plus basement building has a living-dining area, kitchen, three bedrooms and two bathrooms on the ground and first floor, as shown in Fig. 1. The basement is an open plan space with a small bathroom and storeroom. The indoor courtyard and back patio provide natural lighting and ventilation. Neither the basement space nor its entrance hall are considered in the energy evaluation. The useful and built areas are found in Table 3. In order to define the climatic zones for energy assessment purposes, the HE Energy Saving Basic Document of the Spanish Technical Building Code (hereinafter CTE DB HE) [33] classifies each location based on the severity of its winters and summers (Fig. 2). Winter severity ranges from A to E, plus a for the Canary Islands, and summer severity ranges from 1 to 4, with a and A being the lowest winter severity and 1 the lowest summer severity. The building is located in Gines (37°23 ´’N,6°04 ´’ W), in the province of Seville, an inner province of Andalusia, in the South of Spain. According to the CTE DB HE, Gines is a B4 climatic zone, which supposes mild winters and warm summers, reaching the maximum Spanish summer severity, and has a Mediterranean cli- Table 2 Adaptation of Passive House criteria to warm climates. Source: the authors, from PH standard. Passive House 2015 Adaptation to Warm climates Heating Energy Demand 15 kWh/m 2 or Peak demand 10 W/m 2 15 kWh/m 2 Indirectly: Winter thermal comfort according to EN 15251. T indoor 20 °C Cooling Energy Demand 15 kWh/m 2 and dehumidification or Peak demand 10 W/m 2 15 kWh/m 2 and dehumidification Indirectly: Summer thermal comfort according to EN 15251. T indoor 26 °C during > 10 % summer hours Overheating: less than5% summer hours dT in-out 6°CifT out >32°C Airtightness 1 0.60 h 1 n 50 0.60 h 1 n 50 Outdoor Air rate 30 m 3 /h person (Residential buildings) 30 m 3 /h person (Residential buildings) Heat recovery unit Compulsory/Needed Not strictly necessary Primary Energy Demand Renewable Energy Demand: 60/45/30 kWh/m 2 year for Classic/Plus/Premium certification Maximum deviation: ± 15 kWh/m 2 yearRenewable energy generated onsite:  60/120 kWh/m 2 year for Plus/ Premium certification Covers heating, cooling, dehumidification, DHW, lighting, auxiliary electricity and electrical appliances Non-renewable Energy Demand: 120 kWh/m 2 yearCovers heating, cooling, DHW, lighting and electrical appliances 1 verified with an onsite blower door test. M. Borrallo-Jiménez, M. LopezDeAsiain, P.M. Esquivias et al. Energy & Buildings 254 (2022) 111570 3 mate [21,22], characterized by extremely hot, dry summers and mild, partially wet winters. The average annual temperature is 18.0 °C reaching a maximum absolute temperature of 46.6 °C in July and a minimum absolute temperature of 5.5 °C in February. The average maximum temperature during summer is higher than 25.0 °C and the average minimum temperature during winter is lower than 10.0 °C with an average relative humidity higher than 70 %. 2.2. Methodology Taking into account the importance of including passive strategies in building design [28] to achieve nZEB and, in order to evaluate the level to which compliance with the CTE also meets the PH standard requirements, the following methodology has been used: 1. Correlation of pH standard criteria with CTE requirements. PH criteria have been reviewed for warm climates and the equivalent have been sought in the CTE, especially in the demands related to obtaining nZEB. 2. Passive Design of the Dwelling Both location and setting conditions, and urban planning restrictions have been taken into account so that passive strategies can be incorporated into the dwelling design. 3. Energy evaluation and compliance with mandatory regulations. Once compliance with mandatory regulations has been guaranteed, energy evaluation and certification is carried out on the building with the Spanish government’s officially recognised calculation programmes. 4. Compliance with PH standard for warm climates and comparison with the CTE. The ‘‘regulation” dwelling is checked to see if it complies with the PH standard and which level of pH certification it would achieve. Differences with the CTE are detected during this process. 5. Comparative economic study of compliance with CTE and PH standard for warm climates. An economic study is carried out to obtain the additional costs incurred through certifiying PH voluntarily and in addition to complying with current mandatory regulations, which is seen as the reference cost. 3. Results 3.1. PH criteria and regulatory demands for achieving nZEB in Spain The requirements of the PH standard for warm climates relate to heating and cooling demand, airtightness of the envelope and primary energy consumption, as well as interior comfort conditions. Under Spanish code, these questions and the requirements to achieve nZEB are set out in the regulatory documents for Environmental Health [34] and Energy Saving [33]: 1. CTE-DB-HE Energy Saving The demands related to the requirements of the PH standard are: HE-0 for the limiting of energy consumption, in which the requirements of energy consumption in buildings are defined as almost zero (nZEB); HE-1 regarding conditions for the control of energy demand, in which the thermal and airtight properties of the thermal envelope are specified; HE-2 regarding conditions for thermal installations; and HE-4 regarding the minimum contribution of renewable energy to cover demand for domestic hot water. 2. CTE-DB-HS Health This document sets out the demands to ensure minimum standards of health, such as providing adequate interior air (HS-3). This demand is related to the PH standard and establishes the minimum flow of outdoor air which must enter a dwelling. 3. R.D. 235/2013 Standard [35]: Energy Certification This document is for the regulatory adoption of methodology for the calculation of energy efficiency in buildings (Directive 2002/91/EC [36] modified by Directive 2010/31/EU [1]) to offer the user objective information about CO 2 emissions. This information is displayed as a scale on an Energy Efficiency label in which class A corresponds to the most energy efficient buildings. The scale reflects compliance with the minimum requirements of energy efficiency set out in the CTE-DB-H. To be considered nZEB, as set out in the Energy Efficiency and Saving Plan 2011– 2020 [2], a building must be classified A on the primary nonrenewable energy consumption indicator, the limit values of which are set out in the CTE-DB-HE-0 document [33]. Fig. 1. Ground (left) and First (right) Floors. Source: the authors. Table 3 Table of surface areas. Source: the authors. Built Area (m 2 ) Useful area (m 2 ) Ground floor 89.45 66.90 First floor 47.95 42.93 TOTAL Assessed 137.40 109.83 Fig. 2. Spanish winter (left) and summer (right) severity climatic zoning. The circle highlights the province where the case study is located. Source: Spanish Technical Building Code (CTE DB HE). M. Borrallo-Jiménez, M. LopezDeAsiain, P.M. Esquivias et al. Energy & Buildings 254 (2022) 111570 4 Below, the PH standard requirements for warm climates are compared with mandatory regulation requirements for the climate zone in which the case study is located (Fig. 3). Table 4 summarises how the PH standard requirements for warm climates correlate with Spanish regulations for the B4 climate zone and residential use. 3.1.1. Heating and cooling demand The PH standard establishes that demand for heating and cooling should be equal to or lower than 15 kWh/m 2 /year, and additionally, considers the contribution of dehumidification on the demand for cooling where necessary. Furthermore, for a warm climate, it sets out some indirect criteria for interior comfort in line with regulation UNE-EN 16798–1 [37] (Table 4). The determinations related to heating and cooling demand can be found in CTE-DB-HE-1 [33] which establishes the thermal characteristics of the building envelope (thermal transmittance, permeability, solar control) to reduce energy demand. In contrast to the earlier version, the 2019 update does not establish limit values for heating and cooling demand, but instead establishes a global coefficient for heat transmission through the building’s thermal envelope (K lim ) which depends on its compactness V/A [m 3 /m 2 ]. As the compactess of the case study is 1.44, the global coefficient limit Klim is 0.6 W/m 2 K. On the other hand, regulation calculations related to the UNE- EN 16798–1 [37] standard can be found in the CTE-DB-HE-2 document [33], which coincides with the Code for Thermal Installations in Buildings [38]. This document sets out the ranges of temperature and relative humidity which must be reached both in winter and summer for certain clothing and activity conditions. To achieve a low energy demand, the regulations nevertheless establish the following requirements: 3.1.1.1. Thermal transmittance of the thermal envelope. The CTE-DB- HE-1 document [33] sets the thermal transmittance limit (W/m 2 K) of the building elements of the thermal envelope, as can be seen in Table 5: 3.1.1.2. Solar control of the thermal enclosure. The CTE-DB-HE-1 document [33] also introduces the concept of ‘‘solar control of the thermal envelope” as a strategy for controlling cooling demand. This is the relation between solar gains in the month of July in the openings in the thermal envelope with mobile solar shading activated (including awnings and blinds), and the useable areas included. The limit value set for residential buildings is 2 kWh/ m 2 per month. Fig. 3. Climatic classification of Spain: PH (left), CTE DB HE (right) 1. The black circle highlights the province where the case study is located. Source: the authors. Table 4 Passive House requirements for warm climate and their correlation with Spanish regulations. Source: the authors PH Warm CTE Document CTE requirements Heating Energy Demand 15 kWh/m 2 Indirectly: Winter thermal comfort according to EN 15251. T indoor 20 °C DB-HE-1: Conditions for controlling energy demand Requirements depend on the climatic zone and use. For B4 climatic zone and residential use: U-values thresholds: Façades and floors (air): 0.56 W/m 2 K Roofs: 0.44 W/m 2 K Windows: 2.3 W/ m 2 K Vertical Partitions: 1.20 W/m 2 K Horizontal Partitions: 1.55 W/ m 2 K Partitions dif. Use: 1.10 W/m 2 K Dividing wall: 0.75 W/m 2 K Global envelope U- value depends on the compactness (V/A) Case study U thr : 0.60 W/m 2 K Max Solar radiation on windows during July: 2 kWh/m 2 month Cooling Energy Demand 15 kWh/m 2 and dehumidification Indirectly: Summer thermal comfort according to EN 15251. T indoor 26 °C during > 10 % summer hours Overheating: <5% summer hours dT in-out 6°Cif T out >32°C Airtightness 0.60 h 1 n 50 Verified by a blower-door test For windows(air permeability): Q 100,lim 27 m 3 /h m 2 Blower-door test if Sup us 120 m 2 Outdoor Air rate 30 m 3 /h person (Residential buildings) DB-HS-3: Indoor air quality Outdoor air flow depends on the type of indoor space. Ranges between 6 and 33 l/ s Heat recovery unit Not strictly necessary DB-HE-2: Thermal installations conditions Mandatory if the outflow rate is higher than 0.50 m 3 /s Primary Energy Demand Non-renewable Energy Demand: 120 kWh/ m 2 year Covers heating, cooling, DHW, lighting and electrical appliances DB-HE-0: Limitation of energy consumption DB-HE-4: Minimum contribution of renewable energy to cover energy demand Requirements depend on the climatic zone, usable area, and use. For B4 climatic zone and residential use: Max Nonrenewable Primary energy consumption: 28 kWh/m 2 year Max Total Primary Energy Consumption: 56 kWh/m 2 year Renewable energy contribution for DWH: 60 % M. Borrallo-Jiménez, M. LopezDeAsiain, P.M. Esquivias et al. Energy & Buildings 254 (2022) 111570 5 3.1.2. Airtightness of the envelope and air renewal The PH standard establishes that the building envelope should be completely airtight and that air renewal with 50 Pa (n50) differential pressure must be less than 0.60 h 1 and verified by a blowerdoor test. It also establishes that outdoor air flow should be provided equal to or>30 m 3 /h per person. The envelope’s airtightness is controlled in the CTE-DB-HE-1 document [33], although this only states a limit value of air renewal of 50 Pa (n50) if the total useable area is greater that 120 m 2 . As the case study house has a total useable area lower than this, there are no specific demands on the airtightness of the thermal envelope. The outdoor air flow requirement is correlated in the CTE-DB- HS-3 document [34] in which the minimum ventilation flows are set out. Impulse and extraction flows will be at least those obtained in the following table (Table 6) of the CTE: As well as this direct correlation with the PH standard determinations, the CTE-DB-HE-1 document [33] establishes specific values for air opening permeability (glazing-framework, the airtightness of the join between frame and opaque support is not specified), which depends on the climate severity in winter and is established for 100 Pa pressure. For winter climate severity B (case study) the air permeability (Q lim ) of the window product must be 27 m 3 /hm 2 , which corresponds to Class 2. 3.1.3. Heat recovery and other conditions of the thermal installations The PH standard adapted for warm climates considers that air extraction heat recovery, which is one of its 5 pillars, is not strictly necessary [17][23]. This determination is correlated in document CTE-DB-HE-2 [33]. Spanish code considers both the incorporation of units that allow free outdoor air cooling and air extraction heat recovery in the section related to energy recovery. The former strategy is compulsory if nominal cooling power is equal or>70 kW while the latter is compulsory if expulsion flow is>0.50 m 3 /s. Minimum performance of the heat recovery unit must be between 50 % and 75 % and maximum loss between 180 Pa and 260 Pa depending on the explusion flow: from 0.50 m 3 /s to over 12 m 3 /s. As well as establishing the minimum ventilation flow, the CTEDB-HS-3 document [34] establishes whether general ventilation is hybrid or mechanical, allowing for the incorporation of energy recovery units. However, there are no indications related to the thermal treatment of ventilation air. 3.1.4. Primary energy consumption The PH Standard for warm climates limits the consumption of primary energy to 120 kWh/m 2 per year for heating, cooling, DHW, domestic appliances and lighting. The correlation of this limit value is found in document CTE-DB-HE-0 [33] which establishes the limit values for primary non-renewable energy consumption (Cep,nren) and total primary energy consumption (Cep, tot = renewable energy + non-renewable energy). These limit values depend on the winter climate severity and the type of intervention. The values established in the latest update of the HE require a 50 % decrease compared to previous versions which is a determining factor for achieving nZEB. For a new residential build in a Class B winter climate severity zone, the limit values are Cep,nren 28 kWh/m 2 per year and Cep, tot 56 kWh/m 2 per year. As can be observed, the limit value of primary energy consumption is a 53 % reduction on that demanded by the PH standard, which does not establish limits on primary non-renewable energy. On the other hand, with regard to primary energy, those provisions are found in Spanish code. 3.1.4.1. Minimum contribution of renewable energy to cover demand for domestic hot water. The CTE-DB-HE-4 document [33] establishes the percentage of domestic hot water demand that must be covered by energy from renewable sources, allowing for renewable cogeneration or connection to an urban heating system. The new 2019 version establishes coverage of at least 70 % of annual hot water energy demand from renewable sources, and only 60 % if hot water demand is lower than 5000 l per day, as is the case study (112 l/day). This contribution is obtained from monthly demand and contributes to the global balance of primary energy and non-renewable primary energy consumption. 3.2. Passive design strategies in warm climates The European Directive 2010/31/UE [1] expresses that the measures to improve the energy performance of the buildings should take into account climatic and local conditions as buildings have an impact on long-term energy consumption. The achievement of the requirements of the Spanish Technical Building Code related to the energy demand and the nZEB, accredited by the energy qualification of the building, requires a strong commitment to implementing building passive strategies that consider and take advantage of the local climate and characteristics of the building location. In order to achieve nearly zero-energy buildings, it is essential to implement passive strategies which consider and take advantage of the local climate and characteristics of the building location. Thus, passive design of buildings is a determining factor for the achievement of the parameters established by the PH standard, yet it is not exclusive to this standard. The fundamental passive building strategies [41], based on the building orientation, compactness, solar admittance control, quality of the thermal envelope, airtightness, natural ventilation design and other singular aspects, are also considered by the Passive House standard [42], and have been a part of the architectural discipline from its origin [43], when Table 5 Thermal transmittance limit. Source: the authors, from CTE Element U-limit CTE 2019 U-recommended CTE 2019 External walls and floors 0.56 0.38 External Roofs 0.44 0.33 Elements in contact with the ground or non-habitable spaces 0.75 0.69 Windows and Openings (frame + glazing) 2.30 2.00 Table 6 Minimum ventilation flow (l/s). Source: the authors, from CTE Type of dwelling Dry spaces Wet spaces Main bedroom Rest of bedrooms Living and dining rooms Minimum in total Minimum per wet space 0 or 1 bedrooms 8 – 6 12 6 2 bedrooms 8 4 8 24 7 3 or more bedrooms 8 4 10 33 8 M. Borrallo-Jiménez, M. LopezDeAsiain, P.M. Esquivias et al. Energy & Buildings 254 (2022) 111570 6 there were no active systems to compensate the defective passive indoor conditioning. Although selecting the adequate passive strategy depends on climatic and functional factors, several authors have proven certain strategies suitable for warm climates with high solar radiation levels [41,44,45], such as solar admission control (solar shading), energy flow control (thermal insulation, thermal inertia, solar reflective materials) or natural ventilation strategies (crossventilation, night or early morning ventilation). The design process is based on passive bioclimatic strategies for warm climates with the aim of minimizing demand and energy consumption. Some accredited tools and previous research on bioclimatic design for warm climates [46 47] have been used in order to make specific decisions. The adopted constructive solutions within the case study are based on the vernacular passive strategies for warm climates [48] adapted to the specific climatic conditions of the building location. These have subsequently been tested and anlysed using the official building energy evaluation tools, mandatory for the accreditation of the building energy label in Spain [49]. Baruch Givoni psychrometric charts [50,51], were used to ascertain the main passive strategies that must be used in each moment of the year and time of day (Fig. 4). These are: solar gain in winter, solar shading in summer, the use of thermal inertia, night-time convection cooling in summer and selected cross ventilation. 3.2.1. Solar gains in winter and solar shading in summer: Opening dimensions and solar shading based on orientation. The NE-SW orientation conditioned the location of useful areas of the dwelling and the corresponding design of the two façades. In this lattitude, a window-to-floor ratio of 10 % in each espace guarantee the achievement of minimum Daylight Factor. The excessive daylight illuminance provoking glare can be blocked by using curtains and blinds. This practice results in achieving a 12.41 % window-to-wall-ratio (WWR) for the NE façade and 34 % WWR for the SW façade, and there are no skylights (Fig. 5). All openings have solar shading which were dimensionated acording to use and orientation, given that the SW orientation (rear facade) at that latitude, recieves high solar radiation, mainly in the afternoon which is favourable in winter for its solar gains (Fig. 6). There are no adjoining or facing volumes which can provide the building with shade. From the sunlight study of the main (NE) and rear (SW) façades and the rooms, the overhangs dimensions are ascertained. For example, the bedroom windows are almost square in proportion and have a 40 cm overhang to protect against the rain and avoid direct solar radiation from midday (local solar time) to half evening from mid-February to mid-November, for the SW facing window (Fig. 7), allowing the entrance of solar radiation during all the solar exposition hours from mid-November to mid-February. They are complemented by a rolling blind system for solar shading and daylight illuminance control which will be used when is needed, mostly from late spring to early autum at the hours not covered by the overhang. In the large SW facing opening on the ground floor, the rolling blind system is substituted by an awning to avoid elements which prevent exterior vision and natural light gains. As the awning is a mobile textile element, solar shading can be adapted throughout the year (Fig. 8) acording to the need of entrance of solar radiation during winter and avoidance of it from late-spring to early-autum, and daylight illuminance needs. 3.2.2. Quality of the envelope Passive strategies which take advantage of the local climate conditions for interior thermal conditioning are not effective if the thermal envelope does not preserve active and passive efforts to achieve interior comfort conditions. The key elements in this sense will be the amount of surface area which accumulate and transfers heat, controlled through compactness, the thermal inertia, the thermal transmittance and the airtightness of its elements, and the solar control of the enclosure. Fig. 4. Psychrometric chart with design strategies for the climate of Seville. Source: the authors. Fig. 5. Windows and openings: a) Main façade (NE), b) Rear façade (SW). Source: the authors. M. Borrallo-Jiménez, M. LopezDeAsiain, P.M. Esquivias et al. Energy & Buildings 254 (2022) 111570 7 3.2.2.1. Building compactness. The mandatory document ‘‘DB-HE-1: Conditions for controlling energy demand” limits the global envelope U-value based on the building use and compactness (V/A), which is defined as the relationship between the volumen enclosed in the thermal envelope and the area of the thermal envelope. If the envelope of the building was the thermal envelope, the compactness defined in the Spanish standard would be the inverse of the Shape Factor of the building. In climates such as the Mediterranean with high solar radiation levels hot and dry during summers [52], building compactness is traditionally used [48] to avoid solar overexposure, and is therefore an adequate strategy for the Sevillian case [47]. To achieve the greatest compactness possible (Volume/PArea envelope), the building is designed in cuboid form, with the exception of the front volume on the ground floor. The total surface area of the thermal envelope is 258 m 2 , the enclosed volume 371.53 m 3 therefore a compactness of 1.44 m 3 /m 2 is obtained. 3.2.2.2. Envelope construction system: thermal inertia and thermal transmitance. To use thermal inertia as a passive strategy, high density building solutions have been designed for the facades and adjoining walls based on traditional Southern Spain and Mediteranean climate ceramic construction methods. The building solutions for the opaque elements are not only designed to incorporate thermal inertia in the building but must also have a thermal transmittance lower than the limit value (section 3.1.1). The following table (Table 7) shows the building composition of the solutions, indicating the thickness of layers and the properties of the materials necessary to obtain thermal transmittance, thermal mass, cushioning and divergence. The composition of the solutions gives a thermal transmittance of 0.29 W/m 2 K for the façades and adjoining walls and 0.28 W/m 2 K for the roof. To reduce thermal bridges, junctions between building elements are studied so that insulation is continuous and there are no breaks (Fig. 9), which corresponds to the PH standard pencil rule. For this project, the free tool THERM was used to study thermal bridges, particularly around openings, in the search for uninterrupted insulation as well as the correct reception of carpentry in line with UNE 85219:2016 [53] standard. The constructive resolution of thermal bridges of the structure (columns, beams and lintels) have been resolved by means of an external thermoacoustic insulation of lime mortar with 0.042 W / m.k and a thickness of 2.5 cm. With regards to the thermal properties of the openings: orientation, surface and space served by each opening as well as exterior noise levels have been taken into consideration before choosing the quality of the glazing and frame. To minimise air and noise filtrations a casement window system was chosen over sliding panes for its greater airtightness. The chosen frame is aluminium with thermal breakage, 1.3 W/ m 2 K thermal transmittance and class 4 air permeability (UNE-EN 12207:2017 [54]), which carries two types of glazing (G1 and G2) that respond to the thermal insulation, solar control and Fig. 6. Sunlight exposure from 9am to 5 pm at winter and summer solstice: main façade, top and rear façade perspectives. Source: the authors. Fig. 7. Southwest window overhang design: shading mask. Source: the authors. Fig. 8. Temporary solar shading system or awning on the Southwest façade: winter (right) and summer (left) position. Simulation of the thermal impact by means of CypeTherm software (Cype 2020). Source: the authors. M. Borrallo-Jiménez, M. LopezDeAsiain, P.M. Esquivias et al. Energy & Buildings 254 (2022) 111570 8 Table 7 Characteristics of the building solutions of the envelope. Source: the authors Constructive section Layers Thickness (cm) Conductivity (W/mK) Density (kg/m 3 ) U W/m 2 K Thermal capacity (J/m 2 K) Façade 1. Waterproof lime plaster 1.50 1.30 1900 0.29 19025.4 2. Half foot of perforated brick 11.50 0.667 1140 3. Rock wool 5.00 0.0375 40 4. Non-ventilated air gap 4.50 0.45/k1 5. Rock wool 6.00 0.0375 40 6. Gypsum board panel 1.50 0.25 825 Non-trafficable roof 1. Gravel 7.00 2 1450 0.28 133802.9 2. Geotextile cover 0.20 0.05 120 3. Extruded polystyrene (XPS) 8.00 0.04 37.5 4. Geotextile cover 0.20 0.05 120 5. Bituminous cover 0.50 0.23 1100 6. Cement mortar 2.00 1.3 1900 7. Lightweight concrete 8.00 1.35 1900 8. Concrete floor-slab with Expanded polystyrene (EPS) boxes 30.00 0.667 1470 Trafficable roof 1. Ceramic tiles 1.00 1 2000 0.28 59426.87 2. Cement mortar 2.00 1.3 1900 3. Geotextile cover 0.20 0.05 120 4. Extruded polystyrene (XPS) 8.00 0.04 37.5 5. Geotextile cover 0.20 0.05 120 6. Bituminous cover 0.50 0.23 1100 7. Cement mortar 2.00 1.3 1900 8. Lightweight concrete 8.00 1.35 1900 9. Concrete floor-slab with Expanded polystyrene (EPS) boxes 30.00 0.667 1470 M. Borrallo-Jiménez, M. LopezDeAsiain, P.M. Esquivias et al. Energy & Buildings 254 (2022) 111570 9 Acknowledgements The authors want to acknowledge Diego López de la Serna, student of the University of Seville, for his collaboration in the assessment of the case study. References [1] E. Union, Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the Energy Performance of Buildings, European Union, Brussels, 2010. [2] IDAE, Plan, de Ahorro y Eficiencia Energética 2011–2020 Madrid, España (2011). 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