Solar Decathlon Latin America and Caribbean: Comfort and the Balance between Passive and Active Design

This article contains an overall analysis of the results obtained by the four highest scoring teams in the Solar Decathlon Latin America and Caribbean 2015 collegiate sustainable habitat competition. Considering that the prototypes developed were based on energy self-sufficiency when operational, it was considered necessary to propose this analysis based on the degree of suitability of each of these models based on their different performances from the perspective of comfort conditions. It was observed that the design of the prototypes did not manage to properly adjust the relationship between passive and active conditioning elements based on the location’s conditions. Accordingly, this article concludes that a balance of the two aforementioned conditioning modes recorded better results based on the measurements taken.


Introduction
The building sector consumes too many natural resources and is responsible for enormous CO 2 emissions into the atmosphere [1,2]. Therefore, architectural styles must be found that minimize their environmental impact [3,4].
This article is based on a line of research aimed primarily at searching for construction models that minimize environmental impact based on an alignment with the Horizon 2020 (European Union Framework Program, the strategic objectives of which are aimed at scientific excellency and developing technologies), and the UNESCO and Sustainable Development Goals for 2030 (in particular, goal 11: Sustainable cities and communities).
It is based on the premise that in the search for sustainable architectural models, competitions dedicated to generating ideas that are responsive to passive conditioning strategies, as well as maximizing efficiency and self-sufficiency, can and should be a primary research field when it comes to refining future building prototypes.
The Solar Decathlon Competition is the most prestigious sustainable habitat competition on the planet. In collaboration with institutions and companies, universities from all over the world participate with the aim of designing, building, and putting into operation an exhibition pavilion in the form of a housing prototype, with the highest level of self-sufficiency and use of renewable energies.
However, the final construction (which has the dual purpose of acting as both a pavilion that can be visited as well as a prototype that can be monitored) is not the sole purpose of the competition, but rather in the educational and research process, the prototypes undergo the following 10 contests (hence the name decathlon): Architecture, engineering, and construction; energy efficiency; electrical

Methodology
Considering that this is a complex problem that must be analyzed from a singular environmental context (tropical climate and social housing), a two-part methodology is proposed: The first part was based on analyzing the latest advances on the subject and the second focuses on the results obtained in the Solar Decathlon Latin America and Caribbean 2015 competition (SDLAC). These two stages of analysis are represented in Figure 1.
In turn, the first stage of analysis was carried out in three stages: • Firstly, the latest advances in relation to the aim of the competition were analyzed, considering the current strategies/technologies for improving environmental and energy conditions in social housing. In order to do so, a literature review was conducted (mainly scientific articles). With the results from this, a database was developed that can be referenced with the aims and results of the SDLAC competition. • Secondly, the current legislation was analyzed with regard to design and environmental conditioning, both in the country where the competition takes place (Colombia) as well as in other reference countries (Spain). By doing so, the aim was to link the legislative conditions and environmental conditioning strategies (both passive and active) that are applicable to the construction of social housing in a tropical climate.
• Lastly, the rules and guidelines for the different editions of the Solar Decathlon competition were analyzed, displaying their scoring criteria. This information was connected to the literature and legislation of the previous sections in order to verify how far this competition can help to transfer beneficial results into society.
The second stage contains a synthetic analysis of the results obtained by the top four teams in the SDLAC 2015 competition: 1. Casa Uruguaya/Universidad ORT (Uruguay); 2. Casa ALERO/Pontificia U. Javeriana and U. Icesi de Cali (Colombia); 3. AURA Prototype/Universidad de Sevilla (Spain) and U. Santiago de Cali (Colombia); and 4. unSOLAR/U. Nacional de Medellín (Colombia). The four prototypes were compared to the context defined in the first stage and the capacity for transferring knowledge and solutions into society was analyzed, in the context of "social housing in a tropical climate." Sustainability 2019, 11, x FOR PEER REVIEW 3 of 18 In turn, the first stage of analysis was carried out in three stages:  Firstly, the latest advances in relation to the aim of the competition were analyzed, considering the current strategies/technologies for improving environmental and energy conditions in social housing. In order to do so, a literature review was conducted (mainly scientific articles).
With the results from this, a database was developed that can be referenced with the aims and results of the SDLAC competition.  Secondly, the current legislation was analyzed with regard to design and environmental conditioning, both in the country where the competition takes place (Colombia) as well as in other reference countries (Spain). By doing so, the aim was to link the legislative conditions and environmental conditioning strategies (both passive and active) that are applicable to the construction of social housing in a tropical climate.  Lastly, the rules and guidelines for the different editions of the Solar Decathlon competition were analyzed, displaying their scoring criteria. This information was connected to the literature and legislation of the previous sections in order to verify how far this competition can help to transfer beneficial results into society.
The second stage contains a synthetic analysis of the results obtained by the top four teams in the SDLAC 2015 competition: 1. Casa Uruguaya/Universidad ORT (Uruguay); 2. Casa ALERO/Pontificia U. Javeriana and U. Icesi de Cali (Colombia); 3. AURA Prototype/Universidad de Sevilla (Spain) and U. Santiago de Cali (Colombia); and 4. unSOLAR/U. Nacional de Medellín (Colombia). The four prototypes were compared to the context defined in the first stage and the capacity for transferring knowledge and solutions into society was analyzed, in the context of "social housing in a tropical climate."

History and Timeline of the Solar Decathlon
The international Solar Decathlon competition, the most prestigious collegiate competition related to sustainable social habitat throughout the world, took place for the first time in Washington D.C. in 2002, organized by the US Department of Energy. Since then, it has been held every two years in various North American cities.
However, from 2010, the competition has also taken place on other continents, with Spain being the first country to host this event outside of the United States. Subsequently, there were two more editions of the European version of the competition, with the fourth edition being in process (in Hungary) and a fifth edition planned for 2021.
China, Africa, the Middle East, and Latin America are the other areas where this collegiate competition has been held (Table 1), although their histories are shorter as fewer editions have taken place in each of these settings.
Although each of the six Solar Decathlon competitions has different rules, what never changes is the essence of the competition. These are 10 points-based contests on which each team is assessed. The winning team is the one that best combines excellency in design and the production of intelligent energy with innovation, market potential, efficiency, sustainability, and the water cycle, etc.
Since it began in 2002, the competition has held (or is planning to hold or is even currently holding) the following versions in the following locations:

Conditioning Strategies, Legislation, and Competition Rules
We started this literature review with a selective and synthetic study of the current zero-energy building strategies, which may be classified into passive energy saving systems, production technologies, and storage of renewable energies, on the one hand, and efficient energy service systems, on the other [6][7][8].
The last column of Table 2 indicates the bibliographic references that justify the inclusion of the various technologies/strategies and procedures. The reference selection was based on databases with recognized scientific prestige and validity, thus obtaining an updated review of the technologies and strategies studied in this article.

SOLAR ENERGY
Photovoltaic panels Architectural integration Photovoltaic panels for façades [4,9,11,12,[29][30][31][32] Hybrid photovoltaic/thermal systems [9,33] WIND POWER Wind turbines [34] GEOTHERMAL POWER Geothermal heat pump [35] BIOENERGY Biomass boiler [36,37] Biofuels [38] ENERGY STORAGE Batteries [39,40] HVAC (Heating, Ventilating and Conditioning systems) Evaporative cooling [41] Active thermal storage [42] Heat recovery [37,43,44] Radiative heating/cooling [45] Variable air volume (VAV)/variable coolant volume [46,47] DWH Solar water heating (SWH) -Flat plate collectors -Vacuum tube collectors [9,14,32,35,48] Solar heat pump system [37,49] Combined cooling/heating and power (CCHP) [37,50] LIGHTING Light-emitting diodes (LED) [51] Use of daylight [52] HOUSEHOLD EQUIPMENT Efficient appliances [9,32,53] Domotics/Monitoring/Automation [17,30,54] WATER CYCLE Greywater recycling [11,30] Use of rainwater [11] Sustainability 2019, 11, 3498 6 of 17 After analyzing the regulations of the countries being studied (Colombia and Spain), it is clear that the implementation of a certain technology in the architectural process must pass through a legal and regulatory filter. It is for this reason that an updated review of the energy efficiency legislation and renewable energies regulations in both Colombia [55] and Spain [56] was carried out, these countries being the location of SDLAC15 and the field of work of the authors of the article, respectively, which could be assimilated to Latin America vs. Europe. Table 3 shows that although it is true that in Colombia (and in other Latin American countries with similar levels of development) there is a high level of interest in the promotion of renewable energies, in order for this interest to take shape rather than remaining a desire, it is essential that regulations are developed that enable zero-energy building technologies to be implemented. Current Colombian laws do not establish binding objectives and the available economic incentives are indirect [55]. An example of this is the construction sector, for both new buildings and refurbishments (Table 3, BUILDINGS section), which entirely lacks any legislative framework that imposes energy efficiency measures and strategies.
Moving on to the analysis of the competition rules [2], we must point out that these are focused on a series of objectives that are part of the spirit of the competition (Table 4). Thus, based on the process of building sustainable housing cell prototypes, we seek to educate in terms of environmental awareness and serve as a training activity for the members of the participating teams. Hot running water 20 Communications and marketing Evaluates the effectiveness and efficiency of marketing and communications strategies to generate social awareness of the projects and the advantages of using sustainable buildings with a solar energy supply. suitability for the context, both in the contests presented and in the conditioning strategies that could be possible as a result.
Alternatively, the fact of the competition organizers disallowing the storage of energy by means of batteries seems odd (in previous editions of the Solar Decathlon, this prohibition did not exist). This is especially true considering the Colombian electrical system is divided between the national interconnected system (SIN) and the ZNI, or geographic areas where the public electricity service is not available [57], and where the implementation of electric energy storage batteries could be an efficient alternative.

Comparative Analysis of the Winning Prototypes
We will start this comparative analysis by studying the specific results of the SDLAC15 competition, in particular the four teams that finished with the highest scores after 15 days of competition, which are as follows: This prototype consisted of a closed pavilion, very dependent on technology and active conditioning strategies ( Figure 2). However, vertical solar shading was used through an outer layer on its perimeter, with the aim of generating a microclimate between the house and the exterior, thus protecting it from direct sunlight. Low impact materials, such as wood or glass wool, were used with the intention of obtaining low greenhouse gas emissions and generating a reduced ecological footprint. In addition, it was equipped with a system that enables rainwater to be reused for watering plants and hydroponic systems.

Comparative Analysis of the Winning Prototypes
We will start this comparative analysis by studying the specific results of the SDLAC15 competition, in particular the four teams that finished with the highest scores after 15 days of competition, which are as follows:


First Prize: Casa Uruguaya/Universidad ORT (Uruguay) This prototype consisted of a closed pavilion, very dependent on technology and active conditioning strategies (Figure 2). However, vertical solar shading was used through an outer layer on its perimeter, with the aim of generating a microclimate between the house and the exterior, thus protecting it from direct sunlight. Low impact materials, such as wood or glass wool, were used with the intention of obtaining low greenhouse gas emissions and generating a reduced ecological footprint. In addition, it was equipped with a system that enables rainwater to be reused for watering plants and hydroponic systems.
Furthermore, it should be noted that the dwelling was equipped with domotic energy control, enabling the occupant to be informed of the energy demand by the use of a mobile device in order to control the humidity and temperature, depending on atmospheric conditions, with the objective of adjusting the energy balance.  Unlike the previous example, this team presented a completely open prototype with comfort conditions that were based entirely on passive conditioning, which fluctuate depending on the external conditions ( Figure 3). As a result, it was highly dependent on these factors during the final phase of the competition (which, on this occasion, were favorable since there were no rainfalls or excessive temperatures during the competition period).
The operation of the model is based, fundamentally, on its roof, which was designed to provide solar shading at the latitude of Santiago de Cali, and was planted with vegetation to offset the effects of direct solar radiation. The proposal was complemented by a series of balconies that were completely permeable and collapsible, converting the entire house into a covered but open space, as an extension of the outdoor space. Furthermore, it should be noted that the dwelling was equipped with domotic energy control, enabling the occupant to be informed of the energy demand by the use of a mobile device in order to control the humidity and temperature, depending on atmospheric conditions, with the objective of adjusting the energy balance. Unlike the previous example, this team presented a completely open prototype with comfort conditions that were based entirely on passive conditioning, which fluctuate depending on the external conditions ( Figure 3). As a result, it was highly dependent on these factors during the final phase of the competition (which, on this occasion, were favorable since there were no rainfalls or excessive temperatures during the competition period). Unlike the two previous prototypes, this prototype sought a balance, combining both passive and active conditioning strategies (Figure 4)., resulting in a completely open or closed house depending on the weather conditions at the time and adapted to the location where the competition was held.
The theoretical residential building to which the housing cell or prototype would belong is longitudinal: The sides with a greater surface area face north-south, where the sun's position is more vertical. This makes it easier to be protected from the sun. However, it did use solar shading strategies, such as a gallery to the north and a ventilated layer system to the south (constructed using a local bamboo variety called guadua).
Thermal inertia was minimized and natural ventilation was enhanced, always resulting in a side with sunlight and another in shadow, thus generating air flow. The house also had a solar chimney, which is a duct that complements the effect of natural cross ventilation by extracting hot air using the Venturi effect. The operation of the model is based, fundamentally, on its roof, which was designed to provide solar shading at the latitude of Santiago de Cali, and was planted with vegetation to offset the effects of direct solar radiation. The proposal was complemented by a series of balconies that were completely permeable and collapsible, converting the entire house into a covered but open space, as an extension of the outdoor space.
Third Prize: AURA Prototype/U. de Sevilla (Spain) and U. Santiago de Cali (Colombia) Unlike the two previous prototypes, this prototype sought a balance, combining both passive and active conditioning strategies (Figure 4)., resulting in a completely open or closed house depending on the weather conditions at the time and adapted to the location where the competition was held.
The theoretical residential building to which the housing cell or prototype would belong is longitudinal: The sides with a greater surface area face north-south, where the sun's position is more vertical. This makes it easier to be protected from the sun. However, it did use solar shading strategies, such as a gallery to the north and a ventilated layer system to the south (constructed using a local bamboo variety called guadua).
Thermal inertia was minimized and natural ventilation was enhanced, always resulting in a side with sunlight and another in shadow, thus generating air flow. The house also had a solar chimney, which is a duct that complements the effect of natural cross ventilation by extracting hot air using the Venturi effect.
strategies, such as a gallery to the north and a ventilated layer system to the south (constructed using a local bamboo variety called guadua).
Thermal inertia was minimized and natural ventilation was enhanced, always resulting in a side with sunlight and another in shadow, thus generating air flow. The house also had a solar chimney, which is a duct that complements the effect of natural cross ventilation by extracting hot air using the Venturi effect.  After presenting the three award-winning models, which were very different typologies in terms of the use of passive or active conditioning strategies, the unSOLAR prototype ( Figure 5)  After presenting the three award-winning models, which were very different typologies in terms of the use of passive or active conditioning strategies, the unSOLAR prototype ( Figure 5) once again puts forward a completely open design using exclusively passive conditioning strategies, like the casa ALERO.
Regarding its geometry, a notable aspect was its central courtyard that provides cross ventilation to all of the dwelling's rooms, which are protected from solar radiation by the same bamboo elements as those outlined in the previous project. Additionally, it is worth pointing out its traditional construction system, moving away from the prefabrication present in the three previous proposals. From the information gathered from each of the projects, Table 5 was generated, highlighting the use of the different strategies/technologies identified in the first level of analysis.
After analyzing Table 5 and comparing its content to the third section of this article (literature review), the following was surmised: Table 4. Analysis of the 10 contests of the competition: summary table generated from the SDLAC15 Competition Rules, but with our own re-drafting.

Architecture
Evaluates spatial efficiency, the adequacy of the materials in relation to bioclimatic strategies for the 100 Judges Regarding its geometry, a notable aspect was its central courtyard that provides cross ventilation to all of the dwelling's rooms, which are protected from solar radiation by the same bamboo elements as those outlined in the previous project. Additionally, it is worth pointing out its traditional construction system, moving away from the prefabrication present in the three previous proposals.
From the information gathered from each of the projects, Table 5 was generated, highlighting the use of the different strategies/technologies identified in the first level of analysis. After analyzing Table 5 and comparing its content to the third section of this article (literature review), the following was surmised: There are two clearly contrasting models. On the one hand, casa ALERO and unSOLAR correspond to a type of housing that is completely open, entrusting the comfort of the house to passive conditioning strategies. Alternatively, Casa Uruguaya opted for a closed prototype, isolated from the exterior environment, in which the different variables can be managed regarding the exterior, thus being much more focused on active conditioning.
An intermediate position is presented by the AURA project, which proposed a covered but open space (zaguán, in popular Andalusian culture, or antejardín, in popular Colombian culture), corresponding to an adaptation to Latin-Mediterranean vernacular architecture, passively working on the climatic comfort of the different areas of the house. This balance, championed by the prototype presented by the University of Seville, worked remarkably well and, as a result, was recognized with the first prize in the comfort conditions contest (one of the 10 sections of the competition on which each of the participating prototypes was evaluated).

Graphic Results from Monitoring the Different Strategies
In accordance with the above analysis, after establishing the context in which this first edition of the Solar Decathlon collegiate competition was held in Latin America, and comparing the strategies proposed by the four teams with the highest scores in the competition, it is worthwhile to graphically display the results of the continuous measurements carried out by the competition organizers, in order to thereby award the scores for the aforementioned comfort conditions contest of the SDLAC15. These measurements were carried out under equal conditions for all teams, at the same time and therefore with identical weather conditions.
The graphs show the entire competition period during which all the prototypes were monitored, from 5 to 14 December 2015. There was no rainfall during this time. It is worth noting that the city of Santiago de Cali is located at a latitude of 3.42 and an altitude of 926 m. The climate conditions of this location are constant throughout the year, with no conventional seasons as in other latitudes, with the greatest thermal variations occurring between the day and the night.
The monitoring locations of the interior comfort parameters for each prototype were the living room and bedroom. However, the architecture presented by each prototype had no conventional boundaries between rooms and, therefore, the distribution of the houses could vary depending on needs throughout the day. As a sample, a plan of Casa AURA is included (Figure 6), showing the distribution of measurement locations, in this case.
Consequently, the first of the two graphs show the temperatures recorded for the four analyzed teams (Figure 7), verifying how casa AURA achieved a more stable temperature inside the house throughout the day, and obtaining higher temperatures than the completely open prototypes (casa ALERO and unSOLAR) when recording the minimum daytime temperatures, with descending levels in terms of the highest daily peaks.
Similarly, observing the graph of the relative humidity results (Figure 8), we can see how when the outdoor humidity is higher, the open prototypes perform more poorly than the closed prototypes or those equipped with active conditioning systems (casa Uruguaya and AURA). Therefore, as with the temperature graph, we can also see how the results obtained by casa AURA in terms of relative humidity are more stable than for the other competing prototypes.
However, although the graphs show the trends for each prototype in relation to temperature and humidity, showing which prototypes performed in a more stable manner, it is worthwhile to also know the percentage of time during which each of them was within the comfort range set by the competition: Temperature between 24 and 28 • C and humidity lower than 60%. Table 6 shows how the Casa Uruguaya prototype maintained its indoor space in the thermal comfort range for the greatest percentage of time. However, Casa AURA was the prototype that most successfully controlled humidity. As we are dealing with measurements recorded in a tropical climate, the latter is undoubtedly the most significant. In relation to the sum of temperature + humidity (hygrothermal conditions), both the Casa Uruguaya and Casa AURA obtained very similar percentages. latitudes, with the greatest thermal variations occurring between the day and the night. The monitoring locations of the interior comfort parameters for each prototype were the living room and bedroom. However, the architecture presented by each prototype had no conventional boundaries between rooms and, therefore, the distribution of the houses could vary depending on needs throughout the day. As a sample, a plan of Casa AURA is included (Figure 6), showing the distribution of measurement locations, in this case. Figure 6. Plan of the AURA Prototype, with temperature and humidity sensors.
Consequently, the first of the two graphs show the temperatures recorded for the four analyzed teams (Figure 7), verifying how casa AURA achieved a more stable temperature inside the house throughout the day, and obtaining higher temperatures than the completely open prototypes (casa ALERO and unSOLAR) when recording the minimum daytime temperatures, with descending levels in terms of the highest daily peaks. Similarly, observing the graph of the relative humidity results (Figure 8), we can see how when the outdoor humidity is higher, the open prototypes perform more poorly than the closed prototypes or those equipped with active conditioning systems (casa Uruguaya and AURA). Therefore, as with the temperature graph, we can also see how the results obtained by casa AURA in terms of relative humidity are more stable than for the other competing prototypes. Similarly, observing the graph of the relative humidity results (Figure 8), we can see how when the outdoor humidity is higher, the open prototypes perform more poorly than the closed prototypes or those equipped with active conditioning systems (casa Uruguaya and AURA). Therefore, as with the temperature graph, we can also see how the results obtained by casa AURA in terms of relative humidity are more stable than for the other competing prototypes. However, although the graphs show the trends for each prototype in relation to temperature and humidity, showing which prototypes performed in a more stable manner, it is worthwhile to also know the percentage of time during which each of them was within the comfort range set by the competition: Temperature between 24 and 28 °C and humidity lower than 60%. Table 6 shows how the Casa Uruguaya prototype maintained its indoor space in the thermal comfort range for the greatest percentage of time. However, Casa AURA was the prototype that most successfully controlled humidity. As we are dealing with measurements recorded in a tropical climate, the latter is undoubtedly the most significant. In relation to the sum of temperature + humidity (hygrothermal conditions), both the Casa Uruguaya and Casa AURA obtained very similar percentages.
It is worth noting that in the comfort conditions contest, in addition to the thermal and humidity conditions, they were also assessed on light and noise conditions. In the overall calculation of this contest, the Casa AURA scored the most points regarding the other participating teams, and therefore was awarded first prize. It is worth noting that in the comfort conditions contest, in addition to the thermal and humidity conditions, they were also assessed on light and noise conditions. In the overall calculation of this contest, the Casa AURA scored the most points regarding the other participating teams, and therefore was awarded first prize.

Discussion and Conclusions
From the analysis performed (and by studying the applicable regulations), it is clear that there must be specific regulations that oblige all agents and all training and research centers to work towards the production of more sustainable buildings. However, after thoroughly delving into the competition rules, it can be concluded that these are not sensitive to the local component of the location where the final phase of the competition is proposed and carried out. This makes it possible that society would find it difficult to accept solutions that obtained very high scores in most of the 10 contests that comprise the competition, and, therefore, it would not be possible for the desired conceptual and technological transfer to materialize. It is essential that the location is able to industrially handle these technologies so that the prototypes may become a real model for transfer.
Alternatively, and focusing in particular on aspects related to the prototypes' environmental design, it seems that the relationship between passive and active elements has not always been properly balanced. Accordingly, of the four models analyzed, only one (the Aura project) used a strategy that combines a functional typology that was adapted to its context with an adequate balance between passive strategies and active equipment, which provided an adequate performance.
Although the hygrothermal data from the Casa Uruguaya and the Casa AURA were found to be very similar when analyzed regarding the comfort range, an architectural design that depends exclusively on active conditioning actions is considered socio-culturally decontextualised for an environment such as that of Santiago de Cali, in particular when the competition rules impinged on working in a social housing context, for the first time in the history of the competition.
Finally, although the fundamental aspects for transferring results from the Solar Decathlon Competition to the analyzed context are clearly established, it is necessary to continue working to adjust the rules of this collegiate competition for sustainable habitats by producing appropriate national regulations and properly training the agents of the building process if the intention is to truly achieve a high potential for transfer in the short term.
In order to do so, continuing this line of action as a methodological opportunity (for learning through the completion of higher education projects), in search of innovation and transfer, will be a priority.