When delving into the envelope of construction and examining how the interior relates to the exterior, the concept of greenhouses emerges as an opportunity to cultivate life indoors, whether dependent on external factors or not. Defined as spaces enclosed by glass or other transparent plastic materials, greenhouses facilitate the growth of vegetables and ornamental plants even during periods of adverse external weather conditions. However, what does designing for plants involve? Climate, species, structural design, and the type of covering are just a few of the considerations to take into account.
According to the United Nations Food and Agriculture Organization (FAO), it is estimated that 52 million hectares of vegetables are cultivated each year. Considering that 22% (that is, 12 million hectares) is related to protected agriculture and of these, 10% (1.2 million hectares) is made up of permanent structures or greenhouses. The truth is that of the total of these latter, almost one million hectares correspond to China, Egypt, India, and other countries in Asia and Middle East, while the rest are mainly distributed in Australia, Canada, South Korea, Spain, United States, France, Israel, Italy, Japan, Mexico, New Zealand, and the Netherlands.
While the concept of a greenhouse is often associated with transparent walls and roofs in rural areas, there are proposals such as the Fazenda Cubo Hydroponic Cultivation by Estúdio Lava that aim to bring its language into buildings, giving rise to indoor urban farming. In this way, through a hydroponic water recirculation system, the use of photovoltaic lights, and a climate-controlled chamber, a sustainable, self-sufficient system is structured, with low water consumption, clean, and pesticide-free.
Related Article
Greenhouses: Spaces for Coexistence between Nature and People
Furthermore, greenhouses are also capable of fulfilling other objectives such as production, conservation of energy resources, research, or exhibition, among others. This is the case of the Mendel Greenhouse by CHYBIK + KRISTOF, which reinvents itself to accommodate a genetics pavilion, becoming a new public space. Beyond dedicating itself to the permanent exhibition of Mendel's legacy, it adapts to the current needs of the community and opens up to cultural events such as international conferences, talks, and exhibitions.
The Importance of Climatic Conditions in Greenhouses
As stated by BIAS Architects when envisioning the Greenhouse as Home, "The climate conditions us as much as it does the plants. Today, in a time where we must develop new sustainability, a time where we need to start sharing our space with nature, this climatic architecture is what we need to master."
The development of plants is conditioned by four environmental or climatic factors: temperature, relative humidity, light, and CO2. When these factors are within certain minimum and maximum limits, plants can perform their functions by considering the architectural requirements of each species, as well as the technologies and tools to protect them from adverse weather conditions such as heavy rainfall or high temperatures, etc.
Temperature determines the metabolic activity, as well as the growth and development of plants, and its distribution within greenhouses is presented as one of the variables that affect the uniformity of crops. Generally, the optimal temperature for plants ranges between 15 and 25°C, and once inside, it manifests itself based on solar radiation. Like in the Orchid Greenhouse in Punta del Este, the environment must control temperature, lighting, ventilation, humidity, watering, and nutrients, in addition to the external climate. In this case, a double envelope is proposed, composed of an outer membrane that protects against wind and cold, and an inner membrane that blocks direct sunlight.
Sunlight represents a fundamental factor in the life of plants because, without it, they cannot perform photosynthesis involving chlorophyll, atmospheric CO2, soil moisture, and nutrients. Within the greenhouse, solar radiation is the basic energy source, so the covering requires certain characteristics that allow maximum transparency of photosynthetically active radiation (PAR) to the crops. However, the transmitted radiation not only depends on the properties of the covering material but also on the characteristics of the greenhouses, such as the roof angle, the presence of single or double walls, and the orientation.
Understanding the behavior of water vapor and air mixtures sheds light on many phenomena in the greenhouse climate. Relative humidity considers the amount of water in the air relative to the maximum it can hold at the same temperature. Another climatic factor that affects plant performance is the excessive humidity that reduces transpiration and slows plant growth. Conversely, if humidity is low, plants transpire excessively, risking dehydration and hindering photosynthesis. Excessive humidity can be reduced through ventilation, increased temperature, and avoiding wet soils, while low humidity can be corrected with reduced ventilation, watering, water misting, or the presence of water surfaces. In the Araucaria Greenhouse, for example, the architecture has been designed to withstand plant humidity.
On the Path to Food Self-Sufficiency
Advancing towards a more ecological agricultural transformation and in the fight against food and energy poverty, there are greenhouses that aim to contribute to food self-sufficiency. Such is the case of the prototype Solar Greenhouse on the outskirts of Barcelona. As a result of research and the search for new forms of adaptation to modern life, it proposes a self-sufficient cultivation space as a solution to food and energy production in cities.
On the other hand, the Agrotopia Research Center for Urban Food Production in Belgium emerges as an example of future food production, but this time within the city, involving intensive space utilization, circular use of energy and water, and reverting to more sustainable greenhouse horticulture. It aims to train the future generation of urban farmers, encouraging them to learn how to cultivate vegetables and work with new horticultural technologies and business models.
Tips and Recommendations for Greenhouse Design
Solar radiation, winds, precipitation, and extreme temperatures often determine the type, roof slope, and orientation of greenhouses. Additionally, the relationship between their dimensions plays a significant role in the framework of the interior microclimate because it determines the exposed surface area of the greenhouse, i.e., the meters of walls in contact with the exterior. The heat losses of the greenhouse are directly proportional to its exposed surface, so the larger it is, the more the interior of the structure will cool down, which is beneficial in warm regions and detrimental in temperate to cold climates.
Depending on the location, the length and width of the greenhouse are related to the subsequent management of climatic conditions. For colder areas, greenhouses should ideally not be less than 12 meters wide and not greater than 24 meters, with shapes that are shorter rather than longer, to better manage the interior temperature. In more temperate zones, if the length is less than 50 meters, the exposed surface area increases, and widths less than 10 meters end up being inefficient for retaining heat, contrary to what happens in warmer areas.
The exposed surface increases with the slope of the roof and with the height of the structure to a lesser extent than with the length/width ratio. In mid to high-latitude zones, the duration and intensity of sunlight limit vegetable production during winter. Measurements show that curved roofs transmit more light than flat ones, and in the latter, the slope significantly influences light transmission. For example, choosing the correct slope in gable roofs favors the entry of light into the greenhouse.
Greenhouse Typologies and Roof Development
The design and structure of a greenhouse must be adapted to the material chosen for the cover, as it will determine the weight to be supported by the structure, as well as the space between pillars, support bars, rafters, distance between gutter and ridge, and roof morphology. There are different typologies of greenhouses with envelopes whose general shape is conceived within the framework of the nine types characterized by the FAO, involving gable roofs, tunnel-shaped, bi-tunnel, or sawtooth roofs, etc. The Glass House in Chile, for example, consists of two glass block vaults integrating subtle atmospheric variables into the design by linking nature with the supporting structure and mechanical conditioning systems.
The materiality of greenhouse covers proves to be a key factor in their construction. The ideal material should meet several requirements such as providing good insulation, high heat retention and thermal performance, high transparency to solar radiation, and opacity to far-infrared radiation emitted by the ground and plants during the night. Ideally, it should combine the thickness and flexibility of plastics with the optical properties of glass. The materials used for greenhouse covers worldwide are divided into patterned or cathedral glass, rigid plastics (such as polycarbonate, fiberglass-reinforced polyester, polyvinyl chloride, etc.), and flexible plastics (such as low-density polyethylene, ethylene-vinyl acetate copolymer, and others).
Sources:
- Greenhouses. Appropriate technology in the productive regions of the Argentine national territory (from parallel 23 to 54) [Tecnología apropiada en las regiones productivas del territorio nacional argentino (del paralelo 23 al 54)]. Compilers: Mario Lenscak, Norma Iglesias. INTA Editions. IPAF Pampeana Region. 2019.
- Use of different plastic covers in greenhouses to improve the effects of radiation, temperature, and relative humidity [Uso de diferentes cubiertas plásticas en invernaderos para mejorar los efectos de radiación, temperatura y humedad relativa]. José Noé Martínez Ramírez. Saltillo, Coahuila, Mexico. August 2008.
This article is part of the ArchDaily Topics: Building Envelope, proudly presented by Vitrocsa the original minimalist windows since 1992. Vitrocsa designed the original minimalist window systems, a unique range of solutions, dedicated to the frameless window boasting the narrowest sightline barriers in the world: Manufactured in line with the renowned Swiss Made tradition for 30 years, Vitrocsa’s systems “are the product of unrivaled expertise and a constant quest for innovation, enabling us to meet the most ambitious architectural visions.” Every month we explore a topic in-depth through articles, interviews, news, and architecture projects. We invite you to learn more about our ArchDaily Topics. And, as always, at ArchDaily we welcome the contributions of our readers; if you want to submit an article or project, contact us.
