The buildings of the Holcim Apasio Hermosillo plant in the state of Sonora in Northwest Mexico are an appropriate aesthetic, cultural, and physical response to the desert setting, with simple building forms, natural colours, passive and active cooling strategies, and landscaping with indigenous flora.
Holcim Apasco’s Hermosillo plant operates with state-of-the-art production processes, equipment, and control systems, and it meets high standards for safety, quality, energy efficiency, and environmental performance. The plant is extraordinary for two main reasons. First, the administration and service buildings – all the habitable buildings on the site – were designed to meet the stringent sustainability criteria defined by the Holcim Foundation for Sustainable Construction. These criteria call for balanced environmental, social, and economic performance, contextual appropriateness, and innovative and exemplary advancement in construction.
The six buildings are designed to provide efficient, attractive, comfortable, and healthful work environments. Thermal, hygrometric, luminal, acoustical and indoor air-quality conditions determined the design and construction criteria. Hermetic building envelopes were selected to keep out dust, a constant presence in the desert, and noise, constantly emitted from the production machinery. A controlled ventilation and heating or air-conditioning system is installed in all buildings except for the warehouse, where air conditioning would be impractical.
The buildings are designed as energy-efficient green buildings with low environmental impact. They incorporate passive cooling strategies, use locally available materials, and incorporate daylighting, water-conservation systems, and innovative high-efficiency low-emission mechanical and electrical systems.
With a base course of cast-in-place concrete and clad in cementitious panels, the building exteriors are a display of cement and concrete within in a setting of roads and walks paved in concrete. Walls are the colour of the local sand, and the red trim echoes the rosy desert sunsets. This harmony of materials and colours is reinforced by a harmony of form. Drawing upon the local modern vernacular of simple volumes, the architecture aesthetically suits the desert and industrial contexts, and the ensemble is furthermore integrated into its desert setting by the landscaping, which is conceived as an extension of the surrounding nature onto the plant grounds.
The landscaping at the Hermosillo plant meets all these requirements in a straightforward and elegant way. Artificially landscaped areas are limited to the immediate surroundings of the buildings and the areas along main walkways. Materials are limited to crushed rock and indigenous plants, both sourced locally. Two colours and sizes of crush rock are used, creating fields of colour and texture as a setting for the plants, most of which are placed individually or in loose groups. The variety and contrast of forms, colours, and textures produces a pleasant and chromatic landscape that is altogether fitting to the plant and the desert environment. This restrained landscaping concept blends well with the non-landscaped parts of the site, the areas of the site with undisturbed vegetation, and the natural desert beyond.
The plants in the artificial beds are watered by an underground drip irrigation system that deposits the water at the roots, minimizing water loss by evaporation. The desert-adapted gardens require 60 percent less water than a conventionally designed garden would.
A special landscaped zone circles the administration building. The greened earth berm is designed to create a cooler microclimate, reduce the albedo around the building, and direct breezes upward onto the facade, thereby improving thermal comfort within the building. The solar protection and insulating mass of the earth also reduces temperatures in the bottom floor of the building, improving the efficiency of heating, ventilation, and air-conditioning equipment and all other electromechanical components located there, as well as moderating the temperature in the garage area beneath the building.
Nowhere in the world does the sun so completely influence the environment as in the desert. Intense solar radiation provides strong illumination, causes extreme temperatures, and causes rapid evaporation. And among deserts the Sonora is extreme – it is known among engineers as the “Saudi Arabia of solar radiation.” With 332 sunny days per year, Hermosillo is an ideal place to apply solar technologies both proven and new – and the plant does this in several ways. The buildings make full use of the sun as a dependable source of illumination and energy for power generation and cooling.
The buildings are designed to provide comfortable indoor environments by employing three strategies: first, passive control of all forms of thermal gain, by means of solar orientation, shading, reflection, insulation, ventilation, isolation, reducing exposed surface area, and reducing the ambient temperature around the buildings; second, the use of thermal mass to moderate temperature peaks; and third, an ingenious air-conditioning system that is the first commercial system of its kind in Latin America.
Because heat infiltration occurs through the building envelope, the surface area of most buildings has been minimized by using rather cubic than elongated forms. Five of the six buildings are laid out on an east-west axis for optimum solar control. Walls and roofs are well insulated. The thermal resistance of exterior walls is 7.44m²°C/W (U = 0.13W/m²°C). Walls and roofs are light colored to reflect rather than absorb solar rays. Dark paving around buildings is also avoided to reduce the heat-island effect.
Insulating low-emissivity glass was specified for all windows. Nearly all windows of the buildings are fully shaded by protruding metal surrounds. The roof and part of the south facade of the administration building are shaded by the rooftop array of solar concentrators. The emergency stairs outside the east and west walls of the building provide additional shading for those facades. Other roofs are effectively protected by rooftop photovoltaic panels. Several of the buildings feature roof overhangs to shade the facades. A deep wrap-around overhang shades all windows and walls as well as the users and vehicles outside the sales and logistics building.
The warehouse and workshop building is the second-largest building on the site. It is not air conditioned but the indoor temperature is reduced by means of ventilated facades. The walls consist of a steel structure clad with cementitious panels on the exterior and gypsum board on the interior. As the air in the cavity between the panels warms, it rises through the cavity to the high ceiling, where it is expelled through a roof vent. The stack effect uses no energy and it reduces the indoor temperature by several degrees. The indoor comfort is better than in comparable non-air-conditioned structures.
The passive cooling strategies function very well, but of course only to a certain degree. On the hottest days, as the indoor air temperature inevitably rises above the temperature of the building itself, thermal mass comes into play. The massive concrete of the floors and walls begins to absorb the heat from the air, effectively moderating indoor temperature peaks. This cooling mechanism operates with zero energy. The combined array of passive cooling mechanisms greatly reduces the cooling load on the buildings, allowing the mechanical air-conditioning systems to be downsized.
Solar-driven air conditioning
The scorching heat of the desert sun is used to cool the main building. The air-conditioning system is essentially driven by water heated by solar concentrators. The only power required is for three circulation pumps (two 7hp and one 3hp) and for fans to distribute the conditioned air within the building. A single-effect absorption chiller in the basement is fed with coolant (water and lithium bromide) heated close to boiling by 170 rooftop parabolic concentrators. The chiller produces cool water used to cool air that is then distributed via ducts throughout the building. Requiring solar energy, the system typically suffices to cool the building from 7:30 a.m. to 5 p.m. in the summer.
The innovation here is combining the chiller with solar concentrators, which is highly efficient in the desert. Local adoption of this green technology is unfortunately hampered by cheap electrical power, which is sold at even lower rates in the summer.
If the cooling load ever exceeds the capacity of the system, up to four Energy Star vapor compressor electrical chiller units come on line in sequence. Each system operates as close as possible to full capacity to achieve the best energy efficiency at all times. This battery also serves as an emergency backup.