Passive Façade Design for Energy- Efficient and Cost- Effective Envelope
It is now a well-established fact that our resources are limited; however, our demands are not. The architectural industry, one of the biggest contributors towards GHG emissions and waste, is taking adequate steps to face the challenge and is deploying passive strategies to address these issues. In this article, Sonali Rastogi, Isha Anand, and Aarushi Juneja discuss the ways in which sustainability and affordability issues are closely linked vis-à-vis issues, such as identity and liveability parameters.
Hamdard, a research-based health and wellness charitable trust, commissioned the design of their 4,000-sq. m administrative and R&D office in New Delhi, India. This was to imbibe their vision and values of innovation, progression, and humility. The budgetary constraints were imposed by the charitable nature of the company where most of the company’s earnings are diverted towards humanitarian activities.
Therefore, every penny invested in the creation of this project had to be justified. Morphogenesis set out to achieve a cost- and energy efficient envelope through an integrated design approach, illustrated through the design of this administrative office, set in a composite climate.
The Integrated Design Approach
The matrix of SAIL (sustainability, affordability, identity, and liveability) governs the philosophy of an integrated design approach.
The approach of ‘No is More’, that is, imagining one has no resources at one’s disposal, becomes an inspiration for creating truly optimized built-spaces responding to present-day issues of stress on resources. The implementation of passive strategies at the site level (thermal banking and evaporative cooling) and at building level (thermal mass, glazing optimization, and facade shading), as guided by historical precedents, combined with modern-day techniques, strongly influenced the optimization of the built form making it sustainable.
The overall site comprising 15,000sq. m area for the administrative office and an existing factory in New Delhi explored the potential of being net-zero in terms of water consumption and energy. The carrying capacity calculation for the site suggested a potential of rainwater collection at 4,695 cu.m/year.
This, along with recycling of grey water through a bio-digester was sufficient to meet the water demand for the entire office comprising 200 people. The annual energy of this building has been targeted at an EPI of 45 kWh/m2/year (HVAC, lighting and equipment load). As compared to a conventional building, passive methods are known to result in reducing the electricity demand. Further, the integration of renewable resources to offset the energy demand, presented a requirement of a 2,100 m2 solar farm to be net-zero on energy.
Affordability in terms of capital investment was a key component of the brief that led to the use of simplistic materials (brick and concrete), along with locally skilled labour to ensure cost control. Site optimization by working with the existing site levels into the built form led to material reduction. Passive design methods and resource optimization led to cost optimization of both construction and operation cost, thereby further enabling an economized investment in renewable resources.
Historical precedents in the region suggest that the architecture itself was a response to the harsh climate and a lack of availability of resources. Delhi and the immediate site context continue to inspire designs since precedents suggest that the architecture itself was a response to the harsh climate and a lack of resource availability.
. Baoli (stepped well)
A dipped site filled with trees presented the possibility and potential of using sunken courts for creating spill-out spaces for the office. An N-S oriented rectangular volume was formulated to minimize the exposed surface area which was raised above the ground making use of the existing excavated area to create an underbelly. This is banked with earth on all four sides and shaded by the building above thus creating a microclimate with reduced perceivable temperature inspired by Agrasen’s baoli.
Further, the use of water bodies explores the potential of evaporative cooling in the hot and dry summer months to enhance outdoor comfort, and double up as an amphitheatre when these are to be drained out (warm– humid monsoon months).
Courtyard plan has been a predominant and prevalent microclimate control feature of the historic Mughal architecture in hot–dry regions of the country which in turn influences the architectural planning of the office. The central courtyard concept has been taken to the next level to create a pixelated plan format with greens and workspaces. The two-storeyed main office block with a 71 × 31 m footprint has been broken down resulting in creating alternating solids and voids. The solids become work halls while the voids provide visual breaks which allow for daylight and air penetration. This also helps in generating a healthy working environment for users in terms of daylight and indoor air quality, thus increasing their productivity.
The series of courts have been optimally punctured into the work hall with a span of not more than 6 m from the work space and with no work desk more than 10 m away from an accessible court with operable windows. The end result is that the entire floor plate is 90% naturally lit. The office has been planned in an open format with collaborative zones to encourage team interaction.
It has been designed for a modular efficiency using a 7.5 × 10.5 m structural grid that not only accommodates the multiple workstation modules and departmental organization while being adaptable to future changes, but also optimally fits the car parking bay below the main office block, thereby ensuring minimal wastage in a resource-intensive yet relatively non-contributory area. The internal self-shading courts with a resultant modified microclimate act as an extended workspace, thus reducing the need for enclosed areas.
The jaali or the musharabiya, a perforated skin inherent to Mughal architecture, is used to moderate the incoming natural light, which could be harsh most of the time, allowing proper ventilation. Thereby it becomes a second skin which acts as a thermal buffer between the building and its surroundings.
Building a user-centric environment is extremely critical in making a design successful. As discussed above, the precedents so interpreted in the project along with modern-day techniques link to the liveability and well-being of employees. Fresh air, daylight, minimal noise, and a steady temperature are the four main factors for a productive work environment,1 and yet many people spend their working week sitting in sealed up, stuffy offices that are dim and dingy thus severely affecting their productivity and increasing the absenteeism rate. The design aims to develop a strong indoor– outdoor connect which is deeply rooted in the Indian social psyche, but often does not find expression in the workplace. Nowadays, with blurred boundaries between our work and private lives, the aspect of making our workplace more liveable gains utmost importance.
Value engineering is a harsh reality, particularly in the context of emerging economies such as India where projects are highly cost-sensitive and can manifest at any stage of a project. Bearing this in mind, the facade treatments are integrated as an extension of the structure of the building. This integrated facade design approach ensures that the vision of the architect is followed through till the completion of the project.
The application of passive strategies through façade design targets the reduction of solar heat gain by the envelope whilst providing a 90% day-lit workspace and reducing its operational cost for lighting and air conditioning. An optimum balance between solar control and daylight has been achieved to design a user efficient built environment. Shading, glazing area (WWR, i.e., window-to-wall ratio), and building materials determine the performance of the facade.
These three elements are analysed and optimized to determine the best solution for the project. For shading the external facade, the vertical fins and horizontal overhangs need to be optimally spaced as per the various orientations. A solar analysis determined the optimal width to depth ratio (1:1) of shading devices for maximum solar control during the hottest period for all the four orientations. As per ECBC, the WWR should preferably be ≤ 40% for this climate.
The cumulative heat gain from the envelope was calculated to assess its thermal efficiency with a 40% and 30% WWR and facade shading parameters at an indoor operative temperature of 24 °C. The solar heat gain from the envelope was seen to drop by 4W/sq. m by the dual strategies of reduction in the glazing area and facade shading. The humble brick is expressed in a cavity wall format to provide insulation as well as internal and external thermal mass.
. Wall and glazing
Cost constraint being an extremely critical criterion, the potential of cheap, local, and easily accessible materials and strategies, were explored to achieve the desired performance. The high thermal mass facade was achieved by using a double-exposed brick cavity wall which is economical and low on maintenance. Additionally, it absorbs ambient heat during the day while radiating lesser amounts of heat overnight. An exposed cavity wall with insulation is only about 10% higher in cost as compared to a regular 230 mm-thick brick wall with external plaster and paint. The 30% WWR has been distributed as long vertical strip windows punctured into the facade, optimized as per the orientation on the outer perimeter, and maximized around the internal courts as they receive diffused sunlight. High-performance glazing can add significant cost to a building, especially when required in larger spans. Therefore, to reduce cost, the panel has been divided optimally in alignment with the interior arrangement of desk height and within standard available spans.
. Shading devices
The jaali, as highlighted above, has been used as a facade strategy to reduce direct heat gain through fenestrations, yet allowing diffused daylight. Brick as a material for jaali proves to be economical with low maintenance and has flexibility to be arranged in various patterns as per the required perforations. Jaali along with the exaggerated concrete roofs are the primary shading devices. Use of these simplistic and climate-responsive strategies and building materials enable envelope optimization not only in terms of energy but also in terms of construction cost (260 €/sq. m).
Overall Energy Performance
The built form and facade optimization together help in reducing the energy demand of the building. According to the GRIHA baseline, the EPI (energy performance index) for an air-conditioned building of this typology is 90 kWh/m2/yr.3 Passive strategies, explore the potential of reducing the demand load and, therefore, lowering the EPI to 45 kWh/m2/yr., that is 50% better than the GRIHA baseline leading to a significant reduction in the cooling demand of the building.
A comparative analysis between the energy demand of the building and the area required for PV panel installation, highlights that the reduction in energy demand also reduces the space required for installing PV panels, thus reducing further investment as land is an expensive resource too. With an EPI of 45 kWh/m2/yr., the annual energy demand of the building is about 270,000 kWh, which needs a PV system over 2,100 sq. m. of 210 kWp. The south-facing existing factory terrace has been explored to plant this system. The analysis done by the solar energy consultants also clearly stated that 23% of the investment cost could be recovered within the first year of installation of the system and the total investment could be recovered in less than 6 years
This comprehensive design process concluded with an overall cost of construction (civil and facade) at 260€/sq. m. As they say, ‘necessity is the mother of all invention’, the limitations set by the client in the design brief were used as an opportunity to create a design with an integrated approach of SAIL.
source- GRIHA Shashwat Magzine