Interview Miguel Llona, with Mel Patrick Kasingsing
Images Mlkk Studio
Passivhaus Series
Completed: 2022
Area: 250 sqm
Location: Bangkok, Thailand
Scope: Concept, design development, tender drawings, construction administration
Typology: Residential
Project description
Edited for brevity
Passive House (German: Passivhaus) is a voluntary standard for energy efficiency in a building, which reduces the building’s ecological footprint. It results in ultra-low energy buildings that require little energy for space heating or cooling. This design approach hailed from Europe, and is a response to a region with cold climes. This design series hopes to demonstrate the potential and benefits of using the Passivhaus approach, this time, in a tropical environment.
Passivehaus-informed designs often tend to be opaque boxes without windows to control the heat flows through these components. We have incorporated other passive design strategies like shading, conscious siting, and daylighting system with skylights to balance the heat gain in the house and the connection to the outdoors. To account for energy efficiency and savings, we have incorporated rainwater harvesting and renewable energy systems to create an energy surplus, which allows the owner to sell the electricity back to the grid.
The strategic window placements ultimately shape the houses’ designs and anchor both their form and function. The atriums within serve as the central living space, awash with light and air with its openings to the exterior and skylight. It is the perfect spot for the house’s future inhabitants to spend quality time together.
The interview
Because of their different designs and configurations, is each house in the series designed specifically for certain tropical climates? If yes, what were the factors and considerations that influenced each scheme?
This design series aims to demonstrate the versatility of the Passivhaus standards for a tropical region. To give a little bit of background, the Passivhaus design standard began in Europe and is widely used in temperate to cold climates. However, applying the same sustainable concept to the tropical context is relatively new.
A common misunderstanding of sustainable standards is that they allow little flexibility because they aim to achieve the absolute best performance in every design decision. Yet, rather than controlling the design solution, the standard aims to promote a sustainable concept that is more comprehensive based on the overall performance of the building. Architects can therefore innovate on diverse solutions and make better decisions for each design context.
All the design schemes in this series adhere to the same overall performance standard for the same tropical climate, yet with diverse spatial designs and material choices to demonstrate the sustainable design’s versatility.
As a supposed model for an energy-efficient building that requires little energy for heating and/or cooling, the absence of eaves in some of the schemes is conspicuous, given how important those are for tropical homes. How are potential sun-shading issues addressed without the eaves?
It is indeed interesting to discuss how the general public perceives energy saving versus how it works in Passivhaus design. In most cases, eaves are an effective way to shade off sunlight, particularly from the intense high-angle sunlight coming from the perpendicular angle to the building façade. Other strategies like vertical fins can also be effective or even more effective for the daylight coming from the side. However, these are specific and localized shading strategies for reducing the energy gain of the building. In Passivhaus, we consider the building as a whole and the energy balance as one entity. If you receive more energy from one particular area, you may compensate for it in the other area. For example, you can have a shorter eave but a smaller window to receive the sunlight, or you can have more oversized windows but compensate for it with a deeper recess or a higher insulated glass panel. The Passivhaus system will calculate and synthesize all these adjustments as feedback on the optimal articulation for architects to make better decisions. The role of the Passivhaus architect is to balance the trade-off and benefit of the architectural design and the energy consumption simultaneously, so you could have an energy-effective design that is not always like a typical long-span canopy for a tropical region.
Oftentimes, the presence of many windows is not enough to prevent heat gain since cross-ventilation is needed to push stagnant air out. How is the concept of cross-ventilation applied in the scheme to maximize the numerous window openings?
Cross-ventilation is a non-mechanical ventilation concept that uses natural wind to exchange air. By bringing in the cool and fresh air, the hot and moist air is removed for better comfort. However, this can be effective only up to a certain degree. In a tropical region, even the outdoor air is very hot and moist, so most of the time, cross-ventilation won’t achieve the level of comfort the human body needs, and additional mechanical cooling will be needed. However, this would mean we would hope to keep all the cooling effects for the air inside the house and not leak into the environment.
A Passivhaus design has this exact purpose–airtight and highly insulated envelopes with a control air exchange system. In a passive house, all the fresh air will be supplied through a centralized and filtered mechanical system with a heat exchange function. This way, we can ensure all the air is clean, dehumidified, and well-distributed, and also retain the most energy, i.e. coolness, from the exhaust air. It is a more stable and effective way to ensure the level of comfort, indoor air quality, and temperature of the air in a tropical region.
In Schemes A, B, C, and E, there are double-height living room spaces that are encased by wall-to-ceiling glass on one side, with seemingly no openings (or clerestory windows) up top for rising hot air to escape from. How do you minimize heat gain in these spaces? How does hot air escape?
It is an essential question for how architects will design the airflow. In natural ventilation, we usually allow spaces for hot air to flow out of the building or even use the hot air to create a stack effect to draw fresh air in passively. However, in a passive house concept, all the ventilation is designed to be operated by the mechanical flow. Instead of gaps allowing air to flow out, we shall decide where to place the supply air and the return of the air, so no air is trapped or mixed. A rule of thumb is to provide air supply in the habitable spaces like the living room or bedrooms and exhaust from the more “contaminated” area like the kitchen, bathroom, and storage room. We can then ensure the fresh and filtered air supply directly to us most of the time. Furthermore, in a passive house, given the excellent insulation design, the air temperature inside the house is much more even than in a typical house. The worries about heated or cold air drift are much less a problem.
The use of copious glass for tropical houses is sometimes not recommended because of the “greenhouse effect” it creates. How did you configure the window opening locations to prevent heat gain for the interior spaces?
A greenhouse effect is built up of two factors: there’s a lot of heat gain through the glass, and there’s no escape for the heated air, so the temperature builds up as time goes by. In Passivhaus, the indoor air is mechanically ventilated and kept cool, therefore, it is not concerned with building up the interior heat. We are more concerned about the cooling load required to compensate for the heat gain through the glass. The occupant may not experience the over-heating discomfort, but he may see the effect in the electrical bills. A passive house architect not only compares the pros and cons of having a glass or not but also considers what mitigation measures and to what degree the measures he can adopt for fulfilling such architectural desire. Architects can employ many tools, ranging from shading, insulation, orientation, type of glass, coating, efficient heat recovery system, and even operable devices to solve the heat gain issue. Nowadays, a good Passivhaus window can reduce 50% to 75% solar heat gain. It is a concern, but a window is certainly not an evil thing to exist as it also brings in other benefits for the quality of the space; it is our role to find a good solution that justifies its use.
Are any of the schemes designed with extreme weather in mind, like typhoons or earthquakes? What were your design considerations for these scenarios? Will they be able to withstand strong winds and rain, which are common in tropical countries?
We were applying the typical standard of tropical weather in this design series without particular concern about the extreme weather.
Are you specifying any special materials for any of the schemes, which would be aligned with your sustainability goals for this project?
There are many steps architects can take to be more environment-friendly for our building industry. One is to design an energy-efficient architecture, in which Passivhaus is tackling this issue. Another is to minimize the carbon footprint during construction by using local materials and transportation. It is always inspiring and exciting to visit local building material shops or factories to find local materials. Not only does it help minimize the carbon footprint, but it also makes the design relevant to the people. The third is about reusing or recycling material, like the project we did in Xian where we reused 50% of the existing facade for a new design.
Yet when we talk about sustainability, our studio does not stop at being “green.” As discussed in another passage, sustainability includes economic and cultural sustainability, which we believe architecture has a key role in.
It is one thing to be environmentally sustainable and another to derive continuity and embrace of the local community. What aspects of the PassivHaus’ design are open to localized customization?
To be a good world standard, it has to be accessible and applicable everywhere to everyone. While many of Passivhaus’s certified equipment and components are developed in western countries, it does not exclude the use of local or other elements as long as it achieves the overall goal. For example, an advanced heat recovery unit in Europe may not address the humidity issue that a local machine in a tropical region can tackle. With this in mind, local wisdom is always important and is welcome to be incorporated early on during the design. In this design series, we wish such a sustainable concept for architecture can also be adopted and widely used in the tropical region and help achieve a more sustainable building and design industry.
What were the major learnings and insights you gained during this process, and how do you plan to apply these in your future work?
This design series is a fascinating and rewarding process for our studio. We went through all the steps—from concept, design development, and energy simulation to detailings—to achieve the hypothesis that the Passivhaus standard is applicable to tropical climate architectural design. One key finding is that energy evaluation and design iteration must go hand in hand. It helps shape many good decisions early on and challenges us to prioritize the most essential to the architectural quality. We are working on realizing one of the design options, and hopefully, it will guide the future of our work. •
