In a warming climate the coolest buildings are those that are heat resilient

City temperatures in these areas are generally several degrees hotter than in the outer parts due to the way we have previously designed buildings and the ongoing cycle where buildings trap heat, we use energy to cool them and then this energy emits even more heat into the city.

So how do we break this cycle of heating to cool and how can buildings be more heat resilient whilst improving thermal comfort for the users?

Ramboll has been contributing to research on heat resilient buildings to the Urban Redevelopment Authority’s (URA) Urban Lab exhibition on Shaping a Heat Resilient City in Singapore.

The research is based on the Singapore Management University’s (SMU) Connexion building, which is recognised as the country’s first on-site net zero energy building in the city centre, registered under Green Mark by the Building and Construction Authority (BCA) with Green Mark Platinum certification.  This five-storey building uses an Enhanced Passive Displacement Cooling (EPDC) system that uses natural convection to circulate air without drawing power, leading to a 91% air-distribution energy saving.

In this Q&A, Pragas Nadaraja, Associate Director, Buildings tells us how building design is changing to create heat resilient cities.

What are some of the passive techniques that can be used to create heat-resilient buildings and ultimately heat-resilient cities?

This can range from obvious measures to reduce the cooling demand of the building such as maximising natural ventilated space to provide increased thermal comfort, to designing the building to minimise the solar heat gain into the buildings, including self-shading, daylight harvesting and glare minimisation, and optimising façade design to reduce heat load, right through to more innovative techniques such as incorporating an EPDC.

These methods were all incorporated into SMU Connexion. Further, the material composition of SMU Connexion’s façade between air-conditioned areas and the exterior was selected to be insulating to reduce the heat gain from conduction and solar radiation. Vertical shading devices and overall optimised façade design reduces thermal heat gain into the building by 50%.

The building also features an innovative EPDC system that is integrated with lighting fixtures, sensors and controllers and is modular for efficient installation. Photovoltaic panels on the rooftop then generate power to offset any building energy consumption that can’t be managed through purely passive solutions.

What is an Enhanced Passive Displacement Cooling system?

An EPDC system is essentially an innovative air-conditioning system. It started its journey in 2015 as a simple first-generation prototype of passive displacement cooling (PDC) in a small meeting room and a retail space at SMU. The system makes use of natural convection principles and saw its first mass-scale deployment at SMU’s Prinsep Street Residences student facility where we undertook further studies and capability building of the system.

An EPDC system does not consume power to circulate air so it therefore eliminates supply air distribution energy. Fresh air is supplied by Electrically Commutated fans and controlled by CO₂ sensors.

EPDC utilises natural cooling techniques that leverage the density disparity between warm and cool air to establish a pleasant indoor environment. As warm air ascends, it passes through the system's cooling coils, where it is effectively cooled. Subsequently, the denser, cooler air is released into the surroundings, contributing to the overall cooling of the space.

It goes a step further from conventional PDC systems as localised fresh air intake at every floor ensures a lower static pressure in the ducting. The air is filtered without pre-cooling upon entry, only cooled by the cooling coils in the room it enters before sinking into the working plane. This system eliminates the use of energy-intensive air handling units and fan coil units while still maintaining a working temperature of 24°C.

The system benefits of EPDC include:

• major energy savings with greater environmental benefits and cost savings
• it is quieter without the need for fans, therefore creating a more peaceful environment, and
• it saves gross floor area as no air handling unit room is required and the technology is ceiling-suspended eliminating the need for cavity walls and extensive ductwork.

There is also a misconception that older buildings can’t be upgraded to include more passive cooling measures. That is incorrect. We obviously can’t change things such as the direction a current building faces, but incorporating EPDC in high volume existing buildings is certainly possible. EPDC is also well suited to modular construction techniques due to the reduced amount of ductwork. The plumbing networks and the wiring and sensors are plug and play.

Can you explain a bit about the work you have been doing with SMU Connexion and the incorporation of the EPDC system?

In very simple terms we have used passive measures at SMU Connexion to reduce the heat load into the building so that we can in-turn reduce the cooling demand and therefore the active cooling measures. Then with these active cooling measures, ensured that they are optimised to reduce operational energy.

The most significant heat-resilient innovation in this building is the EPDC system, which was applied 100%, making use of a zoning strategy and the natural convection of air to minimise energy expenditure.

An on-site photovoltaic system generates 100% of the total building energy consumption achieving an on-site net zero energy building.

The building also has a SMART Control System that controls the lights during operation. The SMART Control System is used to optimise, monitor and fine tune the energy consumption.

How do you know how much these heat resilience methods will impact a building’s energy use?

We use dynamic energy modelling that identifies all direct and indirect benefits to a project. Our advanced energy modelling tools enable us to capture every aspect of a building and helps the design team develop the right systems for the project.

From overall form, envelope construction and urban context to mechanical, electrical, and plumbing systems, this holistic analysis enables detailed review of componential impacts of building systems to a project’s energy performance and consumption.

We also conduct environmental simulations such as for solar shading, daylighting and glare.

What are some of the other innovative data-driven techniques that are being used to design heat-resilient buildings such as SMU Connexion?

One of the most important is Computational Fluid Dynamics (CFD). This involves numerical analysis and using data structures to analyse and solve engineering problems that involve fluid flows. We have been using this for ventilation analysis and wind-driven rain modelling with SMU Connexion.

Utilising cutting-edge CFD, Ramboll has been devising thermal comfort strategies that work around design constraints to optimise cooling, reduce air conditioning, energy consumption and operational emissions by maximising opportunities for natural ventilation. Several CFD simulation studies helped optimise the design of the EPDC system and ensure the uniform air flow at the occupied level.

We compliment ventilation analysis with wind driven rain (WDR) modelling that aims to reduce the severity of rain penetration into a development’s key spaces. Our extensive simulations allow us to make informed decisions, particularly at preliminary and schematic design stages to mitigate the risk of WDR penetration into spaces during and immediately after rainstorm events.

Are there economic benefits from heat-resilient buildings?

Cost should not be a barrier to creating heat-resilient buildings but that has often been the case in the past where any costs were not factored into the project during the design phase because designers were not thinking about heat resilience as a primary design element. Passive heat resilience measures were a “nice to have” and not a necessity but we are now moving away from that as developers see the long-term economic benefits of sustainable design.

The cost of designing and installing an EPDC system, for example, is similar to a conventional air-conditioning system as long as the passive measures are designed into the project at the start, but the real economic benefit comes from the resilience that these passive measures bring to the building. This economic value can be seen in tenants wanting to rent space in these buildings because their operational costs for energy will be lower, and owners knowing that their building is going to sustain changing heat conditions.

You can’t put a price on a healthy building and that is what can be created through innovations such as EPDC. Our post-occupancy survey on the SMU Connexion building has shown that students want to study in this environment and feel that it is more conducive to learning.

URA’s Urban Lab exhibition on Shaping a Heat Resilient City is running from 17 November 2023 to 1 March 2024 at the URA Centre, Level 1, Atrium in Singapore. Entry is free. You can view more about Ramboll’s EPDC work and the SMU Connexion at the exhibition.