Indochina Kajima, a real estate development joint venture between Indochina Capital and Japan's Kajima Corporation, has established and operates 6 Wink Hotels in Vietnam over the past five years. Their exterior designs, including walls and windows, have progressively improved to effectively resist heat. Lawrence Mbanu, Project Management Director, estimates that newer hotels save between 800 million and 1.2 billion VND annually in air conditioning electricity costs compared to the first property, primarily due to a focus on thermal insulation.

Speaking to VnExpress on the sidelines of the "Building for Heat Resilience" workshop on 13/10, Mbanu stated that one solution employed is the installation of double-glazed insulated glass with a low heat transfer coefficient (U-value).

Mr. Lawrence Mbanu, Project Management Director of Indochina Kajima (second from left), at the event. *Photo: VGBC*

The U-value at the new hotel is highly efficient, measuring 1.2 W per m2.K (where K is the unit for absolute temperature). This means that for every one degree Celsius temperature difference between the outside and inside, the heat loss through each square meter of material is 1.2 W. Mbanu illustrated this by explaining that when the air conditioning is set to 20 degrees C in a closed room, a person outside on the balcony (where the outdoor temperature is 30 degrees C) would still feel the glass warm to the touch, indicating effective thermal insulation by the material.

Conversely, the initial hotel property had a U-value 1.5 times higher, resulting in a correspondingly greater rate of heat loss.

The calculated electricity savings are based on the assumption that both hotels operate at 75% occupancy, with air conditioning used for 6-10 hours daily, and an electricity tariff of 2,000-2,500 VND per kWh.

While improving the building's exterior increases construction costs by approximately 5-10% of the total project capital, Mbanu calculates that property owners can recover this additional investment within 1.5-2 years of operation, thanks to the electricity savings.

Despite its operational benefits, heat resilience is often underestimated in construction projects. Vu Van Dung, Deputy Director of the Institute for Building Materials (Ministry of Construction), noted that while storms and floods cause visible damage, heat gradually impacts human health and operational expenses.

Furthermore, the entities bearing the initial building costs and the monthly electricity bills are often different, as seen in apartment buildings. Consequently, Dung explained that when selecting construction solutions, investors typically prioritize initial costs over the long-term lifecycle costs of a project.

An Indochina Kajima representative echoed this sentiment, sharing his experience of living in an apartment in TP HCM with inadequate natural light and inefficient ventilation, necessitating increased use of lights and air conditioning. "Investors only care about achieving the cheapest cost per m2, without paying much attention to other aspects," he stated.

The heat resistance of buildings is also often overshadowed by the perception of air conditioning as the default cooling solution. The exterior design of a building receives little attention until a power outage occurs or extreme heat sets in.

To improve this situation, Mbanu believes that educating the public when buying a home is crucial. If equipped with knowledge about ventilation systems and energy saving, homebuyers would make decisions based on the long-term operational benefits, rather than participating in "cheap price games from project developers."

"The simplest indicator buyers should consider is how many watts per m2 are needed to cool a room, which allows them to estimate electricity costs," he advised.

Le Truong, General Director of TT-As Architecture - Construction Consulting Joint Stock Company, emphasized that architecture should be the primary solution for heat resistance, not air conditioning. The effectiveness of a building's heat resistance should be evaluated through three groups of indicators: thermal comfort (indoor temperature, hours of overheating, ability to maintain thermal safety during a power outage), energy performance (especially air conditioning electricity consumption), and resilience in case of cooling system failure.

In practice, some developers have begun to prioritize heat resilience and electricity saving. Assoc. Prof. Dr. Le Thi Hong Na, an architect and lecturer at Ho Chi Minh City University of Technology (Vietnam National University, TP HCM), cited an apartment complex in TP HCM that incorporates balcony solar panels with battery energy storage systems (BESS) and climbing plants to shade the building's exterior.

Climate change and global warming make heat-resilient design increasingly urgent. In Vietnam, forecasts indicate that by 2050, the number of very hot days (38-39 degrees C) will increase from 20 to 60 days annually. By 2100, the national average temperature could rise by up to 4.7 degrees C.

This context of rising temperatures means that many traditional solutions are no longer sufficient to ensure human comfort (typically around 26 degrees C). In addition to prioritizing natural solutions, experts recommend that building designs should first integrate advanced construction materials (with insulating and reflective properties) before considering air conditioning.

Thuy Truong