Optimization of Passive Design Strategies for Thermal Comfort and Energy Efficiency in Vietnamese Residential Buildings Using Building Performance Simulation

Overview

This article gives a general overview of how passive design strategies and building performance simulation (BPS), including simulation-based optimization, can be used to improve thermal comfort and reduce cooling energy in Vietnamese residential buildings. It describes a typical workflow; it does not report results from a specific study.

Why passive design matters for Vietnamese housing

Much of Vietnam has a hot and humid climate, and cooling is a major driver of residential electricity use as air conditioning spreads. Urban housing is dominated by row houses (nhà ống, "tube houses"): a study of Hanoi cites an estimate that about 69% of the building stock in Vietnam consists of 3-5 storey row houses (Parkes, 2013, as cited in ¹). Passive design uses form, orientation, envelope, shading and ventilation to reduce heat gain and remove heat without mechanical systems, and can therefore reduce reliance on air conditioning.

In dense cities the urban heat island (UHI) effect adds to the challenge. A simulation study of Hanoi predicted that implementing the Hanoi Master Plan 2030 could raise air temperatures in built-up areas by up to 2-3°C and make thermal comfort by natural ventilation harder to achieve in row houses ¹.

Key passive strategies

Orientation and form: Limit exposure of east and west facades and glazing to low-angle sun.
Natural ventilation: Cross ventilation and stack ventilation (through stairwells, lightwells or air wells) help remove heat and increase air movement. A systematic review of wind flow in row houses in the humid tropics found little research specific to row houses and identified stairwell voids, air wells, facade ventilation and roof openings as under-researched elements ².
Shading: External overhangs, fins, screens and vegetation reduce direct solar gain on windows and walls.
Envelope properties: Roof and wall insulation, thermal mass and the solar reflectance of external surfaces affect heat transfer. Their effect in hot and humid climates depends on how the building is operated (naturally ventilated, air-conditioned or mixed-mode), so they should be evaluated by simulation rather than assumed.
Courtyards, lightwells and greenery: Internal voids and planting can support ventilation and daylight in deep, narrow plans.

Thermal comfort criteria

For naturally ventilated or mixed-mode homes, adaptive thermal comfort models, which relate acceptable indoor temperatures to prevailing outdoor conditions, are generally more appropriate than static models developed for fully air-conditioned spaces. The share of occupied hours within the comfort range is a common performance indicator. Field data from Vietnamese occupants are needed to confirm which comfort limits apply locally.

A typical simulation-based optimization workflow

Representative building model: Model a typical housing typology, such as an urban row house, based on surveys or existing building data, capturing form, orientation, window-to-wall ratios, internal layout and party walls.
Weather data: Use representative weather files for the climate zones of interest (for example Hanoi, Da Nang and Ho Chi Minh City). Consider whether the file reflects urban or rural conditions, given the UHI effect.
Design variables: Select parameters such as orientation, window-to-wall ratio per facade, shading type and depth, wall and roof U-values, external surface reflectance, and the size and position of operable openings, lightwells or courtyards.
Simulation tool: Use a dynamic BPS tool able to model heat transfer, airflow and comfort, such as EnergyPlus or TRNSYS.
Objectives: Typical objectives are minimizing annual cooling energy, maximizing hours within the comfort range, and possibly minimizing construction or life cycle cost.
Optimization: Couple the simulation with a multi-objective algorithm, such as NSGA-II or particle swarm optimization, to explore the design space and identify Pareto-optimal trade-offs between objectives.
Validation and sensitivity: Calibrate the model against measured data where possible and run sensitivity analysis to identify which parameters matter most.

What such studies can show

A study following this workflow can quantify the trade-offs between cooling energy, comfort and cost for a given typology and climate, show which passive parameters have the greatest influence, and show how the best combinations differ between Vietnam's northern, central and southern climates. Results depend on the building model, weather data, occupant behaviour and comfort criteria used, so they should be reported with these assumptions.

Vietnamese context

Regulation: QCVN 09:2017/BXD, the national technical regulation on energy efficient buildings, is replaced by QCVN 04-3:2026/BXD, issued with Circular 61/2026/TT-BXD dated 30/7/2026 and effective from 01/02/2027 ³. QCVN 04-3:2026/BXD applies to new construction and renovation of offices, hotels, hospitals, schools, shopping centres and apartment buildings with a total floor area of 2,500 m² or more ⁴. Individual row houses therefore fall outside its scope, and passive design in this segment depends mainly on voluntary guidance and good practice.
Barriers: Commonly cited barriers to green building practice include perceived higher upfront cost, limited incentives, limited availability of skilled simulation practitioners, and limited data on local materials.
Local materials: The thermal properties of locally available materials should be documented so they can be represented correctly in simulation.

Research needs

Wider coverage of residential typologies and construction practices in different regions of Vietnam.
Life cycle cost analysis alongside energy and comfort objectives.
Field studies to develop and validate thermal comfort criteria for Vietnamese occupants.
Coupling urban climate modelling with building simulation to account for UHI, as in the Hanoi study ¹.
Ventilation elements suited to narrow row houses, such as air wells and roof openings ².
Post-occupancy evaluation of occupant behaviour and measured performance.
Practical design tools, guidelines and training for building professionals.