HVAC

The performance of an HVAC system plays a fundamental role in occupants’ experience of a building. Although guided by standards such as ASHRAE standards, current HVAC systems design is usually based on experience. This approach usually results in great uncertainties, especially when dealing with large spaces and non-standard configurations. Conversely, Computational Fluid Dynamics allows to analyze new and innovative HVAC systems, for which little or no experimental data are available. Simulations can take into account multiple air flow inlets and outlets, fans, thermal effects and solar radiation, humidity and contaminants transport. Using CFD, engineers can improve performance, develop tailor-made and non-standard solutions and eliminate redundant equipment in order to save costs.
CFD can simulate ventilation systems for complex and large buildings and infrastructures such as tunnels and offices, demonstrating what comfortable temperatures and air speeds can be maintained, and optimizing the overall strategy.
Occupant's thermal comfort and indoor air quality are the primary objectives of HVAC design for buildings and vehicles. Using simulation results designers can assess a variety of comfort criteria by predicting indoor environment conditions (air velocity, temperature, humidity, thermal radiation, pollutant concentration).
For high-performance HVAC systems such as radiant heating and cooling, underfloor air distribution (UFAD), and natural ventilation and hybrid systems that use both natural and mechanical conditioning of a building, it is critical to understand how the air flows and the surrounding environment impacts the occupants' comfort. Computational Fluid Dynamics (CFD) simulations are the best available technique to investigate the performance of such systems.

Cases

Himalayan mountain hut

This study has been commissioned by Sara Gottardo, an architect based in Paris, for an international architectural competition. Participants were asked to submit clever and inventive proposals for a feasible and efficient Himalayan Mountain Hut to be positioned along any of the trekking trails in order to provide trekkers safe, comfortable and inviting lodgings. The core of this project is the dome. BuildWind performed simulations of the aerodynamics and heat transfer in order to assess the technical feasibility of the project. The concave interior creates a natural airflow which allows the hot and cool air to flow evenly throughout the dome with the help of return air ducts, and it reflects and concentrates interior heat, preventing strong radiant heat loss.

CFD modeling of a displacement ventilation system for an office space

Displacement ventilation is an indoor ventilation approach able to provide a cleaner indoor environment and with less energy consumption than conventional, mixing ventilation.

Office space indoor air quality assessment

CFD can ensure the compliance with standards and criteria for the indoor environmental quality, such as the ASHRAE 55 and the EN 15251 standards.

Cleanroom design using CFD simulation

A cleanroom is a facility designed to achieve and maintain extremely low levels of particulates. Cleanrooms are used in semiconductor manufacturing, biotechnology and other fields that are very sensitive to environmental contamination. Operating theatres in hospitals are also similar to cleanrooms. The air from outside is filtered before the cleanroom and internal air is also constantly recirculated and filtered through HEPA (high-efficiency particulate air) or ULPA (ultra-low particulate air) filters to remove internally generated contaminants.
Cleanrooms are classified according to the number and size of particles permitted per volume of air. Light-scattering airborne particle counters are used to determine the concentration of airborne particles equal to and larger than the specified sizes.
ISO 14644-1 and ISO 14698 are non-governmental standards developed by the International Organization for Standardization (ISO). The former [1] applies to cleanrooms in general; the latter to cleanrooms where biocontamination may be an issue. ISO standards specify the decimal logarithm of the number of particles 0.1 µm or larger permitted per m3 of air. So, for example, an ISO class 5 cleanroom has at most 105 particles/m3.
Computational Fluid Dynamics (CFD) allows engineers to visualize flow patterns, particle concentration and temperature distribution inside a cleanroom. Simulation are utilized to quickly and efficiently test and improve different design solutions.
Data from CFD simulations also allow to accurately evaluate the effectiveness of a cleanroom by calculating the values of a series of indices that characterize the mixing behavior of air and the distribution of contaminants within a space. Two among the most widely used indicators are the Air Change Efficiency (ACE) and the Contaminant Removal Effectiveness (CRE). The Air Change Efficiency (ACE) is a measure of how effectively the air present in a room is replaced by fresh air from the ventilation system [2]. The Contaminant Removal Efficiency (CRE) measures how efficiently a contaminant is removed at certain location . This parameter is usually evaluated for an occupied zone of the cleanroom.
References
[1] https://www.iso.org/standard/53394.html  consulted online on 19 November 2018
[2] Sandberg M and Skaret E (1985) Air change and ventilation efficiency – new aids for HVAC designers. Swedish Institute for Building Research.

Applications

Building Aerodynamics

Fire and Smoke

Sustainable Building