CFD analysis comprises several stages, including geometry model creation, meshing, and solving for the given physics. In various industries, this analysis is handled either by an in-house CFD team or outsourced to consultancy firms. However, the process demands High-Performance Computing (HPC) machines, licensed and maintained software, resulting in significant costs.

Autonomous HVAC CFD revolutionizes this analysis, particularly for indoor rooms, by automating the entire process. Simply possessing a virtual design model, which can also be created within the app, allows users to obtain results with just a few clicks. This substantially reduces the designer's effort.

Autonomous HVAC CFD presents distinct advantages over other industry tools

In summary, the app takes care of all concerns related to conducting CFD analysis. In line with simulationHub's commitment to empowering designers, the process has been streamlined and automated to yield the best possible results quickly. The extensive CFD expertise of simulationHub has contributed to this effort, ensuring top-notch results for users.

While autonomy is invaluable, reliability and accuracy are equally crucial. Therefore, to address this, a "Validation study" is essential to confirm result accuracy.

This blog highlights three specific cases that showcase the precision of Autonomous HVAC CFD:

In this first case study, we delve into the Comfortina Benchmark Case, a design by Nielsen et al. This study is centered around the investigation of indoor environments. Professor Nielsen from Aalborg University led this research, collaborating with scholars from the University of Tokyo and Keio University.

Our second case study delves into the full-scale experimental measurement of CO2, conducted by G Pei et al. This study involves measurements taken within an environmental chamber designed to replicate a typical one-occupant office setting. The experiment was conducted at the Pennsylvania State University.

The third case study explores our CCTech Office Conference Room. This study focuses on the enhancement of Indoor Air Quality (IAQ) within their office conference room. This research was conducted at CCTech by our inhouse IOT team and provides insights into optimizing the workspace environment.

Each of these case studies offers unique insights and contributes to the validation of the accuracy of Autonomous HVAC CFD. Through these analyses, we aim to demonstrate the capability and reliability of our methodology.

This blog is divided into several parts, each focusing on a specific aspect of the CFD study:

In this section, we provide an overview of the cases under investigation. This includes a description of the scenarios, environments, and objectives of the study.

In this first case study, a manikin is positioned within a rectangular wind tunnel measuring 2.44 m x 2.46 m x 1.2 m. The air flows into the domain from one side at a temperature of 22°C and an average velocity of 0.2 m/s. This incoming air subsequently exits the domain through two circular outlets located on the opposite surface. The manikin is seated and oriented towards the unidirectional inlet air. Moreover, the manikin's placement is symmetrical with respect to the z-plane, featuring a heat flux of 38 W.

The second case study involves the placement of a manikin, a computer, a monitor, and two lights within an environmental chamber of dimensions 4.27 m x 4.27 m x 3 m. The chamber's air intake occurs at a temperature of 18°C with an inflow rate of 0.0385 m^3/s. This inflow is channeled through a low-momentum diffuser measuring 1.215 m x 0.615 m, positioned at floor level. The air subsequently exits the chamber through four circular outlets located at the ceiling level. Notably, to emulate CO2 emissions through breathing, continuous CO2 release is set at a flow rate of 0.026 m^3/hr via the manikin's nose. The heat load within the chamber originates from the manikin, computer, monitor, and lights, with respective values of 91 W, 108 W, 26 W, and 95 W.

The third case examines the arrangement of 3 manikins within an office space spanning 20 ft. x 28 ft. Air circulation is facilitated by a centrally located cassette air conditioner with a 1.5-ton capacity. The room is entirely enclosed by walls that remain shielded from direct sunlight, and though it lacks windows, a dual door system is situated on one side. To mitigate noise infiltration from the neighboring bullpen workspace, the gaps around the glass doors have been outfitted with acoustic seals. Moreover, each manikin contributes to the scenario with a heat flux of 71 W. These manikins additionally emit CO2 at a rate of 40,000 ppm, expelling it at a velocity of 0.88 m/s through their nasal passages.

Here, we delve into the details of the geometry models used in the simulations. We discuss how these models were created and processed for accurate representation. Additionally, we explore the meshing process, which is crucial for obtaining reliable results.

The meshing process was executed according to the application's standards. The mesh was refined around significant geometries, including the manikin, light, and computer. This refinement adequately captured surface intricacies and fulfilled the requirements of the chosen flow and turbulence model.

This segment covers the setup of boundary conditions and the numerical parameters employed in the simulations. Precise boundary conditions are essential to mirror real-world scenarios, and the numerical setup ensures the accuracy of the computational methods.

The numerical schemes were established to align with the application's strategy. A residual convergence criterion of 10^-6 was selected, and simultaneous monitoring of outlet temperatures was conducted. The turbulence was modeled using the SST k-omega two-equation model, and radiation was simulated using the Discrete Ordinates model.

A mesh independence study was conducted. Various mesh sizes and the application's meshing strategy were scrutinized. The subsequent analysis confirmed that the current meshing strategy employed by the application was sufficiently accurate. However, in order to capture the intricate geometry presented in Case Study 1, additional refinements were introduced.

The results obtained from the simulations take center stage in this section. We present the outcomes of the Autonomous HVAC CFD analysis, discussing key findings and insights derived from the data. Additionally, we engage in a comprehensive discussion of the results, drawing connections to the initial objectives and the broader context of the study.

In the case of plane x=0.19 m, the velocity results obtained from the CFD analysis align closely with the experimental findings. However, for planes x=1.69 m and x=2.19 m, the velocity values derived from the CFD analysis exhibit trends that mirror the experimental velocity values.

It's worth noting that the velocity at z=0 on plane x=2.19 m in the CFD analysis slightly exceeds the values recorded in the experimental measurements.

Across all considered points on plane x=2.19 m, at their respective z values, the mean relative deviation stands at 4.47%. Simultaneously, the standard deviation is measured at 18.29% when compared to the experimental velocity values.

These discrepancies in results can be attributed to several factors. Notably, differences in geometry between the experimental setup and the CFD model, variations in the inlet velocity profile, and the distribution of heat flux on the manikin contribute to the observed deviations.

Figure 8 (a) presents the temperature distribution across the manikin's surface. Notably, in areas where the air velocity is low, convective heat transfer is diminished. Consequently, this leads to elevated temperatures on the manikin's surface, particularly evident in the back region. This heightened temperature is a direct result of reduced velocity in the wake region, as illustrated in Figure 8 (c).

In Figure 9 (a), the temperature trend follows an increase with height, in accordance with the fundamental principle of displacement ventilation. Upon comparison, it's evident that while the simulated temperatures don't perfectly match the measurements, the disparity remains minimal, with discrepancies as low as 0.89°C. Despite this, the simulated temperature profile consistently mirrors the observed trend displayed in the measured data.

Figure 9 (b) highlights the stratification of CO2 concentration within the displacement-ventilated room. The simulation results above the breathing plane (1-1.1 m) deviate slightly from the actual measurements. However It is important to acknowledge that below the breathing plane the simulation outcomes don't exactly match the measurements. This can primarily be attributed to the simplified geometry of the manikin used in the simulation. Nonetheless, it's encouraging to note that both the simulation and measurement outcomes exhibit a comparable trend in the vertical CO2 concentration profile

The CFD simulation results closely match the experimental data, particularly within the occupant breathing zone. However, the recommended CO2 concentration of 1000 ppm in the conference room is not achieved. Therefore, CFD analysis can be instrumental in identifying indoor air quality issues during the design phase, well before commissioning, thereby preventing discomfort, health complaints, and the expenses associated with design modifications after installation.

To summarize, the results demonstrate that the app's methodology is capable of accurately predicting the indoor environmental flow physics to a high degree of accuracy.