Many organizations are beginning to implement plans to return to the office. The COVID-19 pandemic has everyone rethinking office spaces, especially the all too common open-office space. While some employers are relying on creating new jobs relating to safety managers and care coordinators, many are turning to simulation to examine how best to reconfigure office designs and HVAC to lessen the chances of transmission. Knowing that our 6SigmaDCX product suite uses simulation to understand ventilation in the data center environment, some OEM organizations contacted us here at Future Facilities to evaluate the effectiveness of their office ventilation system.
Future Facilities was interested to explore what constitutes “office simulation” in our software as well as its strengths and limitations. A simple example outlines how we can simulate different strategies, in this case two vent types, and provide a brief discussion of the results. We set up a project to explore and demonstrate that the type and location of vents can make a huge difference to the ventilation effectiveness and thus help mitigate airborne transmission.
Office simulation is a physics-based computer model of the office space and its ventilation performance. Such models that replicate physical reality and behavior are often referred to as digital twins. While our software has the capability to define the physical geometry, flow, and thermal boundary conditions, it cannot trace larger particles that may be present in a sneeze or cough. However, it is impossible to know where and in what direction the sneeze or cough would travel —there’s no measurable way to know where the employee will be sitting, standing, or walking at the time of the sneeze or cough. Consequently, tracing the larger particles for any one cough or sneeze will not be representative of the general performance. We used our software to assess how well the space was ventilated and specifically how quickly old air was replaced or diluted by fresh air from the ventilation system.
By using our software’s ability to model airflow, contaminant concentration, and transient analysis, we can use the digital twin to simulate a tracer gas decay test for multiple configurations prior to making decisions on the best ventilation strategy to implement. The “tracer gas” concentration decay predicts the rate at which airborne contamination from the sneeze or cough is reduced by replacement with fresh air.
The key question is which strategy, in this case which type of vent, results in the fastest dilution of the old air. Because the digital twin can mark all the air at the beginning of the simulation as contaminated, we can also understand how well ventilated any location is by each system, thus considering the impact of a cough or a sneeze contaminating any location in the room.
Our first example simulates airflow in an office setting using a ceiling vent (i.e. square diffuser), while the second demonstrates airflow using two floor vents (i.e. swirl diffusers) in an otherwise identical office setting.
We simulated an office space where airflow is delivered through a typical rectangular diffuser on the ceiling with 75° inner spread angle and 85° outer spread angle. The flow rate of the diffuser is 32 l/s at 65 °F. The return vent is on the ceiling in a corner of the room. Each computer monitor is dissipating 25W heat to the environment.
Figure 1. Experimental with ceiling vent (pictured right) installed
Figure 2. Transient simulation of contamination with ceiling vent installed
The simulation shows that the contaminant concentration reduces slowly and uniformly in the office space during the time frame. In the first 500 seconds, the concentration of contamination reaches to 0.1 (kg/kg) and after 700 seconds it reduces to 0.07 (kg/kg).
In the second scenario, the only change is that the fresh air is now delivered by two swirl vents on the floor with 15° spread angle and 60° swirl angle. The flow rate of each vent is 16 l/s at 65 °F.
Figure 3. Experimental office with floor vents (pictured right) installed
Figure 4. Transient simulation of contamination with floor vents installed
At first sight, you will notice that the general room conditions vary considerably more with less contamination at low level and some regions of greater contamination at high level. However, as typical with displacement systems, heat draws the cool, cleaner air up, delivering fresher air around warm objects – like people! The result is that the contaminant concentration near the occupants faces with floor swirl vents is almost half that of the ceiling vent scenario.
These two simulations demonstrate that the displacement ventilation through floor vents is likely to deliver cleaner air than the ceiling vent’s mixed ventilation.
Making the move back to the office is scary for many. We all want to take steps to make this transition as safe as possible. A big part of doing so will mean reconfiguring office spaces while keeping the spread of contaminants in mind. Physics-based simulation provides a clear, measurable method to test new configurations and equipment, such as the vents described above. We’re always working to test the bounds of simulation and what our software can do, so if you have any questions on how our software can work for you and your business, please do not hesitate to reach out here.
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