HVAC Analysis Of An Operating Room

fig2 — Fig. 2 appears to be flooded by Velocity_Z or the vertical component of velocity. It is used to illustrate the clearly "reversed flow" in the middle of the room above the patient. This red upward flow is contrasted with the blue downward flow from the clean air entering through the inlets in the ceiling. These are the primary features in terms of vertical flow.

fig1 — Operating room simulation flooded by velocity magnitude. The flow is coming down from the ceiling and fanning out about the patient. The red area in the middle is relatively high velocity flow.

In this project, Faure QEI used the Envenio Onboarding Program to leverage on-demand CFD simulation software, EXN/Aero, alongside support and training from Envenio engineers.

The project set out to assess the performance of a hospital operating room, with the aim of identifying and suggesting any overall improvements that could be made.

Airflow patterns, thermal distribution, and spacial distribution of average age-of-air were modeled and predicted for the hospital operating room. The simulation was first run steady-state, and then run as a transient simulation which demonstrated the highly unsteady nature of the flow and gave a good indication of the range of variability likely to be observed in the immediate vicinity of the operating room table and patient.

Clean air enters through a configuration of inlets above the operating table creating an air-wash that flows downward about the operating table. Air exits the room through two square ducts along one of the walls. The simulated patient and operating room table were heat sources with a specified heat flux applied on these boundaries. Similarly, the operating room lamps above the patient were sources of heat, again using a prescribed heat flux.

Buoyant forces were quite significant; heated air in the vicinity of the patient and lamps participated with a topological recirculation of flow created by the inlet configuration to create significant reversals in flow from the primary flow-direction created by the air-wash. This positioning of the lamps acted to divert the downward air-wash outward which further promoted upward flow in the region immediately above the operating table and patient. The strong upward flow pattern, driven by flow topology and buoyancy, significantly disrupted the curtain effect of the air-wash and resulted in large scale unsteadiness in the region of the table and patient. This unsteadiness resulted in fluctuations in average-age-of-air in the vicinity of the patient which were the key results from this simulation.

It is desirable to have only young air surrounding the patient to reduce risk of contamination and the continual flow of clean air into the room from above is designed to ensure the patient is continually washed in clean air. The simulation indicates the effectiveness of this air-wash, indicates the typical flow patterns and average-age-of-air at various locations in the room, and the transient simulation also indicates the variation seen in these patterns and distributions due to unsteadiness in the flow.

This study demonstrates the capability of determining the effectiveness of clean-air-wash systems and designs in preventing old and potentially contaminated air from encountering the patient. Faure QEI was able to assess the performance of the current design and suggest several improvements based on the simulation as follows:

1) The air-wash inlet configuration consisted of inlets that surround a large central panel on the ceiling from with the lamps and armatures for the lamps are hung. This solid panel is undesirable because it sets up a recirculating flow topology with a node at the ceiling directly above the patient. Hypothesized, is that it would be far better to have an air inlet directly above the patient blowing downward, though no alternative design was simulated or tested.

2) The shape, positioning, and heat produced by the lamps significantly impacts the overall flow and the efficacy of the air-wash system. The positioning may not be easily alternated given the need for specific light sources. However, there may be scope for improvement in the size, shape, and energy efficiency/consumption (as it impacts heat) of the lamps.

Try it for Yourself

The Onboarding Program aims to help engineers get up and running more quickly with EXN/Aero. The program gives engineers the chance to work closely with a member of the engineering team to mesh, set up, simulate, and post-process results. This additional training will help engineers to get the most out of the platform, ideal for HVAC projects such as the one in this article.

Publication date: 4/9/2018

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