HVAC of an Operating Room CFD Simulation
Air conditioning is a set of processes used to control the temperature, humidity, and ambient air quality of an existing environment.
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Heating, Ventilation, and Air Conditioning (HVAC)
There are various types of air conditioners with many uses in HVAC of residential homes, office buildings, libraries, amphitheater, hospitals, dining halls and more. One of the most important requirements in operating rooms is to eliminate particulate matter and environmental pollution. In operating rooms, the air exit the room directly and only fresh air is constantly injected into the interior.
The purpose of designing an air conditioning system is to provide the comfort of the people for a specific process in the desired environment. The design of the Heating, Ventilation, and Air Conditioning (HVAC) is based on the principles of thermodynamics, fluid mechanics and heat transfer. Applying a proper air conditioning system in an operating room prevents bacteria and infections from spreading during surgery. It avoids contaminant particles contacting the patient’s body, too. It also prevents anesthetic gases from leaving the room and provides a comfortable environment for the patient, doctors, and nurses. One of the methods of air conditioning in the operating room is the use of air curtains. In the present case, we simulate the operating room space considering the equipment and the people within it, including the doctor and patient, using an HVAC system.
Operation Room Heating, Ventilation, and Air Conditioning (HVAC) are designed to have higher relative air pressure than outside. In fact, the valves are mounted on the ceiling of the operating room and above the bed of the patient, protected by air curtains. It also acts as a permanent drain valve to make the inlet laminar flow have better behavior. In which case the outflow from the laminar flow diffusers flows to both sides as they flow downward.
It reduces the space for the presence of contaminated particles in the operating room, because of the high-pressure zone. The system uses a laminar flow to purify the air inside the operating room. Also, a linear flow called air curtain to prevent contaminated flow into the fresh air for better ventilation. The inlet air moves through the top to the bottom for the clearing operation and transfers contaminated gases and particles. The curtain prevents air from returning.
Operating Room HVAC Problem Description
In the present case, the operating room HVAC considering the equipment and persons within it, including the doctor and patient, using an air conditioning system, is simulated. The system uses a laminar flow to purify the air of the operating room and a linear flow called air curtain to prevent contaminated flow into the fresh air. The source of the contaminants and excess gases is assumed on the patient’s body. The inlet air moves through the top to the bottom of the operating room for the clearing process and transfers contaminated gases and particles around the patient to the corners of the room. Air curtains prevent polluted air from returning to the room. Eventually, the polluted air leaves the lower part of the room. The air contains oxygen, nitrogen, water vapor (humidity) and pollutants in this simulation.
Geometry and Mesh of the operating room HVAC
Design Modeler software models operating room geometry. We design all effective components in the operating room for HVAC in the present model. These components include equipment in the operating room (a doctor, a patient, and a nurse and so on).
ANSYS Meshing software performs the meshing of the present model. The grid is unstructured and produced a total of 1294914 element numbers.
HVAC CFD Simulation
A summary of the problem definition and problem-solving steps is given in the following table:
|Model for HVAC Simulation|
|near wall treatment||Standard wall function|
|(boundary conditions) HVAC|
|HVAC||inlet air||velocity||0.38 m.s-1|
|inlet air curtain||velocity||0.37 m.s-1|
|outlet air||gauge pressure||0 Pa|
|Methods for HVAC CFD Simulation|
|discretization||momentum||Second order upwind|
|(species transport)||Second order upwind|
|initial temperature||500 K|
|oxygen, nitrogen, humidity, and particle||0|
K-Epsilon Turbulence Model
Since the present model (HVAC) deals with the dispersion of contaminated particles in the environment, the k-epsilon-standard model is suitable.
Standard wall Function
Since the k-epsilon turbulence model is used for HVAC CFD simulation and it is not able to simulate flow vortex near the walls, a wall function must be defined to investigate the fluid behavior near the wall. These wall functions are near-wall analytical flow profiles obtained by explicitly solving the near-wall flow equations; hence, they are more accurate than numerical methods (in simpler models). Also, because of the need for no accurate mesh near the wall, they greatly reduce the computational time. It should be noted that when using the k-epsilon model, due to the lack of accurate mesh near the walls, it is necessary to check the wall functions using Y-Plus (Y+). The suitable Y+ should be between 30 and 300 for the standard model.
Species Transport Model (for HVAC simulation)
The species transport model is generally used to analyze combustion processes in which gaseous species interact. Therefore, since in the present model, the main purpose is to investigate the distribution of pollutants, oxygen, nitrogen and air humidity in the operating room space, this model should be used, but there is no need to define the reaction between the gas species.
All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.