8th Annual International Energy Conversion Engineering Conference
25 - 28 July 2010, Nashville, TN
AIAA 2010-6932
Experimental Investigations of Temperature and Relative
Humidity in Surgical Operating Theatres and their
Numerical Verifications
Eng. Waleed A.Ethbayah and Prof.Dr.Essam E. Khalil
Cairo University - Faculty of Engineering, Egypt
Khalile1@asme.org,
The present work fosters experimental measurements and mathematical modelling techniques to
primarily determine the thermal and the relative humidity characteristics in the air-conditioned
surgical operating theatre. The present work also demonstrates the effect of the various designs of
surgical operating theatres and operational parameters on the flow pattern and temperatures
characteristics. The present work is a part of a more comprehensive investigation of the more
important factors affecting the air environments in surgical operating theatre. Measured and
predicted temperatures and relative humidity profiles are shown to be in good agreement. The
present paper introduces several recommendations regarding the optimum design requirements of
operating theatres to provide hygiene and comfort environment.
Relative humidity affects our comfort in numerous ways both directly and indirectly. It is a thermal
sensation, skin moisture, and discomfort, tactile sensation of fabrics, health and perception of air
quality. Low humidity affects comfort and health. Comfort complaints about dry nose, throat, eyes
and skin occur in low humidity conditions, typically when the dew point temperature is less than
0 oC. Low humidity can lead to drying of the skin and mucous surfaces. On respiratory surfaces,
drying can concentrate mucous to the extent that celery clearance and phagocyte activities are
reduced, increasing susceptibility to respiratory disease as well as comfort. It was found that any
increase in humidity from the low winter levels decreased absenteeism. Excessive drying of the skin
can lead to lesions, skin roughness, discomfort and impair the skin’s protective functions. Dusty
environments can further exacerbate low humidity dry skin conditions; it was also found that drying
from low humidity can contribute to irritation1,2. Eye discomfort increased with time in low
humidity environments with dew point temperature less than 2 oC.
This paper is devoted to the numerical and experimental investigations of the influence of the
surgical operating theatre geometrical and airside design on the temperature and relative humidity
distributions to create sterile conditions in the theatre. The present work offers examples of
measured relative humidity profiles in an operating theatre in (New Kasr El-Aini Teaching Hospital
– 1200 beds – Cairo University – Egypt). These experimental results were carried out to verify the
proposed numerical procedure and particularly in the vicinity of the supply outlets and operating
table.
I. Introduction
International standards and norms had highlighted the importance of the local spatial distribution of air
temperatures and relative humidity on the preferred ambient temperature within the comfort range1-21. The
recommended relative humidity limits have caused a lot of discussions during each revision of standard 551. EN
ISO 773010 recommends a humidity range of 30% to 70% RH. That recommendation is mainly for indoor air
quality purposes. In standards 551, the lower humidity limit is a dew point temperature of 2 oC. The upper limits
are 18 oC wet bulb in winter and 20 oC wet bulb temperature in summer. Requirements for acceptable IAQ,
Berglund3 and Fang et al.8, specified a narrower range for relative humidity.Any deviation from these conditions
can inhibit or promote the growth of bacteria and activate or deactivate viruses. Some bacteria such as
Legionella pneumophila are basically water-borne and survive more readily in humid environment. Codes and
guidelines specify temperature and humidity range criteria in some hospital areas as a measure for infection
control as well as comfort.
The air relative humidity levels affect our comfort in numerous ways both directly and indirectly. It is a thermal
sensation, skin moisture, and discomfort, tactile sensation of fabrics, health and perception of air quality. Low
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Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
humidity affects comfort and health. Comfort complaints about dry nose, throat, eyes and skin occur in low
humidity conditions, typically when the dew point is less than 0 oC. Low humidity can lead to drying of the skin
and mucous surfaces. On respiratory surfaces, drying can concentrate mucous to the extent that celery clearance
and phagocyte activities are reduced, increasing susceptibility to respiratory disease as well as comfort,
Berglund3. Green9; quantified that respiratory illness and absenteeism increase in winter with decreasing
humidity; it was found that any increase in humidity from the low winter levels decreased absenteeism.
Excessive drying of the skin can lead to lesions, skin roughness, discomfort and impair the skin’s protective
functions. Dusty environments can further exacerbate low humidity dry skin conditions. Eye discomfort
increased with time in low humidity environments with dew point temperature less than 2 oC. The relevant
standard specifies that to decrease the possibility of discomfort due to low humidity, dew point temperature in
occupied spaces should not be less than 3 oC.
Elevated relative humidity levels reduce comfort. At lower levels of humidity, thermal sensation is a good
indicator of overall thermal comfort and acceptability. But at high humidity levels thermal sensation alone is not
a reliable predictor of thermal comfort. Nevins et al.17; recommended that on the warm side of the comfort zone,
the relative humidity should not exceed 60% to prevent warm discomfort. The upper relative humidity limit was
a dew point of 17 oC, based not so much on comfort as on considerations of mold growth and other moisture
related phenomena. Standard 55 specified 60% relative humidity as the upper limit, also based primarily on
considerations of mold growth. This limit was challenged for not being based on direct human thermal comfort
and for being too restrictive for evaporative coolers, Berglund2. An occupant’s overall satisfaction with the
thermal environment is probably a cognitive result of temperature, moisture, friction and other sensations. A
recent comfort study of Berglund et al.3 done at temperature of 21 oC to 27 oC with dew points of 2 oC to 20 oC at
three levels of activity (sedentary, intermittent walking and standing, and continuous walking) describes
extensive subjective responses of 20 subjects and measures physiological responses from five subjects. Humidity
and temperature also affect our perceptions of air quality and aspect of comfort and satisfaction with the
environment Berglund2.
The present paper is devoted to the numerical and experimental investigations of the influence of the surgical
operating theatre geometrical and airside design on the temperature and relative humidity distributions to create
sterile conditions in the theatre. The present work offers examples of measured relative humidity profiles
obtained in one of the operating theatres in New Kasr El-Aini Teaching Hospital – 1200 beds – Cairo University
– Egypt. These experimental results were carried out to verify the proposed numerical procedure and particularly
in the vicinity of the supply outlets and operating table.
II. Experiments
The present experimental program describes the test facility setup and the measurements procedure followed in
the present work.
Experimental Facility
The HVAC system that serves the hospital under consideration is all air system (Variable air volume VAV). The
HVAC System is in operation most of year. In new Kasr El-Aini Teaching Hospital, the air conditioning system
of surgical operating theatres was designed as an all air system, which supplies the different operating theatres in
the hospital by air. The supplied airflow to the operating theaters was discharged through four square ceiling
perforated diffusers each 0.6 x 0.6 m; the air was supplied through a High-Efficiency Particulate Air Filter
(HEPA). The four supply diffusers in each surgical operating theatre had the same relative dimensions in each
theatre .Figure 1-a represents a schematic layout of the surgical operating theatres in the New Kasr El-Aini
Teaching Hospital, the figure represents elevation and plan views of the surgical operating theatre. It also
indicates the positions of the supply air outlets relative to operating table, which was located in the center of the
room. The present experiments were performed with the presence of the room furniture, such as the operating
table, operating devices, operating lamp, and all additional accessories, as shown in figure 1-b. The room
dimensions are 6.6 m in length (L), 4.0 m in width (w), and 3.0 m in height (H). The operating table has a length
of 2.0 m and a width of 0.5 m, and is 1.0 m high. Four ceiling square perforated supply air diffusers were located
at the ceiling of the room with dimensions of 0.6 m x 0.6 m; their centres were located at X, Z equal to (1.7,1.3),
(4.9,1.3), (4.9,2.7), and (1.7,2.7) as shown in Figure 1-a.
The extract ports were located on the left wall with dimensions of 0.5 m x 0.3 m and 0.5 m x 0.2 m; the lower
port center point is located at 0.75 m from the floor. The higher extract port center point is located at 2.25 m
from the floor Kameel12. Different studies for other operating theatres at a larger Teaching Hospital (4500 beds)
were also carried out as well as at a Paediatric Teaching hospital of 500 beds.
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Experimental Procedure
Measurements of relative humidity and temperatures were obtained in the vicinity of the bed by dividing the
measuring locations to 10 points at Y direction. Measurements were obtained in the vicinity of the operating
table between 0.0 m and 2.0 m from patient leg to head and at about 1.0 m high above room finished floor.
Heated thermocouple anemometer was used .its probe has a semi-sphere shape with a diameter of 1.0 mm, and
was supported in separate telescopic support of a cylindrical shape with a diameter equals to 12.0 mm at its base
position. That separate telescope has a maximum length of 675 mm, which allowed measurements from remote
distances.
The heated thermocouple anemometer measurements depended on the time averaging the results. Time constant,
(typically 120 seconds in the present work) was set to collect readings that are time averaged to yield the final
time-averaged measured value. The heated thermocouple anemometer measures relative humidity with accuracy
± 2.0%. For more details of the experimental procedure, reference should be made to Kameel12.
Figure 1-a. Schematic layout of the surgical operating theatre (elevation view)
Figure 1-b. General view of the surgical operating theatre under consideration
and the Hospital in the Right Bottom Corner
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III. Mathematical Simulation
Three time averaged velocity components in X, Y, and Z coordinate directions were obtained by solving the
governing equations using a “SIMPLE Numerical Algorithm" [Semi Implicit Method for Pressure Linked
Equation] described earlier in the work Spalding et al.21 and Khalil14. The turbulence characteristics were
represented by a modified and appropriately extended two-equation k - ε model to account for normal and shear
stresses and near-wall functions. Fluid properties such as densities, viscosity and thermal conductivity were
obtained from references. The present work made use of the Computer Program FLUENT, which was developed
Fluent Inc. as commercial code. The non-commercial 3DHVAC, developed by Khalil14 and modified later by
Kameel12, and by Khalil 16 was also utilized. The program solves the differential equations governing the
transport of mass, three momentum components, energy, and contaminant concentration in three-dimensional
configurations.
Numerical Procedure
The Computer Program, FLUENT is used to solve the time-independent (steady state) conservation equations
together with the RNG k-ε model, Chen5, Chow6, El Gharbi 7, and the corresponding inlet and wall boundary
conditions. The numerical grid divided the space of the surgical operating theatre into discritized computational
cells (600000 grid nodes). The discrete finite difference equations were solved with the SIMPLE algorithm,
Patankar, 20. Solution convergence criteria, was applied at each iteration and ensured the summations of
normalized residuals were less than 0.1% for flow, 1% for k andε, and 0.1 for energy.
Model Validation
Previous comparisons between measured and predicted flow pattern, turbulence characteristics, and heat transfer
were reported earlier in the open literature utilizing the present computational capabilities (FLUENT), reference
should be made to these for further details and assessments. The predictions of flow and turbulence
characteristics were reported to be in general qualitative agreement with the corresponding experiments and
numerical simulations published by others, Kameel12, Khalil16. The obtained trends are in adequate agreement
for engineering purposes.
Nevertheless discrepancies exist and particularly in the vicinity of recirculation zone boundaries. More
discrepancies were also observed in situation with heating flows than those of ventilation or cooling. For more
details of validations for present application (Surgical Operating Theatres) review Kameel,12 and Khalil,15,16.
These papers describe the validation of the turbulence model to use it for the prediction of airflow characteristics
in the surgical operating theatres.
IV.Experimental Results
The experimental results of relative humidity measurements and mean air dry bulb temperatures over the
operating table will be presented here in graphical plots. The results are well identified and indicated higher
values near the surgeon stand; these values show a minimum in the middle portion of the table. Figure 2 and
figure 3 show the measured time-dependent air temperatures and relative humidity at various locations along the
operating table.
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Temperature Distribution with Time
At 1.8 from leg
Temperature Distribution with Time
At 0.5 from leg
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Temperatur (C)
Temperature (C)
26
24
22
20
24
22
20
18
18
00:10
00:15
00:20
Time (hr.)
00:25
22:10
22:15
22:20
Time (hr.)
Figure 2. Measured temperatures at different locations
Figure 3. Relative Humidity variation with time over 24 hours
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22:25
Figure 4. Measured Time averaged air temperature at bed from leg to head positions
Figure 5. Measured Time averaged Relative Humidity at bed from leg to head positions
Figures 4 and 5 show the variation of temperature and relative humidity along the bed from the head to leg of
patient.
V. Numerical Results
Figure 6 shows the present numerical predictions of local velocities W in Z direction (vertical), kinetic energy of
turbulence k, air dry bulb temperatures T, K and the relative humidity Rh% as obtained from the present Fluent
Predictions for design of Figure 1.
The temperature contours shown in Figure 6 are based on an inlet air temperature of 286K. It can be seen that for
both vertical and horizontal planes that the temperature variation at the occupants’ zone (zone up to 2 m from
finished floor) from is not more than 3◦C, which satisfies the prevailing norms. A recirculation zone was
observed in Figures 6, these zones are to be avoided and are not advised in operating rooms as these can result in
accumulation of contaminants and the air will not be renewed. The upper corners of the room are also the worst
positions for recirculation zones to exist.
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Predicted downward Velocities w ,m/s
Predicted kinetic Energy of
turbulence k,m2/s2
Air Temperature, T, K
Relative Humidity, RH%
Figure 6: Predictions of mean air velocity m/s, kinetic energy of turbulence m2/s2,
temperature oK , and relative humidity %
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This model presents more realistic prediction of real cases; the effect of bluff body shape table on the air
streamlines was predicted and indicated the respective influence on flow regime and heat transfer. As anticipated
the effect of the light pendent dominates the flow pattern in the immediate downstream vicinity of the supply
diffuser; the velocity contours are strongly deflected by the light pendent. An emerging recirculation zone was
predicted downstream the pendent. Such zone affects the isothermal lines. It should be noticed also that these
changes due to lighting fixture and humans are strong but local in nature; as the rest of the room is not really
affected. The effect of the presence of the surgery team as blocks in the flow pattern is also depicted; the
presence of the surgery team affects the isotherms and iso relative humidity contours to a large extent. From the
computational results shown in Figure 6 , it can be concluded that the operating table, light pendent and surgery
team presence has a pronounced influence on the local air distribution and flow regimes, isotherms and relative
humidity contours. In such room, such observation supports the importance of following comprehensive studies
to analyze operating theatre furniture arrangements for better airflow and temperature distribution and less
contamination.
VI. Discussions and Conclusions
From the HVAC design point of view in this surgical operating theatre, it can be interpreted that the designer
focused to sterilize the operating area (over the operating table) by developing an air curtain surrounding the
operating table area. The designer established this curtain by injecting the supply air from four individual air
supply grilles at the corners of the operating area. From figures 6, one can notice that this design methodology
failed and the operating area is not bounded enough to prevent the airflow crossover the boundaries toward the
operating area. The most optimum way to sterilize the operating zone where surgical team operates is by
flooding this zone by currents of sterilized air to limit the airflow in one direction only, from the ceiling supply
past the occupancy zone and outwards of the operating area.
From the previous results, one can conclude that the airside designs have a strong influence on the relative
humidity distribution and consequently on the IAQ. The location of the supply outlets plays the major role in his
distribution. The extraction ports should be located in the right location to correct the errors of the bad selection
of the supply outlet positions. The restrictions of the architect and civil engineer to use a large supply area in the
center of the room hinder attainment of good indoor air \quality and comfort.
Acknowledgment
Thanks and gratitude is respectfully due to Cairo University New Kasr El-Aini Teaching Hospital for the
technical support throughout the work.
References
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