Healthy Buildings 2017 Europe July 2-5, 2017, Lublin, Poland

Healthy Buildings 2017 Europe July 2-5, 2017, Lublin, Poland Paper ID 0237 ISBN: 978-83-7947-232-1 Evaluation of the Thermal Microenvironment, Generated in a Hospital Bed with Localized Ventilation System Nushka Kehayova 1, 2,*, Zhecho Bolashikov 2,3, Arsen Melikov 2 1 Department of Hydroaerodynamics and Hydraulic Machines, Technical University of Sofia, Sofia, Bulgaria 2 International Centre for Indoor Environment and Energy, Department of Civil Engineering, Technical University of Denmark, Kgs. Lyngby, Denmark 3 NIRAS, A/S, Denmark * Corresponding email: n.kehaiova@abv.bg SUMMARY The Hospital Bed Integrated Ventilation and Air Cleaning Unit (HBIVCU) is an advanced air distribution system that exhausts locally the exhaled/ coughed air form a sick contagious person lying in bed and thus decreases the risk to spread airborne cross-infections in healthcare facilities. The thermal comfort, especially the local thermal discomfort due to draught and non-uniformity of the thermal environment generated in the bed by the HBIVCU, was evaluated based on physical measurements, performed with thermal manikin. The cooling effect provided by the system to different body segments and the body as a whole was calculated. The results show that the HBIVCU created a complex non-uniform thermal environment that requires further improvement of the unit design. Using the manikin based equivalent temperature as a sole index for evaluation of the generated thermal environment was not enough. Subjective measurements with human subjects are therefore recommended. KEYWORDS Hospital ventilation, advanced air distribution, thermal comfort, manikin based equivalent temperature, physical measurements 1 INTRODUCTION In modern hospitals the ventilation rates are kept elevated in order to reduce the spread of airborne diseases via dilution. The standards and guidelines recommend infectious wards to be ventilated with up to 12 air changes per hour (ACH) and recovery wards and normal patient rooms with 6 ACH (Ashrae 170, 2008; CDC guidelines, 2003). However, recent studies report that the high ventilation rates are not sufficient in protecting the medical staff and the patients from exposure to infected coughed or exhaled air by a sick occupant and can in fact enhance the risk from airborne cross-infection (Bolashikov et.al, 2012; Pantelic and Tham, 2013). Furthermore, the high ventilation rates in hospitals increase the energy consumption for transport and conditioning of outside air. The use of larger ducts for transporting the air decreases the usable space in buildings and leads to higher investment and maintenance costs. The large volumes of clean air, supplied by the room ventilation, also increase the room air velocities that may result in thermal discomfort for the occupants. The thermal comfort issues are especially important for the patients, because often they have

increased body temperature and low metabolic rate, thus increased velocities will enhance the heat exchange with the surroundings. A possible way to create comfortable and safe environment for the patients and the medical staff is to use advanced ventilation (Melikov, 2004). The Hospital Bed Installed Local Ventilation and Air Cleaning Unit (HBIVCU), is an advanced air distribution system that evacuates the exhaled air close to the breathing zone of the patient in the bed and thus reduces the spread of contaminated air in the room (Melikov et. al, 2010; Melikov et.al, 2011) The operation principle of the local ventilation unit is presented in Figure 1. The unit is installed on the hospital bed support frame. The HBIVCU is mobile and able to follow the bed adjustments. Two air terminal devices (1 and 2) are mounted alongside close to the patient s head. They are connected to air conditioning and distribution box (main unit), installed at the back of the bed on the head-side (not shown in the figure). The air expired from the pulmonary activities of the sick person lying in the bed is captured and either removed from the room (in this case the unit is connected to room air exhaust system) or it is cleaned from pathogens via UVG light or other cleansing techniques inside the main unit and then discharged back into the room. The operation mode shown in Figure 1 performs as follows: the clean air supplied from a linear diffuser (1) in horizontal direction (3) entrains and guides the expired contagious air toward the opposite bed side linear diffuser (2) where it is exhausted. Clean air is also supplied upwards in a vertical/inclined direction (5) and in downward direction (6) at the two sides of the lying person. The purpose of the two upward vertical air curtains (5) is to prevent the patient from being exposed to contaminated air coming from a sick person (doctor, nurse or other occupants) inside the room and also to constrain the exhaled air between the two curtains guiding it towards the ceiling where it is exhausted. The two downward vertical curtains (6) provide fresh air close to the patient s berating zone and also local cooling to the head region. Control of the temperature and the flow rate of the horizontal jet of clean air and control over the flow rate of the vertical air curtains are provided to the person in the bed. When the unit is not plugged to the room ventilation system it exhausts, filters and disinfects the room air and then supplies it from the linear diffuser (1). Figure 1. HBIVCU working principle: 1- S-ATD; 2- E-ATD; 3- horizontal air jet; 4 exhaled air by the patient; 5 vertical upward/inclined air curtains; 6 vertical downward air curtains. In order to ensure high evacuation effectiveness of the HBIVCU, the flow rate of the local exhaust has to be kept higher compared to the supply (approx. 9 times higher) and the initial

velocity of the horizontal air flow has to be elevated (approx. 1.2 m/s). This poses a concern that the local bed ventilation might have a negative impact on the thermal comfort of the patients and eventually cause local draught discomfort. The objective of this study was to evaluate the thermal environmental conditions, generated by the HBIVCU and especially the risk of local thermal discomfort for the person in the bed. The influence of the vertical distance between the ventilated bed supply/exhaust diffusers and the head of the patient on the provided local body cooling was in the focus of the study. 2 MATERIALS/METHODS Physical measurements were designed to study the performance of the hospital bed with integrated ventilation unit under realistic conditions. The experiments were performed in a full scale test room furnished as a standard single-bed hospital room. The room had dimensions of 3 m x 6 m x 3 m (width x length x height). Mixing air distribution (MV) was used to supply 100% outdoor air to the room through a square diffuser mounted in the middle of the ceiling (Figure 2a). The air was exhausted through a grill diffuser located in the upper corner of the wall. The supply flow rate was constant at 90 L/s which resulted in 6 ACH. The room air temperature was kept at 24 C ±1 C. The relative humidity in the room was not controlled, but was continuously measured (approx. 40% ± 5%). The room layout simulated a patient lying in a bed and a doctor standing next to the bed. Breathing thermal manikin and a heated dummy were used to simulate the patient and the doctor respectively (Figure 2b). The manikin used for the experiment had the physics of an average Scandinavian female with a height of 1.68 m and size 38 (http://manikin.dk). It consisted of 23 body segments. Each segment was individually controlled to maintain surface temperature equal to the skin temperature of an average person in a state of thermal comfort. During the measurements the manikin, simulating the patient, was dressed in standard hospital garments (panties 0.03 Clo; T-shirt 0.09 Clo; thick ankle socks - 0.1 Clo; trousers - 0.28) with total clothing thermal insulation of 0.5 Clo. The patient was covered with lightweight duvet (3.2 Clo). The heated dummy was generating 125 W of heat (standing activity). Figure 2a. Experimental Room Layout Figure 2b. Experimental Set-up Thermal Manikin and Heated Dummy, Simulating Patient and Doctor

The manikin based equivalent temperature is an index for evaluating the thermal comfort indoors. The equivalent temperature is defined as: The uniform temperature of the imaginary enclosure with air velocity equal to zero in which a person will exchange the same dry heat by radiation and convection as in the actual non- uniform environment (ISO Standard14505-2). The cooling effect of the HBIVCU was assessed by the following equation: t = t t (1) eq eq, i eq, i, ref Where teq,i and teq,i,ref ( o C) is the segmental or whole body equivalent temperature obtained for the same room air temperature respectively with and without the HBIVCU in operation. Negative values of Δteq mean that the ventilation unit provides cooling. 3 RESULTS Figure 3 presents the cooling effect, provided by the HBIVCU system s horizontal air jet for three different vertical distances between the bed supply/exhaust diffusers and the patient s head (10 cm, 20 cm and 30 cm). For all cases the cross- section area of the supply nozzle was 1 cm x 25 cm and the supply and exhaust flow rates were 3 L/s and 27 L/s correspondingly. The HBIVCU was cooling the segments of the manikin s body, which were directly exposed to the flow. When the vertical distance between the supply/exhaust diffusers and the head of the patient increased, the cooling effect of the system decreased. Cr.S 1x25 S. 3L/s V.Distance 10 cm Cr.S 1x25 S. 3L/s V.Distance 20 cm Cr.S 1x25 S. 3L/s V.Distance 30 cm Δt eq o C 4,00 2,00 0,00-2,00-4,00-6,00 L.Foot R.Foot L.Low.Leg R.Low.Leg L. Front thigh R. Front thigh L. Back thigh R. Back Thigh Pelvis Back side Crown L. Face R. Face Back of neck L. Hand R.Hand L.Forearm R.Forearm L. Upper arm R.Upper arm L.Chest R. Chest Back All Figure 3. Change in equivalent temperature Δt eq for manikin s segments exposed to the air flow 4 DISCUSSION The results from the measurements, performed with the thermal manikin, showed that there was cooling provided to all of the segments of the body, directly exposed to the flow. When the vertical distance between the local ventilation supply/exhaust diffusers and the head of the patient decreased, the registered cooling effect to the exposed body segments got higher due to increase in the convective heat losses from the manikin s body (the incident velocity increased). It is a concern that the elevated initial velocity of the horizontal air jet (approx. 1.2 m/s) and the proximity of the two diffusors to the person in the bed, might cause thermal discomfort when the system is continuously used. The HBIVCU provides individual control over the temperature and the flow rate of the horizontal air jet. For this reason it is possible that despite the elevated velocities, generated by the system, the HBIVCU can satisfy a large range of personal thermal environment preferences (temperature and velocity of the air flow). Studies related to subjective evaluation of the thermal environment report that the elevated air

velocity at the face region improves the perceived air quality of the occupants (Melikov et.al, 2003; Melikov, 2004; Gong et.al, 2006). If the temperature in the hospital room is high (in case of hot climates), the local bed ventilation has the potential to improve the thermal comfort of the bed-bound occupants. The HBIVCU provides non-uniform cooling to the left and to the right body segments. From the results it can be observed that the cooling of the right face, arm and chest was approx. 1 o C lower compared to the left face, arm and chest (Figure3). The asymmetry in the cooling of the left and the right side body segments is due to difference in the velocity, generated by the supply and the exhaust diffusors of the HBIVCU (results are not reported). This asymmetry might create a risk of draught discomfort for the patients, when they are exposed to the flow for relatively long period of time. Human subject experiment, performed with the HBIVCU system s prototype, show that for exposure period of 1 hour the subjects felt the difference in the cooling at the left and the right side of the body. However, they did not evaluate the thermal environment conditions as uncomfortable. There were no draught complains reported, (Kehayova et.al, 2016). The subjects expressed satisfaction with having the option to adjust the flow rate and the temperature of the local ventilation. They evaluated the acceptability of the individually controlled air movement as high. The design of the HBIVCU needs further improvement. A possible way to create a more uniform bed environment is to change the shape of the initial velocity profile of the horizontal air jet of the HBIVCU. CFD simulations, performed with the bed ventilation system, show that the shape of the initial velocity profile has high influence on the evacuation effectiveness of the HBIVCU and also on the velocities, generated around the head region of the patient (results are not reported). Using appropriate initial velocity profile can ensure high exhaled air removal effectiveness of the system at lower flow rates of the local exhaust. However, further simulations are needed in order to identify a minimum local exhaust flow rate that can keep the unit functional with respect to airborne cross-infection protection Decreasing the flow rate of the local exhaust will reduce the asymmetry in the cooling between the left and the right side of the patient s body and will create a more homogeneous bed thermal environment. Based on the measured equivalent temperature it can be concluded that the thermal environment, generated by the horizontal air jet of the HBIVCU, was non-homogeneous. However, when estimating the indoor climate, it is important to note that the occupant doesn t feel the room temperature, but the amount of energy loss from the body. Since all people are different, they have different perception for thermal comfort and converting the term into physical parameters is difficult. For this reason using the manikin based equivalent temperature as a sole index for evaluating the thermal environment is not enough. Subjective measurements with human subjects under real hospital conditions are recommended. The main purpose of the HBIVCU system is to provide control over the spread of nosocomial airborne infections. This can be ensured by operating the local ventilation continuously when there is a patient lying in the hospital bed. Generating comfortable bed environment is as important for the fast recovery of the patients as ensuring adequate protection against airborne cross-infections. Decreasing the distance between the bed supply/ exhaust diffusers and the head of the patient increases the evacuation effectiveness of the HBIVCU, but also increases the convective heat loss from the body. Positioning the supply/ exhaust diffusers of the HBIVCU close the patient s head may not pose a risk of local thermal discomfort, but having the horizontal flow in the vicinity of the head of the bed occupant might cause eyes, nose and

throat dryness and irritation. For this reason further research is required in order to identify the optimal position of the two diffusers with respect to the head of the patient lying in bed. 5 CONCLUSIONS Based on the results, presented in the current study, the following conclusions can be made: The system provides cooling for the segments of the manikin s body, directly exposed to the airflow. The HBIVCU generates a non-uniform thermal environment which leads to differences in the cooling between the left and right body side of the lying patient. 6 ACKNOWLEDGEMENT This research was funded by the project: GAP project 26389 - Novel ventilation for hospital beds to reduce airborne cross-contamination with bacteria and other microorganisms in old and new hospitals. 7 REFERENCES ASHRAE/ASHE Standard, 170-2008, Ventilation of Health Care Facilities, American Society of Heating, Refrigerating and Air-conditioning Engineers, Inc. 1791 Tullie Circle NE, Atlanta, GA 30329 Bolashikov, Z.D., A.K. Melikov, W. Kierat, Popio-Lek, Z., and M. Brand. 2012. Exposure of healthcare workers and occupants to coughed airborne pathogens in a double-bed hospital room with overhead mixing ventilation. HVAC&R Research 18:602 15. CDC (2003). Guidelines for environmental infection control in health-care facilities. Atlanta, GA 30333, U.S. Department of Health and Human Services Centers for Disease Control and Prevention Gong, N., Tham, K.W., Melikov, A.K., Wyon, D.P., Sekhar, S.C., and Cheong, K.W. (2006) Local air movement in the tropics. HVAC&R Research, 12, 1065-1076. http://manikin.dk/ ISO Standard 14505-2: Ergonomics of the thermal environment Evaluation of thermal environment in vehicles Part 2: Determination of Equivalent Temperature, ISO, Genève 2004. Kehayova N, Bolashikov Z., Melikov A., Subjective Evaluation of the Microenvironment Generated by a Hospital Bed with Localized Ventilation System, Indoor Air Conference, Ghent, Belgium, July 2016 Melikov, A., Bolashikov, Z., Brand, M., (2010). Experimental investigation of performance of a novel ventilation method for hospital patient rooms. 21st Congress of International Federation of Hospital Engineering (IFHE), Tokyo Japan, November 17th to 19th, 2010 Melikov, A., Bolashikov, Z., Georgiev E., (2011). Novel ventilation strategy for reducing the risk of cross infection in hospital rooms. In: Proceedings of Indoor Air 2011.Paper 1037. Melikov A. K, Cermak R, Kovar O., Forejt L. 2003 Impact of airflow interaction on inhaled air quality and transport of contaminants in rooms with personalized and total volume ventilation. Proceedings Healthy Building, Vol.2, pp.500 10 (Singapore). Melikov A. K. 2004 Personalized ventilation Indoor Air, Vol. 14, Sup. 7, pp. 157-167. Pantelic Jovan and Tham Kwok Wai, Adequacy of air change rate as the sole indicator of an air distribution system s effectiveness to mitigate airborne infectious disease transmission caused by a cough release in the room with overhead mixing ventilation: A case study HVAC % Research 2013 (19), p. 947 961