Study on energy-saving design and operation of hospital purification air conditioning system

Study on energy-saving design and operation of hospital purification air conditioning system Abstract In order to ensure the cleanliness of operating room, clean air conditioners are installed in the clean operation departments in hospitals in China. Purification air conditioning system is an air conditioning system with a special function that ensures the cleanliness of the operating room and the required temperature and humidity in the operating room to avoid infection. This paper took the energy-saving design of the clean air-conditioning system of the clean operation department of the First Affiliated Hospital of Wenzhou Medical College, Zhejiang, China, as an example to illustrate the energy-saving methods such as layout optimization, air-conditioning division, secondary return air setting and operation mode adjustment. The energy consumption of primary return air technology and secondary return air technology was calculated. The results showed that energy-saving design could save nearly one-third of energy, improve the level of air-conditioning operation and management, reduce costs, and improve resource utilization, which is of great significance to social development. 1 INTRODUCTION The cleanliness of hospitals, especially the environmental cleanliness of the operating room [1, 2], is directly related to the health of patients and medical staffs. With the further development of medical and health care in China, the level of surgery has been improved [3]. As a result, clean surgical department is born to ensure that operating room environment meet national standards. Clean surgical department should use clean air technology and establish scientific staff, logistics and zoning management to control particulate pollution [4] and ensure the safety of surgical patients. Gniadek et al. mentioned in their work [5] that infection during surgery was a risk factor which intervened in treatment and eradicating microorganisms in the operating room environment might help to reduce the incidence of infection, while laminar air conditioners significantly reduced the number of microorganisms in hospital environment. By collecting and testing fungi in a hospital’s air samples, they found 48 out of 50 air samples with fungal growths. Hence, in order to ensure the cleanliness of the operating room of the hospital, the air conditioning system needs to be properly maintained. As clean air conditioning system design can directly affect the air quality and operating energy consumption, air conditioning energy-saving design is particularly important. In the study of Tabata et al. [6], the combination of desiccant air conditioning system and the cold water large temperature difference water supply system achieved an energy saving of 41% a year. On the basis of comparative analysis of indoor comfort parameters such as temperature and wind speed, Wang et al. [7] used the improved radiation heat transfer method to solve the temperature model of the inner surface of building envelope and calculated the theoretical load index. The flow field and parameters generated by computational fluid dynamics were used to effectively analyze the indoor thermal comfort in full air conditioning and stratified air conditioning design and the stratified air conditioning design was recommended in large space buildings. Taking a Grade A hospital in Wuhan as the research object, Li et al. [8] conducted an audit on the hospital’s energy consumption system. After energy-saving reform on the lighting system and central heating and energy control system, the final comprehensive reform energy-saving rate was 31.71%, saving 318.01tce (ton of standard coal equivalent). The purpose of this study is to save energy and promote sustainable development through the energy-saving design of the clean air-conditioning system in the clean operation department of a hospital. 2 OVERVIEW OF THE CLEAN OPERATION DEPARTMENT The clean operation department of the First Affiliated Hospital of Wenzhou Medical College, Zhejiang, China, is located on the third floor of the medical technology department, and the purification equipment room is located on the fourth floor, with an area of 11 420 m2. Purification central air conditioner with four-pipe system and independent cold and heat source is used. The operation department consists of 43 operating rooms and related functional rooms, including 6 I level operating rooms and 37 III level operating rooms, and involves positive and negative pressure switching department, outpatient department, endoscopy department, orthopedics department and general surgery department. In addition, the clean surgical department is also divided into three regions, OR1–OR13 is region one, OR14–OR26 is region two, and OR27–OR43 is region three; each region is independently controlled. OR22–OR26 are emergency operating rooms and OR14–OR21 are night or emergency rooms (Table 1), which can be used separately. All operating rooms have a ceiling height of 3 m, and some operating room profiles of the clean operation department are shown in Figure 1. Table 1. The overview of the clean operation department. Region No. of operation room Clean class Area of operation room (m2) Category of operation room Region 1 OR2 Grade III 54.1 Neurosurgery (cerebral surgery) OR4 Grade III 52.71 General thoracic OR8 Grade III 31.55 Urinary surgery OR11 Grade I 73.06 Neurosurgery (cerebral surgery) OR12 Grade I 54.53 Cardiac (in vitro) Region 2 OR14 Grade I 71.16 Hybrid (vascular surgery) OR16 Grade III 54.94 Orthopedics OR19 Grade III 52.71 General Surgery OR25 Grade III 27.18 Emergency treatment OR26 Grade III 30.74 Positive–negative pressure Region 3 OR32 Grade III 40.42 Tumor OR35 Grade III 46.8 Ear, nose, and throat OR36 Grade III 31.28 Burn surgery OR39 Grade III 34.92 Outpatient OR43 Grade III 27.76 Outpatient Region No. of operation room Clean class Area of operation room (m2) Category of operation room Region 1 OR2 Grade III 54.1 Neurosurgery (cerebral surgery) OR4 Grade III 52.71 General thoracic OR8 Grade III 31.55 Urinary surgery OR11 Grade I 73.06 Neurosurgery (cerebral surgery) OR12 Grade I 54.53 Cardiac (in vitro) Region 2 OR14 Grade I 71.16 Hybrid (vascular surgery) OR16 Grade III 54.94 Orthopedics OR19 Grade III 52.71 General Surgery OR25 Grade III 27.18 Emergency treatment OR26 Grade III 30.74 Positive–negative pressure Region 3 OR32 Grade III 40.42 Tumor OR35 Grade III 46.8 Ear, nose, and throat OR36 Grade III 31.28 Burn surgery OR39 Grade III 34.92 Outpatient OR43 Grade III 27.76 Outpatient Table 1. The overview of the clean operation department. Region No. of operation room Clean class Area of operation room (m2) Category of operation room Region 1 OR2 Grade III 54.1 Neurosurgery (cerebral surgery) OR4 Grade III 52.71 General thoracic OR8 Grade III 31.55 Urinary surgery OR11 Grade I 73.06 Neurosurgery (cerebral surgery) OR12 Grade I 54.53 Cardiac (in vitro) Region 2 OR14 Grade I 71.16 Hybrid (vascular surgery) OR16 Grade III 54.94 Orthopedics OR19 Grade III 52.71 General Surgery OR25 Grade III 27.18 Emergency treatment OR26 Grade III 30.74 Positive–negative pressure Region 3 OR32 Grade III 40.42 Tumor OR35 Grade III 46.8 Ear, nose, and throat OR36 Grade III 31.28 Burn surgery OR39 Grade III 34.92 Outpatient OR43 Grade III 27.76 Outpatient Region No. of operation room Clean class Area of operation room (m2) Category of operation room Region 1 OR2 Grade III 54.1 Neurosurgery (cerebral surgery) OR4 Grade III 52.71 General thoracic OR8 Grade III 31.55 Urinary surgery OR11 Grade I 73.06 Neurosurgery (cerebral surgery) OR12 Grade I 54.53 Cardiac (in vitro) Region 2 OR14 Grade I 71.16 Hybrid (vascular surgery) OR16 Grade III 54.94 Orthopedics OR19 Grade III 52.71 General Surgery OR25 Grade III 27.18 Emergency treatment OR26 Grade III 30.74 Positive–negative pressure Region 3 OR32 Grade III 40.42 Tumor OR35 Grade III 46.8 Ear, nose, and throat OR36 Grade III 31.28 Burn surgery OR39 Grade III 34.92 Outpatient OR43 Grade III 27.76 Outpatient Figure 1. View largeDownload slide Plan graph of the clean surgical department. Figure 1. View largeDownload slide Plan graph of the clean surgical department. 3 COMMON ENERGY SAVING MEASURES 3.1 Layout optimization of the surgical department Apart from operating rooms, there are subsidiary rooms in the surgical department. Clean auxiliary rooms should be set in the clean area, connected with the clean operating room. Non-clean auxiliary rooms should be set in the non-clean area, while the waiting area and washroom should be set in the comfortable air-conditioned area. Connecting the auxiliary room with the operating room can reduce the waste of time, speed up the surgical procedure and improve the operation efficiency. Through setting the clean auxiliary rooms, non-cleaning auxiliary rooms and other functional rooms in different regions, different design on air supply for the clean air-conditioning can be realized according to the cleanliness of different regions. The energy consumption of decontamination air conditioners is reduced by installing comfortable air conditioners in the air conditioning areas. The layout optimization of the surgical department will not only make the surgical flow more smoothly, but also save air conditioning energy consumption [9]. 3.2 Air conditioning division The air conditioner of the I level operating room applies one-driven-one mode while that of the III level operating room applies one-driven-two or one-driven-three mode; both of them apply the secondary air return system. Each operating room discharges air independently with fresh air delivered. As the area outside the building needs to be chilled in the summer and heated in the winter while the area inside the building needs year-round cooling, the air-conditioning system is divided into the interior and exterior partitions reasonably to avoid the situation that the cooling and heating offset each other [10]. 3.3 Frequency conversion technology The purification air conditioning operating mode is set to working mode and non-working mode while the working mode is divided into two modes: the one on winter and summer and the one on transition seasons. The frequency conversion technology is used in fresh air units and purification cycle units for performing variable frequency regulation on fresh air volume under different working modes [11]. In non-working mode, the air-conditioner operates according to the minimum air volume required, which ensures the cleanliness of the operating room and saves energy. In winter and summer mode, it operates at the fresh air volume required for normal operation. In transition season mode, it operates at the maximum required air volume, which effectively reduces energy consumption and optimizes operation. 3.4 Secondary return air system Purifying air conditioning is different from comfort air conditioning, its air output is large and supply air temperature difference and heat load are small in the process of heat and humidity treatment. Though primary return air system is commonly applied nowadays with its advantages of simple structure and operation, its energy consumption is large due to the hot and cold offset phenomenon between its cooling and heating coils. In contrast, secondary return air system does not have this problem. Instead, by utilizing the return air temperature, the system can greatly reduce equipment operating costs, save energy and promote sustainable energy development [12]. 4 AIR CONDITIONING ENERGY-SAVING DESIGN 4.1 Purification air conditioning system analysis Purification air conditioning system consists of air filters, circulating fans, surface coolers and heating and humidification devices. Air filter has three stalls, namely, rough efficiency, efficiency, high efficiency, which have different degrees of air treatment. Air blowing function is realized through the circulation fan, which forms wind by air motion. Air temperature and humidity control is completed by the surface cooler and heating and humidification device. Different from the industrial clean room, the purification air conditioning system in the clean operating room often uses multi-machine centralized air-conditioning system, installs all units in the air-conditioned room, with the fresh air delivered through the air supply duct at the top of the operating room after filtered by the filter. 4.2 Cold heat source setting and fresh air supply way The cold and heat source setting of the clean operation department is determined based on the cold and heat source setting of the whole medical building. The central cooling (heating) mode and the independent decentralized cooling (heating) source configuration mode are applied. When the central source of cooling (heating) cannot fully meet the requirements of the air-conditioning system of the clean surgery department, the independent decentralized cooling (heating) source can meet the requirements of the operation department, making the clean air conditioner flexible and economical, and can satisfy the emergency use requirements of the operation department. However, its cooling adjustment range is limited, with poor temperature and humidity control performance, and it is difficult to maintain the stability of temperature and humidity. Hence, the local centralized cooling (heating) and independent decentralized cooling (heating) source configuration mode can be used. This configuration can meet the requirements of surgeries with high temperature and humidity stability requirements, with good energy-saving performance [13]. Fresh air treatment is divided into fresh air dispersion treatment and fresh air concentration treatment. Fresh air dispersion treatment refers to the treatment of fresh air after fresh air is mixed with the return air while fresh air concentration treatment refers to the treatment of fresh air before fresh air is mixed with the return air. In this design, fresh air concentration treatment is preferred since it can ensure the simple maintenance of the air conditioning system, save management costs and avoid the change of microbiological equilibrium when return air meets the unprocessed fresh air. 4.3 Various types of clean room parameter indexes Before the design of air conditioning system of clean operation department [14], we need to understand the requirements of air conditioning system design. Although the accuracy requirement of the clean operating room for indoor temperature and humidity is not high, it is necessary to ensure that the bacterial concentration is controlled within a certain range under such conditions of temperature and humidity [15]. Besides, different levels of clean operating room have different requirements on the times of ventilation. There are two levels of clean surgical room in the clean operation department of the First Affiliated Hospital of Wenzhou Medical College, i.e. I level and III level. As shown in Table 2, the I level surgical room requires 0.2 bacteria in the surgical area/30 min · φ90 vessel (5 bacteria/m3) and 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria/m3), while the III level surgical room requires 2 bacteria in the surgical area/30 min · φ90 vessel (75 bacteria/m3) and 4 bacteria in the surrounding area/30 min · φ90 vessel (150 bacteria/m3). Table 2. Clean room level parameters in the clean surgical department. Level of the operating room The maximum average concentration of bacteria of sedimentation (phytoplankton) in the operation area Air cleanliness class Ventilation times (times/h) Working surface height interface average wind speed (m/s) Temperature (°C) Relative humidity (% RH) I level Clean operating room 0.2 bacteria in the surgical area/30 min · φ90 vessel (5 bacteria/m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria /m3) Surgical area: 100 level Surrounding area: 1000 level / 0.25–0.30 22–25 40–60 Clean auxiliary room 0.2 bacteria in the local area/30 min · φ90 vessel (5 bacteria /m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria/m3) 1000 level (local 100 level) / / / / III level Clean operating room 2 bacteria in the surgical area/30 min · φ90 vessel (75 bacteria/m3) 4 bacteria in the surrounding area/30 min · φ90 vessel (150 bacteria/m3) Surgical area: 10 000 level Surrounding area: 100 000 level 20–24 / 22–25 35–60 Clean auxiliary room 4 bacteria/30 min · φ90 vessel (150 bacteria/m3) 100 000 level / / / / Level of the operating room The maximum average concentration of bacteria of sedimentation (phytoplankton) in the operation area Air cleanliness class Ventilation times (times/h) Working surface height interface average wind speed (m/s) Temperature (°C) Relative humidity (% RH) I level Clean operating room 0.2 bacteria in the surgical area/30 min · φ90 vessel (5 bacteria/m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria /m3) Surgical area: 100 level Surrounding area: 1000 level / 0.25–0.30 22–25 40–60 Clean auxiliary room 0.2 bacteria in the local area/30 min · φ90 vessel (5 bacteria /m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria/m3) 1000 level (local 100 level) / / / / III level Clean operating room 2 bacteria in the surgical area/30 min · φ90 vessel (75 bacteria/m3) 4 bacteria in the surrounding area/30 min · φ90 vessel (150 bacteria/m3) Surgical area: 10 000 level Surrounding area: 100 000 level 20–24 / 22–25 35–60 Clean auxiliary room 4 bacteria/30 min · φ90 vessel (150 bacteria/m3) 100 000 level / / / / Table 2. Clean room level parameters in the clean surgical department. Level of the operating room The maximum average concentration of bacteria of sedimentation (phytoplankton) in the operation area Air cleanliness class Ventilation times (times/h) Working surface height interface average wind speed (m/s) Temperature (°C) Relative humidity (% RH) I level Clean operating room 0.2 bacteria in the surgical area/30 min · φ90 vessel (5 bacteria/m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria /m3) Surgical area: 100 level Surrounding area: 1000 level / 0.25–0.30 22–25 40–60 Clean auxiliary room 0.2 bacteria in the local area/30 min · φ90 vessel (5 bacteria /m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria/m3) 1000 level (local 100 level) / / / / III level Clean operating room 2 bacteria in the surgical area/30 min · φ90 vessel (75 bacteria/m3) 4 bacteria in the surrounding area/30 min · φ90 vessel (150 bacteria/m3) Surgical area: 10 000 level Surrounding area: 100 000 level 20–24 / 22–25 35–60 Clean auxiliary room 4 bacteria/30 min · φ90 vessel (150 bacteria/m3) 100 000 level / / / / Level of the operating room The maximum average concentration of bacteria of sedimentation (phytoplankton) in the operation area Air cleanliness class Ventilation times (times/h) Working surface height interface average wind speed (m/s) Temperature (°C) Relative humidity (% RH) I level Clean operating room 0.2 bacteria in the surgical area/30 min · φ90 vessel (5 bacteria/m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria /m3) Surgical area: 100 level Surrounding area: 1000 level / 0.25–0.30 22–25 40–60 Clean auxiliary room 0.2 bacteria in the local area/30 min · φ90 vessel (5 bacteria /m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria/m3) 1000 level (local 100 level) / / / / III level Clean operating room 2 bacteria in the surgical area/30 min · φ90 vessel (75 bacteria/m3) 4 bacteria in the surrounding area/30 min · φ90 vessel (150 bacteria/m3) Surgical area: 10 000 level Surrounding area: 100 000 level 20–24 / 22–25 35–60 Clean auxiliary room 4 bacteria/30 min · φ90 vessel (150 bacteria/m3) 100 000 level / / / / In addition, the I level surgical room requires the working face height interface average wind speed to be 0.25–0.30 m/s, the temperature to be between 22°C and 25°C, and the relative humidity to be between 40% and 60% RH, while the III level surgical room requires the times of ventilation to be 20–24 times/h, temperature between 22°C and 25°C, and relative humidity between 35% and 60% RH. 4.4 Determination of design parameters Cooling load refers to the heat, including both sensible heat and latent heat, taken away from the room by the air conditioning system in order to keep the indoor hot and humid environment and temperature at a specified level. As the clean surgical department does not have doors or windows that have direct contact with the outside world, the solar radiation heat and heat brought through air infiltration can be ignored. Human body heat dissipation, lighting heat dissipation and equipment heat dissipation are considered, that is, human body cooling load, lighting cooling load and equipment cooling load. In the actual calculation, the cluster coefficient which is calculated according to the age, gender, and intensity of members based on the heat and wet dissipation capacity of an adult man needed to be taken into consideration. The heat and wet dissipation capacity of an adult woman is 85% that of an adult men, while that of a child is 75% that of an adult man; therefore cluster coefficient = (number of adult men + number of adult women ∗ 85% + number of children ∗ 75%)/total number of people. Total body cooling load in the operating room was: Cr=crnn', where Cr refers to body heat dissipation cooling load (W), Cr refers to body total heat load (W), n refers to the total number of people, and n' refers to the cluster coefficient. The total body wet load in the operating room was: Hs=hsnn', where Hs refers to body wet dissipation humid load (kg/h), hs refers to body wet dissipation amount (g/h), n refers to the total number of people, and n' refers to the cluster coefficient. According to the parameters in Table 2, the room temperature was set at a constant temperature of 24°C, and the relative humidity was set as 50%. There were 12 people in III level surgical room and 10 people in III level surgical room. Two people were of extreme light physical labor and others were of light physical labor, the results are shown in Table 3. Table 3. Human body load calculation results. Level of the operating room Extreme light physical labor Light physical labor Humidity load (g/h) Cooling load (W) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) I level 2 70 64 96 10 70 112 167 1862 2088 III level 2 70 64 96 8 70 112 167 1528 1724 Level of the operating room Extreme light physical labor Light physical labor Humidity load (g/h) Cooling load (W) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) I level 2 70 64 96 10 70 112 167 1862 2088 III level 2 70 64 96 8 70 112 167 1528 1724 Table 3. Human body load calculation results. Level of the operating room Extreme light physical labor Light physical labor Humidity load (g/h) Cooling load (W) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) I level 2 70 64 96 10 70 112 167 1862 2088 III level 2 70 64 96 8 70 112 167 1528 1724 Level of the operating room Extreme light physical labor Light physical labor Humidity load (g/h) Cooling load (W) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) I level 2 70 64 96 10 70 112 167 1862 2088 III level 2 70 64 96 8 70 112 167 1528 1724 Lighting cooling load was: Cz=czCClz, where Cz refers to lighting heat dissipation cooling load (W), Cz refers to lighting heat dissipation amount (W), and CClZ refers to cooling load coefficient of lighting heat dissipation. The cooling load of the equipment is: Ce=ceCCle, where Ce refers to cooling load of equipment heat dissipation (W), Ce refers to the heat dissipation amount of equipment (W), and CCle refers to the cooling load coefficient of equipment heat dissipation. Based on the power of common equipment and lamps in the operating room, the cooling load of the equipment was 3320 W and the cooling load of the lighting was 420 W. Table 4 shows the total indoor load of the clean operating room under steady-state conditions. Table 4. Heat and wet load in the clean operating room. Level of the operating room Indoor design temperature (°C) Body cooling load (w) Body humidity load (kg/h) Equipment cooling load (w) Lighting cooling load (w) Total cooling load (w) Heat and moisture ratio (kJ/kg) I level (45 m2) 24 2088 1.862 3320 420 5828 11 268 III level (35 m2) 24 1724 1.528 3320 420 5464 12 873 Level of the operating room Indoor design temperature (°C) Body cooling load (w) Body humidity load (kg/h) Equipment cooling load (w) Lighting cooling load (w) Total cooling load (w) Heat and moisture ratio (kJ/kg) I level (45 m2) 24 2088 1.862 3320 420 5828 11 268 III level (35 m2) 24 1724 1.528 3320 420 5464 12 873 Table 4. Heat and wet load in the clean operating room. Level of the operating room Indoor design temperature (°C) Body cooling load (w) Body humidity load (kg/h) Equipment cooling load (w) Lighting cooling load (w) Total cooling load (w) Heat and moisture ratio (kJ/kg) I level (45 m2) 24 2088 1.862 3320 420 5828 11 268 III level (35 m2) 24 1724 1.528 3320 420 5464 12 873 Level of the operating room Indoor design temperature (°C) Body cooling load (w) Body humidity load (kg/h) Equipment cooling load (w) Lighting cooling load (w) Total cooling load (w) Heat and moisture ratio (kJ/kg) I level (45 m2) 24 2088 1.862 3320 420 5828 11 268 III level (35 m2) 24 1724 1.528 3320 420 5464 12 873 4.5 Analysis on the primary and secondary return air system As mentioned before, the primary return air system had severe hot and cold offset phenomenon and large energy consumption while the secondary return air system could greatly reduce equipment operating costs and save energy consumption. In this section, the cooling load and energy consumption of the two systems were analyzed. In summer, outdoor design parameters are as follows: 35°C of dry bulb temperature, 28°C of wet bulb temperature; indoor design parameters were as follows: 24°C of room temperature and 50% of relative humidity. Based on the cross section wind speed and ventilation time requirements of the operating room in Table 2, the amount of air supply of the air-conditioning system was determined. The local air – ventilation system was used. In the I level surgical room, the fresh air volume was 1000 m3/h, the return air volume was 9000 m3/h, the exhaust air volume was 555 m3/h, and the amount of air supply was 10 000 m3/h; in the III level surgical room, the fresh air volume was 800 m3/h, the return air volume was 1100 m3/h, the exhaust air volume was 560 m3/h, and the air supply volume was 1900 m3/h. Hence, it was calculated out that the air enthalpy difference and the machine dew point enthalpy was 0.912 kJ/kg and 2.374 kJ/kg, 35.11 kJ/kg and 35.06 kJ/kg, respectively in the I level surgical room and the III level surgical room. As the primary return air system had a reheat process, its cooling load was composed of the indoor load, fresh air load, reheat load and fan temperature rise load while the secondary return air system had no reheat load, as shown in Table 5. Table 5. Cooling load of the primary return airy system. Level of the operating room Fresh air volume (m3/h) Heat humidity ratio (kJ/kg) Indoor load (kW) Fresh air load (kW) Reheat load (kW) Fan temperature rise load Cooling load (kW) Fresh air (kW) Air supply (kW) Primary return air system I level 1000 11 268 5.828 15.96 36.06 0.53 5.78 64.158 III level 800 12 873 5.464 12.44 11.12 0.41 1.94 31.374 Secondary return air system I level 1000 11 268 5.828 11.86 / 0.53 5.78 23.998 III level 800 12 873 5.464 11.42 / 0.41 1.94 19.234 Level of the operating room Fresh air volume (m3/h) Heat humidity ratio (kJ/kg) Indoor load (kW) Fresh air load (kW) Reheat load (kW) Fan temperature rise load Cooling load (kW) Fresh air (kW) Air supply (kW) Primary return air system I level 1000 11 268 5.828 15.96 36.06 0.53 5.78 64.158 III level 800 12 873 5.464 12.44 11.12 0.41 1.94 31.374 Secondary return air system I level 1000 11 268 5.828 11.86 / 0.53 5.78 23.998 III level 800 12 873 5.464 11.42 / 0.41 1.94 19.234 Table 5. Cooling load of the primary return airy system. Level of the operating room Fresh air volume (m3/h) Heat humidity ratio (kJ/kg) Indoor load (kW) Fresh air load (kW) Reheat load (kW) Fan temperature rise load Cooling load (kW) Fresh air (kW) Air supply (kW) Primary return air system I level 1000 11 268 5.828 15.96 36.06 0.53 5.78 64.158 III level 800 12 873 5.464 12.44 11.12 0.41 1.94 31.374 Secondary return air system I level 1000 11 268 5.828 11.86 / 0.53 5.78 23.998 III level 800 12 873 5.464 11.42 / 0.41 1.94 19.234 Level of the operating room Fresh air volume (m3/h) Heat humidity ratio (kJ/kg) Indoor load (kW) Fresh air load (kW) Reheat load (kW) Fan temperature rise load Cooling load (kW) Fresh air (kW) Air supply (kW) Primary return air system I level 1000 11 268 5.828 15.96 36.06 0.53 5.78 64.158 III level 800 12 873 5.464 12.44 11.12 0.41 1.94 31.374 Secondary return air system I level 1000 11 268 5.828 11.86 / 0.53 5.78 23.998 III level 800 12 873 5.464 11.42 / 0.41 1.94 19.234 Figure 2 is obtained after calculating the proportion of each load in the total cooling. Figure 2. View largeDownload slide Cooling load in the clean operating room. Figure 2. View largeDownload slide Cooling load in the clean operating room. As shown in Table 5, the cooling load of primary return air system in operation room I was 64.158 kW, that of secondary return air system was 23.998 kW, saving 167.35%. The cooling load of primary return air system in III level operating room was 31.374 kW, that of the secondary air return system was 19.234 kW, saving 63.12%. As shown in Figure 2, on the cooling load of the primary return air system, whether it was level I operating room or level III operating room, the proportion of reheat load was the largest. The reheat load accounted for 56.20% of the total cooling load in level I operating room and 35.44% in level III operating room. Without reheat load, the secondary return air system saved most of the energy consumption. 5 CONCLUSIONS In addition to ensure that the indoor temperature and humidity and differential pressure are within the standard range, the clean air conditioner in the clean surgery department also needs to ensure that the indoor air concentration of bacteria and dust particles are within the standard range in order to reduce the risk of wound infection in patients and ensure the health of health care workers. Therefore, the operating effect of clean air conditioning is extremely important. While ensuring the effectiveness of clean air conditioning, we should also consider the energy-saving aspect. In this paper, energy-saving methods were explored and designed to determine the relevant parameters of the purification air-conditioning system and the configuration of cold and heat sources and fresh air supply ways. 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This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Low-Carbon Technologies Oxford University Press

Study on energy-saving design and operation of hospital purification air conditioning system

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1748-1317
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Abstract

Abstract In order to ensure the cleanliness of operating room, clean air conditioners are installed in the clean operation departments in hospitals in China. Purification air conditioning system is an air conditioning system with a special function that ensures the cleanliness of the operating room and the required temperature and humidity in the operating room to avoid infection. This paper took the energy-saving design of the clean air-conditioning system of the clean operation department of the First Affiliated Hospital of Wenzhou Medical College, Zhejiang, China, as an example to illustrate the energy-saving methods such as layout optimization, air-conditioning division, secondary return air setting and operation mode adjustment. The energy consumption of primary return air technology and secondary return air technology was calculated. The results showed that energy-saving design could save nearly one-third of energy, improve the level of air-conditioning operation and management, reduce costs, and improve resource utilization, which is of great significance to social development. 1 INTRODUCTION The cleanliness of hospitals, especially the environmental cleanliness of the operating room [1, 2], is directly related to the health of patients and medical staffs. With the further development of medical and health care in China, the level of surgery has been improved [3]. As a result, clean surgical department is born to ensure that operating room environment meet national standards. Clean surgical department should use clean air technology and establish scientific staff, logistics and zoning management to control particulate pollution [4] and ensure the safety of surgical patients. Gniadek et al. mentioned in their work [5] that infection during surgery was a risk factor which intervened in treatment and eradicating microorganisms in the operating room environment might help to reduce the incidence of infection, while laminar air conditioners significantly reduced the number of microorganisms in hospital environment. By collecting and testing fungi in a hospital’s air samples, they found 48 out of 50 air samples with fungal growths. Hence, in order to ensure the cleanliness of the operating room of the hospital, the air conditioning system needs to be properly maintained. As clean air conditioning system design can directly affect the air quality and operating energy consumption, air conditioning energy-saving design is particularly important. In the study of Tabata et al. [6], the combination of desiccant air conditioning system and the cold water large temperature difference water supply system achieved an energy saving of 41% a year. On the basis of comparative analysis of indoor comfort parameters such as temperature and wind speed, Wang et al. [7] used the improved radiation heat transfer method to solve the temperature model of the inner surface of building envelope and calculated the theoretical load index. The flow field and parameters generated by computational fluid dynamics were used to effectively analyze the indoor thermal comfort in full air conditioning and stratified air conditioning design and the stratified air conditioning design was recommended in large space buildings. Taking a Grade A hospital in Wuhan as the research object, Li et al. [8] conducted an audit on the hospital’s energy consumption system. After energy-saving reform on the lighting system and central heating and energy control system, the final comprehensive reform energy-saving rate was 31.71%, saving 318.01tce (ton of standard coal equivalent). The purpose of this study is to save energy and promote sustainable development through the energy-saving design of the clean air-conditioning system in the clean operation department of a hospital. 2 OVERVIEW OF THE CLEAN OPERATION DEPARTMENT The clean operation department of the First Affiliated Hospital of Wenzhou Medical College, Zhejiang, China, is located on the third floor of the medical technology department, and the purification equipment room is located on the fourth floor, with an area of 11 420 m2. Purification central air conditioner with four-pipe system and independent cold and heat source is used. The operation department consists of 43 operating rooms and related functional rooms, including 6 I level operating rooms and 37 III level operating rooms, and involves positive and negative pressure switching department, outpatient department, endoscopy department, orthopedics department and general surgery department. In addition, the clean surgical department is also divided into three regions, OR1–OR13 is region one, OR14–OR26 is region two, and OR27–OR43 is region three; each region is independently controlled. OR22–OR26 are emergency operating rooms and OR14–OR21 are night or emergency rooms (Table 1), which can be used separately. All operating rooms have a ceiling height of 3 m, and some operating room profiles of the clean operation department are shown in Figure 1. Table 1. The overview of the clean operation department. Region No. of operation room Clean class Area of operation room (m2) Category of operation room Region 1 OR2 Grade III 54.1 Neurosurgery (cerebral surgery) OR4 Grade III 52.71 General thoracic OR8 Grade III 31.55 Urinary surgery OR11 Grade I 73.06 Neurosurgery (cerebral surgery) OR12 Grade I 54.53 Cardiac (in vitro) Region 2 OR14 Grade I 71.16 Hybrid (vascular surgery) OR16 Grade III 54.94 Orthopedics OR19 Grade III 52.71 General Surgery OR25 Grade III 27.18 Emergency treatment OR26 Grade III 30.74 Positive–negative pressure Region 3 OR32 Grade III 40.42 Tumor OR35 Grade III 46.8 Ear, nose, and throat OR36 Grade III 31.28 Burn surgery OR39 Grade III 34.92 Outpatient OR43 Grade III 27.76 Outpatient Region No. of operation room Clean class Area of operation room (m2) Category of operation room Region 1 OR2 Grade III 54.1 Neurosurgery (cerebral surgery) OR4 Grade III 52.71 General thoracic OR8 Grade III 31.55 Urinary surgery OR11 Grade I 73.06 Neurosurgery (cerebral surgery) OR12 Grade I 54.53 Cardiac (in vitro) Region 2 OR14 Grade I 71.16 Hybrid (vascular surgery) OR16 Grade III 54.94 Orthopedics OR19 Grade III 52.71 General Surgery OR25 Grade III 27.18 Emergency treatment OR26 Grade III 30.74 Positive–negative pressure Region 3 OR32 Grade III 40.42 Tumor OR35 Grade III 46.8 Ear, nose, and throat OR36 Grade III 31.28 Burn surgery OR39 Grade III 34.92 Outpatient OR43 Grade III 27.76 Outpatient Table 1. The overview of the clean operation department. Region No. of operation room Clean class Area of operation room (m2) Category of operation room Region 1 OR2 Grade III 54.1 Neurosurgery (cerebral surgery) OR4 Grade III 52.71 General thoracic OR8 Grade III 31.55 Urinary surgery OR11 Grade I 73.06 Neurosurgery (cerebral surgery) OR12 Grade I 54.53 Cardiac (in vitro) Region 2 OR14 Grade I 71.16 Hybrid (vascular surgery) OR16 Grade III 54.94 Orthopedics OR19 Grade III 52.71 General Surgery OR25 Grade III 27.18 Emergency treatment OR26 Grade III 30.74 Positive–negative pressure Region 3 OR32 Grade III 40.42 Tumor OR35 Grade III 46.8 Ear, nose, and throat OR36 Grade III 31.28 Burn surgery OR39 Grade III 34.92 Outpatient OR43 Grade III 27.76 Outpatient Region No. of operation room Clean class Area of operation room (m2) Category of operation room Region 1 OR2 Grade III 54.1 Neurosurgery (cerebral surgery) OR4 Grade III 52.71 General thoracic OR8 Grade III 31.55 Urinary surgery OR11 Grade I 73.06 Neurosurgery (cerebral surgery) OR12 Grade I 54.53 Cardiac (in vitro) Region 2 OR14 Grade I 71.16 Hybrid (vascular surgery) OR16 Grade III 54.94 Orthopedics OR19 Grade III 52.71 General Surgery OR25 Grade III 27.18 Emergency treatment OR26 Grade III 30.74 Positive–negative pressure Region 3 OR32 Grade III 40.42 Tumor OR35 Grade III 46.8 Ear, nose, and throat OR36 Grade III 31.28 Burn surgery OR39 Grade III 34.92 Outpatient OR43 Grade III 27.76 Outpatient Figure 1. View largeDownload slide Plan graph of the clean surgical department. Figure 1. View largeDownload slide Plan graph of the clean surgical department. 3 COMMON ENERGY SAVING MEASURES 3.1 Layout optimization of the surgical department Apart from operating rooms, there are subsidiary rooms in the surgical department. Clean auxiliary rooms should be set in the clean area, connected with the clean operating room. Non-clean auxiliary rooms should be set in the non-clean area, while the waiting area and washroom should be set in the comfortable air-conditioned area. Connecting the auxiliary room with the operating room can reduce the waste of time, speed up the surgical procedure and improve the operation efficiency. Through setting the clean auxiliary rooms, non-cleaning auxiliary rooms and other functional rooms in different regions, different design on air supply for the clean air-conditioning can be realized according to the cleanliness of different regions. The energy consumption of decontamination air conditioners is reduced by installing comfortable air conditioners in the air conditioning areas. The layout optimization of the surgical department will not only make the surgical flow more smoothly, but also save air conditioning energy consumption [9]. 3.2 Air conditioning division The air conditioner of the I level operating room applies one-driven-one mode while that of the III level operating room applies one-driven-two or one-driven-three mode; both of them apply the secondary air return system. Each operating room discharges air independently with fresh air delivered. As the area outside the building needs to be chilled in the summer and heated in the winter while the area inside the building needs year-round cooling, the air-conditioning system is divided into the interior and exterior partitions reasonably to avoid the situation that the cooling and heating offset each other [10]. 3.3 Frequency conversion technology The purification air conditioning operating mode is set to working mode and non-working mode while the working mode is divided into two modes: the one on winter and summer and the one on transition seasons. The frequency conversion technology is used in fresh air units and purification cycle units for performing variable frequency regulation on fresh air volume under different working modes [11]. In non-working mode, the air-conditioner operates according to the minimum air volume required, which ensures the cleanliness of the operating room and saves energy. In winter and summer mode, it operates at the fresh air volume required for normal operation. In transition season mode, it operates at the maximum required air volume, which effectively reduces energy consumption and optimizes operation. 3.4 Secondary return air system Purifying air conditioning is different from comfort air conditioning, its air output is large and supply air temperature difference and heat load are small in the process of heat and humidity treatment. Though primary return air system is commonly applied nowadays with its advantages of simple structure and operation, its energy consumption is large due to the hot and cold offset phenomenon between its cooling and heating coils. In contrast, secondary return air system does not have this problem. Instead, by utilizing the return air temperature, the system can greatly reduce equipment operating costs, save energy and promote sustainable energy development [12]. 4 AIR CONDITIONING ENERGY-SAVING DESIGN 4.1 Purification air conditioning system analysis Purification air conditioning system consists of air filters, circulating fans, surface coolers and heating and humidification devices. Air filter has three stalls, namely, rough efficiency, efficiency, high efficiency, which have different degrees of air treatment. Air blowing function is realized through the circulation fan, which forms wind by air motion. Air temperature and humidity control is completed by the surface cooler and heating and humidification device. Different from the industrial clean room, the purification air conditioning system in the clean operating room often uses multi-machine centralized air-conditioning system, installs all units in the air-conditioned room, with the fresh air delivered through the air supply duct at the top of the operating room after filtered by the filter. 4.2 Cold heat source setting and fresh air supply way The cold and heat source setting of the clean operation department is determined based on the cold and heat source setting of the whole medical building. The central cooling (heating) mode and the independent decentralized cooling (heating) source configuration mode are applied. When the central source of cooling (heating) cannot fully meet the requirements of the air-conditioning system of the clean surgery department, the independent decentralized cooling (heating) source can meet the requirements of the operation department, making the clean air conditioner flexible and economical, and can satisfy the emergency use requirements of the operation department. However, its cooling adjustment range is limited, with poor temperature and humidity control performance, and it is difficult to maintain the stability of temperature and humidity. Hence, the local centralized cooling (heating) and independent decentralized cooling (heating) source configuration mode can be used. This configuration can meet the requirements of surgeries with high temperature and humidity stability requirements, with good energy-saving performance [13]. Fresh air treatment is divided into fresh air dispersion treatment and fresh air concentration treatment. Fresh air dispersion treatment refers to the treatment of fresh air after fresh air is mixed with the return air while fresh air concentration treatment refers to the treatment of fresh air before fresh air is mixed with the return air. In this design, fresh air concentration treatment is preferred since it can ensure the simple maintenance of the air conditioning system, save management costs and avoid the change of microbiological equilibrium when return air meets the unprocessed fresh air. 4.3 Various types of clean room parameter indexes Before the design of air conditioning system of clean operation department [14], we need to understand the requirements of air conditioning system design. Although the accuracy requirement of the clean operating room for indoor temperature and humidity is not high, it is necessary to ensure that the bacterial concentration is controlled within a certain range under such conditions of temperature and humidity [15]. Besides, different levels of clean operating room have different requirements on the times of ventilation. There are two levels of clean surgical room in the clean operation department of the First Affiliated Hospital of Wenzhou Medical College, i.e. I level and III level. As shown in Table 2, the I level surgical room requires 0.2 bacteria in the surgical area/30 min · φ90 vessel (5 bacteria/m3) and 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria/m3), while the III level surgical room requires 2 bacteria in the surgical area/30 min · φ90 vessel (75 bacteria/m3) and 4 bacteria in the surrounding area/30 min · φ90 vessel (150 bacteria/m3). Table 2. Clean room level parameters in the clean surgical department. Level of the operating room The maximum average concentration of bacteria of sedimentation (phytoplankton) in the operation area Air cleanliness class Ventilation times (times/h) Working surface height interface average wind speed (m/s) Temperature (°C) Relative humidity (% RH) I level Clean operating room 0.2 bacteria in the surgical area/30 min · φ90 vessel (5 bacteria/m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria /m3) Surgical area: 100 level Surrounding area: 1000 level / 0.25–0.30 22–25 40–60 Clean auxiliary room 0.2 bacteria in the local area/30 min · φ90 vessel (5 bacteria /m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria/m3) 1000 level (local 100 level) / / / / III level Clean operating room 2 bacteria in the surgical area/30 min · φ90 vessel (75 bacteria/m3) 4 bacteria in the surrounding area/30 min · φ90 vessel (150 bacteria/m3) Surgical area: 10 000 level Surrounding area: 100 000 level 20–24 / 22–25 35–60 Clean auxiliary room 4 bacteria/30 min · φ90 vessel (150 bacteria/m3) 100 000 level / / / / Level of the operating room The maximum average concentration of bacteria of sedimentation (phytoplankton) in the operation area Air cleanliness class Ventilation times (times/h) Working surface height interface average wind speed (m/s) Temperature (°C) Relative humidity (% RH) I level Clean operating room 0.2 bacteria in the surgical area/30 min · φ90 vessel (5 bacteria/m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria /m3) Surgical area: 100 level Surrounding area: 1000 level / 0.25–0.30 22–25 40–60 Clean auxiliary room 0.2 bacteria in the local area/30 min · φ90 vessel (5 bacteria /m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria/m3) 1000 level (local 100 level) / / / / III level Clean operating room 2 bacteria in the surgical area/30 min · φ90 vessel (75 bacteria/m3) 4 bacteria in the surrounding area/30 min · φ90 vessel (150 bacteria/m3) Surgical area: 10 000 level Surrounding area: 100 000 level 20–24 / 22–25 35–60 Clean auxiliary room 4 bacteria/30 min · φ90 vessel (150 bacteria/m3) 100 000 level / / / / Table 2. Clean room level parameters in the clean surgical department. Level of the operating room The maximum average concentration of bacteria of sedimentation (phytoplankton) in the operation area Air cleanliness class Ventilation times (times/h) Working surface height interface average wind speed (m/s) Temperature (°C) Relative humidity (% RH) I level Clean operating room 0.2 bacteria in the surgical area/30 min · φ90 vessel (5 bacteria/m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria /m3) Surgical area: 100 level Surrounding area: 1000 level / 0.25–0.30 22–25 40–60 Clean auxiliary room 0.2 bacteria in the local area/30 min · φ90 vessel (5 bacteria /m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria/m3) 1000 level (local 100 level) / / / / III level Clean operating room 2 bacteria in the surgical area/30 min · φ90 vessel (75 bacteria/m3) 4 bacteria in the surrounding area/30 min · φ90 vessel (150 bacteria/m3) Surgical area: 10 000 level Surrounding area: 100 000 level 20–24 / 22–25 35–60 Clean auxiliary room 4 bacteria/30 min · φ90 vessel (150 bacteria/m3) 100 000 level / / / / Level of the operating room The maximum average concentration of bacteria of sedimentation (phytoplankton) in the operation area Air cleanliness class Ventilation times (times/h) Working surface height interface average wind speed (m/s) Temperature (°C) Relative humidity (% RH) I level Clean operating room 0.2 bacteria in the surgical area/30 min · φ90 vessel (5 bacteria/m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria /m3) Surgical area: 100 level Surrounding area: 1000 level / 0.25–0.30 22–25 40–60 Clean auxiliary room 0.2 bacteria in the local area/30 min · φ90 vessel (5 bacteria /m3) 0.4 bacteria in the surrounding area/30 min · φ90 vessel (10 bacteria/m3) 1000 level (local 100 level) / / / / III level Clean operating room 2 bacteria in the surgical area/30 min · φ90 vessel (75 bacteria/m3) 4 bacteria in the surrounding area/30 min · φ90 vessel (150 bacteria/m3) Surgical area: 10 000 level Surrounding area: 100 000 level 20–24 / 22–25 35–60 Clean auxiliary room 4 bacteria/30 min · φ90 vessel (150 bacteria/m3) 100 000 level / / / / In addition, the I level surgical room requires the working face height interface average wind speed to be 0.25–0.30 m/s, the temperature to be between 22°C and 25°C, and the relative humidity to be between 40% and 60% RH, while the III level surgical room requires the times of ventilation to be 20–24 times/h, temperature between 22°C and 25°C, and relative humidity between 35% and 60% RH. 4.4 Determination of design parameters Cooling load refers to the heat, including both sensible heat and latent heat, taken away from the room by the air conditioning system in order to keep the indoor hot and humid environment and temperature at a specified level. As the clean surgical department does not have doors or windows that have direct contact with the outside world, the solar radiation heat and heat brought through air infiltration can be ignored. Human body heat dissipation, lighting heat dissipation and equipment heat dissipation are considered, that is, human body cooling load, lighting cooling load and equipment cooling load. In the actual calculation, the cluster coefficient which is calculated according to the age, gender, and intensity of members based on the heat and wet dissipation capacity of an adult man needed to be taken into consideration. The heat and wet dissipation capacity of an adult woman is 85% that of an adult men, while that of a child is 75% that of an adult man; therefore cluster coefficient = (number of adult men + number of adult women ∗ 85% + number of children ∗ 75%)/total number of people. Total body cooling load in the operating room was: Cr=crnn', where Cr refers to body heat dissipation cooling load (W), Cr refers to body total heat load (W), n refers to the total number of people, and n' refers to the cluster coefficient. The total body wet load in the operating room was: Hs=hsnn', where Hs refers to body wet dissipation humid load (kg/h), hs refers to body wet dissipation amount (g/h), n refers to the total number of people, and n' refers to the cluster coefficient. According to the parameters in Table 2, the room temperature was set at a constant temperature of 24°C, and the relative humidity was set as 50%. There were 12 people in III level surgical room and 10 people in III level surgical room. Two people were of extreme light physical labor and others were of light physical labor, the results are shown in Table 3. Table 3. Human body load calculation results. Level of the operating room Extreme light physical labor Light physical labor Humidity load (g/h) Cooling load (W) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) I level 2 70 64 96 10 70 112 167 1862 2088 III level 2 70 64 96 8 70 112 167 1528 1724 Level of the operating room Extreme light physical labor Light physical labor Humidity load (g/h) Cooling load (W) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) I level 2 70 64 96 10 70 112 167 1862 2088 III level 2 70 64 96 8 70 112 167 1528 1724 Table 3. Human body load calculation results. Level of the operating room Extreme light physical labor Light physical labor Humidity load (g/h) Cooling load (W) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) I level 2 70 64 96 10 70 112 167 1862 2088 III level 2 70 64 96 8 70 112 167 1528 1724 Level of the operating room Extreme light physical labor Light physical labor Humidity load (g/h) Cooling load (W) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) Number of people Individual sensible heat (W) Individual latent heat (W) Individual moisture gain (g/h) I level 2 70 64 96 10 70 112 167 1862 2088 III level 2 70 64 96 8 70 112 167 1528 1724 Lighting cooling load was: Cz=czCClz, where Cz refers to lighting heat dissipation cooling load (W), Cz refers to lighting heat dissipation amount (W), and CClZ refers to cooling load coefficient of lighting heat dissipation. The cooling load of the equipment is: Ce=ceCCle, where Ce refers to cooling load of equipment heat dissipation (W), Ce refers to the heat dissipation amount of equipment (W), and CCle refers to the cooling load coefficient of equipment heat dissipation. Based on the power of common equipment and lamps in the operating room, the cooling load of the equipment was 3320 W and the cooling load of the lighting was 420 W. Table 4 shows the total indoor load of the clean operating room under steady-state conditions. Table 4. Heat and wet load in the clean operating room. Level of the operating room Indoor design temperature (°C) Body cooling load (w) Body humidity load (kg/h) Equipment cooling load (w) Lighting cooling load (w) Total cooling load (w) Heat and moisture ratio (kJ/kg) I level (45 m2) 24 2088 1.862 3320 420 5828 11 268 III level (35 m2) 24 1724 1.528 3320 420 5464 12 873 Level of the operating room Indoor design temperature (°C) Body cooling load (w) Body humidity load (kg/h) Equipment cooling load (w) Lighting cooling load (w) Total cooling load (w) Heat and moisture ratio (kJ/kg) I level (45 m2) 24 2088 1.862 3320 420 5828 11 268 III level (35 m2) 24 1724 1.528 3320 420 5464 12 873 Table 4. Heat and wet load in the clean operating room. Level of the operating room Indoor design temperature (°C) Body cooling load (w) Body humidity load (kg/h) Equipment cooling load (w) Lighting cooling load (w) Total cooling load (w) Heat and moisture ratio (kJ/kg) I level (45 m2) 24 2088 1.862 3320 420 5828 11 268 III level (35 m2) 24 1724 1.528 3320 420 5464 12 873 Level of the operating room Indoor design temperature (°C) Body cooling load (w) Body humidity load (kg/h) Equipment cooling load (w) Lighting cooling load (w) Total cooling load (w) Heat and moisture ratio (kJ/kg) I level (45 m2) 24 2088 1.862 3320 420 5828 11 268 III level (35 m2) 24 1724 1.528 3320 420 5464 12 873 4.5 Analysis on the primary and secondary return air system As mentioned before, the primary return air system had severe hot and cold offset phenomenon and large energy consumption while the secondary return air system could greatly reduce equipment operating costs and save energy consumption. In this section, the cooling load and energy consumption of the two systems were analyzed. In summer, outdoor design parameters are as follows: 35°C of dry bulb temperature, 28°C of wet bulb temperature; indoor design parameters were as follows: 24°C of room temperature and 50% of relative humidity. Based on the cross section wind speed and ventilation time requirements of the operating room in Table 2, the amount of air supply of the air-conditioning system was determined. The local air – ventilation system was used. In the I level surgical room, the fresh air volume was 1000 m3/h, the return air volume was 9000 m3/h, the exhaust air volume was 555 m3/h, and the amount of air supply was 10 000 m3/h; in the III level surgical room, the fresh air volume was 800 m3/h, the return air volume was 1100 m3/h, the exhaust air volume was 560 m3/h, and the air supply volume was 1900 m3/h. Hence, it was calculated out that the air enthalpy difference and the machine dew point enthalpy was 0.912 kJ/kg and 2.374 kJ/kg, 35.11 kJ/kg and 35.06 kJ/kg, respectively in the I level surgical room and the III level surgical room. As the primary return air system had a reheat process, its cooling load was composed of the indoor load, fresh air load, reheat load and fan temperature rise load while the secondary return air system had no reheat load, as shown in Table 5. Table 5. Cooling load of the primary return airy system. Level of the operating room Fresh air volume (m3/h) Heat humidity ratio (kJ/kg) Indoor load (kW) Fresh air load (kW) Reheat load (kW) Fan temperature rise load Cooling load (kW) Fresh air (kW) Air supply (kW) Primary return air system I level 1000 11 268 5.828 15.96 36.06 0.53 5.78 64.158 III level 800 12 873 5.464 12.44 11.12 0.41 1.94 31.374 Secondary return air system I level 1000 11 268 5.828 11.86 / 0.53 5.78 23.998 III level 800 12 873 5.464 11.42 / 0.41 1.94 19.234 Level of the operating room Fresh air volume (m3/h) Heat humidity ratio (kJ/kg) Indoor load (kW) Fresh air load (kW) Reheat load (kW) Fan temperature rise load Cooling load (kW) Fresh air (kW) Air supply (kW) Primary return air system I level 1000 11 268 5.828 15.96 36.06 0.53 5.78 64.158 III level 800 12 873 5.464 12.44 11.12 0.41 1.94 31.374 Secondary return air system I level 1000 11 268 5.828 11.86 / 0.53 5.78 23.998 III level 800 12 873 5.464 11.42 / 0.41 1.94 19.234 Table 5. Cooling load of the primary return airy system. Level of the operating room Fresh air volume (m3/h) Heat humidity ratio (kJ/kg) Indoor load (kW) Fresh air load (kW) Reheat load (kW) Fan temperature rise load Cooling load (kW) Fresh air (kW) Air supply (kW) Primary return air system I level 1000 11 268 5.828 15.96 36.06 0.53 5.78 64.158 III level 800 12 873 5.464 12.44 11.12 0.41 1.94 31.374 Secondary return air system I level 1000 11 268 5.828 11.86 / 0.53 5.78 23.998 III level 800 12 873 5.464 11.42 / 0.41 1.94 19.234 Level of the operating room Fresh air volume (m3/h) Heat humidity ratio (kJ/kg) Indoor load (kW) Fresh air load (kW) Reheat load (kW) Fan temperature rise load Cooling load (kW) Fresh air (kW) Air supply (kW) Primary return air system I level 1000 11 268 5.828 15.96 36.06 0.53 5.78 64.158 III level 800 12 873 5.464 12.44 11.12 0.41 1.94 31.374 Secondary return air system I level 1000 11 268 5.828 11.86 / 0.53 5.78 23.998 III level 800 12 873 5.464 11.42 / 0.41 1.94 19.234 Figure 2 is obtained after calculating the proportion of each load in the total cooling. Figure 2. View largeDownload slide Cooling load in the clean operating room. Figure 2. View largeDownload slide Cooling load in the clean operating room. As shown in Table 5, the cooling load of primary return air system in operation room I was 64.158 kW, that of secondary return air system was 23.998 kW, saving 167.35%. The cooling load of primary return air system in III level operating room was 31.374 kW, that of the secondary air return system was 19.234 kW, saving 63.12%. As shown in Figure 2, on the cooling load of the primary return air system, whether it was level I operating room or level III operating room, the proportion of reheat load was the largest. The reheat load accounted for 56.20% of the total cooling load in level I operating room and 35.44% in level III operating room. Without reheat load, the secondary return air system saved most of the energy consumption. 5 CONCLUSIONS In addition to ensure that the indoor temperature and humidity and differential pressure are within the standard range, the clean air conditioner in the clean surgery department also needs to ensure that the indoor air concentration of bacteria and dust particles are within the standard range in order to reduce the risk of wound infection in patients and ensure the health of health care workers. Therefore, the operating effect of clean air conditioning is extremely important. While ensuring the effectiveness of clean air conditioning, we should also consider the energy-saving aspect. In this paper, energy-saving methods were explored and designed to determine the relevant parameters of the purification air-conditioning system and the configuration of cold and heat sources and fresh air supply ways. Besides, the energy consumption of primary and secondary return air system was compared and the results showed that the cooling capacity of the secondary return air system reduced most of the energy consumption compared to the primary return air system, the I level surgical room saved energy by 167.35% and the III level surgical room saved energy by 560.20%. Therefore, secondary return air was more energy efficient than primary return air. The energy-saving design of the clean air-conditioning system is of great significance to sustainable development and deserves further discussion. REFERENCES 1 Wahr JA , Abernathy JH . Environmental hygiene in the operating room: cleanliness, godliness, and reality . Int Anesthesiol Clin 2013 ; 51 : 93 – 104 . Google Scholar CrossRef Search ADS PubMed 2 Lecordier J , Plivard C , Gardeux M , et al. . To create a cleanroom controlled environment using a mobile air decontamination unit for the preparation of antineoplastic drugs . 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Google Scholar CrossRef Search ADS 12 Omer AM . Energy and environment: applications and sustainable development . Br J Environ Clim Change 2011 ; 1 : 118 – 58 . Google Scholar CrossRef Search ADS 13 Zhang G , Xiong J , Gao H , et al. . Hospital operating room clean air-conditioning system: design and application . J Environ Health 2010 ; 27 : 814 – 7 . 14 Wang Q , Meng QL . A new energy-saving air handling unit for clean operating room. International conference on digital manufacturing and automation . IEEE 2011 ; 1 : 58 – 62 . 15 Fen X , Xu ZL . Necessity of particulate pollutant control in clean operating environment: Part 2 of the series of research practice of the revision task group of the Architectural technical code for hospital clean operating department . Heat Ventilating Airconditioning 2013 ; 43 : 1 – 5 . © The Author(s) 2018. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

Journal

International Journal of Low-Carbon TechnologiesOxford University Press

Published: Apr 12, 2018

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