A field study on indoor environment quality of Chinese inpatient buildings in a hot and humid region.

In this research, objective physical measurements and subjective questionnaire surveys are used to investigate the indoor environment quality of Chinese inpatient buildings. The relative humidity in the inpatient buildings reaches 65%-75% during summer, resulting in the regular appearance of microbial growth on indoor surfaces. The average outdoor air change rate measured through the CO2 concentration decay method in the sampled inpatient rooms is 1.1 h-1, which is 45% below the standard threshold. The CO2 concentration in over 99% of the functional spaces is below the threshold of 1000 ppm. However, the dissatisfaction rate of the air freshness is higher than 25%, owing to the characteristics of healthcare activities. Insufficient fresh air volume and high supply air humidity ratio of the outdoor air system result in the inadequate dehumidification capacity and the over-humid environment in the inpatient buildings. From the perspective of indoor TVOC and PM2.5 concentration, a hospitable IAQ is achieved in the inpatient buildings. In the nurse unit, the illumination levels in public areas, such as patient corridors and nurse stations, are inadequate. The average noise levels (A) in the inpatient rooms and nurse stations are 50.7 and 61.6 dB, respectively, which exceeds the Chinese standard. According to the subjective survey, the dissatisfaction rates of overall IEQ in the summer for patients and visitors are 7.9% and 10.4%, respectively, while for staff it is 34.8%. Statistical analysis reveals that the satisfaction levels of the patient with the IEQ are higher than that of the visitor and staff.

Introduction

The number of hospitals in China was 31,056 in late 2017, including 1751 large hospitals with over 800 sickbeds. The rate of aging of China's population reached 17.3% in late 2017 and this accelerate aging of the population has created the demand for more healthcare facilities. A hospital includes an outpatient department, a medical service block, and inpatient buildings. The area of inpatient buildings usually occupies 35% of the gross floor area of the hospital. In nursing practice, indoor environment quality (IEQ) has a significant impact on the working efficiency of the hospital staff and both the physical and psychological health of the patients [1]. Poor IEQ would reduce the comfort level of the occupants and increase the risk of sick building syndrome occurrence. Furthermore, the demands of different categories of occupants in the inpatient building are highly variable. De Giuli et al. [2] conducted a Post-Occupancy Evaluation in an Italian hospital and indicated that the staff mostly complained about the lack of privacy, room size, and amount of common areas, whereas patients were more satisfied with both the building-related aspects and the indoor conditions and expressed a higher satisfaction level. It is evident that most studies on building IEQ have considered thermal comfort, indoor air quality (IAQ), lighting, and acoustics as the main parameters to determine the indoor comfort level [[3], [4], [5], [6], [7]]. Numerous studies have integrated physical measurements and subjective surveys on the above four aspects of IEQ to determine the optimal design of healthcare facilities and better built environments [[8], [9], [10], [11], [12]].

With respect to indoor thermal environment, Yau and Chew [13] measured the temperature, relative humidity and air velocity of four hospitals in Malaysia and indicated that only 44% of the examined locations met the comfort criteria specified in the ASHRAE Standard 55-2004. Hwang et al. [14] conducted an extensive field study in a hospital in Taiwan to examine the comfort criteria of ASHRAE Standard 55-2004. They found more than half of all samples were above the relative humidity threshold of 60%. In addition, the results of chi-square tests revealed that physical strength had a highly significant effect on thermal sensation, but gender, age, and acclimatization had not. The frail population expected a warmer condition than the vigorous population.

IAQ in vulnerable environments, such as healthcare facilities where patients with frail strength spend almost 100% of their time, is an important issue. Patients, especially those with weak immune system, could contract life-threatening infections in hospitals as a result of poor IAQ [15,16]. Jung et al. [17] measured the concentration of nine major airborne pollutants, namely CO, CO2, O3, total volatile organic compounds (TVOC), HCHO, PM2.5, PM10, airborne bacteria, and fungus, at 96 sites from 37 hospitals in Taiwan. Their results demonstrated that the CO2 and TVOC concentration in inpatient rooms are higher than that in nurse stations, clinics and clinic waiting areas. The mean CO2 and TVOC concentration in the inpatient rooms are 1063 ppm and 1600 ppb, which are higher than Taiwan's IAQ standard acceptable levels. In five sampled Chinese inpatient buildings, the measured mean concentrations of phthalate esters in the nurse stations, the inpatient rooms and the doctor's offices are 20.66 μg/m3, 20.0 μg/m3 and 16.92 μg/m3, respectively, which are higher than that of newly furnished houses, indicating a seriously contaminated hospital indoor air [18]. An assessment of the chemical and microbiological contamination conducted in French hospitals demonstrated that the most frequently-quantified compounds (ethanol and isopropanol) originated mainly from healthcare activities and uses (hand rubbing) [19]. As multiple pollution sources exist in the inpatient buildings, such as viruses exhaled by patients, bacterial reproduction, and mold breeding, the ventilation system strongly influences the IAQ [[20], [21], [22]]. Yau et al. [23] indicated the multiple-bed hospital wards pose a risk of infection because communicable and susceptible individuals congregate together, resulting in frequent airborne nosocomial transmission. According to the computational fluid dynamics (CFD) simulation in a hospital-based setting by Jiang et al. [24], the safe ventilation rate for eliminating airborne viral infection and preventing cross-infection of severe acute respiratory syndrome (SARS) is to dilute the air emitted from a SARS patient by 10000 times with clean air. ASHRAE 170-2017 ventilation of health care facilities requires a minimum outdoor air change rate (ACR) in an inpatient room of 2 h−1 to control the indoor IEQ for comfort, asepsis, and odor [25]. However, there is little information about the on-site measured outdoor ACR distribution of functional rooms in inpatient buildings. Furthermore, only a few field studies have investigated the indoor airborne contamination control effect of the outdoor air system in inpatient buildings.

Light, especially daylight, affects the lighting performance and psychological state of a person [26]. Improper lighting is associated with visual fatigue, headaches, sleep disorders and irritability. Choi et al. [27] found there is a strong relationship between the indoor daylight environment and a patient's average length of stay in a hospital. The average length of stay of patients in the southeast area of the inpatient building (i.e., brighter orientations) was shorter than that in the northwest area by 16%–41%. In addition, adequate illumination on work surfaces lowers the rates of errors in medication-dispensing [28].

The acoustic environment is one element that has not often been considered within the hospital environment [29]. Ambient noise has strong links with patient outcomes and medication errors by staff [30]. A noisy environment can increase patient stress, thereby resulting in a longer healing process.

With respect to the overall indoor comfort, Liu and Wang [31] conducted a one-year field measurement campaign in two Chinese healthcare facilities and found that among the abovementioned four major aspects of IEQ, IAQ is the least satisfactory and the issue of over-crowdedness is the major reason for the low satisfaction level in large hospitals. However, there is a shortage of comprehensive objectively measured data on the IEQ of inpatient buildings in China.

Therefore, a comprehensive IEQ investigation of inpatient buildings and the performance of the outdoor air system is still required, especially in China, where a large amount of hospitals are being or will be constructed or retrofitted. This will help to improve the design and operation of inpatient buildings, and to improve patient and staff satisfaction levels. In this study, instrumented spot and continual measurements were performed to investigate the IEQ of inpatient buildings in China, including the thermal comfort, IAQ, lighting and acoustic environment. The performance of the outdoor air system in the inpatient buildings on the humidity and contamination control was investigated. Furthermore, the outdoor air change rates of 32 functional rooms were measured using the CO2 concentration decay curve method. The sensation and satisfaction with the IEQ were investigated through subjective questionnaire surveys and the satisfaction level of the patients is compared with that of visitors and staff.

Description of the inpatient building and air-conditioning system

Building information

A major comprehensive public hospital located in Shenzhen, China (22 °N, and 114 °E) opened on July 1, 2012, was investigated. With a hot and humid summer, the average outdoor air temperature in Shenzhen from June 1 to Oct 1 is approximately 27.9 °C and the humidity ratio is approximately 18.5–21.0 g/kg [32]. The studied general hospital has a total area of 367,000 m2 situated on 192,000 m2 of land. Fig. 1 (a) shows a schematic diagram of the general hospital consisting of three inpatient buildings shown in red with 2000 sickbeds in operation. The utilization rate of the sickbeds was approximately 82% in 2017. Fig. 1(b) shows the external view of the three inpatient buildings. The total area of the three inpatient buildings is 77,040 m2, with seven floors above the ground and one floor under the ground. The entrances and exits of the three inpatient buildings are independent, but connected by an outdoor corridor.

Fig. 1

Studied inpatient buildings in Shenzhen, China: (a) schematic diagram of the general hospital; (b) external view photograph of the inpatient buildings; (c) standard floor plan with five typical functional spaces; and (d) schematic of inpatient rooms.

Fig. 1(c) shows the standard floor plan of the inpatient building. The standard floor plan has an area of 3100 m2, consisting of 34 inpatient rooms (1275 m2), 8 offices (300 m2), 4 treatment rooms (50 m2), 2 hazardous material storage rooms (15 m2), 2 nurse stations, 2 lounges (30 m2) and 14 elevators. The inner view of the inpatient building is shown in Fig. 2 . The hospital is situated by the ocean, within 500 m of the coast. The inpatient buildings are positioned such that the seascape is visible and there is adequate sunshine, guaranteeing over 90% of the inpatient rooms face the southeast or south. The nurse stations, treatment rooms, and hazardous material storage rooms are located in the middle of the corridor (the inner zone of the inpatient building), to offer convenient service to the patients. Fig. 1(d) shows a typical schematic of the inpatient rooms. Design elements from hotels are utilized in the inpatient rooms to enhance the quality of living. All inpatient rooms have private bathrooms and balconies with views of the seascape. Currently, the balconies and the external windows are sealed to reduce infiltration of outdoor hot and humid air.

Fig. 2

Internal view of the inpatient building: (a) inpatient room; (b) nurse station; (c) office; and (d) patient corridor.

Air-conditioning system

The air-conditioning system consists of an outdoor air system and fan coil units in functional spaces of the inpatient building. Fresh air processed by the outdoor air system is supplied into the indoor environment throughout the day. Fan coil units are utilized to regulate the temperature and humidity within the functional rooms. Fig. 3 shows a schematic diagram of the air conditioning system, including the outdoor air processor (Fig. 3(a)) and the fan coil unit in an inpatient room (Fig. 3(b)). The outdoor air processor with a rated airflow rate of 6000 m3/h is utilized to dehumidify the fresh air for each standard floor plan. Outdoor air first flows through the precooling coil with a supplied water temperature of 16 °C and a return water temperature of 19 °C. Then, the fresh air flows into the heat pump and is processed to the supply air state (SA) with the required humidity ratio of 9.0 g/kg. Outdoor air is utilized to extract heat from the condenser of the heat pump, and then exhausted to the outdoor environment. Since the chilled water for the precooling coil is produced by high temperature chiller with a COP of 6.46 and the heat pump has a COP of 3.58, the series dual cooling sources with different temperature levels could improve the energy efficiency of the outdoor air system.

Fig. 3

Air-conditioning system in the patient building: (a) schematic of outdoor air processor; and (b) schematic of the fan coil unit.

In the fan coil unit, an air coil with a supplied water temperature of 16 °C and a return water temperature of 19 °C cools the blend of the fresh air from the outdoor air processor and the return air from the inpatient room. Without humidity sensors in the functional spaces, the fan coil units are controlled by the occupants who regulate the indoor air temperature. In addition, in the bathroom of the inpatient room, a fan with a rated airflow rate of 50 m3/h operates throughout the day to exhaust moist air. The exhaust fan in the bathroom is the only mechanical ventilation for the air to leave the space. Since the rated fresh airflow rate is larger than the exhaust airflow rate, the inpatient rooms are pressurized.

Methodology

Indoor environment parameter measurement

Spot measurement on the IEQ of 170 randomly sampled sites in the inpatient buildings was conducted during the daytime. The indoor environment parameters including air temperature, relative humidity, CO2, TVOC, PM 2.5 concentration, illumination level, and sound level (A) were measured on-site during July 1–30, 2018. The selected sites contain inpatient rooms, offices, treatment rooms, nurse stations, corridors, and elevator halls, which cover most of the room types and hospital departments. The measuring points were located in the center of the rooms at a height of 1.2 m. The average values of a 5-min measurement are calculated. The measurement ranges and accuracies of the apparatuses are shown in Table 1 . In particular, the light level meter was positioned horizontally on the floor in the inpatient rooms and patient corridors, and at a height of 0.75 m in the offices, treatment rooms and nurse stations. The noise level was measured by a handheld sound analyzer with an A ponderation curve. The measurement of noise level was performed at least 1 m away from any surfaces.

Table 1

Measuring parameters and instruments.

Parameter	Apparatus	Instrument model	Range	Accuracy
Air temperature	Self-recording hygro-thermometer	BY-WSZJ	0-70 °C	±0.2 °C
Relative humidity	Self-recording hygro-thermometer	BY-WSZJ	10–100%	±3% RH
Air velocity	Anemometer	WWFWZY-1	0–15 m/s	±0.3 m/s
PM2.5 concentration	PM2.5 sensor	dustrak aerosol monitor 8532	0–150 mg/m3	±0.002 mg/m3
TVOC concentration	VOC sensor	Q-Trak 7575 with probe 984	10–20000 ppb	±20 ppb
CO2 concentration	CO2 sensor	Telaire T7001	0–10000 ppm	±50 ppm
Illumination	Light level meter	TES-1339R.	0–99990 lux	±3%
Noise intensity	Sound level meter	Casella CEL-6X0	30–140.2 dB (A)	±0.5 dB (A)

Besides spot measurements, the indoor environment parameters of five functional spaces on the fifth floor, as shown in Fig. 1(c), were continuously monitored for three consecutive days (from 12 p.m., July 11–12 p.m., July 14). The indoor environment parameters included air temperature, relative humidity, and CO2 concentration. The five spaces includes the inpatient room, doctor's office, nurse station, patient corridor, and elevator hall, covering the major functional spaces of a nurse unit. The five spaces were occupied during the test. In addition, the outdoor air temperature and relative humidity were also monitored during the field study. During July 11–14, 2018, the outdoor air temperature ranged from 27 to 37 °C and the outdoor humidity ratio ranged from 19 to 22 g/kg, representing a typical summer condition in a hot and humid region.

Experimental setup for measuring outdoor air change rate

To evaluate the ventilation effect of the outdoor air system, the outdoor air change rate of 32 functional rooms in the inpatient building selected through random sampling, including 20 inpatient rooms, 3 treatment rooms, 3 lounges, 3 offices, and 3 hazardous material storage rooms, were measured via the CO2 concentration decay curve method [[33], [34], [35]]. The minimum and maximum volumes of the sampled functional rooms are 16.8 and 128 m3, respectively. Detailed information about the measured functional rooms is provided in Table 2 . Each test was conducted in a vacant room without occupants. As shown in Fig. 4 (a), CO2 was emitted at two sites by CO2 generators. During the emission of CO2, a fan operates to ensure a well-mixed environment. To reflect normal operating conditions, both the fan coil unit and the exhaust fan were in operation during the test. Meanwhile, the exterior door was closed. The CO2 sensor was located in the center of the room and at a height of 1.2 m. In addition, the outdoor air CO2 concentration was also monitored.

Table 2

Information of functional rooms for measuring outdoor ACR.

No.	Room type	Floor area (m2)	Floor No.	Outdoor ACR (h−1)	Airflow rate (m3/h)
1	Inpatient room	24.8	3	2.01	129.2
2		34.2	5	1.60	142.1
3		24.8	1	1.56	100.5
4		24.8	5	1.39	89.8
5		24.8	5	1.34	86.1
6		24.8	5	1.30	83.4
7		23.1	1	1.08	64.6
8		24.8	3	0.99	63.5
9		24.8	1	0.90	58.2
10		34.2	3	0.85	75.2
11		24.8	3	0.82	52.9
12		33.4	3	0.79	68.8
13		34.2	5	0.79	70.5
14		10.8	3	0.74	20.6
15		24.8	5	1.22	78.7
16		24.8	1	1.18	75.7
17		33.4	2	0.95	61.3
18		23.1	6	0.93	59.8
19		34.2	6	0.96	57.6
20		34.2	7	0.96	57.4
21	Treatment room	11.2	1	2.11	61.3
22		10.8	5	1.34	37.4
23		10.8	3	1.28	35.8
24	Lounge	14.5	3	2.10	79.4
25		18.2	1	1.37	64.7
26		9.7	5	1.43	36.1
27	Office	34.5	2	2.08	186.3
28		49.2	1	0.30	38.3
29		9.7	5	0.69	17.4
30	Hazardous material storage room	6.9	1	2.69	48.4
31		6.5	5	1.47	24.7
32		6.5	5	4.92	82.7

Fig. 4

Measurement of the outdoor air change rate: (a) location of CO2 generators and sensors in an inpatient room; and (b) valid CO2 concentration decay curve.

The generator slowly emitted CO2 until the indoor CO2 concentration reached approximately 2500 ppm. After the CO2 generator was turned off, the time series CO2 concentration was measured for 1 h using a Telaire T7001 with a data logger. A well-mixed single zone model is assumed in this study, which is found to be sufficiently accurate from the extensive investigation in previous studies [[36], [37], [38]]. In a well-mixed single zone, the CO2 concentration change can be expressed as follows:where C (ppm) and C (ppm) are the indoor and outdoor CO2 concentration, and ACR (h−1) is the outdoor air change rate. Fig. 4(b) shows an example of the CO2 concentration decay curve measured in a treatment room. It can be observed that the outdoor CO2 concentration slightly fluctuated around 415 ppm. Therefore, C could be simplified as the average value of the measured outdoor CO2 concentration. The outdoor ACR of the room can be calculated through non-linear fitting of the CO2 concentration decay curve. The deviation of the real outdoor CO2 concentration from the average value (approximately 10 ppm) is far less than the fluctuation of the indoor CO2 concentration (approximately 1700 ppm). Thus, the uncertainty of the outdoor ACR induced by the variant outdoor CO2 concentration can be neglected.

Subjective survey

Because the studied hospital has been operating for 8 years, the Post-Occupancy Evaluation method was used for survey. The subjective responses from the patients, visitors, and staff were compared with the physical measurements to evaluate the IEQ of the inpatient buildings.

Questionnaire surveys were carried out in the inpatient buildings in July 2018. The questionnaire aimed to investigate the sensation and satisfaction levels of the occupants in terms of the indoor environment, including the thermal comfort, IAQ, lighting and acoustics. The paper questionnaires were distributed to occupants in the inpatient buildings. The questionnaire was composed of two parts as shown in Table 3 : 1) basic information about gender, age, type of work and location; 2) satisfaction and sensation on IEQ parameters in summer. A seven-point Likert scale is utilized to quantify the occupants’ satisfaction levels with IEQ parameters, ranging from −3 (very dissatisfied) to 3 (very satisfied), with a neutral value of zero, as shown in Fig. 5 . The patients were not as cooperative to answer our survey as the staff, since they were suffering from illnesses. We collected 760 valid questionnaire feedbacks from 152 patients, 194 visitors and 414 staff. The age of the surveyed patients and visitors mainly ranged from 20 to 60 and that of the staff ranged from 20 to 40. Because the ratio of sampled patients to sampled staff is not equal to the ratio of patients to staff in the inpatient buildings, the satisfaction levels and dissatisfaction rates with the IEQ factors (the proportion of satisfaction votes below neutral) of the patients, visitors, and staff were analyzed individually and compared using the t-test. Further, the dissatisfaction rate was compared with the target of 20% used by the ASHRAE 62.1 standard.

Table 3

Summary of questionnaire.

Category	Questions
Basic information	Gender, age, type of work, location
Indoor thermal environment	Thermal and draught sensation, thermal satisfactory level
Indoor air quality	Air freshness, air cleanliness, odor, odor sources
Indoor light environment	Light satisfactory
Indoor acoustics environment	Noise sensation, noise satisfactory level, noise sources
Overall IEQ	Overall IEQ satisfactory level

Fig. 5

Scale of subjective satisfaction level.

Results and discussion

Temperature and humidity

Spot measurement results of the indoor air temperature, relative humidity, and humidity ratio of 170 functional sites in the inpatient buildings are illustrated in Fig. 6 . The air temperature of the inpatient rooms mainly ranged from 24.5 to 26 °C. The relative humidity of the major inpatient rooms ranged from 65% to 75%. The relative humidity of several inpatient rooms approached 85%. The relative humidity of the air-conditioned offices, treatment rooms, nurse stations and patient corridors ranges from 65% to 80%. In addition, the humidity ratios of the sampled functional rooms were approximately 14 g/kg. According to the ASHRAE standard 170-2017 [25], the required air temperatures in the inpatient rooms should range from 21 to 24 °C and the required relative humidity should not exceed 60%. Besides, architectural and design code for general hospital (GB 51039-2014 [39]) requires that the air temperature in the general inpatient rooms and offices should not exceed 27 °C. The Chinese standard GB 51039-2014 for air temperature is less stringent than the ASHRAE 170-2017 standard. Table 4 presents the standard compliance rate, meaning the proportion of measured results that comply with the current standards. The rate of air temperature compliance with ASHRAE 170-2017 is indicated outside the bracket and that with GB51039-2014 is indicted inside the bracket. In terms of air temperature, 90.6% of the inpatient rooms comply with the Chinese standard, while only 10.2% of the inpatient rooms comply with ASHRAE 170-2017. In terms of moisture control, only 3.9% of the inpatient rooms comply with the relative humidity requirement of ASHARE 170-2017. The relative humidity in the inpatient building including offices, nurse stations and patient corridors, exceeds 60%.

Fig. 6

Measured indoor temperature and humidity at 170 sites in the patient buildings: (a) air temperature; (b) relative humidity; and (c) humidity ratio.

Table 4

Standard compliance rates of IEQ parameters.

Compliance rate (%)	Inpatient room	Office	Treatment room	Nurse station	Corridor
Air temperaturea	10.2 (90.6)	(100)	0 (94.1)	(100)	(88.9)
Relative humidity	3.9	0	11.8	5.9	3.7
Outdoor ACR	5	–	–	–	–
CO2	99.1	100	100	100	100
TVOC	81.5	100	100	81.3	80.1
PM2.5	100	100	100	100	99.1
Illumination	71.4	64.3	100	0	22.2
Noise (A)	0	31.3	–	–	–

The rate of air temperature compliance with ASHRAE 170-2017 is indicated outside the bracket and that with GB51039-2014 is indicted inside the bracket.

Fig. 7 (a) and (b) plot the variation in the indoor air temperature and humidity ratio, respectively, in five functional spaces on the fifth floor in an inpatient building. The air temperatures of the air-conditioned spaces ranged from 22 to 24 °C. However, the humidity ratios of these spaces frequently exceeded 12.5 g/kg. In addition, the humidity ratio in the inpatient rooms was generally higher than that in the patient corridor. This indicates that the air infiltration from the corridor into the inpatient rooms is not the source of indoor moisture. Because of the high relative humidity, the phenomenon of wall mildew in inpatient rooms and patient corridors occurs during summer.

Fig. 7

Long-term monitoring of indoor thermal environment in five functional spaces in the patient building: (a) air temperature and (b) humidity ratio.

According to the subjective responses, thermal sensation of the occupants in the inpatient buildings ranged between slightly cool and neutral, as shown in Fig. 8 (a). Fig. 8(b) shows that the satisfaction votes on the indoor thermal comfort and draught mainly ranged between neutral and slightly satisfied. As shown in Table 5 , the dissatisfaction rate of the patients for thermal comfort was 10.5%, which was lower than that of the visitors and staff. The dissatisfaction rate of the patients for draught was 13.2%, which was also lower than that of the visitors and staff. A typical target, as used by ASHRAE Standard 62.1, is a dissatisfaction rate lower than 20%. As shown in Table 5, the dissatisfaction rate for indoor thermal environment (including temperature, humidity, and draught) is usually within the target. Furthermore, statistical analysis showed that the satisfaction level of patients in terms of thermal comfort was higher than that of the visitors, with a p-value of 0.0014, and it was also higher than that of the staff with a p-value of 0.014, which was also found in previous studies [2].

Fig. 8

Subjective responses on indoor thermal environment: (a) thermal sensation; (b) satisfaction level of thermal comfort and draught.

Table 5

Dissatisfaction rate of IEQ factors.

Dissatisfaction rate (%)	Patient	Visitor	Staff
Thermal comfort	10.5	27.1	18.2
Draught	13.2	16.7	16.7
Air freshness	26.3	37.5	34.8
Air cleanliness	13.2	19.9	19.7
Light environment	10.5	16.7	16.7
Acoustic environment	21.1	31.3	22.7
Overall IEQ	7.9	10.4	34.8

Ventilation

The performance of the outdoor air processor serving the inpatient building was examined. The measured air volume of the outdoor air processor was 5050 m3/h via velocity measurement. The outdoor air processor consists of series dual cooling sources: a precooling module and a heat pump. The chilled water of the precooling module is provided by high temperature chillers with a measured COP of 6.46. The installed heat pump in the outdoor air processor plays the role of the low temperature cooling source for dehumidification. The heat pump operates with evaporating temperature of 10.5 °C, condensing temperature of 54.2 °C, and measured COP of 3.58.

Fig. 9 presents the measured hourly performance (including air temperature and humidity ratio) of the outdoor air processor. As indicated in Fig. 9(a), the outdoor air temperature was approximately 28–35 °C and the supply air temperature stabilized at approximately 18.0 °C. The inlet water temperature for the precooling module is around 14.9 °C, with a supply and return water temperature difference of 3.8 °C. Fig. 9(b) shows the outdoor air humidity ratio was around 20.0 g/kg, while the supply air humidity ratio was 11.3 g/kg. In typical summer conditions, the dehumidification capacity of the outdoor air processor accounts for 40% of the total indoor moisture load. The fan coil unit in the inpatient room handles 60% of the total indoor moisture load.

Fig. 9

Operating parameters of the outdoor air processor: (a) temperature; and (b) humidity ratio.

Furthermore, the fresh air volumes of the functional rooms in the inpatient building were measured through the CO2 concentration decay curve method. Fig. 10 plots the outdoor ACR of the functional rooms. ASHARE 170-2017 [25] requires that the outdoor ACR for inpatient rooms and hazardous material storage rooms exceed 2.0 h−1. The average outdoor ACR of 20 randomly sampled inpatient rooms was 1.1 h−1, which is 45% lower than the standard requirement. The average outdoor ACRs of the treatment rooms and the hazardous material storage rooms were 1.6 h−1 and 3.0 h−1, respectively. The compliance rates of the inpatient rooms and hazardous material storage rooms for outdoor ACR were 5% and 67%, respectively.

Fig. 10

Outdoor air change rates of 32 functional rooms measured through valid CO2 concentration decay curve method.

Currently, the relative humidity in the inpatient buildings generally reaches 65%–75%. As a result, the problem of wall mildew frequently occurs in the inpatient rooms and patient corridors during summer. To prevent the breeding of mold, the hospital managers remove mold and repaint the walls periodically. However, the limited ventilation time of the freshly painted rooms due to the large demand for hospitalization of patients would result in additional indoor air pollution (VOCs and formaldehyde). Therefore, humidity control in healthcare facilities plays an important role in thermal comfort and influences the IAQ.

The low fresh air volume of the outdoor air processor in the design stage results in the insufficient outdoor ACR in the functional rooms of the studied inpatient buildings. The average measured outdoor airflow rate of the inpatient rooms was 74.8 m3/h. The average measured airflow rate of the exhaust fan in the bathroom of the inpatient room was 45.1 m3/h. Because the outdoor airflow rate is larger than the exhaust airflow rate, the inpatient rooms are pressurized. The micro-positive pressure of the inpatient rooms to the outdoor environment suppresses the infiltration of the hot and humid outdoor air. The main moisture source of the inpatient rooms is the occupants and the intermittent shower usage in the bathroom. Owing to the high evaporative temperature of the heat pump, the measured supply air humidity of the outdoor air processor was higher than the design value of 9.0 g/kg. As a result, insufficient fresh air volume and high supply air humidity ratio both lead to the inadequate dehumidification capacity of the outdoor air processor, which further results in an over-humid environment in the inpatient buildings. To solve this problem, the outdoor air processors need to be updated in time to ensure adequate fresh air volume and meet the minimum outdoor ACR requirement and the setting of the heat pumps should be adjusted to supply the fresh air with a humidity ratio of 9.0 g/kg. Therefore, the outdoor air system plays the role of providing ventilation and humidity control separate from temperature control, and the fan coil system plays the role of temperature control in functional rooms.

Indoor air quality

CO2 concentration is widely utilized as a surrogate variable to indicate the air freshness. Fig. 11 (a) plots the CO2 concentration distribution in 170 sampled functional sites of the inpatient buildings. The outdoor CO2 concentration was approximately 410–430 ppm during the field study. It could be observed that the CO2 concentration in 99.1% of the inpatient rooms and in 100% of the functional rooms (including offices, treatment rooms, nurse stations and patient corridors) was below the threshold of 1000 ppm required by Chinese evaluation standard for green hospital buildings (GT/T 51153-2015 [40]), as shown in Table 4. In Fig. 11(b), the CO2 concentration in the inpatient rooms is plotted as a function of the number of occupants in the space. The CO2 concentration increased slightly with the number of occupants. Further, 72% of the sampled inpatient rooms were occupied with over three people, and 98.4% of the sampled inpatient rooms were occupied with more than one person. The average number of occupants in an inpatient room, office and treatment room were 3.9, 2.0, and 1.5, respectively. The average personnel density of the inpatient room, office, and treatment room were 0.105, 0.054, and 0.122 per/m2, respectively. The CO2 concentration was significantly different among all working areas owing to the various occupant densities. Fisher's test results showed higher CO2 levels in inpatient rooms than that in other working areas (p < 0.001), which was also found in the field study conducted in hospitals in Taiwan [17]. Fig. 12 shows the variation in the indoor CO2 concentration in five functional spaces during three days. The CO2 concentration was mostly below 1000 ppm.

Fig. 11

(a) Measured CO2 concentration at 170 sites in the inpatient buildings and (b) CO2 concentration plotted as a function of number of occupants in inpatient rooms.

Fig. 12

Long-term monitoring of indoor CO2 concentration at five functional spaces in the patient building.

Because of the proximity to the sea, the outdoor TVOC and PM2.5 concentration were approximately 110 ppb and 60 μg/m3 during the test, indicating good outdoor air quality. Fig. 13 (a) shows the measured TVOC concentration distribution in different functional spaces. TVOC concentration in inpatient rooms mainly ranged from 100 to 180 ppb. According to TVOC concentration requirement of GB 51039-2014 [39], the compliance rates of the inpatient rooms and the patient corridors were 81.5% and 80.1%, respectively (see Table 4). The TVOC concentration in the offices and treatment rooms complied with the standard. As shown in Fig. 13(b), the measured PM2.5 concentration in the 170 functional sites mainly ranged from 5 to 15 μg/m3. PM2.5 concentration in 93% of the functional spaces is lower than 20 μg/m3. PM2.5 concentration in all of the inpatient rooms, treatment rooms, nurse stations and doctor's offices are lower than the 35 μg/m3 limit established by environmental control organizations [41] (see Table 4). Owing to the excellent outdoor air quality of Shenzhen, the indoor environment in the inpatient buildings was free of particulate pollution.

Fig. 13

Measured contaminant concentration at 170 sites in the patient buildings: (a) TVOC concentration; and (b) PM2.5 concentration.

The CO2 concentration in the inpatient rooms was below the threshold of 1000 ppm, while the survey feedback of IAQ indicated that 35% of the occupants still felt “stuffy”. Fig. 14 (a) shows that the odor sensation ranges between no odor and slight odor. According to the subjective responses, the odor sources in the inpatient rooms were disinfectant (40%), food (21%) and drugs (11%) which are all from indoor healthcare activities and daily life activities rather than outdoor sources. The outdoor air system maintained a low indoor CO2 concentration in the inpatient rooms with an average outdoor ACR of 1.1 h−1; however, the odor is still not improved effectively. As shown in Fig. 14(b), the satisfaction votes of patients on the air freshness ranged between slightly dissatisfied and slightly satisfied. The dissatisfaction rates of patients, visitors, and staff for air freshness all exceeded 25%. Therefore, owing to the characteristics of the healthcare activities, the minimum outdoor ACR of 2 h−1 in the inpatient room is essential in order to realize the freshness of indoor air rather than the CO2 concentration threshold of 1000 ppm. The satisfaction level of the air cleanliness was mainly high and the dissatisfaction rate was below 20%, indicating a sensation of good air cleanliness. Furthermore, the satisfaction level of patients in terms of air freshness was higher than the visitors with p < 0.001, and that in terms of air cleanliness of patients was also higher than the visitors, with p < 0.001. The subjective responses reveal that the patients were not sensitive to the IAQ, when compared with visitors.

Fig. 14

Subjective responses on IAQ: (a) odor sensation; and (b) satisfaction level of air freshness and air cleanliness.

Light environment

The Chinese standard (GB/T 51153-2015 [40]) requires that the minimum illumination level in inpatient rooms and patient corridors at the floor level is 100 lux and that in the nurse stations, offices, and treatment rooms at a 0.75 m height level is 300 lux. The illumination distribution of the 170 functional sites in the inpatient buildings are presented in Fig. 15 (a). The compliance rates of the inpatient rooms and offices were 71.4% and 64.3%, respectively (see Table 4). However, the illumination levels in all of the sampled nurse stations are approximately 120 lux, which is 60% below the threshold. The compliance rates of the nurse stations and patient corridors were 0% and 22.2%. The nurse station is integrated with the patient corridor for considerate service, whereas the illumination levels in these public areas were generally insufficient during the day. The satisfaction votes on the light environment showed that the satisfaction levels of the occupants are mainly high, ranging from neutral to satisfied (see Fig. 15(b)). The dissatisfaction rates of the light environment for patients, visitors and staff were all below 20%. In addition, statistical analysis showed the satisfaction level of patients in terms of the light environment is higher than that of the visitors (p < 0.001).

Fig. 15

Objective measurement and subjective survey on indoor light environment: (a) measured indoor illumination level in 170 sites in the inpatient buildings and (b) satisfaction level.

Acoustic environment

The Chinese standard (GB/T 51153-2015 [40]) requires a maximum noise level (A) in the inpatient room and office during the day of 45 dB. Fig. 16 (a) presents the measured noise level (A) in sampled functional sites in the patient buildings during the day. The average noise levels (A) in the inpatient rooms and nurse stations reached 50.7 dB and 61.6 dB, respectively. The compliance rates of the inpatient rooms and offices for noise are 0% and 31.3%, respectively. As shown in Fig. 16(b), the occupant sensation on noise level ranged from slightly noise to medium noise. The staff perceive noisier than the patients do. According to the survey feedback, the noise sources in the inpatient rooms were the fan coil units and exhaust fan (49%), the occupant conversation (39%), especially in the nurse station area, and the snore (9%). By confirming with the hospital managers, the exhaust fan in the bathroom operates throughout day unless the noise of the exhaust fan strongly interferes with patients’ rest. Since the patients and visitors usually gathered in the nurse station area and asked the nurses about the diseases, it is reasonable that the nurse stations were noisy. As shown in Fig. 16(c), the satisfaction level on the indoor acoustic environment mainly ranged between slightly dissatisfied and slightly satisfied. The dissatisfaction rates of the acoustic environment for the patients, visitors and staff all exceeded 20%, indicating a noisy environment (see Table 5). Furthermore, the satisfaction level of the patients in terms of indoor acoustic environment is higher than that of the visitors with a p-value of 0.0019.

Fig. 16

Objective measurement and subjective survey on indoor acoustic environment: (a) measured noise level (A) in 170 sites in the inpatient buildings; (b) noise sensation; and (c) satisfaction level.

Overview

Fig. 17 (a) illustrates the overall satisfaction votes on the IEQ including the thermal comfort, IAQ, lighting, and acoustics. The overall satisfaction level on the IEQ ranged from neutral to slightly satisfied. The dissatisfaction rates of overall IEQ for the patients and visitors were 7.9% and 10.4%, respectively, which were below the target of 20% used by ASHRAE 62.1. However, the dissatisfaction rate for staff was 34.8%. The satisfaction level of the patients was higher than that of the visitors (p < 0.001) and the staff (p < 0.001). One possible explanation for a higher satisfaction level of the patients than the visitors and staff is the patients pay more attention to the illness and recovery than the indoor environment and suffer from the stress of illness.

Fig. 17

Subjective survey results on IEQ: (a) overall satisfaction level on IEQ and (b) complaints on IEQ aspects.

The correlation between the objective measurements and subjective votes was observed in the field study. The standard compliance rates of the relative humidity, outdoor ACR and noise level (A) were the lowest among the IEQ parameters (see Table 4). Accordingly, the top three complained aspects were the noise, odor, and humidity (see Fig. 17(b)). Similarly, the dissatisfaction rates of the air freshness and noise were the highest. It indicates that the standard and design code for healthcare facilities (i.e., ASHRAE standard 170-2017 [25], GB 51039-2014 [39] and GB/T 51153-2015 [40]) are reasonable for building a hospitable indoor environment in the inpatient buildings.

Further, we compare the finding of this study on IEQ and subjective satisfaction level with previous Chinese hospital field study. Liu and Wang [31]'s field study on IEQ of Chinese hospitals found that in summer, 13% of the relative humidity in Hospital A inpatient rooms located in cold climate area and 60% of the relative humidity in Hospital B inpatient rooms located in hot summer-cold winter climate area exceeded 70%, resulting in the mold problem. In addition, Hwang et al. [14]'s field study on thermal environment of a hospital located in hot summer-warm winter climate area showed that the relative humidity in more than half of the hospital area exceeds 60%. Therefore, improper humidity control in summer is prevalent in Chinese hospitals. Liu and Wang [31]'s field study on Chinese hospitals found IAQ was the least satisfactory among the four major aspects of IEQ (thermal comfort, IAQ, lighting, and acoustics) and indicated that the possible reason is the lack of fresh air supply in the design stage. The dissatisfaction rate of the air freshness was also the highest among the IEQ factors in this paper. The outdoor ACR of the inpatient rooms were proven to be inadequate and 45% lower than the ASHRAE 170-2017 standard threshold through the CO2 concentration decay curve method. Therefore, facility management personnel should pay more attention to the humidity control and actual fresh air volume which are the common problem in Chinese hospitals.

Conclusions

As the population ages, the Chinese health industry is growing rapidly, resulting in an urgent and huge demand for healthcare facility construction and renovation. The evidence-based design for healthcare facilities reveal that the IEQ influences patient physical-fitness and recovery state. In this study, objective physical measurements and a questionnaire based subjective survey were conducted to investigate the IEQ of Chinese inpatient buildings located in hot and humid region. We measured the IEQ parameters of 170 randomly sampled functional sites: temperature, relative humidity, indoor air quality, light and acoustic environment. The indoor environment of five functional spaces in a nurse unit was continuously monitored for three days. Furthermore, the outdoor air change rates of 32 sampled functional rooms were measured via CO2 concentration decay curve method to quantitatively evaluate the ventilation effect. The performance of the outdoor air system and fan coil systems was investigated and how the outdoor air system and fan coil systems contribute to the observed IEQ conditions was revealed. The main conclusions are summarized as follows:

The relative humidity of more than 65% results in the regular appearance of microbial growth on indoor surfaces of the inpatient buildings. The average outdoor air change rate of the sampled inpatient rooms is 1.1 h−1, which is 45% below the ASHREAE 170-2017 threshold. The inpatient rooms are pressurized. However, the insufficient fresh air volume and high supply air humidity ratio of the outdoor air system both result in the inadequate dehumidification capacity and the over-humid environment in the inpatient buildings.

Due to the characteristics of healthcare activity, the CO2 concentration threshold of 1000 ppm cannot completely represent the air freshness in the inpatient buildings. The standard compliance rate of CO2 in the inpatient buildings is over 99%, while the dissatisfaction rate of air freshness is more than 25% due to the insufficient outdoor air change rate. The compliance rate of the TVOC concentration is more than 80%, which accords with the dissatisfaction rate of air cleanliness at less than 20%. Benefitting from the good outdoor air quality, the PM2.5 concentration in 93% functional spaces of the inpatient buildings is lower than 20 μg/m3.

The standard compliance rate of illumination level for the public area (patient corridors and nurse stations) is lower than 25%. Owing to the sound of air-conditioning equipment and occupant conversation, the measured average noise levels of the inpatient rooms and nurse stations are up to 50.7 dB and 61.6 dB, respectively.

The questionnaire surveys reveal that the dissatisfaction rates of overall IEQ for patients and visitors are 7.9% and 10.4%, respectively, which are within the target of 20% used by ASHRAE 62.1, while that for staffs is 34.8%. Patients tend to have a higher satisfaction level on IEQ factors than visitors and staff. With the lowest standard compliance rates of outdoor ACR and noise level, the dissatisfaction rates of air freshness and acoustic environment are the highest among the IEQ factors, representing consistency between the subjective survey and objective measurements.