thermal energy demand and potential energy savings

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THERMAL ENERGY DEMAND AND POTENTIAL ENERGY SAVINGS IN A SPANISH SURGICAL SUITE THROUGH CALIBRATED SIMULATIONS

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A. González Gil a*, J.L. López-González b,c, M. Fernández c, P. Eguía c, A. Erkoreka d, E. Granada c

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a

Defense University Center, Spanish Naval Academy, Plaza de España s/n, 36920 Marín, Spain

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b

SERGAS, Xunta de Galicia, Edif. Administrativo San Lazaro, s/n, 15703 Santiago de Compostela, Spain

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c

Department of Mechanical Engineering, Heat Engines and Fluid Mechanics, Industrial Engineering School, University of Vigo, 36310 Vigo, Spain

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d

ENEDI Research Group, Department of Thermal Engineering, University of the Basque Country, UPV, EHU, Alda.Urquijo s/n, Bilbao, Spain

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* Corresponding author: Arturo González Gil

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Email: [email protected]; phone: +34 986 804 947

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ABSTRACT

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Hospitals present a widely recognized margin for energy conservation due to their elevated final energy use intensity. Specifically, operating rooms are among the functional areas with greatest energy demand in hospitals, given the stringent indoor conditions for patients and surgical staff. However, energy efficiency in surgical facilities has traditionally been overlooked by the scientific literature in favor of guaranteeing adequate air quality conditions. This paper assesses the potential energy savings that could be achieved in a surgical suite in a Spanish hospital by lowering the current ventilation rates to the lowest energy-demanding values recommended by the proper Spanish standard and other international codes. Likewise, the paper assesses the actual hygrothermal and ventilation conditions in the suite based on the results of a continuous monitoring campaign performed for a period of 12 days. Simulations undertaken with a dynamic energy model specifically developed and calibrated for this work revealed that the average energy intensity of the suite is 1021 kWh/m2/year (1685 kWh/m2/year for operating rooms), with 80% of the total annual thermal demand corresponding to periods of inactivity. In addition, energy savings between 40% and 80% are possible while complying with both national and international standards.

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KEYWORDS

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Energy conservation; operating rooms; thermal energy demand; energy modeling; calibration; TRNSYS; GenOpt.

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1. Introduction

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Energy consumption in buildings has been continuously rising for the last several decades and is currently the largest end-use sector, accounting for approximately 40% of the total final energy requirements in Europe [1]. Within the building sector, healthcare facilities account for approximately 3.2% of the total final energy consumption, while representing only 1.7% of the total building floor area [2]. These figures may appear relatively minor in overall terms. However, these findings reveal that healthcare buildings are major consumers when energy use intensity is considered. This category has been reported to represent the highest energy-intensive type of buildings in Europe, with an average final energy consumption per unit of floor area of approximately 350 kWh/m2/year [2]. In comparison, the equivalent values for the residential and non-residential sectors are 200 kWh/m2/year and 280 kWh/m2/year, respectively [1, 2].

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Healthcare buildings encompass a broad diversity of facilities with the function of offering a health service for patients. These buildings range from small clinics providing primary care to large complex hospitals offering multiple services, such as specialized medicine, surgery, critical care and emergencies. However, healthcare buildings are all characterized by having a high rate of occupancy and stringent standards for indoor environmental requirements. Accordingly, healthcare buildings in general and hospitals in particular consume large amounts of energy in air-conditioning, heating, ventilation and lighting, their energy use patterns being influenced by many factors, such as building design, size, location, ownership, management, type of patients and level of services provided [3]. Thus, an investigation of the energy performance of nondomestic buildings of Greater London (UK) concludes that primary care facilities present an energy use intensity between 115 and 570 kWh/m2/year, whereas values for hospitals range from 194 to 1270 kWh/m2/year [4]. In addition, it has been recently reported that the average energy consumption of hospitals in Spain is 270 kWh/m2/year [5], while the average energy consumption is 86 kWh/m2/year for small centers in Southwest Spain [6]. In other non-European countries, the mean energy intensity of healthcare centers in the US has been reported as 302 kWh/m2/year, with 358 kWh/m2/year for inpatient buildings and 164 kWh/m2/year for centers not admitting patient hospitalization [7]. In addition, a survey of the energy performance of Brazilian hospitals shows that their energy use intensity goes from 89 kWh/m2/year to 460 kWh/m2/year [8]. Likewise, a recent study on 20 Chinese public hospitals and health facilities reveals energy consumption from 300 to 1000 kWh/m2/year [9]. Lastly, it has been reported that the average consumption of major and regional hospitals in Australia is approximately 414 kWh/m2/year [10].

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On those grounds, it is commonly accepted that hospitals present considerable potential for energy savings worldwide given their actual high energy use intensity [11]. However, the extensive implementation of energy efficiency measures in this sector is frequently hindered by a series of issues, including economic constraints, technical difficulties, political barriers and behavioral reasons intrinsically related to the healthcare sector [8, 9, 11]. Nevertheless, a burgeoning literature on this field exists, with a clear focus on minimizing the energy consumption and emissions of heating, ventilating and air-conditioning (HVAC) equipment, as such systems account for a remarkable fraction of hospital end-use energy, typically ranging from 50% to 75% [3, 7, 12-15]. Hence, studies evaluating different retrofitting strategies and technologies, such as 2

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refurbishing the building envelope [16, 17], developing and optimizing polygeneration plants [8, 18-27], introducing renewable energy sources and fuel cells [28-32], using heat pipe heat exchangers on existing air-conditioning systems [33], or improving the ventilation efficiency [3439], have been reported.

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Interestingly, most of the investigations listed above refer to energy efficiency improvements either at the building level or at room level (inpatient wards). However, limited studies examine the energy consumption of HVAC systems in operating rooms (ORs), though operating rooms are among the functional areas with the largest energy use intensity in hospitals and thus with greater potential for applying energy saving actions [40, 41]. The functions of the HVAC equipment in a surgical suite, which typically comprises a group of one or more ORs, adjunct work areas and their interconnecting hallways, are to minimize infection risks while maintaining staff and patient comfort [42, 43]. Hence, temperature and humidity in surgical areas must continuously be maintained within determined limits to inhibit the growth of bacteria and deactivate viruses while providing acceptable indoor thermal conditions for the surgical personnel [44]. In addition, an elevated number of air changes per hour (ACH), as well as an adequate air distribution design, are needed to guarantee an aseptic environment and healthy comfortable working conditions [45-47]. Table 1 shows the indoor conditions recommended for surgical suites in a selection of countries, which is helpful to illustrate that hygrothermal and ventilation requirements may be significantly different, depending on the standards or guidelines considered.

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Table 1 Recommended indoor conditions for operating rooms in different countries Ventilation Country

Type of room

Temp. (ºC)

Spain

OR

22-26

RH (%) 45-55

France

2400 m3/h or 20 ACH a)

50% of total airflow

[48]

[49]

20-24

20-60

20 ACH

4 ACH

Ancillary rooms

22-26