In the past few decades, energy consumption in buildings has been increased to 30% worldwide (Ji et al., 2017; Si et al., 2018). Renewable energy is not a new concept to work with. Many researchers are already working on various renewable energy systems to reduce capital costs and increase energy production. In a study, the water management of PEM fuel is inspected, and, according to the results, the effectiveness of PEM fuel cells is at maximum at 80°C with the removal of wastewater periodically (Taner, 2015a). In another research, the importance of simulation and optimization techniques is highlighted by working on PEM fuel cells in the energy sector. Results conclude that by the simulation of operating pressures and voltage parameters as working parameters, the energy and exergy efficiencies are 47.6 and 50.4%, respectively (Taneer, 2018). In a study of the PEM electrolyzer, the payback period for the hydrogen generation systems is observed. Operating parameters were the current and voltage. According to the results, the simple payback period was thought to be 2.32y (Taneer et al., 2018). In another research, a techno economic analysis was performed for sugar production processes. The main aim of the research was to reduce capital cost with an increase in the production of turbine power. So, by way of a well-structured analysis, the unit cost ought to be 3.142 [$/kW] with a payback period of 4.32 years (Taneer and Sivrioglu, 2017).

In recent times, China has emerged as a major global energy consumer in terms of the building sector (Wang et al., 2014). However, the energy consumption of hospitals is more than double that of other ordinary buildings in society. Energy use in hospitals is important due to the high heating, cooling, and ventilation thermal loads, critical medical equipment, and operational requirements (Balaras et al., 2007). Hence, energy-efficient designs for hospitals can play a vital role in sustainable development in society (Meegoda et al., 2012). In the past years, many studies have been conducted in different countries especially for hospitals. For example, Ahmed H·S (Sherif, 1999) proposed in 1999 that cost-effective and technical aspects should be considered for the designing of hospitals in developing nations, particularly for low-income groups. In a study in the United Kingdom in 2007 (Shu et al., 2007), primary energy consumption was reduced by 15% by simply implementing sustainable healthcare goals. Also, a sensitivity analysis for the building energy consumption and energy-saving potential optimization of the hospital energy supply system was conducted by Japanese researchers in Asia (Schweber, 2013). According to the research, there is little available data for energy consumption related to hospitals, especially energy data for climate diversity in different regions of Asia. Moreover, for the designing of NZEBs (Alfano et al., 2014), two characteristics have to be measured, namely, indoor environmental quality (IEQ) and energy reduction per capita. The new regulation demands that the NZEB goal must be achieved with an acceptable IEQ level for residents, especially for medical institutions, i.e., hospital buildings. Moreover, with the help of two different groups of people, i.e., medical staff and patients, the IEQ demand can be standardized. Therefore, a lot of literature is available on IEQ in hospital buildings (Skoog et al., 2005; Han et al., 2007; Yau and Chew, 2009; Pourshaghaghy and Omidvari, 2012; Del Ferraro et al., 2015; Golbazi and Aktas, 2016; Alfano et al., 2017; Khalid et al., 2017; Sattayakorn et al., 2017). One of the best researches in the area of indoor environmental quality is Fanger's research, which describes various factors regarding human thermal comfort and indoor air quality in the hospitals (Skoog et al., 2005).

Presently, non-residential buildings are major power consumers in developed countries, consuming 20–40% of the total primary energy (PE). For example, in 2010, the Dutch environment consumed 41% of the total energy consumption in the Netherlands (Vanhoutteghem et al., 2015). For these reasons, the European Union issued the “Energy Performance Directive for Buildings” (EPBD) in May 2010 (EIA, 2011). The directive sets forth requirements to accomplish the goals of the NZEBs regulations and EU member states (MS) legislation by 2020. Generally, from January 1, 2019, new buildings under the government must be NZEBs, and the rest of the new buildings be they either residential or public utilities must meet the NZEB requirements from January 1, 2020. As there is in the Netherlands no clear definition of NZEBs for 2020, the Dutch administration has issued a public plan to encourage NZEBs (Dutch governments, 2012), which illustrates different schemes to decrease overall energy consumption. In another research (REHVA, 2010), the total energy consumption by the Dutch healthcare sector accounts for 1.64%. There are 120 hospitals in the Netherlands, 8 of which are academic hospitals (Ministerie van Volkshuisvesting, 2010; Zurghulpatias, 2015a,b).

Similarly, in the past decade, NZEBs in the United States have received increasing attention from different organizations, i.e., ASHRAE and the American Architectural Institute (AIA). ASHRAE has set a target to develop a tool by 2020 that will facilitate the building community to develop a viable NZEB approach in the market by 2030 (AIA, 2011). The AIA 2030 has the goal of attaining new carbon-neutral buildings all over the country (Entrop and Brouwers, 2019). In previous literature, only a few studies were based on the actual measured performance and efficiency of NZEBs. For example (AlAjmi et al., 2016; Zhou et al., 2016; Kneifel and Webb, 2018; Wu and Skye, 2018), worked on NZEBs. AlAjmi et al. (2016) worked on simulation-based studies to examine the possibility of converting existing institutional buildings to NZEB in the hot and humid climate of Kuwait. In the study, solar PV and thermal cooling systems were installed in Kuwait, and feasibility analysis was performed for NZEBs.

Also, there are many established healthcare regulations available in Europe, the USA, and the UK. Building Research Establishment Environmental Assessment Method (BREEAM) is the earliest green building rating system, established in the UK in 1990 (Schweber and Haroglu, 2014; Alhorr et al., 2015). Among BREEAM products, the BREEAM healthcare version was developed for green hospital buildings in 2008 (Ferreira et al., 2014). Leadership in Energy and Environmental Design (LEED) is another green building rating system, and it was launched by the US Green Building Council in 1998. In the LEED product family, the U.S. Green Building Council (USGBC) released LEED for healthcare in 2011. In addition, the US healthcare industry steering committee has also formulated the Green Healthcare Guidelines (GGHC) (Azhar et al., 2011; Wu et al., 2017). The rating systems of these developed countries set an example for other countries. However, different regions have different energy consumption attributes and impact methods, and the evaluation method must thus be suitable for the real situation of the country. Therefore, in 2006, China formulated the “Evaluation Standard for Green Buildings” (ESGB), which was the first assessment standard for the “environmental performance rating” of green buildings in China (Younger et al., 2008; Pradinuk, 2009).

In developed nations, there are many international communities that are already working on NZEBs. However, in underdeveloped nations like Pakistan, the energy consumption of buildings was 44% from 2016 to 2017. The degree of energy consumed in the building sector will be doubled in the year 2030 (Liu et al., 2014). Similarly, buildings also account for 43% of greenhouse gas emissions and 75% of the electricity usage in Pakistan (Jian et al., 2017; Zhang et al., 2017). More than 38% of the total building energy is consumed in heating, ventilation, and air conditioning. The energy needs of commercial buildings account for a considerable part of the total energy consumption (Chen et al., 2008). In Pakistan, hospitals account for 18% of the energy use and they occupy 17% of the total non-residential area [Pakistan Integrated Energy Model (Pak-IEM), Ministry of Planning Development Government of Pakistan, 2011].

In order to solve this problem, one of the two solutions can be used: minimizing the building energy usage or adapting the renewable energy resources. Analysts believe that it is possible to achieve 70% financial savings by applying better design strategies and efficient tools during the building design phase (Rafique and Rehmanb, 2017). Energy shortage in Pakistan is attributed to an ever-increasing population size, followed by consumers being subjected to frequent load shedding. Pakistan, being the sixth most populous country in the world, makes up about 2.56% of the total worldwide population (Khan and Pervaiz, 2013; Raheem et al., 2016). Pakistan relies on fossil fuels to fulfill its energy demands and has to spend 20% on crude oil imports (Haves, 2019). Additionally, energy demand is growing by 8–10% annually, in contrast to an annual supply growth of only 7% (Farooqui, 2014).

By reviewing the literature, it can be inferred that the development of NZEBs is not a common practice in underdeveloped countries. Likewise, there are no set regulations and targets related to renewable energy usage in the building sector. Also, only a few studies were based on the actual measurement performance and efficiency of NZE hospitals in Asia and none in Pakistan. Furthermore, the previous studies and pre-existing energy planning modules neglect the importance of renewable energy for the commercial sector in Pakistan. Therefore, the ensuing renewable energy solutions are actually deterministic. Furthermore, the International Energy Agency (IEA) has outlined 13 tasks for the development, performance, and analysis of NZEBs in (OECD) countries. Pakistan is not an associated member of the IEA. Therefore, there is a dire need for research on energy-efficient non-residential buildings as per task 47, which is not available in Pakistan (Fritjof and Asplan Viak, 2014). Hence, the current research will be a feasibility analysis of an efficient and effective grid-connected NZEB model for a hospital using efficient optimization techniques along with intelligent simulation and modeling methods in accordance with the IEA standards in Pakistan.

The developed model of the NZE hospital would be used during the building and community project planning stages. Also, it will guide decision-makers toward much more efficient energy options and will attract investors toward a better adaptation of RE at the community level in Pakistan.

Key objectives of current research are as follows:

This section is followed by six subsections as follows: building design and site selection, estimation of thermal load of the hospital building, description of the HOMER program, design of hybrid microgrid NZEB, NZEB microgrid feasibility, and optimization step.

In this particular research, a hybrid microgrid NZEB is proposed for the hospital building situated in Taxila, Pakistan. A complete methodology is given in Figure 1. The aim of the current research is to minimize the electricity consumption expenditure of the hospital by implementing RE techniques as well as to check the feasibility of NZEBs for the Pakistani climate. So, the total thermal load is calculated for a hospital located in Taxila, Pakistan, using ASHRAE thermal load equations. Also, an energy-efficient model is developed in HOMER Pro software by using variables of NPC, operating cost, and payback period. Later on, sensitivity analysis and optimization of the parameters are performed.

To design the building, the most important task was the selection of a site in order to perform a feasibility analysis of NZEBs in Pakistan.

The current hybrid on-grid system is designed to meet the electricity needs of a hospital building in Pakistan using solar energy as an alternative energy resource in addition to a conventional grid. The estimation of the thermal load is carried out carefully, taking into consideration the load requirements of the hospital building for the peak summer season. Design parameters for the building are given in Table 1.

July is selected as a peak month due to the high thermal load demand in the building. Design temperatures are selected on the basis of set regulation of ASHRAE for hospitals. Also, for estimation of thermal load of the building, external as well as internal loads are calculated using ASHRAE standard equations (Delisle, 2011; Lenoir et al., 2011; J, 2013) and the equation given below (Sandeep, 2015).

HOMER is one of the best tools for designing renewable-energy-based systems. Moreover, it can simulate the operations of a hybrid system for an entire year in time steps from 1 min to 1 h. It also enables us to compare and evaluate the disadvantages and advantages of economic and technical features. In HOMER, the design process is performed in three steps: simulation, optimization, and sensitivity analysis. In this paper, all three processes are followed to get the best overview of the feasibility of NZEBs in Pakistan.

NZEB model development of the current hospital building in HOMER is illustrated in Figure 6. The yearly thermal load and solar irradiation potential of the building are the input parameters for HOMER.

Solar radiation is converted directly into DC by using PV modules. So, the deviation of the output of the electrical power produced by PV modules is estimated using Equation (10). The output energy of a PV module is dependent on several parameters, including the following: the structure of cell type, nominal performance of the PV panel, solar radiation, derating factor, solar cell temperature, climatic conditions at the panel area, temperature coefficient, and weather conditions (Fritjof and Asplan Viak, 2014).

where;

Economic evaluation for NZEB conversion of a hospital building is performed by three main operations of HOMER software: simulation, optimization, and sensitivity analysis. In the current section, different obtained results will be discussed.

The current study is an economic evaluation and feasibility analysis of hybrid microgrid NZEB. A hybrid PV power system is created to supply energy to the hospital building located in Taxila, Pakistan. The objectives were to decrease the total electricity price and feasibility analysis of hybrid NZEBs in Pakistan for non-residential buildings. To attain maximum advantage from the proposed hybrid NZEB system, the designing of the building, calculation of thermal load, simulation, and optimization of the suggested hybrid microgrid NZEB were all performed in HOMER Pro. An optimal range of design parameters was acquired using thermal data and solar irradiance as input. Additionally, an economic analysis was performed to evaluate the feasibility of the proposed hybrid system over the duration of 25y. The main findings of the current system were as follows: solar radiation potential, operating cost, initial capital cost, the energy produced by PV, payback period, and net present cost. The optimal NPC of the proposed NZEB is $20.49 million, the operating cost for the whole installation of a hybrid NZEB system is $0.151 million, and the initial capital cost is $0.111 million. By adaptation of the hybrid NZEB system, the electricity unit price has dropped from 0.14 to 0.12 USD/kWh. The maximum electricity generation by PV panels is 344,733 kWh. Consequently, the proposed hybrid NZEB system is economically 10.24% more profitable than the grid system only. Moreover, the proposed NZEB system has a payback period of 2.53y, thereby making it a cost-efficient and economically feasible method. Primarily, on the basis of the analysis of all the above-stated variables, it may be concluded that the current design is able to satisfy the aim and objectives of the current research by making renewable energy a viable solution to the energy shortages in Pakistan. The developed framework will assist in the decision-making of feasibility analyses and economic evaluation of NZEBs in Pakistan. Also, it will facilitate municipal and provincial planners in NZE community planning. This work will be further supported by the implementation of a federal renewable energy plan, which could act as a long-term roadmap for sustainable community planning.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.

By literature review it can be inferred that development of NZEBs is not a common practice in underdeveloped countries. Likewise, there is no set regulations and targets related to renewable energy usage in building sector. Also, only a few researches were based on the actual measurement performance and efficiency of NZE hospitals in Asia and none in Pakistan. Furthermore, the previous studies and pre existing energy planning modules neglect the importance of renewable energy for commercial sector in Pakistan. Therefore, the ensuing renewable energy solutions are actually deterministic. Moreover, IEA have outlined 13 tasks for the development, performance and analysis of NZEBs in (OECD) countries. Pakistan is not an associated member of the International Energy Agency (IEA). Therefore, there is a dire need of research on energy efficient non residential buildings as per task 47 which is not available in Pakistan. Hence, current research will be the feasibility analysis of an efficient and effective grid connected NZEB model for a hospital using efficient optimization technique along with intelligent simulation and modeling method in accordance with the International Energy Agency (IEA) standards in Pakistan.

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.