Empirical validation and analysis of the energy performance of an ecological Net Zero Energy Building (NZEB) in Benguerir-Morocco

. Within the framework of the sustainable development and carbon-neutrality, the building sector is a key target of the national energy strategy towards zero-carbon economy in Morocco. This article comes in response to this need by assessing the energy performance of a solar-powered low-embodied-carbon building in the semi-arid climate of Benguerir-Morocco, which refers to the fifth climatic zone in the thermal regulation for constructions in Morocco (RTCM). To do so, we’ve used Openstudio as the building energy modeling tool to investigate the energy self-sufficiency of a detached Net Zero Energy Building (NZEB) that has a floor area of 47 m², uses earth-based material as the main component part of the building envelope and has a photovoltaic installation with a capacity of 4 kW. The accuracy of the building energy model was empirically validated following ASHRAE 14 guidelines by monitoring hourly indoor temperatures for 8 days during summer season. Results show that annual thermal needs for cooling and heating are 123.4 kWh/m²/year and the calculated annual self-sufficiency (SS) of the building is 1.25, which means that the solar technology greatly offsets the electrical needs of the building and rech the goal of Zero Energy Building.


Introduction
The depletion of energy resources, global warming, and the increase in energy demand are just a few of the numerous energy concerns that the contemporary global energy context is dealing with [1]. A promising alternative would be to rationalize energy use and raise the share of renewable energy sources into the energy mix [2]. Undoubtedly, efficient use of energy and sustainability has become a key issue for the most energy policies. Sustainability and energy saving terms take place in building construction industry as well since buildings are one of the most significant energy consumers. In that perspective, 25.4% of the total energy consumed in Morocco is dedicated to residential sector. And as cities grow and the number of energy-intensive structures rises, the energy demand will continue to rise. Therefore, there is a huge opportunity for energy consumption reduction in the residential sector. Morocco must therefore concentrate its efforts on the development of energy efficiency programs and renewable technologies that are best suited to its needs and environment.

Building sector Decarbonization
Following IEA pathway to NET ZERO by 2050, all buildings should be Zero Carbon Buildings by 2050. For that, zero-carbon building should cover building operations as well as emissions from the manufacturing of building construction materials and components [3].

Earth-based construction materials
Sustainability is becoming a paramount concern to key stakeholders in the construction industry. Increasing research has been performed on the thermal insulation of buildings to optimize and reduce energy consumption [4] [5]. This approach is one way to reduce energy losses from buildings made with industrially manufactured materials [6]. However, most of these building materials, either for insulation (such as rock wool) or for wall manufacturing (such as concrete), are major energy consumers during both their production and implementation (embodied energy), and their recycling is not always practical or feasible [7]. Consequently, the development of earth-based buildings appears to be a sustainable alternative to conventional constructions.
The major asset of earth lies in the fact that it is a local material that can be taken and used immediately on the construction site or nearby and does not require industrial processing. Therefore, earthen materials have excellent properties in the circular economy framework. Moreover, the sustainability of this material was recognized long ago, as highlighted by the significant heritage of earth construction all around the world.
Earthen construction is considered to be a sustainable building form for its low carbon footprint and lower operating costs (e.g. heating/cooling). From an ecological perspective, an earthen material offers recycling potential and reduced environmental impact on disposal.
The current study uses an earth-based construction material for the building envelope and focuses on assessing its thermal performance under the semi-arid climate of Morocco.

Focus on energy efficiency in buildings
A consequence of the Morocco's rapidly expanding middle class is an increase in electricity consumption per person (0.56 tep/capita in 2014). The nation seeks to reduce its end-use energy intensity by 20% by 2030, and for that goal, incentive programs are rolled out through supporting legislations (thermal regulation for construction), governmental subsidizes for advanced technologies, among many other measures. This is because there cannot be a realistic change in the energy sector without a vigorous energy efficiency component.
And with respect to the building sector, it is crucial to take into account various energy efficiency measures during the design of low-consuming building stocks. Furthermore, the prevailing hot temperatures in countries like Morocco make space cooling a necessity. As a result, this will trigger a dramatic increase in the demand for cooling along with the rising needs for comfortable built environments. Considering that, research studies should further evaluate adapted energy efficiency measures such as external walls' insulation and high thermal mass [8], improved glazing types on the windows [9], airtightness, earth-to-air heat exchanger [10], highly performing and reliable HVAC systems [11], solar shading technics, optimized orientation, and all other approaches and systems that serve to increase the efficiency of the building operation and mitigate the increasing energy demand for indoor comfort.
While the Energy efficiency in buildings is a growing area of focus in Morocco, its success depends on the investments made into research and implementation of sustainable solutions.
In the Moroccan context, RTCM [12] is applied on new buildings, and renovated buildings around the nation. And it's a tool for validating the building envelope's thermal and energy performances across the six different thermal zones in Morocco during the design phase.

Zero energy buildings (ZEB)
A Net Zero Energy Building (NZEB) is a gridconnected highly energy-efficient building that produces as much energy as it consumes annually. By implementing energy efficiency strategies as well as the integration renewable energy technologies, the "Net Zero" balance is achieved [13].
The Net Zero Energy Building concept emphasizes the role of energy efficiency while promoting more onsite, localized renewable energy generation [14].
Our study focuses on the assessment of a Net Zero Energy building under the semi-arid climate of the city of Benguerir-Morocco.
While in this study we've considered the three pillars of Zero Carbon Building, we didn't calculate the embodied carbon of the built environment. And since our study is focused on the operating phase, we will be limited to Zero Energy Building Concept.

Case study description
The monitored building used in this study, shown in Figure 2, is located in Benguerir City -Morocco. This building is a one-storey detached residential house, composed of two bedrooms, a toilette, a living area and a kitchen and has a total floor area of 47 m². The building is mainly constructed from earth-based material. The Table 1 & Table 2 summarize the thermal characteristics of the construction materials used in the case study building.
Benguerir city is known for its hot semi-arid climate which is extremely hot in the summer season and relatively warm in the winter season ( Figure 3). The city is known for its semi-arid steppe weather with hot summers, pleasantly warm winters, and comfortably warm springs and autumns ( Figure 3). Benguerir has an average temperature of 23.6°C, a minimum temperature of 1.7 °C and a maximum temperature of 44.3 °C. And it is situated at latitude 32° 14′ North and longitude 7° 57′ West. In addition, January is the coldest month of the year, and August is the hottest.
The mean monthly temperatures in this climate range from 10.7°C in January to 30.9° C in August. The mean relative humidity is 57.7% and fluctuates from 47.5% to 66.9% over the course of an average year. Figure 3 demonstrates that the city has extremely high temperatures, especially from May to October. Figure 3 & Figure 4 show the average monthly outdoor daily air-dry bulb temperature and monthly irradiance in Benguerir city for the typical year.
For the methodology developed in the aim of this paper, the first step was the creation of the building energy modeling using the OpenStudio simulation engine [15]. Then, an empirical calibration was conducted for the hourly indoor temperature of the building. The calibration validation has been undertaken according to ASHRAE's statistical indices. According to ASHRAE guideline 14 [14], the calibration of hourly building data should respect the following ranges: CV(RMSE) should be less than 30% and NMBE should be less than +/-10%.
For the purpose of calculating thermal needs, The cooling setpoint is 26°C while the heating setpoint is 20°C, following the Moroccan thermal regulation [12].

Empirical validation
The thermal energy simulation software evaluated the earth-based detached building's indoor thermal environment, and it was compared to the experimental measurements from a wireless temperature sensor, providing hourly-averaged measurements for indoor temperature from September 20 th -27 th , 2022. The Building Energy Model (BEM) should reflect real conditions as closely as possible. Then the BEM basically acts as the backbone for calculating the cooling and heating energy requirements over the entire typical year necessary to maintain comfortable indoor environment.
The computational approach then involves using the dynamic thermal simulation program to evaluate the thermal performance over the course of an entire typical year. Figure 5 presents the actual real indoor temperatures recorded with thermocouple sensor inside the building versus the simulated indoor temperature corresponding to the same period.
The calculated CVRMSE was 1,85%, the calculated NMBE was 0,83% and R² is 0,96 (Figure 7). These values respect the allowable ranges of ASHRAE's guideline 14. The results show that the model is well reliable to reproduce the measured indoor temperature conditions. Figure 8 illustrates the simulated annual thermal need and the combined heating and cooling needs amounts to 123.4 kWh/m²/year, based on the unoccupied scenario. Also, it shows that the thermal demand for space heating is low, less than 8% of the total thermal needs. This is due to the solar gains and low thermal inertia of the building envelope. Conversely, it leads to higher demand of cooling during summer.

Annual thermal needs of the building
The variation of the outdoor temperature and the high solar irradiance are reflected directly at the indoor temperature. 62.7% of all time is above 26°C.
The indoor temperatures of the house ( Figure 6) show an alarming overheating problem. This is due mainly to non-shaded high exposed facades on the South and Ouest and exposed roof and inactive overnight ventilation. Solar shading and increased ventilation should be able to mitigate the problem. Our building experiences the very large heat radiation that characterizes this region (DNI=2120kWh/m² [16]).
Worse, the high thermal transmittance of the building envelope and high WWR (12.5%) of the building are the main cause for high thermal needs.
According to many studies of the thermal assessment of buildings in this semi-arid climate [17][18] [19][20], inefficient passive design strategies trigger high energy demand for thermal needs.   Even though the earth-based building may be considered a sustainable low-embodied solution, the thermal simulation shows that the operating costs for cooling and heating are excessively high and that we should implement a series of energy efficiency strategies and improve the hygrothermal characteristics of the building material in order to allow a significance decrease in annual thermal needs and improve the internal thermal comfort for future buildings.
One of the fastest growing sources of new energy demand is cooling and especially in hot-humid and hotdry climatic parts of MENA region [21]. Cooling season is much longer than the heating season. Furthermore, in hot-dry climate heat storage capacity of the envelope becomes more important issue than heat insulation for the energy efficiency of buildings.

Energy Use Intensity (EUI) of the building
In our case study, the Energy Use Intensity (EUI) is composed of the energy consumption of various building systems and appliances. The three main characteristics to evaluate the EUI are as follow: 1. HVAC (Heating, Ventilation, and Air Conditioning) system: we consider a COP=3 and for the building's mechanical ventilation, we benefit from the local natural energy resources in order to improve indoor thermal comfort and reduce energy needs. The natural ventilation is activated when outdoor temperature is between 20°C and 25°C. 2. Lighting : Lighting is another major contributor to EUI, especially in buildings with high levels of occupancy or extended operating hours. Energy-efficient lighting technologies such as LEDs can significantly reduce lighting energy consumption. The lighting power density is estimated at 7w/m². 3. Appliances and equipment -This category includes any electrical appliances, such as television, washing machine and kitchen equipment, that are used within the building. The equipment power load is estimated at 200W. The building is considered occupied by a family of 3 people and the schedule of occupation, equipment and lighting of residential building is provided by Ashrae 90.2 [22]. The results of the simulations are summarized in Figure 9.

PV production
In this case study, an integrated photovoltaic system has been considered to produce on-site carbon-free energy. The photovoltaic system has a peak power of 4 kWp, oriented south and with a tilt of 30°.
Electricity generated from the modules is simulated using EnergyPlus for semi-arid climatic conditions of Morocco.
The solar energy plays a key role in reaching Net Zero Energy Buildings, particularly in the urban context. And for our case study, we assess the potential of the installed solar technologies to offset the tota Energy Use Intensity (EUI) of the building. Subsequently, we can assume that we've reached a NZEB when the PV production surpasses the electrical demand of the building.
In our case study, the yearly SS, which is the ratio of solar production to Energy Use Intensity, is equal to 1.25 which highly shows that we can reach NZEB on yearly basis. However, the yearly metric is a very basic and simple consideration of annual energy balance between energy load and generation and Zero Energy Buildings shouldn't be evaluated exclusively on the basis of their quantitative energy balance [13].
To determine the synergy capacity between the building and the grid and the requirement for seasonal or monthly energy storage, a thorough analysis of the energy load match in monthly timeframes is necessary [23].
The monthly data (figure 10) provides a better understanding of the interplay between load and generation profiles. The Energy needs is always lower than the PV production except on the summer season when the energy needs for cooling demands exceeds the PV production. Which raises an important issue about the exposure of the occupants to heat stress during summer season.
Besides, managing the dynamic behavior of loads and generation may require reinforced grids and advanced solutions to grid management.

Conclusion
Due to the urging call to preserve the environment and reach carbon neutrality by 2050, this article supports the goal of promoting Zero Carbon Buildings. While it is possible to achieve Net Zero Energy Buildings, the high thermal needs of the earth-based building shows https://doi.org/10.1051/e3sconf/202339604023 IAQVEC2023 that it is still required a comprehensive strategy to consider a number of measures combining passive building design strategies, efficient building envelope measures and highly effective active solar systems.
The ultimate aim is to create a green ecological building, compatible with the semi-arid climate of the region that beautifully combine the techniques and methods used in our traditional houses with the advanced modern technologies.