1. Introduction
Rapid growth of a civilization has adverse effects on the environment, some of which are caused by deforestation and the dumping of water body. This may be the primary cause of long-term shifts in temperatures and weather patterns. These movements may be natural, but human activity has been the primary cause of climate change since the 1800s, mostly owing to the combustion of fossil fuels (such as coal, oil, and gas), which creates heat-trapping gases. Almost all geographical regions are experiencing an increase in hot days and heat waves. The year 2020 was one of the warmest years on record. Heat-related diseases become more common as temperatures rise, making it more difficult to work and move around. An elevated environmental temperature leads to an increase in heat and humidity. According to the Environmental Protection Agency (EPA), the optimal range for indoor relative humidity lies between 30% and 50%. Mold and material damage are reduced if building sites stay within this temperature range. Different construction designs have been adopted to protect structures from both the outside and the inside [
1,
2]. It is vital to note here that humidity and condensation do not constitute dampness. Instead, it is the repeated accumulation of humidity and condensation in the same location that can lead to the appearance of dampness. Dampness on walls creates unhygienic conditions for both living and nonliving bodies [
3,
4,
5,
6]. Indoor humidity levels are directly related to physical health and construction stability. Healthy environmental conditioning is only possible by both creating and controlling it. The main concern here is the side effects on human health. Healthy environmental conditioning can be possible with the adaptation of the traditional/natural habitat or with controlled deforestation/urbanization. In order to have good air quality inside the house, the management of heat and moisture at appropriate levels throughout the year is essential [
7,
8,
9]. One cannot create a natural climate that is exactly like nature itself, but it can be managed by controlling air conditioning units, for which different sensors have been created and implemented in different smart system integrations. These types of integrations are complicated and the failure of one can cause serious data interpretation. Energy loss due to the use of a larger system is an additional issue. The idea of green building has gained popularity over the past 10 years, and more people are becoming aware of its potential environmental advantages over more traditional building methods. Green building places a great emphasis on lowering energy consumption (via greater insulation, more energy-efficient appliances, and HVAC systems) as well as lowering the negative effects on human health and the environment [
10]. Designing and creating low-energy structures as well as utilizing recycled or environmentally friendly materials are current trends in civil engineering [
10]. In this context, investigations are being conducted to better understand and describe the hygrothermal performance and durability of novel recycled composites that are being developed [
11]. Among building materials, wooden-based products appear to have interesting hygrothermal properties. Several researchers have aimed to determine the effectiveness of metamodels in forecasting building reactions [
11,
12,
13,
14]. Moreover, researchers are working on rammed earth folk house [
15], construction and demolition waste [
16], recycled expanded-polystyrene-based mortar [
2], and hemp and stone wool insulations [
1], among others. The purpose of this research work is to develop a composite material [
17] for a wood-frame wall structure’s interior wall, as well as a sensing material.
Researchers have been working to develop smart concrete composites to protect constructions as well as maintain the health of living and non-living bodies. Researchers are still working on the development of smart concrete composites to protect constructions [
18,
19,
20], which will also help in controlling room temperature, moisture, and so on, mitigating any damage to non-living things or the health of human beings. The proposed work is a simulation study using ZnO–fly ash composite as a smart sensing material. The simulation work was carried out using COMSOL multiphysics software. The simulated environment performance analysis is based on thermal and hygric simulation [
21]. It is predictable that hygrothermal simulations can help in analyses of the overall performance of buildings [
10,
11,
14,
22]. This study investigates the hygrothermal performance of building components, which are the fly ash–ZnO nano composite as the interior sensing layer of relative humidity, cellulose phase change material as the insulation layer with wood supporting the partition board, and concrete wall structures verifying the humidity level in the various building layers. The remainder of this paper includes the background of the study with proper justification for finding day-to-day problems, with a proper simulation design proposed, followed by the results and discussions. The data acquisition system with the overall instrumentation and control of the proposed research work is depicted.
2. Proposed Model Design
The hygrothermal simulation model for a domestic house with a core brick wall, concrete roof, and floor is described in this section.
Figure 1 depicts the schematic diagram of the proposed design model. In this figure, the brick wall has covered with false partition and the false partition has three layers from outside to inside naming as: oriented standard board (OSB), compressed wood strands (flakes) and cellulose material based insulation layer. The third layer or the interior layer is made up off fly ash-ZnO nano composite based sensing material layer. The OSB is fabricated in the form of wide mats from cross-oriented layers of different wooden strips. They are compressed and bound together with wax and synthetic adhesive resin (95% wood, 5% resin, and wax). For insulation of the building from heat, thermal conductivity was employed using a wood and cellulose mixed insulation layer. This helps to reduce heat loss in the building.
The sensing material layer is proposed here to accurately sense the humidity, and LM35can be implemented to sense the temperature at various layers of the model. The popular temperature sensor series LM35 is a précised integrated circuit (IC) whose output voltage linearly proportional to centigrade temperature. These are having advantage over conventional linear temperature sensors calibrated in kelvin, as the users are not needed to substrate huge amount of constant voltage from the output for obtaining convenient centigrade scaling. LM35 sensor does not require any external trimming or calibration. The typical accuracies of these sensors for room temperature and elevated temperature (−55 °C to 150 °C) are ±0.25 °C and ±0.75 °C respectively. The liner output, precise inherent calibration and low-output impedance of LM35 device makes interfacing to control circuit especially easy. As like temperature sensor, copper plates are used to sense humidity. These plates are adjusted as 4 probe resistance method. The change in humidity has an effect on the electrical resistance. The change in resistance due to the change in humidity at a constant supplied DC voltage results in current. The resulting current is used to control the ON or OFF condition of the aurdino circuit with the AC compressor. This research work is divided into two parts. Primarily, the hygrothermal simulation model is designed using COMSOL Multiphysics®6.0, after which we propose a schematic model where LM35 temperature sensors are used with an arduino microcontroller to control AC. The sensing and circuitry details are depicted in later sections of the article.
The hygrothermal simulation model using COMSOL Multiphysics
® [
22]: COMSOL Multiphysics
® software is used by engineers and scientists to simulate designs, devices, and processes in all disciplines of engineering, manufacturing, and scientific research. COMSOL Multiphysics
® is a simulation platform that allows for both fully linked multiphysics and single-physics modeling. The Model Builder encompasses all of the modeling workflow phases, such as establishing geometry, material characteristics, and the physics that explain specific phenomena, as well as solving and post-processing models to obtain correct results.
Figure 2 represents a portion of two-dimensional models with width and thicknesses of 0.8 m and 0.1475 m, respectively. The geometrical descriptions of each component are as follows. In the figure, the exterior and interior panels have thicknesses of 0.0125 m and 0.015 m, respectively. The exterior and interior panels are separated by two pine wood studs with a width of 0.045 m and height of 0.12 m. Three isolation boards made of cellulose are placed between the wood frame. In the wall-frame structure, cellulose is used as a filler material to fill the various cavities.
Wall structure: Under a given climatic condition, the moisture performance of the wall construction system is over-reliant on the system consonance, as well as the thermal and moisture characteristics of the constituent elements. Under Indian climatic conditions, moisture characteristics of wood and concrete wall structures are scrutinized. The exterior wall is a brick wall made of cement. The false wall is made of pine-wood-based OSB attached to the conventional brick wall. The isolation board is made from cellulose, with a bracing made of a wooden panel and interior siding made of fly ash–ZnO composite.
Weather condition and modeling parameter description: Convective moisture and heat flux surroundings are applied on the top and bottom margins to model the indoor and outdoor air flows next to the wall. The outdoor and indoor heat transfer coefficients are set as and , respectively. The outdoor and indoor moisture transfer coefficients are set to and , respectively, according to the correlation of the heat and mass transfer boundary layers. The side boundaries are designed for complete isolation in terms of heat and moisture. The indoor climatic situation is based on EN 13788. This comprises the high moisture load profile of buildings.
Dynamic modeling of heat and moisture transport: The idea behind this hygrothermal study is to analyze the moisture performance of buildings. This study is carried out using dynamic modeling of the transport of heat and moisture. Through this approach, both transport of liquid moisture by capillary forces and transport of vapor by diffusion are computed. Moreover, the latent heat effect due to vapor diffusion is modeled. In addition to the above, heat and moisture storage is also considered using moisture-dependent thermal properties.
Static modeling of heat and moisture transport [
21]: By ignoring heat and moisture storage, the latent heat effect, and capillary transport of liquid moisture, the following equations are obtained for transport of heat and moisture. The Glaser method is developed to assess the moisture balance of a building component by considering the vapour diffusion transport process. The Glaser technique uses a simple calculation of the interstitial condensation level based on average monthly temperatures, vapour pressure, and steady-state heat conduction if critical condensation thresholds are achieved within one year. Glaser’s [
21,
22] calculations are not a replica of reality, but rather a technique for determining the danger of interstitial condensation. The state of condensation was determined using the effective volumetric heat capacity at a constant pressure, effective thermal conductivity, temperature, latent heat of evaporation, vapour permeability, relative humidity, and vapour saturation pressure. Accordingly, moisture storage capacity and moisture diffusivity were determined. These equations are known as the Glaser method. They can be solved in the moisture transport in building materials interface by setting the moisture diffusivity to 0, as well as in the heat transfer in building materials interface by setting the vapor permeability to 0.
Modeling of the vapor barrier: Upside and downside moisture fluxes are defined and applied at the interface between the interior siding and the isolation board to model the vapor barrier. The moisture transfer coefficient β is defined, where δ is the vapor permeability of still air (SI unit: s), Psat is the saturation pressure of water vapor (SI unit: Pa), μ is the vapor resistance factor (dimensionless), and ds is the vapor barrier thickness (SI unit: m).
Evaluation of hygrothermal performance: The effect of boundary and exposure conditions: The relative humidity between the wall structure due to the variation in temperature plays a role in moisture buildup. The change in indoor temperature can cause an unusual temperature profile of the building construction material. The low temperature value leads to a higher moisture accumulation potential. Thus, it leads to condensation in the insulation layer during summer as well as when it is hotter outdoors than indoors. Basically, an air conditioning unit helps to lower the indoor temperature.
These analyses are performed with the consideration of leading a comfortable life through automatic control of moisture levels. This control also helps extend the life of construction materials. Using waste products like FA and converting them to FA–ZnO composites to be used as a sensing material is a rather challenging task. The research work was conducted. The results of the model are analyzed and discussed in the section following the data acquisition system and instrumentation section.
3. Data Acquisition System and Instrumentation
The data acquisition system with sensor integration for the proposed model is depicted in
Figure 3a. In this research work, we propose a system comprises of four probe sensory system with proper isolation, false wall (OSB and wood-cellulose composite) coated with FA-ZnO sensing material (inner side of the wall), arduino microcontroller with power supply setup, three numbers of temperature sensor (LM35), four numbers of LED, one display unit respectively. At each layer, one LM35 is installed. For each unit change in the temperature, the corresponding LED indicates the change values. The change values are then displayed in the display section. Depending upon the resistance value, the humidity of the indoor unit sensed by the sensing layer and the corresponding current value triggers the automated switch for AC operation. The setup is designed such a way that the insulation, which absorbs the maximum amount of water droplets, can be automatically cooled down or heated up by the AC unit. This helps to maintain a comfortable and healthy living environment inside the home. The room temperature and humidity values are also monitored by the mobile app, as shown in
Figure 3b. The temperature and humidity values are sent to the mobile through the SIM900A modem, Easy Electronics, India. SIM900A is a dual-band GSM or GPRS-based modem from SIMCOM. Its operating frequency is 900 or 1800 MHz with baud rate, which is configurable from 1200 to 115,200 through a programming command. The GSM or GPRS modem with internal TCP/IP stack enables the device to connect to the internet via GPRS. Once the SIM900A is connected to a power supply and an arduino controller, it automatically selects the operating frequency of 900 or 1800 MHz. The baud rate is set to 115,200. Once the internet connection is established, the data from the sensing device are transferred to the app, and the parameters are displayed on the mobile as shown in
Figure 3. From the app, values of outside temperature, room temperature, and room humidity can be monitored. The setting and adjustment of the room temperature and room humidity, with fan speed and the ON or OFF condition of the AC compressor can performed remotely with the mobile app. The user can also turn the AC OFF or ON directly from the app