Utilization of Solar Energy for Water Heating Application to Improve Building Energy Efficiency: An Experimental Study

Abstract

The manuscript is written for flow escalation based on an experimental data for a Solar Assisted Heat Pump Water Heater (SAHPWH) increasing building energy efficiency. For the investigation, a Solar Assisted Heat Pump (SAHP) was conceived, manufactured, and tested in real time. The findings of the experiments shows that single glazing with average sun radiation of 600–750 W/m², COP of approx. 6 can be obtained with identical heat gains. This study shows that when a flat plate collector of area 1.83 m (L) × 1.22 m (W) × 0.1 m (T) with a 0.5-mm-thick black copper plate absorber with clear glazing as a cover receives average radiation of 700 W/m², then setup can supply 60 litres of water for residential use from 15 °C to 45 °C in approx. 70 min. In addition, the study finds that the collector efficiency factor F’ is likewise shown to have a direct connection with the absorber and an inverse relationship of tube spacing. The findings indicated that the technology has significant commercial potential, particularly in sectors such as with solar resources for improving building energy efficiency.

1. Introduction

For every country’s economic growth, energy is a fundamental requirement. Currently, fossil fuels provide 80% of world’s primary power, but they are a finite resource that releases considerable GHG emissions, notably CO₂ [1]. Sources involving renewable energy have a favorable impact on the environment and economic challenges around the world. The fundamental benefit of renewable energy systems is that they reduce pollution by replacing traditional fuels and therefore lowering air emissions. When it comes to price, renewable technology has a high initial investment but low ongoing costs if compared to fossil fuels.

Among all the renewable energy Sun is an enormous source of energy, known as solar energy (Figure 1). This is a basic need of all human beings, plants, and animals. This is a non-polluting, eco-friendly, and easily available source of energy from nature. Solar energy can be used by three technical methods namely (1) heliochemical (2) helioelectrical and (3) heliothermal. The heliochemical photosynthetic process sustains life on Earth by creating food and turning CO₂ to O₂.

The helioelectrical technique, which employs photovoltaic converters, generates electricity for spacecraft and is employed in a variety of terrestrial applications. The heliothermal method can generate a significant portion of the thermal energy needed either solar water heating and buildings warming. In all the heliothermal processes, the collector is the most important part of the process [2]. In all the collector’s flat plate collector is very useful to fulfil domestic hot water requirements. It is simple to use and understand. to manufacture. Two systems that are currently receiving a lot of attention around the world are the solar household water heater (SHWH) as well as the heat pump system that draws the power of the surrounding air or geothermal heat.

1.1. Global Scenario

Figure 2 shows the energy consumption, which has doubled in the last 20 years, has become a fundamental determinant of a nation’s development, demonstrating how important it is to protect the source from which this energy is created. It necessitates a more dependable, as every nation strives for a faster, more sustainable, and greener energy source, and development [3].

Developing countries have always excessive energy consumption to meet their growth and development. As stated by the Intergovernmental Panel on Climate Change (IPCC), the urban environment accounts for 71% to 76% of net global energy use [4]. In future as the population increases, worldwide power consumption is predicted to increase especially in developing countries. The pollution resulting from producing electricity with coal is unavoidable. The effects of these polluters on the environment have been noted as being more damaging in the form of climate change, which has resulted in issues such as ice melting, sea-level rise, floods, earthquakes, and tsunamis, which have harmed humans, cattle, and poultry in the form of pandemics.

1.2. Energy Crisis

Industrialization and economic growth are the two main components on which the essential availability of resources to produce the required amount of energy is sustained [6,7]. It creates a situation of crisis, as the natural energy resources are getting vanished at a very high speed. A clear vision of a terrible future in this regard, all outsourcing needs alternatives.

The hype of disaster changed from the choice taken through the predominant oil-generating countries to taking hype with the charges. Hence, it forced the importer countries to search for an opportunity for a useful resource that could be domestic, effortlessly available, economical, and found in an ample amount. Therefore, all evolved and growing countries are trying to set new notions to create to remove the scenario of disaster throughout the globe.

To take the essential movement the scenario that ends in a disaster is the purpose that needs to be identified, accompanied via way of means of the instantaneous consequences resulting from the disaster. They want to research the effects that emerge as an awful lot essential for the nation, in the order, that they may be pressured to do so in rectifying the crisis and locate the feasible answer sooner. The feasible answer redirects to the obligation of each character in the direction of the environment, to a few reliable, sustainable, promising supply of strength to keep away from the scenario of disaster in addition to environmental degradation.

1.3. Causes of Energy Crisis

Figure 3 shows overconsumption of non-renewable resources (oil 32%, coal 27%, and natural gas 22%) puts a burden on the environment by polluting water and air, which is a direct result of rising pollution. Electricity is a primary source of energy in industry, and it is primarily produced from natural resources. Many times, old machines are used without modification, resulting in increased energy waste [8]. Frequently, obsolete equipment with minimal safeguards leads to irresponsible usage of chemicals. Without an indigenous perspective on renewable energy sources, the concept of resolving this situation without energy is nearly unthinkable. The power that already exists in plants is insufficient to meet rising demand, resulting in a delay in commissioning new ones. Figure 4 consolidates the above reasons of energy problems in developing countries.

The situation is exacerbated by plants. In addition, there is a lack of distribution and unavoidable natural disasters. These reintroduce the same situation of the escalating crisis. Renewable energy sources are not being used to their full potential. This is one of the important causes of the energy crisis [9]. The energy crisis is also caused by a lack of awareness about energy conservation, effective energy storage, and an imbalance between energy production and consumption.

1.4. Indian Renewable Energy Scenario

Figure 5 shows the annual growth of world renewable energy supply. India has high contribution in annual growth of world renewable energy supply as it is committed to increasing renewable energy capacity to 0.45 TW by 2030; having 0.089 TW installed capacity, as part of the Paris Agreement. India has a high potential for solar energy because of more than 300 days and 3000 h of annual sunshine. The amount of sunlight in India is strong, varying from 4 to 7 kWh/m²/day [10,11]. Average With over Rs 4.7 lakh crore in investment, India emerged as the most desirable destination for renewable energy investors. In India, the current Levelized cost of solar energy is roughly Rs 2.5 per kWh, down from Rs 12 in 2010. CERC was brought closer to providing a business opportunity for efficient power energy, which at the time endorsed the trading of environment-friendly power contracts on the energy market under the Green Term Ahead Market (GTAM) [12].

A pan India green market can drive and urge the nation to reach its environmentally friendly electricity ambitions by providing strong incentives such as transparency, serious costs, adaptability, payment security, and monetary reserve funds that the trade market provides. Finally, the green market will compel green generators to accept a variety of offer and exchange models. Renewable energy has paved the path for developing countries like India to reduce their reliance on conventional resources. According to the Ministry of New and Renewable Energy (MNRE), solar energy can prove to be helpful, inexpensive, and accessible, addressing both climate change and energy security concerns.

The objective of this manuscript to improve the execution of direct expansion solar assisted heat pump water heating system in composite climate of India for application in building sector to improve efficiency. A detailed study evaluates performance analysis of SAHPWH, Comparison of energy consumption of SAHP and electric heaters, Cost analysis for SAHP, comparison of total water consumption and Electricity consumption. These studies were not performed in previous literature research studies. The composite weather conditioning experimental analysis of northern hilly region (Uttarakhand) of India is not available in the literature.

2. Experimental Setup, Components and Mathematical Modeling

To examine the effectiveness of SAHP water heating systems indigenous experimental setup has been developed as shown in Figure 6. Following are the various components of the SAHP water heating system.

• Evaporator or Flat Plate Collector
• Compressor
• Condenser
• Expansion Device

The SHWH system as seen in Figure 7 is based on Vapor Compression Refrigeration Cycle, wherein on the place of evaporator we use a solar collector in the cycle. Due to its high thermal conductivity (k) low cost compare to silver, copper is used for manufacturing of solar collectors. Refrigerant R-134a is used because of its Zero Ozone layer depletion qualities and an excellent alternative for R-12, which was previously known to be harmful to the Ozone layer. This experimental setup mainly consists of four components:

• Collector: In study, we use a flat plate collector having dimensions 1830 mm (L) × 1220 mm (W) × 100 mm (T) made with an aluminum frame. Use transparent glazing on the to the head of the collectors to minimise heat loss from the thin copper plate of dimensions 1405 mm (L) × 975 mm (W) × 0.5 mm (T). This copper plate is coated with just a matt black color to absorb maximum radiation. A copper tube of outer and inner diameters 10 mm and 9 mm is brazed with this absorber plate (Figure 8). The amount of heat collected by this absorber plate is passed on to the refrigerant R134a flowing in copper tube.
• Compressor: Hermetically locked reciprocating compressor with a 245 W input power and a rate of flow of 5.79 cm³/rev propellant were once installed and operated according to a simple principle. To increase by lowering the volume of liquid, the force of the refrigerant is reduced. The compressor raises the pressure of the refrigerant, which contributes importantly to increasing refrigerant temperature.
• Capillary: The refrigerant’s temperature and pressure had to be normalized before it could re-enter the evaporator. Thus, an optimized copper capillary with a radius of 0.455 mm and a length of 3048 m. used in construction. Therefore, the pressure decreases after the loss of latent heat. This can be achieved through diffusion inside the capillary, thus raising the volume. Due to the liquid refrigerant, the pressure between the refrigerants decreases.
• Condenser: The condenser is used as a heat exchanger because it extracts heat from the refrigerant as well as transfers that energy to the tank’s water After the heat is removed from the refrigerant, the refrigerant cools and turns into a liquid form Copper tubes with an outer diameter of 10 mm and a length of 9.75 m made up the condenser. It was assumed that the storage tank was not stratified; therefore losses could be ignored when calculating the coefficient of performance.

The performance of the heat pump powered by solar energy can be improved either by decreasing the top heat loss or by raising the convective heat transfer coefficients through the use of a heat exchanger and a different working fluid. The primary focus of this study is the improvement of SHWH’s thermal efficiency. To increase the efficiency of the flat plate collector and increase its commercial uses, the effects of several parameters, including glazing material, environmental factors, and solar intensity, were explored. Mathematical models were used to first optimize these necessary parameters and component specifications, like the thickness of the absorber plate and the diameter of the tube (Figure 8). Variations in the climate were also measured with various measuring instruments.

2.1. Working of Experimental Setup

The radiation from the sun having shorter wavelength, penetrates the glass of the collector and transmits its energy to the blackened copper sheet which further transmits the absorbed energy to the serpentine copper tubes. During this process the shorter wavelength radiations gets converted into longer wavelength and remain trapped in the collector. Now, the refrigerant present in the serpentine tube gets heated up and its phase shifts from liquid to vapour and moves to the compressor as saturated vapour. Compressor circulates the refrigerant throughout the system, and adds pressure to the refrigerant. These results increase in refrigerant temperature. Now in condenser this heat is transmitted from the refrigerant to water. When refrigerant enters in throttling valve, it expands and releases pressure and as a result, the temperature has dropped at this point. As a result, the refrigerant exits the throttle valve as a mixture of liquid and vapor, typically in proportions of approximately 75% and 25%, respectively. Thus, the cycle repeats itself for next cycle.

The complete flat plate solar collector is so designed to avoid the heat loss by convection, radiation and conduction process and it traps 98% of the heat and almost negligible heat emits out because of glass wool insulation on the bottom as well as on the side walls of collector.

2.2. Mathematical Modelling

To analyse the one-dimensional model and anticipate thermal performance, the following assumptions are required:

• Within the selected time interval, the system is in a semi-steady condition;
• In evaporator, condenser, and pipe, the pressure decrease is insignificant;
• At both the evaporator and condenser exits, the refrigerant is deemed saturate;
• It is hypothesised that the compression of refrigerant increases is a polytropic process;
• The expansion of the coolant fluid is regarded as isenthalpic;
• The coverings are resistant to infrared radiation;
• There is negligible temperature drop through a cover;
• Temperature gradients around the tubes could be neglected;
• The properties are temperature independent;
• The losses via the front and back are to the same ambient temperature;
• Effect of dust and dirt on the collector are negligible;
• The storage of hot water tank is considered to be non-stratified [13].

2.3. Collector

Based on assumptions above, authoritative equations characterising the heat performance of the proposed system’s various components were iterative numerical formulation and solution procedure that takes interactions into account between the different system components. The useful energy gain (Q_u) is dependent on the collector efficiency factor (F′), effective transmittance-absorptance product of the cover glazing material ($\mathsf{\tau }\mathsf{\alpha })$, The solar radiation that falls on the collector (I_T) and overall loss coefficient (U_L) [14,15].

Useful energy gain

$$Q_u=A_c\left[\left(\tau \alpha \right)I_T-U_L\left(T_{in}-T_a\right)\right]$$

(1)

$$Q_u=A_c{F}^{\prime }[\left(\tau \alpha \right)I_T-U_L\left(T_{in}-T_a\right)$$

(2)

where,

• F′ = Collector efficiency factor
• FR = Heat removal factor
• UL = Overall loss coefficient
• $\mathsf{\tau }\mathsf{\alpha }$ = Effective transmittance-absorptance product of the cover glazing material (0.9)
• IT = Solar radiation falling on the collector

$$\raisebox{1ex}{$Q_u$}\!\left/ \!\raisebox{-1ex}{$A_c$}\right.=\left[\left(\tau \alpha \right)I_T-U_L\left(T_{in}-T_a\right)\right]$$

(3)

F′ and FR is the collector efficiency factor and the heat removal factor which are defined as:

$$F^{\prime }=\frac{Actualusefulenergygain}{Possibleenergygainiftheentirecollectorisatlocalfluidtemprature}$$

(4)

$$F_R=\frac{Actualusefulenergygain}{Possibleenergygainiftheentirecollectorisatfluidinlettemperature}$$

(5)

2.3.1. The Overall Heat Loss Coefficient

The convection and radiation heat transfer from the collector’s top surface to the surrounding environment is primarily responsible for the overall heat loss coefficient (U_L) [16,17]. The overall heat loss coefficient U_L is the sum of the bottom (U_B), top (U_T), and edge loss coefficient (U_E) shown as follows [18]:

U_L = U_T + U_B + U_E

(6)

2.3.2. When Tubes Are Soldered below the Absorber Plate

When tubes are connected below absorber plate the following calculation established by HottelWhlliar Bliss used to calculate collector efficiency factor F′ [19,20,21]:

$$F^{\prime }=\left[\frac{\frac{1}{{\mathrm{U}}_{\mathrm{L}}}}{\mathrm{W}\left[\left(\frac{1}{{\mathrm{U}}_{\mathrm{L}}\left[D_0+\left(W-D_0\right)\right]}\right)+\frac{1}{C_b}+\frac{1}{\pi D_i{h}_{fi}}\right]}\right]$$

(7)

$$\mathrm{F}=\frac{tanh\left[m\left(W-D_0\right)/2\right]}{\left[m\left(W-D_0\right)/2\right]}$$

(8)

$$\mathrm{m}=\sqrt{U_L/k_p{\delta }_t}$$

(9)

where, δt is thickness of tube (m), W is pitch of tube (m), Cb is bond conductance (mK/W) and kp is thermal conductivity of absorber plate (W/(m K).

2.3.3. COP of Direct Expansion Solar Assisted Heat Pump System [22]

The performance of the direct expansion SAHP system can be evaluated from the COP. The COP of a heat pump is expressed by the following formula:

$$\mathrm{COP}=\frac{Thermalenergyrejectedbythecondenser}{Energyinputtothecompressor}=\frac{Q_c}{W_{comp}}$$

(10)

2.4. Condenser

Based on system configuration, SAHP water heating systems with storage tank are classified into two types, i.e., split systems and boxed units [23]. Split systems are widely used for commercial purposes. The initial cost of this system is high, and it takes more space. On the other hand, packaged units are compact in size and used for domestic water heating [24,25]. To minimize the heat loss caused by the condenser thermal insulation is used. The refrigerant enters as a super-heated vapour and passes through several before emerging as a sub-cooled fluid, as expected [26]. The condenser is essential to the system’s overall performance, yet there has been little research into its design. A study found that there are two possible configurations named based on the basic arrangement of refrigerant flow with regard to water flow in the tank, counter flow and parallel-counter flow [27,28]. In this system condenser is used as a heat exchanger. There are numerous types of liquid-to-liquid heat exchangers use in literature [29,30]. But in Indian solar water heating system, only concentric tube and within tank heat exchangers are used. These are simple to maintain, cost-effective, and affordable. In vapor compression refrigeration cycle (VCRS), hot refrigerant from outlet of compressor become the temperature of inlet condenser (T₂). The temperature of cold-water inlet (T_wi) of storage tank for maximal heat transmission, is permitted to travel in the opposite direction of the refrigerant flow. ${\left(q_{cond}\right)}_{max}$. The inlet temperature of condenser (T₂) and cold-water inlet temperature (T_wi) are considered known, and outlet refrigerant temperature of condenser (T₃) and hot-water outlet temperature (T_w) of storage tank are to be determined. The maximum quantity of heat transferred from the condenser to storage tank can be expressed as:

$${\left(q_{cond}\right)}_{max}=m_f{c}_f\left(T_2-T_{wi}\right)$$

(11)

The real heat transfer between the refrigerant and the heat exchanger (T₂) and cold water (T_wi) may be represented as a percentage $𝜀$ of ${\left(q_{cond}\right)}_{max}$, where $𝜀$ is the effectiveness of the heat exchanger. So, actual heat transfer:

$${\left(q_{cond}\right)}_{act}=𝜀m_f{c}_f\left(T_2-T_{wi}\right)$$

(12)

where $m_f$ is refrigerant mass flow rate used and $c_f$ is specific heat of fluid.

The performance of heat exchanger is measured by effectiveness. The ratio of actual heat transmission to maximum achievable heat transfer is the efficacy [24]:

$$𝜀=\frac{{\left(q_{cond}\right)}_{act}}{{\left(q_{cond}\right)}_{max}}$$

(13)

Effectiveness of the heat exchanger (condenser):

$$𝜀=\frac{\left({\mathrm{T}}_2-{\mathrm{T}}_3\right)}{\left({\mathrm{T}}_2-{\mathrm{T}}_{wi}\right)}$$

(14)

2.5. Compressor

To investigate performance of the solar assisted heat pump system, a quasi-dynamic mathematical model was built, which is primarily made up model of system components and iterative criteria. The assumptions were made to simplify the problem [31,32]:

• The distribution of temperature inside the storage tank is uniform
• Pressure is constant in evaporator, condenser and pipes used for connection
• In Expansion Valve the Throttling Process is Isenthalpic Process
• Resistance during thermal contact is negligible
• Insulation used for water storage tank is adiabatic [33]

The compressor is described by using efficiency equations which associated to volumetric and isentropic efficiency of compressor to compression ratio $r_p$ (which is ratio of discharge pressure ($p_c$) and suction pressure ($p_e$) of compressor) [34].

$$\mathrm{Compression} \mathrm{ratio} \left(r_p\right)=\frac{p_c}{p_e}$$

(15)

The output refrigerant temperature of compressor $({\mathrm{T}}_2)$ can be computed as follow:

$$T_2=T_1{\left(\frac{p_c}{p_e}\right)}^{\frac{k-1}{k}}=T_1{\left(r_p\right)}^{\frac{k-1}{k}}$$

(16)

where, $T_1$ is the inlet temperature of compressor, $p_c$ and $p_e$ are the discharge and suction pressure of compressor. $k$. is the refrigerant vapor’s polytropic index, and it is calculated as:

$$k=a_1{r}_p+a_2.$$

(17)

where $a_1$ and $a_2$ are experimentally verified correlation coefficients [35,36].

The refrigerant mass flow rate is described as [14]:

$$m_f=\frac{N{\eta }_V{V}_d}{60v_{com,i}}$$

(18)

where N is compressor speed, $V_d$ is displacement volume of compressor, $v_{com,i}$ is specific volume of the compressor, and ${\eta }_V$ is volumetric efficiency of compressor [37].

The power of compressor is calculated as:

$$W_{com}=\frac{\left(h_{com,o}-h_{com,i}\right)m_f}{{\eta }_{com}}$$

(19)

where $h_{com,i}$ is specific enthalpy of refrigerant at inlet of compressor and $h_{com,o}$ is specific enthalpy of refrigerant at outlet of compressor, ${\eta }_{com}$ is overall efficiency of compressor and $m_f$ is mass flow rate of refrigerant.

2.6. Throttling

Throttling process can be done by capillary tube. Working fluid is flow through capillary tube. When a fluid flow through a narrow passage, there is an appreciable drop in pressure. The process is throttling process [14]. To simplify the problem, the following assumptions were made:

• No heat transfers
• No work transfers
• Constant enthalpy
• Irreversible process
• So, we can say that:
• Enthalpy at inlet (h₁) = Enthalpy at outlet (h₂)

As fluid flow through capillary its velocity increase as per continuity equation (AV = Constant). Hence conversion of pressure energy into kinetic energy takes place. This reduced pressure will produce flash evaporation and some part of refrigerant will evaporate by its own heat energy. This will reduce its temperature. In a study of CO₂ based SAHP, it was found that for throttling process, capillary tubes are suitable and the cost is also affordable [38]. It is more flexible is response to changes and almost acting in such a way as to provide optimal pressure adjustment [39].

2.7. Selection of Refrigerant

In 1850, diethyl ether became the initially marketed available refrigerant for vapor compression systems, then after NH₃, CO₂, CH₃Cl, SO₂, C₄H₁₀, C₂H₆, C₃H₈, C₄H₁₀, C₈H₁₈ and CCl₂F₂ ammonia, carbon dioxide, methyl chloride, sulphur dioxide, butane, ethane, propane, isobutane, gasoline, and chlorofluorocarbons, were used. Chlorofluorocarbons (CFCs) are chemically synthesized substances that were widely employed as working fluids prior to 1990 due to their superior chemical and thermodynamic characteristics [40]. In recent times, hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), primarily R22 [41,42], R134a [43,44] (refrigerant overview

Table 1. Overview of refrigerant R-134a [49].

Refrigerant	Chemical	Group	Name	Substitute for	Application Max Min
R134a	CF3CH2F	HFC	1,1,1,2-tetra fluoroethane	R12, R22	25 °C–20 °C

), and R410A [45], have been popular in solar assisted heat pump systems [46]. Properties of these refrigerants are mentioned in

Table 2. Refrigerants that can be used in SAHP system.

Group	Refrigerants/Name	Refrigerant Properties
Chloroflurocarbons (CFCs) [50]	R11, R12	High Ozone Depletion Potential High Global Warming Potential
Hydrochloroflurocarbons (HCFCs) [51]	R22, R123	Low Ozone Depletion Potential High Global Warming Potential
Hydroflurocarbons (HFCs) [52]	R134a, R152a, R125, R32, R404A, R407C, R410A	Zero Ozone Depletion Potential Low Global Warming Potential
Natural refrigerants [53]	R290, R1270, R744, R431A, R43A, R433A	No risk of ozone depletion. Negligible Global Warming
Hydrofluroolefins (HFO) [14]	R1234ye, R1234yf	There is no risk of ozone depletion Negligible Global Warming
HFC/HC mixtures [54]	R417A, R422A, R430A	Zero Ozone Depletion Potential High Global Warming Potential

.

Even though ammonia is poisonous as well as the industrial and heavy commercial sectors were still using this and are highly satisfied with it. The reason behind this was the cost of ammonia was low and improved thermodynamic and transport characteristics, resulting in better heat transfer coefficients. Ammonia’s main disadvantage is its toxicity, which makes it unfit for residential use [46,47]. R-22 was used in previous heat pump water heating systems. However, due to its ozone depletion potential, it is presently being phased out. [27]. R-134a is a commonly utilized refrigerant in heat pump water heating systems these days [40].

When choosing a refrigerant, the most significant characteristic with which the refrigerant exchanges heat is the refrigerated space’s temperature and environment. A temperature differential of 5 °C to 10 °C should be kept between refrigerant and medium with which it is exchanging heat for heat transfer to occur at a suitable rate. If there is a refrigerated space is to be kept at −10 °C, the refrigerant should indeed be preserved around −20 °C while absorbing heat in evaporator. The evaporator has nethermost pressure in refrigeration cycle, therefore this pressure should be higher than pressure in atmosphere to avoid leakage of air into the refrigeration system. In this scenario, refrigerant with 1 atm of saturation pressure or above at −20 °C is required. R-134a and Ammonia are two examples of such chemicals [35]. The system which uses R-134a increases COP of the system more than 50%, when compare to R22 refrigerant [48]. So, in this experiment, R-134a has been used.

3. Result and Discussion

The primary goals of this study the SAHP water heating system and parametric optimization of the system. Discussions and outcomes are based on experimental observations on heat pump powered by solar energy using a single glazed flat plate collector cum evaporator, which have been conducted during the period of April 2022 (summer), January and February (winter) 2022 [55]. The typical schematic illustration of SAHP system is shown in Figure 9, all data of experimental runs was recorded, but only few cases were reported after seeing the similar pattern to avoid the error in the system. Experiment was performed in different time of the day to analyse the impact of environmental temperature and solar radiation on heating time for water and condenser outlet flow. During morning to evening at different solar radiation experiments were performed.

In the above figure,

• T₂ = Inlet temperature of Compressor
• T₂ = Inlet temperature of Condenser
• T₃ = Inlet temperature of Expansion Valve
• T₄ = Inlet temperature of Evaporator/FPC (flat plate collector)
• Tw = Consumable water temperature

When the experiment was performed in the morning at 07:30 AM, the temperature outside rises, from 22 °C to 32 °C slowly as sun was rising. Due to this, the solar intensity was also increased. At starting of the experiment, it was recorded 244 W/m², and at the end of the experiment, it was 683 W/m². It is shown in the Figure 10.

Figure 11 shows sun radiation and ambient temperature influences on temperature at various locations of SAHP water heating system. It is clearly showing the solar influence radiation on the system’s performance. The temperature after compression (T₂), is the highest among all the temperatures shown in the Figure 11. Depending on the time, the temperature ranges between 34 °C to 69 °C. This heat is transmitted to consumable water once it reaches the condenser. As a result, temperature of the consumable water increases. In this temperature of consumable water (T_w) is raised from 21 °C to 45 °C. We can see from the above Figure 11, the temperature after condenser (T₃) also rises starting from 21 °C to 43 °C. Temperature of refrigerant entering the compressor (T₁) is also rises starting from 11 °C to 32 °C as the time increases. The temperature of refrigerant enters to the FPC (T₄) increases from 14 °C to 31 °C as the time increases. From the Figure 11 it is clear that influence of sun radiation on evaporator temperature is more than other when temperature of solar radiation decreases temperature of evaporator decreases lowly. It means that the system performance will increase as the evaporator temperature start increasing. But at the same time evaporator temperature should not increase above the compressor safety pressure to avoid the compressor failure.

It can be observed from Figure 12, that solar radiation is high in the afternoon time. At the start of the experiment solar radiation was 699 W/m², and it increases to 857 W/m².

The temperature after compression (T₂), is the highest among all the temperatures shown in the above Figure 13. Depending on the time, the temperature varies between 56 °C to 77 °C. This heat is transmitted to consumable water once it reaches the condenser. As a result temperature of consumable water increases. In this temperature of consumable water (T_w) is rises from 21 °C to 45 °C. We can see from the above Figure 13, the temperature after condenser (T₃) also rises from 24 °C to 43 °C. Temperature of refrigerant entering the compressor (T₁) also rises from 27 °C to 38 °C as the time increases. Temperature of refrigerant entering the FPC (T₄) rises from 25 °C to 31 °C as time increases.

It can be observed from Figure 14, that solar radiation is high in the afternoon time. At the start of the experiment solar radiation was 432 W/m², and it decreases to 0 W/m².

Figure 15 shows the temperature at various location of the system with time. The temperature after compression (T₂), is the highest among all the temperatures shown in the above figure. Depending on the time, the temperature varies from 45 °C to 47 °C. This heat is transmitted to consumable water once it reaches the condenser. As a result temperature of the consumable water increases. In this temperature of consumable water (T_w) is rises from 25 °C to 45 °C. We can see from the above Figure 15, the temperature after condenser (T₃) also rises from 30 °C to 42 °C. Temperature of refrigerant entering the compressor (T₁) is also decreased from 24 °C to 13 °C as time increases. Temperature of refrigerant entering the FPC (T₄) decreases from 27 °C to 13 °C as time increases.

The

Table 3. Comparison of COPs at the different time frames.

Time Interval	Temperature Raised		Energy Consumption (kWh)	Time (Min)	COP
	Initial (°C)	Final (°C)
08:00 to 09:45	20 °C	45 °C	0.4	105	4.359
	ΔT = 25 °C
10:20 to 11:25	20 °C	45 °C	0.3	65	5.628
	ΔT = 25 °C
16:40 to 19:00	25 °C	45 °C	0.7	140	1.993
	ΔT = 20 °C

shows the average value of system performance with different time interval. When our system runs in the morning, the solar intensity will also increase. If the solar intensity is in the middle of 244 W/m² and 683 W/m² we achieve COP 4.359 if initial water temperature is 20 °C and we consume it at 45 °C. During this time ambient temperature is also increases from 22 °C to 32°C.

As the sun rises, the intensity of solar is also increase, and if it lies between 699 W/m² and 857 W/m², the COP will be 5.628. If the initial water temperature is at 20 °C and we consume it at 45 °C. As solar intensity increases, ambient temperature will also increase from 32 °C to 38 °C.

If we assume that the ambient temperature rises in the evening as compare to morning, the initial water temperature rises as well. If we assume it increases from 20 °C to 25 °C. So, our initial water temperature will be at 25 °C. As the sun begins to set, solar intensity will also decrease. If it lies below 432 W/m² we can achieve COP 1.9. If initial water temperature is at 25 °C and we consume it at 45°C. During this time period, ambient temperature dropped from 39 °C to 29 °C.

The COP value may also be affected with the water consumption during different time interval. The Table 3 shows the COP value with different time zone. It can be clear from the Table 3 that the value of COP is more than the 5 in morning time because of proper solar radiation value. The reason for the increased COP is that rises in heat transfer rate in condenser.

During experiment, solar collector was tilted at 45°. Result shows that on day of experiment, solar radiation increases from 244 W/m² to 683 W/m². During this solar radiation, 60 L of water may be heated from 20 °C to 45 °C in 105 min with energy consumption about 0.4 kWh and COP of 4.359. In the second case when solar radiation reaches at 699 W/m² and increases to 857 W/m², then the same 60 L of water at 20 °C will reach at 45 °C in only 65 min, energy consumption during this will be 0.3 kWh and COP reaches up to 5.628. In the third case when experiment performed in evening solar radiation reaches at 432 W/m² and decreases up to almost 0 W/m² as the experiment going on. During this time interval the same 60 litres of water from 25 °C to 45 °C will take 140 min and COP will also decreases and achieved 1.993.

The sun is rarely visible in peak winter in Roorkee, Uttarakhand, and range of sun irradiation is 25 W/m² to 300 W/m². During those days, it has been found that heating water from 15 to 45 °C uses roughly 0.8 kWh of energy. And, depending on the solar irradiation, time it takes to heat water varies from 3 to 5 h. During February, the weather was sunny and clear, and we noted that the energy consumption to warm water from 15 to 45 °C was about 0.5 kWh. And, depending on the solar irradiation, the time it takes to heat water varies from 1 to 2 h. When compared to an emulsion rod, it consumes nearly 3 kWh of energy. As a result, we are saving 2.5 kWh of energy to heat 60 L of water, demonstrating the power and future solar energy potential. Solar and other renewable energy is the future of electricity generation, and their use is quickly growing year after year. We have an abundant solar power source, but efficiency of solar panels is still less than 30%.

In

Table 4. Total water consumption—45 L (Electricity consumption—0.3 kWh).

Time Interval	Average Irradiance (W/m2)	Wind Velocity (m/sec)	Ambient Temperature (°C)	Hot Water Flow Rate (Liters/min)	Total Water Consumption (Liters)	COP
10:00 to 10:15	684	3.2	32.8	0.66	10	5.580
10:15 to 10:30	715	1.5	33.1	0.66	10	5.580
10:30 to 10:45	750	2.8	32.9	0.80	12	6.696
10:45 to 11:00	783	1.8	34.5	0.86	13	7.254

, it shows that at every 15-min interval total water consumption is shown and maintains the storage tank temperature at 40 °C. In flow water temperature was at 15 °C. Overall COP of system is 4.375 when the average irradiance varies from 684 W/m². We can achieve the hot water flow rate shown in the table at that average solar irradiance.

Table 4,

Table 5. Total water consumption—35 L (Electricity consumption—0.3 kWh).

Time Interval	Average Irradiance (W/m2)	Wind Velocity (m/sec)	Ambient Temperature (°C)	Hot Water Flow Rate (Liters/min)	Total Water Consumption (Liters)	COP
15:00 to 15:15	635	1.4	39.4	0.66	12	8.371
15:15 to 15:30	580	1.9	39.2	0.66	10	6.975
15:30 to 15:45	532	0.7	39.2	0.80	08	5.580
15:45 to 16:00	468	2.1	38.9	0.86	05	3.487

,

Table 6. Total water consumption—32 L (Electricity consumption—0.3 kWh).

Time Interval	Average Irradiance (W/m2)	Wind Velocity (m/sec)	Ambient Temperature (°C)	Hot Water Flow Rate (Liters/min)	Total Water Consumption (Liters)	COP
09:00 to 09:15	521	0	32.6	0.4	6	3.348
09:15 to 09:30	563	1.5	33.0	0.53	8	4.464
09:30 to 09:45	604	0	33.6	0.53	8	4.464
09:45 to 10:00	650	1.2	33.9	0.66	10	6.975

,

Table 7. Total water consumption—20 L (Electricity consumption—0.2 kWh).

Time Interval	Average Irradiance (W/m2)	Wind Velocity (m/sec)	Ambient Temperature (°C)	Hot Water Flow Rate (Liters/min)	Total Water Consumption (Liters)	COP
16:00 to 16:15	401	1.2	38.9	0.53	8	5.284
16:15 to 16:30	347	1.5	38.7	0.4	6	3.963
16:30 to 16:45	303	1.7	38.6	0.2	3	1.981
16:45 to 17:00	225	0.9	38.4	0.2	3	1.981

and

Table 8. Total water consumption—13 L (Electricity consumption—0.3 kWh).

Time Interval	Average Irradiance (W/m2)	Wind Velocity (m/sec)	Ambient Temperature (°C)	Hot Water Flow Rate (Liters/min)	Total Water Consumption (Liters)	COP
17:00 to 17:15	144	1.9	38.4	0.33	5	1.937
17:15 to 17:30	90	1.3	36.7	0.26	4	1.550
17:30 to 17:45	48	0.6	34.8	0.13	2	_
17:45 to 18:00	29	0.9	32.8	0.13	2	_

show performance analysis SAHP water heating system from morning to evening at different time interval. That clearly shows the best performance in the morning time because of proper solar radiation and increasing temperature in the environment. At evening time due to less solar radiation energy consumption of the system will slightly increase. Hot water consumption from the storage tank for domestic purpose can be seen and optimized based on the system performance. As, domestic hot water need is quite high in the morning time so if this system is designed properly and hot water need in the domestic purpose can be meet effectively. Consumption at different levels of solar Irradiance at 15-min intervals is shown.

4. Cost Analysis for SAHP

The application of SAHP hinges on cost-effectiveness, SAHP is financed in order to to reduce reliance on the traditional system for producing domestic hot water.

A complete cost analysis research is given by (Govind and Tiwari, 1984) [56].

If “P” is initial investment of SAHP, “r %” as annual rate of interest, “n” as a number of useful years to which system will perform and “S” as salvage value of the SAHP then,

$$\mathrm{CRF} (\mathrm{Capital} \mathrm{recovery} \mathrm{factor})=\frac{r{(1+r)}^n}{{(1+r)}^n-1}$$

(20)

Final annual cost of system = (CRF) P

$$\mathrm{SFF} (\mathrm{Sin}\mathrm{king} \mathrm{fund} \mathrm{factor})=\frac{r}{{(1+r)}^n-1}$$

(21)

Annual salvage value = (SFF) × S

(22)

Annual cost = First annual cost + annual maintenance cost − annual salvage value

(23)

For SAHP Materials

The cost break-up for SAHP has been given in

Table 9. Analysis of costs for SAHP.

	Materials	Cost in India Rs.
(a)	SAHP parts (For 1.36 m2 collector area)
	Compressor (Hermetically sealed 1 unit)	6000
	Copper plate (1.3698 m2)	1000
	Copper tube (25 m)	1400
	Refrigerant (1.2 L)	1200
	Matt black paint (800 mL)	400
	Aluminum frame (1060 mm × 1510 mm)	4000
	Water tank	3000
	Insulation	2000
	Control panel	1000
	Brazing charge	1000
	Labor	2000
	Glass glazing (1000 mm × 1450 mm × 5 mm)	2000
	Total cost	25,000
(b)	Salvage value
	Salvage value of SAHP	4000

.

• P = Rs.25,000
• S = Rs.4000
• Assuming n = 15 years, r = 12% and maintenance cost = 10% of total cost,
• The cost calculation can be done as follows
• CRF = 0.1467
• SFF = 0.0268
• The Final annual cost of system = CRF × P = 0.1467 × 25,000 = Rs.3667.5
• Annual salvage value = SFF × S = 0.0268 × 4000 = Rs.107.2
• Annual maintenance cost = 10% = 0.10 × 3374.1 = Rs.366.75
• Annual cost = 3667.5 + 366.75 − 107.2= Rs.3927.05

So, payback period of this system is six years and four months.

The

Table 10. Comparison of energy consumption of SAHP and electric heaters.

S. No.	Volume of Water (Liters)	Change in Temperature (°C)	Solar Intensity (W/m2)	(a) Energy Consumption in SAHP System (kWh)	(b) Energy Consumption in Electric Heater (kWh)	(b − a) Save in Energy (kWh)
1	60	25	244–683	0.4	1.75	1.35
2	60	25	699–857	0.3	1.75	1.45
3	60	20	432–0	0.7	1.4	0.7
4	45	25	635–740	0.3	1.31	1.01

compares electricity consumption in the SAHP system and electricity consumption in electric heater. In the first case, when solar power is in between 244 W/m² to 683 W/m², then energy consumption is 0.4 kWh with energy consumption by electric heater is 1.75 kWh. The total saving during this is 1.35 kWh. As in the second, third, and fourth cases, electricity saving is 1.45 kWh, 0.7 kWh, and 1.01 kWh.

So, from the Table 10, it is concluded that when solar intensity is more than 150 W/m², this system will work efficiently and will improve building efficiency [47,57,58,59,60,61,62].

5. Experimental Error

The experiment’s measured values weren’t precise. These are impacted by the numerous mistakes’ variances. Errors come in two types: systematic error and random error. Instrument mistakes and environmental errors are the causes of systematic mistakes Random mistakes occur as a result of random and unexpected fluctuations in the experimental settings, such as temperature, voltage supply, mechanical vibrations in the experimental set-up, and so on, as well as personal errors by the observer collecting data. [63].

During the experiments, the measurement instruments’ error is calculated.

• Percentage measurement inaccuracy in intensity = 2%
• Percentage temperature measurement error = 0.3%
• Percentage inaccuracy in measuring water amount = 0.025 %
• Total percentage error for the SAHP = 1 × 2 + 4 × 0.3 + 1 × 0.025 = 3.225%

Total error in process is 3.225% which is within the acceptable range of experimental study.

6. Conclusions

This study aims to assess SAHPSWH’s performance and determine the optimum configuration for composite climate of India. The following are the major conclusions:

During the experiment, it has been observed that COP of experimental setup increased along with increase in solar radiation.

In case of flow rate of hot water, it has been found that at an average solar radiation of 308 W/m², the temperature of 18 L of water can be increased from 15 °C degree to 41 °C degree in a time frame of 60 min. The COP of the system in this case has been calculated as 3.835.

This model can be used as a best energy saving water heating system in sustainable buildings. Especially, prominent for regions with a composite climate of India. The present study has verified that SAHP water heating system as correctly planned and operated, it is extremely dependable.

In future the study can be extended to use of advanced tools ANN, fuzzy logic to analyse flow sensors application in buildings [63,64,65,66], advanced coating materials for photo voltaic applications and their thermal contact conductance analysis for roof-top solar plants & window paneling [67,68,69,70], nano techniques for energy conversion and storage devices with special emphasis on high performance piezoelectric nanogenerator for energy harvesting [71,72] in sustainable buildings.