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Contents

Abstract.

Indoor Unit.

Outdoor Unit.

Literature Review..

Use of Variable Speed Compressor.

Thermal performance of a building.

Aims and objectives.

Theoretical content.

Implementation.

Analysis.

Applications.

Conclusions and recommendations.

Future work.

References.

Abstract on Variable Refrigerant Volume System

Population of the world is increasing and there is a number of residential and commercial buildings are being constructed with time. With the increase in number of buildings there is also a tremendous increase in the requirement and use of HVAC systems. Previously used HVAC system consumes a large amount of electricity and the losses in the systems are much higher. As there is a large increase in the electricity requirement so the companies and countries are considering the more efficient electrical devices consuming less electricity and providing better results. In this project we have considered two types of cooling systems for the building which are HVAC and variable refrigerant flow of building layout. We will design the systems and compare their properties and effects on the environment. Our major focus in this project is to implement the use of VRF for the buildings and to explore its properties benefits and installation in the buildings for the sake of heating and cooling. The report also includes the improvements required in the future and the comparison of different types of VRF systems used in building design.
Introduction

The variable refrigerant volume system is considered as a larger sized version of the split air conditioning system which comprises of a compact configuration of condensing unit that is air cooled and located outside further linked to different unit of fan coil placed inside. The compressor possesses varying speed and makes the refrigerant pump through a pipe network into the evaporators at the terminal side. The flow rate of the refrigerant is then regulated by the system into the terminals in accordance with the demand of cooling of the specific zone that the indoor unit serves (Zhou, Wu, & Wang, 2008).

There are various simulation programs of building energy which are available as well. But there is no performance evaluation related to the refrigerant volume system which can be incorporated in these programs. A complete simulation program regarding building energy was developed by the government of United States referred to as Energy Plus. This program basically comprised of a simulation engine with features which included time steps, data structures for input and output, functions related to HVAC and integrated zone simulations based on balance of heat and mass. These features are added to assist the third party module as well as the interface development. Through implementation of empirical tests, a number of validated work as well as researches on the interaction of energy between the infrastructure of the building and the heating, ventilation and cooling systems (Karunakaran, 2010).

For over a decade there have been numerous researches and innovations in the fields of heating, ventilation and air conditioning. The main factors that are considered for the HVAC system include thermal comfort, controls of HVAC and saving in energy along with quality of the indoor air. The role that is provided by humidity regarding the acquisition of thermal comfort along with optimum quality of the indoor air can be acquired through the accurate monitoring of the temperature of the supply air as well as the supply of the rate of air flow on the basis of fluctuated conditions of thermal load (Zhao, 2016).

The incorporation of energy in the air conditioning systems is considered to be a vital part of the requirements associated with the operational functioning of the building. The engineers related with HVAC systems on the other hand have begun to go over different design concepts in order to bring about a minimization in the usage of energy in handling air systems. The drawback associated with the constant volume systems is the fact that they use up more energy. On the other hand variable configuration of volume systems have come up as newly developed and optimum systems for energy conservation for the air conditioning of building (Zhao, 2016). Among the most popular applications related to HVAC systems the variable configuration application of air volume is developed for the provision of low cost of energy, low level of maintenance, less waste of thermal energy and optimum thermal performance along with optimum quality of indoor air. These systems are considered to efficient through the analysis of design. The variable refrigerant system developed initially in Japan in the year 1982 and is now employed worldwide. The volume of the refrigerant is modulated by the variable refrigerant volume system in accordance with the requirements related to capacity. The savings in energy can be acquired through a variable refrigerant volume system and it can be further based on the load efficiency of the high part of the system (Aynur, 2010).

The total amount of energy that is consumed in buildings is increasing with a rapid rate over the recent years. This consumption also includes about 40% of the total consumption of energy in the countries and regions that have developed. According to the relevant researched the system of heating, ventilation and cooling uses up about 50% of the energy that is consumed by the buildings that possess comfortable requisites. The accurate prediction model for energy consumption is considered of vital importance to both the utility companies as well as the owners of the building. Along with this many researches are focusing on the consumption of energy of the HVAC systems (Zhou Y. W., 2007). It has been inferred that a number of models have been brought forward for the accurate prediction of consumption of energy in various kinds of buildings. These various models can be further classified into two methodologies which include a methodology based on mechanism which is an energy simulation program as well as data based methodology that included data mining. The new design can be facilitated through energy simulation program of various kinds of buildings if the relevant information is available. It mostly includes both the forward and inverse nature of modeling. Another alternative of inverse modeling is driven by data from which it is inferred that it is a hybrid integration of both the relevant data and energy simulation program (Liu, 2010).

Due to the increasing demands of thermal comfort as well as a healthy environment of the living areas or buildings, the feature of air conditioning for both the commercial as well as residential buildings has become an important requirement. The relevant concept of the application of air conditioning has extended its range from supplying to one unit of one house to various independent units for different zones in one house.

A multi split air conditioning system includes the technology of the variable refrigerant volume system and can comply with the specific needs for installation of several units with less amount of space. The main reason for this is that the specific system comprises of one outdoor and multiple units for indoor location. The multi split variable refrigerant volume consists of a refrigerant system which includes the varying the flow rate of the refrigerant through the inclusion of compressor at variable speed along with electronic expansion valves that are situated in every indoor unit. This is done to match the relevant space cooling or heating load for the maintenance of the specific air temperature of the zone at the set temperature of the indoor (Shi, 2003).

Indoor Unit

The indoor units in a typical configuration of multi split variable refrigerant volume system are connected to the unit located outdoor in parallel configuration through incorporation of refrigerant pipes. Through bringing about an adjustment in the four way valve which is located in the outdoor unit, the refrigerant system can be made to operate in reverse. This can also lead to the multi split variable refrigerant volume being used for both the application of air conditioning as well as heat pumping.

For the cooling operation, the refrigerant that is discharged from the compressors is made to flow in the heat exchanger at the outdoor unit through the four way configuration valve. The refrigerant which is at low temperature and high pressure level is the throttled down to a low pressure value by EEV after which it enters the heat exchanger at the indoor unit. The heat is absorbed by the indoor unit from the indoor air which cools it. The refrigerant which is now superheated and at low pressure is made to go back to the compressors after which the cycle is finished (Yu, Yan, Sun, Hong, & Zhu, 2016).

For the heating mode, the path taken by the refrigerant is reversed by the four way valve. The refrigerant that is discharged from the compressor enters the heat exchanger of the indoor unit. The heat is then expelled off by the indoor unit to the indoor air which results in further heating. The refrigerant that is then at a low level of temperature and at high pressure is then reduced to a low value of pressure by the EEV. The low temperature refrigerant which is now at low value of pressure goes into the outdoor unit heat exchanger which is employed as evaporator. The superheated refrigerant at low level of pressure is then sent back to the compressors after which the cycle finishes (Goetzler, 2007).

Outdoor Unit

The outdoor unit of a multi split configuration of the VRF system comprises of two or three compressors, among which one has a variable level of speed. The compressors possessing variable speed that are driven by inverter provide the feature of wide capacity modulation along with high efficiency for the multi split VRF systems. The frequency of the inverter varies with the range of 20-30 to 105-120 Hz respectively. By bringing about variations in the frequency of the inverter, the capacity of the outdoor unit changes in accordance with the varying of the flow rate of refrigerant mass that is discharged for the requisite matching of the total cooling or heating that is required. The multi split VRF system can respond to the fluctuations regarding the conditions of space load. The outdoor units are also available in sizes that range up to 70 kW. Until the year 2000, all the multi split configurations of the variable refrigerant volume were cooled but this application was further extended through the introduction of versions that were water cooled (Yu, Yan, Sun, Hong, & Zhu, 2016).

In accordance with the definition, the cooling of the air cooled multi split configuration of variable refrigerant volume systems is done through ambient air whereas the water cooled systems are cooled through water. The water cooled multi split configurations of the variable refrigerant volume systems consist of heat exchangers of the plate type system. Similar to the infrastructure of air cooled multi split VRF system, the outdoor unit of the water cooled system provides the feature of being easily connected with many indoor units. The water cooled VRF system is different from the air cooled VRF system on the basis of the fact that the requirements is that the outdoor unit be linked with the cooling tower and placed indoors. There is no specific requirement regarding the length of pipe for the water cooled multi split VRF system. The requisite connection between the circuits of the refrigerant as well as water loop is provided by the plate heat exchangers. The overall temperature of water that is provided to the plate heat exchanger from a cooling tower lies within the range of 10 to 45 degrees Centigrade. Same as the air cooled multi strip configuration of variable refrigerant volume systems the refrigerant lines provide relevant connection of the outdoor unit with indoor unit (Zhou Y. W., 2007).

The indoor unit of the multi split VRF system comprises of heat exchanger, temperature sensor, fan and EEV. A number of different indoor units can be connected to one outdoor unit in the VRF technology. A number of different indoor units can be incorporated which possess varying capacities and configurations. By bringing about variations in the frequency of the inverter, the capacity of the outdoor unit changes in accordance with the varying of the flow rate of refrigerant mass that is discharged for the requisite matching of the total cooling or heating that is required. The multi split VRF system can respond to the fluctuations regarding the conditions of space load. The multi split variable refrigerant volume consists of a refrigerant system which includes the varying the flow rate of the refrigerant through the inclusion of compressor at variable speed along with electronic expansion valves that are situated in every indoor unit. Among the most popular applications related to HVAC systems the variable configuration application of air volume is developed for the provision of low cost of energy, low level of maintenance, less waste of thermal energy and optimum thermal performance along with optimum quality of indoor air. These systems are considered to efficient through the analysis of design (Zhou, Wu, & Wang, 2008).

Literature Review of Variable Refrigerant Volume System

The energy usage related with the system of variable refrigerant volume has been explained and a new variable refrigerant volume module system was developed on the basis of the simulation of Energy Plus. Along with this the consumption of energy of variable refrigerant volume system with the systems of fan coil and fresh air as well as variable air volume were investigated and further analyzed. From the results of the conducted simulation it was inferred that the potential of saving of energy that was expected for the variable refrigerant volume system was better than the VAV as well as FPFA systems respectively Invalid source specified.. The significance of a multi evaporator configuration of air conditioner that featured the optimum technology of variable refrigerant volume was explained in order to meet the conditions related to the comfort of the occupant. In this specific work the speed of the compressor was modulated followed by the altering of the valve opening of the electronic expansion. The strategies that were considered for control were pressure of the suction and temperatures of room air.

It was inferred from the implemented controllability test that both the control strategy along with the algorithm was viable Invalid source specified.. A calorimetric test along with analysis was implemented on the system of variable refrigerant volume system. This was followed by the estimation of the overall performance of the system in order to commence with the identification of the heating as well as cooling emission of every indoor unit. Along with this the thermodynamic properties possessed by the refrigerant were also assessed Invalid source specified.. Another research work analyzed both the flexibility as well as retrofit capability of the variable refrigerant volume system which could in turn be integrated virtually into any building whether it is old or new, through bringing about minimum amount of alterations in the structural infrastructure. Along with this it was inferred that the variable refrigerant volume systems could incorporated a single unit for condensation which could be further connected to the multiple units placed indoor possessing varying levels of capacity and overall configuration Invalid source specified.. In another work a control strategy comprising of multiple input as well as multiple output for the direct level expansion system was developed for controlling of the temperature level of the indoor air along with humidity.

The variations in humidity were brought about through changes in the speed of the compressor as well as the speed of the supply fan. The artificial decoupling of the temperature of the indoor air that was coupled was eliminated through the implementation of the control strategy. It has been reported that the specific sensible heat ratio of the equipment of an A/ C unit could be easily changed. This can be done through modulation of compressor along with the speed of the supply fan for equalization with the space SHR for effective controlling of temperature the indoor air and humidity Invalid source specified.. The modeling in dynamic configuration related to individual components that exist in DX VAV A/ C systems was demonstrated. The dynamic model was developed on the basis of the principles related with the conservation of mass and energy and through incorporating the correlations that could effectively define the operational performance of the components of the system which have been tested in the field or acquired from different manufacturers. A comparative analysis was conducted between both the steady state and transient state responses of the model as well as experimentation on the basis of the five operational parameters. Through usage of the data acquired through experimentation the dynamic model was approved and validated. In order to comply with the conditions of the thermal load an investigative analysis was also carried out on the operational characteristics of the valve operated through electronic expansion on the basis of flow of refrigerant Invalid source specified..

Use of Variable Speed Compressor

The potential usage of compressor possessing variable speed was determined. The compressor functioned on a controller that provided the enhanced conservation of energy, capabilities regarding the matching of load along with the feature of thermal comfort for the application of air conditioning. On the basis of data acquired from experimentation it was determined that the energy savings from the system of air conditioning were viable. This also provided the explanation that the feature of thermal comfort along with conservation of energy can be acquired through accurate selection of the parameter of gain for specific controller. The controller that has been incorporated in this work was the proportional and derivative configuration type. The concept related to the DCV and ventilation techniques of economizer cycle have acquired significance in the modern applications of HVAC. The main reason for this is that these techniques can lead to the provision of extensive conservation of energy on the cooling systems as well as the ventilation systems Invalid source specified..

A split signal strategy control was developed that provided the required control of the outdoor air possessing minimum drop in pressure in economizer damper followed by conservation of energy on both the supply and return fans. The strategy includes two dampers at full open along with controlling of the outdoor air through incorporation of one damper. These results in a drop in the pressure of economizer dampers along with an overall reduction in the consumption of power by both the fans specified for supply and return. Through incorporation of a model that was previously developed the simulation was conducted for analysis of the rates of airflow along with pressure values in the air handling unit as a function of the damper positions. Validation related to the control strategy along with the developed model was carried out through the annual amount of data acquired on the existing variable air refrigerant system Invalid source specified..

Another research work involved the proposition of the methodology for the estimation of the generation rate of carbon dioxide along with the relevant flow parameters by making use of a model for the prediction of the carbon dioxide concentrations in the return air within the environment premises of a commercial building. For this two techniques were analyzed for the estimation of parameters by making use of simulated data. All the specific carbon dioxide concentrations were accurately estimated by every strategy ensuring that every technique was different on the basis of the identified parameters. In accordance with the site type that was selected the errors related with the carbon dioxide concentrations that were predicted were based on the coefficient related to variation which lied within the range of 4 to 15 percent. The total duration of time that was determined for the concentrations of carbon dioxide were assessed to be within the specified range as well as and was in compliance with the measured data of the field. The determination of carbon dioxide levels within the premises of the commercial buildings that make use of DCV technique and equipped with packaged system of HVACC have been provided followed by identification of a viable model for prediction of space carbon dioxide levels Invalid source specified..

Thermal Performance of A Building

The thermal performance of a building has also been analyzed followed by implementation of predicted mean vote index for assessment of the comfort of the occupants. The techniques that have been considered to carry out the simulation of the building include cooling technologies using up low energy like chilled ceiling, pre-cooling techniques along with economizer for both the seasons of summer and winter. It was inferred from the results of the simulation that optimum thermal comfort was provided by the technology of chilled ceiling to the occupants of the building in the perspectives of temperature as well as relative humidity. These results were then further approved through the data that was measured acquired on the days of typical design in the conditions of both seasons Invalid source specified.. Another research investigation included the thermal performance of the single zone building and the relevant energy requirements for both the heating as well as cooling seasons by making use of a thermal network model. The variations that have been provided are the temperature of the indoor area followed by establishment of energy requirements for fixed configuration of ventilation along with those ventilation methods that are controlled by temperature. The results obtained after simulation of both the cases showed that the cooling as well as heating loads both gets directly affected by the overall influence of formation of slab structure, control of indoor temperature and ventilation Invalid source specified..

Another work focused on resolving the control issues related with combination of DCV control with economizer through implementation of strategy of robust control. For this digital controllers that were provided with AHU of building were implemented to conduct extensive analysis on the control strategies. This also included the simulation process by using dynamic as well as realistic models. The control strategies related with the fixed level of ventilation as well as DCV functioning at economizer ventilation mode was tested for a total of four different conditions of weather. The control strategies that were implemented were observed to have a better level of IAQ and conservation of energy under different conditions of load. This has been under discussion by many researchers that concept of fuzzy logic control can be incorporated for solving different HVAC applications Invalid source specified.. The importance of incorporating fuzzy programming for a centralized application was explained for provision of proper maintenance of the temperature of indoor area and relative humidity factor to comply with the conditions of comfort. The inputs information for the fuzzy programming was acquired from sensor pairs that were installed for temperature as well as measurement of relative humidity while another sensor pair was installed in every room that was served by the centralized system without having to move the thermostat to the AHU room Invalid source specified..

It has been suggested that the temperature of the supply air in the air conditioning system can be properly controlled through the implementation of the prediction methodology that is based on the fuzzy model. The determination of the relative functions for the fuzzy control was classified through the fuzzy decision making schemes. For the prediction of expected behavior of the system the generalized neurofuzzy model was also developed. This provided the prediction of the behavior of the system that was expected through incorporation of training data that was acquired from the simulations that were implemented for cooling coils. It was suggested and inferred from the test results that through minimum activity of the control, the temperature of the supply air could be controlled through usage of fuzzy control logic for both high as well as low airflow rates Invalid source specified.. Another research involved the effective monitoring of the thermal conditions of the indoor area of buildings through implementation of fuzzy logic for controlling. Moreover the fuzzy logic control assisted in the solving the issues relevant with the characterization of PMV index and provision of optimum control over thermal environments Invalid source specified..

The energy consumed in the building sectors of worldwide is 30% of total energy. The consumption of energy exceeded in commercial sectors of developed countries. Variable refrigerant volume system is a type of heating, air conditioning and ventilation in the buildings. Usage of variable refrigerant volume system in Building 37 is made by Mitsubishi Heavy Industries. This system is practically installed with two pipe system in 2011. The objective of this installation is to understand Variable refrigerant volume system and reason of its problem in Building 37,Aagensi Nuklear Malaysia.

VRV is a technology that alternates the refrigerant volume in a specific system to meet a building’s requirements. Minimum amount of energy is enough to maintain a set temperature in the system and ensure that system autocratically shuts off when no occupants are detected in the room.

 The first multi split air conditioner for buildings was developed by Daikin in 1982. Individual control zone for air conditioning was a big challenge before arrival of VRV (Variable refrigerant volume). The launch of VRV changed the expectations for air conditioners built specially for commercial buildings. Water cooled VRV air conditioner was developed by Daikin in 1990. VRV air conditioner achieves heating and cooling simultaneously with heat recovery technology. Daikin enhances its technology according to need of people of different regions. Later on, highly heat efficient pump developed for VRV air conditioner. The system is built for regions where temperature drops as low as -25.

Aims and Objectives of Variable Refrigerant Volume System

In this project our major aim was to find if the variable refrigerant volume system is energy efficient or not. The focus was on the idea of controlling the operation of air propulsion fans in central air conditioning systems and also the calculation of outdoor unit size required for the heating and cooling process of a building. Define the pressure and flow difference.

The research aims to calculate the pressure and flow difference for centrally air conditioned system and then by comparing the power efficiency of separately installed air conditioned systems and a variable refrigerant volume flow system for a building to find the less energy consuming system and its different impacts in the design and structure of building. The major focus of this research was to observe compare and verify the best air conditioning system for the building in terms of less energy consuming, reliable and good in efficiency. In this perspective we different type of variable flow refrigerant system were compared with the centrally air conditioned system. While designing the air conditioning system for any building it is very necessary to calculate the area requirement of refrigeration in total number of tons and also the calculation of space in cubic meters for cooling and heating of the building. The use of variable refrigerant is also important because we can calculate the area and thus by the available information of total space occupied by the building we can calculate the total ton of refrigeration and thus by using an outdoor single unit of variable unit refrigerator we can fulfill the building refrigeration requirements as a single outdoor unit. (Aynur, 2010)

Theoretical Content on Variable Refrigerant Volume System

VRF flow systems, such as air conditioners, aim to cool the air in one or more rooms by drawing internal heat from the house and distributing it outside. Some of the variable cooling media can also be used in the heating mode. Unlike domestic air conditioners, variable cooling media can be connected to a large number of indoor units. Usually used in shopping malls, administrative buildings, hotels and hospitals. There are several follies that control the approved basic air conditioning system, and they are:

  • First: Control the vent valve opening in each room according to the need for cooling or heating for a scoop.(Liu, 2010)
  • Second: Control the compressor speed according to the external temperature, the temperature of the cooling medium, and the pressure in the tubes.
  • Third: Control the fan speed according to the static pressure in the airway.
  • Four: Control cold and hot water valves according to the desired temperature.

 In order to conserve the electrical energy consumed, efforts to improve control fools should always be sought mentioned above, and we will focus on controlling fan speed.

The fan will greatly reflect the lease capacity according to relationship

P2 / P1 = (N2 / N1)

Where:

N: Fan speed.

P: the electric power of a fan.

Energy consumption, but control by

The VAV variable air conditioning system achieves energy efficiency. The pressure sensor alone does not achieve optimum working efficiency for the supply fan. The fan speed control method depends on setting value. A specific reference for a pressure in the airway and when this value is exceeded, it sends a command to a fan to reduce the speed, so that the pressure returns

To the reference value, the pressure is related to velocity according to equation (2) (8):

dP2 / dP1 = (N2 / N1)

Where:

dP is pressure difference.

However, in partial loads, when the vents are closed in some unoccupied rooms, the flow can be achieved. What is required is when pressure values are lower than the specified value, and this saves savings in the consumption of electricity. This has been verified and

Experimental in our research, so another parameter will be introduced to control the fan speed so that it will produce the desired flow at a lower level which is possible, therefore, to save on the consumption of electrical energy.

Two parameters were adopted to determine the required fan speed, which is pressure and flow, for specific flow values determine the appropriate fan speed to ensure the desired flow at the lowest possible pressure, thus at the lowest fan consumption.

It has the third determinants of flow, pressure and fan speed, and the presence of continuous changes in the flow by opening the vortex valves in the air-conditioned rooms are dependent on the variable heat loads, as there is no clear mathematical relationship between these three parameters and here. A floating controller can be used to inflate pressure, flow, and fan speed exits and have been designed and piloted in the laboratory. (Yu, Yan, Sun, Hong, & Zhu, 2016)

Implementation of Variable Refrigerant Volume System

After performing a literature review I got familiar with different types of air conditioning equipment, processes, their features and their performances. I compared the properties of three types of VRF which are variable speed compressor plus fixed speed compressor, single variable speed compressor and multiple variable speed compressor and single variable speed compressors. I have selected the variable speed compressor plus fixed speed compressor for the implementation in this project so I did all the assumptions, calculations and designing according to this specific unit. The reason behind the selection of this specific unit was that it has two operational compressors. One is variable and the second compressor is fixed speed. (Shi, 2003)

It behaves in such a way that when the cooling process of building is started, variable speed compressor starts and ramps up with the requirement of building and once it reaches to its maximum value, the constant speed compressor turns on while shutting down the variable speed compressor and it starts working again when it needs to be turn on to meet the requirements. Next stage required me to do the practical implementation of the concept of variable refrigerant flow of a building layout. The software that I used for the implementation was AutoCAD which is a basic and well-known software being used for creating building layouts and structural diagrams. In which I designed two basic structures of buildings having four rooms at ground floor and four rooms at first floor. The drawings were drawn in 3-D environment of AutoCAD.

There were few major factors which were considered during the designing of layout including the building orientation, the peak season load requirement and type of load either heating or cooling and the distribution of the load in different zones of the building. After drawing the layouts of floors in AutoCAD a complete VRF flow system was designed in which we installed and outer unit of. Here is the flow diagram of a variable refrigeration flow system for a building in which a single outdoor unit is connected with a number of indoor unit and fulfill the necessary heating and cooling requirements of indoor units installed in different sections of the building. If more heat or cooling is required in a specific section then it can be provided to that section by increasing the speed of fan in that section. Similarly by controlling the speed of fan and using a variable outdoor compressor unit we can reduce the power consumption and can use it more efficiently.

Flow Diagram of VRF

Below is the diagram that shows our proposed model in which we have designed the VRF system for a building and we have used a single outer unit and distributed the energy in the through the pipes in different zones of the building. Every single zone has its own different energy requirement so we have calculated the area occupied by the sections of the building and then calculated their tons of refrigeration requirements. This calculation helped us in better designing of the pipeline outer unit and to improve the performance of the system. The building layout also includes the orientation and we kept in mind the maximum requirements season while designing this system. (Zhou Y. W., 2007)

We also designed another building layout for the calculation of power consumption units of outdoor HVAC and also their efficiency of the system. In this part I designed another building layout having four zones and same area as in our previous design. We connected four different outdoor units using ducts for every single unit to link it with the indoor unit. The second system was also design for the same space and area of the building requiring same tons of refrigeration in order to compare the performance of each part. (Zhou Y. W., 2007)

Analysis of Variable Refrigerant Volume System

After the designing of the system for two identical buildings we analyzed the resulting layout and the performance of the system. The VRF system designed for a building was more energy efficient as compare to the HVAC system. It is more customizable in terms of installation and consumes less energy. The losses in the VRF system were much less than the HVAC and it setup was more comfortable and provides a better indoor placement. One of the best things regarding the VRF was its indoor zoning in which we divide the indoor units into a number of zones and then it is easy to heat and cool any specific area or zone. VRF system is less noisy as compare to the HVAC and it has very good control in the energy distribution. (Zhao, 2016) There are multiple compressors having variable speed so they can be easily adjustable and the cleaning process of VRF is much easier than the HVAC and it does not occupy a large area. While in case of HVAC a number of outdoor units are used which occupy a large area and they require cleaning

Applications

variable refrigerant flow of a building is usually used in restaurants buildings and other facilities where a specific level of heating and cooling is maintained and all indoor units are either working in heating mode or cooling. Variable refrigerator flow systems are used in large buildings and facilities such as offices, shopping malls banks and schools where the system is designed for the simultaneous heating and cooling. There are a number of advantages related to the use of VRF system for the heating and cooling of a building. This system is very efficient in heating and cooling of the building while saving the energy up to 30% as compare to the individual HVAC system for the different parts of a building where a single unit is used for the heating or cooling process of any specific room. They have also better efficiency than relative to the systems using constant air volume and variable air volume system with gas heat. (Zhou, Wu, & Wang, 2008) Since there is a controlled operation of the fan in VRF system so its output efficiency can be varied from 10% to 100%.it has a very good control on zoning and can provide heat and cooling simultaneously. The losses are reduced due to the reduction in ductwork that can cause duct losses which are dominant in conventional HVAC systems and this loss is approximately equal to the 20% of its efficiency. Here is the graph plotted according to the energy efficiency ratio and the load on a VRF system. (Shi, 2003)

As it is clear from the graph given above that in VRF and traditional HVAC system that how the energy efficiency of both the systems vary from no load to full load. Plain curve is for the HVAC system and the dotted curve is for VRF system.

Conclusions and Recommendations on Variable Refrigerant Volume System

Through this study, we show the importance of the subject of building control to provide energy consumption and air conditioning better control and improved control. The VRF system has well features providing power and comfort conditions, although features are still in progress

Spread in Syria So the POE control mechanism was explained and new suggestions were made to use the floating controller to improve POE control in proportion to the climatic conditions in the area. The research shows that the use of the proposed technologies applied to the laboratory model shows that the application of these technologies maintains the optimum consumption of fan power to give the required flow with the lowest possible capacity, and these methods can circular blindly to the rest of the air conditioning system making floating processing done within the computer gives a high processing speed. The electrical power is highly compared to achieved the use of controlled floating blindness laboratory model of a fan runs at full speeds and 63% compared to the use of pressure-sensitive control. In consumption electricity reaches 49% of the floor fan consumption. The study was applied to the supply fan with generalization that similarly; the study of applying this method can be studied compressor and coolant (thus achieving Kirby in the overall system of air conditioning and refrigeration. (Karunakaran, 2010)

Future Work of Variable Refrigerant Volume System

During this time of global warming where the temperature of the world is increasing and heating and cooling of the large buildings has become a very important part of building design and layouts there are few things to be done in the heating and cooling process in order to avoid the environmental pollution and damages caused by the excessive use of HVAC. The cost of installation of the VRF system is much higher than the other traditional HVAC system and it needs a backup in case of any issue in the system. These cooling devices emit carbon mono oxide and other gasses which are causing the environmental effects and damaging the ozone layer so it should be considered and a VRF system should be improved to reduce the emission of these gases to avoid the environmental effect. (Zhao, 2016) There are few other technologies that can overcome these traditional ways of heating and cooling in future such as magnetic cooling in which a magnet is brought in a magnetic field where it heats up and when it is brought to a gap in the field it gets cool down by cooling the enclosed area. In this process electricity is used but the amount is much less than the technologies are being used.

Thermo acoustic is another technology that will be the future of VRF and HVAC system in which a loud speaker is used turn the electricity in a sound signal this sound signal when passes through the helium gas it pushes the gas back and forth which causes a cooling effect in the gas to get condense. Once this condensation is achieved the helium starts absorbing the heat from the environment and thus it can reduce the temperature of the surrounding. This method is very harmless and environment friendly. It will be the future of the VRF systems and will be much efficient than the previous one. More electricity efficient system should be induced in order to overcome the high use of electricity. Previous systems employ refrigerant like CFC which absorb the heat from the enclosed spaces and then expel it to the outer environment. In order to save energy the coolant fluids with solid materials such as telluride which will not have any moving part thus they will be energy efficient. (Karunakaran, 2010)World is focusing more on the use of renewable energy apparatus in order to make the buildings and area self-dependent in their energy production.

HVAC systems are mostly used in the areas where the cooling effect is required and in few cases for the heating effect in some areas. The areas where the sunlight has a good duration throughout the month such as Middle East countries, so there should be used solar energy based HVAC and VRF system in order to reduce the electricity load on the main grid. All the HVAC systems in the buildings should be replaced with VRF so that the environmental effects could be reduced. With the increase in the population of world the need of HVAC and refrigerants is increased in order to save the food and for buildings and offices. So there should be a lot of improvement in the HVAC systems in order to meet the requirements. Hybrid radiant HVAC systems should be designed for a better development distribution and energy saving purpose. There should be used techniques to absorb the gases that can harm the environment and there should also be reduction in size and weight of the outer units in order to occupy less space. VRF are the future of traditional HVAC system and all the individual units installed in previous buildings should be replaced with them to save the consumption of electricity and provide a better experience to the user while saving the environment from the damages. (Aynur, 2010)

References for Variable Refrigerant Volume System

Aynur, T. (2010). Variable refrigerant flow systems: A review. Energy and Buildings, 7(42), 1106-1112.

Goetzler, W. (2007). Variable refrigerant flow systems. Ashrae Journal, 24-31.

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