ABSTRACT - Shodhganga

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ABSTRACT
In the quest for an energy conservative building design, there is now
a great opportunity for flexible and sophisticated air conditioning systems
capable of addressing better thermal comfort, Indoor Air Quality (IAQ) and
energy efficiency that are strongly desired. Most of the software Airconditioned buildings operate for a majority of hours at part-load conditions.
As people spend more number of hours indoors, research on indoor air quality
and energy conservation have become imperative. The present Conventional
Chilled Water (CHW) based air conditioning systems are less effective at
part-load conditions.
But the Variable Refrigerant Volume (VRV) Air-
conditioning (A/C) system has aspects like low energy consumption, low cost
and less space requirements. The application of the inverter air conditioner for
commercial and residential purposes becomes increasingly wide owing to its
low energy consumption and its capacity to maintain comfort. With a growing
emphasis on adaptive flexibility, the part played by optimum controls has
become a vital aspect in deciding the overall system performance.
Applications of intelligent control like Fuzzy Logic Controller (FLC)
especially to combined Variable Refrigerant Volume and Variable Air
Volume (VRV-VAV) air-conditioning systems, have attracted more interest
in recent years than classical control systems.
The variable air volume (VAV) system is a recent innovation in
Heating, Ventilating and Air Conditioning (HVAC) design. It is aimed at
reducing building energy consumption while maintaining the primary role of
air conditioning. The temperature of a space is maintained at the desired level
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by counteracting the cooling load with a certain volume flow rate of supply
air at certain supply temperature. A small temperature difference requires
lower compressor power and a large volume flow rate requires more fan
power. If the same load is met by a low supply air volume flow rate at a large
temperature difference, then it will require less fan power and high
compressor power. A low supply airflow rate leads to poor temperature
distribution in the space. Hence, a certain combination of supply airflow rate
and temperature is required so that the total power requirement will be
minimal. In a Constant Air Volume (CAV) system, the volume airflow rate is
kept constant at its maximum value and the supply air temperature is varied to
counteract the cooling load, which limits the scope of optimizing the CAV
system. But in the case of the VRV-VAV air conditioning system, both the
airflow rate and temperature of supply air can be changed, which gives scope
for optimizing the fan power and compressor power. The performance of the
HVAC system can be improved through the optimization of the supervisory
control strategy. Genetic Algorithms (GAs) can adjust the variable air volume
HVAC system controller set points, to maximize the overall operating
efficiency.
A healthy indoor environment with sufficient fresh air is a
prerequisite for the well being and high productivity of the occupants of the
building. The CO2 based DCV optimizes and resolves the traditional conflict
between reducing ventilation to save energy while maintaining adequate
ventilation for air quality, in summer conditions. Therefore, in air-conditioned
spaces where occupancy levels vary, CO2 based DCV can prove to be an
energy efficient method for meeting ventilation needs while maintaining
better IAQ. Further, an economizer cycle can be used to save cooling energy.
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This design scheme takes advantage of the cold climate to supplement or
satisfy the cooling load. When a Proportional Integral and Derivative (PID)
controller is adopted, it will respond only to linear variations with single input
and single output operations. It also needs higher order mathematical models
to design the conventional controllers and these problems can be solved by a
FLC.
Simulation and experimental works have focused on Energy
conservation, thermal comfort and IAQ in VRV-VAV air-conditioning using
the Genetic based fuzzy logic controller. A scale model of software laboratory
building was developed for the experimental work to analyse different cases.
Simulation was also carried out using the MATLAB-Simulink for the scale
model. The results were compared with the experimental data and the
deviation was within acceptable limits.
In the present work, a new fuzzy based simulation model of the
VRV system blended with the VAV system has been developed based on a
dynamic MATLAB-Simulink environment and the energy utilization of
VRV-VAV air conditioning system was also analysed. The simulation model
was built based on the control strategies required to control the rotational
speed of the compressor, the mass flow rate of the refrigerant to the
compressor and the desired flow rate of supply air to be delivered into the
conditioned space. The simulation analysis has been executed for summer and
winter conditions that included the fixed ventilation, the DCV and the
combined DCV and Economizer Cycle (EC) techniques. The simulation
results infer that the VRV-VAV A/C system controlled by the fuzzy logic
methodology effectively yield a maximum of 59% and 86% of per day energy
saving in summer and winter conditions respectively. The simulation results
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show that the control strategy and algorithm are feasible. The developed
system has been optimized using the GAs approach. The results obtained
using the GAs inevitably expressed that the VRV-VAV A/C system on
optimization produced an appreciable increase in the energy savings potential
of the system.
Further, an experimental analysis was performed to investigate the
inherent operational characteristics of the combined VRV-VAV air
conditioning system under the fixed ventilation, the DCV and the combined
DCV and economizer cycle techniques, for two seasonal conditions in India.
The temperature, velocity, RH, pressure and CO2 measurements were made in
the existing software laboratory. The scale model of the original set-up has
been made for experimentation by varying the locations of air terminal
devices, VRV system, VAV boxes, Genetic based FLC and required sensors.
The effect of thermal comfort, IAQ and energy savings for two seasonal
conditions have been studied and presented.
The test results of the VRV-
VAV A/C system for each technique are presented. The test results infer that
the VRV-VAV A/C system with combined DCV and EC controlled by the
genetic based fuzzy logic methodology effectively yields a maximum of 62%
and 86% of energy saving at part load in summer and winter conditions
respectively. The energy saving per day is obtained a maximum of 49 % and
68 % in summer and winter conditions.
The results of the present investigation have proved that the VRVVAV air conditioning system with the combined DCV and economizer cycle
using a Genetic based Fuzzy logic controller is an efficient energy saving
technology along with thermal comfort and IAQ.

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