of invention
Present invention explicitly relates to the improvement of ventilation system efficiency by
optimally operating the entire air supply unit in accordance to the occupants comfort and
availability state. This invention can be applied to both new and existing ventilation system
Background of invention
Growth in demand for electricity is rising day-by-day, and at similar pace the limited stock of
fossil fuel is also getting consumed. In this regard usage of renewable energy is getting a mode;
yet this energy has not come in full fledge due to infant research and grid integrity issues.
Another way of reducing rate of usage of electricity is by adopting energy efficient equipment, or
with energy conservation measures. Among all energy consuming sectors demand of electricity
is growing at faster rate in building sector. Currently, the domestic and commercial buildings in
India consume almost 32% (-89 GW) of total electricity generated. This accounts to be the
second highest after industrial sector. India being a tropical country, in buildings major amount
(-39%) of energy is consumed by heating, ventilation and air conditioning (HVAC) system. The
HVAC system mainly comprises of fans, chiller, heating, pumps, cooling towers etc. Among
above listed fan consumes almost 34% of HVAC consumption; i.e. around 12 GW in all India
basis. There is a great scope lies to improve the fan efficiency, that would bring substantial
amount of energy saving potential. Improvement of efficiency in HVAC system can be obtained
by two methods; (i) minimization of load on system, and (ii) optimum/efficient operation of the
system.
Even today's ventilation system suffers many issues towards which no adequate solution does
exist, and even though some improvement has happened they are mainly towards pollutant
control, air quality control and to avail better luxury. Some of the major issues pertaining to
current ventilation system at commercial and residential buildings are listed below. One of the
persistent issues with HVAC system is non-uniformity in temperature distribution in space. This
happens mainly because of variation in supplied air temperature to the space and accumulation of
air. Another issue with supply air temperature is to attain the set temperature air is supplied at
relatively lower temperature (-17"C), which is unhealthy to occupant. In addition, the supply of
the air is monitored according to the thermistor setting; hence the occupant plays almost no role
in comforting his own space. In office space and residential houses, height of the roof is below
five (5) mtr, thus the conditioned air is supplied horizontally to the floor. In this situation most of
the times air get accumulated near the fan or lights, leading to wastage of conditioned air. The
widely used variable air volume (VAV) type ventilation system has addressed many of the
occupants comfort issue. Yet, it requires enormous amount of ducting system and in turn higher
pumping power. In case of displacement type ventilation system, where air is supplied at floor
level and extracted at roof level assumes homogenous distribution of pollutant in the room. This
assumption is erroneous for densely populated and furniture office spaces. Demand based
displacement ventilation system (DCDV) is introduced to improve the displacement ventilation
system. DCDV system takes care of COz concentration in the room but failed to ensure adequate
temperature and flow distribution. In mixed ventilation system air is supplied at ceiling level and
extracted at the floor level; it is found that for such case pollutants mostly stays inside the room.
The most preferred stratum ventilation system supplies air at breathing level ensuring better
comfort, but implementation of this system requires major amount modification has to be done in
the ducting system. The Regional Air Conditioning Mechanism (RACM), which is explicitly
designed for close air condition modules like bus, truck, factory etc., almost eliminates
temperature gradient between free and occupied zone. However, as the conditioned air flow is
continuous energy saving potential is slightly on the lower side. In case of Personalized
Environment Module (PEM) that offers occupant control over flow, direction and temperature
improves the productivity of employee, meanwhile makes the ducting system complex yet
efficient. Same case is with Personalized Ventilation (PV) system, where authority is given to
individual occupant that leads to lower efficiency. The Variable Refrigerant Flow (VRF) system,
which uses refrigerant as cooling and heating medium offers higher efficiency and occupant's
control over building interior temperature control. However, this system requires additional
inverter to the compressor to allow vary motor speed thus makes the compressor unit expensive.
Thus elementary needs to overcome the problems of existing ventilation systems are as follows.
1. Minimum temperature gradient among different regions in a given space.
2. Supply of conditioned air in-accordance to the occupancy level.
3. Occupant's participation in setting the atmosphere inside the room and in turn participation in
energy saving effort.
4. Ease of controlling the ventilation system at the occupants end.
5. Instead of personalizing the ventilation system, delivery of air to a zone considering the
cumulative demand the occupant in that zone.
6. Maximizing energy saving of the system by using efficient equipment and with adequate
operation, also by educating the occupants to participate in energy conservation procedure.
7. Efficient control of fan, compressor, chiller and air delivery system for better performance and
efficiency. Ensuring their performance individually and synchronously.
8. Adequate ducting system design, so as to deliver required level of air with least amount of
pumping work.
9. Maximum usage of conditioned air by avoiding delivery to roof level or to needless areas.
10. Improved damper system design and operation to facilitate and controlled air flow supply to
occupant's zone.
11. Robust and reliable control system design for the ventilation system to monitor and operate
the entire system concurrently and efficiently.
12. Development of a ventilation system that would fit in a newly constructed building and also
could easily retrofit to an existing ventilation system.
13. An efficient and comfortable ventilation system with least payback period against its
deployment expense.
Obiects of the Invention:
Overall present invention has three major objectives to counter most of the unsolved issues of
available ventilation system.
First objective of present invention is to allow occupants to set their own environment in the
leaving space, with an easier procedure. Additionally, to reduce temperature gradient within the
space by limiting the temperature band at delivery end.
Second objective is to improve efficiency of the HVAC system by maximizing the efficiency of
fan unit, without compromising its performance. The air flow supply will be controlled for flow
direction and delivery rate at occupant's zone. For this purpose a control system would be
developed to control and monitor the entire system in reliable and efficient way, with minimum
wiring in the space.
Third objective is to develop an efficient ventilation system that could be used in both new and
existing ventilation system. Further, the ventilation system should be less complicated and easy
to deploy and also the payback against the cost of deployment should be less.
Statement of invention
Present invention combines the actual total occupants demand in a given space with the
operation of fan and delivery of air at occupants place. In this regard, the occupants demand is
considered as the input signal and in accordance the fan and damper system is modulated. A
novel butterfly damper is designed to maximize the usage of conditioned air. In addition, a
competent and reliable control system is designed and developed to ensure concurrent operation
of all devices in the planned ventilation system. Advantage of present invention is that the
designed ventilation system can be implemented both new and existing ventilation system.
Summarv of invention
An experimental set-up is indigenously developed at Smart Grid laboratory, Power Grid
Corporation of India Ltd., Gurgaon - 122001, to establish the energy efficient features of the
newly invented ventilation system. The experimental set-up has three major sections: (i) air
conditioning unit, (ii) ducting system with dampers, and (iii) measuring devices. The fan in the
air conditioner at the delivery end is equipped with a variable frequency drive (VFD) to control
air supply. The damper is equipped with modulating type actuator. Measuring instruments like,
Energy meter, thermocouple, anemometer are used to quantify energy consumption, temperature,
velocity of air respectively. Later the same are used for result analysis.
With the intention of reducing number of experiments and to get details of flow distribution in
the ventilation system the thermo-fluid problem is simulated with computational fluid dynamics
(CFD) technique. Following the CFD technique, a novel damper system is designed and
developed to give best effect in terms of usage of conditioned air. The computational result
showed very much similarity with the experimental result, confirming accuracy of the simulation
procedure.
<
For operating the entire system in close co-ordination a control system is indigenously
developed. The system takes input electrical signals from occupants end and monitors the
damper system. The same signal is also passed to the VFD equipped fan unit through an
Integrated Chip (IC) based electronic computation system. The control system is so designed that
the actuator, VFD and electronic computation system are separate modules working in tandem
ensuring robustness of the system.
In order to establish advantages of present invention with respect to (w.r.t.) conventional, results
from experiment and computation are discussed in detail. Results are discussed with plots,
contours and tabulated values in terms of velocity, temperature, predicted mean value (PMV),
energy and efficiency. Newly developed damper system and conventional damper system is also
compared against similar parameters. Finally, the developed ventilation system is deployed for
field testing that exhibit significant energy saving potential.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 (a) Schematic diagram, and (b) pictorial view with instrumentation of experimental set-up
Fig. 2 Butterfly damper with flap and lever
Fig. 3 Computational domain with boundary condition and axis; Inset: Typical office dimension
Fig. 4 (a) Damper modification with different deflector size, and (b) boundary condition for the
modified damper design case
Fig. 5 Convergence plot showing residual value w.r.t, number of iterations
Fig. 6 Mesh generated for conventional (a) and modified damper (b); zoomed vied for normal
(c), 10% (d), 20% (e), 30% (f), 40% (g), and 50% (h)
Fig 7 Lines Y 1, Y2 and Y3 chosen for data reduction and entire plane for flow distribution
-- - - --- -- - ----- -- -. - -- - _ -
Fig. 8 i12 Volt dual supply for OpAmp I Fig. 9 Overall circuit diagram I Fig. 10 Air flow distribution at exit of damper 1 (a) and 2 (b)
Fig. 1 1 Dimensionless velocity (a) Contour, (b) along line Y 1, Y2 and Y3
Fig. 12 Velocity at occupants place with varying position of damper in normal ventilation system I Fig. 13 Flow variation with inclusion of deflector at damper exit I Fig. 14 (a) Air flow distribution for modified damper, and (b) non-dimensional velocity value at I different height levels in the room I Fig. 15 PMV variation w.r.t. temperature and air velocity I Fig. 16 Fig. 16 Operation of VFD for simultaneous operation of multiple dampers I Fig. 17 Velocity variation inside duct w.r.t. %frequency variation I Fig. 18 Variation of velocity at occupants zone with varying Reynolds of flow, at Y2
Fig. 19 (a) Energy consumption by fan, and (b) efficiency of fan for Smart ventilation system
DETAILED DESCRIPTION
This section is organized in five parts. First, the overall operation principle of the invented
ventilation unit is discussed. In second part, the experimental methodology, instruments and
measurement procedure is discussed. In third part, computational methodology followed to
simulate the ventilation system is discussed. Fourthly, the automation and control system related
procedure is discussed in detail. In fifth section, results from computation and experiment
pertaining to flow and heat transfer characteristics are presented. Results from field study are
given in last section.
1. OPERATING PRINCIPLE OF SMART VENTILATION SYSTEM
Present invention is named as "Smart ventilation System". Overall the Smart ventilation system
consists of regulating knob at occupant's zone to set comfort condition, variable frequency driver
controls the fan, modulating type actuator to operate the butterfly type damper, and a central
control system to concurrently monitor and operate entire ventilation system considering
occupants demand as input signal. As discussed earlier maintaining uniform temperature in a
given space is a cumbersome task, hence in present invention the delivery temperature is kept at
constant level. Considering, Indian healthy temperature standard 24OC is proposed to be the set
temperature. Setting up of.constant temperature value will ascertain uniform temperature in the
living space and hence the comfortness of occupants can be categorized in terms of air velocity
at occupant's zone. Maintaining constant temperature in space has following benefits; (i)
favourable to occupant's health and comfort, (ii) least fluctuating load to the compressor,
(iii) constant load on chiller plant ensures efficient operation etc. It is to be noted that, the said
24OC can be altered as per weather, location of or occupants demand.
The system operates in following manner; occupants from their working place set the comfort
condition by setting the regulating knob position. This acts as input signal to the control system.
The control signal then sends signal to the actuator and changes position of flap to fix the air
flow rate through the damper. Simultaneously, another signal goes to VFD to alter the fan speed
in turn the air flow rate in duct. In office buildings as there are multiple zones the control system
combines entire input signal from occupants and send a cumulative requirement to the VFD to
modulate the air flow rate in the duct. But individual signal is sent to the actuator system as per
occupants demand in that zone. The total flow in the duct gets segregated automatically as per
the opening portion of the damper and demand of each zone is met: The damper design is also
exalted so as to provide uniform air distribution irrespective of any damper opening condition.
2. EXPERIMENTAL METHODOLOGY
The experimental set-up developed in accordance to the objective listed in previous section. The
designed experimental model has three sections: (i) air conditioner with fan, (ii) ducting system
with damper, and (iii) measuring devices. Experiments are conducted with varying fan speed and
damper opening positions. The experimental results are used for checking correctness of
computational result and establishing energy efficiency features of current invention.
2.1 Experimental Set-up
Figure 1 (a) and (b) shows the schematic and pictorial view of the experimental set-up
respectively. The three sections of the set-up constitutes several sub-items as listed below; (1) air
conditioner (A.C.) with fan has, (i) A.C. unit, (ii) voltage stabilizer, (iii) energy meter, and (iv)
variable frequency driver (VFD); (2) the ducting section has, (i) diffuser, (ii) rectangular duct,
(iii) butterfly type damper, (iv) modulating type actuator, and (v) lever mechanism; and (3) the
measuring devices include, the (i) thermocouple, (ii) anemometer, (iii) energy meter, (iv)
voltmeter, (v) ammeter, (vi) data acquisition system, and (vii) controlled power supplier etc.
2.2 Air Flow Path and Governing System
Conditioned air at constant temperature is supplied from the air conditioning A.C. unit. The A.C.
used for experiment is split type, and is equipped with a voltage stabilizer, to ensure safe
operation. An energy meter is fitted with the air conditioner to quantify the total energy
consumption. The A.C. unit has two fans, one outdoor unit for compressor and condenser, and
the other one is to deliver air inside the room. In present invention compressor is left untouched,
and delivery air fan is equipped with VFD. The variation of fan speed with VFD is an efficient
way, which is explained in later section.
Once the air exits from the air conditioner, it passes through the diffuser so as to reduce the
fluctuation in flow and then enters to the horizontal duct. The duct is 3 100mm in length, 450mm
in width, and 300mm in height. Duct is properly insulated from outside so as to keep the air
temperature constant from fan exhaust to delivery end. The thermal conductivity of the insulator
is close to 0.1 W/mK, as specified by the manufacturer. Two numbers of butterfly type dampers
are used to supply air horizontal to the floor. Both the dampers are spaced with equal interval.
The flap in the damper decides the air flow supply that can be fixed anywhere between fully
open to close position where, 0" and 90" to the floor confirms fully open or close situation
respectively. For present case, the positioning of the flap is controlled by modulating type
actuator. The actuator operates as per occupant signal, elaborated in later section. Considering
the differential pressure across the flap and friction in the shaft packing, it is calculated that the
torque required to operate flap is nearly 4 Nm. The actuator and damper are connected by a lever
as shown in Fig. 2.
For quantifying the effects of the modified ventilation system multiple instruments namely,
thermocouple, anemometer, energy mete;, voltmeter, ammeter are used. A controlled power
supply module is used to develop the control system. Data acquisition system is used to store and
monitor the air flow temperature in the system.
2.3 Measurement System
For present investigation three basic parameters are measured, i.e. temperature, velocity and
energy consumption.
Resistance temperature detectors (RTD-sensor) are used at multiple points in the ducting system
and room for temperature measurement. All the RTD-sensors are calibrated against the standard
thermometer. The uncertainties of the sensors are found to be below *O.l°C. RTD-sensors are
connected to the data acquisition system to continuous monitor and store the temperature data.
Temperature inside the duct ensured a maximum rise of 0.1 5°C from A.C. unit exit to delivery
end, which is acceptable. The temperature variation inside the room also checked, and a
maximum variation on 0.5"C is observed.
Velocity of air is measured both inside and outside the duct. For measurement inside the duct
pitot static tube is used that gives differential pressure value. The differential pressure value is
later converted to velocity using Bernoulli's equation. Minor variation (h0.1 mlsec) is noticed
within the duct along its cross-section. Velocity distributibn at the delivery end is measured by
vane anemometer. The vane anemometer has a speed range of 0.1 to 10 mlsec, with an accuracy
level of 0.01 mlsec. Velocity measurement is done in two places, i.e., (i) immediate downstream
of the exit of damper, and (ii) in the occupants zone. For flow distribution in occupant's zone, a
2mtr * 2mtr area is marked O.5mtr above the floor, temperature is also measured at those
locations.
Energy consumption is measured to quantify the benefits of the Smart ventilation system. The
A.C. system is equipped with a single phase AC static watt hour meter, IS-13779 comply energy
meter. Another energy measurement is done at the delivery fan unit, where the VFD itself has
provision to measure and display the energy consumption by the fan at various speed levels. To
measure the energy consumption by VFD and modulating type actuator, voltmeter and ammeter
are used. Summing up energy 'value from all above mentioned devices energy consumption
before and after deployment of Smart Ventilation can be assessed.
2.4 Experimental Procedure
Two types of experiments are carried out; one on a normal A.C. unit, and after implementing the
smart ventilation system. In lSt type, the A.C. was set at different speed and temperature levels as
given by the manufacturer. Temperature value is varied from 16 to 3 1°C, and fan speed varied as
slow, medium and fast. For each case, energy consumed to attain the set temperature is noted.
Experiments are conducted till the room temperature reaches within *0.5"C of the set
temperature.
After deployment of smart'ventilation system first the A.C. is turned on and allowed to run for
10 to 15mts to supply stabilized flow. Energy meter reading is noted and temperature is fixed to
a certain value (24°C). Out of the two dampers, one damper flap position is fixed and other
dampers flap position is varied to find out the flow distribution both at damper exit and
occupants zone. To confirm mutual effect of damper similar process is repeated by keeping flap
position of later damper at fixed position and varying the first one. Velocity variation inside the
duct with damper flap positioning is also measured with pitot static tube. Similarly, with opening
and closing of damper flap the frequency and power consumption of the fan unit changes. The
fan speed was varied in the range of 30 to 50Hz; reason behind the same is clarified in later
section. Energy consumption by fan and entire A.C. unit at different damper opening is noted,
including the power consumption in 'actuator and VFD. Temperature variation inside the duct
and in the room is continuously monitored by the data acquisition system.
2.5 Data Reduction
The results presented in this report centre around distribution of dimensionless velocity,
percentage f rated fan frequency, energy efficiency, and predicted mean value (PMV).
a. The dimensionless velocity (V') is the ratio between air velocity at any location and
maximum air velocity in entire location in the same plane.
i.e. VY= (Air Velocity/Maximum air velocity)p~,,~-xx
b. Percentage of rated frequency Cf') is the percentage of operating frequency of fan against
its rated operating frequency.
i.e. f' = (Operation frequency1Rated frequency)* 100
c. Energy efficiency of Fan (qf) unit is calculated with following formulas;
qf = [{(Rated - Actual) power consumption in fan)/Rated Power consumption) * 1001
d. Predicted mean Vote (PMV) is an IS0 standard, refers to the thermal scale that ranges from
cold (-3) to Hot (+3). Where, the feeling sensation is collected by subjecting large number
people to different comfort condition. The PMV sensation scale is given below;
PMVSensation: Cold Cool Slightly-Cool Neutral Slightly-Warm Warm Hot
PMV Value: -3 -2 - 1 0 1 2 3
As per ASH.KAE-55 recommendation the acceptable range of PMV is -0.5 to 0.5 for an
interior space.
3.1 COMPUTATIONAL METHODOLOGY
In order to get flow insight and reduce number of experiments the investigation problem is
simulated computationally using CFD technique. Major goal of present computation is to design
the damper system, so as to obtain desired flow distribution and maximize usage of conditioned
air. In this regard a computational domain similar to the experimental set-up is generated,
meshed and then simulated with finite volume model (FVM) based technique. Details of the
computational methodology are discussed hereunder.
3.2 Compr~ta tional Domain
The computational domain used for present analysis mimics the physical experimental model
shown in Fig. 1 (b). As mentioned earlier that the delivery air temperature is kept constant, hence
the fluid flow problem is formulated for two dimensional steady state systems. Due to similarity
in geometry and to reduce computational time three dimension technique is avoided.
Geometrical details about the model are discussed in following section.
The computational domain can be divided into two sections, i.e., damper system, and model
room, as shown in Fig. 3. The air enters to the damper and after passes through the length of
damper enters into the room. Uniform velocity condition is specified at the damper inlet.
Atmospheric pressure outlet condition is specified to both vertical ends the modelled room and
the roof & floor surface are declared as wall. The damper is separated from the room by an
impervious wall. The damper has a cross section of 300mm in length and 250mm in height. The
model room is 2mtr * 2mtr in cross-section (refer inset in Fig. 3, from floor up to O.5mtr is
avoided as these zones does not play much role towards comfort). The Reynolds number of flow
at the inlet of damper is varied as 81900, 54600, 40950, 27300, and 13650 corresponding to inlet
velocity of 3 mls, 2 mls, 1 mls and 0.5 mls respectively. The Reynolds number exhibits turbulent
regime for all four situation.
With the purpose of optimizing the exit flow distribution, the damper exit shape is varied. The
modified cross-section of the damper looks like a right isosceles triangle, where the height (=
base) is varied as lo%, 20%, 30%, 40% and 50% of the height of damper, as shown in Fig. 4 (a).
Corresponding computation domain is given in Fig. 4 (b).
3.3 Governing Equation
The fundamental governing equations used for simulation are the continuity and momentum
(Navier-Stokes) equation. To solve the above problem following assumptions are made;
(a) Fluid is incompressible
(b) Fluid properties are constant
(c) No viscous dissipation
(d) Steady flow situation
(e) No buoyancy effect
Equations solved for this purpose are listed below;
The equation for mass is:
v . (F~)= o eq.I
Conservation of momentum in an inertial (non-accelerating) reference frame is:
v.(p w)=-vP +v.(;)+pg eq.2
-
Where, p is the static pressure, z is the stress tensor (described below), and p g i s the
gravitational body force respectively.
--
The stress tensor z is given by,
r = p (VV+VVT)--V.VI
= [ eq.3
3 I
Where p is the molecular viscosity, I is the unit tensor, and the second term on the right hand
side is the effect of volume dilation. For incompressible flow [V.VI] becomes zero.
Based on the nature of the flow interaction and available literature practice the K-E model is
adopted for modelling of turbulence, where K is turbulent kinetic energy and E is turbulent
dissipation. The standard wall function is used for simulation of near wall treatment.
Transport equations for standard K-E model are given below;
For turbulent kinetic energy, K
-(dp mi)=- p+- - +PK--pE--YM+ SK
a [[ :K):l eq.4
axi dx,
For turbulent dissipation, E
d E &2 -h(i~ i ) = ~a[x(, p + ~ ) ~ ]a+x, C , 6 ; ( p K ) - C 2K6 p - -+YsM6 eq.5
The turbulent viscosity pt is modelled as,
K2
A=&/,- eq.6
E
The production of turbulent kinetic energy K is modelled as,
-au.
PK = -p~$*2. eq.7 ' hi
2 pK = p l s eg.8
Where, S is the modulus of the mean rate of strain tensor, defined as;
s = J W
Other model constants are as follows;
C1, = 1.44; C2, = 1.92; C3, = -0.33; C,, = 0.09; o, = 1.0; 9 = 1.3
Results from computation are validated against the experimental data, and very good agreement
(maximum deviation 8%) is found confirming precision of the chosen model.
3.4 Boundary Condition
The values of velocities and turbulence intensity, selected from the experimental condition are
imposed at the inlet to the damper. The average grid generated turbulence intensity and
dissipation rate is found to be around unity (1). Boundary conditions used to solve the governing
equation are as follows;
(i) No Slip boundary condition: On the solid wall, VWa=II 0
(ii) Velocity condition at damper inlet: Vinle=t V,; Vy = 0
(iii) Entrainment condition: Outlet, P = Parnosphere
3.5 Solution Methodology
To solve the governing equation with boundary condition FVM technique is followed. For
pressure velocity coupling SIMPLE (Semi Implicit Method for pressure Linked Equation)
algorithm is used. Second order upwind is used for all momentum, turbulent kinetic energy and
dissipation rate equation discretization. The solution is considered converged, when the
maximum residual value is in the order of lo-' for momentum and turbulence quantities, shown
in Fig. 5. All computations are continued till entire domain reaches steady state.
3.6 Meshing technique
To multi-block mesh suitable for FVM technique is used for meshing the model shown in Fig. 6
(a) and (b). In the conventional damper model completely hexahedral structure is used, refer Fig.
6 (c). For the modified damper both hexahedral and tetrahedral mesh is employed, Fig. 6 (d to h).
The near wall dimensionless wall distance ( ~is 3kep t at around 40. The final mesh size for all
the models are close to 40,000. This number is arrived after carrying out adequate grid
independence study. Final grid size for all the models are tabulated below.
Table 1: Table showing model type, mesh size and type
ModelType
Grid Size
Mesh type
3.7 Planes Lines Chosen for Data Presentation
The calculations are two dimensional and hence the results, the earlier said quantities (in data
reduction section) are presented in certain chosen lines and planes. Multiple horizontal lines
parallel to the surface (x-direction), viz. Y1, Y2, Y3 at 0.5, 1.0 and 1.5mtr respectively, chosen
above the floor (Y = 0), refer fig. 7. Flow distribution is presented as contour in entire plane, and
velocity distribution as plot along line Y 1-3.
4. SMART VENTILATION CONTROL SYSTEM
4.1 Introduction
40%
40912
Hybrid
50%
41024
Hybrid
Conventional
40000
. Structured
10%
40237
Hybrid
20%
40421
Hybrid
30%
40678
Hybrid
The electrical control system of the Smart Ventilation System is designed with the objective of
increased energy efficiency and enhanced occupant comfort in work place. The execution of the
Smart Ventilation System will follow the mentioned steps:
a. The occupant will adjust the setting of a knob from his cubicle.
b. The change of position of the knob will result into a change of a voltage signal.
c. The aforementioned voltage signal will be used as the control signal to the actuator.
d. Depending on the magnitude of the control signal the actuator will drive the damper to a new
position that suits the need of the occupant.
e. The voltage signals from all the occupants will be passed through an analog electronic
computation system which will decide the speed of rotation of fan and corresponding voltage
signal will be generated.
f. The output voltage signal of the electronic computation system is relayed (via wire or RF
module for wireless) to the Variable Frequency Drive control pin and the VFD changes the
frequency of the output AC voltage signal accordingly.
g. The AC output voltage of the VFD is used to power up the fan which changes speed according
to the change in rated frequency.
4.2 Components of the Control System
The components of the components of the smart ventilation control system are described as
follows:
a. DC Power Supply: The power signal of the actuators, Variable frequency drive and electronic
components are supplied through a continuous DC Power Supply. The available supplies are:
i) 0-32 V continuously variable with both voltage control and current control: Used for actuator
power signal. (24 V DC)
ii) -15 V- 0 V- +15V, continuously variable: Used for dual supply op-amps.
iii) 0-5V: Controlled DC voltage supply with more resolution
b. Actuator: The actuator is equipped with a stepper motor. The degree of rotation of stepper
motor will depend upon the voltage signal applied to the control pin of the actuator. The actuator
is mechanically coupled to the damper. Hence by applying suitable control signal to the control
pin of the actuator the opening and closing of the damper can be controlled. For its normal
operation the actuator requires a 24 V ACIDC supply. The actuator requires a control signal
between 2 V to 10 V for a rotation between 0 to 90'.
c. Variable Frequency Drive: The Variable Frequency Drive (VFD) accepts an input signal of 1
phase or 3 phase AC voltages. The frequency of the output signal can be varied between 0 to 400
Hz using suitable control signal. The VFD selected in this project operates in two modes: Auto
mode and Hand-on mode. In hand on mode the Frequency of output signal can be changed
between lower and upper limits by adjusting a potentiometer provided on the control panel of the
VFD. In auto-mode the device accepts an analog DC signal in its control pin in the range of O10V.
Depending on the control voltage the VFD changes its frequency. If output frequency range
is between lower limit FLL and upper frequency limit FUL and a control signal of V volts ( V is
between 0 to 10 volts) is applied, the output frequency of the VFD will be F=V/lO(FUL-FLL).
d. Radio Frequency Module: To keep the wiring of the system to a minimum a radio frequency
module is used. The control signal of the VFD, generated by the electronic circuitry, can be
communicated to the device both via wire and wireless RF communication. Using EF module the
wiring can be kept to minimum and the Electronic circuit does not need to be close to the VFD.
For implementing wireless transfer of VFD control signal a radio Frequency transmitter-receiver
pair is used. The RF module accepts transfers and delivers only digital signals. To convert the
analog DC signal into digital signal suitable Analog To Digital Circuit (ADC) is used on
transmitter side, whereas, on the receiver side an R-2R ladder network is used to convert the
digital signal into an analog signal.
The transmitter part of the wireless system consists of two components: an Encoder and a
transmitter. The encoder is capable of converting a 12 bit parallel data to serial data output. 8 bits
are used as address byte and 4 bits as data bit. The address byte should be same on transmitter
receiver pair for proper pairing. The 4 bit serial data transmitted via the transmitter to the
receiver. The receiver consists of a receiver and a decoder. The receiver after receiving the data
relays on to the decoder which extracts 4 bit parallel data from the serial data. The parallel bits
are then transformed into analog signal and used as the control signal of VFD.
4.3 Brief Description of Electronics Circuitry
The inputs for the Smart Ventilation System will be knob position from the occupants.
Depending on the knob position of the occupant the opening/closing of the corresponding
damper will be controller.
As mentioned earlier the actuator accepts an input of 2V to 10V DC. For testing purpose the DC
power supply module was used. However, to make a standalone system a separate DC supply is
required. To make a DC supply a center tap PT is required and a bridge rectifier is used. The
two output points of the bridge rectifier are then fed as input to two ICs, namely 78 12 and 79 12
i.e. to give +12V and -12V, refer Fig. 8. The center point of the PT out is taken as ground
reference.
The + 12V supply will be required for using op amp which is discussed later.
The 12V output of 7812 is connected to potential divider circuit. The potential divider circuit
consists of 2 KR fixed resistance and a 10 KR potentiometer. The 2KR resistance always
maintains 2V fixed-bias as the input of the actuator is from 2V to 10V. The 10 KR pot is
connected to a knob which the occupant has control over. The output of the potentiometer is
connected to the control pin of actuator which will in turn control the position of the damper.
The outputs of all the potentiometers are connected to an analog average circuit built using an
OP amp. The average of the inputs from the user is the connected to a potential divider. The
output of potential divider is connected to frequency control pin of VFD.
It was seen the VFD has an input impedance of 15 KR. The lower input impedance of VFD
lowers the output of the pot divides circuit. To increase the input impedance a buffer circuit was
introduced between the output of the potential divider and the control pin of VFD.
The above discussed circuit shown in Fig. 9 is completely analog and the control signal of the
VFD is continuously variable between 0 to 10V. However, to make the wiring of the system
minimum it is prudent to deploy a wireless solution. Making the transmission of control signal
via radio Frequency not only minimizes the system wiring but also frees us from the limitation of
keeping the VFD close to the actuators.
The advantages of the RF solution surely outweigh the minor limitation it brings in. The signal is
digitized for transmission over RF. As a result the control signal of VFD is discrete. 4bits used
here gives us a control voltage of resolution of 0.625 V. The lower and upper limit of the VFD
output frequency was chosen as 30 Hz and 50 Hz. Hence the frequency resolution obtained is
1.25 Hz which serves the purpose of speed control of the fan.
4.4 Speed Control of Fan
The Fan used here is a single phase induction motor. The speed control of a single phase
induction motor can be done by changing the applied voltage and also by changing the
frequency.
The speed decreases with the decrease in applied voltage. However, the speed vs. voltage
characteristic is generally non-linear. Moreover, the speed-voltage characteristic of induction
motor depends on load characteristic. Even if we assume a particular load characteristic we
would have to apply complex curve fitting to determine the required voltage to set a particular
speed.
On the other hand, the speed control of induction machine using frequency control is much
simpler. The change in frequency proportionately changes the synchronous speed of the motor
and for a constant slip the speed of the motor also changes linearly with applied frequency.
Hence frequency control of the induction motor (fan) is chosen in' the smart ventilation system.
To control the frequency of the supply voltage a VFD is used. The output frequency is varied
between 30 Hz and 50 Hz. Below 30 Hz frequency the air flow from the duct was observed to be
minimal and as the fan is rated for a particular speed it is not safe to go beyond 50 Hz owing to
the risk of mechanical damage.
4.5 Advantages
The advantages of the designed smart ventilation control system can be summarized as below:
a. The actuator-damper system, electronic computation system and the Variable Frequency drive
system are designed as modular units. The failure in one of the components does not affect the
other hence making the system more reliable and robust.
b. The choice of frequency control of fan speed provides accurate control of speed. The speed of
the fan varies linearly with the control voltage applied to the VFD.
c. The wireless design of the system decreases the requirement of electrical wiring. This also
avoids the limitation of keeping the VFD close to the control knob provided to the occupant.
d. Changing the fan speed according to the opening or closing of all the dampers together
ensures energy efficiency. When the requirement is less not only the damper opening changes
but also the speed of the damper decreases and hence energy wastage is minimized.
5. CONVENTIONAL vs. SMART VENTILATION SYSTEM
5.1 Conventional Ventilation System
5.1.1 Flow Distribution
The flow distribution is discussed at dampers exit and at occupant's zone.
a. Damper Exit
Figure 10 (a) and (b) shows the velocity distribution at damper exit 1 and 2 respectively. To
measure velocity at damper exit, a temporary surface is fixed 0.3m away from the butterfly
damper exit. Eight locations are marked to get a clear view of flow exit pattern at different
elevations and positions of the damper, refer inset in Fig 10 (a). The velocity is normalized
against the maximum velocity in the measuring surface. The velocity values are taken against
varying the damper - 1 flap position from full open (100%) to 20% open case, while keeping
damper 2 flap position at a fixed location. For fully open case two distinct velocity zones are
observed, where location 1 to 5 exhibits higher velocity and location 6 to 8 has lower velocity
values. Among location 1 to 5, maximum velocity is observed at location 3, which is at the
bottom end on the damper exit. Due to symmetry in flow, velocities at point 2 & 4 and 1 & 5 are
almost the same. Thus, velocity values from 1 to 5are almost the same with a variatioli of
maximum 15%. At location 6 to 8 the velocity values are almost 50% lower compare to the
location 1 to 5. Location 7, exhibits the lowest value among all. Because when flow exits
horizontally from the damper due to gravity it takes a projectile motion as shown in inset of Fig
10 (a). Thus, the velocity 'at upper area of the damper is comparatively lower. Similarly,
location 6&8 showed lower velocity and of equal range.
The percentage of opening of the damper is controlled by the positioning of the flap, refer inset
in Fig. 10 (a). At 80% opening the flap restricts the flow and diverts it towards other exit point,
in turn reduces the velocity of air. At 80% opening, the pattern of velocity variation from 1 to 5
and 6 to 8 remain almost the same as in case of fully open conditio'n. The velocity however
reduces by around 10% with 20% 'closing of the damper. With further closing of the damper the
velocity magnitude reduces gradually at all locations, shown in Fig 5(a). For 20% open case, the
velocity magnitude is almost 50% lower to fully open case.
Figure 10(b) shows the velocity distribution at damper-2 exit. Velocity values are nondimensionalized
w.r.t. the maximum velocity in the measuring plane opposite to damper-2 exit.
The velocity distribution remains almost the same as discussed in case of damper-1. It is
observed that the measured values are marginally lower for damper-2 as compared to damper-1.
This is because of damper - 1 is located closer to fan and damper-2 is farther.
b. In Occupants Zone
Velocity distribution in the occupant's zone is shown both computationally and experimentally
in Fig 11 (a) and (b) respectively. When the flow exits from the damper it has higher momentum
compare to the quiescent room air. Thus rapid momentum exchange takes place between the two
fluids. The flow exiting from the damper behaves like a jet, which after emanating from the
damper rapidly diffuses in all direction of the room, as shown in Fig 11 (a). In the process of
mixing the jet velocity reduces and shears layer forms surrounding it. The distance till which jet
flow remains active depends upon the exit velocity from the damper. The shear layer spreads
evenly, hence even at roof level high velocity zones are also observed which are nothing but
waste of conditioned air towards ceiling light & fans.
The occupants breathing zone starts mostly lmtr above the ground and leg space is usually at the
height of 0.5mtr. In standing condition the breaking zone goes up to 1 .5mtr height. Figure 1 1 (a)
shows that in the height ranges of 1.5 to O.5mtr the flow almost diffuses down. The same is
clearly depicted from Fig 11 (b), where velocity variation is drawn across horizontal surface at
different elevation from ground. The experimental data at same locations are merged over
computational plot, and they show good agreement with maximum variation of 8%, which is
acceptable for present flow situation. From plot it is observed that at a height a 1.5mtr (Y3),
maximum flow velocity reduces up to 50% of damper exit velocity. This higher velocity zone is
also limited to a narrow space, i.e. front side of the damper. At a height of 1 mtr (Y2) the velocity
reduces up to l/loth of damper exit velocity. The space below the damper (x = 0 to 0.75mtr) has
a further lower velocity compared to zone in front of the damper (x = 0.75 to 2mtr). Thus to
obtain a comfortable breathing space, the velocity of air supply need to be kept at higher AND
HENCE higher fan speed. The air circulation in leg space is negligible and hence will lead to
stagnation of pollutant. Evacuation of the same is always cumbersome task.
5.1.2 Fan speed & Energy Consumption
Figure 12 shows the velocity variation at occupant location w.r.t. variation in damper position.
For this purpose feedback from two occupant's zone are considered to fix the damper position at
their location with actuator. As the total amount of air flow remains constant in the duct and both
the dampers are part of same duct the flow through one damper is mutually depends upon the
position of flap in second damper. For example if the occupant at location-1 sets damper 1
position at 40% then the dimensionless velocity will range from 0.1 to 0.35. In other words is
damper-1 is set at 40% and damper-2 at 20%, air from damper 1 will deliver air at a velocity of
0.35, but if damper-2 position is changed to fully open (100%) condition irrespective of damper-
1 demand the air flow velocity will reduce to 0.1. This will raise uncomfortable situation and
occupants have'to adjust their damper position frequently.
The energy consumption in the conventional ventilation system varied by varying the voltage
supply. The power consumption the proportional to torque of fan, with reduction in fan speed
power consumption also reduces. Further, speed control by varying voltage supply is not a very
efficient way of controlling. The fan speed change with voltage variation is usually done in a
step wise format, thus there are not many choices for setting fan speed. Energy consumption by
fan with three available setting (slow, medium and fast) is tabulated below in Table-2.
Table 2: Fan energy consumption with varying speed level
Rated Energy
135 Whr
Slow Spped
85 Whr
Medium Speed
100 Whr
Maximum Speed
135 Whr
5.2 Smart Ventilation System:
5.2.1 Damper Modification:
As mentioned earlier, in order to equally distribute the condition air in occupant's zone and to
maximize the usage of the same air the damper design is modified, refer Fig 4. The velocity
distribution with change in damper shape is shown in Fig. 13. With change in damper exit shape
(10% to 50%) drastic change in exit flow situation took place. For present flow situation uniform
and equal flow condition specified for both conventional and modified damper design. However,
due to change in damper exit condition although the inlet conditions are same the flow pattern at
the exit differs from each other. It is noticed that when 10% deflector induced the maximum
velocity is shifted from inlet of damper (as seen in Fig. 13 (a)) to the exit of the damper. Further,
the maximum velocity is increased by almost 21% compare to inlet velocity, refer Fig. 13 (b).
The increase in velocity is because exit area gets contracted and to follow conservation of mass
flow the velocity increases. The deflector at the exit also directs the flow towards occupant's
space and less flow moves towards roof section. However as the room size is much bigger
compared to damper not much of change is observed compared to conventional damper. The
flow will almost diffuses out while reaching occupants zone. With 20% deflector, the exit
velocity increases up to 40% compare to inlet velocity, refer Fig 13(c). The flow is now more
deflected towards occupant's zone and very less amount of air diffuses towards roof level. The
dissipation of jet starts almost O.5mtr below the damper height which give comfortable working
condition in occupants place. Now with further increase in deflector size to 30%, 40% & 50%
the exit velocity increasing around 60%, 90% & 120% respectively, in Fig 13 (d), (e) and (0. In
30% case, the exit flow is strongly defected and the jet core is retained almost up to O.5mtr below
roof. This case, higher velocity will be available but to the occupant sitting in front of the damper
exit. Similarly, with 40% & 50% the flow situation will be more severe and uncomfortable
situation for the occupants. Thus 20% deflector size is presumed to be the optimum shape for the
damper design. Flow distribution corresponding to the same is discussed in following section.
5.2.2 Distribution at occupant's place
Figure 14 shows the flow distribution in the occupants place for modified damper (20%
deflector) both computationally and experimentally. The computed flow distribution in Fig. 14
(a) shows that a very uniform air velocity is obtained in entire horizontal length and up to lmtr
height from bottom level. Only in one corner at floor level a small hot sport is notice which may
be because of existing computation error. It is observed that least amount of air is diverted
towards the roof level assuring maximum use of conditioned air. Generally area below the
damper gets very less air compared to zone opposite to the damper. This issue is also resolved by
properly utilizing the shear layer generating from the flow. The jet type flow exiting from the
damper mostly gets diffused at a height of 0.75mtr from the roof, so it guarantees that no
occupant will be directly affected by the flow from the damper.
Figure 14 (b) shows the data drawn across the horizontal length of floor at three different
elevations (i.e. Y = 0.5, 1.0, and 1.5m). The experimental data are also plotted in same fashion
against the computation. Very good agreement is perceived between the two results confirming
the accuracy of the computational procedure. At an elevation of 1.5mtr, non-uniform velocity
distribution is noticed; this is because of existence of the effective jet length. However, in
general occupants in both office and residence does not get expose to this height very often.
Now, at a height of lmtr which is cruc'ial almost uniform distribution with a dimensionless
velocity band of 0.3 to 0.5 is observed. This will be very comfortable for all the occupants in the
particular zone. In the leg space, i.e. O.5mtr from ground also 0.15 to 0.3 dimensionless velocities
is maintained. This situation will ensure no accumulation of pollutant and hot zone in the leg
space or comers of the room. Overall, from floor to 1 .Omtr height air is supplied in the band of
0.2 to 0.5 Limes the damper inlet velocity to the entire zone which will create uniform demand
among occupants and comfortable situation in leaving space. Uniform air distribution also
it~~iireavs oidance of unnecessary temperature gradient in the room.
5.2.3 Predicted mean Vote
Calculation of PMV is most widely used.procedure to assess thermal comfortness of a zone. The
PMV is calculated with six room air variables, namely: air velocity, air temperature, mean
radiant temperature, relative humidity of the air, and clothing with physical activity. As
mentioned earlier the PMV level varies from -3 to +3, where comfortness lays between-0.5 to
0.5. As per the standards for temperature, approximately at 24°C air feels neither cold nor hot.
Further, in order to manage indoor room quality literature suggests a temperature range from 23
to 25.5"C for summer, and for winter the range is 20 to 23.5"C. In addition, to avoid sick
building syndrome the temperature should not go below 22°C.
Therefore to quantify PMV, three temperature levels are considered i.e., 22 "C, 24 "C and 25.5"C
with five velocity levels, as 3, 2, 1.5, 1.5 and 0.5 mlsec. The PMV index calculation requires
room atmosphere parameters and detailed'methods for the same are given in IS0 7730. The
sitting activity level is -1.0 met, and with clothing thermal resistance of 0.6 clo is approximated.
Relative humidity is measured by hygrometer to'be 55% in the room and MRT is calculated by
using PI radiation model available in ASHRAE Hand Book. The PMV levels for various cases
are shown in Figure 15, where all the measurements were carried out at the breathing height
(lmtr) level from the floor.
The results showed that for 22 "C case, velocity level 1 and 0.5 m/sec offers satisfied comfort
condition. At 24°C the PMV index mostly follows the specified comfort criteria, where covered
range is -0.8 to 0.3. But, at 25.5"C only at 3mlsec comfort condition is met. Therefore 24 "C is
the suggested temperature level and the velocity range is from 3 to 0.5 mlsec. For the ease of
control at occupants place, the regulating knob is specified with five comfort conditions as
tabulated below:
Table 3: comfortness table with temperature and velocity of air supply
Comfort Requirement
Cool
Slightly Cool
Temperature of Air Supply
24OC
24°C
,Air Velocity
3.0 ids.
2.0 mls.
1.5 m/s.
1.0 m/s.
0.5 m/s.
Neutral
Slightly Warm
Warm
5.2.4 Fan Speed Control:
In the conventional ventilation case the issues faced due to independent operation of damper and
fan is discussed. In case of Smart Ventilation System entire system works concurrently.
Figure 16 shows the reference frequency of VFD w.r.t. occupant's for zone 1 and 2 respectively.
In the Smart Ventilation System, when occupants set their individual requirement a combines
signal of all goes to the VFU and accordingly the fan speed changes. The dimensionless
frequency (%) variation w.r.t. the demands from location 1 and 2. For example, if location 1's
occupant set their actuator at 60% and at location-2 same 60% then the VFD will operate at 60%
of full speed refer Fig 16 (a). Further, if then at location-1 the setting is change to 20% and
location-2 requirement is still 60% the VFD will correspondingly change fan speed to 40% of
full speed. As the flap creates an obstruction and to maintain continuity flow equation, the
damper having higher opening will allow high amount of flow. It also to be noted that, if both
locations set their requirement to zero it will cut of the VFD and relay the same to A.C. System,
thus entire system will shut down.
Figure 17 shows the velocity w.r.t. reference frequency value for a cumulative demand from both
the locations. It is observed that the variation is linear, which is as expected. In this fashion with
simultaneous operation of actuator and VFD requirement of each zone will be taken care
individually. Figure 18 also confirms that with change in Reynolds number of flow at damper
inlet, uniform flow distribution can be ascertained at occupants place.
5.2.5 Fan Energy Consumption & Efficiency:
As mentioned in the objective, improvement of energy efficiency of ventilation system is one of
the major goals of present invention. Figure 17 (a) & (b) shows the fan energy consumption and
energy efficiency w.r.t. occupants demand respectively. The rated power of fan used in present
equipment is 135 Walt. It is well known that the frequency of fan operation and corresponding
energy consumption almost varies linearly. Through VFD any levels of speed of fan can be set,
which is again an efficient procedure. Figure 17(a) shows the energy consumption by fan while
varying the requirement of the occupants in Location 1&2. When, both the location demands
cool air, only in that situation the fan runs at its rates speed. For any other case the power
consumption is comparatively less than rated power. For example, if location-1 sets slightly
warm and location-2 sets slightly cool, then the energy consumption will be 78 Watthr.
Figure 17(b) shows the fan efficiency w.r.t. occupants demand. The fan efficiency increases with
decrease in power consumption. For above stated cases for location-1 & 2 set at slightly cool and
slightly hot respectively the fan efficiency will be 42%. Figure 1 l(b) reveals that up to 60%
energy towards fan operation can be saved by implementing Smart Ventilation System. The
energy required towards modulating type activator operation and VFD operation is very minor
(-10 Watt), hence neglected from calculation. Thus, considering a centralized HVAC system
where the fan consumes almost 40% of total energy, up to 24% of overall energy can be saved,
along with high comfort level to occupants, longer life to compressor and reliable operation of
24OC
24°C
24OC
entire system.
6. FIELD TESTING
The Smart Ventilation System prototype is developed in lab by following extensive experimental
and computational work. In order to check its performance in real office situation a field study is
carried out at the store section of POWERGID building. The store section has multiple rooms
and the staff seats in a designated space. Air conditioning is provided to each part of the store for
safe keeping of precision materials.
There are total seven (7) 2.0ton capacity split A.C. used to cool the entire store section. The
power consumption is almost 16 kW and total fan consumption is about 800Walts. When smart
ventilation system is deployed, a ducting system is constructed that covers entire store section
with multiple delivery points corresponding to the material stored section. The duct has provision
to take conditioned air from all air conditioners. Entire store section has 10 delivery points fitted
with butterfly damper with modulating type actuator. Each A.C. fan is equipped with a VFD. At
the staffs seat 10 controlling knobs are given corresponding to all ten sections of the store
including their own space. Additionally, in order to monitor temperature situation at each section
of store, temperature sensors are deployed at those location and a display unit is kept near the
staff place.
The occupant's feedback about the new ventilation system is very encouraging; they could easily
turn onloff conditioned air supply as per the space requirement. As all A.C. are connected to the
same duct most of the time by running three (3) nos. of A.C. system entire requirement is met.
The energy consumption report showed that the deployed system saves almost 48% energy
against the usual 16 kWhr energy consumption. The deployed system is effectively working till
date since past eight (8) months with no failure.

claim:
1. A ventilation system used for air conditioning in commercial/residential building comprising
of a control system that concurrently reglates the delivery-air fan speed and the damper
opening/closing function, by considering the occupants demand as input signal to the system.
2. The system that claimed in claim 1 segregates entire room space into multiple zones and
delivers air individually as per occupant's cumulative demand in the zones.
3. The system as claimed in claim 1 equips each zone with a regulating knob marked with cool,
slightly cool, neutral, slightly warm and warm comfort condition to set the zone requirement.
4. 'I'he cla~mm ade In claim I uses a var~abletr equency driver ('VTU) to control the speed of fan
meant for delivering air to space.
5. The claim made in claim 1 uses butterfly type damper to deliver air at occupant's zone. The
zone stated in claim 2 covers an approximate area of 2.5mtr * 2.5mtr that may accommodate
4 to 6 number of occupants for which the damper diameter would be around 250mm;
however for larger space higher diameter damper can be used.
6. The claim 5 made for system claimed in claim 1 redesigned the butterfly damper's exit cross
section by including a deflector at the upper end. The height and width of deflector is 20% of
the damper diameter.
7. The damper in claim 5 uses a modulating type actuator to position its flap anywhere between
fully open to fully closed conditions.
8. The ventilation system claimed in claim 1 has a control system that regulates the dampers
and computes the speed of fan, by taking input through the knob and computing output signal
by an electronic computation system.
9. The control system as claimed in claim 8 collects voltage input through the knob, i.e. a
variable potentiometer type, and relays that information to the actuator over radio frequency.
10. The voltage input as claimed in claim 9 controls the rotation of actuator that in turn controls
the rotation of the damper mechanically coupled to its shaft.
11. The input voltage signal as claimed in claim 9 is used by the electronic averaging circuit
consisting of operational amplifiers to generate an output signal to control the fan speed.
12. The output voltage signal of the electronic computation circuit as claimed in claim 11 is
connected to the control pin of the VFD to adjust output frequency. Accordingly the
frequency of the output voltage varies the fan speed.
13. The system claimed in claim 1 can be seamlessly retrofit to an existing ventilation system
and to a new system as well.
14. The system claimed in claim 1 will work more effectively in a residential or office building,
where the height of the roof is less than 5mtr from floor