Using IESVE for Loads, Sizing and Heat Pump Modeling to Achieve Decarbonization
97 rajesh
1. IV th International Conference on Advances in Energy Research
Indian Institute of Technology Bombay, Mumbai
P ro c e s s C o n t ro l S t r a t e g y A n d I t s I m p a c t O n
Performance Of The Cold Box Of
G u a r d e d H o t B o x Te s t F a c i l i t y
F o r U - v a l u e M e a s u re m e n t
Debasish Chowdhury, Rajesh Chatterjee, Subhasis Neogi
School of Energy Studies
Jadavpur University
2. School of Energy Studies
Jadavpur University
OUTLINE
Introduction
Guarded Hot Box Test Facility
Experimental set-up
Result and discussion
Conclusion
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INTRODUCTION
Recent times have seen a tremendous increase in
building energy consumption.
Therefore, reducing this load becomes one of the most
effective ways to conserve energy in buildings.
U-value of any material can be used as a tool for
thermal characterisation of any material.
Use of low U-value building material thus save
energy
A Guarded Hot Box Test Facility is used to measure
the overall heat transfer coefficient of any material.
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U-value can be defined as:
Lj
1
h ce
1
h re
n
j 1 k
j
1
h ci
h ri
where,
h is heat transfer coefficient.
c & r refer to convection and radiation respectively.
i & e refer to internal and external environment.
k is thermal conductivity of layer or layers having
thickness L.
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GUARDED HOT BOX
TEST FACILITY
Fan
Metering
Box
Plate Heater
Fan
Baffle
Specimen
Heater
Fan
HE-Fan Coil
Unit
Guard
Box
Cold Box
Baffle
Heater
Surround
Panel
Schematic view of Guarded Hot Box Test Facility complying with
BS EN ISO 8990:1996
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The Guarded Hot Box design is based on BS EN ISO
8990:1996.
It essentially consists of metering box which is
enveloped by a guard Box and cold Box.
Sandwiched between the two chambers is a surround
panel holding the sample.
Walls of Guarded Hot Box including the Surround
Panel are made of extruded polystyrene blocks.
Purpose of guard box is to limit heat transfer via
Metering Box wall.
Baffle plate is placed parallel to the surface of test
element in both the boxes.
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Virtual PID based controller maintains constant
temperature in guard box and metering box.
Traditional air condition system using thermostatic
control is avoided.
Chilled
ethyl-glycol
based
storage
system
incorporating a Heat Exchanger-Fan coil unit is used.
A simple PID controller is used to turn on and off the
circulation of chilled fluid (via relay) through the heat
exchanger to maintain constant temperature inside
the cold box.
The purpose of the heat exchanger provided is to
continuously remove the heat entering into the cold
box for maintaining appropriate temperature
conditions.
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Temperature measurement involves use of K-type
thermocouples.
Thermocouples measure temperature of air, baffle
and surface of sample in both Metering Box and Cold
Box.
AGILENT 34970A Data logger
Air temperature values from thermocouples located
inside the guard box and metering box are averaged
respectively to form input signal to the virtual PID
controller
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Out of three sensors located in the air curtain in front
of the sample inside the cold box, the sensor located is
used as input sensor to controller.
Steady state thermal transmittance is calculated by
measuring the heat flux the specimen and measuring
the air temperature in Cold and Metering Box.
U
Q
A
T
W /(m 2 K )
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Metering
Box
Surround
Panel
Baffle
Guard
Box
Power
Supply
Unit
Cold
Box
Guarded Hot Box Test Facility at School of Energy Studies
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Surround Panel
containing the Sample
Cold Box
Guard Box surrounding
the Metering Box
Components of Guarded Hot Box Test Facility
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EXPERIMENTAL SET-UP
The experimental set-up consists of :
Heat exchanger – fan or Fan-Coil assembly,
COLD BATH-35 make chilling plant,
Circulating pump along with interfacing circuit for
controlling circulation of chilled ethyl glycol inside
the heat exchanger.
Schematic overview of control circuit
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COLD BATH-35 make
chilling plant
Heat exchanger – fan or
Fan-Coil assembly
Relay
PID
Controller
Line terminal of
Circulating pump
Interfacing circuit for controlling circulation of
chilled ethyl glycol inside the heat exchanger.
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Control strategy implemented by the controller is
actually Pulse Width Modulation or PWM control.
By varying the duty cycle (% of Cycle time for which
relay is ON), the rate of heat removed by heat transfer
fluid is controlled.
The controller compares the set value (SV) with
process value (PV) i.e. the cold box air temperature
and turns on or off the circulation as required.
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Time temperature profile of air temperature inside the guard
box, metering box and cold box.
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Diagram showing varying duty cycle of relay
Zone 1: Duty cycle is 100% Zone 2: Duty cycle is 80%
Zone 3: Duty cycle is 60% Zone 4: Duty cycle is 40%
Zone 5: Duty cycle is 20%
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The set point for metering box and guard box was set
at 40°C and that of cold box was set at 0°C.
The effect of varying the parameters of the controller
namely Proportional Band (P), Integral Time constant
(Ti)and Derivative Time constant (Td) on cold box air
temperature profile is studied.
The surround panel is provided with a sample fixing
window of 500 x 500 mm where an insulation sheet of
50 mm thickness is used as sample case.
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RESULTS & DISCUSSION
Cold box air temperature profile for default values of controller
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• Temperature profiles in case 1 and case 2 are almost similar.
• Derivative action is required to damp out rapid changes in process
value
• In other words it has a stabilization effect on the system.
• Structural heat load, cooling load due to circulating fans and
leakages create an inherent stabilization effect.
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• Temperature profiles in case 3 and case 4 are also similar.
• But steady state error in case 3 is more than case 2.
• This is because control action steps in much closer to set point in
case 4 where proportional band is kept at 1ºC.
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In proportional control, control action takes place
only when process value (PV) enters the Proportional
Band (PB).
Below & above the PB, no control action takes place.
Proportional action is also sluggish in nature and
leaves a resultant steady state error.
This error can be reduced by decreasing PB but can be
eliminated by integral action only.
This is evident from the case studies above.
In case 1 and case 2, controller operates in PID and PI
mode respectively.
It is expected that both of them result in similar
nature of response.
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The only dissimilar is being that :
For case 1: (Controller operated in PID mode)
Steady state average value is 0.15°C.
Minimum temperature reached was -0.890°C after
about 1.088 hours from start.
For case 2: (Controller operated in PI mode)
Steady state average value is 0.262°C.
Minimum temperature reached was -0.262°C after
about 1.685 hours from start.
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This can be explained from heat exchanger fluid
temperature profiles of two cases.
35
Ethyl Glycol Inlet Temperature
Ethyl Glycol Outlet Temperature
Air Outlet Temperature
Air Inlet Temperature
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Ethyl Glycol Inlet Temperature
Ethyl Glycol Outlet Temperature
Air Outlet Temperature
Air Inlet Temperature
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TEMPERATURE (oC)
TEMPERATURE (oC)
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15
5
-5
-15
5
-5
-15
-25
0
0.5
1
TIME IN HOURS
1.5
2
Time temperature profile of heat
exchanger fluids for Case 1
-25
0
0.5
1
TIME IN HOURS
1.5
Time temperature profile of heat
exchanger fluids for Case 2
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2
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CONCLUSION
In this paper a PID based controller was designed for
maintaining a constant air temperature inside the cold
box.
Experimental results showed that when the controller
was operated in PI and PID mode, the steady state air
temperature achieved inside the cold box was closest
to the set point.
Moreover while operating in P mode, steady state
error is more in the case where proportional band is
larger
Thus from the above experimental results it is evident
that
in
the
present
cooling
strategy
implemented, varying the parameters of the
controller has a significant effect on the cooling
performance.
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