1. IV th International Conference on Advances in Energy Research
Indian Institute of Technology Bombay, Mumbai
Performance Evaluation of a Guarded Hot Box
U-value Measurement Facility under Different
Software Based Temperature Control Strategies
By:
Amrita Ghosh
Supratik Ghosh
Subhasis Neogi
School of Energy Studies, Jadavpur University

2. School of Energy Studies
Jadavpur University
Overview
• General Introduction
• Setup Description
• Experimental Details
• Performance Evaluation of the System
• Results & Discussions
• Conclusions
2

3. School of Energy Studies
Jadavpur University
Introduction

Overall Heat Transfer Coefficient or U-value gives a
quantitative measure of amount of heat flowing through
unit area of any material for every degree differential
temperature across the material.

The lower the U-Value, lower is the heat transfer
through the material, better is the thermal performance
of the building component.

In India energy consumption in the residential and the
commercial and public services sectors: 40.84%

Method of determination of U-Value of a material:
Guarded Hot Box Method.
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4. School of Energy Studies
Jadavpur University
Guarded Hot Box U-value Measurement
Facility
Fans
Fan
Plate
heater
Baffle
Fans
Metering
Box
Tubular
heaters
Surround
Panel
Baffle
Heat
Exchanger
Cold Box
Guard
Box
Specimen
Guarded Hot Box U-value Test Setup (complying with BS EN ISO 8990: 1996)
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5. School of Energy Studies
Jadavpur University

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.

Walls of the guarded hot box is made of extruded
polystyrene blocks.

Baffle plate is placed parallel to the surface of test
element in both the boxes.

Purpose of guard box is to limit heat transfer via
Metering Box wall.

Basic method involves measurement of heat flux through
the test element at thermal equilibrium.

6. School of Energy Studies
Jadavpur University
Metering Box

Heat is supplied from a 100 W plate heater and two 60 W
tubular heaters.

It is highly insulated to minimize heat loss.

A baffle plate placed parallel to the surface of the test
element provides a radiating surface of uniform
temperature.

Circulating fans are installed inside the metering box to
bring uniformity in the temperature.
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7. School of Energy Studies
Jadavpur University
Circulating Fans
Plate Heater
Tubular Heater
Location of heaters inside Metering Box
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8. School of Energy Studies
Jadavpur University
Guard Box

The guard box surrounds the metering box.

Heat is supplied by two 120 W tubular heaters.
Circulating fans are provided.

The purpose of the guard box is to minimize the heat
flow through the metering box walls.
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9. Location of heaters inside Guard Box
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10. School of Energy Studies
Jadavpur University
Cold Box

The cold box provides a controlled environment at
a constant low temperature.

A Chilled ethyl-glycol based storage system
incorporating a Heat Exchanger-Fan coil unit is
used for maintaining the desired environmental
conditions.
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11. School of Energy Studies
Jadavpur University
Experimental Details
ysp
e
c
a
m
y
+
Temperature
Controller
DAC
Heating
Units
Guard Box/
Metering Box
-
ym
Thermocouple and Data
Acquisition System
Block diagram of the system
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12. School of Energy Studies
Jadavpur University
Experimental Details (contd.)

A software based controller has been developed.

In the program, three air temperatures of the metering
box and two air temperatures of the guard box are
averaged out individually.

K-type thermocouples are used to measure the air
temperatures at different locations of the metering box
and the guard box.

The signals are logged into the Data Logger via
(34901A 20-Channel Multiplexer) and then fed to the
computer program via GPIB-USB interface.
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13. School of Energy Studies
Jadavpur University
Experimental Details (contd.)

The average temperatures are used as the input signal
parameter of the virtual temperature controllers.

The output signals of the controllers are fed to the
DAC slot .

A 12V DC voltage is obtained from the DAC
depending on the output value of each controller .

This DC voltage is used to operate control relays.

These relays in turn operate the heating units installed
inside the metering box and the guard box.
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14. School of Energy Studies
Jadavpur University
Experimental Details (contd.)

Three experiments were performed for evaluating the
system performance using different control strategies.

The set point temperatures were kept constant at 40oC.

The AC circulating fans of the guard box were
operated at a power of 30W to reduce the heat
dissipation from the fans.

In these three cases the cold side of the Guarded Hot
Box setup was maintained at certain low temperatures.
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15. School of Energy Studies
Jadavpur University
GUI showing Real-Time Process Control
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16. School of Energy Studies
Jadavpur University
Experimental Details (contd.)

The average ambient
temperature for the
test period was 28.5oC.
45
40
Temperature (oC)

Case 1:
The controller outputs
were evaluated with
PID logic, and then
on-off control was
implemented.
35
Metering Box Temperature
Guard Box Temperature
Set Point
30
25
0
1
2
3
4
Time (hour)
5
6
7
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17. School of Energy Studies
Jadavpur University
Experimental Details (contd.)

The average ambient
temperature for the
test period was 29oC.
45
40
Temperature (oC)

Case 2:
The controller outputs
were evaluated using
P logic, and then onoff
control
was
implemented.
35
Metering Box Temperature
Guard Box Temperature
Set Point
30
25
0
1
2
3
4
Time (hour)
5
6
7
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18. School of Energy Studies
Jadavpur University
Experimental Details (contd.)


A proportional band of
5oC and a cycle time of
10
seconds
were
selected.
The average ambient
temperature was 33oC.
45
40
Temperature (oC)

Case 3:
The controller output
was calculated using
the P term. This output
was used to control the
duty cycle of the
heating units.
35
30
Metering Box Temperature
Guard Box Temperature
Set Point
25
0
1
2
3
4
Time (hour)
5
6
7
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19. School of Energy Studies
Jadavpur University
Performance Evaluation of the System
Performance Parameters
PID (On-off
control)
P (On-off
control)
P logic
(duty cycle
control)
Minimum metering box temperature after
reaching set point (steady state for case 3)
39.95 oC
39.97 oC
39.49 oC
Maximum metering box temperature after
reaching set point (steady state for case 3)
40.15 oC
40.14 oC
39.67 oC
Maximum fluctuation (offset for case 3) of
the metering box temperature from the set
point
0.3762 %
0.3572 %
1.27 %
Achieved metering box temperature range
after reaching set point (steady state for
case 3)
0.2044 C
0.1772 C
Root Mean Square Deviation of the
metering box temperature from the set
point
0.0500 oC
0.0456 oC
o
o
0.1792 oC
0.4042 oC
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20. School of Energy Studies
Jadavpur University
Performance Parameters
PID (On-off
control)
P (On-off
P logic
control) (duty cycle
control)
Minimum guard box temperature
after reaching set point
39.86 oC
39.88 oC
39.93 oC
Maximum guard box temperature
after reaching set point
40.41 oC
40.41 oC
40.46 oC
Maximum fluctuation of the guard
box temperature from the set point
1.03 %
1.04 %
1.15%
Achieved guard box temperature
range after reaching set point
0.5495 oC
0.5359 oC
0.5281 oC
Root Mean Square Deviation of the
guard box temperature from the set
point
0.1149 oC
0.1015 oC
0.2027 oC
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21. School of Energy Studies
Jadavpur University
Results and Discussions

Controllers with PID and P logic (case 1 and case 2)
showed almost similar results.

In these cases the controller outputs were calculated
using PID and P logics respectively. Based on these
outputs on-off control was implemented.

Usually, the integral action is provided to eliminate
the steady state offset. In the second case with P logic,
this offset was eliminated since the heating units were
operated at full power whenever the controller output
was positive.
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22. School of Energy Studies
Jadavpur University
Results and Discussions (contd.)

As the cold side was maintained at a temperature
much below the ambient, there was continuous heat
flow through the specimen to the cold side. This
helped to bring the required stabilizing effect, which is
generally offered by the Derivative control action.

Thus, the on-off controllers with PID and the P logic
offered similar performance.

In case 3 the average offset for the metering box
temperature during the last 3 hours of the experiment
was found to be 0.403 oC.

In case of the guard box temperature, fluctuations
were obtained. This may be due to the presence of low
circulating air velocity in the guard box.
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23. School of Energy Studies
Jadavpur University
Conclusions

The on-off control systems with PID and P logic
showed almost similar performance.

The maximum fluctuations for the metering box
temperature from the set point obtained in these two
cases were 0.3762% and 0.3572% respectively, which
are within the maximum limit of 1%.

For the guard box the maximum fluctuations were
1.03% and 1.04% respectively. However the
fluctuations gradually decreased with time.
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24. School of Energy Studies
Jadavpur University
Conclusions (contd.)

In the third case of duty cycle control the average
offset obtained for the metering box temperature was
0.403 oC. The controller needs to be tuned in order to
minimize the offset.

For the guard box temperature, fluctuations were
obtained probably due to the low circulating air
velocity.
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