A Study on the Performance of Cooling Ceiling Panel

A S H R A E T h a i l a n d C h a p t e r
ASHRAE Journal 2004-20052
A Study on the Performance of
Cooling Ceiling Panel
Dr. Chirdpun Vitooraporn1
and Aryut Wattanawanichakorn2
1
Lecturer at Building Technology and Environment Laboratory,
2
Former graduate student
Mechanical Engineering Department, Chulalongkorn University,
Phyathai Rd, Patumwan, Bangkok, Thailand, 10330
Tel: 662-2218-6622 Fax: 662-2252-2889 E-mail: chirdpun@chula.com1
In this research the performance of cooling ceiling panel in transferring heat is studied. The
parameters considered in the experiment are supplied chilled water temperature, supplied chilled water
flow rate, and the cooling performance of the panel. From the experiment, it is found that supplied chilled
water temperature has an effect on the surface temperature of the panel, the room temperature and the
heat transfer rate of the panel at the steady state condition. Low supplied chilled water temperature
increases the heat transfer rate of the panel, and, at the same time, decreases the surface temperature
of the panel as well as the room temperature. In the contrary, the supplied chilled water flow rate does
not significantly affect the surface temperature of the panel, the room temperature, and the heat transfer
rate of the panel at the steady state condition. However, the supplied chilled water flow rate has an effect
on the time gradient required for the surface temperature of the panel, the room temperature and the
heat transfer rate of the panel to approach the steady state condition. The surface temperature of the
panel, the room temperature and the heat transfer rate of the panel approach the steady state
condition faster as the supplied chilled water flow rate increases. Furthermore, heat load also plays an
important effect on the surface temperature of the panel and the room temperature at the steady state
condition. Higher heat load results in higher surface temperature of the panel and room
temperature at the steady state condition. Results from experiment are used to derive the equations that
represent the cooling performance of the panel at the steady state condition.
Abstract

ASHRAE Journal 2004-2005 3
1. Introduction
The cooling ceiling panel transfers heat to
or from a room by convection and radiation. The
radiant loads from the wall as well as from the
persons and objects within the room are treated
directly. The natural convection occurs at the air
layer near the cooling ceiling panel. This heated air
then moves and mixes with the air inside the room
under the buoyancy force. This mechanism hap-
pens because of the low panel temperature. The
panel is the metal ceiling panel bonded to the cop-
per tube. The tube contains the re-circulated
cooling media which is water. The combined
radiant and convection heat transfer is then trans-
ferred to the panel through the conduction heat
transfer happened at the tubes. Water inside the
tube is then gradually heated up and circulated back
to the chiller where all the heat contained is
dissipated.
2.1 Radiation Heat Transfer
The radiation heat transfer rate for the
cooling ceiling panel is calculated using the
equation from Walton (1980). The mean radiant
temperature (MRT) method is used to calculate the
radiation heat transfer in the multi-surface
enclosure. This multi-surface enclosure is reduced
to a two-surface approximation. For radiant
interchange in a room, one surface is occupied by
the cooling ceiling panel where the average
surface temperature is tp
. The other surface is oc-
cupied by other multi-surface enclosure. This sur-
face is assumed to be a fictitious surface that has
an area emissivity and temperature giving, tr
, about
the same heat transfer from the surface as the real
multi-surfaceenclosure.TheMRTequationisshown
in equation (1)
(1)
where
Fr
= Radiation interchange factor (dimensionless)
= Stefan-Boltzman constant = 5.669x10-8
(W/m2
-K4
)
qr
= Net radiation heat transferred by cooling
ceiling panel (W/m2
)
The fictitious surface temperature, tr
, is
calculated by using the weighted average
temperature and the emissivity of all un-cooled
surfaces. When the emissivities of un-cooled
surfaces are closely equal then the fictitious
surface temperature, tr
, can be approximated from
the weighted surface temperature of all un-cooled
surfaces.
2. Related Theory
The cooling loads considered for the
cooling ceiling panel in this research are radiation
load from floors and walls, natural convection load,
and heat load from lighting fixtures.
Figure 1 Heat transfer mechanism of the cooling ceiling panel
radiation
convection
heat transfer profile
heat source
cooling water
pipe
cooling
element

In practice, the emissivity of nonmetallic or
painted metal nonreflecting surfaces is about 0.9.
When this emissivity is used, the radiation
interchange factor is about 0.87 for most rooms.
Therefore equation (1) can be rewritten as follow;
(2)
where
tp
= Surface temperature of the cooling
ceiling panel (o
C)
AUST = Area-weighted average temperature of
un-cooled surfaces in room (o
C)
2.2 Natural Convection Heat Transfer
The convection heat transfer in the
cooling ceiling panel system is normally natural. The
air motion is generated by the cooling of the
boundary layer of air near the panel. However, in
practice, many factors such as, infiltration or the
movement of persons may interfere and affect
natural convection or even induces forced
convection.
The convection heat transfer for the
cooling ceiling panel is calculated by using the
equationfromSchutrumandVouris(1954).Schutrum
and Vouris also showed that the room size
normally has no significant effect to the rate of
natural convection heat transfer except for the
very large size of room. Therefore the natural
convection heat transfer rate for the panel is
calculated as follow;
(3)
where
qc
= Heat transfer by natural convection (W/m2
)
tp
= Surface temperature of the panel (o
C)
ta
= Air temperature (o
C)
2.3 Radiation Heat Transfer from
Lighting Fixtures
The heat load inside the set up room in
this research comes from the 40 W light fixture.
The number of light fixture used are varied
depended on each case study. This heat load can
be calculated from
(4)
where
qb
= Radiation heat transfer from light fixture to
panel (W/m2
)
tb
= Surface temperature of light fixture (K)
tp
= Surface temperature of the panel (K)
Ab-p
= Surface area of light fixture (m2
)
nb
= No. of light fixture per unit area (set/m2
)
b
= Emissivity of light fixture surface
= Stefan-Boltzman constant = 5.669x10-8
W/(m2
-K4
)
3. Experimental Set Up
The set up room is 1x2 m. with 1 m. in
height. Eight ceiling cooling panels with size
50x50 cm. are installed inside the room. Closed
cell insulation is used to cover the top of the panel.
Details of the panel is shown in fig. 2. Figure 3
shows the chilled water circuit used in the
experiment. The supplied chilled water

Figure 2 Details of cooling ceiling panel
Figure 3 Chilled water circuit
temperature, supplied chilled water flow rate, and
heat load inside the room are varied in order to
study the effect of these parameters to the cooling
performance of the panel. Five case studies are set
up where the supplied chilled water temperature
to the panel is 6.3, 8.5, 11.1, 14.4, and 16.3 o
C.
Seven additional sub-case studies for each constant
supplied chilled water temperature are also set up
as shown in table 1. Therefore the no. of
experiment is in total of thirty five case studies.
Table 1 7 sub case studies for each constant
supplied chill water temperature
In each experiment, the following
parameters are measured at various time until they
reach the steady state condition, ie. surface
temperature of the panel, floor and internal wall
temperature, supplied and return chilled water
temperature to the panel, and room temperature.
No. Flow rate Internal heat load
1 0.5 liter/min. -
2 1.0 liter/min. -
3 1.5 liter/min. -
4 1.5 liter/min. 1 set of 40 watt light fixture
5 1.5 liter/min. 2 sets of 40 watt light fixture

4. Data Analysis
4.1 Chilled Water Temperature Effect to
the Cooling Performance of the Panel
Results from the experiment in all cases
show that the panel surface temperature decreases
rapidly at the beginning. After that the rate is slow
down and the temperature becomes constant. It is
also found that lower supplied chilled water
temperature results in lower panel surface
temperature provided that the internal heat load is
unchanged. The supplied chilled water temperature
also affects the rate of change of panel surface
temperature at the beginning, ie. at low supplied
chilled water temperature, the panel surface
temperature changes faster than that at high
supplied chilled water temperature as shown in
fig. 4.
The effect of supplied chilled water
temperature to room temperature is shown in fig.
5. With the same heat load, low supplied chilled
water provides lower room temperature at steady
state condition than that at high supplied chilled
water temperature. The supplied chilled water
temperature also has an effect to the rate of change
of room temperature, ie: with low supplied chilled
water temperature, the room temperature changes
faster than that at high supplied chilled water
temperature.
Figure 4 Comparison of mean panel surface temperature for
various chilled water temperature at 1.5 liter/min.
with 2 light fixtures at 40 W. each
Figure 5 Comparison of room temperature for various
supplied chilled water temperature at 1.5 liter/min.
with 2 light fixtures at 40 W. each
Figure 6 Comparison of heat transfer amount of the cooling
ceiling panel and room temperature at steady state
condition for supplied chilled water temperature 6.3,
8.5, 11.1,14.4, and 16.3 o
C at 1.5 liter/min and
2 light fixtures with 40 W each.

The effect of supplied chilled water
temperature to the rate of heat transfer of the panel
is shown in fig. 6. With the same heat load, low
supplied chilled water temperature provides higher
rate of heat transfer of the panel than that at high
supplied chilled water temperature. This is because
the panel surface temperature at steady state
condition is lower at low supplied chilled water
temperature as mentioned earlier. The cooling
performance of the panel increases as the panel
surface temperature decreases. Since the cooling
performance of the panel increases when supplied
chilled water temperature is low, then the panel
can maintain lower room temperature than that
in the case of high supplied chilled water
temperature for the same internal heat load.
4.2 Effect of Chilled Water Flow Rate
to the Cooling Performance of the Panel
Supplied chilled water flow rate has an
important effect to the time required for the panel
surface temperature to approach the steady state
condition. With constant supplied chilled water
temperature, the panel surface temperature
approaches the steady state condition faster at high
supplied chilled water flow rate than that at low
supplied chilled water flow rate. However, supplied
chilled water flow rate plays no effect to the panel
surface temperature at steady state condition as
shown in fig. 7. Similar effect also occurs for the
room temperature as shown in fig. 8.
Fig.9. shows the effect of supplied chilled
water flow rate to the heat transfer rate of the
panel. There is no vivid effect of supplied chilled
water flow rate to the amount of heat transfer of
the panel at steady state condition since the
supplied chilled water flow rate has no effect to
the panel surface temperature at steady state
condition as mentioned earlier.
Figure 7 Comparison of mean panel surface temperature when
supplied chilled water temperature is 8.5 o
C at 0.5,
1, and 1.5 liter/min with no internal heat load
Figure 8 Comparison of room temperature when supplied
chilled water temperature is 8.5 o
C at 0.5, 1, 1.5
liter/min with no internal heat load

Theinternalheatloadalsoaffectstheroom
temperature at steady state condition as shown in
fig.11.Theroomtemperatureapproachesthesteady
state condition at higher temperature for high
internal heat load. The amount of internal
heat load also affects the rate of change of
room temperature at the beginning. The room
temperature changes slower when high amount of
internal heat load is applied.
Figure 10 Comparison of room temperature for 0, 1, 2, 3,
and 4 light fixtures at 40 W. each at 8.5 o
C and
1.5 liter/min. of supplied chilled water flow rate
4.3 Effect of Internal Heat Load to the
Cooling Performance of the Panel
The amount of internal heat load has an
effect to the panel surface temperature at steady
state condition. The panel surface temperature is
higher at high amount of internal heat load while
the rate of change of panel surface temperature is
slower at high internal heat load as shown in
fig. 10
Figure 9 Comparison of heat transfer amount of the panel
and room temperature at steady state condition
when supplied chilled water flow rate is 0.5, 1, 1.5
liter/min at 11.1 o
C with no internal heat load
Figure 10 Comparison of mean panel surface temperature with
0, 1, 2, 3, and 4 light fixtures at 40 W. each for
8.5 o
C and 1.5 liter/min. supplied chilled water flow
rate 5. Derivation of Equations
Data received from the experiment are used
to develop the equations for the panel. The
equations developed are proposed to use as a
guideline to design the cooling ceiling panel.
5.1 EquationforCalculatingtheSurface
Temperature of the Panel
Since conduction heat transfer occurs
between the surface of the panel and chilled water

inside the tube, therefore the main parameter is
the total thermal resistance of the panel (Ru
). It is
the result from the thermal resistance of the tube
wall (rt
), the thermal resistance between the chilled
water tube and the panel (rp
)
Consider the total thermal resistance of the
panel per unit area
(5)
where
Ru
= Total thermal resistance of the panel(m2
-K/W)
rt
= Thermal resistance of the tube wall per unit
distance between the tube (m-K/W)
rs
= Thermal resistance between the tube and
panel per unit distance between the tube
(m-K/W)
rp
= Thermal resistance of the panel (m2
-K/W)
M = Distance between the tubes measured from
center of the tube (m)
rt
and rp
of the panel can be calculated using the
following equations;
(6)
(7)
where
Do
, Di
= Inside and outside diameter of the tube
(m)
kp
= Thermal conductivity of the panel
(W/m-K)
xp
= Thickness of the panel (m)
For the thermal resistance between the tube
and panel per unit distance between the tubes,
ASHRAE (1992) indicates that the thermal
resistance depends on the installed configuration
of the tube to the panel which has no relation to
the tube diameter. Therefore this thermal resistance
can be calculated by developing the relationship
between the difference of panel surface
temperature and mean chilled water temperature,
ie. tm
shown in equation 8, and the amount of
heat transfer through the panel at steady state
condition (qt
) . The result is shown in equation 9
(8)
where
tp
= Mean surface temperature of the panel (o
C)
twi
= Inlet chilled water temperature (o
C)
two
= Outlet chilled water temperature (o
C)
or
(9)
where k is the constant value determined
from the regression analysis and equal to 47.46943
W/m2
-o
C. This k value is in fact the total heat
transfer coefficient of the panel (U) or
(10)
where U is equal to 0.02107 m2
-o
C/W
The total thermal resistance is then used,
along with the rt
and rp
, to calculate the thermal
resistance between the tube and the panel
according to equation 5. Its value is 0.2106 m2
-o
C/W.
Equation 5 is then rearranged along with
tm
from equation 8, rt
and rp
from equation 6
and 7 such that the surface temperature of the
panel is in the left hand side of the equation. The
new arranged equation, equation 11, can be used
to predict the surface temperature of the panel at
steady state condition when the dimension related

where
qt
= Heat flux of the panel at steady state
condition (W/m2
)
tr
= Room temperature at steady state
condition (o
C)
tp
= Mean surface temperature of the panel at
steady state condition (o
C)
A,B= Constants to be found from the
experimental results
The coefficient A and B found from the
experimental results are equal to 7.9194 and 1.1675
respectively. Therefore equation (12) is then
(13)
Substitute tp
from equation 11 into equation 13
The equation above can be used to
calculate the cooling performance of the panel when
knowing the configuration of the tube inside the
panel.
to the panel and the chilled water temperature are
known.
where
tp
= Mean surface temperature of the panel at
steady state condition (o
C)
qt
= Heat flux of the panel at steady state
condition (W/m2
)
tw_avg
=Mean chilled water temperature =
0.5 (twi + two) (o
C)
M =Distancebetweenthetubemeasuredfrom
center of the tube (m)
Do
=Outside diameter of the tube (m)
Di
=Inside diameter of the tube (m)
kt
=Thermal conductivity of the tube (W/m-K)
xp
=Thickness of the panel (m)
kp
=Thermal conductivity of the panel
(W/m-K)
The equation above is then used to develop
the equation for calculating the cooling performance
of the panel.
5.2 Equation for Calculating the
Cooling Performance of the Panel at Steady
State Condition
Results from the experiment are used to
find the relation among the cooling performance of
the panel, the surface temperature of the panel,
and room temperature at steady state condition.
The relation found is shown in equation below
(12)
(11)
(14)

6. Conclusion
Result from the experiment can be concluded as follow;
4. Total rate of heat transfer of the panel
depends on the level of supplied chilled water
temperature. Low supplied chilled water
temperature results in higher rate of heat transfer
of the panel. In the contrary, supplied chilled water
flow rate has no vivid effect to the rate of heat
transfer of the panel at steady state condition.
1. Supplied chilled water temperature has
an effect to the surface temperature of the panel
and room temperature at steady state condition.
Low supplied chilled water temperature results in
lower surface temperature of the panel and room
temperature at the same internal heat load.
2. Supplied chilled water flow rate has no
vivid effect to the level of surface temperature of
the panel and room temperature at steady state
condition. However it affects the time for the panel
surface temperature and room temperature to
approach the steady state condition. High supplied
chilled water flow rate to the panel results in faster
approaching time for the surface temperature of
the panel and room temperature to reach the steady
state condition.
3. The amount of internal heat load has
an effect to the level of surface temperature of the
panel and room temperature at steady state
condition. Higher internal heat load results in higher
surface temperature of the panel and room
temperature at steady state condition.

References
[1] ASHRAE, 1992, ASHRAE Systems and Equipment Handbooks (SI) 1992. Atlanta:
American Society of Heating, Refrigeration and Air-Conditioning Engineers, Inc.
[2] Incropera, F.P., and Dewitt, D.P., 1996, Fundamentals of Heat and Mass Transfer.
4th
ed. New York : John Wiley & Sons.
[3] Walton, G.N., 1980, A new algorithm for radian interchange in room loads calculations.
ASHRAE Transactions 86, p.190-208.
[4] Schutrum, L.F. and J.D. Vouris, 1954, Effects of room size and non-uniformity of panel
temperature on panel performance. ASHRAE Transaction 60, p.455.
[5] Aryut Wattanawanichakorn, 2003, A study of the performance of cooling ceiling panel,
ME thesis, Department of Mechanical Engineering, Chulalongkorn University.

A Study on the Performance of Cooling Ceiling Panel

More Related Content

What's hot (20)

Similar to A Study on the Performance of Cooling Ceiling Panel (20)

More from ООО "ЭкотермоИнжиниринг" (15)

Recently uploaded (20)

A Study on the Performance of Cooling Ceiling Panel