Heat Loss and Power Dissipation in Air Conditioning Duct

Abstract
The calculations in test A for determining heat loss between temperature T2 and T4 together
with the calculation of the heat loss between temperature T4 and T5 where all determined and
found to be 7.4318 J and 7.4578 J and 7.444 J and 7.3773 J at the first 40% of the relative power
of preheater and the second 60% of the relative power of preheater of power of the heater.
The comparison was made between test A and B and was found out through calculation that heat
loss in test B were higher than those that were calculated in test A, because of a higher change in
temperature in test B.
Moreover, the calculation of heat loss in test B between temperature T5 and T1 and also
calculation of heat loss between temperature T4 and T5 were determined to be 14.16557 J and
14.919 J and 14.1762 J and 14.933 J at the first 40% of the relative power of preheater and the
second 60% of the relative power of preheater.
Furthermore, the calculation of power dissipated by the preheater was also determined in test A
between the temperature T1 and T2 as 7.443 W for the first 40% of the relative power of
preheater and 7.447 W for the second 60% of the relative power of preheater, similarly in test B
between the temperature T1 and T2 as 14.176 W for the first 40% of the relative power of
preheater and 14.931 W for the second 60% of the relative power of preheater.

Introduction
Operation of the air conditioning duct
Air conditioning comprises of several components that effectively helps it effective operations
that ranges from, recirculating duct, preheater and reheater, velocity meter, temperature sensors,
fans and louvres.
The process involves pumping air through ducts, with which its role is to keep the air inside the
system cool as it move through it, for energy efficiency of the air conditioning to be achieved the
system will be zoned, this will help the system to operate effectively at a constant sections that
will help the system not to be fully closed, in order to avoid building up pressure around the duct
that may cause damage.
Existence of regulators will help control the air that will enter through the diffuser into
circulation through the system zones, the diffusers role is to ensure that air is allowed to enter
through each and every required section, the regulators opens and close to ensure that fresh air
enters the system.
The system will receive back the air through grilles that helps to purify the air in circulation.
Objectives
1. To determine heat flow rate and heat losses
2. To determine the heat loss between T2 and T4 and the heat loss between T4 and T5 in
test A
3. To determine how heat loss is affected by temperature T2
4. To determine power supplied by preheater in test A and test B and discussing their there
difference.
5. To determine heat loss between T5 and T1, and heat loss between T4 and T5 in test B.

Results and Calculations
Equipment
Recirculating duct, preheater and reheater, velocity meter, a room model, five temperature
sensors (T1 to T5), sensors RH1 to RH5 and three louvres.
The following will be assumptions that will be used;
a) The air is assumed to be dry
b) The flow and temperature are taken to be uniform in the duct
c) The ideal gas law will be used to determine air density
d) The specific heat of air will be calculated based on the formula
Cp = 28.11+0.1967∗10−2∗T + 0.4802∗10−5∗T 2−0.1966∗10−9∗T3
28.97
Procedure
1. The air condenser absorbs the air into the ducts through the vents
2. The air is used to cool the gas in the evaporator, and in the process of removing heat
from the air it will be cooled,
3. The duct supplies the air back into the room.
4. Continuous supply cold air to the room until the air inside the room reaches a desired
temperature (Yau, 2008).
5. The thermostat sensor senses the temperature inside the room as reached a desired level
in order for it to automatically shut down the air conditioner
6. The process that will raise the temperature again in the room the thermostat is sense and
starts the air conditioner on again and the process
7. The process will continue again until, an ambient temperature will be achieved once
again (Yang, Yan, and Mullen, 2012).
8. Record the temperatures and velocities in the table below at 40% and 60% of relative
power of preheater

Results from the lab
Tests Relative
speed
of the
fan(%)
Relativel
y power
of the
preheater
(%)
V1(m/s) V2(m/s) T1 (0C) T2 (0C) T3
(0C)
T4 (0C) T5
(0C)
Test A
Open
system
1 50% 40% 0.9 0.1 22.6 27.2 26.8 26.5 25.3
2 50% 60% 0.9 0.1 22.6 29.8 29.3 28.9 27.5
Test B
Closed
system
1 50% 40% 0.9 1.0 28.5 32.8 32.2 31.8 29.5
2 50% 60% 0.9 1.1 29.2 35/0 34.2 33.6 30.5
Calculations
Test A
a) Determination of heat loss between T2 and T4 at first 40% power of the preheater
From the lab results
T2 = 27.20C = 300.2 K
T4 = 26.50C = 299.5 K
Change in temperature = T2 – T4 = 27.2 – 26.5 = 0.7 K
At T4 = 299.5 K
Cp4 = 28.11+0.1967∗10−2∗299.5+0.4802∗10−5∗299.52−0.1966∗10−9∗299.53
28.97
= 1.00534 kJ/kg.K
At T2 = 300.2 K
Cp2 = 28.11+0.1967∗10−2∗300.2+0.4802∗10−5∗300.22 −0.1966∗10−9∗300.23
28.97
= 1.00545
∆ Q2-4 = ̇m(Cp2*T2 - Cp4*T4)