Heat Loss Calculation in Air Conditioning System Unit

Abstract
The aim of this report has been achieved since from the calculations in test A the 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 7.484 J and 7.45 J and 7.442 J and
7.461 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.
In addition, 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 14.912 J and
14.935 J and 14.924 J and 14.936 J at the first 40% of the relative power of preheater and the
second 60% of the relative power of preheater.

Introduction
Air conditioning system unit comprises of several components that ranges from recirculating
duct, preheater and reheater, velocity meter, a room model, five temperature sensors (T1 to T5),
sensors RH1 to RH5 and three louvres. The components help the system cool the air below its
dew point, the process involves a release of moisture by a humid air, and is drained and collected
on a drain pan and subsequently from the air conditioning system that will help minimizes the
moisture from the room. The process involves mixing hot a humid air from the outdoor with
stale, the mixed air is cooled and the moisture it contains is exhausted by cooling coil. The
supplied air to the room is first reheated electrically, the moist and heat will be collected from the
surroundings of the room and leaves as air in return, in which its nature will be warmer and
more moist as compared when it initially entered. A fraction of this air in return is mixed with
fresh out of door air and further is supplied back to the room, while the other fraction is lost to
the ambient. It is approximated that the air that will leave the cooling coil will be about 12
degree Celsius to 138 degree Celsius and at 100% relative humidity, while the air in supply is
about 16 degree Celsius to 188 degree Celsius at about 50% relative humidity, always supply of
energy is supposed to be applied on reheat coil to help moderate air at its comfort ability level
before the air is supplied to the room and also the energy is applied to the cooling coil to cool
and dehumidify the process.
The loss of cold air is used to cool again and again warm out of door air by applying a recovery
heat coil, that comprises of rotary heat fan that may have or lack desiccants, heat that is being
supplied to the coil for cooling will be reduced by the recovered energy in the heat exchanger,
noting that a coil for precooling will be fixed at the upstream while the coil that is used for
reheating will be fixed at downstream on the system, therefore the air that is precooled will be
hotter as compared to the air that is supplied after is reheated by reheat coil, and hence energy
that is recovered from the precooling will be used to counterbalanced the reheat load, this will
help in lowering the requirement of operating energy.

Methodology
Equipment
Recirculating duct, preheater and reheater, velocity meter, a room model, five temperature
sensors (T1 to T5), sensors RH1 to RH5 and three louvres.
Procedure
The air conditioning is mixed with the hot and moisture air from the room with stale, the moist
air and warm air that is recirculating will return back to a space of air conditioning, the air that is
in a mixed form will be cooled and its moisture is removed by the cooling coil. The air is then
electrically reheated by reheater before it is supplied to the room. The heat and humid is
collected from the environs of the room and leaves as air in return, in which its nature will be
warmer and more moist as compared when it initially entered. A fraction of this air in return is
mixed with fresh out of door air and further is supplied back to the room, while the other fraction
is lost to the ambient, the temperature will be recorded by temperature sensors while the
humidity will be recorded by RH1 and RH5.

Results of calculations
Assumptions
1. The air is assumed to be dry
2. The flow and temperature are taken to be uniform in the duct
3. The ideal gas law will be used to determine air density
4. 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
Test A
a) Determination of heat loss between T2 and T4 at first 40% power of the preheater
From the lab results
T2 = 28.50C = 301.5 K
T4 = 280C = 301 K
Change in temperature = T2 – T4 = 28.5 – 28 = 0.5 K
At T4 = 301 K
Cp4 = 28.11+0.1967∗10−2∗301+0.4802∗10−5∗3012 −0.1966∗10−9∗3013
28.97
= 1.00558 kJ/kg.K
At T2 = 301.5
Cp2 = 28.11+0.1967∗10−2∗301.5+0.4802∗10−5∗301.52−0.1966∗10−9∗301.53
28.97
= 1.00567