Environmental Engineering Reference
In-Depth Information
I
NTRODUCTION
After the 1973 oil crisis and subsequent rise in fuel prices, there was a change in
approach on a world scale, both in political circles as well as among the population who
realised their dependency on oil producing countries. As a result of these events, interest has
grown in reducing energy demand at all levels, together with a search for more efficient
energy equipment.
The circumstances currently favouring the use of conventional energy
sources not only involve facing up to increased costs as well as the foreseeable exhaustion of
sources, but also include the costs involved in environmental protection and the harmful
effects on the planet arising from their use (increase in the greenhouse effect due to greater
CO
2
emissions into the atmosphere or the destruction of the ozone layer due to emissions
from coolants used in mechanical compression processes for cooling). Nowadays, energy
saving is not an option but rather a priority concern. Using energy efficiently is, in many
cases, the most effective and economic alternative for achieving environmental protection.
In HVAC installations, a solution in terms of improving energy efficiency is the use of air
conditioner recoverers. The systems used can be considered as heat recoverers when they use,
as secondary air, that which is provided by the air-conditioned premises, or just a mixture of
this and outdoor air.
This is the target of this work, in which experimental research has been carried out whose
aim is the energy study of combined recovery equipment, consisting of an evaporative cooler
and a heat pipe device to recover energy at low temperature in air conditioning systems. To
characterize the device empirically, an experimental design technique was employed by
calculating all the characteristics which are involved in the energy analysis developed.
E
VAPORATIVE
C
OOLING
S
YSTEMS
Evaporative cooling offers an alternative for reducing water or air temperature in the
systems that operate using this principle, thus enhancing the performance of the air
conditioning installations in which they are used [1]. Traditionally, three different types of
evaporative cooling systems were available: Direct Systems, Indirect Systems or a multi-step
combination of both systems (Mixed Systems).
In Direct Systems, the water evaporates directly into the supplied air, cooling and
increasing the amount of water in this air in an adiabatic heating process; the air supplies heat
in order to evaporate the water, so the dry bulb temperature decreases and the humidity
increases. The quantity of heat exchanged from the air is equal to the quantity of heat
absorbed by the evaporation of water. If the water is recycled inside the device, its
temperature is almost the wet bulb temperature of the air used in the process.
In the Indirect evaporative coolers, water evaporation takes place in a secondary
airstream which only allows sensible heat exchange with the primary airflow using an
interchanger. The heat transfer surface is cooled by contact with this secondary airflow and
simultaneously, on the other side of the exchanger, the primary airstream is cooled (involving
just sensible heat so humidity is not added). This is the reason why this process is called
indirect and is especially used in those applications where humidity addition is not allowed in
