Compression/Absorption cycles for large heat pumps - Systems simulations
The compression/absorption cycle can, in many situations,
give an improved performance compared to the single-fluid
compression heat pump. Also other advantages can be
achieved such as the possibility to use an already known
refrigerant within a new temperature range. From environmental aspects this is important since it offers a
possibility to reduce the use of the halogenated
hydrocarbons Rll, R12 and Rl14 which are destructive to
the ozone layer.
In this work three different compression/absorption
cycles, using a mixture of ammonia and water, were simulated.
From the beginning the three mixtures H2o/LiBr,
CH 30H/LiBr and NH3/H2o were considered but since NH3/H2o
gave the better performance it was chosen for the further
study. The three cycles were chosen with the intention to
achieve an improved performance for three different
- when the temperature gradients of the heat sink and the
heat source are large and of the same magnitude
- when the tempe~ature gradient of the heat source is
large compared to the gradient of the heat sink
- when a large temperature lift is required
A comparison between the compression/absorption cycle and
a compression cycle working with the optimal refrigerant
within each temperature range shows an improvement in COP
for the former cycle ranging from 0% to 30%. The specific
capacity shows an even larger improvement for the
compression/absorption cycle, between 35% and 55%. When
considering the compression/absorption cycle in different
case studies the greatest improvement is achieved for the industrial cases where the temperature level is high.
Also at lower temperature levels there is an improvement
for the situations where the temperature gradients of the
sink and the source are large.