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1.5. Heat driven cooling
The rich solution (rich in ammonia) from the absorber (point 5) is sent
to the desorber (generator). Heat from an external source (Q G ) evaporates
some of the ammonia which is then sent to the condenser (point 1) and
the cycle starts over.
In theory the Platen Munters cycle could reach the same COP as the
Carré single stage cycle. But since it is difficult to build a large plant, a
COP of only 0,2 to 0,3 is what is achieved in practise [18].
1.5.4 Adsorption
An adsorbent is a material which attracts water vapor. Zeolite is an
adsorbent which has a surface area of 1000 m2 . Another example of a
g
adsorbent is silica-gel/water.
Closed loop
The closed loop is similar to the Carré cycle described previously, but a
significant difference is the intermitted operation.
The adsorber, which contains refrigerant (water vapor), is heated
by an external source while it is isolated from (not connected to) the
evaporator and condenser. This makes both temperature and pressure
increase. When the pressure reaches the condensation pressure of the
refrigerant the adsorber is connected to the condenser while heating of
the adsorber continues.
The condenser and adsorber are disconnected. The condensed
refrigerant is expanded through a valve and sent to the evaporator.
The adsorber is cooled down to the initial temperature. When this
temperature is reached the adsorber is connected to the evaporator.
The evaporating refrigerant is adsorbed by the adsorber. Finally the
adsorber and evaporator are disconnected and the adsorber is heated.
The cycle start over.
The cycle can be upgraded to a quasi-continuous cycle by applying an
extra adsorber bed. The two-bed adsorption cycle is shown in appendix
B.3 page 230. In practise the COP can reach 0,7 if the adsorber is supplied
with heat at 90 ◦ C [35].
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