Active Thermal Cooling Technologies - Low Energy Cooling for Sustainable Buildings - page 184

Table 5.8 Description of air-based cooling systems with achievable supply air temperatures and cooling
power

System description Supply temp./ ◦ C Cooling power/W

1: Heat exchanger (HES) 22.0 671

2: Adsorption wheel (AWheel) 19.6 832

3: Contact matrix (CMAU) 19.4 846

4: Heat exchanger absorber (HEAU) 18.8 886

Model Development

To evaluate the potential of the different system technology options for optimization,
a numerical model was set up for both the HEAU and the CMAU.

Heat ExchangerAbsorberUnit (HEAU) The differential control volume including
the ambient air, water film, desiccant solution film and return air, in a typical absorber
chamber of the HEAU, is shown in Figure 5.73. Heat and mass balances developed
separately for the three nodes (ambient air node 1, water/heat exchanger wall/desiccant
solution node 2 and return air node 3) are shown below. The following subscripts are
used: A , ambient air; R , return air; W , liquid water in film; D , water vapour; S , salt
solution; a , air.

Ambient Air Node 1 Energy balance: the differential enthalpy of the air h A corre-
sponds to the convective heat transfer from water film to air Q c,A plus the evaporation

h W,out , m h S,in , m

, ξ S,in

W,out S,in

h R,in ,x R,in

h A,out ,x A,out

z

h Abs

h ev

1 2

m W

3

m W

y

Q

Q

C,R

C,A

h A,in ,x A,in h R,out ,x R,out

h W,in , m

W,in

h S,out , m

ξ S,out ,

S,out

Figure 5.73 Temperature nodes, enthalpy and heat transfer coefficients of the HEAU