Solar hybrid air-conditioning design for buildings in hot and humid climates - Solar Energy Sciences and Engineering Applications - page 497

chilled beams are 64.7% and 63.9% less than that of ACVCC and WCVCC respec-
tively, while those of the SHAC-Ad system are 41.2% and 39.9% less respectively. On
the other hand, the yearly E p of the SHAC-Ab system using active chilled beams are
50.8% and 49.6% less than the two conventional systems, while those of the SHAC-
Ad system are 20.0% and 18.1% less. It has been found that passive chilled beams
have higher SF and lower yearly E p compared to active ones. This is because the better
COP ch of absorption/adsorption chillers results in less frequent heat demand for gener-
ation/desorption from the solar-thermal gain. On the other hand, active chilled beams
require substantial energy demand from the additional supply air and return air fans.
In this hybrid design it is clear that the adsorption chiller also has an essential role in
overall energy merit. By adopting an appropriate high temperature cooling approach,
the feature of low driving temperature of adsorption chillers can be effective.
From this study it can be seen that using passive chilled beams is the best choice for
SHAC systems working in hot and humid regions. Passive chilled beams also have other
merits, such as silent operation and free from drafts, making this option more attrac-
tive. Of course, prevention of condensation is of primary importance during humid
weather. The involvement of desiccant cooling in SHAC can control indoor humidity
effectively. The problem of infiltration of the building envelope can be avoided by
use of good-quality building materials and workmanship, together with positive air
pressurization in the building zone.
15.3.4 SHAC coordinated with new indoor ventilation strategies
In the conventional design of indoor air distribution of supply air, mixing ventilation
(MV) is used in order to have homogenous air conditions within the entire building
zone. The supply air temperature of MV is generally around 15 ◦ C. If the supply air
temperature is raised without sacrificing thermal comfort, this can help to enhance
overall energy performance. Therefore displacement ventilation (DV), which allows a
supply air temperature of 19 ◦ C for office use (Lin et al., 2005), has been promoted.
This provides a useful strategy for high temperature cooling for solar air-conditioning.
In this sense, the supply air flow rate of DV can be maintained or even reduced com-
pared to that of MV, but a higher return/exhaust air temperature results. This can also
reduce ventilation load, and hence the cooling capacity of the entire air-conditioning
system. As such, SHAC combined with appropriate indoor ventilation strategies gives
another alternative, as described in Section 15.2.3.2. In this hybrid design, either the
absorption or adsorption chiller can be paired with the desiccant cooling unit for the
return air scheme. As the latent cooling load of the building zone can be handled by
the desiccant cycle, the problem of insufficient latent capacity due to the higher supply
air temperature of DV can be solved.
Figure 15.3.3 depicts the configuration of SHAC coordinated with DV. In DV,
air is supplied to the building zone at floor level and exhausted at ceiling level. A
temperature gradient, and subsequently a humidity gradient, is developed along the
zone height, maintaining thermal comfort mainly within the occupied zone, regard-
less of the level above it. A common hot water storage tank is used to provide the
driving heat for both the desiccant cycle and the heat-driven chiller, but separate aux-
iliary heaters can be added. The results of cooling and energy performances of SHAC