Solar hybrid air-conditioning design for buildings in hot and humid climates - Solar Energy Sciences and Engineering Applications - page 499

from 445 kW/m 2 to 310 kW/m 2 (a 30.3% drop) in SHAC-Ad. A higher percentage
reduction in primary energy consumption can be achieved by the hybrid system with
the adsorption chiller; this is because there is a more significant percentage rise of SF in
the adsorption chiller, and hence the decrease in the driving energy is more substantial.
Recently, a novel indoor ventilation strategy, called stratum ventilation (SV), has
been advocated (Lin et al., 2009). Stratum ventilation uses an even higher supply
temperature than displacement ventilation, and the energy saving potential of SHAC
can be further advanced. This will undoubtedly enhance solar energy deployment in
air-conditioning for buildings.

15.3.5 SHAC for premises with high latent load
In conventional AC design, a cooling coil is used to conduct both the cooling and
dehumidification processes for the supply air. This is suitable for typical offices and
residential units, where the zone sensible load is more significant in the total cool-
ing load. However, some commercial premises have a high zone latent load with
which conventional AC provision cannot cope effectively. Such commercial premises
are common and include restaurants, indoor food markets and entrance lobbies. The
latent heat gain of these building zones comes from humid fresh air, the building's
occupants and indoor services such as hot food, spas and water ponds. Additional
latent heat gain can be caused by excessive infiltration and frequent opening to the
outdoors.
Because of the high latent load for this kind of building zone, substantial sub-
cooling followed by reheating of the supply air is needed in conventional AC design,
causing high energy requirements. In addition, it is common for these AC systems to
suffer over-cooling problems in these premises. As AC equipment is designed to suit
the latent load, so its sensible cooling capacity naturally becomes over-provided. If
there is no reheat provision, and no simultaneous temperature and humidity control,
this can cause thermal comfort problems. As a result of this over-cooling potential, it is
common for people to wear jackets or additional clothing, thus defeating the primary
objective of air-conditioning: i.e. thermal comfort. In addition, there is risk of con-
densation at the supply air grilles because of low supply air temperature. To alleviate
the high energy demand and thermal discomfort problem associated with conven-
tional AC design, SHAC with desiccant cooling can fit the purpose; the appropriate
system for premises with high latent load is illustrated in Figure 15.2.7 of Section
15.2.4.2. Solar-thermal energy is primarily used for desiccant cooling, and electric-
ity from the power grid for the VCC, so this solar hybrid design is represented by
SHAC-VCC.
In a previous study carried out by Fong et al. (2011c), dynamic simulation was
used for energy evaluation of a Chinese restaurant in which the ratio of the installed
collector area and the conditioned space was again 1:2. The restaurant used in the
stuady - typical of premises with a high latent load in subtropical Hong Kong - had an
area of 196 m 2 and an occupant density of 1 m 2 /person. The daily occupancy schedule
covered 17 hours between 6:00 a.m. and 11:00 p.m. The design outdoor air amount
was determined at 0.01 m 3 /s/person. The lighting heat gain was 20 W/m 2 (with 70%
radiative). The other sensible and latent heat gains were 1.23 kW (with 50% radiative)
and 1.77 kW respectively. The total net area of the evacuated tubes was 100 m 2

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