Solar hybrid air-conditioning design for buildings in hot and humid climates - Solar Energy Sciences and Engineering Applications - page 500

the size of the hot water storage tank was 5 m 3 . Based on the design indoor condi-
tions of 22 ◦ C and 60%RH, the estimated design zone sensible and latent loads came
out at 19 kW and 13 kW respectively, reflecting the relatively high latent component.
The performance results of the SHAC-VCC and conventional systems for the restaurant
are presented in Table 15.3.5.
For the design RH of 60% in Table 15.3.1, the total primary energy consumption
of the SHAC is lower than that of the conventional system by 49.5%. The huge dif-
ference is due to the substantial sub-cooling and reheating of the supply air, as well
as the large supply air flow rate. It is also apparent that the SHAC-VCC can offer T z
without overcooling and close to the design value of 22 ◦ C. In the SHAC-VCC, the zone
thermostat and the zone humidistat can control the supply air cooling coil (mainly for
handling the sensible cooling load) and the heating coil (mainly for the latent load)
separately, so the zone temperature and humidity can be maintained more steadily
throughout different loading and climatic conditions in the course of a year. However,
this is not the case in the conventional AC system. Although zone thermostat and zone
humidistat are provided, they are used to control the one, and only one, cooling coil,
which handles both the sensible and latent load simultaneously. As such, the supply
air temperature, and hence the zone temperature, tends to be sub-cooled very low in
order to fulfil the design humidity. Thus, the independent humidity and temperature
controls are not as effective as that of the SHAC. Table 15.3.5 also shows that the
annually averaged COP ch of the SHAC is better than that of the conventional system
by 5%. The solar fraction of the SHAC is about 0.3, indicating that auxiliary heating
has a role in supporting the year-round operation.
In order to prove better performance by the SHAC system, a scenario of a higher
indoor RH of 70% is involved, since this may be favourable to the conventional AC
system. To evaluate this, the minimum dewpoint temperature is decreased to 10 ◦ C
and the supply air temperature is lowered to about 12 ◦ C. Since the reheat demand is
cut, the capacity of the chiller is therefore reduced and the supply air flow rate drops
accordingly. The lower part of Table 15.3.5 presents the performance results of this
scenario. It can be seen that the total primary energy consumption of the conventional
system is still higher, but much closer to that of the SHAC. Now the SHAC can have
22.7% less E p at 70%RH, instead of 49.5% less at 60%RH.

Table 15.3.5 Summary of cooling and energy performances of SHAC and conventional systems for
Chinese restaurant at 60%RH and 70%RH.

Year-round Year-round

Design averaged Year-round total E p per Energy

relative T z ( ◦ C)/ Year-round averaged AC area saving vs.

(kWh/m 2 ) Type of system humidity RH z (%) averaged SF COP ch /COP dc WCVCC

SHAC-VCC 60% 22.2/56.2 0.295 3.39/0.63 1,699 49.5%

WCVCC 60% 21.4/63.0 NA 3.23/NA 3,362 NA

SHAC-VCC 70% 22.4/59.8 0.441 3.41/0.80 1,348 22.7%

WCVCC 70% 20.2/72.4 NA 3.23/NA 1,743 NA

Remarks: NA means not applicable.