In this section, possible system configurations of the solid desiccant-assisted MAC are discussed. For the MAC application, a polymer desiccant can be applied which can be regenerated with low temperature. Depending on the location of the DW and components,five different DW-applied MAC systems are proposed as follows:
• SD-MAC option 1: The evaporator is located before the DW, and two fans are installed in process air-side and regeneration air-side. Airflow for the DW is the counterflow.
• SD-MAC option 2: The DW is located before the evaporator, and two fans are installed in process air-side and regeneration air-side. Airflow for the DW is the counterflow.
0 5 10 15 20 25 30 35
0.000 0.005 0.010 0.015 0.020 0.025
T [°C]
Humidity Ratio
Pressure = 101.3 [kPa]
10°C
15°C
20°C
25°C
0.2 0.4
0.8 0.825
0.85 m3/kg
AirH2O
1
2 3
2'
Fig. 7.11 Psychrometric chart of air cooling and dehumidification process
• SD-MAC option 3: The evaporator is located before the DW, and only one fan is installed in process air-side and regeneration air-side. Airflow for the DW is the counterflow.
• SD-MAC option 4: The DW is located before the evaporator, and only one fan is installed in process air-side and regeneration air-side. Airflow for the DW is the counterflow.
• SD-MAC option 5: The evaporator is located before the DW, and only one fan is installed in process air-side and regeneration air-side. Airflow for the DW is the parallelflow.
Figure7.12 shows the schematic diagram of the SD-MAC option 1. Two fans are installed to operate the process air-side (evaporator-side airstream) and regen- eration air-side (heater core-side airstream). The cooling capacity of the radiative evaporator is obtained from the VCC. The radiative evaporator is optionally applied. When cooling and dehumidification are required, the damper becomes“a” mode, which directs the air to go to the evaporator. With“a”mode, outside air (or returned air from the cabin) goes to the evaporator and DW (1–2–3–4 as shown in Fig.7.12). Then, cold and dry air is provided to the cabin. When heating is required, the damper becomes“b”mode. Outside air goes to the heater core and then provided to the cabin (1–5–3–4 as shown in Fig. 7.12). In this case, the evaporator and DW do not work.
Figure7.13 shows the schematic diagram of the SD-MAC option 2. Working principle is the same as SD-MAC option 1. The difference from the SD-MAC option 1 is the location of the DW. DW is installed before the evaporator. The advantage of SD-MAC option 1 is that hot and humid air is cooled down at the evaporator. Then, the air exiting from the evaporator is very humid, and in other
Evaporator
Heater Core
Defrost Vent
Foot Vent Face Vent
Cabin
Radiative Evaporator (Optional)
Outside Air
DW
To Outside a
b
1
2 3 4
5
Fig. 7.12 Schematic diagram of SD-MAC option 1
words, the relative humidity is very high. Therefore, the DW performance can be maximized. This means DW size can be compact. However, the air temperature exiting from the DW is increased, since this is an isenthalpic process. In addition, there could be a latent heat transfer in the evaporator. For SD-MAC option 2, hot and humid air goes to the DWfirst, and then, hot and dry air is cooled down by the evaporator. Since the evaporator only takes care of sensible heat transfer, con- densate water from the evaporator can be minimized. In the MAC system, con- densate water in the evaporator causes odor problem. Therefore, this option 2 can significantly reduce odor problems caused by condensate water.
Figure7.14shows the schematic diagram of the SD-MAC option 3. This option is similar to the SD-MAC option 1, but uses only one fan. The fan is installed to take the outside air (or recirculated air). When cooling is required, the damper mode is “a” mode, and the fan pushes the air to both airstreams, evaporator-side and heater core-side. When heating is required, the damper acts as“b”mode. Then, air exiting from the fan only goes to the heater core. For the heating mode, the fan power can be reduced. As a same manner, the evaporator and DW do not work at the heating mode. Figure7.15shows the schematic diagram of SD-MAC option 4.
The DW is located before the evaporator and the system are operated with one fan.
The working principle is the same as SD-MAC option 3.
Figure7.16shows the schematic diagram of the SD-MAC option 5. This option utilizes only one fan. The airstream can be simpler than other options by applying parallel airflow. The performance of the typical DW can be maximized by designing counterairflow as shown in SD-MAC option 1–4. For SD-MAC option 5,
Evaporator
DW
Heater Core
Defrost Vent
Foot Vent Face Vent
Cabin
Radiative Evaporator (Optional)
Outside Air To Outside
Fig. 7.13 Schematic diagram of SD-MAC option 2
Evaporator
Heater Core
Defrost Vent
Foot Vent Face Vent
Cabin
Radiative Evaporator (Optional)
Outside Air
DW
To Outside a
b
Fig. 7.14 Schematic diagram of SD-MAC option 3
Evaporator
Heater Core
Defrost Vent
Foot Vent Face Vent
Cabin
Radiative Evaporator (Optional)
Outside Air
DW
To Outside
Fig. 7.15 Schematic diagram of SD-MAC option 4
the DW performance can be degraded, which means DW size would be designed larger than other options. However, this option does not require major modification of the current MAC system and easily applicable.