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DOAS is anall air system without return air, and it eliminates intercross-ing infection existing in all air system with return air. DOASalso exhibits better effect of energy saving. When the effec-tiveness of total heat exchanger is 65%, DOAS using CC asSHRTD can save the electric energy by 42%, compared withconventional VAV systems (Jeong et al., 2003). As the energyconsumption of DOAS highly depends on the efficiency of to-tal heat recovery devices, it would be important to developthe heat recovery devices with high efficiency. In addition,to ensure that DOAS runs effectively and safely, furtherwork needs to be done to improve automatic control system, and to enhance the compatibility among different parts ofDOAS.3.1.2. Independent control of temperatureand humidity system (ICTHS)Conventional AC systems firstly cool air below the dew-pointtemperature in order to condense moisture out, and thenreheat it to the supply comfortable temperature before deliv-ering it to the occupied spaces. This leads to low evaporatingtemperature, a poor COP value for the chiller, and higherenergy consumption.Moreover, the FCUmay become the hot-bed ofmany kinds ofmildew due to the existence of condens-ing water, which will deteriorate IAQ. The reason for all theseproblems is that the cooling process and the dehumidifyingprocess are in the same unit and at the same time, but thereis an essential difference between the two processes (Chenet al., 2004). ICTHS can realize the independent control oftemperature and humidity, and resolve the problems above.An ICTHS is shown in Fig. 2 (Liu et al., 2006). The ICTHSconsists of a liquid desiccant system and a cooling/heatinggrid system. The liquid desiccant system is composed of out-door air processors (serving as dehumidifier in summer andhumidifier in winter), a regenerator, and a desiccant storagetank. LiBr solution is used as liquid desiccant in the system,and the regeneration temperature is about 60 C. The cool-ing/heating grid system is composed of the power driven re-frigerator, the heat grid, and the FCU or radiant ceiling. Insummer operations, valves A and C are turned on and valveB is turned off, and the ICTHS performs dehumidificationand cooling of the air. Chilled water with temperature of 15–18 C flows from the refrigerator into the outdoor airprocessors and the indoor terminal devices. The outdoor airprocessors remove the total latent load and a portion of sensi-ble load of the occupied space, while the indoor terminaldevices deal with the remained sensible load. IAQ is greatlyimproved because of the following two main reasons: (i)indoor terminal devices operate in dry condition, and nocondensing water will be produced on the surfaces of the ACsystem; (ii) the liquid desiccant can remove a number ofpollutants from the air stream. In winter operations, valvesA and C are turned off and valve B is turned on, and the ICTHSperforms humidification and heating of the air. Hot waterfrom the heat grid flows into the outdoor air processors andindoor terminal devices. The operating principle of the out-door air processor is shown in Fig. 3. The outdoor air processorconsists of two parts. The left of the broken line is a three-stage total heat recovery device using liquid desiccant,and the right of the broken line is a single-stage spray unit(Li et al., 2003).The ICTHS can not only improve IAQ but reduce energyconsumption and operation cost. In summer, when the latentload of the building covers from 10% to 50%, the primaryenergy consumption of the ICTHS is 76–80% and the operationcost is about 75% of that of the conventional AC systems. Inwinter, when latent load of the building are 5%, 10% and15%, the primary energy consumption of the ICTHS is 77%,62% and 45%, respectively, and the operation cost is 75%,57% and 42%, respectively, compared with that of a conven-tional AC systems (Liu et al., 2006). If solar energy or wasteheat is used to regenerate desiccant, and ground water is used to cool indoor air,more energy and operation cost wouldbe saved. However, the FCU in ICTHS is only used to cool in-door air and is different fromthe FCU in conventional AC sys-tems. So the FCU in ICTHS needs to be redesigned.3.1.3. Cooling ceiling and displacement ventilationsystems (CC/DV)DV system performs well on eliminating indoor pollutantsand improving IAQ, but it sometimes is incapable of meetingindoor cooling load due to the limitation of temperature andvelocity of air distribution, which may lower the indoorthermal comfort. CC system performs well on indoor thermalcomfort, but it cannot improve IAQ due to its configuration. Soit can be found that DV system and CC system can offset thedisadvantages each other. In combined CC/DV systems, theCC panels remove part of sensible cooling load by convectionand radiation, while DV system removes indoor pollutants,latent cooling load and the other part of sensible cooling load.For combined CC/DV systems, the vertical temperaturegradient should exist because it indicates stratified airflowpattern and vertical stratification of pollutants. On the otherhand, the temperature gradient should be small for anacceptable thermal comfort. Table 1 presents the verticaltemperature gradient in the occupied zone (0.1–1.1m abovethe floor) obtained from several studies. The temperaturegradient in the occupied zone varies from 0 to 2 Km 1, whichimplies that it is almost completely uncertain. These differences are due to different experimental thermal condi-tions and fluid flow conditions, such as cooling loads, ventila-tion rates, supply air temperatures and CC paneltemperatures. Velocity is another important thermal comfortparameter. Loveday et al. (1998) reported that a low CC tem-perature, which increased the CC cooling capacity, could in-crease air velocities in the occupied zone.