Daily performances

In this section, data and performance figures of the system in a typical day of operation are presented. Figure 2 shows on a psychrometric chart the measured air status in the typical cooling and dehumidification process of the system. It has to be noted that the measured values of humidity ratio are affected of errors probably due to the accuracy of the relative humidity transmitters used. For instance, the outlet humidity ratio of the pre-dehumidification coil CC1 is slightly different from the outside air value, even if the coil was set to off. Also the slope of the dehumidification line (1-3) is lower than the enthalpy line, contrarily to the well known thermodynamics of the process.

1 Подпись: 5 7 9 11 13 15 17 19 21 23 Humidity ratio [g/kg] Fig. 2. - Measured values of the desiccant cooling process in the T-x-diagram - date: 25.07.2008 time: 16.00 — 2 cooling coil — CC1

2 — 3 dehumidification — DW

3 — 4 HX and infiltration of return air

4 — 5 cooling coil — CC2

5 — 6 building

6 — 7 humidification of return air — HU

7 — 8 heat exchanger — HX

8 — 9 condensation heating coil HC1

9 — 10 solar heating coil HC2

10 -11 regeneration — DW

In addition, the humidity ratio at outlet of the heat exchanger (point 4) is higher than at outlet of the desiccant wheel (point 3), probably due to the air leakages from the return air side to the supply air side. For the considered operation conditions, it was estimated a leakage flow rate of about 18% of the whole return air flow rate. In order to reduce the relevance of leakages into the supply air it will be necessary to improve the air sealing system.

Подпись: 90 80 70 60 50 „ О о 40 “ 30 20 10 0 Подпись: O c-i rn ^ IT, 6 К CC C О c-i rn ^ IT, 6 К CC C О -2 cj Fig. 3. Solar radiation, collectors thermal power, heating coil power and various temperatures - date: 25.07.2008 I sol — Solar radiation

P_coll — Solar collectors P_HC 2 — Solar heating coil

T_coll out

Подпись: — — T coll in

T regeneration

4

Figure 3 shows the performance of the solar plant and the regeneration temperature achieved in the heating coil HC 2. It can be noted that the maximum regeneration temperature achieved was 63°C, providing a heating power of 6.4 kW to the regeneration air flow.

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In Figure 4 some results related to the regeneration process are presented. It can be noted that the operation of condensation heat recovery coil HC1 is not continuous but intermittent according to the switching on and off of the chiller. The temperature rise up achieved by means of the condensation coil HC1 is in the range of 12-13 °C. The same figure shows the distribution of the heating power for the regeneration by the heat exchanger, the condensation and solar coils (PHX PHCi P HC2 ) and the efficiency of the heat exchanger ranging from 54 to 70%.

Подпись: Figure 5 shows the results of the cooling power produced in the AHU. It can be noted that the supply temperature of 20°C is met by means of the second cooling coil CC2. No additional dehumidification is generally required to reach the desired supply humidity ratio, due to the moderate humidity ratio of the outside air of about 14 g/kg. The contributions of the cooling power produced by the desiccant cycle PDEC and the auxiliary cooling power PCC2 are shown for the considered sample day of operation.Подпись: OJ) O' image332P CC2 — Cooling coil P DEC — Desiccant cooling P CC1 — Pre-dehumidification coil

——— x set point supply

x supply —•— T supply

——— T set point supply

— — x ext — Outside humidity ratio T ext — Outside temperature

Fig. 5. Cooling power of desiccant cooling cycle and auxiliary cooling coils — date: 25.07.2008