The impact of varying supply inlet temperature and inlet relative humidity at regeneration humidity matching supply air conditions (varying regeneration air humidity) are shown in the following graphs. This is equivalent to using supply air at ambient conditions, heat it up to regeneration temperature and use it for regeneration purposes. Therefore, the difference in absolute humidity between supply and regeneration air flow is zero.

Figure 6. Moisture removal in supply air stream for
varying supply inlet humidity and temperature at 50°C
regeneration temperature.

Figure 6 shows the moisture removal for 50 degC regeneration temperature. At supply inlet conditions of 40°C/95% RH the maximum moisture removal was measured at 5.1 g/kg d. a.. In this point the driving temperature difference is only 10K between supply and regeneration air, however the difference in absolute humidity between supply and regeneration air is zero. Figure 7 shows the results for a regeneration temperature of 80 degC. Here, the maximum moisture removal at supply inlet conditions of 40°C/95% RH was measured at 14.5 g/kg d. a., the difference to Figure 6 being the higher driving temperature difference. It can be seen in Figure 6 and Figure 7 that the moisture removal is considerably lower using heated ambient (supply) air for regeneration purposes, even though the regeneration air is supplied at the same temperatures as that in Figure 4 and Figure 5. This is mainly due to the higher humidity in the regeneration flow. The moisture removal capacity of the desiccant wheel is now mainly determined by the temperature difference between supply and regeneration flow since absolute humidity of supply and regeneration air is equal.

3.1. Silica gel comparison

Two standard materials used for desiccant wheels are silica gel and lithium chloride, with silica gel being the more popular of the two. One aim of this study is therefore to compare the performance of a FAM-Z01 material wheel to a standard silica gel wheel. Eicker et. al [9] investigated the moisture removal of a silica gel wheel over varying wheel speed and regeneration temperature. Their data is
used for the comparison, Figure 8. Eicker et. al tested the silica gel wheel at the conditions given in Table 1. The wheel had a diameter of 1000mm and flow rates of 1500 and 2000 m3/hr were used for regeneration and supply air, respectively. The FAM-Z01 wheel has a diameter of 300mm, hence the flow rates used in the presented work have been reduced as given in Table 2. However, the ratio of regeneration to supply air flow of 0.75 has been kept in the FAM wheel experiments to allow comparison with the results from Eicker et. al. All experiments were undertaken in counterflow mode.

It can be seen in Figure 8 that the moisture removal in the FAM-Z01 wheel is always greater than in the silica gel wheel for the same conditions. The silica gel exhibits a considerable drop in moisture removal at lower wheel speeds while the FAM material shows almost no drop for 60 °C and only a small drop for 75 °C. At a wheel speed of 20 revelations per hour the FAM wheel has a 48% higher moisture removal at 60°C and a 39% higher moisture removal at 75°C regeneration temperature. This excess moisture removal becomes smaller at the highest wheel speed of 85 1/hr. There, the FAM wheel has a 9% higher moisture removal at 60°C and a 4% higher moisture removal at 75°C regeneration temperature.

3. Conclusion

CSIRO Energy Technology is developing a small-scale desiccant-based air-conditioning system for residential applications. In this context, a desiccant wheel made of FAM-Z01 has been experimentally tested for its dehumidification performance.

It was found that for constant regeneration humidity the maximum moisture removal capacity of the material is 17 grams of water per kg dry air at 50°C regeneration temperature and 24 grams of water
per kg dry air at 80°C regeneration temperature from an inlet air stream of 40 °C and 95% relative humidity. The difference in moisture removal between 50 and 80°C regeneration temperature for supply inlet temperatures between 10 and 30°C and supply inlet relative humidity between 20 and 50% was found to be less than 1 g/kg d. a. This shows that a regeneration temperature of 50 °C can almost achieve the same moisture removal at lower inlet humidity supply air.

At varying regeneration humidity (matching ambient conditions) it was found that the moisture removal is considerably lower, even though the regeneration air is supplied at the same temperatures like in Figure 4 and Figure 5. This is mainly due to the higher humidity in the regeneration flow. The moisture removal capacity of the desiccant wheel is mainly determined by the temperature difference between supply and regeneration flow since absolute humidity of supply and regeneration air is equal. Maximum moisture removal was 5.1 g/kg d. a. and 14.5 g/kg d. a. for supply inlet conditions of 40°C/95% RH at 50 degC and 80 degC regeneration temperature, respectively.

The comparison with silica gel performance data yielded a greater moisture removal of FAM-Z01 material under all conditions. At a wheel speed of 20 revelations per hour the FAM wheel has a 48% higher moisture removal at 60°C and a 39% higher moisture removal at 75°C regeneration temperature. This excess moisture removal becomes smaller at the highest compared wheel speed of 85 1/hr. There, the FAM wheel has a 9% higher moisture removal at 60°C and a 4% higher moisture removal at 75°C regeneration temperature.

4. References

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[2] Jia C. X., Dai Y. J., Wu J. Y. and Wang R. Z. (2007). Use of compound desiccant to develop high performance desiccant cooling system. International Journal of Refrigeration 30 (2007) pp345-353

[3] Tokarev M., Gordeeva L., Romannikov V., Glaznev I. and Aristov Y. (2002). New composite sorbent CaCl2 in mesopores for sorption cooling/heating. Int. J. Therm. Sci. 41 (2002) 470-474

[4] Cui Q., Chen H., Tao G. and Yao H. (2005). Performance study of new adsorbent for solid desiccant cooling. Energy 30 (2007), pp 273-279

[5] Restuccia G., Frenia A., Vastaa S. and Aristov Y. (2003). Selective water sorbent for solid sorption chiller: experimental results and modelling. International Journal of Refrigeration 27 (3) 2004, pp. 284­293

[6] Kakiuchi H. (2004). Novel zeolite adsorbents and their application for AHP and desiccant system. Proc. of IEA Expert meeting, IEA Annex 17, Advanced Thermal Energy Storage Techniques, April 18-20 2004, Kizkalesi, Turkey.

[7] Oshima K., Yamazaki M., Takewaki T., Kakiuchi H. and Kodama A. (2006). “Application of Novel FAM Adsorbents in a Desiccant System”, KAGAKUKOGAKURONBUNSHU, Vol. 32, pp.518-523 (in Japanese).

[8] Belding W. A., Delmas M. P.F. and Holeman W. D. (1996). Desiccant aging and its effects on desiccant cooling system performance. Applied Thermal Engineering 16 (5) pp 457-459

[9] Eicker U., Huber M., Schurger U., Schumacher J. and Trinkle A. (2004). Simulation and operation of sorption supported air-conditioning with air collectors in a European comparison. Proc. of 3rd Symposium Solar Cooling, University of Applied Science, April 26-27 2004, Stuttgart, Germany.