IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C1 Report, 31 October 2010
Table 2: Process data in case of dry heat rejection for four locations (single stage,
continuous operation, evaporation at 0°C, NH3/H2O)
Location
Outside air
temp.
Low
process
temp.
High
process
temp.
Condensation
pressure
Heating
medium
temp.
WF
concentration
°C °C °C bar °C %
Naples 30 40 98 16,0 105/95 47/41
Athen 33 43 112 18,0 117/109 43/37
Johannesburg 28 38 96 15,5 101/93 48/42
Abu Dhabi 41 51 118 22 123/115 40/34
2.5 Relevant references – Ammonia/Water Systems
In particular, references [2] and [3] give the reader the answers to the key questions of
absorption refrigeration technology.
[1] Mouchot, Augustin, La chaleur Solaire et ses Applications Industrielles, (German
translation 1987, published in Olynthus Verlag, 1987)
[2] Niebergall, W., Sorptionskältemaschinen, Handbuch der Kältetechnik, Bd 7, Springer
Verlag, 1959.
[3] Bogard, M., Ammonia Absorption Refrigeration in Industrial Processes, Gulf Publishing
Company, Book Division, Housten, Paris, London, Tokyo
[4] Grosman, G., Bourne, J.R., Ben-Dror, J., Kimichi, Y., Vardi, I., Design improvements in
LiBr absorption chillers for solar applications, Transactions ASME, Journal of Solar
Energy Engineering, 103 56-61 (1981)
[5] Podesser, E., Solare Kühlung, Dissertation an der Technischen Universität Graz, Fakultät
für Maschinenbau, Institut für Wärmetechnik (Prof. P. V. Gilli), 1984.
[6] Podesser, E., Enzinger, P., Gossar, H., Monschein, W., Taferner, I., Proceedings of the
XVII International Congress of refrigeration, Vienna 1987.
2.6 Description of the technology – Water/Lithium Bromide Systems
Robert Ghirlando (University of Malta)
The principle of operation of absorption cycles has already been described in detailed in the
preceding sections. Hence this section will limit itself to pointing out some important
differences between the two working fluid pairs, i.e. ammonia/water and water/lithium
bromide.
The most common combinations of refrigerant and absorbent are ammonia/water and
water/lithium bromide. Since in the water/lithium combination, the refrigerant is water, the
condensing temperature cannot go below 0 0 C; in fact the minimum temperature that can be
reached is 3 0 C. This is a problem in refrigeration, but not in air-conditioning. On the other
hand, in the ammonia/water pair, the refrigerant is ammonia which can condense at
temperatures below zero and can therefore be used in refrigeration applications. Water has a
high latent heat and its use as a refrigerant in H 2 O/LiBr systems is an advantage. It is
important to point out that in the H 2 O/LiBr system, for the water to evaporate at the very low
temperatures required to produce the desired cooling effect, it needs to be at a very low
pressure. At 4 0 C, for example, water vapour pressure is only 0.8kPa, i.e. 8millibar. On the
other hand, ammonia-water systems operate above atmospheric pressure. Also LiBr tends
to crystallize, and methods have been devised to prevent this from happening. These
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