Liquid Desiccant Air Conditioning Summary
Section 2.3 has provided a review of the literature surrounding liquid desiccant air
conditioning. Key conclusions are as follows:
- • The use of membrane based contactors eliminates the issues of desiccant carryover, resulting in improved indoor air quality, reduced plant corrosion and solution losses. Latent (dehumidifier) effectiveness in the 30-60 % range has been reported.
- • A small amount of work exists regarding the use of potassium formate as a working fluid in liquid desiccant air conditioning applications, demonstrating good dehumidification capacity, particularly in high humidity applications. There is limited published and available literature within the public domain regarding the specific physical characterisation of the CHKO2 solution in the required operating range for liquid desiccant air conditioning applications.
- • The low regeneration temperatures requirement of liquid desiccants, particularly potassium formate, means it can effectively utilise a range of low grade waste or renewable heat sources i.e. fuel cell. Many solar driven systems have been demonstrated.
- • In most cases the required solution temperature in the dehumidifier are 15-20 °C and in the regenerator are 45-55 °C.
- • A liquid desiccant air conditioning system has many variables that have an impact on performance (air, solution and water flow rates, solution concentration etc.). Matching of these variables will be critical to achieving balanced dehumidifier and regenerator operation and successful tri-generation system integration.
- • A compact design is possible, especially when internal contactor cooling is used, however system size/complexity does increase when a further stage of supply air evaporative cooling is required.
- • Liquid desiccant systems can improve the performance of evaporative based coolers, particularly in hot and humid climates. However when using IEC, consideration should be given to the process air requirement.
- • Hybrid desiccant systems demonstrate good overall COPei, improved VCS performance and a more compact form; however the increased electrical consumption compared to the stand-alone systems is undesirable for a tri-generation system application.
- • Low electrical requirement and high COPth makes stand-alone evaporative based systems an attractive option for effective waste heat utilisation. Operating COPth of up to 0.8 has been reported, demonstrating the potential for tri-generation system integration.
- • The effectiveness of stand-alone liquid desiccant evaporative systems is dependent upon inlet air conditions; therefore the geographical location needs careful consideration, and for the tri-generation system control of the inlet environmental conditions may be required.
It is apparent that a membrane based stand-alone liquid desiccant air conditioning
system is the most appropriate system in the development of an efficient and effective tri-generation system.
Next, Sect. 2.4 discusses the use of fuel cell CHP in (domestic) built environment applications.