Re ECF Project: 2008-22

Project Title: Study on the Feasibility and Cost-effectiveness of a Hybrid Desiccant and Evaporative Cooling System Applied in Hong Kong

Applicant: The Hong Kong Polytechnic University (Dr. Fu XIAO)

Total Approved Grant: $204,000

Duration: 4/1/2010 to 3/1/2011

Project Status/Remarks: Completed

Scope:
The project is to study a hybrid desiccant and evaporative cooling system dedicated to application in Hong Kong. In view of the stringent schedule for phasing out CFC and HCFCs, alternative air conditioning scheme is urgently required. The hybrid system is an environmentally friendly alternative to conventional vapor-compression based air conditioning systems. The hybrid system does not use CFC and HCFCs as refrigerant and it is capable of saving a large amount of energy consumed for air conditioning and providing more healthy and comfortable built environment.

Summary of the Findings/Outcomes:
(1) It is feasible to adopt the hybrid liquid desiccant and evaporative cooling system in HK considering HK's climate condition. However, indirect multi-stage evaporative cooling is necessary due to the high wet bulb temperature in HK, which results in high complexity, high initial cost and very large installation space. Thus, the evaporative cooling is not recommended as sensible load removal technology in air conditioning with independent dehumidification in HK.

(2) The power saving ratio of the liquid desiccant based system drops when the fresh air ratio increases. The fresh air ratio is recommended at the range of 40% to 50% considering HK's climate conditions.

(3) Heat pump is suitable option for desiccant solution regeneration in HK. A well capacity matching performance among the heating capacity, the cooling capacity, the regeneration capacity and the dehumidification capacity, can be realized by adjusting the solution flow rate and compressor revolution.

(4) In liquid desiccant based all air conditioning systems, the fresh air and the return air mixed after the dehumidifier, the total energy consumption is lower and the system COP is higher than those when they are mixed before dehumidification.

(5) The annual energy saving of liquid desiccant based air conditioning system with high efficiency heat pump is 17.47% of conventional system in the simulation case study. As for the annual operating costs and green house gas emissions, heat pump and solar heat pump have better performance than gas and electrical boilers.