Liquid Dessicant Solar Air-Conditioner - Methodology

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The objective of this project is to design and manufacture the desiccant dehumidification and evaporative cooling module (to operate initially without desiccant regeneration) to be installed in a specified test area of approximately 100 m².

a) Identification of indoor space to be conditioned by the module

The indoor space to be conditioned is the engineering office site of the Milton Brewery located at Black Street, Brisbane. The office area is approximately 100 m² with a ceiling height of 2.4 m; therefore, it has a volume of about 240 m³. Presently the office is served by 4 Carrier DX reverse cycle air conditioners located in four different compartments of the office as indicated on the plan. They have different power ratings, which are: 6.4 kW, 4.2 kW, 2.12 kW and 2 kW. Therefore, the maximum power consumed by the air conditioners is 14.7 kW. Furthermore, based on a cooling load calculation an LDSAC with a maximum of a single PHE with dimensions: 570 x 570 x 1175 mm as dehumidification/indirect evaporative cooling module would be sufficient to produce the same amount of power rating (14.7 kW) and the necessary cooling and dehumidification for the conditioned space.

Design drawings of the LDSAC casing showing the components to be incorporated into the system have been provided. It has also been decided that in order to facilitate the manufacturing of the conditioner unit, a model casing using cardboard material be initially built. The reason for this is due to the fact that extrusion moulding technique has to be employed in the production of the casing using FRP (Fibre Reinforced Polymer) which is resistive against the corrosive nature of the desiccant solution. The installation of the air conditioner will be carried out using split duct system in which each office compartment will be conditioned through a register mounted in the ceiling. The whole air conditioner should, therefore, be located on the concrete roof of the engineering office site.

b) Specifications for module components

As was already described the conditioner dimensions depend on the component sizes to be included inside the system, consequently, the dimensions of all the unit components, such as the PHE, fans, pumps, cooling pads, etc. have to be identified prior to system design. The QUT and the industry partner (DACO Building Services Pty, Ltd) are making efforts to get the whole conditioner unit built, installed and tested on the site by the summer 2004-2005. This will, however, depend on the availability of the components and materials, most of which have already been placed on order.

Another important component of the project is the solar hot water system that is waiting for installation on the roof of the test site building. This will provide the hot water at necessary temperature and flow rate from flat plate solar collectors to regenerate the weak desiccant solution obtained from the dehumidifier using gas or electrical energy as the back up.

The regeneration process is by heating the solution up to about 85 °C in a regenerator (typically a liquid-liquid heat exchanger) using hot water from the flat plate solar collectors. To facilitate the boiling of the weak liquid desiccant and removing the water vapour a vacuum pump could be used to produce vacuum over the solution. The vapour thus produced has to be, subsequently, separated from the liquid using a vapour separator device.

Outcomes

The outcomes of this project will include:

• Development of a comprehensive, experimentally tested prototype for LDSAC.  The prototype will be tested and monitored for several weeks to investigate the key attributes of the design to permit optimization of LDSAC products.
• Enlargement of the geographical area (within and outside Australia) where evaporative air conditioning technology can be used.
• Reduction of peak energy demands during the cooling periods.
• Reduction of CO₂ emissions.
• Facilitation of the local production of a new range of air conditioning systems with potential worldwide applications.

The application of desiccant technology to provide a healthy indoor environment in an energy efficient manner is a technology that can be adopted by the building services engineer in the application of good building design. Desiccants can reduce and even eliminate reliance on refrigerants and contribute to a reduction in carbon emissions, thus reducing the negative impact of buildings. The market for energy efficient cooling systems is increasing rapidly because of the concerns about the effects of global warming, energy use and life cycle costs.

Calculations indicate that the electrical requirement for the peak design load system is 4kW and the daily electrical energy consumption is about 60kW.  Assuming an electricity tariff of approximately 10cents/kWh in Australia, the total annual cost would be A$80,000 and the total annual amount of electricity consumption for the whole office building is about $12,000. 

Solar Regeneration using Solar Hot Water Collector from KATHABAR INC. (U.S. based company)