טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentEvron Yigal
SubjectHybrid Air Conditioning Based on Combined Closed-Cycle
Absorption Cooling System and an Open-Cycle liquid
Desiccant System
DepartmentDepartment of Mechanical Engineering
Supervisors Professor Emeritus Gershon Grossman
Dr. Khaled Gommed
Full Thesis textFull thesis text - English Version


Abstract

An Air-Conditioning (A/C) system operating in the summer is more often than not required to dehumidify the air, in addition to cooling it. The dehumidification and cooling capacities are termed the latent and sensible loads, respectively. The conventional dehumidification method is achieved indirectly, by over cooling the inlet Process air below its dew point, thus forcing water vapor in the air stream to condense. The condensed water is then collected and removed from the Process air stream and the remainder air stream, the treated air, exits at a cooler and drier state, compared to the inlet state.

There are three main drawbacks to this conventional approach - 1) it may not be sufficient for intense dehumidification requirements, 2) it forces the system to reach lower temperatures than are required by the sensible load alone, thus paying a thermodynamic as well as a practical price, and 3) The treatment of the sensible and latent loads is coupled, which minimizes control and may force the system to over-cool and then reheat the air, a process which is very energy expensive.

None of the above drawbacks apply for a Hybrid Desiccant AC system, which decouples the treatment of the latent and sensible loads by utilizing a hygroscopic substance that chemically absorbs water vapor from the air and thus dehumidifying it. This theoretical research focuses on simulating a particular type of such a hybrid system, one that utilizes Absorption technology for both dehumidifying and cooling. The cooling is achieved by a closed cycle absorption chiller, and the dehumidification is achieved by an open cycle liquid desiccant system.

Each of these systems is powered predominantly by low-grade heat, i.e. low-temperature heat (60-130°C), such that is rarely useful for power generating applications, and may be supplied as waste heat or even by flat solar panels - meaning such an A/C system may potentially be powered primarily by renewable energy sources.

In addition, the Hybrid configuration, if done right, may compliment the performance of both systems thus achieving higher efficiencies and/or lower temperatures and humidity ratios than is possible by the standalone cycles.

There are three main drawbacks for such a Hybrid system - 1) the system is relatively complex, 2) the absorbing substances, although being environmentally friendly, may be corrosive or unhealthy, and 3) this technology is typically less energy efficient than conventional electrically driven vapor compression cycles, however - the main energy source itself, heat, is usually cheaper than electricity, and may even be free.