In any HVAC system, selection of chillers involve many factors to be considered judiciously.These factors simultaneously present many advantages and disadvantages to end users.For the selection of water chillers, HVAC engineers consider all these factors keeping in view all the resources they have at their facility.
Comparison of Absorption Chillers and Electric (Compression) Chillers
Following is the comparison of absorption chiller and electric chiller is presented below with aim to help you to decide the type of chillers for HVAC system.
- Absorption chillers have COP (coefficient of performance) of only 0.54–1.1 and it competes poorly with electric chillers (rotary compressor chillers). Electric chillers on other hand have COP from 1.0 ~ 8.0.
- Absorption HVAC chillers occupy approximately 50% more floor area than the equivalent electric chillers (vapor compression chillers).
- Additionally due to height of absorption chillers, mechanical equipment rooms must be 6–10 ft taller than rooms housing electric chillers. Finally, because the liquid solution is contained in long, shallow trays within an absorption chiller, the floor must be as close to absolutely level as possible.
- In HVAC system, Absorption chiller will weight at least twice as much the equivalent electric chiller (vapor compression chiller).
- Due to greater size, absorption chillers are sometimes shipped in several sections, requiring field welding for final assembly.This is not case with counterpart electric chillers or compression chillers.
- Most of electric water chillers are shipped from the factory with their refrigerant charge installed.While the refrigerant and absorbent (including additives) must be field installed in absorption HVAC chillers.
- When we talk about noise and vibration, absorption chillers (unless direct-fired) are quiet and essentially vibration-free as compared to compression chillers (electric drive chillers). Noise and vibrations in HVAC system annoy more than anything else .
- Due to the potential for crystallization of the lithium bromide in the chiller if it becomes too cool, the condenser water temperature must be kept above 75–808F.There is no problem of crystallization in electric chillers (vapor compression chillers). Forget about the crystallization and stay cooled if you have installed compression chillers .
- Absorption water chillers require sometimes an emergency power source if lengthy power outages are more often expected. Without power and heat input, the chiller begins to cool and the lithium bromide solution may crystallize. However, as absorption chillers consume very little electric energy so a small dedicated back-up generator can serve this purpose well.
- HVAC system also gives importance to the amount of heat to be rejected in condenser by water cooling or air-cooling media.The heat rejection rate from the condenser of lithium bromide chiller is 20–50% greater than for the equivalent electric chiller, requiring higher condenser water flow rates and larger cooling towers and condenser water pumps.
- Finally, an indirect-fired absorption water chiller will be at least 50% more expensive to purchase than the equivalent electric-drive chiller. Direct-fired absorption chillers will cost almost twice as much as an electric machine, and have the added costs associated with providing combustion air and venting (stack).
- Absorption water chiller or lithium bromide chiller uses natural refrigerants such water and eliminate the need of CFC or HCFC refrigerants which have high global warming potential.
- If you have plenty of waste heat or direct fire available ,and want to reduce your electric load ,then probably absorption chillers are the best solution.But obviously all above factors are to be considered for the selection of HVAC water chillers.