Choosing a chiller system
Hybrid systems are popular because they offer choices such as gas chiller operation during peak electrical periods and standard electrical chiller usage during off-peak hours. In some instances, standard electrical chillers have not been used because of the efficient operation of the main gas-chiller system.Do you want to learn more? see this
The process of gas absorption uses an evaporator and condenser much like conventional vapor compression units. However, instead of using a standard electrical compressor and motor, a thermal compression system is used.
Within a simplified thermal compression system, an absorber and generator are integrated along with a pumping system. An evaporator removes heat from the circulating water system to produce cool water. From the evaporator, refrigerant vapor moves to an absorber where it is compressed and absorbed into a solution, usually lithium bromide. This solution then moves to the generator where heat – either direct-fired gas or steam – is added to remove the refrigerant from the solution.
The solution then goes through heat exchangers and is returned to the absorber. The refrigerant returns to the condenser where it is liquefied and sent back to the evaporator. The entire cycle then starts over again.
Gas-fired steam absorption chillers work in much the same manner as direct-fired gas chillers. The main difference is that the heat source for the generator is usually an external gas-fired boiler system. These systems are favorable for facilities that have a boiler system already installed on site.
In addition to being either gas-fired steam absorption or direct-fired gas, chillers are categorized into two different types: Single-effect and double-effect. There is a triple-effect being developed. Single-effect, or single-stage, absorption chillers usually require low internal pressures around 20 psig to produce chilled water. Double-effect, or two-stage, absorption chillers work at a much higher pressure, around 40 to 140 psig. These chillers also have an extra generator integrated into the absorption system that increases the efficiency by about 30 percent. Double-effect chillers are currently more popular than the single-effect types.
Many direct-fired absorption chillers are dual-fuel rated. Natural gas is commonly the primary fuel, however No. 2 fuel oil can be used as an alternate. If for any reason the natural gas supply is interrupted, having the capability to use an emergency fuel may be invaluable. This fuel redundancy may be an important purchasing factor for many facility professionals.
Maintenance requirements for gas-absorption chillers are minimal. Pump seals need inspecting periodically if the pumps are not hermetically rated. In addition, scaling and sludge build-up are areas of concern with this equipment. However, automatic chiller and purge controls, along with periodic general maintenance checks, will alleviate most of these potential problems.
Equipment size can be a concern for some facilities. Typically, gas absorption chillers are larger than standard electrical chillers of the same Btu rating. Adequate space needs to be allowed for any gas chiller retrofit or new installation.