HVAC Natural Gas Chillers Can Help Manage Peak-need Electrical Loads
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.
the time of action of gas absorption uses an evaporator and condenser much like traditional 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 additional to remove the refrigerant from the solution.
The solution then goes by 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 complete 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 popular 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 additional 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 dominant 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 highly useful. 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 regularly 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 regular general maintenance checks, will alleviate most of these possible 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.
One of the benefits of using gas-absorption chillers is that it produces enough heat to also activate certain dehumidification systems, which are becoming important elements of HVAC systems. Molds, mildews and bacteria prosper in high-humidity conditions. Controlling humidity reduces risks to human health and ensures that sensitive manufacturing processes can be conducted. Dehumidification also increases cooling efficiency. In some instances, installing a dehumidification system can reduce a building’s cooling load by as much as 50 percent.
substantial desiccant dehumidification systems remove moisture from the air by implementing a heat-activated material. Although a complete system contains many elements, the main internal part is the desiccant wheel. Usually the desiccant wheel is divided into two halves. One half allows unconditioned air to go into where the air is then dried. When this half becomes saturated with moisture, it is rotated into a heated area that afterward regenerates the desiccant in that half of the wheel. Within this rotating cycle, one half of the wheel regenerates while the other half absorbs moisture.
Absorption chillers are not the only method in which gas can be alternation to conserve electrical consumption. Gas-pushed chillers are another viable method to reduce peak electrical costs. The chiller portion of this unit is really just a standard vapor compression system pushed by an externally powered internal combustion engine. Typically, with this kind of unit, the engine couples directly to the input shaft of a rotary-kind chiller. The engine can be operated with many fuels, including natural gas, LP or diesel. Cogeneration systems are a possible addition when an external engine is used in this way. Hot water, steam, dehumidification, cooling and electricity production all use an internal combustion engine as a strength source.
Although most gas chiller systems are not in addition-known as the traditional electrically pushed chiller systems, they are becoming more popular because of rising electrical costs. Many facility executives are experiencing lower electrical consumption since they have made the change to gas cooling. When making gas chiller decisions, it may be a good idea to get advice from facility executives that have already made the change. Their input and the help of qualified energy management engineers will help in making a wise energy choice.