Gas-Fired/Oil-Fired Hitachi Absorption Chiller-Heater
- Product Range 30 TR to 1400 TR
- EXH Series : High Efficiency Absorption Chillers/Heaters
- COP =1.43 (GAS) COP = 1.40 (OIL)
- EXS Series : Middle Efficiency Absorption Chillers/Heater
- COP =1.36 (GAS)
- V Series : Standard Efficiency Absorption Chillers-Heaters
- COP= 1.12 (GAS & OIL)
- High Efficiency Achieved by Hitachi’s Creativity and Advanced Technologies
- [EX(W)H, EX(W)S Series]
- stage evaporation and absorption cycle
High efficiency was achieved by employing a 2-stage evaporation and absorption cycle. By dividing the evaporation and absorption cycle into two (upper and lower) stages and running the lower-stage evaporation and absorption cycle in the ranges of 15°C to 11°C chilled water temperature and 32°C to 34.5°C cooling water temperature, the concentration of solution can be lowered to the same as that of light light load operation. As a result, the concentration difference between generator and absorber can be increased and the flow rate of circulating absorbent in the whole cycle can be reduced. Thus we succeeded in increasing cycle efficiency by reducing the flow rate of circulating solution, which in turn cuts not only the heat radiation loss that results from the cooling water’s heat deprivation, but also the heat (flue) that is used for heating in the high-temperature generator.
High-efficiency plate heat exchange
Low-and high-temperature solution heat ex changers are important elements that have a great influence on the efficiency of the absorption chiller-heater. We employed plate heat exchange’s of welded construction that are high in efficiency and can easily be miniaturized and connected to keep flow velocity at an optimum level even when the flow rate of circulating solution is low.
Drain heat exchange
The drain heat exchange exchanges heat between the warm refrigerant that is returned from the low-temperature generator and cool solution that comes from the absorber and thus preheats the solution that is sent to the high-temperature generator.
“Parallel Flow” System Greatly Contributes to Miniaturization, Energy Saving and Higher Safety
Parallel Flow System
The Parallel Flow System divides the flow of weak solution coming out of the absorber in two at the outlet of the solution circulation pump and pressure-feeds them separately to the high-and low-temperature generators. Because this system feeds solution separately to the high- and low temperature generators, it is unnecessary to arrange the high-temperature generator on an elevated place.
As a result, it becomes possible to arrange the high-temperature generator at a lower part of the chiller-heater main unit, which greatly contributes to down-sizing. On the other hand, the conventionally used Series Flow System feeds the all the weak solution at once to high-temperature generator and then feeds concentrated solution to the low-temperature generator, which requires the high-temperature generator to be located on an elevated place. As a result, it is inevitable that the whole unit becomes slightly larger in size. The parallel flow system contributes not only to miniaturization but also to safely and maintainability.
Effects of Introducing Parallel Flow System
- Low internal pressure during operation
The internal pressure of the high-temperature generator depends on the concentration of lithium bromide in the low-temperature generator. With the parallel flow system, the weakest solution coming out of the absorber is fed to the low-temperature generator, so that it is possible to keep the internal pressure of the high-temperature generator considerably lower than atmospheric pressure. As a result, the system can be operated in a cycle with a sufficient margin with respect to atmospheric pressure.
- Because of its compact size, the whole unit can be carried in at once
Bcause it is unnecessary to feed solution from the high- to low-temperature generator, the high-temperature generator can be arrange diagonally beneath the main unit shell. This results in a smaller width of the whole unit.
Therefore, the unit can be carried in and installed without being divided into pieces
- Energy saving
Because the parallel flow system divides the flow of solution in two to feed the two generators (high-temperature generator and low-temperature generator) with solution, the quantity of solution that is handled in the solution heat ex changers can be almost halved.
Therefore, it is possible to greatly save energy by using a small heat ex changers. As a result, an additional energy saving effect can be realized with an uncomplicated reasonable design.
- Stability and High Reliability
The concentration of solution at the absober inlet where the temperature is lowest is lower with a parallel flow system than with a series flow system, and sufficiently distant from the limit of crystal precipitation (the limit for solution to crystallize). Therefore, the system operates safely with no anxiety of crystallization.
Because of its compact size, the whole unit can be carried in at once without being divided into pieces. Therefore, the reliability proved by strict air tightness test in the fabrication plant is not degraded.
“Large Temperature Differential System” Saves Energy and Facilities of Total Air Conditioning System and Large Temperature Differential Air Conditioning System
Features of large temperature differential air conditioning system
The absorption central system connects the air conditioner, absorption chiller-heater and cooling tower by piping and ducts and controls room temperature according to the temperature of the water and air that circulate through them.
The large temperature differential system increases the temperature difference between outgoing and returning chilled water to reduce the flow rate of circulating water while increasing the cooling water outlet temperature to make the temperature difference larger, for the purpose of cutting the amount of power required for conveying cooling water.
Large temperature differential technology for absorption chiller
It is comparatively easy to increase the temperature difference in a chilled water system. On the other hand, to increase the temperature difference in a cooling water system, it is inevitable that the chiller be larger in size because a one-rank larger absorption chiller needs to be employed. For this reason, large temperature differential technology is rarely applied. Utilizing its unique technologies, Hitachi succeeded in achieving a large temperature difference in both chilled and cooling water systems without resulting in an increase in the unit’s size.
The driving power of chilled and cooling water pumps can be cut by employing a large temperature differential system. The flow rate of chilled water and cooling water can be reduced by employing the large temperature differential system.
Fine control realizes efficient and energy-saving operation. Hitachi absorption chiller-heaters are distinguished not only by their energy saving effect under rated conditions but also by a high energy saving effect under partial loads. Its energy saving effect is available also in winter and intermediate seasons when cooling water temperature is low. Besides, due to the unique solution circulating flow control developed by Hitachi, they operate stably in a whole range from high to low load conditions. The figure at left shows a sample relational curve between cooling capacity (%) and fuel consumption (%).
Energy Saving, High Reliability and Stability Are Assured even during Long-Term Operation Optimal control of dilution operation time contributes to energy saving in the whole system. Solution diluting operation time before stopping the chiller-heater is calculated and controlled by microcomputer to optimize stop time. As a result, the operating time of the pump and cooling tower during dilute operation can be reduced, making it possible to save energy in the whole system.
Adapted for heavy load operation (annual operating time of 4,000 hours or more) as standard In addition to the 2-stage evaporation and absorption cycle (EXH and EXS series) and ACA flow (V series), a parallel flow system is employed to realize a low-concentration cycle. Even under loads as heavy as 4,000 hours of annual cooling operation time, you can operate the system at high reliability without worry. Safe operation assured by reinforced protective maintenance and abnormality prediction functions protective maintenance and abnormality prediction functions are incorporated to assure efficient and stable operation.