Absorption Chiller Valve Control for Simultaneous Heating and Cooling
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Solution Overview
Problem
Conventional tri-generation systems face challenges in simultaneously meeting cooling and heating demands due to control instability and the need for pre-selection between modes, leading to impractical operation in moderate climates where both heating and cooling are required within a single day.
Innovation Solution
A system with feedback control loops and a multiple-valve controller adjusts energy input, hot water, and chilled water valve positions based on desired cooling and heating capacities, using performance maps to characterize dynamic characteristics and prioritize heat/cool demands, allowing stable operation without mode switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional control systems pre-select between cooling mode or heating mode, then the control system is simpler to implement, but the system cannot simultaneously meet both heating and cooling demands in moderate climates
Solution Approach 1:
The control system dynamically adjusts valve positions based on real-time heating and cooling demands rather than being fixed in a pre-selected mode. The energy input valve, hot water valve, and chilled water valve are continuously modulated to meet changing load requirements, enabling the system to adapt to moderate climates where both heating and cooling are needed within a single day.
Solution Approach 2:
The absorption chiller is designed to perform multiple functions simultaneously - providing both heating and cooling outputs at the same time. The single absorption chiller unit serves dual purposes by extracting heat from the evaporator for cooling while recovering heat from the condenser and absorber for heating, eliminating the need for separate heating and cooling systems.
2Reliability
If control valves are used to modulate flow rates in various circuits, then the system can control heating and cooling capacities, but the control becomes unstable when trying to meet both heating and cooling setpoints simultaneously
Solution Approach 1:
The control system uses feedback from temperature sensors and flow meters to continuously monitor actual heating and cooling outputs. The controller compares these measurements with desired setpoints and automatically adjusts the energy input valve, hot water valve, and chilled water valve positions to eliminate deviations, ensuring stable and reliable simultaneous control of both heating and cooling capacities.
3Measurement precision
If the system operates in cooling mode with conventional control, then the cooling capacity can meet the desired setpoint, but the heating capacity cannot be simultaneously controlled to meet the hot water setpoint
Solution Approach 1:
The control system is segmented into separate control loops for heating and cooling, each with its own feedback mechanism. The energy input valve controls the overall heat input to the absorption chiller, while the hot water valve and chilled water valve independently control the distribution of heat to heating and cooling circuits respectively. This segmentation allows precise control of both heating and cooling capacities simultaneously without interference between the two functions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables stable and simultaneous control of heating and cooling outputs across the entire operating envelope, eliminating the need for mode switching and ensuring practical operation in conditions requiring both heating and cooling.
Implementation Method 1
absorption cooling can be an effective means for using heat output from a turbine to provide heating and/or cooling to condition the air of a building
Implementation Method 2
an internal refrigerant loop 160 for transferring heat among the cooling water 120, the chilled water 110, and the hot water 130 circuits
Data Source
AI summary
A system for controlling an absorption chiller includes feedback control loops determining adjustments to system cooling and heating capacities and a controller for simultaneously adjusting positions of an energy input valve, a hot water valve, and a chilled water valve. The controller adjusts valves based on desired adjustments to system cooling and heating capacities and performance maps characterizing relationships between cooling capacity and heating capacities and valve positions. A method for controlling an absorption chiller includes the step of obtaining a performance map characterizing heat energy input to cooling and heating loops as functions of valve positions. To obtain the map, the hot water valve is held in a substantially constant position while the chilled water valve is modulated. Similarly, the hot water valve is modulated while the chilled water valve is held in a substantially constant position.