HVAC Compressor and Fan PI Control for Space Temperature Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing HVAC systems prioritize controlling discharge air temperature over space temperature, leading to inefficient energy consumption and reduced reliability due to over-ramping of the compressor speed.
Innovation Solution
A temperature control system utilizing variable speed compressors and fans, with separate proportional-integral (PI) loops for each, prioritizing compressor speed based on space temperature delta and supply fan speed based on discharge air temperature set points, to optimize energy usage and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If existing HVAC systems control compressor speed based on discharge air temperature, then discharge air temperature can be regulated, but compressor speed becomes higher than needed for space cooling, leading to increased energy consumption
Solution Approach 1:
The control system is segmented into two independent PI loops: one controlling compressor speed based on space temperature delta, and another controlling supply fan speed based on discharge air temperature. This segmentation allows each component to be optimized for its specific control objective, preventing the energy waste caused by using discharge air temperature to control compressor speed.
Solution Approach 2:
The patent inverts the conventional control approach by making space temperature (rather than discharge air temperature) the primary control variable for compressor speed. This inversion resolves the contradiction by aligning compressor operation with the actual cooling demand of the space, thereby reducing unnecessary energy consumption.
2Temperature
If existing HVAC systems prioritize discharge air temperature control, then discharge air temperature can be maintained, but space temperature regulation becomes less efficient and reliable
Solution Approach 1:
By separating the control of compressor speed and supply fan speed into distinct PI loops with different control objectives, the system ensures that space temperature regulation (compressor control) and discharge air temperature regulation (fan control) both achieve their targets reliably without compromising one for the other.
Solution Approach 2:
The system employs feedback control through two PI loops that continuously monitor space temperature and discharge air temperature, adjusting compressor and fan speeds respectively. This feedback mechanism ensures both temperature parameters are regulated reliably according to their specific setpoints.
3Productivity
If existing HVAC systems use discharge air temperature delta to control compressor speed, then compressor capacity can be adjusted, but initial compressor speed is higher than needed, reducing system efficiency
Solution Approach 1:
The patent changes the control parameter for compressor speed from discharge air temperature delta to space temperature delta. This parameter change enables the compressor to operate at the minimum necessary speed to meet space cooling demands, thereby improving efficiency while maintaining adequate compressor capacity through the variable speed capability.
Data Source
AI summary
A temperature control method includes obtaining, by a controller, a space temperature value, a space temperature set point, a discharge air temperature value, and a discharge air temperature set point. The method further includes determining a compressor speed using a first PI loop based on the space temperature set point and the space temperature value, and determining a supply fan speed using a second PI loop based on the discharge air temperature set point and the discharge air temperature value. The temperature control method further includes outputting a first control signal that controls the speed of a variable speed compressor based on the determination of whether the compressor speed is within the compressor operation range and a second control signal to control the speed of a variable speed supply fan based on the determination of whether the supply fan speed is within the supply fan operation range.