System and method for freezing protection
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Solution Overview
Problem
High-efficiency run-around coil energy recovery systems (HE-RAR) face challenges with freezing protection, particularly in cold climates, as existing methods degrade energy efficiency and are not flexible enough to handle varying humidity and temperature conditions, limiting their application in environments with high humidity or extreme temperatures.
Innovation Solution
A system with multiple split coils in both the exhaust and supply air streams, allowing for controlled partial or full bypass of coils using electrically controllable valves, combined with individual optimization of each coil for freezing protection and energy recovery, and the use of sensors for real-time monitoring and control to maintain efficiency and prevent freezing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If anti freeze medium is added into the energy recovering liquid to prevent freezing, then the freezing protection is improved, but the energy exchanging performance of the liquid deteriorates
Solution Approach 1:
The system dynamically changes the flow parameters of the energy recovering liquid to maintain optimal energy exchange performance while preventing freezing. By adjusting flow rate and distribution across multiple coils, the system achieves freezing protection without adding anti-freeze medium that would degrade thermal performance.
Solution Approach 2:
The energy recovery system is divided into multiple separate coils (first coil in exhaust air stream, second coil in supply air stream) with independent flow control. This segmentation allows selective operation of coils to prevent freezing in specific locations while maintaining energy recovery efficiency in others, avoiding the need for anti-freeze additives throughout the entire system.
2Reliability
If the liquid flow is bypassed over the supply air coil to handle freezing, then the freezing protection is improved, but the energy efficiency of the system deteriorates
Solution Approach 1:
The system employs dynamic flow control that continuously adjusts liquid distribution between coils based on real-time temperature and humidity conditions. This dynamic adaptation allows the system to maintain high energy efficiency by optimizing which coils receive liquid flow, rather than using static bypass arrangements that permanently reduce efficiency.
Solution Approach 2:
The control system uses feedback from temperature and humidity sensors to continuously monitor system conditions and adjust liquid flow distribution accordingly. This feedback mechanism enables the system to respond to freezing risks while maintaining optimal energy recovery performance, avoiding the efficiency losses associated with fixed bypass configurations.
3Productivity
If high efficiency coils are used to improve energy recovery, then the energy efficiency is improved, but the risk of freezing in the exhaust air coil increases
Solution Approach 1:
The system segments the heat exchange function into multiple coils with independent control, allowing the high efficiency coils to operate at optimal performance while separate flow control prevents freezing in vulnerable exhaust air coils. This segmentation decouples the efficiency gain from the freezing risk.
Solution Approach 2:
Different coils are assigned different functions and operating conditions based on their location in the system. The exhaust air coils are protected from freezing through localized flow control, while supply air coils can operate at high efficiency. Each coil's liquid flow is optimized for its specific thermal and humidity conditions.
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
This approach enables flexible and efficient freezing protection while maintaining high energy recovery performance across a wide range of conditions, even in humid environments and low temperatures, surpassing the limitations of prior art solutions by allowing continuous optimization and preventing frost formation.
Implementation Method 1
The energy is transferred from one air flow to the other indirectly, via air to liquid energy exchangers, typically a coil, and a liquid medium, which is pumped around in a circuit between the energy exchangers
Implementation Method 2
The RAR is used to recover energy from the exhaust air and transmit the energy to the supply air
Implementation Method 3
This is generally prevented by adding anti freeze medium into the energy recovering liquid, which lowering the freezing point of the liquid
Implementation Method 4
When the exhaust air is cooled down by the RAR system condensation may occur in the exhaust air coil, and below 0 °C the condensate will freeze and block the air passage
Data Source
Figure 1
AI summary
The invention regards a system and method for freezing protection and continuous optimization of energy recovery of a run around coil system (1) in connection to an air handling unit (2). Said air handling unit (2) comprises one exhaust air side (A) and one supply air side (B), and said run around coil system (1) comprises an energy recovery circuit (3) with at least one pump (4) for circulation of a fluid. The run around coil system (1) further comprises at least one supply circuit (5) for supplying additional heating or cooling energy from an external heating or cooling source (6) and the supply circuit (5) is connected to the energy recovery circuit (3) via at least one energy exchanger (20). The system is also arranged to adjust the fluid flow in the energy recovery circuit (3). The system further comprises at least one first set of coils (7) in the exhaust air side (A), and at least one second set of coils (8) in the supply air side (B), and at least the second set of coils (8) comprising at least two coils (81,...8n) arranged in the same air stream. For controlling the system and method said run around coil system (1) further comprises a control unit (9) designed for controlling freezing protection and for continuous optimization of energy recovery of the system. The system is characterized by that at least one coil (81,...8n) in the second set of coils (8) is arranged to be at least partially bypassed, on the fluid side, and at least one coil (81,...8n) is arranged to not be bypassed, on the fluid side. The method is characterized by performing at least one step in each set of steps - a first set of measuring steps, a second set of evaluation and control steps and a third set of steps of sequences to combine based on evaluation of the measurements.