Critical area recirculation and exhaust system
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Solution Overview
Problem
Hospitals often lack sufficient negative pressure isolation rooms during pandemics, necessitating a solution to convert standard hospital rooms into negative pressure isolation rooms capable of meeting ASHRAE Standard 170 requirements.
Innovation Solution
A critical area recirculation exhaust (CARE) system that includes an airflow device with a fan filter unit, flush-face radial flow diffuser, and controllable dampers to manage airflow, enabling conversion between normal and isolation modes, and ensuring negative pressure through filtered air recirculation and exhaust.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard hospital room with a standard air distribution system is used, then the device complexity is low and ease of operation is high, but the room cannot provide negative pressure and cannot supply more than 4 ACH, failing to meet isolation requirements
Solution Approach 1:
The CARE system merges the fan filter unit with the existing flush-face radial flow diffuser to create a combined airflow device. This integration allows the system to provide both supply and exhaust functions through a single integrated component, reducing the number of separate devices needed and managing complexity while achieving negative pressure capability
Solution Approach 2:
The airflow device is designed to operate in multiple modes: normal mode using the air handler, and isolation mode using the fan filter unit. The system can selectively switch between these modes through controllable dampers, providing universal functionality that adapts to different operational requirements without requiring completely separate systems
2Stress or pressure
If the fan filter unit exhausts filtered air to create negative pressure, then negative room pressure is achieved, but air change rate requirements may not be met simultaneously
Solution Approach 1:
The system employs controllable dampers that can dynamically adjust airflow paths between supply and exhaust. The controller selectively opens and closes dampers based on operational mode, enabling the system to adaptively manage the balance between maintaining negative pressure and achieving required air change rates
Solution Approach 2:
The system changes operational parameters by switching between different damper positions and fan speeds. In isolation mode, the exhaust damper opens and supply damper closes to prioritize negative pressure; in normal mode, dampers are repositioned to maximize air change rates, allowing flexible parameter adjustment to meet different requirements
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
The CARE system effectively increases air change rates and maintains negative room pressure, converting standard rooms into functional isolation rooms capable of handling highly infectious patients.
Implementation Method 1
The fan filter unit of the airflow device draws contaminated air from the room and filters the air with a MERV 8 pre-filter and a HEPA filter
Implementation Method 2
The exhaust air outlet of the fan filter unit has a manually adjustable balancing damper to adjust the volume of airflow that is exhausted or recirculated when the CARE system is installed. The exhaust air duct has a controllable two position exhaust air duct damper that controls airflow from the fan filter unit to a location outside of the room
Data Source
AI summary
A critical area recirculation and exhaust system for a room operates in a normal operating mode where fresh air is delivered from an air handler through a diffuser and returned to the air handler through a room return duct. In a selected isolation operating mode, a fan filter unit is activated to draw contaminated air from the room through one or more filters and to expel the filtered air through the diffuser and through an exhaust air duct to create an increased air change rate and a negative pressure in the room.