CO Detection & Control Systems for Basement Car Parking

(1)  Introduction

• Carbon Monoxide (CO), one of the most toxic components of vehicle exhaust and it is a significant safety concerns in Basement Parking area. When concentrations of CO approach unsafe levels, the ventilation system must be activated to normalize Co level of the Parking area.

(2)  What is carbon monoxide

• Carbon monoxide gas has a simple molecule one part carbon and one part oxygen.
• Carbon monoxides produce due to incompletion combustion (Fails to burn due to not enough Oxygen) of carbon containing compounds like wood, gasoline, coal, propane, natural gas, and heating oil.
• CO produce when there is not enough oxygen to produce carbon dioxide (CO2) such as when operating a combustion engine in an enclosed space.
• These carbon-containing compounds aren’t dangerous when it burns them in an open area with plenty of ventilation. But carbon monoxide is hazardous in confined spaces like basements, kitchens, garages, or campers.
• Carbon monoxide is hard to detect without a sensor, which is one of the reasons it’s so dangerous.
• Carbon Monoxide (CO) is dangerous for human beings and will cause even death within minutes. This is mainly formed in underground parking, basements etc.
• The level of CO concentration is measured in parts per million (ppm). For example, 100 ppm CO

(3)  Effects of Carbon Monoxide

• Carbon monoxide (CO) is a colorless, odorless and tasteless gas that is highly toxic for humans and animals; it bonds with hemoglobin and reduces the oxygen-carrying capacity of blood in the body.

(4)   How Carbon Monoxide is generated in Basement:

• In a basement of a building, oxygen levels may not be sufficient, and the combustion may not be complete. This can occur in vehicles exhaust, gas stoves, boilers, coal heaters etc. which are operated in the basements. Under such conditions, Carbon Monoxide is generated. The occupants of the area will be unaware of the same and hence it becomes a dangerous environment. Hence continuous Carbon Monoxide (CO) monitoring is important for such area.

(5)   Components of CO Monitoring system for Car Parking

• The following components are essentially form a CO detection & CO monitoring system for a basement car parking.
• CO sensors

• A CO sensor is used to detect the level of CO and give an output signal. The number of required sensors is decided based on the size of the area or car park.
• All sensors will be wired to the common PLC panel.
• Location of CO Sensor:
• The distance between the Co sensor and the source of CO is important. The air polluted with hazardous gases have to be in physical contact with the gas sensors. Because carbon monoxide is slightly lighter than air and it may be found with warm rising air Hence, CO Sensor is fitted at a distance of 3 feet to 5 feet from the ground surface

• Do not place the detector right next to or over a fireplace or flame-producing appliance
• Each CO sensor can cover approximately 5,000 to 10,000 sq ft of open space. CO gas will disperse and flow with natural air current and car movement.
• Using the average of 7,500 sq ft per sensor and a circular radius of 49 feet, the sensors area coverage could be scaled and placed on the Basement layout to cover the open floor area. Based on the number of CO sensors and the location of the exhaust fans and make-up air handlers.
• The most practical mounting location for a CO sensor within a basement area is the side of the support column away from traffic.
• CO sensors will be more effective if placed in areas where CO levels are likely to be high. For example, do not place sensors adjacent to the fresh air intake.
• Programmable Logic Controller (PLC) panel
• All the inputs from the CO sensors are connected to a PLC (Programmable Logic Controller) for proper control functioning. The PLC will provide output signals to the VFD based on the inputs from the sensors.
• Variable Frequency Drive (VFD)

• A VFD is used to operate a motor at different speeds. This VFD will be controlled by the PLC and will control the exhaust fans. If the CO content is more, the exhaust fan operates at a faster speed.
• Exhaust Fans / Fresh Air Fans

• The number of required Exhaust / Fresh Air fans will be decided based on the size and shape of the area. The Exhaust Fresh Air Fans are controlled by the VFD. Basically, the Exhaust Fans / Fresh Air Fan have to remove the contaminated air at a fast rate.

(6)  Working Principle and System Architecture:

• A number of CO monitoring sensors are installed at various points of the basement car parking. The number of required sensors is decided based on the size of the area or car parking.
• All CO sensors are wired to the common PLC panel to VFD to Exhaust Fan operations.
• CO sensors detect various types of smoke, Smoke radicals, and fumes and generates a control signal according to PPM level.
• This Control signal continuously feed to PLC panel.
• The PLC continuously takes inputs from all sensors. In case any of the sensors have high pre-defined value, the PLC gives an output signal to the VFD.
• The VFD then operates (ON) the Exhaust Fan / Fresh Air Fan.
• The Exhaust Fan / Fresh Air Fan immediately remove the contaminated air from the area and brings Fresh Air in Basement.
• Normally VFD control is preferred so that we can control the speed of the Exhaust Fan / Fresh Air Fan based on the ppm level.
• As soon as the CO content is reduced as predefined PPM Value, the exhaust fan stops after a certain time delay.
• Based on pre-defined logic, it will operate, regulate, stop-start ventilation Fan system, dampers etc.
• Underground car parking CO detection system is installed for energy cost saving and environmental protection. Ventilation rates can be decreased to save energy if there is no exhaust gas pollution present.

(7) Logic Diagram of Fresh Air System:

• Low setpoint of 26 ppm and a high of 75 ppm. When any CO sensor exceeds a threshold (ppm level in air) the following shall happened:
• Threshold # 1= Lower than 26ppm (OFF)
• Exhaust Fan / Fresh Air is in OFF Condition.
• Threshold # 2= 26ppm (START)
• Whose Zone’s CO level is 26ppm, Start the Exhaust Fan / Fresh Air of that Zone at minimum speed to bring in fresh air and reduce the CO level.
• Threshold # 3= Higher than 26ppm but Low than 75 ppm (RUNNING)
• Whose Zone’s CO level is 26ppm but less than 75ppm.Fan Speed of that Zone is linearly / proportionally with 0 to 40hz according Actual ppm Level.
• This will run Fan on Low to Normal to High speed according to ppm Level to increase more fresh Air in contaminated Zone.
• Threshold # 4=Higher than 75ppm (Full Speed)
• Fan runs on 50hz at 100% Speed. This High Speed bring more fresh air and reduce the CO level.

(8) Operation of Basement Ventilation system:

• The Basement ventilation system shall comprise of Supply of Air, Make-up of Air and Exhaust of Air by Natural ventilation or by Mechanically ventilation Method (By Fresh Air Fans).

• During normal mode, these Fans will Run on lower speed based on CO concentration in the Basement Area. During high CO level / fire conditions, fans shall run on higher speed to meet 12 ACPH.
• Since ventilation fan shall work round the clock, it is desirable to provide VFD to conserve the energy. The fan shall be operated through VFD actuated by Carbon Monoxide (CO) sensor.
• In Basement area there are various number of Fresh Air Fans are available. Zone for Each Fan should be decided as per capacity of Fan.
• Fresh Air Fan through VFD is run according to CO Level of Basement Car Parking from 0% to 100% as per PPM Level. It also run 100% in case of Fire due to increase level of CO.

Basement Ventilation in Day-to-Day Condition:

• For day-to-day operation, Various CO Sensors generates output signal as per the PPM Level. These Signal continuously feed to PLC Panel.
• The PLC continuously takes inputs from all sensors. and gives an output signal to the VFD.
• Following condition’s for VFD Automatic operation:

1. When the Carbon Monoxide (CO) level less than 25 ppm all fan will switched to OFF conditions.
2. When the CO level raise above (26 ppm to 70 ppm) then one Fresh Air Fan ON / RUN as per Normal mode to modulate as per PPM level in basement.

• When the CO level reach above (70ppm) then Fresh Air Fan (FAF) shall be achieved 100% speed.

(9)  Routine Check List: