A good ventilation system is vital in car parks. It must provide fresh air and ensure harmful pollutants such as carbon monoxide, nitrous oxides and various fumes from the vehicle’s fuels do not accumulate and reach toxic levels.

Traditionally car parks are fitted with a maze of ductwork which carries fresh air from one part of the building to another.

The introduction of impulse ventilation systems has revolutionised car park ventilation in Australia. Impulse ventilation systems use small strategically located high velocity jet fans (also known as induction fans) mounted directly beneath the ceiling in place of ductwork. The fans provide a constant air flow that mix the air, ensure pollutants do not accumulate in dead areas and direct them towards the main extraction fan.

Impulse technology operates on well-proven longitudinal tunnel ventilation principles. The fans produce a high velocity jet of air, in turn moving a larger quantity of air surrounding the fan through a process known as entrainment. The amount of air entrained by a single fan increases with the velocity and the quantity of air being discharged by the fan. The ability of a fan to do this is measured by its thrust rating which is measured in Newtons (N).

Fully ducted systems typically require a larger extraction fan with the capacity to generate higher static pressure development to overcome resistance within the ducts.

One of the key advantages of impulse technology is that it largely eliminates the need for air distribution ductwork within the car park and because the mechanical supply and exhaust systems have less resistance, these fans can be smaller and therefore consume less power.

Other savings may occur during construction, for example, the reduction of site excavation due to the low ceiling height made possible by using jet fans. And with no duct to navigate around concrete beams, other building services such as cable trays, water and gas pipes are easier to install with potential savings in labour and material costs.

EC motor technology

To reduce power costs and the building’s carbon footprint, fans can be made to reduce their speed during times of low activity and speed up again at times when ventilation is required. This is usually achieved by using variable speed drives (VSD) paired with a conventional 3 Phase induction motor. VSDs have become accepted as ‘normal practice’, so it is often forgotten that they take up valuable plantroom space and that wiring the shielded cable from the VSD to the fan is an added expense in time and money.

By using an electronically commutated (EC) motor to drive a fan, speed control becomes an integral part of the unit, removing the extra installation, space, and costs associated with conventional motors and VSD pairings. Also, by having the speed control as an integral part of the motor, shielded power cables do not have to be used in the power connections to the fan motor. Lastly, because the EC motor is specifically designed to be speed controllable, the result is a motor that is efficient across a huge range of operating speeds and does not have the electronic hum that is characteristic of VSD driven induction motors.

Digital communication system

In order to achieve speed control of an EC motor, sophisticated motor control strategies are integrated into its on-board electronics. EC motors provide digital/high level communication which allows the fan to respond to and send relevant information to a controller's BMS.

EC motors enable each fan to get full functionality using only a single twisted pair communications wire. This can provide substantial savings, because each fan function normally requires its own pair or trio of wires, which can very quickly add up to significant cost over a large site. For example, some fans in a system may need to be variable speed controlled, provide run/stop indication, and have a fault alarm signal/switch. In some installations current monitoring may also be required. It means that this fan would require six separate wires to operate the first three features and a smart power meter to monitor power consumption. With the EC motor over digital communication, all of the four required features can be monitored by communicating over the communications bus.

Most EC motor solutions available for HVAC applications with high-level communication, support the MODBUS protocol over RS485 serial connections. With specific reference to JetVent EC applications, the following ways of applying high-level communications are available:

• A. Jetvent Digital EC – Integrated Zone Controller: In this mode of operation, the Jetvent EC system is supplied with a matching carpark pollution monitoring system and a speed controllable fan. In addition to the benefits of high-level communication noted above, this solution also allows pollution sensors to be powered and directly connected to the nearest fan to further reduce wiring costs, while still allowing the integrated zone controller to set the speed of Jet Fans in the system in accordance to any individual sensor readout in the carpark.
• B. Jetvent Digital EC – Integrated Zone Controller with BMS Monitoring: The Jetvent EC system with its powerful zone controller can also be connected to the main building BMS. The controller is connected as per the above method (A), but with additional communication lines connected to the BMS, which can communicate to the controller with a choice of BACnet over MSTP, BacNET Over TCP/IP, and MODBUS over RS485 protocol and connections. This option allows the facilities manager to monitor CO levels, fan speeds, status, and alarms without leaving the office.
• C. Jetvent Digital EC – Direct BMS Control: It is also possible to fully address the fans in the Jetvent System with MODBUS protocol over RS485 connections. If the BMS in the building has enough available programming points and processing capability left free, this will give the building’s facilities manager full BMS monitoring and control of the carpark Jetvent System. It will also be advisable to use MODBUS based sensors for this setup to take full advantage of this arrangement.