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Home TechTime May 2015 Where Is The Airflow Switch

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The second edition of TechTime is here! TechTime is a new Neptronic publication aiming to inform you of common issues highlighted by our technical support team and the best way to deal with them. Each edition will contain three new topic and will be posted on neptronic.com.

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Where is the Airflow Switch?!

Electronic Airflow Sensors

Some people could get confused when they do not see an airflow switch with a pitot tube (probe) on installations featuring Neptronic electric heaters.

 

That is because our open coil, modulating heaters are equipeped with Electronic Airflow Sensors (EAS) and do not come with the typical probe that we normally see with fixed or adjustable airflow switches (PDN or PDA). EAS is installed on the top of the frame next to the automatic thermal cutout.

The EAS does the same thing as the PDN/PDA but in a different way. To keep it simple, there are two temperature sensors installed (Upstream and downstream of the heating element). These sensors constantly calculate the delta T across the coil. As long as there is a temperature difference, meaning there is airflow, the heater will keep running and modulate the output according to demand. When these sensors detect zero temperature difference, meaning there is no airflow; they will send a signal to the HEC (Neptronic electronic controller) and shut off the heater. The EAS is factory installed, wired and ready to go. No onsite connections needed. Good for low airflow applications, like VAV box applications, the EAS will allow the heater to run at air velocities as low as 100 FPM whereas the PDN/PDA requires a minimum of 300 FPM.

 

Note that the EAS are available only on open coil, full modulating heaters with maximum dimensions of W48" x H40" and a maximum current of 50 Amps.

 

Patented EAS

Electronic Airflow Sensors (US Patent 7,012,223)

1.  Accepts any industry standard input signal
In this example there is a demand for 6kW, which requires a minimum 500FPM.

 

2.  Precise air velocity readings (as low as 100 FPM)
Using both temperature sensors and other known values, the HEC controller calculates the precise air velocity. These readings can go as low as 100 FPM, which is excellent for VAV applications. In this example it is 200 FPM.

 

3.  Load shedding: overrides demand if velocity is insufficient
Protects elements from overheating and eliminates unnecessary shutdowns if velocity is insufficient for actual demand. In this example, the demand of 6kW requires a minimum 500 FPM, but the HEC controller detected an actual velocity of 200 FPM. The HEC controller lowers the output to 2 kW for 200 FPM. As opposed to air flow switches that simply shutdown the heater.

 

4.  Additional overheat protection.
If heater element is too hot or if there is no air flow, electronic shutdown of the heater prevents cycling of the contacts. This is in addition to the thermal cut-off.

 

5.  No air flow switches required
The velocity is calculated using the factory installed temperature sensors and built-in algorithms. Using the temperature readings, the HEC controller also automatically determines the orientation of the air flow. This saves cost and reduces labour as expensive air flow sensors are not required and there is no need to fine tune air flow switch positioning.

 

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Patrick Victor

Technical Support – Electric Heaters

Contact him at this email address pvictor@neptronic.com