I have an IBC DC 33-160 boiler that burns propane. The boiler can ramp up or down between 33k and 160k BTUs depending on heating requirements of the house.
Because of this ramp up/down I can't simply monitor the thermostat contact closure to determine gas usage.
A gas meter is a potential solution, but that's quite expensive and would be quite cumbersome to install.
What I would like to try and do is monitor the air flow on the boiler's fresh air intake, which is a 1.5" PVC pipe. If I know the airflow, it should be relatively easy to calculate the gas consumption.
The question is what kind of sensor would be best for this application? There are three options that I've found while searching:
- Mass Air Flow - a powered wire element is put into the air flow and depending on the resistance of the wire, you can determine the airflow. MAFs are commonly used by car ECUs to meter the air and spray the appropriate amount of fuel. The problem with this one is that most MAFs are 12v for auto applications and I'm not sure how I would calibrate it to a known value.
- Pitot Tube - these are used to measure air speed and I found that they are also commonly used in HVAC applications to measure air flow - I just don't know if its sensitive/accurate enough to calculate gas consumption.
- Ultra Sonic - apparently you can determine air flow using ultrasonic sensors aimed at an angle at each other in a tube - I've found some articles about it, but this option seems like the most complicated of the three