Really cool David!
Could you explain a bit more about how you monitor your propane?
What size tank? What sensor(s) you use?
The tank is an older 450 gallon and unfortunately the gauge cannot be retrofitted with any type of electronic device to transmit the level of the propane inside without completely emptying the tank and changing the level indicator socket and float. If the propane supplier had provided a different tank this would have been a lot easier.
In order to know how much propane was left at anytime without the luxury of a meter or the availability of sensors which I would have preferred, I came up with a way to monitor the usage of every gas appliance we have and use that to determine how much fuel was left. The only sensors involved are discreet Inputs to my PLC monitoring the gas valves on every appliance being monitored.
This is how I did it
Establish some constants and multiply them by variables. Each appliance has an input BTU rating on its nameplate.
1 Gallon of propane is 91,452 BTU. Starting with whatever percentage of fuel is in the tank, you calculate the amount of fuel to reduce it by Multiplying the time your appliance gas valve is open x the input BTU of the the appliance. For example: If a 80,000 btu per hr furnace gas valve is open for 7.5 hours in a week, the fuel it used is:(80,0000 X 7.5) / 91,452 or 7.5 x 80000 / 600,000 / 91,452= 6.560818790185015 Gallons for the week. Of course to have a constant update every cycle an appliance runs, we multiply the time the gas valve is open for each cycle. The fuel used for all appliances combined is totaled each time a gas valve closes in every appliance. The math gets a wee bit more complicated that way since we are multiplying by seconds the valves are open not hours. This has proven to be surprisingly accurate. We only have to make adjustments a couple times a year. When it was first set up we did watch and tweak the input BTU values of the appliances to get a more accurate value then what is on the nameplate Adding all appliances usage every time an appliance gas valve shuts off gives a constant real time amount of propane left in the tank. In addition all values are moved to a memory location for each appliance at midnight and used to calculate daily averages weekly averages and monthly averages PER DAY. This data is kept for 6 months before being overwritten. This way we can also project how much fuel we will need to buy the next season. The projection of days to 20% or 60 Gallons is based on the average gallons used per week. -
As a side note, I have been involved in discussions with electricians and other engineers about how to compare the cost of heating a building, a house etc. with one method of heating vs another and quite frankly I am surprised at the ignorance of people that have more formal education than I have.So for anyone that cares to know, To compare your heating cost with your neighbor based on the heating source used You MUST as in any math equation reduce the formula to a common unit. In this case BTUs. Determine from the bill how many BTUs were used to heat each home based on the heat type used so many BTUs per cubic ft of NG, so many BTUs, Gal LP GAS, So many BTUs per Kilowatt of electricity.Then the cost per BTU from the supplier of the source. I can tell you from years of study it is NEVER less expensive to heat with electricity, The cost per BTU for electricity has historically been much higher then the cost per BTU of all other fuels.You have to know how many BTUs are in the source being sold in order to compare.
