bb_94401 wrote:
Chuck and Di wrote:
Propane boils at -42C. There is no need for complex heaters or concern. I used it to heat my home for over 25 years in a climate similar to where they are going. Depending on the size of the tank, temperatures would have to be sustained for many hours below -42C for there to be an issue.
The key point to the above, is the size of the tank. A 500 gallon tank at a home with the primary stage of the regulator set to handle the temperature can easily meet the input needs of a furnace in very cold weather. The larger the volume of the gas cylinder compared to the load, the less likely freeze up at very cold temperature is. Thus the common statement about not needing to heat a tank based on a 500 gallon tank.
However this is not the case with the 20lbs tanks in the TC as they are small compared to the load. This can be seen by the fact that a sweat line forms or freezes around the tank at normal temperatures. The tank's ability to vaporize fuel is dependent on the heat transfer from the air to the tank and then to the propane. This depends on the temperature and the wetted surface area of the tank (amount of propane in the tank). Below is a table showing the amount of fuel per hour that a tank can produce at various temperatures and fill levels.
When my insulated TC is at 0°F the 25,000 BTU input (20,000 BTU output) furnace runs a total of 20-30 minutes per hour depending on the thermostat setting. So at colder temperatures I need more than 8-12,000 BTU/hr for my TC.
When we camped at -10°F (-23°C) to -20°F (-29°C) the heater ran almost continuously. From the table you can see what the problem was. At -20°F not enough propane can be vaporized per hour, so the furnace can't produce enough heat.
The second point of the table above is that in cold weather, as your tank empties, less propane can vaporize per hour due to less wetted surface area, so even though you have propane it doesn't heat your TC much because it is the equivalent of boiling water on LOW on the gas range, instead of HI.
Supplemental electric tank heat solves this problem and provides a greater reserve capacity in the event of a power failure. The thermostatically controlled cylinder blanket can be powered by a small generator. Having a larger tank (100 gallon; 400L or greater) helps, as well as having the first stage regulator pressure set at 10 psi vs 15 psi for weather around -20°F (-29°C) to avoid re-condensation of propane or regulator icing.
That is a very good explanation and information , well worth repeating .
