Dew Point

It was a fine week on the farm, with lots of hot weather and a needed day of rain. The tomatoes, peppers, and eggplant are coming along nicely. They will be ready in quantity soon.

The thing that is so great about farming is that there is always something new to learn. When we make a mistake or a misjudgement, we just say “Learning!”, forgive, then move on. The latest thing we’ve been learning about is called the ‘soil battery’ or ‘low grade geothermal heating system.’ The idea is to bury several runs of perforated drain pipe in a gravel bed under a greenhouse. During the day, when temperature and humidity rise, a fan blows air from the top of the greenhouse through the pipes. The heat is transferred into the ground by conduction and also by condensation since the temperature under ground is almost always below the ‘dew point’ which is the combination of temperature and water content of the air at which water vapour will condense. By taking advantage of the extra heat that is generated by this phase change, we can store a lot of heat in the ground while drying out the greenhouse, which is a great help in reducing fungal diseases.

At night, when the greenhouse needs extra heat, the fans turn on again, this time blowing warm air into the greenhouse from all of the heat that was trapped in the huge thermal mass of the gravel bed.

I’ve been told that this kind of system can keep a greenhouse in our region around 5C through the winter. This extra heat would double our yields of greens in the winter and allow us to plant warm season crops in late March instead of early May.

Since we are about to put up a large greenhouse, finding out about this technology last week was good timing.

Sounds like a greenhouse game changer to us! Now we just have to look into the total cost and decide if the investment makes sense.

Below are this week’s photos: