As you may have read in previous posts. One of the main challenges that we have found with this bioshelter, and its relatively air tight design, is how well it holds moisture when closed up for the winter.
High humidity has been causing mold problems for us. And some plants have been effected as a result. [For a more detailed humidity science explanation see the blog post Humidity]
There are two ways that seem to temporarily resolve high humidity for us. First, we try opening the door and window to let drier winter air inside. This technique is limited due to cold outside temperatures. The second method is waiting for the sun to raise the inside temperature, which changes the physics of the air. Warm air being able to hold more moisture, the Relative Humidity can drop.
There is a limit to these techniques, and the mold is still around as a result.
So, I’ve been thinking of other ways to deal with the extra water in the air of the bioshelter. I could use a fan to move the air around which would in theory change the humidity dynamics at the surface of the leaves of plants, reducing the ability of mold to get a foothold. But, I am concerned that the same “wind” will blow mold spores around, making a small mold issue into a large mold issue.
At one point in the design process, before the bioshelter was built, we considered installing a Subterranean
Heating and Cooling System (SHCS), otherwise known as an Earth Charger or Climate Battery. These are specifically designed to trap heat in the ground underneath the greenhouse for release of that same heat at night. It would have involved considerable
excavation of earth and added material cost and labor to the project, so we decided against it.
Now, with the concern of mold, I’ve returned to researching this technology, not for it’s heating effect, but more for its dehumidification.
From, Testing Technologies for Affordable Bioshelters, a S.A.R.E. project:
“Warm, moist greenhouse air is blown through 4” buried drain pipe. As the air cools underground, it drops most of its moisture and with it a large amount of latent heat, heat which is released during condensation. At night, when the air becomes cooler than the soil, the blown air delivers the heat stored in the soil by day. In addition to being a cost-effective form of heat storage, SHCS keeps the air dry and cool, aiding transpiration and reducing fungal growth.”
Can the “dropping of moisture” in this kind of system really help our high humidity issue?
Of course we are not going to dig up the entire floor of the bioshelter now to run a thousand feet of underground pipe. Can we somehow retrofit the existing greenhouse to utilize this technology?
One option might be to install a large above ground container filled with stone, warm moist greenhouse air is pushed in with a fan, and it acts like a climate battery, to drop out the moisture. In theory the air coming out the other end of this contraption should be less wet. Why? Because the “colder” stone has condensed the water from the air “out” onto itself.
Option number two… Digging a smaller trench at the back of the bioshelter, and installing a climate battery, just for reducing humidity, not for significant heat storage.
The next step is to do some calculations and find out if a 40 square foot climate battery will be sufficiently large for our dehumidification needs.
Find out in a future blog post.