we have a similar system- but used horizontally cut barrels inside of pallet walls (insulated with plastic on both sides), instead of digging. Our pest control is FROGS. Ours is partially open most of the year, surrounded by a greenhouse fence frame for a trellis and greenhouse roof. The greenhouse walls are added for winter. Large barrels of water not only serve to water plants and frogs, but also as a thermal. Water is collected off the greenhouse roof into the barrels. Currently our system is 40 square feet of grow space, plus two indoor systems, and raised beds for root crops not under canopy. We hope to expand next season, another 40 feet. No elec used at all. It works great! And our pest control is self-sustaining and organic. They live inside the frame, which also has a 4 foot high insect screen around it, sitting just above the bed area. This allows pollination but limits insects to the frogs management ability. Also keeps baby frogs from hopping away.