Mr. Editor:
Like Margy, I also found myself building an ‘above ground cellar’ for temperature stable storage of food and other goods. Working with a detached three-car garage that had just a two-car door, I converted the extra ‘bay’ to a bonus room. With standard framing and insulation I noticed that that room remained noticeably more even in temperature throughout the day.
I also have warm summers, 100F and occasionally more. Winters rarely drop below freezing for more than a day or two.
I did some research once on passive temperature control and learned that water has a high specific heat and in significant quantity can stabilize the temperature of a given space. I acquired several 55 gallon plastic drums and placed them in a row along the interior wall of my room. I filled them in place with water I treated with bleach and sealed them. Within days I noticed that the temperature remained nearly constant regardless of time of day. The barrels are about 3′ high by 2′ deep, and it is easy enough to construct shelving above them.
I improved on this further by adding more barrels and increasing the insulation. I bought 2″ thick foam panels at Home Depot, the kind with reflective metal coating. These I cut to shape for the windows and blocked them off. I also bought a box fan and some furnace filters. This I mounted in a window on a clock timer. The fan pulls cool night air into the space, pulling air through a furnace filter and an exterior screen. Now that the summer has passed I have disabled the timer and will cover the fan assembly with an insulation panel as the temperature drops. I may even use it to pull warmer afternoon air in during winter.
With these steps and no significant heat sources inside the insulated envelope I have found that with no energy consumption I have managed a cool place for long term storage.
Water is cheap and readily available. Once purified, it requires no maintenance when properly stored. – Vlad