European wine cellars are built into hillsides or basements, and have the property of keeping wine at a very constant temperature year round. This allows wine to age gracefully. The temperature must be cool to prevent fast aging of the wine. Our wine cellar offered an opportunity to not use a refrigeration system and make use of shade and thermal mass.
The cellar was built lower into theground than the rest of the basement. Its floor is at about 12 feet underground. The limestone used on the walls serves two functions: it directly couples the air in the cellar to the temperature deep underground, the limestone also stabilizes humidity.
Keeping temperature constant and cool in summer
We live in an area where the summer daytime temperature can get quite hot. The thermal mass of the cellar keeps daily temperature swings down, but gradual influx of heat from the top of the foundation can gradually increase temperature over weeks. To counteract this, we placed some foam insulation on the outside of the foundation along the upper three feet,, we also placed PEX tubing in the upper six feet of the foundation (before it was poured). Irrigation water absorbs a bit of heat out of the upper walls every night.
Just how much does such a wine cellar vary in temperature during a day (compared to a refrigeration unit), and how much does it vary over the course of a year?
At this point we have recorded data from a thermometer showing summer temperatures at 58F and winter temperatures at 55F. This is a 3 degree swing, which is more than the average temperature would change using a commercial refrigeration unit.
A refrigeration unit, however, would cause quite large temperature swings all the time. It allows the temperature to climb slowly, then when it is a few degrees above the desired temperature,it turns onand blows chilled air many degrees cooler into the cellar to cool it down. On the other hand,our wine cellar stays very constant in temperature -the graph below shows the temperature variation over 24 hours. Note that the temperature of the Hobo logger took a while to settle to the cellar temperature.
The phenomenally low daily temperature variation of 0.05 degrees Celsius will keep the wine very happy. There is no way a conventional cooling unit would achieve such small temperature variations.