I am interested in applying some of the principles outlined in Chuck Marken’s article “Overcoming Overheating” (HP142). I am especially intrigued with the idea of routing the excess solar heat produced during the summer to a heat dump for melting winter snow. The question is how to manage the process to store the heat.
We have a second home in the San Bernardino Mountains at an elevation of 7,200 feet, near Green Valley Lake, California. Here, snow can accumulate to several feet—and it can remain for months.
In 2010, we installed nine 4-by-10-foot solar collectors in an antifreeze-based system for space and water heating. To prevent system overheating during warmer months, I cover several of the collectors, which are mounted on the roof. In April, I cover about 20% of the array; by the end of May, about 75% is covered. I reverse that process beginning in August.
While this strategy is effective, it is very labor-intensive and does not accommodate cloudy days well. Lately, we are experiencing more cloudy summer days. Since it is impractical to climb onto the roof to uncover collectors as the clouds come and go during the day, we now find ourselves relying on imported power for domestic water heating. Installing a heat-dump controlled with a thermostat is my next choice for dealing with overheating, since I could still make use of the excess heat.
Walter Farmer • via homepower.com
Beyond heat storage in a bed of sand under a radiant floor, I don’t know of anyone who has had success with seasonal storage and retrieval systems. Even sand beds only provide a few days’ worth of heating. A successful seasonal thermal storage system is an idea waiting for innovation and, to my knowledge, has been waiting for 40 years.
A heat dump, however, is a pretty straightforward solution. A motorized and dedicated pump that diverts the glycol solution to a radiator or underground tubing is not my favorite solution since it uses up some parasitic energy to dump the heat. I prefer a passive inline radiator—a thermostatic valve diverts the glycol solution to the radiator when the system is running normally and when the fluid is warmer than 170°F. An example can be found at bit.ly/Dissipater.
You’ll need about 8 feet of 3/4-inch hot water fin tube element per 4-by-10 collector—maybe less.
Chuck Marken • Home Power solar thermal editor
We normally recommend one Apricus heat dissipater for each 4-by-10 flat-plate or 30-tube evacuated-tube solar collector. They must be located outside—with good airflow—to maximize heat transfer. They can be installed in parallel (not series) to increase energy dissipation.
For winter heating, we normally recommend that the collectors are tilted at an angle that’s 20° to 25° greater than the location’s latitude. This helps maximize winter, fall, and spring output, while reducing summer output. Another good option is to mount collectors on a south-facing wall at 60° to 70°. In the winter, the collectors will benefit from diffuse radiation from the snow-covered ground, which further helps increase output during the cold months.
Mick Humphreys • Apricus.com