The solar collector we are building at my future house, 78 Main St, has been in place for a couple of weeks now, and we have been collecting temperature data. I’m hoping to have some “live” data at the website at some point in the future, but for now I have downloaded 8 days of data and created some graphs to help understand how the system is working.
The charts below show the rise and fall of various temperatures in my solar heating system. Each chart represents readings taken for one day, from midnight to midnight of the next day.
Out of the 8 days of graphs below, there were 3 days that were bright and sunny: March 10, March 16 and March 17. You can see a nice rise of the solar collector temperature (blue line) above 100 degrees. For these sunny days, the temperature stays there for all the daylight hours and then falls as the sun sets. Once the collector temperature rises above 130 degrees, the pumps start moving water through the heat exchanger.
The red, yellow and green lines represent the temperatures at various points in the heat exchanger. The fact that there is a nice difference between these temperatures (the red is higher than the yellow, and the yellow is higher than the green) means that my storage tank is getting a lot of heat.
The storage tank itself is massive (see “Solar Storage Video“) and requires many good sunny days to get it to 180-200 degrees, which is the goal. It started out at about 40 degrees when we first commissioned it 3 weeks ago and it hit 80 degrees on March 17th. By the fall we expect we will have hit the goal and in early winter we will begin drawing off that heat to keep the house warm. On each of those sunny days the storage tank heated up between 3 and 10 degrees.
Another thing we can notice from these graphs is that on very cloudy and rainy days, the middle of the storage actually drops in temperature. You can also see that many of the lines (especially the green one) have a jagged tooth shape to them. The jagged tooth looks like it occurs every hour (there are about 24 of them on any one chart). I know that the controller turns on the storage tank pump for 15 seconds every hour. Perhaps this affects the temperature in the heat exchanger and may be the cause of slight heat loss in the storage tank.
Information from data… good stuff!