SOLAR HEAT CONTROLLER

The solar heat controller is used to regulate the collection, storage and distribution of solar heat. 

The controller operates in either the differential or heat loop mode.

The controller displays temperature in degrees Fahrenheit or degrees Centigrade. 

The differential-on and differential-off temperatures may be digitally programmed within a few degrees.

The room set temperature is controlled within one degree.

The minimum set temperature of the storage tank has a range between 40⁰ F and 150⁰ F.

The Freeze Protection is set to shut the pump off at temperatures below 40⁰ F

The Boil Protection is set to shut the pump down at temperatures below 200⁰ F

The controlled relay can regulate an AC or DC pump.

Differential Mode
The temperature difference between the collector and storage is known as the differential temperature or simply the differential. Because of the intermittent nature of sunlight the temperature inside a solar collector varies. Since a net heat gain from the sun is needed we need a control system that collects more heat than it looses. Just activating a pump when a collector is hot is not sufficient to insure a practical heat harvest. A differential controller senses the difference between solar collectors and heat storage chambers and activates a pump when the collector temperature is higher than the storage temperature. That makes sense. Right? ... BUT... How much hotter should a collector be compared to a storage chamber to turn a pump on and how low should that differential be to turn a pump off?  
To adjust this control we must first be in the differential mode. We do this by simply installing a jumper labeled “DIF” . Once the DIF jumper is in position we may adjust the Diff-On and Diff-Off set points. These set points determine the the temperature differential needed to turn the heat collection pump on or off. In addition to these adjustments Freeze and Boil limits are built into the system for additional protection. If the collector temperature is above 200 °F(95°C) the Boil limit is exceeded and the pump is shut down. The same kind of shut down feature is also activated when the FREEZE LIMIT of 40 °F(5°C). Both of these set points are fixed and cannot be changed. These two functions rely on the the sensors that come with the unit and these are the only sensors that should be used.

Differential On Set Point

The two line LCD display normally shows the collector and storage temperatures. To set the Diff-On set point, press the upper button when collector and storage temperatures are displayed. The Diff-On set point is shown. Then use the upper button to increase the set point and the lower button to decrease the set point. After releasing the buttons for 5 seconds the display returns to normal and the collector and storage temperatures become visible.. The Diff-On set point has a minimum setting of 2 and a maximum setting of 40. It also cannot be set lower than the Diff-Off set point + 2.

Diff-Off Set Point
The two line LCD display normally shows the collector and storage temperatures. To set the Diff-Off set point, press the lower button when collector and storage temperatures are displayed. The Diff-Off set point is shown. Then use the upper button to increase the set point or the lower button to decrease the set point. After 5 seconds the display returns to normal and displays the collector and storage temperatures. The Diff-Off set point has a minimum setting of 0, and cannot be set higher than Diff-On – 2.

Temperature Sensors
The controller uses two MCP9701 solid state sensors powered with a +5 volt regulator on the controller. These sensors are made into probes and they can be used with open loop and closed loop hydronic and pneumatic systems, but they should not be immersed in water. Collector temperature should be sensed from the output pipe of the collector and storage temperature should be sensed from the cold water return pipe between the storage chamber and the pump. In Heat Loop Mode the storage probe is still the storage probe, but collector probe is used to sense room temperature. 

Heat Loop Mode
With the jumper labeled “DIF” is removed Heat Loop control is selected. In Heat Loop mode two set points are available, Room and Storage Minimum (Str-Min). The room set point is the desired temperature of the room being heated by the loop. When the Room temperature is 1 degree lower than the set point the pump is turned on. When the Room goes 1 degree above set point the pump turns off. When the storage temperature is below the Str-Min set point the pump is not allowed to run. This prevents the room from heating the storage. Heat Loop mode can also be used to control blowers for hot air collectors that blow directly into the living space. Place the Storage sensor in the hot air collector and the room sensor in the room. The relay output will cycle 1 degree above/below the room set point as described above. When the collector goes below the Str-Min set point the blower will turn off. Maximize the heat collection by setting the room set point at its maximum 95°F(32°C) . Set the Str-Min set point to the lowest acceptable temperature for the room.

Room Set Point
The two line LCD display normally shows the room and storage temperatures. To set the Room set point, press the upper button when room and storage temperatures are displayed. The room set point is shown. Use the upper button to increase the set point or the lower switch to decrease the set point. 5 seconds after the buttons are released the display returns to normal  and displays the room and storage temperatures. The room set point has a minimum setting of 35 °F(2°C) and a maximum setting of 95 °F(32°C) . 

Storage Set Point
The two line LCD display normally shows the room and storage temperatures. To set the Str-Min set point, press the lower switch when room and storage temperatures are displayed. The Str-Min set point is shown. Then use the upper switch to increase the set point or the lower switch to decrease the set point. 5 seconds after the buttons are released the display returns to normal and the room and storage temperatures become visible. The Str-Min set point may be adjusted from 40 °F(5°C)  and 150 °F(65°C) .

Controller Power Supply
The controller power supply may vary between 8VDC and 18VDC and a 9VDC wall adapter provides an ideal no load voltage output of 14VDC. A 12VDC photovoltaic power supply may also be used to power the controller, but the controller output should never be used to drive a pump directly since a current source from the controller is only .25A at 12VDC.

Relay Power Supply
The relay is activated by a 12VDC output from the controller. It's controlled by the controller and it's needed to drive AC or DC pumps.

Click on the above illustration for more information