A Trouble Shooting Conversation

Below is a conversation between Jeff and Paul related to the settings on the SHEM Controller.

Jeff: The system uses the 16° and 4° degree temperature difference to turn on and off the solar water pump.

This is an indication, as when I visited with Paul by phone, that all temp sensors appear to be operating, and reading temperatures correctly. That's why the next sentence is confusing. The system reads T1 and T2 to operate the pump. I believe the controller does read T2 (bottom of tank).

Paul: However, the system totally ignores the current temp at T2. We use very little water in the AM. Right now, T1 is 96 and T2 is 83° and T3 is 141°. I have learned that 141° is plenty of Hot water for a bath or a shower.

These numbers would be reasonable given a tank that's NOT been pumping water. Stratification is very real! 58° degrees isn't unreasonable. The tank bottom is where the coldest water sinks, while the hottest water rises to the top. This is the major reason we bring the cold feed into the top of the tank! A tank that is circulating will yield different readings.

Jeff: When the solar is turned on at T3=141°, The pump actually lowers the temp in the tank down to whatever the T1 can provide. That is low, for this particular time of the year. So I am paying for electricity to heat the water in the AM and then dissipating the hot water when the Solar water pump comes on.

The pump should come on, the collector will quickly cool, and the pump will then shut off! This short cycle occurs as the day begins. The collector (T1) is reading 96° degrees, and that's likely a stagnation temperature (no water in collector). The minute water runs into the manifold, temperature will drop fast. The collector's heat will be transferred, temperatures will drop to a delta t of 4 degrees, and the pump will quit. Only a tiny bit of energy will result. Later, as the collector heats up, the pump will stay on. By the way, this is a single 4' by 8' collector. Turn the flow down to half a gallon per minute. This will extend pump cycles.

Paul: I changed the electric to only 2 hrs in the AM and one hour in the PM.

Jeff: With the insulation wrap the tank holds temp fine.

We tested wraps. Wraps improve performance 11%!

Paul: Am I missing some setting that will read T2 and wait until T1 is 5° or 10° degrees hotter than T3 or even a difference between T1 and T2.

Jeff: With a single 4' by 8' collector, the BTU available is limited. There is only 32 sq. ft. of surface, and that's not enough to really cook unless it's a hot sunny day. In the fall and winter, you should not expect a lot of production. Reducing the flow to half a gallon per minute will prolong pump cycles as lower flows don't strip the collector btu as fast.

Paul: There is something missing in the program design when this controller is used on a single tank system.

Jeff: The pump comes on, then shuts off. This is a result of small temperature differentials, with smaller collector size yielding small btus. The pump should have cut off at delta t of 4°, which it did. The system is shutting off at a delta t of 4° degrees, correct?

We can always return to factory settings, then re-program again. You'll know when the factory settings are back by the "Beep Beep Beep" sound that the controller will make.