The Taco SmartPlus hot water recirculation pump is designed to push domestic hot water around a recirculation loop, so that hot water is at the taps when you want it, saving time as well as water down the drain while you wait. It’s designed to learn your schedule, to avoid energy losses associated with pumps that run 24 hours a day, due to both the electrical energy used, and the lost heat in the loop when there is no hot water demand.
The SmartPlus pump is supposed to be “smart” in the sense that it uses a temperature sensor on the output of your water heater to learn when you use hot water, and adjust its run schedule accordingly.
So I had to find out, “is our smart pump learning?” And so far, I have to say it’s not. (edit: I think power loss to the pump is the reason, read on)
Above is a graph of the electricity used on a circuit dedicated to the water heater and the recirc pump. As you can see, it’s got activity at all hours of the day. (The weird modulation is because the pump runs 2.5 mins on, 10 mins off, and the datapoint averaging wasn’t lined up with 12.5 minute periodicity…).
During the same time period, here’s the temperature on the water heater output (Ignore the fact that it says input, I mislabeled it) :)
In theory the pump works by detecting a sustained rise in temp, indicating a hot water draw. It must have to notice this during its 10 minute non-circulation phase, because when it’s circulating, it’s causing the temp rise on its own. I have to admit, looking at the graph doesn’t make me feel any smarter than the pump. There was a rise around 7am; that was a shower this morning. The rise later in the afternoon I can’t explain. The big dip last night was an unnamed person using all of the hot water, so the output temp dropped due to that. All the little sawtooth bumps are due to the pump circulating water, and drawing up more heat.
At least the pump’s “pulse” operation (running 2.5 mins on, 10 mins off) cuts down on electrical energy use compared to a pump that runs constantly. When running, it uses 55W in my system. It pulses about 155 times per day for 2.5 mins, so runs about 5 hours per day, not 24. That ends up using about 8kWh/month. If it could smarten up a bit, it’d use less!
edit: Now that I’ve RTFM’d again, I see that power loss causes the pump to start its learning cycle all over again, and “pulse” for a week while it learns. And in my fiddly nature, I’ve dropped power to i.e. set up the monitoring. So perhaps I’m not giving it a fair shake. I promise to leave it alone for a week, and report back! Still, with the giant capacitor in the unit, I’d hope it could survive a brief power loss. Oh well.)
FWIW, the graphs above are from xively.com, with data pushed there from a Brultech ECM-1240 electricity monitor and Matthew Wall’s mtools scripts, as well as temperature data fed from an Electric Imp.