Recirculation pump wastes a huge amount of electricity

2 months ago

We are a wildfire rebuild and even though I had said initially I didn’t want a recirculation pump, but do tankless heaters in the bathrooms and kitchen instead, we somehow ended up with a regular water heater with a tank, a solar water heater on the roof and a recirculation pump. It was something about getting enough points for the green inspection that made the solar heater a must.
Anyway.... Our architect and contractor decided to just turn on the recirculation pump to run all the time. They had looked at some numbers and determined that it was not going to use very much power at all.
Well, we have been having inexplicably high power bills (we are all electric) and I have been trying to figure out why, because we are built to all the highest CA standards. I have asked the contractor about the recirculation pump but was told it was absolutely insignificant.
Now we just had our solar panels installed, along with two shiny new Tesla Powerwalls. With that came the ability to monitor our electricity usage in the app. Right away we noticed regular spikes in about 5kwh usage, at least every 15 minutes. The oddest thing was that they happened all through the night, but when our house was busiest, with everyone up and doing things, the spikes would disappear.
So by the time we woke up around 7 am we had already used up about 9 kwh since midnight!
Could it be that the water heater was busy all night reheating the water that had cooled down in the pipes because no one was using it? I had been told that the pipes were insulated but couldn’t help thinking that long skinny tubes, even insulated would be the worst type of container shape for limiting heat loss.
So, I took a look at our pump myself (Grundfos PM comfort auto adapt) and switched the mode from 100% (running all the time) to AutoAdapt (learns our use pattern and initially is basically off).
Low and behold the spikes completely disappeared from the usage graph and we are now saving a full 10 kwh per DAY (which in the Bay Area is about $4).
So my hunch had been correct and in two short months the recirculation pump had cost us more than $240, because our high use also pushed us into a punishingly high rate tier for all our other electricity usage towards the end of both months.
We need to and want to save water but with a pump that can learn your habits and learn to turn itself on accordingly and stay off throughout the night I have no idea WHY they would have decided to just run it continuously. And poohpooh me for my concern (that is a whole other subject).

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