Anyone use a smart pump for hot water recirculation?
minmaxdesign
| Posted in Energy Efficiency and Durability on
Has anyone used one of the smart circulators, such as Taco Smartpulse, for hot water recirculation? Looks like it uses machine learning of sorts to try and predict hot water usage. Seems reasonable for highly predictable events like showering, somewhat reasonable for semi-predictable events like cooking, dishwashing, and maybe laundry, and not really useful for handwashing. Seems particularly more challenging as the number of occupants and activity increases: active family of five vs a retired couple.
Curious to know more about circulating when not needed and not circulating when needed.
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Replies
Normally recirculating line are only installed for fixtures more than 100' away.....
I installed a Taco D'Mand in my condo unit--we are on the third floor, with the water heater in the basement, so it is typically a loooong wait for water to get to the sink. It uses a push-button control--press the button, the pump circulates, and then shuts off when hot water is at the sink. It was a retrofit job--it is a cross-connection between the hot and cold sides. Now that it is installed, it does exactly what I want it to.
Perhaps I don't live like other people, but my schedule would never be regimented enough for a machine learning algorithm to do any good on predicting hot water draw times.
It looks like the D'Mand has been replaced by the TacoGenie:
http://apps.taco-hvac.com/uploads/FileLibrary/REV3_TacoGenie_Catalog_100-15_072619.pdf
One strange failure was that due to the cross-connect, if you have a major draw of cold water (e.g., washing machine) connected past the pump, it can depressurize the cold side, which draws hot water into the cold side. I fixed this later with a solenoid valve, powered off the pump switch.
I installed a thermostatic on-demand electric heater (EEMAX) below the sink as I didn't want to install a small tank (2.5 gal). The on-demand heats the water quickly (a few seconds) until the water arrives from the whole house gas powered on-demand - then it stops heating. The hot water line from the gas on-demand to the sink (furthest fixture) is in conditioned space so it's at room temperature, thus I am not faced with a large temperature rise. The EEMAX has a few settings, I don't mind the relay click on/off (not too loud) otherwise it can be in an always "ready" state where the relay is closed, though you might get the usual relay hum. If I want really hot water immediately, I just keep the flow low, around 0.5 gpm. For me, it's been a better option that recirculation. EEMAX LavAdvantage comes in various power ratings, including 120V models. If your hot water line is in conditioned space (between main heater and fixture) you don't need a high amperage electrical on-demand (as you may need if the water is at the exterior/utility temperature in a cold climate). I have a home run system, so recirculation is not really an optimal choice. If you need immediate at each fixture, then you would need a small on-demand electric or small holding tank (e.g., 2.5 gal) at each fixture. For a 2.5 gal holding tank, at 2.5 gpm, that's one minute. If your main heater isn't supplying that fixture in one minute, then you need a larger holding tank (e.g., 4 gal) - or just go for an electric on-demand that is thermostatic (can shut off when the hot water arrives from the main heater).
I could not find a control for my recirculating pump that would work the way I wanted it to. So I built my own
The control on my recirculating pump loop with electric tankless heater works this way
Anytime there is a water draw from a hot water faucet that will turn on start my system. The flow turns on the water heater. My control senses the heater current. If the current loop temperature is below the set point of 110° the pump will run until the loop reaches the set point. The pump timer stops the pump after 3 minutes regardless of loop temp.
It takes a little less than 2 kWh and 3 minutes to heat my 175 foot loop.
So I splash on the hot water for a second or two and then turn it off get undressed and put the laundry in the hamper by the time I get back the shower has hot water.
The down side is if you turn on hot water and change your mind the loop will still heat and I wasted 22 cents of electricity to no benefit.
I have not changed the system since it was installed 3 years ago.
You may want to read this old post.
https://www.greenbuildingadvisor.com/question/thermosiphon-vs-recirculating-pump
Walta
I think 2000watts for 3 minutes = 0.1kwh
Hopefully you don't use 2kwh in 3 minutes, that would put your heater at about 40,000watts or 166amps at 240volts. :-)