The idea is that you could briefly turn on the hot water tap and immediately shut it off, which would turn the Chilipepper on and then you wouldn’t need to press a button. When you hear the pump shut off you know you will have instant hot water when you turn on the hot tap. Personally I don’t think a pressing a button is any more difficult than turning the hot water on and then off.
You could, I suppose, turn the hot water on and just leave it on until the water gets hot, but with the Chilipepper pump it won’t get the hot water to the faucet quicker and you won’t save any water.
In fact, the Chilipepper requires a momentary contact between its control wires to activate it. The Chilipepper comes with a pushbutton, pretty much a doorbell button. When you push the button the contact is made between the two wires, and when you release the button the contact is broken. It’s not until the contacts are broken that the Chilipepper pump turns on.
This means that if you turn the faucet on and then off the Chilipepper will start and shut off when hot water gets there. Next, you turn on the hot water faucet, and begin using your hot water. But the flow switch will keep the contacts closed for as long as you are using the hot water.
In the meantime, if the Chilipepper sees the control wires make contact and they remain in contact for more than 15 seconds, the microcontroller in the Chilipepper thinks there is a short circuit on the control wires. In response the Chilipepper will turn on for two brief spurts about every 15 seconds until the contact between the control wires is broken.
We can overcome this problem by using a capacitor and a resistor. Placing a capacitor in series with the switch contacts creates a momentary short on the control wires. When the switch closes, the cap allows a rush of current to flow and causes a voltage drop on the input pin of the microcontroller. As the capacitor charges up and the voltage rises above about 2.5 volts the microcontroller sees it as an open contact and starts the pump.
After the flow switch opens its contacts when you shut off the faucet, the capacitor needs a way to discharge. Placing a resistor in parallel with the capacitor provides a discharge path. The control wires consist of a hot wire and a ground wire. A resistor in parallel with the cap discharges the cap when the contacts open.
A 1uf capacitor in parallel with a 10k resistor works good. Use a non polar capacitor so you don’t need to worry about which lead is positive and which is negative.
It’s a nice solution to eliminate the need for a button if that is the kind of thing you want to do. However, flow switches are pretty expensive. Trying to use flow switches for several sinks would be very expensive and you would need to do a lot of plumbing and wiring as well.
I will cover using a “whole house” flow control for the Chilipepper hot water demand system in my next blog.
Related Articles:
Motion Sensing for Residential Hot Water Demand Systems
Freeze Protection with a Chilipepper?
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