How to save water by installing a circulation pump and get instant hot water (Part 2 – Save energy)

Appliance module near water heater  with Kill-A-Watt

Appliance module near water heater with Kill-A-Watt



In Part 1 of this series (How to save water…) we looked at how a circulation pump can save several thousand gallons water per year. In this part we improve that setup to not only save water but to also minimize the energy consumption by turning it into an on-demand recirculation pump.

The added energy consumption originated from the fact, that he pump has to be running during the times that hot water is usually in demand in the house. If you want to cover different schedules, the pump might be running a big part of the day and that will consume energy.

The first improvement solves the timing problem – when and how long do we need the pump running? A motion detector installed in the bathroom will turn the pump on when a person enters the room and shuts off after a set time when no more motion is detected. Now the pump runs only when somebody is in the bathroom and hot water is most likely required. Instead of running for hours a day, the pump is now running only for a few minutes.

The downside with the on-demand setup is that it takes a few minutes for the pump to bring the hot water up. So if someone enters the room and opens the hot water right away it will still be cold, but most of the time it takes some time until people are ready for their shower or washing their hands and that is enough time for the pump to deliver hot water.

Adding the automation to the circulation pump is now really saving energy because the water in the pipes is most likely warmer that the incoming city water and it will take less energy to heat up. The pump does not have to run extended hours just to be ready at a set window of time. Instead it is converted into an on-demand pump without a bulky setup underneath the sink.

The on-demand Upgreen:

The installation requires three additional components to be installed:

  1. An X10 Active Eye (MS16A) or Eagle Eye motion PIR (Passive InfrarRed) sensor to detect someone entering the bathroom. A motion detector could be placed in each bathroom.
  2. A wireless transceiver module (TM751) receives the radio frequency signal from the motion detector and converts it to X10 signals which will be carried over household wiring. It should be placed somewhere close (max 100 feet in open space) to the motion detector. Transmitting through the power line allows the signal to be transmitted longer distances (down to the basement) to the remote switch that will control the pump on the water heater.
  3. The remote switch, an appliance module (AM466) which receives the signal from the transceiver module and powers the pump on and off.

The pump timer must be disabled with this setup and set to be always on. The recirculation pump will be controlled by the appliance module and the motion detector.

The components may be purchased here:

This website offers fairly inexpensive starter sets that contain most of the components:

http://www.x10.com/promotions/cm15a_complete_new_2012.html

The site is a little “busy” but if you find a set that includes all components you need you can usually save some money. The remote control “PalmPad” is handy to overwrite the motion detector signal and control the setup manually. I have had some rare instances where the motion detector would not shut the pump off.

Another good source is here: http://www.thehomeautomationstore.com/

 

Configuration of the EagleEye:

Programming the unit is a little cumbersome but the directions walk you through it in a couple minutes. Make sure the ActiveEye dawn/dusk mode is not set since we want to turn the pump on even during the day if motion is detected.  The device has a programmable delay to shut off after no motion is detected. We use that to keep the pump running until the water is hot.  The shut off delay can be set from 1 to 60 minutes. I would start with a setting of 2 minutes and see if that is sufficient for you. I have set it to 4 minutes, which is enough to get hot water in the second floor of our house even on a cold winter night. You might have to increase the time if the water is still cold when the pump shuts off. Your pipes runs might be longer or not well insulated.

 

The convection Upgreen:

I noticed that the hot water pipe on the water heater was always hot, even though the pump has not been running for several hours. I have heat traps installed on the water heater, so I know that the pipe should be cold if no hot water is running anywhere in the house.

The heat traps are Anti-Thermosyphoning loops which prevent heat loss from convection. The water in the water heater expands and becomes less dense. This less dense water travels up the water pipe and is replaced by cold water flowing back into the tank. The heat traps prevent that process in a normal household piping (without the sensor valve present).

When the sensor valve is open, it creates a connection between the hot and cold waterline and essentially subverts the heat traps by allowing the hot water push into the cold water line. This convection loop produces a constant heat loss which has to be compensated by the water heater heating up the water again.

T-connection for cold water line

T-connection for cold water
line

The solution is a shut-off valve between the hot and cold water lines in line with the sensor valve. The valve prevents those convection losses when it is closed. It only opens when the pump is running and is closed all other times. Controlling the valve is easy with an additional appliance module (AM466) listening to the same motion detector signal as the pump. The hot water line on the water heater is now cold when hot water is not running.

Installation of the shut-off valve:

The sensor valve has a build-in T-connection so that water can get to the faucet even when the valve is closed. The shut-off valve has to be installed between the water supply and the sensor valve and therefore we need an external T-adapter to allow water flow even when the shut-off valve is closed. I capped the usual connection to the cold water faucet on the sensor-valve and added a T-connector that delivers cold water to the faucet even when the shut-off valve is closed. So the T-adapter connects the cold water supply, the cold water faucet and the sensor valve input.

Sensor valve with cold water outlet capped

Sensor valve with cold water outlet capped


We disconnect the pump and transceiver in the summer months since the water is hot much quicker and we use more cold water anyway.

With these upgrades installed, the system is a little more complex but we eliminated the heat loss of a standard recirculation pump setup, we are saving thousands of gallons of water and energy at the same time.

Please leave a comment if you like or dislike this setup or need more information about it.

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