A design chalange, build a smart water heater timer.

[Ryland]

From talking to people about water heater timers it seems like people biggest issue is figuring out how to program it so they don't get stuck with cold water and that it either resets or stays set after a power outage.
So what I'm wondering is if anyone with knolage of off the shelf parts thinks that a smart water heater timer could be built, it would need some sort of "brain" and that is the part that I don't know about, then it would need a flow meter on the output side of the water heater, a heavy relay to turn the water heater on and off, maybe a thermostat in the tank and a 7 day clock, it seems like a pretty short list of parts.
The idea that I have is to have it programed to run full on for the first week, then after "seeing" your water usage start cutting out times that water is being heated, it would need to track water use over time so if your needs changed it would adjust to those needs, it seems like having a "visiting guest" button would be a good idea as well, something that would leave it on and heating water just a bit longer for when extra people were in the house.
Anyone know of what should be used as the brain for something like this? it seems like there are devices out there that can do it, I'm just not sure what they can do or what they are called, or how to work with them.

[Xringer]

Tankless on-demand sounds like a good bet..

Tankless Water Heater Buying Guide


One that is activated by a pressure drop in the HW pipe. Not by temperature.
It only makes HW when you need it.

[Ryland]

I have a friend who services tank less water heaters, $150 or more every other year or they start to get a scale build up on the inside, making them less efficient and if you leave it a few more years your water flow is going to be noticeably restricted.
They also tend to use some pretty nasty acid to remove the scale built up, I like the idea of on demand but the flaws that they have in real life keep me from wanting to install one, most of that negative feed back comes from people who install and service them, saying they would not install them in their own house.

[Xringer]

I did not know about that.
I just read this: Tankless Water Heaters 101 - Tankless101 at Plbg.com the most popular plumbing discussion board

And since I have hard-water (that eats all the plumbing), I would have to avoid getting a tankless..

I guess if you have good water, they might be pretty good.

Cheers,
Rich

[NiHaoMike]

Digital timers are pretty cheap nowadays.
Digital Timer
That one has built in battery backup. (I know because I have one. At the store, you'll even notice that the display is on in the package.) A small 120v water heater that uses 15A or less can be directly plugged into it. Use a contactor with a 120v coil to control a 240v heater.

If something more elaborate is needed, it shouldn't be too difficult to use a microcontroller. To allow for variable power, use a pair of SCRs (or even IGBTs) for phase angle control. Glue a piezo element to the pipe to sense flow through vibration. The temperature sensor can either be put between the insulation and inner tank or mounted as close to the outlet connector as possible. Extras such as wireless communication can also be added.

Those who are billed by peak usage can lower that peak by using a relay to turn off/down the water heater when another large load such as an A/C, oven, or EV charger is active.

[Ryland]

I hadn't thought of checking for vibration on the pipe to sense flow, I was thinking either an inline flow sensor or a temp sensor that could tell when a sudden change in pipe temp happened, but I like the vibration sensor and that seems like it should work, might need to be near an elbow or some other joint to get a good reading.
The main reason I think that a timer like this is a good idea is that people who I suggest water heater timers to don't understand when to have them turn the water heater on and off, so it seems like a self setting timer would appeal to a large market, then the naysayers of water heater timers would have one less reason to tell you not to get one as well, after all people tend to like saving energy up until the point that they notice something not working, they don't like being in the dark, they don't like tepid water, they don't like having to think about it.
The people that are around here who really like their on demand water heaters are the same people who keep the number of the service guy written on the wall next to it.

[Ryland]

I've been reading a bit about the Arduino, a micro controller that is mass produced and so far it sounds like it might work for this kind of project! $30 for the micro controller, plus sensor cost... inline sensors are $100-150 it looks like, so the glue on piezo electric sensor on the pipe really does sound like the way to go as it looks like the micro controller might be able to respond to sound input so figuring out the sounds that water in the pipe make would be all that is needed.
It also sounds like some nifty inputs from things like blue tooth and network connections can be added on as well, so remote over ride could happen, or remote monitoring of your hot water tank and water use can happen as well.
From my reading an on demand water heater can cut your hot water bill by 25% (advertised number, 75-85% efficient compared to 95% or so for a tank) but my water heater timer cut our water heating bill by half... sees like it could be more if it kept an eye on what we used.

[Xringer]

A while back, my wife and I tried on-demand planning to save oil (for hot water).
We would leave the boiler off all the time during warm weather.
When we knew that we wanted to shower or wash laundry,
we would turn on the boiler ahead of time and let it run for 20-30 minutes.

Interestingly, my wife does almost all the laundry using cold water.
And, the dishwasher has it's own instant-water heater sanitize-mode.
So, most of our planning involved bathing. Not too hard on the old brain..

During really hot weather, we would warm up the tank (76 gallons)
just about every morning. That burned some extra oil,
but, it was a Lot less than just letting the burner free-run.
I hate it when the boiler comes on at 1AM, when I'm least likely to want hot water!!

Planning ahead was a big success.. We just had to stay on the ball.
My wife liked the savings, but didn't like the planning.
Like when the weather would suddenly allow for a nice long bike ride,
but when we got home, ready for a shower.. Dang! Cold water!

I've been thinking of installing a timer that will keep the boiler off between 17:00 and 08:00.

It should be easy to do. I would install a 20A AC solid-state relay, in-line
with the hot-side and drive the DC control with an old programmable
thermostat.. (Low-power 5VDC wall-wart application).

[Ryland]

Originally Posted by Xringer

Planning ahead was a big success.. We just had to stay on the ball.
My wife liked the savings, but didn't like the planning.
Like when the weather would suddenly allow for a nice long bike ride,
but when we got home, ready for a shower.. Dang! Cold water!

Most people seem to have issue with planing, I thought long and hard about how my current water heater timer is set and I set it up so it would click off around 9pm as we tend to shower in the evening and my co-home-owner likes live music and showering afterwards and that can be 1am, that is why a 7 day timer would be nice, live music tends to be on the weekend.
The one stipulation that I was given when installing our timer was that no one wanted to be inconvenienced and we've managed that while cutting our cost in half, I really want to see how far we can push it, then figure out a way to repeat it for others in a way that they get the maxim benefit with the least input at a reasonable cost.
So far it is sounding like a temp sensor is going to be the cheapest and easiest way to set up an Arduino.
A friend of mine works for a low income housing non profit that got a large grant to retrofit houses to use less energy, he was hired to head up these projects and his first project is a $60,000 retrofit of a duplex, adding R40 to the walls, solar hot water and PV to the roof with a goal of reducing the utility bill by 90%, he has other projects going on that are not nearly as impressive as well but the over all goal is still the same, cut the long term costs for those that need it most, he said that in his research a smart water heater timer could have a huge impact nation wide.

[Daox]

Very interesting idea. Using the arduino is pretty easy. I've only done a few things with it, but its a very nice controller to use for whatever you need.