Hot water Heater automation

mikei-ma

Active Member
Using Elk M1 Gold I am creating a process to turn down my hot water heater during non-peak times. In addition to turning it down I will also automate the hot water loop back system to shut it off when we don't need it (really only in the am and evening for an hour). The general idea is to use off the shelf products to automate the thermostat. Replacing the thermostat is not ideal due to cost and the thermostat on the hot water tank is not terribly granular anyway. I only need to 'turn the knob' down to a lower temp. I am going to do this by programming the elk to communicate with the servo micro controller over the M1data bus + serial expander. The controller has 6 input/outputs on it so I can use it for other items. Initially I may just throw a relay across one of the inputs on the controller to tell it to 'set back' the thermostat by moving the servo. It may be easier (less time) than dissecting the serial protocol and using the serial expander, as the controller has a bit of memory to store a program.
For the loopback, I'm still looking for an inexpensive water valve, although I may just go with a higher torque servo, that's phase 2.

So far I have the following design:
  1. Embedded Motor microcontroller
  2. Servo
  3. Gears (have from building R/C cars)
  4. Elk Serial Expander
So far I've ordered the parts and started to setup my c++ development environment. More to come!
 
There have been other threads along these lines in the past. The main question that has arisen is that water heaters are surprisingly efficient at holding heat, and that unless you're leaving home for more than a day or two at a time (most people come home once a day and use hot water) the efficiency gain is not too high.

I've tossed the idea around here before myself, and Elk themselves actually makes a relay suitable for cutting and restoring power entirely to a water heater. Problem is I just can't get the math to work out where it is worth the cost of doing it.

In your situation, where you're simply reducing the setting on it, it seems like the effect would be even more mild.


Now inserting a relay to cut your continuous hot water loop system when you're away from home is an easy one and WILL save you power. Just do the numbers well before you go to your efforts on the water heater. A lot of people smarter about it than I have done them and participated in threads where we just found it hard to break even the initial expense.


I've always wanted to hook a power meter specifically to my water heater for a week or two, one of the weeks using normally and the other week cutting the heater off when i leave home. A cheap way to test the actual savings. Have yet to find a meter I want to buy though.
 
it does sound like a fun project, but why turn the dial vs. just cutting power?

And I totally agree that practically speaking, you'll never recoup the cost of materials from this project. Any heat lost will have to be recouped when it turns back on, eating up the energy that would've been consumed during the day anyways. If the system isn't being used, the cost to maintain temperature is negligible.
 
I did a lot of research on water heaters before designing and building my current home. I installed a 105 gal Marathon Water Heater in 2007. It's like a big insulated thermos bottle and retains an incredible amount of heat. Unlike the average hot water heater, the shell remains cool to the touch. There's enough hot water to have three showers going at the same time without anyone running out of hot water. I had considered tankless water heating, but decided on traditional tank heating. First, it's a lot cheaper. Second, with the Marathon unit, I could lose power and have hot water for a long time since it's so well insulated. Tankless heaters: No power = No hot water = very low WAF!

Since this unit retains heat so well, turning it off when out of the house would have a negligible effect. If I go away for a few days or longer, I throw the breaker. Automating this adds an additional failure point at a cost that would likely never be recouped. Of course, that can be said for most of the HA we do!

Kevin
 
Since this unit retains heat so well, turning it off when out of the house would have a negligible effect. If I go away for a few days or longer, I throw the breaker. Automating this adds an additional failure point at a cost that would likely never be recouped. Of course, that can be said for most of the HA we do!

The emphasis is mine, please note that a breaker is not a switch and will deteriorate rather quickly. It could fail closed (slight possibility). Consider putting a switch in.
 
Good point, Neil. At this point, since I work like a dog, the breaker only gets thrown a couple of times per year.

Thanks,
Kevin
 
Second, with the Marathon unit, I could lose power and have hot water for a long time since it's so well insulated. Tankless heaters: No power = No hot water = very low WAF!

Are you referring to Electric only? I had a tankless in my last house, Natural Gas. I chose the model that was electrically controlled, since it was 95% efficient, vs. the model that was NOT, which was only 90% efficient. And only a $50 difference.

However, I just ran mine on a UPS. I never had issues getting hot water, even without power in the house.

--Dan
 
Are you referring to Electric only? I had a tankless in my last house, Natural Gas. I chose the model that was electrically controlled, since it was 95% efficient, vs. the model that was NOT, which was only 90% efficient. And only a $50 difference.

However, I just ran mine on a UPS. I never had issues getting hot water, even without power in the house.

--Dan

Yes, Dan, I was referring to electric. Forgot about gas, since I don't have it here. There's not a lot of gas pipe laid here since we don't have much need for heating. I wish I did have nat gas in the street, since I have a whole-house genset. Had to sink a 500 gal tank in the yard, and at best, would only last about five days or so. If I had natural gas in the street, I wouldn't have to worry about refilling.

I never had experience with tankless. The only reason I considered it was for the instant hot water. I have four showers and nine sinks in the house. Too many units. If I got a bigger unit that could handle the house, then it wouldn't be instant. When I found the Marathon Heaters, for a thousand dollars we've been very happy.

Kevin
 
Unlike the average hot water heater, the shell remains cool to the touch.
This makes me wonder if this is another case where California code is too advanced... but I can't remember a hot-water heater I've touched in the last 10 years that was any different from room temperature on the outside (and earthquake anchored, but that's a different story). They're unbelievably efficient here - like $70/year to operate.
 
This makes me wonder if this is another case where California code is too advanced... but I can't remember a hot-water heater I've touched in the last 10 years that was any different from room temperature on the outside (and earthquake anchored, but that's a different story). They're unbelievably efficient here - like $70/year to operate.

Certainly in California you would want to be as efficient as possible. Crazy high rates from what I hear.
 
3 Tiered electric rates; after a "baseline", my rates hit $.419/KWh. ~$800+ electric bills during the summer!

Man, that's just nuts! I'm in SW Florida, so we use AC for most of the year. My highest bills are in the $300 - $350 range, equal to about 11 cents per KWh. That's with 3700 sq ft under air, running the pool pump 10 hours per day, and at last count, 29 hard drives running 24/7.
 
Well, I have been interested in automating my water heater and did some study on the energy savings from turning it off during some periods. The main problem is that you have to heat the water in the tank for at least an hour till 135F at the coldest point every few days to control the legionella bacteria. Given the high insulation efficiency of the modern tanks, there is just not enough energy savings and it is potentially putting you in danger of contamination, which will be difficult to detect until it is too late. The only potential savings may come during lengthy vacations when you'll turn the heater on for a couple of hours every few days, but it wont be much savings to be worth the trouble imo.

Please look up info on legionella bacteria before you attempt to automate your water heater!
 
Great point, Picta. I forgot about that. Another good reason to buy an efficient heater and just never turn the heater off.

Thanks,
Kevin
 
I'm surprised you still have a dial on your hot water heater. Mine has pushbutton temp settings... potentially easier to automate, but also may be something you run into when you have to replace your water heater in ten years, but it's also gas, and also has a powered vent system.. and also in california... but unlike work2play, I've never had a combined gas/electric bill above $200.
 
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