I have a regular hot water tank in my house that never seems to have the correct amount of hot water available, without leaving it on all the time (which is really wasteful).
I have just bought a Shelly relay, with the addon board and three temperature probes.
I am hoping I can use this to make my tank a bit smart.
A few initial questions:
Where should I put the temperature probes? I was going to but one on the pipe coming out of the tank, one underneath and one about half way up. However, I am not now convinced that this is the best method.
How can I use the three sets of temperatures to make sure that adequate hot water is available at the right time, without heating unnecessarily? The more I think about this, the more I cannot get my head around the logic of it.
it needs to maintain 60c (140f) at a MINIMUM to ward off Legionaires disease. You also must have proper safety bleed offs to prevent BLEVE and thermostats to ensure you cut off long before you're in that temp range... Plan accordingly.
Properly insulated water tank does not need much energy to maintain the minimum temperature of 60 C when there is no usage.
The risks taken by letting it cool down can lead to more expenses, than leaving it on.
At my job-site we have several tanks and we do use 3 sensors on all of them. Bottom, middle and top.
Just to confirm, my hot water tank is gravity fed and therefore has an overflow that can dump overheated water into my cold water tank as a failsafe. I also have a regular thermostat that is located half way down the tank and set for 60 degrees.
So, if I put a thermostat at the top, middle and bottom, is this purely as a guide so I can see hot much usable hot water there is?
I wasn't sure if I was getting too clever by having the hot water timer come on earlier if it sense water was colder than usual.
With regard to Legionaires disease - does this mean that I should be heating my water until the hot water thermostat cuts off the power?
I'll start by saying I'm far from an expert, but I did research the topic pretty well when I was automating my water heater. I could be wrong, but so far I haven't suffered any ill-effects with the below recommendations.
Looks like you only need to maintain it at 60 for 30 mins according to this.
As to how long it takes for the bacteria to grow again, it seems like even at optimum temperatures, they take a few days to reach danger levels (according to an AI summary of this highly technical paper).
Obviously, no one would want to ever risk waiting for it to reach dangerous levels. so running a 60 degree cycle for 30 minutes daily should keep everything in check. Unless my math is off, that's 48x less energy wasted on heating water for no additional benefit.
Is not that easy...
If we heat the tank to 60C, we use a lot of energy to do that and leaving it cool down again we loose all that energy. As a side effect, next time we want to use the water, we need to reheat and so we have a long time to warm it up again.
If we maintain the temperature, we only need short bursts of energy to keep it at level and the readiness for use is almost instant, so very comfortable. And we do not need to worry about species living in the water
So, if the tank is used only sometimes (like once a week or even less), it's fine to cool down.
Is it used daily, and it is very well insulated, keeping the temp up is well recommended and actually cheaper.
Just for reference: At the hospital I work, we even use recirculating waterlines, so that water in all pipes thru the building never stand still. Good against sediment and necessary to fight legionella.
We have a 23 hours long setpoint of 60 C in the tanks, and middle of the night we even have 1 hour of 75 C setpoint, which ensures, that all pipes in the building get theirs 60 C for 30 minutes. We need to be sure, that not the exit temperature of the tank is 60 C, but the return water after the travel thru the house must be 60 C.
Yes, that would probably be a bit overkill for a regular house. I'm just giving a perspective...
