Finalizing H2O system design - feedback welcome

[Iceni John]

Originally Posted by Tejon7

I read another forum member here (can't remember who) that had a brass momentary push-button valve of some kind where you pushed the button and waited until you could feel the brass warming up.

I think that was me! I haven't yet installed it, but the 1/2" return line into one of the fresh water tanks is already in place. I'll only use it for the bathroom hand basin; the shower and kitchen sink are very close to the water heater, so there's not much water inside their 1/2" PEX feed lines.

John

[Rucker]

Originally Posted by TaliaDPerkins

In my experience with industrial systems, it works if the sensors are located in the better for it areas of piping in the loop, such as right after a holding tank and just after the load (of course there's usually only one load in such a loop . . . ).


But apparently a recirc system of some sort is the proposed solution to the cold water sandwich.


https://www.countrysideph.com/blog/s...ndwich-effect/


" Installing a recirc loop which will return the cold water back to the heater through the help of flow check valves is a common solution."

I agree with your discussion about sensor placement.

For the kinds of systems we put in buses, in my experience, recirc doesn't work. That link is another one of those website opinions that is not based on actual experience with instant gas water heaters.

Here's why, I think: these instant gas water heaters monitor inlet temperature in addition to flow pressure. Since they're just designed to raise the water temp by n degrees I'm guessing their solution to scalding is to make sure the inlet water temp doesn't exceed a certain value. Could be wrong on that, but the result is the same: any close recirculating loop will kick the inlet water temp above the max, causing the unit to error out. With my system, it actually errors and needs to be power cycled. Kind of like an open faced cold water sandwich, actually.

If you build a recirc system with a holding tank and can somehow quickly bring the water temp in the holding tank up to a nice warm temp without exceeding the inlet temp, maybe that would work. But you're fighting three variables: the time to bring that water up to a certain temp to avoid a cold water sandwich; the actual amount of time using the hot water; and the inlet temp max threshold. You want the temp rise to be quick, like with the use of a timed or momentary recirc pump switch; then you want it to stay that way--maybe with the recirc pump on a couple of sensors.

In my testing, after which I abandoned the whole idea of recirc, I also found that any kind of backflow device on the water supply line prevented the water heater from turning on unless I had really high flow. Apparently there's quite a bit of pressure drop before the backflow valve opens to allow water into the water heater, keeping the unit from turning on. My system needed almost full force water coming out of the shower head to turn on the system until I realized the backflow valve was screwing things up.

Others have found slightly different (and more expensive) water heaters that avoid some of these problems.

I had similar challenges with a thermostatically controlled mixer valve, which works great with domestic water heaters. But in the temp, pressure and flow ranges that my instant water heater operates at, I couldn't balance the thermostat without the water heater kicking out.

Now I just open the shower wide and adjust the knob on the heater, dancing around the sandwich. There are two knobs, really, and it's a bit of a dance, but hey it's a bus.

I'd love to know if others have had more success in this space and would love to learn from them...

[TaliaDPerkins]

Originally Posted by Rucker

Since they're just designed to raise the water temp by n degrees.

I confess I'm working with 16bit minimum precision equipment for PID, when not 18, or 24bit . . . Lots of math for conditional integral replacement. Kind of what I had in mind, even if only 8 bit.


Open face and in your face...

[sdHeights]

You can run your RO waste water back into the fresh tank. As long as your are using it for something other than RO, no buildup will happen.

[Rucker]

Originally Posted by TaliaDPerkins

I confess I'm working with 16bit minimum precision equipment for PID, when not 18, or 24bit . . . Lots of math for conditional integral replacement. Kind of what I had in mind, even if only 8 bit.


Open face and in your face...

This comment was lost on me.

[Albatross]

Originally Posted by Rucker

This comment was lost on me.

It's regarding digital sensor provision, and is coding/computer engineering terminology. It isn't really too terribly far off from some of the stuff I've had to deal with in the past, but it's still a bit hazy.

Regardless, it only matters to the kinds of people that are looking at designing their own system controllers/software/electrical schematics using those kinds of things, and thus is not worthy of a response if it doesn't apply to you.

[incubus]

Originally Posted by tomrasdf

The water being recirculated back into the fresh tank never leaves the pipes. It bypasses the shower valve and goes directly back into the tank.

The idea is to reduce the amount of water put down the drain while waiting for the hot to come up to temp.

The idea is as follows:

• Rather than running the hot water and waiting for it to heat up...
• you turn on the hot water recirc, which pulls hot water into the shower circuit, but bypasses the head and redirects to fresh
• Once line is hot, you turn off recirc valve and turn on shower, getting instant hot water
• Hence, zero wasted cold water down the drain
• (This could also reduce the change of the water heater turning off due to low pressure if shower-head draw is too low)

Overkill? I just don't like the idea of wasting water waiting for the shower to warm up.

It is not over kill. Every large building or long building has a hot water return line so your not wanting 5 minutes for hot water. Yes it saves a fair amount of water , important when dry camping. I put tee in line under sink with ball valve on it. Open it pump for minute have hot right at bathroom. Valve had tabs allowed me to mount it on side of cabinet

[HamSkoolie]

Originally Posted by sdHeights

You can run your RO waste water back into the fresh tank. As long as your are using it for something other than RO, no buildup will happen.

It helps to quote the person your responding to. Some of us block certain users and so if one of those users makes a comment you're responding to we'd never know it.

[Bluthebus00]

To the OP, I agree with the rbirling. You'd definitely want to install dedicated check valves between your 12v water pump and city water supply sources. The check valves aren't expensive and save a lot of headache if the plastic check valve in the 12v pump fails.

Outside of that, nice setup! I had to read through it a few times to ensure your city water isn't feeding your 12v pump. It looks like you have a valve to bypass the pumps?

I did mine this way:

City water - sediment filter - check valve-------\
____________________________________|-------> Out to water fixtures---->
fresh water tank - 12v pump - check valve---/

This way both water sources can operate without impacting the other. They can also work together when I need to boost water pressure in the rig. All of this works automatically without needing to manually open or close any valves

[djdalfaro]

Here's my take. The valve close to the shower on the purple tempered line would feed back to the cold water inlet. If I open that valve, the shower line will fill with tempered water. A couple seconds and then I can close it once it is warm.

[incubus]

If you ty in from hot side of shower to water inlet,the pressure will be the same and there won't be any flow. Gotta go back to tank, vented,no pressure. And yes you have to have a check valve to protect the pump. If not water seeps through pump and starts filling the tank,eventually over flowing it.

[TaliaDPerkins]

Having a momentary switch which turned on a volumetric pump long enough to circulate the volume of the loop and pushing it before each shower should resolve every issue discussed, as well as prevent warmed water from dumping back in the tank.

[DeMac]

Originally Posted by Rucker

This comment was lost on me.

Ancient Greek.

[rossvtaylor]

I've installed several systems with a fresh water bypass/recirculation, which has worked so well I'm doing the same on our own Crown conversion. It's hard to retrofit to an existing system, without good access, because it requires adding a water line back to the tank. But in a new system, I just install a Tee fitting in the hot water PEX near the last fixture in the line and add a 12V solenoid valve there...connected to a momentary switch. Pressing the switch starts a simple 555 timer, resistor adjusted for about 10 seconds (or whatever it takes to get hot water to the fixture), and that opens the valve. Opening that valve lets water run through the pipes, from the hot water heater, and back into the top of the fresh water tank.

This saves running the tap or shower until the water is hot, which wastes water in my eyes. There's not enough hot water returned to the tank, in this scenario, to impact the tank temperature or interfere with the operation of the CampLux CA318 water heaters I like to use.

One thing I recently did, and also plan to use in our personal conversion, is adding a second temperature-controlled switch to this valve. This function opens the valve when the tank water approaches freezing and runs enough water through the circuit to warm the tank above the freeze-danger point. I think I had it set to open at 35F and close at 45F. I've tried using the resistive tank warming pads but I think the propane warming is a better option when electrical energy is not unlimited. Obviously this doesn't work with the black/gray tank, but I usually install them side-by-side in the same foam and plywood enclosure so I believe that having the fresh water tank in there would keep the pooh or pee or shower water from freezing...and so far so good.

Like I said, I like both of these enough that they're going in Stevie the Atomic Crown.

[turf]

Ross's valve sounds like a cool setup!

ok, i did the math for my own setup.

my water tank is 16 feet of 1/2" pex pipe away from my shower head.

1/2" pex pipe holds .00961 gallons per foot.

16 x .00961 = .1536 gallons = just under 2.5 cups of water

unless you are very efficient at showering, the loss of hot water for the first 2.5 cups of water seems insignificant.

unless i had a bidet

[rossvtaylor]

Originally Posted by turf

Ross's valve sounds like a cool setup!

ok, i did the math for my own setup.

my water tank is 16 feet of 1/2" pex pipe away from my shower head.

1/2" pex pipe holds .00961 gallons per foot.

16 x .00961 = .1536 gallons = just under 2.5 cups of water

unless you are very efficient at showering, the loss of hot water for the first 2.5 cups of water seems insignificant.

unless i had a bidet

Well, damn...it sure seems like more water than that when it's running down the drain. When you put it that way (darn you, mathematics...) it seems like I'm complicating things for very little gain.

I still like it for the tank anti-freezing function, but 2.5 cups of water is probably not worth the trouble.

[turf]

im not familiar enough with industrial plumbing, but a urinal flush valve that went from the hot side back to the tank seems like a reasonable way to prime that hot water.

some of the other solutions border on creating a closed loop heated pressurized boiler setup and they sounds sketchy.

i see text is copied off the water heater website and not their personal setups.

[rossvtaylor]

Originally Posted by turf

some of the other solutions border on creating a closed loop heated pressurized boiler setup and they sounds sketchy.

This is a good point and worth mentioning. I always install an open air vent tube on the tank, so even if something went haywire and I overheated the freshwater tank it will never pressurize.

Somewhere on the forum, months ago, I posted a photo of the stainless tank in our MCI...which was not properly vented. Even though it's sturdy, welded stainless steel it swelled up like a balloon and is now permanently wedged in place. A bit more pressure and it would have ruptured...perhaps violently.

[TaliaDPerkins]

Theoretically as something heating water to near boiling, the instant hot water heaters do not heat when there is no flow and, have a relief mechanism built-in.


Theoretically.