What is this black Tee in the Alde compartment?

m_lewis

I'm looking for the right location to install a back flow preventer, hoping to cure the problem of cold water / hot water flows in the wrong direction. Example: Run shower, adjust temp to suit, turn off flow at shower head, a minute or so later, after lathering up, turn flow back on. Ice cold! Where did that come from? Another example: turn on cold water at sink, hot water comes out! It gets back to cold in a bit, telling me that somehow hot water had gotten into the cold piping.
I can see the shower situation, to a point. The hot water in the line will cool to a degree while off, but I get cold, just as if only the cold faucet was open for several seconds.
Clearly, there are issues with water flows in the plumbing system. Normally, the hot tap will run cold for a bit until the hot water gets through the pipes, then it stays hot as long as I run it (within reason). That's OK. But never should I open the cold tap and get hot water.
So, I figure that somehow the cold water is being forced into the hot lines, and conversely the hot water is being forced into the cold line. How? What in the world have they done to the plumbing to allow this to occur?
So I am tracing the water lines in the Alde compartment (2019 400 Boondock) and come across a strange tee, plumbed in an unusual fashion. One arm connects to the input of the Alde Flow via blue PEX. Another arm connects to the hot water output of the thermostatic mixing valve, via a white PEX. The leg of the Tee connects to the cold supply line via blue PEX. See attached photo.
Now I am baffled. Why would a Tee connect the cold supply to the tempered hot supply? Obvious answer, this isn't an ordinary Tee. Then what is it? Why would there be any path between the hot and cold water mains? Is this the source of my flow problems? Is it defective, and shouldn't allow the conditions I have, or does everyone with this model T@B have these same water temperature problems. I might add there is a cutout in the panel behind this Tee, so there may be an additional line, knob, or something that is out of sight. I can't see where anything might go from the back, but it might.

qhumberd

I believe that is the behind the Bypass lever for the Alde flow tank, which separates the hot water tank from the rest of the plumbing when sanitizing or adding RV antifreeze. Just was looking at it as we were cleaning up under the bed preparing for our first trip this year.

qhumberd

See here is the front of the valve, showing the two positions. Bypass should block both the inlet and the outlet lines and isolate the hot water tank

qhumberd

Also if you have not tried adjusting the hot water mixing valve, there are several threads on here as to how to adjust so you get more stable temps, particularly with the Alde flow system. But it is an RV after all, so you have to make allowances for small PEX pipes and no temp control in some of the compartments.

m_lewis

YES, that is indeed what it is. Thank you. 

I have adjusted the mixing valve, as it was set too cool for our tastes. 

The temp is fine after 30 secs or so. I don’t think that is the problem. 

I don’t fully understand the Alde Air Cushion thing. I assume it is a bubble in the water heater section in the Alde. Is that different if the is a Flow installed?

Sharon_is_SAM

@m_lewis - the Alde air cushion is just an under filled tank with air at the top of the tank.  It prevents pressure surges.  Still need it even if you have the Flow.

m_lewis

Sharon_is_SAM said:

@m_lewis - the Alde air cushion is just an under filled tank with air at the top of the tank.  It prevents pressure surges.  Still need it even if you have the Flow.

I agree. Even after following the regenerate the air cushion videos and comments, I still have two problems that it doesn’t solve. 

1. Water hammer whenever the sink’s hot tap is closed. This manifests itself as a banging noise under the bed in the Alde compartment. I am concerned this will damage either the Flow or the boiler. 

2. Short cycling of the pressure pump. It is irritating to me that the pump will turn on and off quickly when running a low flow of water. I intend to install an accumulator tank in the supply line, just after the pump, to solve this. 

If the air cushion is in the Alde’s boiler/heat transfer tank, then hot water would be forced back into the cold supply as the air cushion expanded when pressure dropped, then back into the boiler as the pump raised pressure. This could account for some of the hot water in the cold lines. To solve this problem, I intend to install a one-way valve (back flow preventer) to stop this. Question is where. 

qhumberd

So there may be a difference when the Flow is installed. I found this out when I recently flushed my system. There are two circulator pumps. In normal heating mode only one circulator pump was operating. When flow is installed and you activate hot water at the highest boost on the control, The main circulator pump does not seem to operate and the pump next to the flow tank operates. This is different from systems without the flow tank, and is designed to provide a steady flow of hot water. It turn to regular hot water after 30 minutes use, but you could try it on that setting. I did that with mine and got a pretty even temperature at the sink for about 15 minutes. Prior to this I was getting variable temperatures as well. I believe we have the same model and Alde 3020 with Flow? We have not experienced the water hammer but our pump seems to work as expected as well. I have read that there is a pump adjustment that could be considered in your situation. It is a small Allen screw on the top of the pump which in our unit is at the bottom as the pump is upside down.

Denny16

Lewis, The short bit of cold water is coming from the hot water temp mixing valve, this is how is works.  If you have the mix temp set too high (hot), the valve will sense the hot water, than add cold, but for the first  few seconds to prevent scalding, it runs cold first, shutting off the hot water flow, and adding hot back in to get the set temp.  

Try backing off the mixing vale setting to a slightly cooler mix.  You have the Flo, which will provide lots of hot water, no need to have the temp mixing valve set too high towards hot.  Set it for the temp you want the hot water to be at the tap (no cold water), and let the temp vale regulate the hot water temp.

You could try setting the hot water temp at the mixing valve to the correct hot water temp or slightly above for your shower comfort, and mix a little cold in at the tap.  Older Alde systems without the Flo, have less hot water available, so owners set the hot water temp up to mix down with cold at the tap, to reduce the hot water being used.  From what I understand, doing this with a Alde Flo is not needed and causes situations like yours.  Also, make sure when you want max hot water to set the Alde control panel hot water setting to max (shower) position.
cheers

Denny16

@qhumberd, the main Alde pump is on during normal operation to circulate hot glycol to the heater convectors as required.  When you set max hot water/shower, the Heater pump (on main Alde boiler) shuts off, and the Flow pump then comes on to circulate hot glycol into the Flo tank to pre-heat the water, which then (water) goes to the main boiler tank and to the shower/galley sink.  When in Max/Shower mode, you do not get glycol flowing the the heater units.  In Max Hot Water mode, the glycol is only circulated between the Flo tank and the main boiler.  Hope this helps.
cheers

ScottG

That makes sense. I was never really clear how the Flow worked but it sounds like it's not really any different than the boiler in my house--one circulator pumps heating fluid to the baseboard convectors, a different circulator pumps heating fluid to the  heat exchanger in the hot water tank. Separate heating loops with separate pumps that can operate independently of one another.

Denny16

Yes, I just finally worked this out myself, based on my research and taking with our local dealer tech.  The only difference from your home unit, is the Alde pumps do not both work at the same time.  You either get heat or extended hot water, unfortunately, not both.  But again max hot water use is just for a short period, and has a time limit, so the heating system doesn’t cool down that fast.
cheers

qhumberd

Denny16 said:

Yes, I just finally worked this out myself, based on my research and taking with our local dealer tech.  The only difference from your home unit, is the Alde pumps do not both work at the same time.  You either get heat or extended hot water, unfortunately, not both.  But again max hot water use is just for a short period, and has a time limit, so the heating system doesn’t cool down that fast.
cheers

Bravo @Denny16 for solving this mystery. I was able to see this happen while out for our first night. Turned on Alde and needed hot water, but not heat. On propane. Set hot water to normal position and furnace turned on for a bit and then shut down. Could not tell if regular or flow pump was on. Hot water at 70 degrees. Not wanting to wait I increased hot water to max setting and furnace kicked in and pump started and I had 120 degree water in about 10 min. Max setting turned itself off after 30 min and unit maintained hot water thru night.

No longer confused by the Alde!

ScottG

Does anyone have a schematic or other image showing exactly how the glycol circulates in units having the Flow? I'm wondering if/how this extra glycol circuit may impact glycol changes.

qhumberd

@ScottG That would be helpful since with the Flow pump glycol may be a closed loop that might remain after draining and flush? Having seen it it could not be more than a cup or two it seems. Would Truma share that?

Sharon_is_SAM

@ScottG - Denny posted this photo in this thread:  https://tab-rv.vanillacommunity.com/discussion/11616/adding-alde-flow-in-a-2021-320-cs-s

ScottG

Oh never mind, I found this image that sure clears everything up. Ha ha.  :-)

ScottG

Thanks, @Sharon_is_SAM. I've seen that image but couldn't quite follow it at first. It looks like the glycol flowing from the boiler passes through the flow regardless of which function is being used, so it's not really a separate loop as I had surmised above.

There are two glycol return lines, however, that merge just before the main pump. I'm guessing that when activated the circulator pump on the Flow effectively short-circuits the cabin heating loop and returns the glycol directly to the boiler. I can see in that case why the two pumps should not operate at the same time.

Now I think I get it!   

Denny16

Yes Scott, this is about how it works in a nutshell.  Took me a bit to work out the Flo pump glycol direction, which takes the cooled glycol back from the Flo to the boiler.  Normally, if not in max (shower) hot water mode, the heated glycol loops through the Flo and then on to the heater.  Once I found out that only one pump comes on at a time, it clicked, the Flo pump was a boiler return pump to reheat the glycol.  This keeps the glycol circulating, which I think is a better way to go, than just having the glycol sit in the boiler not moving.  That said, I am not a plumber or heating systems engineer.  
cheers