Does my piping look correct…adding OWB to Rinnai Combi boiler

schweg2

Hello, first post here…I’m looking to get some advice on my heating install,
everything works fine when I’m using the combi to heat my radiant in floor heat, but as you can see in the picture I have a plate exchanger on the secondary loop from my OWB.

The highest flow I can get is less than .5 gpm on the manifold going through the plate exchanger, I can get a little higher if I bypass plate hx via mixing valve. Do I need to add another pump on the primary loop to solve this?
When I’m using the plate exchanger I’m bypassing the “TT” on the boiler so the onboard pump in the boiler is not running. Do I need to find a way to have the boiler pump turn on without it firing?

My secondary loop return is only around 7” leaving the purge valve to the 90 fitting, I realize after the fact that should have been longer?, would that be part of the issue.

Please excuse the wiring mess and the pump dangling as I was testing different things..

Any help would be appreciated, Thanks

pedmec

Gonna ask questions on a coupling of things.

1) why do you have a mixing valve on the boiler side of the HX
2) where is the circulator for your radiant loop coming out of the HX.
3) why isn't there a mixing valve on the radiant loop.
4) how do you expect to heat the loop if the boiler is not firing?

hilltown

I believe your plate hex return needs to be on the return or in your case the right hand side of your p/s header.. and the boiler pump should run anytime either of your system pumps are running..

hot_rod

How are you measuring that flow rate?
20 plate is a small hx, how many btu are you moving?

with closely spaced tees, the flow from the HX may not be what you are reading at the manifold. The Taco us only moving flow from the hx, through the mix valve and back to the hx

The system pump after the air purger is moving flow through the manifold. How long are the loops on the manifold

The boiler has a pump inside, it only needs to run when that boiler is adding heat to the loop, or dhw if it is a combi

schweg2

Flow rate was on the supply manifold, I have 3 loops roughly 275' each.
Combi Boiler is 60k BTU on the heating side, the space I'm heating is 1000 sq ft.

Do you think my plate exchanger is undersized?

Mixing valve is so I don't feed water from OWB over 140* to my floor.

schweg2

In the picture below highlighted in yellow, do I need another pump added for that section of piping when using the plate ex, since the combi pump would not be running.
Or do I need to look into bypassing the combi from firing some way and have it's pump run to move flow through that section of piping.

leonz

UMMM, why did you do this? A pair of headers and a mixing valve would have worked better.

When was the last time the heat exchanger was cleaned?

schweg2

leonz said:

UMMM, why did you do this? A pair of headers and a mixing valve would have worked better.

When was the last time the heat exchanger was cleaned?

I guess I don't follow, I was told to do a primary/secondary loop with closely spaced tees.
boiler was descaled a couple weeks ago, also is less than a year old.

hot_rod

Turn off the white handle valve next to the check and it should work. Three loops is a pretty small load, 1.5 - w gpm. Is that the entire load?

The 3 way valves tempers the flow from the OWB into the system, I think

schweg2

hot_rod said:

Turn off the white handle valve next to the check and it should work. Three loops is a pretty small load, 1.5 - w gpm. Is that the entire load?

The 3 way valves tempers the flow from the OWB into the system, I think

If I turn the 3 way purge valve to direct the flow towards the plate hx I get zero flow at my manifold.
Do you think I should relocate my pump on the OWB loop?
As you can see it's on the supply side currently.
If I adjust the mixing valve to bypass majority of the water to the plate, I can get flow.

GroundUp

It should work just fine as piped, though your plate exchanger is mounted wrong (should be vertical for sediment reasons). Is that a 5x12 exchanger? What model is the mixing valve? With that purge tee closed if you're getting no flow, you have an airlock somewhere or the mixing valve is being held shut. I'd suspect that the mixing valve has too much restriction and should be replaced with a higher cV model, and/or there is an airlock somewhere especially since you just replaced the circulator. There is no reason that this piping method should not be adequate- I've piped dozens of OWB radiant systems this way without issue.

hot_rod

Either you need you add another pump in the primary loop or turn off that white handle valve

all the closely spaced tee valves must be open

a thermostatic mix valve never turns off completely, as one side closes, the opposite side opens the same amount. It could be plugged up somewhat if flow stops in one setting?

it us a 3 Cv valve so you should be getting 4-5 gpm in the loop with that pump

here is your system and a simpler straight piping to show how either the boiler or plate HX inject in to the radiant/ primary loop

PeteA

Just a set of novice eyes looking at this but:
I don't see how you're getting any circulation on the loop that goes down through the floor if there's not a pump. I see the pump and the mixing valve controlling the temp at the heat exchanger but what is circulating the water through the floor to pick up and distribute the heat that's at the plate to the area to be heated.

GroundUp

hot_rod said:

Either you need you add another pump in the primary loop or turn off that white handle valve

Why? The extra 3 feet of piping running past the combi isn't hurting anything. The zone circ on the far left is serving the same purpose whether or not the combi is online. The internal combi circ doesn't run when the OWB is hot. The circ pulling through the plate doesn't run when the OWB is cool. Closing that valve is only going to stop flow completely.

hot_rod

I see it now, I though the loop connected under your yellow highlighter

The mix valve looks like it has  a high head circ it should be moving whatever that plate HX can exchange 

The spec on the plate HX would indicate the flow capacity and btu exchange

schweg2

Thanks guys, I'll get back with you with my findings and specs of the mixing valve and plate hx.

hot_rod

It possible that the hx us getting plugged on the A side, is the oWF new?

its nice to install a hx with Webstone flush valves to clean them or pump an descaler through them

schweg2

I found the problem guys... I didn't realize there was a screen on the hot side of the mixing valve which was plugged, I guess from my well water when filling the system.
I suppose I should look into adding a dirt Seperator now.

Thanks for all the help.