Custom Rain Shower

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ideabrdg

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First, I'm in over my head on this one -- plumbing is not in my wheelhouse. I have a complicated design but do not have sufficient knowledge to even know what questions to ask. The plumber I'm working with says that the design complexities are above his confidence level. So, I'm hoping this brain-trust can help me close in on a solution. I've read a number of posts here to educate myself and appreciate the expertise.

Objective: install four (4) Kohler ceiling panels (K-98740) resulting in a total 16 showersprays.

There is 0.6 gpm maximum flow rate from each sprayhead for maximum combined flow of 2.4 gpm per panel using 1/2" NPT connections, max pressure 80 psi. So, total, max volume is 2.8 gpm * 4 = 11.2 gpm (well supply). Each shower panel set calls for a pressure-balanced loop.

Upstream, is a 1" 3Way "L" ball valve, that is used to break the vacuum so that water doesn't rest in the assembly and drip out.

This is fed by a 1" Pex line containing hot/cold mixed water.

This line comes from a Rohl U.5555BO rough in valve. 3/4" in and out; flow rate 14-16GPM.

The rough in valve is fed by two 1" hot/cold lines. Hot lines comes from a dedicated Rinnai Sensei 11 GPM on-demand water-heater.

The problem: how/do we need to pressure-balance the 4 panels with 4 pressure-balanced showersprays each?

One idea proposed is stacked pressure loops. One loop per panel, then a loop across each panel loop inlet. Another idea is to use a manifold after the 3 Way valve : https://www.amazon.com/4-Loop-Valve-Brass-Manifold-Tubing/dp/B07541X9D4/ref=sr_1_1?dchild=1&keywords=4+loop+Plumbing+Manifold+1"&qid=1616254672&sr=8-1

4-loop-pex-manifold.jpg


Obviously, there are a lot of constrictions here which I imagine is a concern. Pressure balancing seems like another.

Again, I don't know the precise questions or what to research. Thanks in advance for all your help and guidance.

Sources in reverse stream order:
Kohler WaterTile: https://www.us.kohler.com/us/watert...sprayheads/productDetail/rainheads/925557.htm
WaterTile installation instructions: https://www.us.kohler.com/webassets/kpna/catalog/pdf/en/1207715_2.pdf
Ball valve: https://www.electricsolenoidvalves.com/1-inch-brass-3-way-electric-ball-valve-3-wire/
Rohl rough-in: https://houseofrohl.com/thermostatic-rough-valve-with-volume-control-u-5555bo/

kohler-pressure-loop-01.jpg



 

Jadnashua

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A rain shower head doesn’t have enough restriction to cause acceleration of the water...it’s intended to dribble out, so you may not notice a big issue with lack of volume, but it will likely exist. Keep in mind that pex’s wall thickness means that the ID wiol be considerably smaller than the equivalent copper line, so your valve may not provide its maximum value when fed by pex, especially when you consider the connectors that must fit INSIDE the pipe, creating an even smaller ID restriction.

I’m not saying you’ll be dissatisfied, but do not believe you will achieve the volume those devices were designed for. Also keep in mind that with a well, your incoming water temperature should be relatively stable, but the specs on tankless systems are based on expecting 50-degree water. If, in the winter, it’s less, either the volume, or the outlet temperature or both will decrease.

Does each panel have one inlet, or one for each head?
 

ideabrdg

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A rain shower head doesn’t have enough restriction to cause acceleration of the water...it’s intended to dribble out, so you may not notice a big issue with lack of volume, but it will likely exist. Keep in mind that pex’s wall thickness means that the ID wiol be considerably smaller than the equivalent copper line, so your valve may not provide its maximum value when fed by pex, especially when you consider the connectors that must fit INSIDE the pipe, creating an even smaller ID restriction.

I’m not saying you’ll be dissatisfied, but do not believe you will achieve the volume those devices were designed for. Also keep in mind that with a well, your incoming water temperature should be relatively stable, but the specs on tankless systems are based on expecting 50-degree water. If, in the winter, it’s less, either the volume, or the outlet temperature or both will decrease.

Does each panel have one inlet, or one for each head?

Thanks for the reply. I've also been examining a boost pumpt to assist with volume risk. (BTW -- volume is supported by a catchment system -- so the water only has a temporary storage before completing its journey to groundwater). The temp rise on the water heater is enough given our setup.

There is an inlet per sprayhead. So, for a given panel, there is a pressure balance loop with one inlet.
 

wwhitney

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For the pressure balancing question, if you have enough height above, I'd suggest improving on the loop structure Kohler suggests by feeding the central leader from the middle rather than from the end. Then feeding the 4 WaterTile loops from an identically structured 3/4" or 1" loop. So cascading loops.

In theory any branching structure in which the path from the last common supply point to any spray head is identical in terms of pipe size, length, layout and type of fittings should give you equal pressure at each spray head, whether or not you have loops (e.g. a structure with tees similar to how NCAA basketball brackets are commonly portrayed). In practice there may be little discrepancies between parts that are beyond your control, and the loop provides redundant pathways that help average out any such discrepancy.

The upshot is that symmetry is advantageous here, and that's why an end fed manifold is not best (although in practice the asymmetry may not matter, I'm not sure). A center-fed H-shaped manifold would be a more symmetric way to do 1 in / 4 out.

Cheers, Wayne
 
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