Commercial Dishwasher

Tom_133

Hey all you wallies!

Guys I have been struggling with an LVO FL10E commercial dishwasher not getting enough rinse PSI for years!!!!
Its on a well pump with a 40/60 switch, it was purchased new 4 years ago and was fed 180 degree water from an indirect water weil McLain gold tank 40 gallon, with 3/4" L copper about 100' from the unit. It had a recirc that kept the loop hot. With that setup it occasionally got to 8psi on the rinse cycle.

Now there is a Rinnai CU199IP 199,000 BTU, Commercial on demand set at 185 with 30' of 3/4" L copper and less than 2psi on rinse. It has a pretty steady 40-55psi static but when rinse kicks in, bam, nothing.

Early on I gave Rinnai the FL10E spec they recommended 3- CU199IP units, and my customer just could not do it, not enough money or space.

So my question is can anyone help me with a piping diagram that I can use to pipe a 50 gallon electric that can be used as a storage tank and perhaps have the CU199IP heat that tank? Or I am open to other suggestions?

Thanks for the help in advance

Tom

Jamie Hall

It's not the piping diagram -- although that would be straightforward enough -- it's the head loss through that Rinnai when the rinse heads kick in. That's a lot of flow. It's probably specified in the dishwasher installation or operation manual or the manufacturer can give it to you.

So... you are going to need a booster pump for the rinse. You might be able to push the required flow through the Rinnai, although the inlet pressure might be too high to be safe or within the rating. If you can get the head loss characteristic for the Rinnai, you can figure out what the inlet pressure is going to have to be. The other approach will be to feed the dishwasher from a regular water heater with enough volume capacity to complete the rinse cycle. If you still want the Rinnai to also heat water, you could pipe the regular water heater as an indirect off the Rinnai -- but the regular heater will still have to have a direct connection to the building supply.

hot_rod

But if it was a pressure issue on the old indirect must be some other restriction.

a solenoid on the rinse? sometimes they have screens that could be plugged, or a limed up passage way in the solenoid or other valve. Nipple on the old tank limed close? A bucket at the connection would be a good flow test.

Is the 8 psi a flowing, dynamic pressure reading? With a 40 psi supply thru 100' of 3/4 K on the old system that 8 psi seems pretty low.

Here is a pressure drop chart for 3/4 K, run out to 8 gpm or whatever you require, over to pressure drop X 100 feet and some fittings I suppose. Maybe 15 psi drop in 100' copper at 8 gpm?

Doesn't matter if you shortened to 30' I suppose.

A small Grundfos variable speed booster would be ideal, not sure about temperature rating.

Probably why Rinnai offers these units.

mattmia2

Can the well pump supply that volume at that pressure? What happens if you open a large cold water faucet or drain? Perhaps there isn't enough pressure at that point in the well pump curve to overcome the drop of the tankless with at that flow and depth.(also is the well tank charged properly).

Is there any filtration or water treatment between the well and the water heater?

Tom_133

There are 4 wellmate tanks, there is a bunch of filtration but I won't lie, I dont know what all of it is. I need to be there Monday I can take a pic or two.

I would love to put a booster on if it would help. Would that be just before the Rinnai?

Tom_133

Sorry also wanted to say the unit Hotrod described from Rinnai was outta his price range. Now If I can make possibly a 50 gallon Hybrid electric water heater work (it will also help cool the hot room) that may help us a lot.

Solid_Fuel_Man

Where are you taking your pressure reading on the rinse cycle?

If you take readings before the Rinnai, after it, and wherever else you are taking and draw us a diagram of pipe sizes, and pressure reading points that would be helpful.

Jamie Hall

A booster before the Rinnai may help, @Tom_133 -- but before I go way out on a limb, the pressure readings and diagrams that @Solid_Fuel_Man suggested would be really useful.

hot_rod

Yeah, any filtration equipment will cost you some ∆P, if it is only on the supply to the water heater, certainly start your flow testing there.

If the equipment has not been serviced properly, even more pressure drop is possible.

retiredguy

If the rinse temperature is too low because you are not supplying the dishwasher with 140F temp water you must find a way to preheat that water. You could add a smaller gas heater or add an electric booster somewhere in the water line. If the hot water supply pressure to the washer is high enough at the source but is too low at the heater look for strainers, screens, inlet screens or strainers on the 1/2" solenoid, the wrong setting on the adjustable pressure regulator on the supply line or it's inlet screen or strainer. If you can, check the pressure drop across each item in the hot water supply line to see which device is restricted. (remember that those instantaneous heaters need to be cleaned and flushed on a regular basis). For the pressure to fall to around 8PSI when the rinse cycle is on that indicates that there is a restriction somewhere.

rick in Alaska

I have two restaurants that I inherited that were trying to use an on demand for the dishwasher, and neither one would work. The dishwasher needs a lot of hot water fast, and the typical on demand can't do it.
I wound up installing an electric heater next to it and used a circulation pump hooked to the on demand to heat the water in the tank, and then took the water from the tank to the dishwasher. So far it has worked good. Also, I wired up the water heater so that when the on demand is down for some reason, the tank can still be heated up. The electric only can't keep up, but it helps.
And, like the others have said, you have some kind of restriction in the line that can drop the pressure that much, and you need to fix it before trying anything else. You might be able to solve all your problems by just cleaning a filter.
Rick

hot_rod

rick in Alaska said:

I have two restaurants that I inherited that were trying to use an on demand for the dishwasher, and neither one would work. The dishwasher needs a lot of hot water fast, and the typical on demand can't do it.
I wound up installing an electric heater next to it and used a circulation pump hooked to the on demand to heat the water in the tank, and then took the water from the tank to the dishwasher. So far it has worked good. Also, I wired up the water heater so that when the on demand is down for some reason, the tank can still be heated up. The electric only can't keep up, but it helps.
And, like the others have said, you have some kind of restriction in the line that can drop the pressure that much, and you need to fix it before trying anything else. You might be able to solve all your problems by just cleaning a filter.
Rick

I thought commercial tankless were specifically for that type of application. Seems all the new hotel chains have banks of tankless exhausts out the side.

Back when I did service work for restaurants the dishwashers all had Hatco electric boosters next to them. Mainly for temperature boost they were a high powered 10 gallon water heater basically.

With the soaps and chemicals they use now I don't think 180F is as common?

rick in Alaska

One is a Rinnai Rl94 with the commercial control on it. The other is a Navien. There was no way to install more than the one Navien because the only way to get the exhaust out was to run it up through two floors and out the roof, and there was no more room to run any others. I am a Rinnai fan, but could not get one that used the pvc exhaust at that time.Once it gets running, it will put out about 3.4gpm's into the storage tank, which keeps up with them. The Rinnai runs about the same output.
The hard part was getting the pump size figured out. I got conflicting info first, but then talked to the right guy and got the right pump. I think I am running a Taco 009, but that might have been the first one. Seems like it was something like 27 feet of head.
Rick

Tom_133

I will get that drawing done soon, but just so you know, I put gauges on incoming and outgoing water at the Rinnai, and when the rinse came on the psi in to the Rinnai was 40 and outgoing 0. That is really weird. I didn't think the Rinnai would drop like that. I wasn't sure if I had a bad orifice in the dishwasher, or what. So I bypassed the Rinnai and ran only cold to the Rinse and got 8psi at the dishwasher.

Still seems really low, So my thinking was as someone else said, there may be a dirty filter or a nearly closed gate valve. Its a hard place to work, its very busy and the only access to the water equipment is through the bathroom floor.

Jamie Hall

Not a bit surprised the Rinnai dropped that much. That's what I expected. Though there may be some partly clogged filters etc. too.

Solid_Fuel_Man

Remember an on demand will throttle the water when the burner reaches max fire to maintain set point.

hot_rod

Take a stick of 3/4 pex and feed the heater directly from the well tank, check the let screen.
I don 't think a 60 psi pressure drop is correct? If in fact you are flowing 8 rpm at the DW, look like a 25 psi drop is about expected. You mentioned the well switch runs 40/ 60 psi?

What is the flow rate at the DW when the pressure drops to 0? temperature of the water?

Wonder where Jack from Rinnai is, he knows all the ins and outs of these units.

rick in Alaska

Jack is retired! And probably loving it.
However, since he says he bypassed the Rinnai, it can be ruled out. There must be a restriction in the piping getting to that point. The comment about a partially closed gate valve makes a lot of sense, or a filter that is partially plugged.
Rick

motoguy128

A hybrid tank water heater isn’t a bad idea. You are correct it would cool the hot kitchen a little and be pretty efficiency so long as you degrease The coil not and then.

Tom_133

Could someone post a good way to pipe a Rinnai to an electric water heater?

retiredguy

@Tom 133; If you are going to install an electric/hybrid water heater/storage tank, you could add a circulating pump to come on and circulate heated water between the Rinnai and the new hybrid/electric water heater when hot water to the dish washer is not needed. This would boost the temp of the pre-heat storage tank. There are a lot of things you could do to make this installation work that are not in the purview of normal operation for example, if continuous operation is not needed you could add a time element into the equation so a storage type tank could be pre-heated to help satisfy the hot water load. My first thought would be to see how much money there is available to spend and see how much room/floor space is available.