Tankless water heater for hot liquor tank - Need advice

[Cascadia]

We're getting ready to buy a brewhouse and the manufacturer is recommending that we use a tankless heater in a circulation loop to heat the HL tank. It seems like a good idea, but I called Noritz, one of the manufacturers of commercial systems, and they pointed out a problem. Their heaters will put out up to 180 degrees, but they say there is a minimum of 10 degrees drop at the inlet for the burner to turn on. In other words, the water coming out of the tank needs to drop to 170 for the burner to turn on.

Our brewer says he needs to have 180 degrees in the tank. What do other folks do? Do you have a secondary heater to push it the extra 10 degrees and maintain it at temperature? I've seen some other posts that people are using systems like this.

[Graydon]

Resistive Temp Probes

I had a problem using a cold room controller several years ago. The operational range of the controller was 20 F to 200 F. I needed to control my kettle so I looked up the resistance of the probe and put a 1% resistor in parallel with the probe. This gave a reading of 190 F at 212 F, so I adjusted my temp setting and the kettle worked fine.

R Total = (R1 + R2)/(R1*R2)

Look up the resistance at 180 from the probe and make it look like 170.

Talk to the manufacturer before testing the system, but you should be able to make it work.

Graydon

[BeersmithMT]

We have built a couple of similar systems over the years. The latest uses a Rinnai C85 (commercial 180k btu, 185F output) tankless heater. We have had no problems with theinput temp differential issue you describe. We have however had some problems with the Rinnai when its very windy (gives a combustion error code), and when heating water that is way below the desired temp (as in like from 45F). After 3+ years of continuous daily use, it does seem to be getting more finicky regarding those problems - might be soon time for a new one.

[CaptainEBC]

We have a commercial Rinnai heater plumbed to an insulated tank as our HLT. We run the water out of the heater at 185 and it gets to the tank in the high 170s dumping right from the top of the tank. It would probably be hotter if I plumbed a down-tube in it. I put a 2" NPT port in the side in case we needed to have additional heating power but it seems to work out just fine, so its plugged.

I also called one of the manufacturers about the recirculation. You can do it as long as you put a thermostat on the return line to shut the recirculation off. Also, if you plan on recurculating with acidified water, you run the risk of causing "pin-holes" in your copper or even introducing more scale to the heating coil with salt additions.

[Cascadia]

I called up Rinnai's engineering line and they advised me that a tankless would not be a good choice for that application and that their systems require a 15-20 degree delta from input to output. They say the issue is that there is a minimum BTU setting on the heater and if the inlet water comes in over that temperature, the output exceeds the spec. The guy I spoke with did not seem like the most knowledgeable guy, though...

He pointed me to their commercial boiler line and said that is the way to go for our application. Unfortunately a tankless heater with 380k BTU is around $3500, but a 205k BTU boiler is over $5k and we'd need two of them to get our HL tank to recharge within an hour.

I wonder if having an electric heater in the tank as a booster to an external tankless system would be a good way to go. The tankless heater would allow it to come up to temp quickly and then the electric would take over keep it at the set point.

[CaptainEBC]

We spent about $1200 for our Rinnai R98hpi and it delivers a continuous 4 gpm at 185 F.

Tankless heater with a big heating element in the HLT is a good idea.

Another benefit of a tankless heater is that its great for spraying hot water to assist in cleaning.

[chaser]

I called up Rinnai's engineering line and they advised me that a tankless would not be a good choice for that application and that their systems require a 15-20 degree delta from input to output. They say the issue is that there is a minimum BTU setting on the heater and if the inlet water comes in over that temperature, the output exceeds the spec. The guy I spoke with did not seem like the most knowledgeable guy, though...

He pointed me to their commercial boiler line and said that is the way to go for our application. Unfortunately a tankless heater with 380k BTU is around $3500, but a 205k BTU boiler is over $5k and we'd need two of them to get our HL tank to recharge within an hour.

I wonder if having an electric heater in the tank as a booster to an external tankless system would be a good way to go. The tankless heater would allow it to come up to temp quickly and then the electric would take over keep it at the set point.

I used a system like that and it did the trick. Just takes a LONG time to fill with the on demand water heater.

[South County]

I used a system like that and it did the trick. Just takes a LONG time to fill with the on demand water heater.

If you have the water gpm input you can gang these units in parallel up to 30 plus units depending on what control, heat, gpm you want from them. We have (2) 200 btu units we got off of eBay for about $1400. We just run directly off of the units.

[Bierkoenig]

If you have the water gpm input you can gang these units in parallel up to 30 plus units depending on what control, heat, gpm you want from them. We have (2) 200 btu units we got off of eBay for about $1400. We just run directly off of the units.

That's what I do. I have two Rinnais (R94 Lsi -- exactly the same as the "commercial" unit, you just need the MCC-91 controller to get 185F out of it). Although I can recirculate my HLT, I simply mash in and sparge directly from the heaters. I only use my HLT to capture water from my hx which I then use for cleaning. 10 bbl kit, btw.

[kramling]

We have 4 of the R94 LSI Rinnai units in parallel with the MC-911 running up to 185F. We are able to get up to 15GPM of 185F for not only back filling our HLT but for sanitizing knockout lines, preparing a tank for CIP etc... Having a few of these in parallel is key to success. You have to have a decent flow rate otherwise you are waiting on water.

I have a recirculation loop in place just in case my HLT is not up to temp but rarely ever use it. When I did use it there was no problem with input/output temperature delta.

One thing I wish I was able to do is to fine tune the MC-911 to step up and down in one degree increments at the higher range. Right now I can step down from 185F to 160F to 150F. I have to blend cool water with my 185F to get to my target strike temp of 174F. I called Rinnai to see if this can be done and they said no. Anyone ever tried to tweak one of these units or replace it with another solution?

Cheers,
Steve

[Moonlight]

If you use a mixing valve...or just some hand valves with a thermometer, you can blend that un-heated water with water heated to 10F higher than you need to make the brewer and the water heater both happy.
On a separate note, I have high mineral water and need to frequently acid wash the inline heaters to remove scale. If you are designing a set up, and have high mineral water, you might want to include easy valving to be able to circulate mild acid, and flush.

[South County]

If you use a mixing valve...or just some hand valves with a thermometer, you can blend that un-heated water with water heated to 10F higher than you need to make the brewer and the water heater both happy.
On a separate note, I have high mineral water and need to frequently acid wash the inline heaters to remove scale. If you are designing a set up, and have high mineral water, you might want to include easy valving to be able to circulate mild acid, and flush.

That's what we have, a hot and cold valve that runs into a single manifold with a thermometer then into a mashing hydration ring. Works great. Not a ton of accuracy just being copper tubing and simple gate valves, but usually can hold within a degree.

[Ale]

The biggest/only factor is capacity. How much 180 water do you need and how fast, consider gpm and your time. More importantly a boiler can keep water hot in a tank, a tankless HWH only delivers, so depends on your system as well.

[Cascadia]

After more phone calls I've uncovered a few more things... First, a typical tankless hot water heater is designed to be under pressure. This makes it incompatible with a low pressure circulation loop that you'd have with a HLT.

Noritz tells me that they recommend using the tankless heater to initially fill the tank from the tap, but to install a secondary electric heater to then bring it up to the set point and maintain the temperature. That seems kinda hokey to me...

I talked to Laars who makes a product called the Mighty Therm. It is designed for recirculation applications and seems to do most of what we need. The catch there is they make two models. One is for hot water tank applications and the other one is for heating applications. The only difference is the temperature controller and the pressure relief valve. Apparently there are some code issues with installing heaters that go above a certain temperature which is why they have two models that are otherwise the same. The water heater version could only bring the tank to ~170-175 while the heating version could take it up to ~190+. Now I'm looking into the local code to see what the deal is.

[Bierkoenig]

a typical tankless hot water heater is designed to be under pressure. This makes it incompatible with a low pressure circulation loop that you'd have with a HLT.

Uhh... Not only is recirculation through tankless heaters common amongst breweries that use them, but is is also common in residential and commercial hot water and hydronic heating applications. In fact, that is why most of these heaters are designed with recirculation applications in mind. It doesn't take too much pump to get the minimum 20 psi in a 3/4 inch pipe that a Rinnai requires.

It sounds like the vendors are looking at their script, not finding a tab for breweries, and telling you it won't work.

I see you're in Hood River. You might want to get in touch with Jonathan at Imaginenergy (www.imagineenergy.net). He works with a lot of tankless heaters and has done a number of different types of hot water and heating installations, including some breweries.

Also, Tom Allender (Tom Allender Plumbing) has done a number of breweries including tankless setups and is a very good guy (though super busy, and not sure if he travels outside of Portland).