Navien as a commercial water heater

john coulson

I work for a plumbing and HVAC wholesale supplier and am often asked to quote navien water heaters and a storage tank instead of the more appropriate chioce, an Lochinvar Armor water heater and storage tank. My contention is that the Navien and its limitations in terms of flow are a bad choice. The trouble is, the contractor sees that the Navien is 199,000 btu as would the Armor (in this case) My contention is that this heater is not going to last not to mention the pumping complications. Has anyone seen any publications that one might compare duty cycles of both products in such an application?

kcopp

look at ....

the warranty. See what the limitations are for commercial and residential. My guess is that the Lochinvar will be longer.

Jack

perhaps...

you should look at this with a more open mind. Your mind is made up, prior to the sale. What your customer needs is a solid technical/cost/feature analysis. Tankless/storage systems work really well, but yes you have to understand both the pumping and piping requirements. They are not limitations. If you understand them, they are features. You can tell your customer that he will probably never get the the 199k input out of the tankless. GPM X Delta T X 500 = BTU Unless he pumps the bejeepers out of it the tankless will not deliver the max input except at possibly cold start-up.



I have done a lot of tankless/storage systems. I never want to size the circ for max flow. I'll generally hit the 80% of capacity range and let the equipment do its thing. I don't like to drive my car at redline all the time and I won't do it with equipment. As well, whenever someone wants to use a single tankless with storage, especially on commercial I always try to get at least a second unit. I'll trade storage for btu capacity. In a commercial application having redundancy allows the business to stay open if one unit fails. If you have only one unit and it fails you are managing the catastrophe. IN comparison to commerical water heaters I can generally make the numers work for tankless. This has been a tremendous plus for me in commercial jobs. Have you looked at how many units it would take to eliminate the need for storage? There are definitely times I want storage with tankless depending upon the flow characteristics and physical lay-out of the job, but there are also systems where storage is jsut shifting the cost form burner capacity to gallons.



As always, I want to acknowledge my bias. I represented Rinnai for 20 years and that is the tankless I would recommend.

meplumber

Listen to the man.

John, I wanted to add that I have worked with Jack on many projects and

"He knoweth what he speaketh."

HDE

Plus

I like jacks response, a couple more things:



It's true you don't want to push the envelope on flow rate through a Tankless when a pump is added since you must remember, a tankless was meant to see intermittent flows, typically nowhere near max design and when it does it's not frequently for too long. For instance a residential unit may publish 7, 9 or much as 11 GPM, yet average is 2-4 GPM in a standard home, and that's usually not more than 1-3 hours of usage a day.



Pumping through a tankless for extended periods of time with a storage tank requires caution since excessive velocity is the typical killer of over pumping. Take a look at the passageways, exceeding 3-4 GPM on a consistent basis can subject the unit to velocities as much as 10+ when 6 GPM is reached, so in my opinion exceeding 50% can result in premature failures.

However, there are creative ways of piping a Tankless/storage system so the circ inlet and flow through Tankless sees coldest water introduced to system during tank DHW draws. At the same time when tank DHW flow exceeds tankless/pump combination designed capacity the remaining cold water inlet is back fed to tank to meet higher DHW draws off the tank. Since Tankless fire on combination of flow and rise, coldest water drives unit into higher fire versus only drawing blended temp water from tank, reducing the fire rate. Piping in this manner can maximize the Tankless potential firing rate, while during smaller draws and reheat the Tankless fires at lower levels due to the DT.



In the end the differences in systems tend to be affected by budgets, desire to use existing storage, and most often the lack of gas capacity to support enough Tankless units to meet peak flow requirements without storage.

Kal Row

economics rules...

sure it a "water heater" not a "boiler" - but at the end of the day, there is a fire and a heat exchanger and real btus going from fire to water - so it's going to work - sure, u need more head through it, and it wont last as long, - but who cares, the tankless was meant to compete with gas fired directs - so it could never be more than twice as much money, no mater how much it saved, which is still half of any boiler, let alone a modcon - so people put it in, and use it wrong, and replace it - get over it!!! - it's the economics of "now" - by the GEN-Xers

i have 3 rinnais and a 40gall tank doing the hot water for a wedding hall, - in the same hall, i made a backup to the hot-water booster - that precedes every commercial dishwasher - which consisted of 1 rinnai and a 30gal tank - and a wilo star32 which is like a 009 - and after taking abt 20min to bring the tank to 175-180, - it delivers the 180F water at 1.2gpm to the dishwasher  - as needed, they typically take 1gal per dish rack of 180f water - rack after rack

they spray wash the floors with 140f water - i hate it and think it sucks - but they are very happy with the system, they like the fact that when they shut down - nothing is on - and the non stop water delivery

i would much rather do armor's and/or modcons driving tube-bundle generators in tanks - but look at the cost difference - 10 to 1, a real tough sell in these times

Jack

restaurants and tankless

I never do a restaurant without the make and model of the DW and a call to Rinnai Engineering. They have all the specs on CDW's and have developed some interesting systems. They generally will not allow a comm DW without a booster. I prefer that too. I will fed 140F water to the booster and then the rest of the kitchen can run confident that no 180F water is going to go squirting wround the place. Not a small concern! The other reason not to run the really high temps is that is you look at the ASHRAE guide (as well, it is in Rinnai's Hot Water Design Manual) they show the amount of precipitant that come out of water at various temps from 100-180F. The tankless will do the 180, but you had better have pristine water quality and/or a pretty aggressive maintenance program