Domestic Water System Design Contest- Win $100!!!

Kevin_in_Denver_2

I have a few 20 unit apartment buildings where the sidearms were removed years ago.

The commercial tank-syle water heaters don't last very long, and their EF rating is only about 0.60.



So I'm looking for a new approach. The cost should be in the low to mid four figures.

If you have a great idea, make sure your email address is available so I can send you a check. The right design will save at least $300/year per building, so I feel guilty asking for ideas without a offering a reward. (and it might make the brainstorming more robust).



I'm not afraid of using "residential" or Home Depot equipment if you think it will hold up in this application. It should last at least 12-20 years.



3/4" pipe and fittings are OK if they are kept to a minumum. The main lines are mostly 1", but there are never more than 3 showers going at the same time.



The current gas usage for DHW, which should drop, is about 10 therms per unit per month. I should stay with natural gas, so no heat pumps.



The space heating system isn't ready to upgrade yet, so no combination systems. It should stand alone. I can upgrade the flue if I have to.



Expected reliability is just as important as first cost. Maintenance costs should be estimated. Extra points for high efficiency without extra maintenance. It's Denver Water, so water quality is not an issue.

tim smith

Re: dhw for mid 4 figures?????

Thats what conventional commercial tanks go for in your application.  Look at Eternal on demand,  Not a bad option but cant say long term reliability but same with all the other high eff water heaters.   I still prefer condensing boiler and indirect awh!  Oh well.

Kevin_in_Denver_2

Condensing with Indirect tank

A good condensing boiler heating a tank with an immersed heat exchanger would last a long time and be very efficient.



The cost would probably be 5 figures though.



So I'm looking for a strategy to reduce the installed cost. Maybe using a 120 gallon residential electric water heater as buffer/storage somehow could reduce the materials cost.

Paul Pollets

Cost vs. Performance

You won't find a system that can deliver at least 15gpm-20gpm of DHW at 120 degrees for under $5K. Can't be done. You can either do a boiler and indirect tank, or a commercial gas-fired water heater that can deliver the required flow rates for 20 units.

Kevin_in_Denver_2

15 gpm isn't necessary

"You won't find a system that can deliver at least 15gpm-20gpm of DHW at 120 degrees for under $5K" I agree, Paul, but that's not what I need.



A gpm rating is not applicable to a tank style water heater. Gallons per hour is really more important. I currently have a 75gallon/75,000btuh heater installed. It has a 105 GPH rating (50F to 110F), and I haven't had a complaint in six years. It has 1" tappings.



I realize that there are plumbing codes that dictate the hot water flow requirements in a 20 unit apartment building. But in a replacement situation, I don't believe a plumber would get in any trouble by installing a heater that was matched more closely to the actual load than a worst case code requirement.



I also realize that most plumbers like to minimize the possibility of a callback. That's understandable, but for my building I'd prefer equipment that just barely satisfies the load at the lowest life-cycle cost.



All the showerheads are 1.6 gpm. Even for the morning rush, 105GPH is apparently enough. So that's really only 53,000 btuh at 100% efficiency.

NYplumber

L or H

Lochinvar or HTP condensing units will work wonders. The Lochinvar Shield is an all inclusive package. You get what you pay for, so a few dollar savings may have your tenants w/o hot water at the most inconvenient time. Contact Mark E.

Henry

Hot water

For the safety of the dwellers, one cannot have a hot water tank or storage tank at 120F. Legionnaire survives up to 139F!  There is no such thing as a 120 gallon residential tank! You figure of 105 gph is a first hour rating. Your actual is a lot less, unless your ARE trying to kill the tenants with 110F hot water. Our water temperatures during January/Feb go down to 34F. I would think that Denver is below 40F. So, you do NEED a 100F rise. Using several programs for sizing your needs here are the results: 191GPH for 100F rise. An A.O. Smith BTH 199 would be OK and cheap to operate.Otherwise, you would need 250,000 BTU atmospheric with at least 65 gallons of storage. The condensing tank will outlast the atmospheric and be much cheaper to operate.



The condensing tank is the cheapest solution that we have used in hundreds of only DHW type of jobs. The most reliable units are the A.O. Smith Cyclone XI!

Kevin_in_Denver_2

Legionella?

Since the water heater turns over at least twice a day, I didn't think Legionella would be an issue. I thought the water had to stagnate for a little while. In a 20 unit building, the longest stagnation period is about 6 hours.

Kevin_in_Denver_2

Condensing tank is an good choice

And AO Smith has the best selection.

Henry, you are definitely in the lead for the contest.



It's not worth risking Legionella, so I'll turn it up to 131F if Wikipedia can be believed:

"At 55 °C (131 °F): They die within 5 to 6 hours

Above 50 °C (122 °F): They can survive but do not multiply"



They do make a 120 gallon residential electric water heater: http://www.pexsupply.com/Bradford-White-M-2-120R6DS-120-Gallon-Energy-Saver-Electric-Residential-Water-Heater



But the AO Smith would be more cost effective .

Kevin_in_Denver_2

A. O. Smith Cyclone Xi

This water heater has apparently been around since 2007.



It is 95% efficient for the same price as an old style natural draft .60 EF heater.



http://www.wallingfordsales.com/proddetail.asp?prod=42289&cat=47

Mark Eatherton

If it were me...

I'd kill two birds with one stone.



I'd set a good quality 200K btuH modcon BOILER, and a 30 or 40 gallon reverse indirect for the DHW system. I'd repipe the P.O.C. atmospheric boilers as a secondary, and also set the modcon up so that it can contribute to the shoulder season space heating needs, and then in the middle of the winter, when the modcon's capacity is exhausted, bring the atmospheric dinosaur back on line to carry the load, while the modcon goes back to doing DHW. I think you'd be AMAZED at how much time the modcon is capable of spending on line for a given WInter season... If I am not mistaken, Lochinvar either has or is getting ready to introduce a control module to interface modulating equipment with non modulating equipment for this very application. Worth looking into for sure.



It is going to take more of your hard earned money to do so, but will also have a bigger impact on the flow of dineros out of your wallet. I think you will find that the ROI of doing only a condensing water heater don't pencil out in a reasonable time frame.



ME

ColoradoDave

ON Demand

My first choice and probably the one I'd look at going with would be indirect water heaters plumbed in parallel with the appropriate isolation to remove a tank in the future without taking the whole system offline.

By using the new Triangle Tube Tri-Max boiler with built in staging, you'll be primed for replacing the heating system when the time comes.  Two Heat-Flo 50g in parallel.  A single Solo 110 could handle both indirects by itself and the efficiency should be in the 80's (I usually see 83% eff on DHW).  Depending on the heat load for the building, you might even go with a larger Solo for staging with the heating system in the future.



A second option, although, I'm not as familiar with sizing, would be Rinnai tankless.  Water Systems / Rampart Supply in Denver could get you in touch with a rep for sizing and requirements.  Rampart Supply had Basic  and Advanced Service training classes available in Colo. Springs, so I'm sure they can arrange it in the Denver location.

Kevin_in_Denver_2

Cost Discussion

Mark,



I think that is a great strategy, I just have to spend some time comparing the cost vs. savings.



Threads like this one are tough when cost discussion is disallowed by the forum rules.

Kevin_in_Denver_2

Heat Flo Indirect tanks

Dave,



Thanks for turning me on to Heat Flo indirect tanks. Although I've seen stainless tanks fail prematurely in the past (Glowcore) I believe in their potential to outlive glass lined steel tanks. HF is very reasonably priced: http://www.houseneeds.com/shop/heatflo/heatflostoragetankbuy.asp



The warranty doesn't fall in line with this hope, though. HF gives you 5 years, but the AO Smith Cyclone has a ten year warranty. It seems like the ten year tanks all have TWO anode rods. Can I get 20 years lifetime if I replace the rods? (That might be another thread)

kcopp

How about...

A Triangle tube Challenger Solo boiler and a storage tank or two (electric water) heater piped in parallel. Solo has a 95% afue and they claim you can use it for hot water  or heat....

http://www.triangletube.com/TriangleTubeProduct.aspx?CatID=1&PID=32