The Tank › Hotel Hot Water Heaters
- March 11, 2013 at 4:27 pm #19634
Good afternoon. I am seeking some advice on our three 100 gallon tank system at a 100 room hotel. We are experiencing quite a bit of buildup in our mixing valves causing them to not function. The units have non-sacrificial anodes in place. Since we have very erratic flows and low buffered (alkalinity) incoming water does it sound like sacrificial anodes should be in place? They are 2 year old AO Smith units.March 11, 2013 at 4:39 pm #19635Randy SchuylerKeymaster
Are they gas or electric? If gas, what Btu input? If you can see a hex anode on top of the tanks, does it have a flat hex nut or does the nut have a bump on top?
There is a chance the anodes are aluminum, which creates a lot of gunk as corrosion byproduct, and once in awhile, that finds its way out of the heater and into the plumbing system.
Can you describe the nature of the stuff in your valves? Also, do you have a recirculation system? If so, are there check valves on it?
Randy SchuylerMarch 12, 2013 at 8:16 am #19639
Thanks so much for your assistance. They are gas fired units (AO 199,000 BTU/HR) and there is a recirc line with check valves. Looking at the top of the unit there are indeed two powered anodes with single wires attached to the top of them. As far as a “bump” I can’t really tell. The literature said they are titanium rods. The mixing valve (actually there are two – one on the main line and the other is a trim on the recirc line) are made by Leonard. Essentially the they are a dual-metal coil and the mainifold comes as one unit (TM-2020B). The problem that we are seeing is fouling in the valve coil itself causing it to need to be pulled and cleaned every so often. We don’t have a deposit analysis of the sample but looks like scale / rust. HOWEVER, our incoming water analysis and LSI calculation of a 0.8 indicates “aggressive” water with little buffering (alkalinity) and this may be the issue. I have a water background and feel that maybe the LACK of alkalinity in the water is chewing things up. I will add, the system is 99% copper except for the mild steel (2 foot or so) discharge lines from the units. They actually needed to be replaced after one year of service as they were pretty plugged up and corroding. The incoming water wample from the city again shows little turbidity, TDS of 78, Calcium of 15.2 and hardness of 43. The significant thing I see in the cold incoming versus hot water is the copper goes from 0.046 to 0.062 indicating copper corrosion. So, are the anodes not doing their job? Can they not keep up during high flow periods? Should sacrificial anodes be used instead? Does our water need to have alkalinity increaser added befor going into the units?
LOTS OF QUESTIONS AND I APPRECIATE ANY ADVICE – THANKSMarch 12, 2013 at 1:43 pm #19641Randy SchuylerKeymaster
What is the model number of the heaters?
If they use powered anodes, that eliminates my aluminum gunk theory. There is still a possibility, though, that sediment is being drawn off the bottom of the tank and backward through the recirc line at times of high demand.
Larry Weingarten, who answers many questions here and wrote the Water Heater Workbook, has long advocated using spring check valves, but all the rest of the world uses swing valves. Those can stick in the open position in hard water, and then you have no check valve.
Take a look at this page on my main website: http://www.waterheaterrescue.com/pages/WHRpages/English/Commercial/recirc-valving.html for more of our thinking on this.
Randy SchuylerMarch 12, 2013 at 3:46 pm #19644
Very interesting and helpful information. Maybe our issue is that the recirc line never re-enters the vessels. It comes off the main discharge, through a smaller trim mixing valve and then re-enters the main header further downstream; I think. When we last had to pull things apart for mixing valve cleaning and system flushing the recirc line, when drained, was coffee color as compared to the rest of the system. I would have expected at least to see “uniform dirtiness” throughout the lines. Why this line was so badly fouled may lead to more of a flow issue than a water chemistry one.
I know on the main header there are flapper-type checks but not 100% sure on the recirc.
Thanks again; any more thoughts or ideas are appreciated.March 13, 2013 at 9:02 am #19646
The recirc line branches off from the main header directly off the heater’s main header. From there it goes to on our building’s 2nd floor and returns through a recirc pump and brances into the cold water supply to the heaters and mixing valveMarch 13, 2013 at 2:01 pm #19652Larry WeingartenParticipant
Hello: I’m a bit confused about the plumbing layout. It sounds almost like primary – secondary piping for recirculation but a diagram would be nice. Photos of the near heater plumbing would be nice too. 😉 The water does sound aggressive. Leonard has long been making good equipment, but nothing will withstand difficult water for long.
Other concerns are about the dirty water in lines that should be clean and reasons for the mixing valve not behaving. Dirty water suggests poor or no flow and the cause should be looked into. The mixing valve may be getting “chewed up” by the water and/or it might be installed so it constantly sees the heat of the water heater. This would tend to make it get stuck open. There should be a heat trap between heater and mixing valve to protect the valve.
Water treatment to prevent further erosion of the copper might be worth looking into. Lastly, the steel nipples at the heater can be changed to plastic lined to avoid the problems you’re having.
ps. Do you need mixing valves because you have laundry run off of the same system and want two temperatures? Or, is it because this was a way to store more BTUs in smaller heaters?
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