Trouble Shooting Hotel Hot Water Recirc Systems

Summary: This article is about trouble shooting hot water recirc systems for hotels.  For many different reasons,  hotel hot water recirc systems can be a major challenge to commission at the opening of a hotel.  My goal here is catalog all the problems and associated solutions to hot water recirc systems that I or anyone else knows.  I encourage readers to share their examples.   This will be an article that continues to grow over time.

Related Article: Hotel Hot Water Recirculation Systems

Problem:  Cold water entering the hot water system:  If you are observing cold water entering the hot water system, it is likely that cold water pressure is higher than the hot water pressure.   When this pressure difference exists,  there will be a natural tendency for cold water to migrate through mixing valves into the hot water system.  This problem often occurs when a water softener is installed serving only the hot water.  This problem is easily fixed with a pressure regulating valve for each of the hot and cold water systems.  Locate the hot water pressure regulator on the outlet side of the water softener.  Then set the pressure of the hot water regulator a few pounds higher than the cold water.  This will assure any migration of water through the mixing valves will be toward the cold water, which is a forgivable situation in most cases.

Problem:  Plumber installs more risers than originally designed.  Sometimes a plumber will decide that it is easier to install a separate riser for each stack of fixtures instead of combining risers to serve several fixtures via horizontal branch connections.  This change is OK, but it creates more risers than included in the original design.  With more risers to serve, the recirc system must be upsized to maintain the original design flow in each riser.  Generally this will involve upsizing the recirc pump and the return piping. 

Problem: Recirc lines leaking after several years of operation:  Recirc lines need to be sized for continuous flow or they will erode in a few years and develop pin-hole leaks.   The sizing criteria for recirc lines should be a maximum velocity of about 3 feet per second.  This is much slower than the criteria used for domestic water lines, because water lines operate very intermittently. 

Problem: Oversized Recirc Pump:  We all know it is better to oversize a recirc pump than undersize it.  But this is only true if balancing valves are installed.  If the oversized pump is allowed to operate without balancing, the circ lines will erode from excessive water flow velocity.  I recommend a conservatively sized recirc pump (i.e. oversized), and the installation of a balancing valve at the outlet side of the pump.  Of course, someone must actually perform the balancing, which often is the greatest challenge of all.

Problem: Hot water entering the cold water system:  There are many ways this can happen, but one example I encountered was a high rise hotel with two zones of domestic water.  Since PRVs were involved to create the two pressure zones, the recirc loop was required to circulate through a PRV.  This required the pump to have a very high head to overcome the PRV pressure drop.  The result was a back-pressure that forced hot water into the cold water system system in the mechanical room.  This problem only occurred under low flow conditions, since at that time there was no other release for the hot water system.  The solution was to install a check valve in the cold water pipe serving the boiler.  This eliminated any reverse flow caused by the recirc pump. 

Aside:  Although we solved the problem, I was never fully satisfied I understood the physics.  Here is why.  The mystery was how could the recirc pump force hot water back against the cold water source?   If you “count” molocules of water coming and going, there is no way that a hot water recirc pump can create a net increase in system water that would force hot water back into the cold water.  My only guess is that there really was no perfect separation of the hot and cold water systems due to the mixing valves throughout the hotel.  And what was really happening was that the high pressure recirc pump was recirculating hot water through the mixing valves with the resulting “appearance” of hot water being forced back into the cold water.  Regardless, the check valve solved the problem.  Howver, I felt very unsatisfied not really understanding why the fix worked.  I would be interested in hearing about similar cases.

7 Responses to “Trouble Shooting Hotel Hot Water Recirc Systems”

  1. Mark Robison, P.E. » Blog Archive » Hotel Hot Water Recirculation Systems Says:

    […] Related Articles: Trouble Shooting Hotel Hot Water Recirc Systems […]

  2. james k williams Says:

    I work at a hotel our probelm is no water in showers and tiolets on 4th & 5th floor rooms when we are at 100%.Hotel is only four years old circulating pumps push water to 5th floor.Only happens in the morning when everyone takes a shower can you give me some advice?

  3. Rick Lambeth Says:

    The hotel has sporadic hot water complaints in mid rise and high rise sections. No ryhme or reason as to specific risers or time of day. The hotel has 12 risers and 30 floors serving approx 500 guestrooms. One return line comes down from the 30th floor. About 6 years ago, the hotel replaced original balancing valves from each riser on the 30th floor feeding the return line with Griswold Autoflow devices. They were sized at 1 GPM each with a 2-32 psi insert.

  4. Spike Says:

    I have 2 different hotels, however the new 22 floor hotel has been open for a year now and we have had constant problems with the domestic water – cold backing into the hot, hot backing into the cold etc. Obviously the water problems tend to happen during times of lower water use – during higher volume days we tend to keep enough water moving for the system to be happy. We have a two zone system with PRV’s to maintain pressure at each zone then to make matters worse we have mixer valves installed at each sink in every room & to add to this within the shower valves are Pressure balancing valves. Now let me throw one more thing into the line-up here – on the upper floor mechanical room at the domestic hot water boilers are dual Symmons Temp mixer valves for setting the water supply temp (OK hope everyone followed that). What I have found is that the piping when installed was not sufficiently flushed, I am finding metal shavings getting caught in PRV’s, “Y” strainers, mixing valves, shower valves, just everywhere. This is my procedure when I run into the problem:
    1) Basement mechanical room – make sure the cold and hot water pumps are pumping close to the same pressure up the tower.
    2) Check the different zone PRV’s- make sure the pressures are close to the same, I like to have my cold water slightly higher then the hot (it’s more acceptable to customers to wait a minute for the hot water then to try to figure out why there is no cold water) I like to change the setting on the PRV’s for each zone just so I can make sure they are working – as we are speaking I have 3 prv’s not working that I have to pull today (like normal suspect debris causing the issue).
    3) If it’s hot backing up into the cold – I go to the upper floor mechanical room and check the cold water side of the Symmons temp mixers, if the cold water side is hot I Turn the mixer to as cold as it can get and go to the affected floors and run as much water as I can (both hot and cold to flush the problem out – you’ve got to get the hot out of the cold system, then once you’ve got the hot out of the cold readjust your mixers to maintain the correct temp usually 120 degrees.
    4) Then try to determine where the problem is- perhaps you found the problem when you check the Basement pumps or the PRV’s that may have had too much differential pressure or not working at all, was it just one zone affected and if so what group of rooms – were the rooms spread out to different risers? Knowing the rooms can tell you if it was a under sink mixer within that riser that could have been causing the problem. You have to isolate where the problem is coming from in order to determine what is causing the problem, THEN you can resolve it. Keep in mind the “Needle in a haystack” scenario if you have a setup like mine – the culprit tends to change each time it happens – other then the primary culprit with is usually a debris problem.

    Note to James’s problem above: James I would look at the size of the circ pumps, sounds like they may have been undersized. Now it this is a problem that just started to happen I would consider the age of the circ pumps and that perhaps the impeller has worn or become damaged – or perhaps the wear rings internally have opened up- you might need to rebuild the pumps, are you able to maintain pressure sufficient to get to the upper floors? (Remember it takes 1psi of pressure to climb 2.31 feet of height and that you want to add to this figure to the 40-50 psi that you want coming out of those upper floor fixtures so the guest can have a nice shower). Good luck. If I can be of any assistance you can email me at spikesamuels@yahoo.com

  5. Chin Joong onn Says:

    Dear Sir,
    What is the international standard of when you turn on the hot water and within how many second you will get the hot water. We are having 9 sec.
    Please advice.
    Thanks.
    Chin Joong Onn.
    Chief Engineer

  6. Jessie Says:

    I manage (2) hotels as the Chief Engineer – I am having some opportunities with no cold water on all 5 floors. I played with the balancing valves on the 4ht floor, adjusted the 2 symmons mixing valves temps set at 120 – I have 2 circ pumps running 24/7 the timers have been by passesd why? And how can I begin this process of eliminations I am getting complaints at all hours. Please assist me with good pointers to get this fixed.

    Thank you,

  7. Snw Says:

    I recently took over a poorly maintained 10 story, 220 room hotel that had a 20plus year problem of the hot water circ pump not operating properly. The building has 18 risers and returns for hot water circulation ( in addition to prvs, mixing valves, etc). Initially we found a failed check valve allowing hot water from a 5″ line to bleed into the cold water supply. We replaced that, and whilewe definitely corrected a problem, it did nothing to solve our circulation issue. There were several returns that would never stay warm, thus leaving all those rooms with poor hot water distribution(up to 20 or more minutes). We determined the problem to be air trapped at the top of the return lines that would not allow water to flow from the supply side to the return side, meaning they essentially got bypassed by the circ system because water will choose the path of least resistance. Our solution was to close every return riser, turn each one back on individually to force out the air, close that one, then repeat with all of them. We were successfull in pushing substantial air out of the pipes and then we opened all return risers starting at 50% open, to make sure we had adequate pressure to push water through all risers. It worked and we have hot water to all rooms in 30 seconds or less now. Hopefully this can help someone in the future!

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