Archive for the ‘Plumbing’ Category

Lime Build Up in Hotel Tankless Water Heaters

Tuesday, December 1st, 2009

Summary: Lime build up is an issue for tankless water heaters in residential installations. In a hotel, this should not be an issue if a water softener is installed.

Mullinax Solutions posted an interesting article on the differences between tank-type and tankless water heaters. In the article they noted that lime build up in a tankless water heater from hard water is a significant problem compared to a tank type water heater. This is counter to manufacturer claims, but the research cited pointed out what most engineers, including myself, would intuitively expect. The Mullinax article explained that the elevated temperatures and the slower flow rates through a tankless water heater contribute to lime build up.

But does this concern for residential installations translate to hotels? I believe not. Hotels located where hard water is an issue generally have water softeners for the hot water system. As noted in the research, a water softener mitigates this concern about tankless water heaters. Therefore, this disadvantage of tankless water heaters should not be a problem in a hotel.

Of course, the challenge in a hotel is to identify any application for a tankless water heater. But applications in hotels do exist. My two favorite applications are for the hot water recirc lines in water zones separated by pressure reducing valves, and for spot water loads such as remote kitchens. But the fact remains that the high demand of a hotel is best served by a system with large storage capacity.

Hotel Hot Water System Legionella Remedies Still Elusive

Saturday, March 21st, 2009

Summary:  Legionella in hotel hot water systems remains a potential risk for hotel owners and designers.  This article summarizes the status of the progress toward dealing with Legionella in hotels.

Janet Stout, PHD and her colleague Dr. Victor Yu, MD are leading the research in Legionella in buildings in general.  In my efforts to find the best solution to this problem in hotels, I have begun conversations with Dr. Stout to see what we as designers can do to make sure our buildings are not at risk for a Legionella incident.  Here is some of what I have learned so far.  Please note that this subject is still under study and there are few conclusive statements that can be presented at this time.  I will be following this article with updates as my investigation progresses.  Anyone is welcome to call and discuss.

Matthew R. Freije is another expert I have discovered from his article “10 Ways Plumbing Engineers Can Prevent Legionnaires’ Disease” in the March 2009 issue of PME magazine.  He is teaching a seminar on “Performing High Quality Legionella Assessments” in May 19-21, 2009.  I will be attending to learn more and will share what I learn.

What we know about Legionella:

  1. Legionella is prevalent to some degree in almost all hot water systems.
  2. Most people have adequate immunity to low levels of Legionella bacteria, otherwise it would be a more serious problem.
  3. Immune compromised people are at higher risk to Legionella in situations that would not otherwise be a concern for the average person.
  4. Our practice of keeping hot water at 120 degrees creates a breeding ground for Legionella.
  5. Raising the temperature of hot water to above 140 degrees is helpful, but not the full answer.  Legionella is not fully killed at higher temperatures and no hot water system has a homogeneous temperature throughout.  For example, the bottom of a hot water storage tank may seldom reach the average tank temperature, especially near the cold water inlet.
  6. There are recognized methods of reducing the presence of Legionella, but none are 100 percent effective.  The common methods include:
    • Thermal Eradication: Boil the suckers!
    • Superchlorination: Kill them with chlorine like in a swimming pool.
    • Copper-silver ionization: Copper ions break down the skin of the Legionella, and the silver ions mess up the DNA.  (or something sinister like that)
    • Filtration with 0.2 micron filters.  At least the critters are fat enough to capture.

Testing for Legionella is the first step to knowing if your hotel has a problem.  The testing costs about $150 per sample, and it is recommended that a typical hotel be tested at about 5 places.

See Legionella Sample Collection for how to do this at your hotel.

ASHRAE is funding research into the issue of Legionella in cooling towers.  This is another breeding ground for Legionella that concerns many full service hotels.

Since I am just beginning to understand the subtleties of this topic, I will conclude this article for fear of continuing on and spreading untrue information.  However, it is my intention to continue learning about this subject and sharing what I learn along the way.

Update April 3, 2009: Here is a link to the best article I have found so far encompassing the full range of Legionella issues:  Legionella 2003 by the Association of Water Technologies.

Hotel CPVC Expansion Joints

Wednesday, February 18th, 2009

Summary: No sooner had I published the article on the double standard of CPVC pipe vs Copper pipe, a leak developed at one of my hotels with CPVC domestic water pipe.  Here is the story.

In my article “CPVC vs Copper in Hotels: Is there Still a Double Standard?” I shared my observation that the double standard for CPVC and Copper pipe was behind us with regard to pipe failures.  But within hours of publishing that article, I awoke to see the email trail of a hotel in Bellevue, Washington experiencing leaks in the piping.  Here is the story.

The mains of this 7 story hotel are a brand of CPVC called Coristan, which is a high grade of CPVC suited for larger diameter pipes.  As it turns out, there was no problem with the pipe.  However, we all know that CPVC has a higher coefficient of expansion than copper.  Thus, it is mandatory to use expansion joints to compensate for pipe expansion as the water in the pipe rises from 50 degrees to 120 degrees.  In a long hotel, this can be a significant expansion and without the expansion joints, the risers would be stressed and possibly sheared off.

What happened in this instance was a failure of the expansion joint.  Fortunately, the leak was small and the amount of water involved was limited.  Of course, even a small amount of water on ceiling tiles and carpet can cause significant monetary loss, but consider that other extreme of a 6 inch main water pipe flowing at full pressure.  That would be enough water to fill the hotel basement before someone could find the valve.  But, again, that is not what happened.

Below are pictures of the failed expansion joints.  Note the cracks in the bellows.  At one point it was thought that the flexing of the expansion joint had caused the failure, but the final analysis determined that the bellows failed from lengthwise stress caused by the water pressure, not the temperature fluctuations.   Be aware that there is a continuous stress on the pipes from the water pressure.  For a six inch pipe, the stress at 80 psi is about a ton of force.  It is less for smaller pipe diameters and is stricktly proportional to the area of the inside of the pipe cross section.

What was missing were extension limiting rods that keep the expansion joint from extending too far.   If you use this type of expansion joint, specify the joint expansion rods.

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A more traditional means to control expansion is a “U-loop” as shown in the two photos below.  This is fool-proof, but requires extra space that may not be available.

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Below is a response from the manufacturer regarding the failure mode of the bellows expansion joints in the previous photos.  You be the judge of whether this is an accurate assessment.

PROCO PRODUCTIONS, INC response to failure

CPVC vs Copper in Hotels: Is there Still a Double Standard?

Wednesday, February 18th, 2009

Summary:  Is the risk for engineers specifying CPVC in hotels still higher than for specifying copper?

CPVC for domestic water appears to be an accepted product by the industry and is no longer judged by a different standard than copper when a failure occurs.

Over the past ten years I have investigated many cases of pipe failures in hotels.  Of those cases, there was always a different view of a failure of CPVC (or PEX) as compared to a similar failure of copper piping.  If there was a failure of CPVC, the insurance company immediately launched a massive investigation looking for someone to blame and another insurance company to subrogate.  But if a copper pipe failed, there appeared to be far less litigation involved.

As an example, one hotel in San Francisco about six months after completion had a lav fitting fail simply because it was not actually soldered.  (It is amazing how flux and a tight fit can hold water for a limited period of time.) Anyway, there was a quarter million dollars of water damage, but little fan fare.   But in a hotel in Seattle, the CPVC pipes failed due to poor isolation of the pipe from the fire stopping and a huge insurance investigation followed.

The copper failure in San Francisco was simply poor quality control, not the systematic failure of a piping system.  The CPVC failure in Seattle was a systematic failure of a product incompatibility. (The fire proofing dissolved the CPVC upon contact, and metal tape was used to separate the pipe from the caulking.  Any tear in the tape would result in consistent failure.

Any time an engineer specifies a product that is considered non-traditional, there is a greater risk of liability for a similar failure compared to a traditional product.  It appears, however, that CPVC has had sufficient time in service to expose and correct the deficiencies of the early product. I generally do not specify CPVC, but if a developer requests the product as a cost savings, I am OK specifying it.

Two Zone Hotel Recirc Systems

Tuesday, February 10th, 2009

Summary: Tall hotels require two or more pressure zones for domestic hot water.  Here are some approaches to the hot water recirc systems.

Hotels over 15 floors generally have two or more pressure zones for the domestic hot water.  These pressure zones are controlled with Pressure Reducing Valves (PRVs).  Assuming there is one hot water boiler and storage tank system, the PRVs separate the hot water storage tank from the hot water piping zone.  If a conventional recirc system is installed, the recirc pump must pump through the PRVs.  If the pressure drop through the PRV is 60 psi, then the recirc pump must be selected with a pump head to include the 60 psi plus the pressure loss through the system which is generally about 5 to 10 psi.  The required pump must then have a total head of about 70 psi.  The result is a pump which uses significant horse power to generate the required flow. 

An alternate approach is to avoid a recirc loop that includes the PRV.  Rather, provide a recirc pump for each pressure zone and return the recirc water back to the header down stream of the PRV.  Of course, this creates a recirc loop that does not pull new hot water from the storage tank.  So how do we keep the loop from gradually going cold during the night?  The answer is to provide a separate source of heat in the loop. 

One source of heat is an electric or gas hot water heater.  Refer to Hot Water Recirc Booster Heaters Simplify Hotel Commissioning for sizing this auxilary heater.

Another approach is to utilize a heat exchanger to transfer heat from the low pressure hot water loop to the high pressure hot water loop.  The heat exchanger acts as a pressure isolator and allows the heat of one loop to move to the other loop without pumping across the pressure drop of the PRV.  The drawing below shows how this is done. 

 

 

Note that the upper level is the low pressure zone.  This makes sense because the natural head loss due to elevation eliminates the need for a PRV.  The lower floors are served by a zone downstream of a PRV.  The heat exchanger primary takes it’s heat from the main upper zone riser which is always at 120 degrees due the recirc action of its recirc pump.  The secondary of the heat exchanger is then the source of hot water for the hot water zone served by the PRV.  The water temperature of the secondary of the heat exchanger will be slightly less than 120 degrees due to the approach temperature of the heat exchanger, but it will be satisfactory for purposes of keeping the loop warm.  Of course, a practical adjustment of the water temperatures would be to have the low pressure loop initial temperature set at 125 degrees.  Any initial temperature up to 127 degrees is generally considered safe since the water temperature drops before reaching the guestrooms anyway.

Here is an enlarged diagram for piping the heat exchanger.  Note the cross flow to assure efficient heat transfer. 

Minimum Hotel Bathroom Plumbing Clearance

Wednesday, January 21st, 2009

Summary:  Just how little space is required to accommodate bathroom plumbing? 

Hotel developers and architects are always complaining that engineers ask for too much space above a bathroom ceiling for plumbing.  Well, maybe they have a case.  Typically, 10 inches clear for toilet and bathtub fittings in the easy answer.  We have found a jobsite where the plumber has proven it can be done in 6 inches clear.  The picture below is from the San Diego Gas Lamp Residence Inn being plumbed by Sherwood Mechanical Contractors.  As you can see, the clear space is only the length of the pen, which measures 6 inches.  Obviously, there were no long runs with slope.  Also, this was partly made possible by full 3D shop drawings which provided excellent coordination between trades.  There is no space for random pipe crossings.  Notice that one of the sheet rock supports was trimmed to fit the trap.

Hot Water Recirc Booster Heaters Simplify Hotel Commissioning

Saturday, January 3rd, 2009

Summary: A small water heater in the recirc line is a simple way to avoid low flow recirc temperature drift when the storage water temperature is greater than 120 degrees.

Hot water mixing valves function effectively when hot water is in heavy use and cold water is mixing with the hot water.  However, when there is no net usage of hot water, such as at night in a hotel, the recirculation line can become progressively warm until it reaches the temperature of the hot water storage tank.  This temperature is often at 160 degrees, and the first user of hot water in the morning gets a slug of extremely hot water.  Of course, the common answer is to configure the mixing valves properly and balance the low flow condition.  The flaw in this concept is that many plumbers are not experienced in performing this work and it falls on the shoulders of the engineer to come to the hotel during the first few weeks of operation and perform the balance.

But there is a fool-proof alternative that requires no guesswork.  The method is to place a small hot water heater in the recirc line to compensate for the temperature loss in circulation.  Since the heater has its own internal thermostat, the only commissioning effort required is to set the water heater thermostat to 120 degrees.

But what BTUH rating is needed for the hot water heater?  The answer is not easy because it depends on the heat loss rate of the hot water piping in the path that is being recirculated. One could compute the heat loss of the piping, but that is an arduous task.  The approach I use is to start with the basic assumption that the recirc flow rate will be designed to achieve a return temperature with maximum temperature drop of 15 degrees.  This matches real experience where we supply 120 to 125 degree water with a return temperature of about 110 degrees.   Since we all have experience in selecting the flow rate in the risers to achieve a delta T of about 10 to 15 degrees,  this approach has a practical starting point as compared to computing the heat loss of a piping system.  So multiply the total circulation flow rate by 15 degrees and by 500.  For example, if the hotel has 20 risers with 1/2 gpm per riser, the total flow is 10 gpm.  This results in 15 degrees x 10 gpm x 500 = 75,000 BTUH.  That is a small water heater if it is gas, or a 20kw heater if it is electric.

Aside: It is interesting to think about the implications of this heat loss as it relates to energy waste.  This heat loss is not only a direct loss of heating energy, but it also requires constant mechanical cooling to remove this wasted heat.   So this is a double argument for better hot water system insulation.

Trouble Shooting Hotel Hot Water Recirc Systems

Tuesday, December 30th, 2008

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.

Hotel Shower Head Height

Thursday, November 20th, 2008

Summary: Study of shower head height and related issues.

The Marriott standard for the rough-in height of a shower head is 6′-11″ (83 inches) above the unfinished floor.  With the addition of the floor tile and the depth of the tub, plus the distance from the pipe outlet to the bottom of a typical shower head, the resulting shower head height from tub surface is about 6′-6″ (78 inches).  Although this is the Marriott standard, if you have no other direction for a different brand, this is a good choice.

A related issue to coordinate during the design is the height of the tub tile surround.  Avoid having the pluming penetrate the wall near the edge of a material transition such as from tile to wall board.  Tile surrounds that extend to the ceiling are nice, but often considered too expensive.