Mark Robison, P.E.

Summary: Comparison of a Marriott mid-rise smoke control and building construction requirements compared to a Marriott under full IBC code high-rise smoke control and building construction requirements.

Marriott construction guidelines define a mid-rise hotel as any hotel more than six stories and less than 75 feet tall.  For this mid-rise classification, Marriott requires certain aspects of a high-rise building to be included in the design.  The following is a comparison of the these requirements relative to what is required by the IBC for a fully  classified high rise hotel.

As is often the case, when a local jurisdiction is informed that a mid-rise hotel is going to be designed per the Marriott criteria, full high-rise criteria is imposed.  Check with your local jurisdiction regarding this issue at the start of your project to avoid surprises.

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.

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.

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

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.

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. 

Summary: Here is a photo tour of a successful VRV installation in an operational hotel.

VRV HVAC systems are making their way onto the American scene.  Although the VRV technology is common in Europe and Japan, it is a newcomer to America.  As such, there are few installations for engineers to observe.  At the Sheraton Carlsbad Resort & Spa, California,  the Mitsubishi City-Multi VRV system has been successfully installed.  I visited the site and was impressed by the equipment and performance.  Most notably, the guestroom unit is almost completely silent.  This photo tour was made possible by Bruce Zelenka who enthusiastically allowed me to see all the pieces of the system from the roof to the guestrooms.

Bruce Zelenka was instrumental in getting the Mitsubishi City-Multi VRV system installed in the Sheraton Carlsbad Resort & Spa.

The condensers are modular and can be placed like soldiers shoulder to shoulder.  Here they are about six inches apart, but if space is at a premium, they can be shoved completely together.

A custom curb is used to create a platform to support the condensers.

The refrigerant piping is light weight and can be routed above the roof membrane on off-the-shelf supports.  Here is an example of the piping stacked two layers high.

Here is an overall view of the piping neatly racked across the roof.  The electrical is extended through roof jacks from disconnect switches mounted on the wall of the parapet.  Alternatively, the disconnects could be located at the roof penetration, but this is a cleaner installation.

The piping transition from the roof to a shaft down the building is shown here.  Typically, refrigerant piping penetrates a roof with a roof jack, but with this large number of pipes, it is more efficient to create a roof hatch that handles a bundle of pipes.  Also, the risk of a roof leak is very low with this detail.

The BC Controller is what Mitsubishi calls the unit which manifolds the refrigerant lines to the guestroom units.  The best analogy to describe it is an electrical branch panel.  Only one pair of refrigerant lines extend to the roof like a panel feeder, and each guestroom unit is separately served by refrigerant lines like branch circuits.

Looking up at the ceiling of the corridor, the refrigerant piping can be seen routed horizontally.

In a guestroom the fan coils are mounted in ceiling spaces near the corridor.  This is no different than a four-pipe fan coil installation.

In this installation, the air filter is mounted behind the return grille to simplify filter replacement.

This is the standard Mitsubishi thermostat.  This thermostat is under review by Marriott and Hilton for acceptance in their hotel brands.

Mitsubishi has a fantastic design, but there is still no magic to deal with condensate.  Here the condensate from the fan coil unit in the ceiling is piped to the bathroom lav trap.

Mitsubishi offers a variety of fan coil unit styles.  Here is a four-way cassette unit suitable for a kitchen or work area.  This unit is installed without a ceiling, but as the trim would indicate, it is intended for a ceiling installation.

Mitsubishi has a special condensate trap that does not require a vertical loop.  This simplifies installation in ceiling cavities with limited clearance.

This wall mounted style of fan coil is an economical alternative to a built-in type for a guestroom.  Although this installation made no attempt to conceal the electrical power or the condensate drain, these units can be installed in guestrooms with a clean look not too different than a PTAC.  However with this unit, it is mounted high on the wall and does not require any floor space near the outside wall.  I have seen these units successfully applied to a college dormitory.