Archive for November, 2008

Ducted Ventilation to Guestrooms from Corridors

Wednesday, November 26th, 2008

Summary: The new codes now allow ducted guestroom ventilation for hotels in the west coast states which have now moved from the Uniform Building Code to the International Building Code.

Discussion:  The following code analysis is presented to document the conclusions stated in the summary above.  This topic requires a step-by-step analysis of the code and there is really no short cut to what appears below.  Just to be clear, the question is: Are fire/smoke dampers required at the penetration of the duct into the guestroom at the corridor wall?

Code Analysis:

1.    The code defines four relevant types of separation that must be addressed as part of the code analysis.  Those types are: Fire Barriers, Fire Partitions, Smoke Barriers, and Smoke Partitions.

2.    Addressing each type of separation, we find the following:

a.    Section 706 Fire Barriers: This applies to the hotel corridors.
b.    Section 708 Fire Partitions: This applies to the separation of hotel sleeping units (guestrooms)
c.    Section 709 Smoke Barriers:  This section does not define where smoke partitions are required. It is silent regarding where the section is applied.
d.    Section 710 Smoke Partitions: This section does not define where smoke partitions are required. It calls upon other sections to provide that definition.

3.    Are smoke barriers and smoke partitions involved with guestrooms?

a.    Section 419 Group I-1, R-1, R-2, R-3:  This section applies to guestrooms and states that walls separating sleeping units shall comply with Section 708.  That means the walls between guestrooms are Fire Partitions.  It does not elaborate and extend the rating to Fire Barrier, Smoke Barrier, or Smoke Partition.

4.    Section 706 requires ducts and air transfer openings comply with Section 716.

5.    Section 708 requires ducts and air transfer openings comply with Section 716.

6.    Section 716 addresses duct and air transfer openings of all types.  Paragraph 716.6 Where Required defines where fire dampers, smoke dampers, and combination fire/smoke dampers are required for each type of separation. There are then two cases to analyze the hotel guestrooms. The first case is a duct routed in the corridor with taps to each guestroom through the corridor wall. This case involves crossing a Fire Barrier. The second case is a duct routed from guestroom to guestroom which involves crossing a Fire Partition. These two cases are analyzed below.

7.     Duct Routed in Corridor: Since we know from above that guestroom separation from the corridor is a Fire Barrier, then the applicable sub-paragraph is 716.5.2 Fire Barriers:

a.    This code requires fire dampers except where the duct system is constructed of 26 gage steel and the ductwork is continuous from the air handling equipment to the air outlets in the guestrooms.
b.    Conclusion: The 2006 IBC allows air supply to guestrooms from a common duct in the corridor without fire dampers or smoke dampers as described above.

8.    Duct Routed in Guestrooms: Since we know from above that guestroom separation is only a Fire Partition, then the application sub-paragraph is 716.5.4 Fire Partitions:

a.    716.5.4 Fire Partitions:  This sub-paragraph requires fire dampers in ducts and air transfer openings except when all of the following conditions are met:
i.    Building is sprinklered.
ii.    Duct penetration is less than 100 square inches.
iii.    Duct is 26 gage steel.
iv.    No openings communicated to corridor.
v.    Duct installed above a ceiling.
vi.    Duct not terminated at the corridor wall.
vii.    A 12 inch steel sleeve through the corridor wall is provided for the duct.
b.    Conclusion:  The 2006 IBC allows an air supply to guestrooms from a common duct in the corridor without fire dampers or smoke dampers if the conditions of 716.5.4 are met.  The following is a review of those conditions:
i.    Sprinklers:  No problem.
ii.    Duct less than 100 square inches:  We need 30 cfm of air per guestroom, therefore, a 4″ diameter duct is sufficient for a guestroom.  A 4″ duct has an area of 12.5 square inches and meets this criteria.
iii.    26 gage steel is standard.
iv.    The duct would have no openings to the corridor since the corridor air system would be a separate system.
v.    A ceiling would be provided for the corridor.  This is not always the case, but would be necessary (and desirable) under these conditions.
vi.    The duct could not be terminated at the corridor wall of the guestroom.  This requires some form of soffit in the guestroom, which is easily accomplished.  The grille can then be installed at the wall of the soffit.
vii.    A 12 inch sleeve through the corridor wall is easily provided.  The requirements for this sleeve are detailed further in the code.

 

Proper Sizing for Hotel Guestroom Units

Monday, November 24th, 2008

Summary: Reduce noise with proper sizing of guestroom units.  But be careful with undersizing the heating capacity.

One of the big temptations for designers of hotels is to oversize the guestroom units.  This is especially true of the cooling mode.  My observation has always been that the most important time for a guestroom to perform properly is at night, and at night there is no solar load.  So by oversizing a unit for peak solar load plus all other extreme assumptions about the load in the room, the result is a unit is far over sized for the night.  This always translates into excessive noise. 

The only caution is to make sure the units are sized adequately for heating at night in cold climates.  At night there is no heat gain from such things as lights and the television once the guest goes to bed.  The in-room refrigerator is the one exception that produces heat all night long, but it is not significant. 

If you are using heat pumps, make sure the supplemental strip heat is large enough.  In the case of hydronic systems, make sure the boilers can maintain water temperature in the extreme cold conditions with ample spare capacity for the very extreme cold.  Unlike cooling, guests have no tolerance for an occasional cold night.  An occasional hot day is expected, but not a cold night.

Two Pipe Water Source Heat Pumps for Hotels

Thursday, November 20th, 2008

Summary: Analysis of water source heat pumps.

The water source heat pumps are a popular choice for mid-priced hotels, and for hotels more than 4 stories. Marriott has a policy of not allowing PTACs and VTACs on hotels above six stories, even if that is the brand prototype. Therefore, water source heat pumps are often the choice of taller projects.

The advantages of water source heat pumps include:

  1. Only two pipes for water distribution.
  2. No insulation of pipes or potential for sweating.
  3. High efficiency from central cooling towers and boilers.
  4. High efficiency from the ability to transfer heating and cooling from one side of the building to the other depending on solar exposure
  5. Easy maintenance compared to central chiller plats of 4 pipe systems.

The disadvantages of water source heat pumps include:

  1. The noise of the compressor is present in each guestroom.
  2. less smooth temperature control compared to fan coil units
  3. Assuming the common spaces are also served by heat pumps, the problem of temperature control is significant compared to air handlers with heating and cooling coils. Any spaces requiring high percentages of outside air such as meeting rooms and corridors are difficult to control in extreme climates. In hot and cold climates, pre-coolers and pre-heaters are sometimes necessary.

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.