ASHRAE 62.1 LEED Credits for Hotels

December 9th, 2008

Summary: Example of how to apply ASHRAE 62 to achieve a LEED credit. 

Applying ASHRAE 62 to a hotel to get LEED credits is very easy to do because hotel spaces generally have separate air handlers serving each type of space.  Therefore, to achieve ASHRAE 62 ventilation is as simple as setting the air handler minimum outside air to the ventilation requirements for the respective zones computed according to the ASHRAE 62 method.  This includes an area factor and a occupancy factor, of course.  The only situation that truly challenges the designer is where a single outside air unit is used to serve several air handlers each serving zones with different ventilation requirements.  For those cases, the ventilation minimum outside air setting must be computed according to the involved formulas.  ASHRAE has a spreadsheet available to help with these calculations, or you can use a design program such as Design Master which has this feature integrated into the load calculations.

Below is an example of an ASHRAE 62 computation performed for a simple building with diverse zones served by common air handlers.  The example is offered to assist in understanding what is involved.  The computations are performed using the ASHRAE 62 spreadsheet and Design Master for comparison.

Sample Analysis:

ASHRAE 62 ventilation concept is a method for setting the minimum outside air for an air handler, which serves rooms that have different percentage outside air requirements.

The building consists of five zones, each zone served by a separate HVAC unit. Within each zone are a number of rooms ranging from one room to eight rooms. The single room zones are a trivial case of the ASHRAE 62 concept. For those zones, the minimum outside air setting is simply the ventilation rate prescribed by the ASHRAE 62 ventilation amount based on occupancy and room area.

For the zones with more than one room per zone, there are three possible methods of calculating ventilation rates that could be used, each with a different effect on air quality and energy consumption. The first method is to simply add up the individual room ventilation rates and set the HVAC unit to a minimum outside air based on that sum. This results in an amount of outside air at the low end of the spectrum. This is the most energy efficient selection, since this minimizes the outside air heating and cooling load on the system. However, it may not provide sufficient ventilation for the room, which requires a higher percentage of outside air compared to other rooms in the zone. For example, if a conference room and an office are both served by the same HVAC unit, and the conference room requires 50% outside air and the office requires 20% outside air, then the office will not receive sufficient ventilation based on this method.

One method to absolutely guarantee that every room receives the required ventilation is to set the outside air at the HVAC unit to the percentage matching the room with the highest percentage ventilation requirement. The drawback to this approach, however, is that the rooms such as offices compared to conference rooms would receive far more ventilation than necessary. Thus, energy would be wasted.

The ASHRAE 62 approach is to find a middle amount of ventilation between the two extremes described above. Based on extensive research and analysis, the ASHRAE approach gives credit to the mixing effect of return air from one room to another. For example, if an office needs 20% outside air, but it is being served with 25% outside air, then a portion of the air returned to the HVAC unit is still “fresh” and could be counted as outside air when recirculated. The trick is to determine just how to translate this general concept into actual usable outside air values. This is what the formulas of ASHRAE 62 accomplish. ASHRAE 62 computations result in a setting for the outside air that is a proper compromise between the most efficient energy setting, and the maximum case ventilation setting.

The following table shows the five zones, the supply air for each room, and the amount of ventilation required for each room within the zones. In the least ventilation amount case, the sum of the room ventilation cfms is shown for each zone. In the maximum ventilation amount case, the ventilation for each room is computed based on the percentage of ventilation of the worst case room applied to all the other rooms. This percentage is then applied to the zone to show the worst case outside air setting. The column between the least and the worst-case ventilation rates is the ASHRAE 62 rate as computed using the ASHRAE 62 formulas. Note that this amount is between the two extremes in all cases except the cases where the zone has only one room. In those cases, the ventilation rate simply matches the minimum amount required for the room.

The ASHRAE 62 calculations were performed using Design Master HVAC software, which combines load calculations, ductwork design, and the ASHRAE 62 calculations. As a further check of this method of computing the AHSHAE 62 values, the official ASHRAE spreadsheet was used. The values matched and confirmed the correctness of the solutions. 

 The following exhibits are included for reference:

  1. Floor plans showing the five zones and rooms. Each room is labeled with the occupancy and ventilation requirement: LINK
  2. Summary of the outside air settings recommended for each HVAC unit. Note, this is the minimum setting and any economizer cooling operation may and should increase these values during economizer operation: LINK
  3. Design Master printouts showing the ASHRAE 62 results: LINK
  4. ASHRAE 62 spreadsheet showing a comparison analysis: LINK

Ducted Ventilation to Guestrooms from Corridors

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

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

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

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.

Delta High Leg Can Now Be the “C” Phase

October 28th, 2008

Summary: 2008 NEC allows the high leg of a delta high leg system to be labed as the “C” phase instead of the “B” phase.

A change to the 2008 NEC now allows the high leg of a delta high leg system to be labeled as the “C” phase instead of the “B” phase as was the traditional phase designation.  The high leg must be identified by an orange color (it was often referred to as a red-leg delta) or by other effective means and is usually the B phase. However, to accommodate meter configuration the high leg is permitted to be the C phase where metering is part of the switchboard or panel board. The Code change in this section requires legible, permanent field marking of the switchboard or panel board. 

Below is the traditional arrangement of the high leg delta system with the “B” leg as the high leg.  The high leg has a phantom 208 volts phase to neutral which is seldom used.  The difference between the first and second diagrams is the designation “CLOSED” and “OPEN”.  This refers to whether or not the delta is formed with three transformers (CLOSED delta) or two transfomers (OPEN ansformer.

The 2008 NEC now allows the high leg to be the “C” leg, which then allows the first two busses in a switchboard to be across the 120/240 volt side of the delta.  Single phase meters can then connect to these two busses without having to bridge the center bus.

 

 

 

 

 

 

 

 

 

 

Hotel Bath Exhaust Subducts

October 25th, 2008

Summary: A subduct is a duct inside a vertical exhaust duct routed between floors of a building.  The subduct replaces the role of a fire/smoke damper at much lower cost.  This article presents a discussion of issure surrounding the design and installation of a subduct exhaust shaft.

I could write a small book about subducts, but here is the short version.  You either got to this web page because you don’t know what a subduct is, or your got here because you do and you are looking for more information about them.  For the rookie, a subduct is simply a trick of duct construction to avoid a fire/smoke damper in an exhaust duct routed between floors of a building.  As we all know, any shaft up through a building must maintain the fire rating of the floor assembly,  So if you have a single duct routed in a shaft and there is an opening at each floor, the fire rating must be maintained.  Since fire smoke dampers are expensive, the code offers an alternative as follows: provide an inner duct boot with a minimum 22 inch upward extension inside the main duct and maintain a constant negative pressure on the duct.  The idea is that fire and smoke will not climb down the boot if exhaust air is being drawn up the main duct.  It seems reasonable and I’m sure it has been tested.  So why is this worth a blog entry?

Here is a photo of a real subduct before installation. 

The reason I am writing this entry is because the code has so much room for interpretation, and the methods of constructing a subduct can vary significantly, with vastly different performance and cost implications.  Let’s start with the subduct construction.  The best construction is a sheet metal main duct with sheet metal subducts.  The cross sectional area of the main duct is sufficiently large so that the subduct does not excessively restrict the airflow from below.  Since the airflow is greatest that the top of a building, the air speed at the top subduct is a critical design point.  The speed of the airflow around the top subduct should not exceed 400 feet per second.  One trick is to reduce the size of the subducts at the upper floors to allow more free area in the main duct at the top where the airflow is greatest.  This also has the benefit of accomplishing some degree of self balancing since the static pressure is greatest at the upper floors.  Regardless, balancing dampers are recommended at all floors.  The bottom floor balancing damper may be omitted since the balancing process should start with that damper fully open anyway.

A common VE recommendation is to eliminate the sheet metal duct and utilize the fire rated shaft as the main duct.  The subducts remain as sheet metal elements.  There are two major issues with this approach.  First, there is always concern that the shaft material will develop mold, especially with the moist air of the showers in a hotel.  The counter argument to this issue is that mold-resistant paint can be applied to the inside of the shaft walls.  Also, since the shaft is always in exhaust (note, subducts are not allowed for supply systems), any mold will be exhausted.  Also, since the exhaust air is moving 24/7, there might be a slight moisture build-up for a few minutes, but the moisture will rapidly be removed by the constant airflow.  This may be true for dryer climates, but I would have some concern in the humid areas of the country.

The second issue is the integrity of the shaft which is generally gypsum board.  The construction challenge is to get the shaft sealed so it does not leak.  One can argue that the leaks will simply come from the same place as the bath air, but that could potentially rob the lower floors of proper air exhaust.  As for my opinion, I prefer to have a sheet metal duct liner.  But in dry climates on hotels four floors or less, I allow the shaft to act as the duct. 

The code also says that the airflow will be continuous in the subduct shaft.  So what does continuous mean?  First, we all agree it means the fan runs 24/7.  But what about when there is a power failure?  Some jurisdictions require subduct fans to be on emergency power.  To take it a step further, some jurisdictions require airflow monitoriing with a trouble alert at the fire control panel.

Hotels with attics:  This next comment is about subducts in regard to buildings with attics.  With a flat roof, the subduct shaft terminates at a curb on the roof and the exhaust fan is installed at that curb.  However, if there is an attic, where does the shaft terminate?  It is not uncommon to see the shaft terminate at the upper floor ceiling with a fire damper installed at the attic floor.  From that point unprotected ductwork is routed within the attic to a common exhaust fan.   So here is my question: If the fire damper is activated, the exhaust air stops, is the subduct still code compliant?  For this reason, I have always extended the subduct shaft through the attic to the exterior of the building.  If you do not want to install the exhaust fans on the sloped roof, then simply install the exhaust fans inside the shaft in the attic with a fire rated access door.  For the sake of the maintenance staff, remember to have the architect provide a catwalk to each fan.

Mushroom fans or Utility fans:  There are two types of fans that can be used for a subduct exhaust.  The first is a simple mushroom fan mounted on top of the roof curb.  This is good if some type of acoustical treatment is included in the neck of the fan curb.  A simple sound lined baffle is my favorite detail.  Remember to have enough height on the curb that the subduct at the top floor bathroom does not stick up above the curb. The other type of fan is a small utility fan mounted a few feet away from the roof curb.  This installation allows a horizontal section of ductwork which can contain vibration isolation and a sound trap.  This is probably the best installation, but it costs more than a mushroom fan.  And regarding direct drive vs. belt drive for the fans, I like belt drive for balancing, but direct drive is nice for maintenance.  A typical hotel with belt drive exhaust fans generally has at least one exhaust stack not functioning due to a broken belt.

Tall Buildings:  What about really tall buildings?  A subduct cannot be balanced for more than about 20 floors.  If the shaft is very tall, keep the shaft large and the airflow slow so it behaves as a plenum rather than a duct.  If the building is more than 20 stories tall, install multiple sections of duct with no section of duct serving more than 20 stories.  Another approach is to provide an exhaust fan in each guestroom as a “pusher” at each floor.  This is a typcial Hyatt design standard.  I have seen this done, but the code really does not address this approach.  I can imagine a code reviewer arguing that the fan could force smoke from one floor to the next and defeat the subduct smoke control concept.  Hyatt specifies that that pusher fan be relatively weak compared to the exhaust fan.  So one could argue that the pusher fan would not push smoke from one guestroom to another.  Since Hyatt does this as a standard approach, it appears plan reviewers are not chanllenging it. 

I recently found a manufacturer of pre-fabricated subduct inserts that have a profile to minimize air resistance.  See this product at http://www.subductriser.com/LSR060829.pdf

Multiwire Branch Circuits

October 20th, 2008

Summary<: 2008 NEC requires a common handle tie or multi-pole breaker.

The 2008 NEC has a new requirement for multiwire branch circuits.  The new requirement is for a common handle tie or multi-pole breaker rather than separate single-pole breakers.  For example, devices that are wired with a common or shared neutral can no longer be served from single phase breakers.  The breakers must have a handle tie or be a mult-pole breaker.  The motivation for this added requirement in the NEC is to assure that all the energized conductors which may be present at a device or outlet box are degenergized during maintenance or fault. 

So as a designer, what do you show differently on the plans?  One approach is to consider this just a code issue that the electrician must address.  However, the practical issue is the purchasing of the breakers.  If the proper mult-pole breakers are not purchased, then the only means of being code compliant is to field install handle ties.  Some plan reviewers have begun looking for the panel schedules to indicate the multi-wire branch circuits.  Design Master will have this feature incorporated in the next release.

Making 3D BIM Work For You

October 15th, 2008

Summary: The following is a step by step introduction to designing and communicating ideas with 3D BIM.

There are many different ways to approach designing systems for a 3D BIM coordination model. I have found that the best way to create a 3D model is to start by designing in 2D, the way you normally would. Once you have the basic design in, all you have to do is add a third dimension. By breaking up the drawings by floor and by system you are giving yourself the flexibility to both have a 3D model which can be exported and a 2D plan which can be plotted. Splitting it up in this manner also helps with file size. Working with a model of the entire building will slow down all but the fastest computers. Another benefit to having both your 2D and 3D plans in the same drawing is that when you have to make a change, you only have to make it to one drawing.

The process of constructing a 3D model obviously begins with designing it, but at some point you are going to want to see how it fits together with everyone else’s models. The first step to is to export the 3D work on each floor of each system. If you are using Design Master you would click on the export 3D button. AutoCAD users can use the WBLOCK command to export their work. Next, you need to compile all the systems of each individual floor together into a single model. To do this I created a file for each floor of the building and started XREFing in the exported models which corresponded with that floor. Once this is done, you are left with a full MEP system separated into floors. The next step, is to go into each floor and adjust the orientation of the XREFed models so they all line up at the insertion point. Then adjust the ‘Z’ coordinate so the model is elevated to it appropriate location in the building. You should be left with a full MEP model for each floor, which, when compiled into a model of the whole building will snap together seamlessly.

One practice that is becoming quite common is group meetings between the different trades involved in creating a building coordination model. The building coordinator, who created a single presentation model comprised of each trades model, will share the model with all the designers involved in the project. This allows the different trades to see what each other have created and to work through conflicts in the design. The meeting can either be held in a single physical location or over the internet with a service such as GoToMeeting or WebEX. Either way, a projector is generally used to show the 3D model which is being manipulated in a BIM program such as NavisWorks JetStream. The participants in the meeting should also have 2D plans on the conference table for quick reference. If you are partaking in the meeting from a remote location you will need a speaker phone to join in the discussion.

Once the meeting is complete, you should have a list of changes you will need to make to your model before the next coordination meeting. This process will repeat until each trades model fits together without any conflicts. Then the physical building can be constructed.

Introduction to BIM

October 8th, 2008

Summary: Introduction to the concept of Building Information Modeling in contemporary engineering.

In the visions of the future, 3D-BIM starts at the concept phase and is carried through to the construction documents and beyond. That is the future, perhaps. For today, we still “design” using a range of tools including arm waving and architectural flimsy, you know, that tracing paper architects always have. I recall watching an architect working with a client over a set of plans. The architect grabbed some flimsy and drew a rectangle, laid it on the plans, and asked, “A room about this size?”. He then tilted the room at an angle and exclaimed, “In fact, this is how it should be”. The client nodded in concurrence and the design process continued.

Someday the computer will be as fast as flimsy, but it is not there yet. But as the design moves from flimsy to CAD, the process turns from “design” to “construction document” creation. And at some point it is appropriate to add detail to the elements toward being a 3D-BIM. I’m sure the creators of Revit and ArchiCad would cringe to hear me say anything but that the process should begin immediately, but that is why we have blogs, so people like me can share real life experiences.

The fact is that there is still both a culture of transition and a practical basis for that culture that does not match full 3D-BIM at the start of a project. I don’t think anyone should apologize for this condition. Don’t be thinking that you are somehow failing to keep up with technology just because you find it easier to think in stages. The human mind can only solve so many problems at once. In fact, don’t we often teach the concept of breaking a tough problem into smaller, easier problems, and solving each one separately. So rather than trying to think of door swings and egress path lengths at the start of a concept design, an architect draws big mass blocks and space planning diagrams. The door swing and lock set details would just get in the way of some really challenging issues. Likewise, working in 2D removes one dimension from the problem during a system layout. The third dimension can be added later after the engineer has the plane solution figured out. When you think of it in terms of dimensions, and time being the fourth dimension, you would never try to solve all four dimensions simultaneously. The fourth dimension is called “means and methods” for the contractor, and engineers are not suppose to address that issue. Of course, at some point it is good to think about that dimension, because sequence is of huge concern to the contractor. But even within design/build contractor organizations, there is generally a separation between the design phase and the shop drawing (third dimension) phase. And then further separation between shop drawings and project sequencing. (fourth dimension)