Archive for the ‘Electrical’ Category

Mitsubishi City Multi goes into Ontario Airport

Wednesday, September 22nd, 2010

Embassy Suites, California

The new Embassy Suites hotel located at the Ontario airport in California will have guestrooms served by a VRV system by Mitsubishi.  This is following the Embassy Suites in Palmdale with the identical system completed in early 2010. 

Here are a series of photos taken during construction to showing how this system is constructed in the corridors and guestrooms.


This photo shows a typical guestroom fan coil unit located above the guestroom entry soffit.  The units are very compact. 


This shows a closer view of the fan coil unit.  The ductwork to the guestroom space is flex duct.  The two black pipes in the foreground are insulated refrigerant pipes.   The white PVC pipe is the condensate drain.  The strange grey tube with corrugations between the PVC and the fan coil is the proprietary Mitsubishi condensate trap.  It solves the problem of the P-trap which otherwise requires additional ceiling cavity height to accommodate.  Note that the electrical J-box is in the upper left corner of the photo.  All connections are on one side of the fan coil.


This photo shows the BC controller located in the corridor ceiling cavity.  Note the refrigerant piping connected to the left side with the brass fittings.  There are two pipes per guestroom and each pair of pipes is stacked vertically.  There are thirteen rooms connected to this BC controller.  For a typical hotel floor with about 26 guestrooms per floor, two BC controllers are provided.


This is another view of the BC controller with the condensate piping and main refrigerant connections shown on the end of the unit.


This shows the BC controller nestled amongst the other systems in the corriodor including the ventilation supply duct nearest the wall.


This photo shows the refrigerant piping as it splays out to the guestrooms along the corridor.  As we move further from the BC controller, the congestion becomes less and less as refrigerant pipes “drop off” to the guestrooms. 


This shows a small bundle of refrigerant pipes near the most remote guestrooms.  Note that the ceiling space becomes very comfortable at this point. (If we could only rent out this unused space. J)


This photo shows an electrical J-Box with the access panel framed in.  I have included it just so my electrical engineers do not feel left out.

Corridor Guestroom Supply Systems

Wednesday, September 22nd, 2010

Both Hilton and Marriott now require ducted ventilation air to guestrooms.  This means that outside air openings at each guestroom via PTAC or VTAC is no longer acceptable.  Likewise, operable windows are not acceptable.  In response to this requirement, designers are now providing central HVAC units to supply corridor ventilation that also includes ductwork along the corridor with branch ducts to each guestroom. 

The photo below shows the ductwork on each side of the corridor with sprinkler pipes and electrical routed in the center above the drop ceiling. 


This is a typical condition along most of the corridor.  However, the conditions become much more crowded where the main supply duct first enters the corridor as seen in this photo:

Here the duct must exit the vertical shaft and cross the corridor as it splits into the two branches extending the length of the corridor.

You might ask why two ducts and not just one, and the answer is that the small duct into each guestroom would have to cross over (through) the sprinkler piping in the center.  Here is a photo of the duct into a typical guestroom:

In most states there is no requirement for a fire / smoke damper.  However, California is one state where a fire/smoke damper is required at the duct penetration to each guestroom.  Here is a photo of  a typical fire/smoke damper:

Terminating the ventilation air inside the guestroom can be done in three different ways.  One approach is to run the duct to a diffuser on the other side.  The second is to connect the duct to the return side of the guestroom fan coil unit.  The third method is to terminate the duct inside the return air plenum of the ceiling space where the guestroom fan coil unit is located.

The advantage of this approach is that the return grille for the plenum can also function as the access panel for the fire/smoke damper.  This is the configuration shown in this photo as taken through the ceiling opening for the return grille.  The fire/smoke damper is seen as accessible from this opening. 


It should be noted that the return air plenum concept can only be used in a non-combustible building construction.  Also, any wiring routed through this plenum must comply with plenum rating requirements.  Therefore, no smurf tube in the plenum.

Rain City Solar is Hope for Seattle

Friday, September 25th, 2009

Summary:  After years of waiting for solar power to come of age, we have finally begun installing solar PV systems in the Seattle and Puget Sound area.

The favorite comparison for solar power in Seattle is Germany.  Germany has a similar solar exposure as Seattle and Germany has been on a rampage to install PV solar.  Germany has an historical need to become energy independent from the world.  Even during WWII when oil was cut off from Germany, the country still produced synthetic gasoline.   And now the Germans see the value of solar power.

For me, I see solar power as a gift to my children and their children.  It is a gift that never stops giving.  It is better than stock certificates.  It is like having a family farm that stays in the family for generations.

Some people still think in terms of rate of return (ROI) or payback.  I find this analysis silly when compared to the ROI of buying a Lexis or some other expensive car.  Does anyone every consider the ROI of a luxury car?  Does anyone ever think, “I’m buying this $50,000 car for my children and their children?”  Of course not, yet the price tag is seldom an issue.  So rather than buy luxury cars, I am installing solar on my home and all the homes of my children.

Check out Rain City Solar if you live in the Seattle or Puget Sound area.  We know what we are doing and will make sure you get a system that will make your grandchildren look at the roof and say thanks to you long after you have left them on their own.

Marriott Mid-Rise vs. Code High-Rise

Monday, February 23rd, 2009

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.

Emergency Generator Stair Fans Only All Fans
Smoke Report and
Rationale Analysis
Third Party Testing of
Smoke Control
Fire-Fighter’s Control
Fire Command Center X X
Exit Stair Pressurization X X
Mechanical Smoke Exhaust
for Corridors
Mechanical Smoke Exhaust
for Public
Elevator Pressurization X
Full Smoke Control
System per Section
Fire Alarm Speaker
System for Zoned
Secondary Water Supply
for Sprinkler
Emergency voice/alarm
Automatic Fire Detection
Two hour protection for
control and
power wiring (907.2.12.1)
Fire Department
Communication System
Vestibule at Exit Stairs
on Each Floor
Exhaust Fans Rated for

Hotel Dual Electrical Services for LEED Credits

Friday, January 2nd, 2009

Summary: Requesting two service transformers with two voltages from the utility service is energy efficient and cost effective.

Large hotels generally have a 480/277 volt service provided by the utility and step-down transformers for 208/120 volt loads.  Since a hotel is largely 120 volt loads, the size of the step down transformers is about half of the capacity of the service.  This results in dual transformation of a large amount of power.  The energy efficient approach is to request two service transformers from the utility:  One transformer at 480/277 volts, the other at 208/120 volts.  The lower voltage transformer will eliminate all the losses from stepdown transformers in the hotel while keeping the utility losses the same.  For a large hotel, this is generally allowed by the utility.  The following is an example of the analysis applicable for computing energy savings from dual service transformers.

Based on an actual hotel of 333 rooms, the following LEED energy analysis was performed:


Hotel Room Count:  330 guestrooms

120/208 volt load per NEC:  948 kva (Say 1000 kva)

Heat losses from distributed dry-type transformers  throughout the building:  2.0% of NEC load

Cost of electricity:  $0.08 per kwh

Load Factor:  Verified load factor data for hotels was not available at the time of this study.  However, load factor data for other facility types was available, and the data indicates a load factor of 30% to 50% is probable.  Since the load factor is an important part of this analysis, a continuing effort is in progress to obtain better load factor data specific to hotels.  However, we know that the magnetizing losses are a constant regardless of load and represent about 1% of the transformer losses based on nameplate data.  Therefore the I squared R losses will vary with load factor, but not in some fraction of a proportion.  For this study, the load factor is assumed to be included with the transformer loss number of 2%.  Peak losses for small transformers are commonly stated at 3%, which is the sizing criteria for cooling equipment.

Cooling Efficiency: Transformers located within the hotel require mechanical cooling to remove the heat generated by the transformers.  Since utility transformers are allowed to be cooled with ventilation air, there is an additional energy cost for dual transformation that must include the cost of mechanical cooling of the transformers.  This study is based on 1 kw per ton of cooling.

Computation of Savings:

Transformer energy savings per year in dollars =  1000kva x 0.02 efficiency x 8760 hrs/yr x $0.08 /kwh  =   $14,000 savings

Associated Cooling Savings =  1000kva x 0.02 efficiency x 3413BTUH/kw / 12000 BTUH per ton x 1 kw/ton x 8760 hrs/yr = $4,000 savings

Total Savings = transformer savings + cooling savings = $14,000 + $4,000 = $18,000 per year.

Hotel Guestroom Fault: Limiting to Under 10,000 Amps

Thursday, December 18th, 2008

Summary: Save money on costly high AIC rated breakers by adding length to panel feeders.

Hotels with 208/120 volt services can have very high fault currents near the service entrance.  It is tempting to locate some of the branch panels in the electrical room to serve nearby loads, including the guestrooms in that vicinity.  However, this can result in excessive fault current exposure to the guestroom circuits.

One simple way to reduce the fault at nearby guestrooms is to route the feeders down and back the corridor with sufficient extra circuit length to bring the fault current below 10,000 amps.  The impedance of small circuits is quite high and has the effect of reducing fault current effectively with relatively short runs. 

As an example, suppose you have a 100 amp guestroom panel in the room adjacent the service electrical room.  The feeder size is probably #1 copper conductors and the length of the feeder to the panel is 25 feet including conductors within the switchgear.  Assume the fault at the switchboard is 65,000 amps.  The fault at the panel would be 24,000 amps symmetrical.  By simply routing the feeder 30 feet down and back the corridor to extend the feeder length to 75 feet the fault is reduced to about 9,000 amp symmetrical.  This added feeder length is only required for the first few rooms until the feeder length exceeds 75 feet anyway.


Below is the Design Master fault printout with the guestroom panel feeder only 25 feet long based on shortest route from switchboard to panel.  Fault is above 10,000 amps and the lowest cost panels would not be adequate to handle this fault.


Below is the same system in Design Master but showing the fault below 10,000 amps with the feeder length extended to 75 feet.


Delta High Leg Can Now Be the “C” Phase

Tuesday, 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.











Multiwire Branch Circuits

Monday, 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.