CAD layering standards

In response to Howard McKew's "Tomorrow's Engineer" column about construction CAD layering standards (April 2005, page 78), it seems to me that the AEC industry as a whole would benefit from having such standards, although this would likely be difficult to achieve. With each company having their own standards, the transfer of information becomes infinitely more difficult, and it would be interesting to watch how the use of building information models might force such a change. What are your thoughts?

Marcus D. Hale, CEng MIMechE, LEED® AP
Project Engineer
McGuire Engineers, Inc.

McKew responds:

I've been sending out to readers a portion of a specification requiring field coordination CAD layering standards as it pertains to turning over a "select few" files to the facility management staff who will take ownership of the project at the end of construction.

I could come up with more facility layers, but I believe that we need to start simple facility management layers so that the construc-tion industry will begin to issue CAD layering standards, and not be overwhelmed with a comprehensive CAD layering agenda.

In regard to other construction CAD layering standards, a construction firm could consider the following if it is prepared for a more aggressive CAD field coordination layering system:

  • Sheet metal trade: Post all supply air system distribution on one layer and all return air distribution on another layer. Post exhaust air layers on a specific layer.
  • HVAC piping trade: Chilled water supply, hot water supply, and steam supply all on individual layers.

The same for return systems:

  • Plumbing trade: Post special plumbing systems (medical gas, etc.) on their own layers. Post the basic plumbing systems on individual layers.
  • Electrical trade: post special electrical systems (nurse call, etc.) on their own layers. Post light fixtures on its own layer.

The additional layers allow the contractor to sort similar to how designed sort information via CAD layering. The difference is that contractors are not taking advantage of CAD layering, and they are missing the opportunity to turn over useful CAD documents to the building operator.

Keeping the power on

This letter refers to Lindsay Audin's "Energy Wiz" column titled "Back-Up Power" (February 2005, page 26).

I, too, have some experience installing supplemental power systems into homes and businesses - our own farm with its multiple outbuildings, our community fire station, our neighbors, even in urban settings for friends and business acquaintances.

For those initially expressing interest, I have consistently discouraged the use of what I call "selected circuits" transfer switches. The cost is not that much greater to install a whole-house transfer switch sized to carry the maximum worst-case total load.

Although service to most homes in our area falls into the 100 to 200A range, (with a few new-builds as high as 400A), most owners are hard-pressed to actually "pull" half their rated input capacity. Even installing a 100A manually switched whole-house transfer box will most always serve their needs and is far better than only being able to energize particular circuits.

Why design an artificial limitation into the system? I've never grasped this approach. The user may really need or want to use another device not manually transferred to one of the few now-energized circuits: a sump pump, a small electric heater, a vacuum cleaner for the broken glass dropped in the kitchen in the dark. Result? A messy hazardous trip-prone (both types of trips) array of constantly rearranged extension cords, most all of which are undersized by most all consumers.

My argument: Install a whole-house transfer switch and exercise judicious control of lighting and appliances during the outage: unplug all the ‘wall-wart' transformers, clock radios, cycle the freezers and refrigerators once a day, unplug all the spare televisions and "sleeping" electronic equipment - be cognizant and control the cold and dark of an outage to best suit the need, not be limited by dedicated circuits.

While I realize that in your geographic area an inverterbased system might serve your immediate and short-term needs, rest assured that in about the tenth hour, an engine-driven generator will start looking pretty attractive. In our world, daylong outages are neither rare nor is the occasional multiple-day or even weeklong event. Tornados, winds, and ice storms account for most local outages but there is also the occasional brushfire or errant vehicle. An inverter just won't work long enough in winter weather to make it a primary backup system.

I truly think your neighbor with his $4,000 "over-killed" installation is the way to go in most all cases, although I suspect corners could be cut in order to save a few dollars and still have sufficient and capable standby power capacity. For instance, rather than storing time-sensitive liquid fuel one might consider using propane or natural gas; a manual transfer switch could be used rather than the automatic type mentioned. As in all things, the need and level of risk-aversion should be evaluated.

One caveat: common small semi-portable gas-engine generators are, in most all cases, an "intermittent" machine; from a practical standpoint after about 40 hours or so runtime they're mostly used up. A little shopping and some time will typically yield a wide selection of good used low time "industrial-level" generators that will quietly sit and run for weeks with nary a bobble. We've had especially good results using name-brand engine-driven arc welding machines for auxiliary power generation up to about 10kW - a plus for the hobbyist: two uses from the same machine.

I trust these comments are accepted in the spirit in which they are intended: not necessarily a criticism but rather another point of view, perhaps even a point of view influenced by local conditions somewhat different from yours.

Timothy Hartsfield, P.E., CAPM
McAlester, OK

Audin responds:

I concur that in some geographic areas a generator-based system would make more sense to handle half-day (or longer) blackouts. With regard to installing a whole-house transfer switch and depending on occupants to run around the house unplugging devices, I do not believe such a policy reflects a realistic perspective of a family's immediate response during a blackout. The system I installed was designed to backup a home's heating system, not other devices that run on electricity. If one's desire is to keep his toaster working, that is a subject for a different column.


The closing statement of Howard McKew's "Tomorrow's Engineer" column titled, "Facility Condition Index or Facility Business Plan?" (December 2001) states the following:

"In 2002 we will continue with roundtable sessions that look at facility assessment and how to benchmark the current conditions of buildings in various industries. When we do, we will share with you what we are hearing."

I would like to know if this has taken place, how and where I can have access to this information.

Leonard Henriëtte
Refineria ISLA Curaçao
Willemstad, Curaçao Netherlands Antilles

McKew responds:

The book isManaging the Facility Portfolio - A Practical Approach To Institutional Facility Renewal And Deferred Maintenance.At the bottom of the cover it states, "National Association of College and University Business Officers." It is a 1991 publication and it was written by Applied Management Engineering, P.C. with an address at 120 S. Lynnhaven Road, Virginia Beach, VA. If you do a search on the Internet for this book, you will come across several publications on FCI.

As far as my continued roundtable discussions, we have had informal discussions that focused on a campus-by-campus assessment. I have not published anything since my column, although I use the FCI format.