Off Grid Building 2

[Mbrooke]

So I'm designing a co-gen power system for an off grid remote research building. I'm not really sure where to begin- I need a few pointers/guidance on where to start...

Does this look like a good design? Should I get creative with how the gensets are interconnected?

Or just keep things really basic?

Anything I've missed? Go/no go? Or am I way off?


Power is normally produced by natural gas and solar with onsite diesel tanks to meet the requirements of article 700.

https://files.engineering.com/getfi...abd-4b3c-8a21-98610d4667c5&file=IMG_0040x.jpg

https://files.engineering.com/getfi...ad1-4634-8dbf-62914832e2a8&file=IMG_0041x.jpg

 

[Mbrooke]

@David- I'm confused. Code would require at least 3 ATSs for emergency as I interpret NFPA 70.

 

[davidbeach]

Admittedly it’s been 15+ years since I had to follow every in and out of all of the code changes. But, at least once, not a hospital meant that a facility with life safety needs required one ATS. If you triggered other requirements there could be more. Regardless, normal power should come from a power plant that feeds the whole thing. Physically segregated as necessary to limit the impact of single events.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Mbrooke]

@FreddyNurk: I've never seen a large scale co-gen in person, however at the same time I know that code requires emergency power along with dedicated branches for life safety, cops, legally required ect where the AHJ determines so. Saying co-generation lets you skip article 700 due to a lack of utility power is without basis.

So yes, either these folks are not following the code or are simply dealing with buildings where emergency requirements do not go past bug-eyes.

Right, paralleling can be done with more than one gear, in separate rooms, however cost and complexity goes up (in addition) now that you need to worry about fault protection between tie conduits.

The system still has a central computer which can fail, stuck breaker which will not open, ect.

Right, mobile sets can be paralleled- those which have the capability and are compatible with each other. However there is no guarantee compatible sets can be scored in an emergency. While this facility has the ability to to say "hey, send me 3 vagabonds, 208-240Y, 60Hz, 400-600kw range", there is no guarantee these units will be identical or have paralleling abilities. The genset stash is a one size fits all comprised of various units of varying ages, makes and alternators.

Even if I do parellel via redundant normal systems, I will still need an emergency set, 3 ATSs, and separate branches.

 

[Mbrooke]

@David: If you have just life safety (egress lighting) than one ATS is enough. However COPs requires its own ATS. Ditto for legally required. Fire pumps adds a forth. Optional might even push you to five ATSs.

Here is what is typical today:

Some design standards (like those for VA hospitals) don't like large ATSs (ie over 800amps) so high capacity emergency branches often result in additional ATSs over the code minimum.

 

[davidbeach]

So, what the heck is the facility? What’s even relevant? For an off-grid building I’d use an engine driven fire pump located in its own outbuilding separate from everything else.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Mbrooke]

Think of this as any other municipal or low rise office type building. Just off grid.

Engine driven fire pump would work as well in this scenario.

 

[davidbeach]

At low-rise how do you get beyond the need for a life safety system?

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Mbrooke]

You don't. You still need emergency lighting in the corridors, basement, stair wells and alcoves. Shelter in place or evacuate, both require occupants leave the fire floor.

FWIW, if I was to go the parallel route, my system would look something like this- minus the utility of course:

 

[davidbeach]

What drives the need for either Critical or Equipment? Not every installation that needs an emergency generator needs more than Life Safety.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Mbrooke]

COPs comes from the fact this building could be used for continuity of government during times of need- hence meeting the requirements of article 708. When the building is not needed for emergency operations or command, its still nice to have a dedicated, protected branch for the computers and sensitive lab equipment. Legally required comes again from article 700 of the NEC- loads that while essential can not share the life safety ATS.

Regarding an equipment ATS Elevators and essential motors need delayed transition in order to demagnetize. Not doing so can cause inrush high enough to trip OCPDs and even damage elevator equipment. The elevator cab lights are on the life safety circuit, no one notices when the elevator stops for a few seconds and then restarts.

 

[Mbrooke]

From the 2020 NEC:

 

[davidbeach]

Are you confusing “shall be permitted to” with “shall”? You still haven’t defined a use that goes beyond egress lighting. Any facility with a legitimate “continuity of government” function certainly wouldn’t go for a 1001 ATS fantasy system.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Mbrooke]

David, do you have a code 2014, 2017 or 2020 book on hand? I think excerpts from the code may help in conveying my point of view-

If this building ever takes the roll of emergency management during a disaster, the power system aiding in the efforts (computers, radio devices, hard wired phones, liaison devices, meeting room lighting, projection screens, ect) is considered essential and thus those having jurisdiction of (or over) this building have the discretion to require (or at least ask for) a COPs system.

The cops system itself must be seperate from all other electrical, including life safety, so that alone will require at least one ATS or an independent piece of gear with two sources of power.

A COPs system isn't unique, some local police and fire departments might have them, 911 centers, municipal buildings, financial institutions, ect all the way up to military sites and nuclear research faculties.

Think of it exactly as the critical branch in a hospital, but instead of medical equipment you've got a computer plugged in tracking a hurricane or taking emergency dispatch reports. Nothing more special than that.


Here is a slide share going more in depth-

https://www.slideshare.net/michaeljmack/cops-an-arresting-look-at-nec-article-708

 

[Mbrooke]

Earlier I made a claim that some standards either require, force, increase, or limit the size of ATSs in addition to what is already required by the NEC.

Here is an example from Department of Veterans Affairs Design Guide for Hospitals, Laboratories and Animal Research Facilities:

Paralleling of gens is permitted, however an emergency system totally separate from the normal system is still required with a minimum of two EM feeders. ATSs are shown despite motorized breakers, and both the normal and emergency branches are limited to 800 amps maximum.

Thus a large facility may have upwards of 56 or more ATSs.

Just to be fair I'm not trying to "rub" anyone or prove them wrong, rather referencing like standards which are influencing or dictating my designs.

VA design doc:

https://files.engineering.com/getfi...1-7b615d10481e&file=VA261-15-R-0359-012-1.pdf

800 amp ATS limit:

https://files.engineering.com/getfi...-4747-9620-4d11f075690a&file=Clipboard01x.jpg

"Ultimate" Generic Design:

https://files.engineering.com/getfi...-4934-b671-078c8ac7abd5&file=Clipboard01z.jpg

It may seem silly, but smaller subdivided equipment is more reliable day to day. In an emergency it is easier to deal with small 225 amp ATS than a 4000 amp behemoth.