Emergency Generator for Multiple Buildings

[hforney500]

Which would be the best solution? There are three (3) fifteen (15) story apartment buildings within 50 yards of each other. Each building is supplied with it's own service. Elevator, NFPA required loads, and the community room lights and power in each building will be connected to emergency stand-by system. Would it be best to install an emergency generator for each building or install one larger generator for all three. My company will be hiring an A/E firm to do the design. I would like the pros and cons of both installations since I will be on the selection committee.

[ August 27, 2003, 11:23 AM: Message edited by: hforney500 ]

 

[Ed MacLaren]

Re: Emergency Generator for Multiple Buildings

Are these buildings existing or yet to be built?

If existing -
1. Do they now have separate utility services, or are they supplied by feeders from a common service?
2. Is there an electrical room in each building that can accomodate a generator?

Ed

 

[hforney500]

Re: Emergency Generator for Multiple Buildings

Originally posted by Ed MacLaren:
Are these buildings existing or yet to be built?

They are existing buildings.


If existing -
1. Do they now have separate utility services, or are they supplied by feeders from a common service?

Separate services.

2. Is there an electrical room in each building that can accomodate a generator?

The electrical room is not large enough, but there is a large storage room which could be used.

Ed

 

[bennie]

Re: Emergency Generator for Multiple Buildings

The physical size, weight, and space, plus the location for ease in servicing, are important things to consider.

Install one unit if primary is connected. 3 units if secondary is connected.

With 3 units, lift the utility neutral.

[ August 27, 2003, 11:06 AM: Message edited by: bennie ]

 

[jerryb]

Re: Emergency Generator for Multiple Buildings

How about using two generators in parallel for the three buildings? The problem with one large unit is the fact that if one building goes off line then the generator will need to start and it will only develop a small load. This condition is not good on large generators (wet stacking).

If you use two generators, then they could be programmed to run based on load requirements.

 

[hforney500]

Re: Emergency Generator for Multiple Buildings

Originally posted by jerryb:
[QB] This condition is not good on large generators (wet stacking).


I was not aware of that "wet stacking".

If you use two generators, then they could be programmed to run based on load requirements.

Using two generators to run based on load requirements would probably cost the same as installing three separate generators. Yes or No?

Your response has been helpful, as the more I learn from this forum the easier it will be to convince "accountants and non-technical persons" of the best solution. I have found out in the past that some A/E firms will sell you more than you need if you don't have a clue as to what is right and wrong.

 

[caj1962]

Re: Emergency Generator for Multiple Buildings

to continue what has already been said to have 1 gen set for 3 buildings, what happens in the gen set fails? you have 3 buildings to respond to with no power. if 1 of 3 fails it limits the area affected. in the great scheme of things ask yourself the question, which is more likely to fail, utility power or a gen set. Your answer should be the gen set. in most areas the utility is more reliable than a generator. I agree having to back up sources would be better than 1 although having 3 would be better and have them all connected together to pick the loads that are set by priority in the controller
1. legally required systems
2. essential equipment
3. nonessintal loads

The wet stacking comment has to do with diesals only. Having a large gen set with minimal load would cause unburned fuel to collect in the exhaust to cause the wetstacking.

Just my humble idea

 

[jhines]

Re: Emergency Generator for Multiple Buildings

We've had similar situations. If possible, use separate generators at each building. If not, then your engineer needs to consider grounding and will probably want to use 4 pole transfer switches. On site fuel is required for emergency use, usually diesel. So, fuel truck access is important. Have the engineers look at sound control, and air flow for cooling.

 

[ron]

Re: Emergency Generator for Multiple Buildings

If there are three separate services, then I would put three seperate generators. If these are life safety gens, than you get additional reliability and not put all eggs in one basket.
The local inspectors may require three seperate gens, since the buildings are currently autonomous, and may someday be owned by different people.
Unless the A/E fee is based on a % of construction cost, they have no reason to spec a larger gen than needed, since it will take more time to design a larger arrangement.

 

[bwyllie]

Re: Emergency Generator for Multiple Buildings

I agree with all the techinal issues raised and it would be the best way to go if this was new construction. Since this is existing buildings there are other issues that factor into this besides what would be ideal. Is there room in each building or on the building property(for 3 generators vs 1 generator)? If the generators go inside each building and are diesel, you must consider the exhaust and fire rating of such buildings. Also by installing 3 generators, you now have 3 pieces of equipment that need service & testing instead of 1(saves money on labor). Also, on a similar project like this we installed one generator for 3 buildings for the life safety systems not only due to space limitations but also the reality of trying to get a generator of 500KVA into an existing building. I am comfortable with the design on 1 generator for these buildings as the likely hood of a generator failure is small.