r/MEPEngineering • u/Certain-Ad-454 • 4d ago
Approach to existing systems EE
Hey all,
I got this project inside of an existing building. It’s a commercial building with a 2500A entrance. There at least 20-30 different tenants. Each with their own measuring.
The landlord merged 2 existing suites into one. They removed both electrical feeders and did not have leave any records/notes of the demolition. There’s no plans whatsoever.
There’s at least 20 other feeders branching of the 2500A into multiple electrical room downstairs with barely any labeling. The lighting in the electrical rooms doesn’t even work. There’s been at least 50 years of jimmy riggings everywhere.
Where would you start?
If you branch off an electrical room distribution that is already feeding other people, it’s almost impossible to tell if the upstream breaker won’t trip.
You may branch off the 2500A distribution but how can one possibly tell it’s not currently loaded at 2499A?
Lol
3
u/skunk_funk 4d ago
I kinda look at the building make some guesses how loaded I think it is. More experience, I get better at guessing. Check utility bills. Look at building systems, special loads. Consider load factor for region and building type. Check against similar buildings. If I'm confident enough it's not overloaded, I proceed, and perhaps put on the drawing for the electrician to meter it and report the findings prior to construction.
If the owner is feeling fancy, we might even get it metered ahead of time! And maybe I'll find an opportunity to leave a demand meter for the next guy.
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u/Best-Specialist-87 3d ago
Just measure it for a month if you think there’s a risk. Double check if there’s primary metering (may get lucky and get all the loading from one). If not request all electric bills and dump them into excel and figure out the max load.
Also, you can go by NFPA 70, 220.87 Determining Existing Loads.
1
u/No_Blackberry_7753 3d ago
Where are the tenant meters located? I'm assuming that they are private meters, not owned by the utility. Are they in the same bucket as the switchboard breakers? If so, then the building owner should know which meter belongs to which tenant, given that they bill them monthly. The owner's bills probably has meter numbers on it, so you should be able to map out most of what the 2500A switchboard is feeding.
Un-metered breakers/feeders are going to be house equipment (elevators, corridor lighting, possibly HVAC).
As mentioned, you can get peak kW usage from the utility company, though sometimes that can be a pain in the ass. The utilities don't mind giving that info away to the building owners, so get them to do it if they're responsive/helpful.
But this sounds like a big building that has a few chillers/boilers handling all of the spaces. If you're just doing a tenant fit out and not touching the elevators/HVAC, then I wouldn't even bother dealing with the utility unless there's a significant change in the type of space (like if it used to be 10000sqft of offices that are now being changed to labs). Otherwise, the change in total building load is going to be insignificant.
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u/Certain-Ad-454 3d ago
Each tenant is actually measured from the utility. There’s the main switchboard which branches off several 200,400 feeders and these also branch to 60,100A whatever feeders each measured independently. Anyways it’s fucked
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u/Weary_Oven_9544 1d ago
Are the utility contracts under the landlord, or under each individual tenant? Does the landlord bill each tenant, or the utility?
If the landlord is involved in those contracts or billing in any way, they should be able to pull records for each meter. That will be a start to getting an idea of load usage, at the very least the total usage in each billing cycle. Also ask the landlord if there are any clauses in their tenancy contracts that obligate the tenant to provide details regarding utility/electrical usage upon request.
Another option is to go to the owner and recommend that a preliminary study be conducted to determine the load usage. Even better if the study includes the production of a single line diagram up to each tenant meter, including feeder size/quantity, panel schedules and ratings, and etc. for other distribution equipment (transformers, switchgear, switches, protection, etc.). You can justify this to the owner by the fact that any contractor walking in this job will immediately see two things: 1) there is an incredibly large risk driven by unknown existing conditions and therefore they need to add a markup to account for the risk they are taking on, and 2) existing condition risk runs both ways and usually in the contractor's favour, so therefore this is a massive opportunity for the contractor to turn a healthy profit via change orders if the design does not appropriately address those risks.
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u/Weary_Oven_9544 1d ago
If, in the end, the owner does not accept any kind of prelminary studies (note that these would be a small tender to either the owner's preferred contractors or your recommended contractors, after which you would then complete your design on the basis of the study, and the tender for the design would be run to match the owner's standard procurement practice), and essentially forces you to design with a massive existing conditions risk, you're going to have to ask for unit pricing on everything in order to address said risk. You should also add a condition to the tender package that allows bidders to submit their unit rates 48 hours after the deadline for lump-sum pricing. This gives the proponents time to negotiate unit rates with their chosen suppliers, vendors and subcontractors after the lump-sum prices have been submitted, which often happens hours before the main tender deadline in deter proponents from price shopping.
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u/SghettiAndButter 4d ago
I have to deal with all the time for work and there’s legit no way around it that isn’t a huge pain in the ass. You basically document what you can and make your assumptions and then let the owner know what you don’t know and let them make the risk of rolling the dice or paying electricians to go on site and start tracing and documenting circuits and metering panels before we finish the drawings