How do you cal./estimate the actual KW demand for a building for utility contract limit?

[zemingduan]

Hi I am an electrical designer. We do the load calculations according to the NEC to size the electrical equipment rating and determine the service conductors size. The utility company(PECO) is asking the client/us for a contract limit for PECO's High Tension service (13.2KV service) of a building we design. The contract limit is a KW demand. If the actual demand is less than 40% of the contract limit, the client will still be charged based on the 40% of the contract limit for the transmission.

The NEC calculated KVA/KW is overkilled for the actual KW demand. If we use the NEC calculated KW, there will be money loss for the client. But how do we estimate the actual KW demand to avoid money loss for the client but still reserve enough power from the utility power grid? Do you have any similar experience?

This building has 247 apartments, one CVS pharmacy and one Aldi supermarket. Who usually calculate/estimate the actual KW demand? Shall we ask the Aldi and CVS stores in the same area of the similar size for the actual demand?

Thank you!!

 

[charlie b]

I doubt that you will get any useful information from Aldi or CVS.

Do you have all the information you need for a service load calculation (e.g., square footage, typical unit's appliances, the building's HVAC and plumbing loads, any fire pump, recreational rooms or common amenities, or other house loads)? Start by doing that calculation. If you give that KVA result to the utility, they will size their transformer around 40% of that value.

Your situation is a bit unusual. Giving the utility your calculated service load is not the same as telling them that their contract with the building's owner should include a clause that limits the maximum demand. You need to NOT be in the middle of that discussion. I suggest that you give your client a "recommended" value for the contract limit, and more importantly, tell them the basis for that recommendation. Leave it to your client to make the decision.

As you pointed out, the actual maximum demand will never exceed the calculated service load. Here would be my approach: Let's say the service calculates at 2000 KVA. The utility will likely give you a 750 KVA transformer. The actual max load is likely to be under 500 KVA. You want the client to not have to pay for 40% of the contract limit, if the actual load is under 40%. 500 KVA is 40% of 1250 KVA. If you recommend a contract limit of 1250 KVA, and still show a 2000 KVA load in your design documents, then your client won't have to pay for 800 KVA (i.e., 40% of 2000 KVA).

Play with the numbers and see what works best for you and for your client.

 

[electrofelon]

What happens if the actual demand is over what you tell them?


It's kinda odd/annoying/strange they won't help you with this, as they certainly have very accurate figures of what an apartment building with the same parameters will draw. Also seems like they could easily look up the demand from another CVS store. If someone put a gun to my head and said come up with a figure now, I would guess 40-50% of the NEC calc value would be very close.

 

[MyCleveland]

Have you ran into this issue on previous projects ? I have never seen this before.
What I have seen is LOWER rates promised IF a large customer always maintains a large demand, and if not the rate schedule changes.

I would start with discussions with the metering department for clarification and the State Utilities Commission to see if this is even legal.

Most importantly, as CB stated, let the owner finalize the billing arrangement. Your job is done with a valid load schedule per NEC requirements.
If this becomes a norm for your area, your company needs a policy adopted on how to address this going forward.

Please follow up later on how this ends.

 

[jim dungar]

We have had similar utility billing practices/contracts for almost 30 years.

Many developers are good with the contract for utilities, do not take this on as your responsibility.

One key thing to remember is the POCO is interested in the actual KW Demand, while the NEC is worried more about service size. Decades ago, before LEDs, the lighting load had by far the largest impact on the KW demand for a store, like CVS, I would assume the refrigeration would also an issue for a supermarket like Aldis.

 

[zemingduan]

I am so glad that you guys willing to join the discussions! Thank you so much!

I also found that the transformer sized by the utility company is usually 40%-50% of the NEC calculated load especial for the residential building or residential building with light duty commercial tenants. But I am not able to say if this rule still applies to the heavy duty commercial application such as supermarket, or restaurant using all electrical cooking's since most of our projects are residential buildings.

Here is an example for what we did for another project regarding the contract limit. It is a (128) apt. residential buildings with no commercial tenants. The calculated NEC load for the whole building is around 1887 KVA including the loads of (128) apt., fire pump, amenities spaces (such as gym, work lounges, parking garage) and all other house loads. For this building, the loads do not exceed the limits of the so called "General Service" (208Y/120V 3ph or 480Y/277V 3ph service). For General Service, the utility own the transformers (either pad mount or transformers bank in the vault room). PECO is willing to tell us the transformer sized by them is 750 KVA (around 40% of the NEC calculated loads). But the owner decided to go with 13.2 KV high-tension (HT) service since limited site space for the pad mount XFMR. Thus PECO ask contract limits for HT service. We just suggest the owner to set the contract limits as 750 kw.

I like charlie b approach better, It has some safety for us.

Here would be my approach: Let's say the service calculates at 2000 KVA. The utility will likely give you a 750 KVA transformer. The actual max load is likely to be under 500 KVA. You want the client to not have to pay for 40% of the contract limit, if the actual load is under 40%. 500 KVA is 40% of 1250 KVA. If you recommend a contract limit of 1250 KVA, and still show a 2000 KVA load in your design documents, then your client won't have to pay for 800 KVA (i.e., 40% of 2000 KVA).

Play with the numbers and see what works best for you and for your client.

But for this projects, the loads exceed the limit of the General Service and PECO can only provide HT service. PECO refuse to provide us their calculations of the KVA loads for the HT service....

Luckliy, we only design the apartments and house part of the building but not fit-out of the CVS and Aldi. We decide to only provide the numbers for the residential and house parts based on the 40%-50% of the NEC loads of that part and make some adjusting of the numbers to have some safety. But defer the other part to the owner/ fit-out engineer.

 

[zemingduan]

What happens if the actual demand is over what you tell them?

I also ask the utility similar questions. I asked them if I can reduce the contract limit if the actual demand is much less the contract limits and what will happen if the actuals demand is higher than the contract limits, Here is their answer.

"Yes, contract limits can be adjusted however once the contract limit is reduced there may not be available capacity in the future (without cost to the customer) to return to the original contract limit if the customer’s load increases. That capacity could be used for another customer.


And no there won’t be any penalty or surcharge is you go over your max contract limit. If you choose to set your max at 750 and you end up using 850 you will just pay for 850 kw. Now if you continue to go over your contract limits then we will need to have a conversation about changing them. But we also understand that this can happen from time to time, especially during the summer months when customer typically use more usage. So I wouldn’t be too concerned."

My understanding and guess is that if you set the contract limit too low to a point that the actual demand is constantly higher than it, and if the area's utilities has no more capacity for you, the utility will ask you to pay the upgrade.

 

[JoeStillman]

I would try not to underestimate it. If they pay a ratchet penalty in the first year or two they'll learn a good lesson about the difference between connected load and demand, then adjust the limit downward.

PECO has a better crystal ball than you do. They just give you disclaimers because they can't control a customer's usage. Only the customer can.