Multiple A/C Units_Share Service
Multiple A/C Units_Share Service
(OP)
Hi everybody, I'm working on the calculations for a strip mall consisting of 10 tenant spaces. 2-10kVA Heating units for two spaces and 8-8kVA Heating units for the remaider spaces. Cooling load is less than Heating, so only the heating load is considered. Is there any rules that allow derrating the 10 units in order to size the service or do I have to use 84kVA? Since chances that all units run at the same time are very, very low. Each tenant space will have a panelboard which will feed the Heating units. The supply voltage is 120/208Y 3-phase 4-wire and the Heating units are rated for 208V 1-phase.
Thanks.
Thanks.






RE: Multiple A/C Units_Share Service
RE: Multiple A/C Units_Share Service
And, if the power has been off for a while, you can be certain that they will all be on at the same time for as long as it takes for them to catch up once the power comes back on.
RE: Multiple A/C Units_Share Service
How are you metering?
Individual spaces, one meter?
Corona
RE: Multiple A/C Units_Share Service
RE: Multiple A/C Units_Share Service
Or are you trying to determine the proper size of transformer to supply all of them with?
On the load side of the meter, I don't believe the NEC will allow you to diversify the load.
On the line side of the meter, take the total load (kVA) of all units and multiply by 70% to size the transformer.
Happiness is a way of travel, not a destination.
RE: Multiple A/C Units_Share Service
steelerfan28655, I'm trying to size the service main breaker for the main disconnect. The utility company will size the transformer. I think you are right, the NEC don't let you diversify this type of load. Is just that with all the lighting, show window lighting, sign lighting receptacles & misc. the calculations result in a 800A service 782A to be exact(Non-Continuous + Continuous). The problem is that if the owner has to add more load right after it is built because some tenants will require it, based on the calculations the service may not be enough to accomodate the new load. Until all the spaces are fully occupied we wont have any data from the Utility company or can't perform a study to determine the actual demand from the building to prove that the actual demand is lower than the calculated per NEC. Is a 11,500 sq-ft building, to me 800A service seem to be a lot for this building.
RE: Multiple A/C Units_Share Service
RE: Multiple A/C Units_Share Service
RE: Multiple A/C Units_Share Service
RE: Multiple A/C Units_Share Service
Pechez les vaches.
RE: Multiple A/C Units_Share Service
This large of a building is also allowed to have a dedicated sevice lateral from the utility transformer to each tenant, what is known as the large area building rule. Also, each tenant will have a fire rated wall between the other tenant which would qualify this structure as 10 buildings for electrical service purposes. Therefore, you can have up to 6 service switches for each tenant. For instance, on some utilities commercial electric heat has to be on its own meter because of discount rates such as Ohio Edison's rate 22 seasonal rate.
You also did not tell us how many square feet for each tenant. The other loads can add up really fast and could also necessitate a second air conditioner. You also did not tell us what kind of climate that you have or what kind of electrical rates that you have. If you live in an area where power is cheap such as Bonneville Power Administration tenants will tend to plug in and turn on all kinds of power hungry toys.
For what an air conditioner costs you could upgrade these units to air source heat pumps which will save your tenants a lot of money curing mild weather. Here in Cleveland, Ohio about 75% of the heating season can be handled by an air source heat pump. Just remember than a heat pump needs to be on an elevated base so that a foot of snow will not block it. I have also installed York's relay box for a heat pump that is added onto a fossil fuel furnace.
RE: Multiple A/C Units_Share Service
But also the load for the Show Window Lighting as calculated per NEC is a lot. All the tenant spaces have open window from side to side. The calculated load is (238 l-ft*200 VA/l-ft) 47.6 kVA. Do you know of any rule that allow me to derrate this type of load. I have seen some similar buildings with a 800A service and with tenants using a lot of lighting, so I'm just wondering how they can do it.