Shutting down AC units to save power .

[Davebones]

We have a 300,000 square ft manufacturing area . We have the AC units mounted on the roof . Parts of the building sometimes work 24-7 .The units over these area's are left running if they are working . There's the question is it more efficent to turn off other area units completely or raise the set points of the units to save power .The whole building is pretty much open space .

 

[masterinbama]

I had an energy management engineer tell me the rule of thumb is 5 degrees or 5 days. If the area is to be unoccupied for less than 5 days move the set point no more than 5 degrees.

 

[sgunsel]

This is a complicated question that needs a thorough engineering evaluation to arrive at an intelligent answer. It depends on (at least): ambient temperatures and humidity, cooling capacity and efficiency of each unit, energy costs including time of day differentials, AC unit spacing, available air moving capability, insulation, bulding tightness, controls, and the desired workspace temperature and humidity requirements. I would not rely on "rule of thumb".

 

[kingpb]

This is a complicated question that needs a thorough engineering evaluation to arrive at an intelligent answer. It depends on (at least): ambient temperatures and humidity, cooling capacity and efficiency of each unit, energy costs including time of day differentials, AC unit spacing, available air moving capability, insulation, bulding tightness, controls, and the desired workspace temperature and humidity requirements. I would not rely on "rule of thumb".

I agree with everything you stated. Just going to add that the expertise required to make these determinations is mostly mechanical engineering, with some electrical input.

 

[Article 90.1]

Not sure where this job is, but remember that AC's also reduce humidity from their area, which may be important for your material inventory, even if the space is unoccupied. You may be better off to raise the set points when unoccupied because of this.

 

[broadgage]

This may be a case where experiment is of more use than theoretical arguments.
Try both approaches, perhaps on alternate weeks, and note the energy used.
If the A/C load is a large proportion of the total bill, then simply read the utilty meter frequently.
Alternatively fit check meters to the A/C plant.