Ventilation Requirements of Warehouse with LPG Forklifts
Ventilation Requirements of Warehouse with LPG Forklifts
(OP)
I was asked to look at the energy consumption of a small (55,000 sq. ft) conditioned warehouse (72 deg. F) in a mild climate (Los Angeles Area). The warehouse has six 30 ton package units with economizers and exhaust dampers. What I don't understand is that it has twelve 42"x48" gravity hoods (about 6" screen opening around the perimeter of each). I assume that these are for fresh air requirements for the use of some forklifts (maybe six forklifts max.). I have a couple of questions:
1) Does anyone have a good rule of thumb (or more rigorous method) of determining the amount of outside air that is coming in through these gravity hoods? I looked in the ASHRAE Fundamentals but the natural ventilation calculations looked very complicated with not much hope of being very accurate even for all of the trouble. At the moment my best guess is looking at an equivalent Greenheck gravity hood flow at the lowest pressure drop (.057"), about 6600 cfm. I know that with the package units running it won't exactly be natural convection.
2) Does anyone know of any requirements for ventilation for forklifts? It would seem that closing off the uncontrolled air entry of the gravity hoods and using demand control ventilation by measuring CO2 and CO and controlling the OA to the package units would be better.
I might also suggest using electric forklifts which most of the cold storage warehouses use.





RE: Ventilation Requirements of Warehouse with LPG Forklifts
RE: Ventilation Requirements of Warehouse with LPG Forklifts
I agree with BronYrAur that these may be remnants of a intake/exhaust system prior to the current warehouse mechancial cooling RTUs. Perhaps these can be closed off now that the 30-ton units have intake and relief capabilities, unless there are off-season times when they want to exhaust/intake without running the RTUs. Are there other independent mechancial fans for intake or exhaust at the warehouse? At any rate, if these gravity hoods are always "open", and they are needed at certain times, a revised set-up where you can positiviely open and close dampers at these devices would probably save some energy.
Regarding forklift ventilation, a good book for your arsenal in addition to the ASHRAE stuff should be the ACGIH Industrial Ventialtion--A Manual of Recommended Practice (I have Edition 22). In here they give some rules of thumb for dilution ventilation for lift trucks:
5,000 CFM/propane-fueled lift truck
8,000 CFM/gasoline-fuled lift truck.
Hope that helps.
RE: Ventilation Requirements of Warehouse with LPG Forklifts
Thank you for reminding me of the ACGIH Industrial Ventilation Handbook. I have access to one.
I think that you both are right in that the gravity hoods are left over from when the warehouse was not conditioned. I have estimated from the power bills that the facility uses 235,000 kWh for air conditioning and have modeled in eQUEST that it should only use 35,000 kWh so I am going to suggest that motorized dampers be installed on the gravity hoods. Also intake and exhaust fans could be installed on some of them and then a night air cooling system could be used for cooling instead of using the air conditioners.