![]() The reduction in pressure is measured at the OA measuring station as lower, along with a reduction in OA supplied. As the demand in the building lowers from a SA of 9000 to 2250, VFDs on the supply fan reduce airflow, which in turn reduces velocity and static pressure. Same thing happens, we return 2250, and exhaust 500 before mixing the 1750 back in with 500 OA. ![]() In minimum airflow, we need 500 OA and 2250 SA. The OA measuring station figures out the velocity pressure required for 500 CFM at this max flow rate and sets its dampers, along with the RA dampers, to maintain this. If we mix that 9000 RA with 500 OA, we are above our requirement, so we exhaust 500 EA. but most common is directly measuring OA flow rate with a OA measuring station and modulating the OA and RA dampers to maintain a constant OA, reliving at excess airflow to exhaust.įor example in your maximum airflow rate, we need 500 OA and 9000 SA. OA is held constant at 500 CFM no matter if your AHU is supping your minimum 2250 CFM or the maximum 9000 CFM. Set up your AHU to handle Vot and allow it to distribute in your building as loads change. To answer your question about maintaining individual VAV box OA rates, you do not worry about this. Basically the higher the fraction of OA from 6.2.5.1, the lower your efficiency:Ħ.2.5.3 is the basic uncorrected outdoor air rate (number of people times people ventilation rate, plus square footage ventilation rate times square footage).Ħ.2.5.4 Takes your Vou (uncorrected outdoor air) answer and accounts for the efficiency of the ventilation system found in 6.2.5.2 to give you your corrected outdoor air flow rate: Vpz is the minimum expected primary airflow to the zone from the air handler including recirculated airĦ.2.5.2 Establishes ventilation efficiency from Table 6-3. This is for three simple zones only, what about 40 zones or more?Īm I right, or reading the standard in a wrong way? RE: VAV box minimum postion and ventilation equirments RandomUserName (Mechanical) 15 Sep 15 12:54Ħ.2.5.1 Calculates your primary outdoor air fraction. To reach 100 cfm in zone A in this case, we need either a total outdoor air of 1166 cfm, means double of full load requirement, or to increase the minimum position to 1052 cfm instead of 500 cfm, then we have to recalculate again. The outdoor coming to zone A in this case would be 500x500/5250 = 47 cfm. Now if all boxes are in minimum, each zone would get his outdoor requirement, but,if zones A&B were in minimum and zone C was in full load, then the total cfm would be 5250 cfm, the outdoor is still 500 cfm Standard says ventilation should be available under any operation condition. Minimum VAV position 25% each (500, 750, and 1000 cfm) Outdoor air in breathing zone requirement 100, 150, and 250 cfm with total of 500 cfm. Supply air rates are 2000, 3000, and 4000 cfm with total of 9000 cfm. Let us say all efficiencies mentioned in the standard equal to 1, Three zones, A, B, and C, served by three VAV boxes. I am reading ASHRAE 62, 2007, multiple zone calculation and trying to apply on an example from my imagination. How do we consider the VAV box minimum position.?
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |