Outdoor airflow rate, building static pressure, supply airduct static pressure, and relief air plenum static pressure, ascontrolled variables, are maintained by modulating the speedof the supply and return fans and the position of the outdoor,recirculating, and relief air dampers in an air-handling unit(AHU). The three dampers are often interlinked completely orpartially to match independent control inputs with thecontrolled variables. The traditional damper control has allthree dampers interlinked with no control over the relief airplenum static pressure. Reverse relief airflow might occur asthe outdoor air damper approaches the closed position. Toprevent reverse airflow, one solution is to decouple the reliefair damper and maintain positive static pressure at the reliefair plenum. Two control methods are available based on thecontrolloopdesign.Thefirst controlmethoduses the return fanspeed to control the relief air plenum static pressure and therelief air damper to control the building static pressure,and thesecond control method switches two control inputs.The purpose of this paper is to evaluate the controllabilityof the reverse relief airflow and building static pressure of thesetwo control methods. The system performance is investigatedthrough steady-state simulations on an AHU at differentoutdoor airflows using a nonlinear network solution. Thesimulation results show that both the control methods can wellpreventreversereliefairflow.However,thefirstcontrolmethodwith a constant pressure setpoint may result in negative buildingstatic pressure at lower outdoor airflow ratio and eitherexcessivelypositivebuildingstaticpressureorexcessivereturnfan power at higher outdoor airflow ratio. The second controlmethod shows better control over the building static pressurecontrol. A reset pressure scheme should be associated with thefirst control method when the relief damper is fully open.
Citation: 2016 Winter Conference, Orlando, FL, Transactions 2016, Vol 122 pt. 1
Product Details
- Published:
- 2016
- Number of Pages:
- 12
- Units of Measure:
- Dual
- File Size:
- 1 file , 3.2 MB
- Product Code(s):
- D-OR-16-028
