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Lecture Objectives:

Lecture Objectives:. Learn about automatic control Use life-cycle cost analysis integrated in eQUEST. Basic purpose of HVAC control. Daily, weekly, and seasonal swings make HVAC control challenging Highly unsteady-state environment

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Lecture Objectives:

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  1. Lecture Objectives: • Learn about automatic control • Use life-cycle cost analysis integrated in eQUEST

  2. Basic purpose of HVAC control • Daily, weekly, and seasonal swings make HVAC control challenging • Highly unsteady-state environment • Provide balance of reasonable comfort at minimum cost and energy • Two distinct actions: • 1) Switching/Enabling: Manage availability of plant according to schedule using timers. • 2) Regulation: Match plant capacity to demand

  3. Example: Heat exchanger control Modulating (Analog) control Cooling coil air water Basic Control loop x (set point temperature)

  4. Cooling coil control valve Electric (pneumatic) motor Position (x) fluid Volume flow rate Vfluid = f(x) - linear or exponential function

  5. The PID control algorithm For our example of heating coil: constants time e(t) – difference between set point and measured value Position (x) Differential Proportional Integral Differential (how fast) Proportional (how much) Integral (for how long) Position of the valve

  6. The control in HVAC system – only PI Proportional Integral value Set point Proportional affect the slope Integral affect the shape after the first “bump” Set point

  7. Detail control system simulation MatLAB - Simulink Control system simulation - take into account HVAC component behavior but focus more on control devices and stability of control scheme

  8. Models integrated in HVAC System simulation Example: Economizer (fresh air volume flow rate control) Controlled device is damper - Damper for the air - Valve for the liquids fresh air damper mixing recirc. air T & RH sensors

  9. HVAC Control Economizer (fresh air volume flow rate control) Controlled device is damper - Damper for the air - Valve for the liquids fresh air damper mixing recirc. air % fresh air 100% T & RH sensors Minimum for ventilation

  10. Economizer – cooling regime How to control the fresh air volume flow rate? If TOA < Tset-point→ Supply more fresh air than the minimum required The question is how much? Open the damper for the fresh air and compare the Troom with the Tset-point . Open till you get the Troom = Tset-point If you have 100% fresh air and your still need cooling use cooling coil. What are the priorities: - Control the dampers and then the cooling coils or - Control the valves of cooling coil and then the dampers ? Defend by SEQUENCE OF OERATION the set of operation which HVAC designer provides to the automatic control engineer % fresh air 100% Minimum for ventilation

  11. Economizer – cooling regime Example of SEQUENCE OF OERATIONS: If TOA < Tset-point open the fresh air damper the maximum position Then, if Tindoor air < Tset-point start closing the cooling coil valve If cooling coil valve is closed and T indoor air < Tset-point start closing the damper till you get T indoor air = T set-point Other variations are possible Sequence of calculation in energy simulation modeling is different than sequence of operation ! We often assume perfect aromatic control

  12. Example of Sequence of calculation in energy simulation models

  13. Life Cycle Cost Analysis • Engineering economics

  14. Life Cycle Cost Analysis • Engineering economics • Compound-amount factor (f/p) • Present worth factor value (p/f) • Future worth of a uniform series of amount (f/a) • Present worth of a uniform series of amount (p/a) • Gradient present worth factor (GPWF)

  15. Parameters in life cycle cost analysis Beside energy benefits expressed in $, you should consider: • First cost • Maintenance • Operation life • Change of the energy cost • Interest (inflation) • Taxes, Discounts, Rebates, other Government measures

  16. Example • Using eQUEST analyze the benefits (energy saving and pay back period) of installing - low-e double glazed window - variable frequency drive

  17. Example project T3 T4 Floor heating system Solar radiation Floor heating tank Perforated tube P2 Floor heating system

  18. Solar collector system Total solar radiation Area Solar collector Property of solar collector Water flow Water tank Used energy coefficient which define lost of energy from solar collector surfaces to surrounding define lost of energy from water tank to surrounding

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