Announcement Course Exam: Next class: November 3rd In class: 90 minutes long Examples are posted on the course website

Final Projects Your choice of topics –Visit me during office hours One possible topic AEI Student Competition A mixed use boiling in New York »/Organizational/Department/Engineering Programs/AEI/AEI STUDENT DESIGN COMPETITION/AEI Student Design Competition 2016/AEI Student Design Competition 2016 Project Drawings/Organizational/Department/Engineering Programs/AEI/AEI STUDENT DESIGN COMPETITION/AEI Student Design Competition 2016/AEI Student Design Competition 2016 Project Drawings »/Organizational/Department/Engineering Programs/AEI/AEI STUDENT DESIGN COMPETITION/AEI Student Design Competition 2016/2015 Winning Teams Submissions/Organizational/Department/Engineering Programs/AEI/AEI STUDENT DESIGN COMPETITION/AEI Student Design Competition 2016/2015 Winning Teams Submissions

Lecture Objectives: - Review for the exam -Learn about modeling of HVAC systems -Discuss life cycle cost analysis

Review Heat transfer Building elements External and internal boundary conditions Weather data for boundary conditions Modeling procedures –Numerical methods for solving of model equations

Review of heat transfer How to model: –Convection at surfaces –Radiation between surfaces –Conduction through building elements Steady state or unsteady state

Building elements

Weather data (TMY database) Use them for External boundary conditions Convection Long-wave Radiation Solar radiation Direct Diffuse Reflected (diffuse)

Discretization

Discretization for conduction Section considered in the following discussion Discretization in space Discretization in time T – temperature [C] ρ – density [kg/m 3 ] c p – specific capacity [J/kgK] k- conductivity [W/mK]  – time [sec] x distance [m]

Finite volume (difference) method Boundaries of control volume Internal source for node “I”

Implicit methods - example  =0 To Tw Ti  =36 system of equation Tw Ti  =72 system of equation Tw Ti After rearranging: 2 Equations with 2 unknowns!

Explicit methods - example  =0 To Tw Ti  =360 To Tw Ti  =720 To Tw Ti There is NO matrix to solve! Time

System of equation for implicit method Matrix equation M × t = f for each time step Air b 1 T 1  +  +c 1 T 2  +  =f(T air,T 1 ,T 2  ) a 2 T 1  +  b 2 T 2  +  +c 2 T 3  +  =f(T 1 ,T 2 , T 3  ) a 3 T 2  +  b 3 T 3  +  +c 3 T 4  +  =f(T 2 ,T 3 , T 4  ) a 6 T 5  +  b 6 T 6  +  =f(T 5 ,T 6 , T air ) ……………………………….. M × T = F

Linear systems M * t = f finding matrix inverse is a BAD idea fro large system! Use liner equation solvers. M -1 is matrix inverse: M * M -1 = M -1 *M = I Therefore, t = M -1 *f t1t2t3t1t2t3 f1f2f3f1f2f3 m 11 m 12 m 13 m 21 m 22 m 23 m 31 m 32 m 33 * = M * t=f

Modeling steps Define the domain Analyze the most important phenomena and define the most important elements Discretize the elements and define the connection Write the energy and mass balance equations Solve the equations (use numeric methods or solver) Present the result

Building HVAC Systems (Primary and Secondary Building Systems) AHU Building envelope Cooling (chiller) (or Gas) Electricity Gas Heating (boilers) Fresh air For ventilation Distribution systems Air transport Secondary systems Primary systems AHU – Air Handling Unit HVAC systems affect the energy efficiency of the building as much as the building envelope

Integration of HVAC and building physics models Building Heating/Cooling System Plant Building Heating/Cooling System Plant Load System Plant model Integrated models Q buiolding Q including Ventilation and Dehumidification

Building-System-Plant Plant (boiler and/or Chiller) Building HVAC System (AHU and distribution systems)

T OA water Building users (cooling coil in AHU) T CWR = 11 o C T CWS =5 o C Evaporation at 1 o C T Condensation = T OA + ΔT What is COP for this air cooled chiller ? COP is changing with the change of T OA Example of Plant Models: Chiller P electric (  ) = COP (  ) x Q cooling coil (  )

Plant model Refrigeration Cycle T outdoor air T cooled water Cooling energy (evaporator) Released energy (condenser) - What is COP? - How the outdoor air temperature affects chiller performance?

Chiller model: COP= f(T OA, Q cooling, chiller properties) Chiller data: Q NOMINAL nominal cooling power, P NOMINAL electric consumption for Q NOMINAL Cooling water supplyOutdoor air Full load efficiency as function of condenser and evaporator temperature Efficiency as function of percentage of load Percentage of load: The coefficient of performance under any condition: The consumed electric power [KW] under any condition Available capacity as function of evaporator and condenser temperature

System models Processes in AHU presented in Psychrometric in psychrometric OA Case for Summer in Austin IA MA SA

Example of Detailed System Models: Schematic of simple air handling unit (AHU) m - mass flow rate [kg/s], T – temperature [C], w [kg moist /kg dry air ], r - recirculation rate [-], Q energy/time [W] Mixing box

eQUEST HVAC Models Predefined configuration (no change) Divided according to the cooling and heating sources Details in e quest help file: For example: DX CoilsNo Heating –Packaged Single Zone DX (no heating) Packaged single zone air conditioner with no heating capacity, typically with ductwork. –Split System Single Zone DX (no heating) Central single zone air conditioner with no heating, typically with ductwork. System has indoor fan and cooling coil and remote compressor/condensing unit. –Packaged Terminal AC (no heating) Packaged terminal air conditioning unit with no heating and no ductwork. Unit may be window or through-wall mounted. –Packaged VAV (no heating) DX CoilsFurnace Packaged direct expansion cooling system with no heating capacity. System includes a variable volume, single duct fan/distribution system serving multiple zones each with it's own thermostatic control. –Packaged Single Zone DX with Furnace Central packaged single zone air conditioner with combustion furnace, typically with ductwork. –Split System Single Zone DX with Furnace Central single zone air conditioner with combustion furnace, typically with ductwork. System has indoor fan and cooling coil and remote compressor/condensing unit. –Packaged Multizone with Furnace Packaged direct expansion cooling system with combustion furnace. System includes a constant volume fan/distribution system serving multiple zones, each with its own thermostat. Warm and cold air are mixed for each zone to meet thermostat control requirements.

Life Cycle Cost Analysis Engineering economics

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)

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

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