Lecture Objectives: Finish wit introduction of HVAC Systems Introduce major ES software

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

Example of 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

Energy and mass balance equations for Air handling unit model – steady state case m S is the supply air mass flow rate c p - specific capacity for air, T R is the room temperature, T S is the supply air temperature. w R and w S are room and supply humidity ratio - energy for phase change of water into vapor The energy balance for the room is given as: The air-humidity balance for room is given as: The energy balance for the mixing box is: ‘r’ is the re-circulated air portion, T O is the outdoor air temperature, T M is the temperature of the air after the mixing box. The air-humidity balance for the mixing box is: w O is the outdoor air humidity ratio and w M is the humidity ratio after the mixing box The energy balance for the heating coil is given as: The energy balance for the cooling coil is given as:

Non-air system Radiant panel heat transfer model

The total cooling/heating load in the room The energy extracted/added by air system The energy extracted/added by the radiant panel: T he radiant panel energy is: The energy extracted/added by the radiant panel is the sum of the radiative and convective parts:

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 (  )

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

Energy Simulation (ES) Programs

Structure of ES programs Solver Interface for input data Graphical User Interface (GUI) Interface for result presentation Preprocessor Engine Preprocessor ASCI file ASCI file

Modeling steps Define the domain Analyze the most important phenomena and define the most important elements Discretize the elements and define the connection Write energy and mass balance equations Solve the equations Present the result ES program Preprocessor Solver Postprocessor

Characteristic parameters Conduction (and accumulation) solution method – finite dif (explicit, implicit), response functions Time steps Meteorological data Radiation and convection models (extern. & intern.) Windows and shading Infiltration models Conduction to the ground HVAC and control models

ES programs Large variety DOE2 eQUEST (DOE2) BLAST ESPr TRNSYS EnergyPlus (DOE2 & BLAST)

eQUEST (DOE2) US Department of Energy & California utility customers eQUEST - interface for the DOE-2 solver DOE-2 - one of the most widely used ES program - recognized as the industry standard eQUEST very user friendly interface Good for life-cycle cost and parametric analyses Not very large capabilities for modeling of different HVAC systems Many simplified models Certain limitations related to research application - no capabilities for detailed modeling

ESPr University of Strathclyde - Glasgow, Scotland, UK Detailed models – Research program Use finite difference method for conduction Simulate actual physical systems Enable integrated performance assessments Includes daylight utilization, natural ventilation, airflow modeling CFD, various HVAC and control models Detail model – require highly educated users Primarily for use with UNIX operating systems

TRNSYS Solar Energy Lab - University of Wisconsin Modular system approach One of the most flexible tools available A library of components Various building models including HVAC Specialized for renewable energy and emerging technologies User must provide detailed information about the building and systems Not free

EnergyPlus U S Department of Energy Newest generation building energy simulation program ( BLAST + DOE-2) Accurate and detailed Complex modeling capabilities Large variety of HVAC models Some integration wit the airflow programs Zonal models and CFD Detail model – require highly educated users Very modest interface Third party interface – very costly