Final Project Format and Deliverables Examples http://www.ce.utexas.edu/prof/Novoselac/classes/ARE383/Projects.html Examples http://www.ce.utexas.edu/prof/Novoselac/classes/ARE383/Handouts.html

Lecture Objectives: Finish with Building-System-Plant connection HVAC Systems Accuracy of the Modeling Software

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

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

Energy and mass balance equations for Air handling unit model – steady state case The energy balance for the room is given as: mS is the supply air mass flow rate cp - specific capacity for air, TR is the room temperature, TS is the supply air temperature. The air-humidity balance for room is given as: wR and wS are room and supply humidity ratio - energy for phase change of water into vapor The energy balance for the mixing box is: ‘r’ is the re-circulated air portion, TO is the outdoor air temperature, TM is the temperature of the air after the mixing box. The air-humidity balance for the mixing box is: wO is the outdoor air humidity ratio and wM 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:

Cooling coil model To enable coupling of air handling unit model with the chiller model We need cooling coil model: Models gives a relationship between the supply temperature (Tref_in) and return temperature (Tref_out) of the circulating fluid for a given mass flow rate (mref) of this fluid thorough the cooling coil Cooling coil Tair_in Tair_out mair Air wair_in wair_out mref Tr_in Tr_out The cooling coil effectiveness (E) describes this relationship: E = f(Tair_in ,wair_in ,Tr_in , mair ,mref) Also, it depends on the cooling coil geometry and type of circulating fluid (water or refrigerant)

Non-air system Radiant panel heat transfer model

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: The energy extracted/added by the radiant panel is the sum of the radiative and convective parts: The radiant panel energy is:

Integration of HVAC and building physics models Load-System-Plant model does not work in cases when HVAC components radiate to other surfaces We have to use Integrated models: Qrad_plant T surrounding surfaces Tw_out Building Heating/Cooling System Plant T surrounding surfaces mw, Tw_in External weather parameters Solve simultaneously system of equation or use iterative procedure.

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.

Accuracy of Building Energy Simulation Tool Large number of: Analytical Numerical Empirical models for energy and mass transfer calculation in building envelope and building systems

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

Accuracy of energy simulation There are many different factors for inaccuracy of energy simulation results …..... …….

Accuracy of energy simulation Depends on 2 Assumptions - simplification which you introduced to solve the problem - level of details in your analytical and numerical models 1 Input data geometry material properties weather data operation schedule 3 Numerical methods - used to solve equations from analytical and numerical models Find the balance ! Always think what you want to achieve (what kind of analysis you want to provide)

How to check the validity of the larger simulation models? Energy balance Building room: large number of analytical and Numerical equations (sub-models)

How to evaluate the whole building simulation tools Two options: Comparison with the experimental data - monitoring - very expensive - feasible only for smaller buildings 2) Comparison with other energy simulation programs - for the same input data - system of numerical experiments - BESTEST

Comparison with measured data Cranfield test rooms (from Lomas et al 1994a)

BESTEST Building Energy Simulation TEST System of tests (~ 40 cases) - Each test emphasizes certain phenomena like external (internal) convection, radiation, ground contact Simple geometry Mountain climate COMPARE THE RESULTS

Example of best test comparison

What are the reasons for the energy simulation Design (sizing of different systems) Economic benefits Impact on environed Budget planning

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