1. Final Project Format and Deliverables Examples
Examples

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

3. 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

4. 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]

5. 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:

6. 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)

7. Non-air system Radiant panel heat transfer model

8. 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:

9. 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.

11. 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.

12. 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

13. 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

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

15. 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)

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

17. 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

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

19. 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

20. Example of best test comparison

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

22. 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