1. Lecture Objectives: Finish with software intro HVAC Systems
Specifics for eQUEST
HVAC Systems
and modeling of HVAC Systems

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

3. 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

4. ESPr University of Strathclyde - Glasgow, Scotland, UK
Detailed models
– Research program

5. 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

6. Component-based simulation programs - Trnsys

7. 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
Till last year
Very modest interface
Third party interface – very costly
Recent development: open studio

8. EnergyPlus

9. 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

10. eQUEST Download it at http://doe2.com/equest/ Examples related to:
Defining envelope and internal loads
Selecting HVAC system
Presenting results
Finding design cooling and heating loads
Extracting simulation detail

11. HVAC systems Review Building-System-Plant connection Psychrometrics
Air-conditioning in Air Handling Units (AHU)
Refrigeration cycles
Building-System-Plant connection

12. Psychrometrics – review

13. Air-conditioning in Air Handling Unit (AHU)
Roof top AHU
Gas/Electric Heater
to building
Fan
air from building
fresh air
Evaporator
filter
mixing
AHU schematic
Exhaust
From room
Return fan
flow control dampers
Supply fan
Compressor and Condenser
Fresh air
To room
Outdoor air
hot water
cool water

14. Processes in AHU presented in Psychrometric in psychrometric
Case for
Summer in Austin OA MA IA SA

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

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

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

18. 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

19. 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]

20. 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:

21. Non-air system Radiant panel heat transfer model

22. 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: