1. Lecture Objectives:
Differences in Conduction Calculation in Various Energy Simulation Programs
Modeling of HVAC Systems

2. Methods for conduction calculation
Finite difference or finite volume method
Weighting factor method
Response factor method
or Response function method

3. Methods for conduction calculation
Finite difference or finite volume methods
Used in your HW assignments
Energy simulation program
ESPr
Some models in TRANSYS
Some models in EnergyPlus

4. Conduction with finite difference (volume) method
Example room

5. System with the finite difference (volume) method for conduction calculation

6. Weighting factor methods
The simplest method
T external air
T internal air
Q solar
Orientation and
Wall (or element) structure
Heat flux on
internal surface
database q
Q HVAC q
Building

7. System when we know the fluxes thought building walls
We need to find other way to calculate fluxes

8. Response function methods
Used in eQUEST program

9. Response function methods
NOTATION: θ(x,t)=T(x,)

10. Laplace transformation
Laplace transform is given by
Where p is a complex number whose real part is positive and
large enough to cause the integral to converge.

11. Laplace transformation table

12. Principles of Response function methods
The basic strategy is to predetermine the response of a system to some unit excitation relating to the boundary conditions anticipated in reality.
Reference:
JA Clarke
Book form the Reference List

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

14. Psychrometrics – review

15. 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

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

17. 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)

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

19. 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

20. HW3 System simulation Simplified model (use ii in your HW3a):
Use the results from HW2 and calculate the sensible cooling requirement for 24 hours for ten identical rooms like the one from HW2b.
If infiltration/ventilation provides 1 ACH calculate the latent load from infiltration 24 hours for ten identical rooms like the one from HW2b.
Calculate the total cooling load for 24 hours for ten identical rooms like the one from HW2b.
Use this as Q cooling () for HW3b
Note: This method:
- assumes perfect process in AHU
to control RH sometimes we need to heat and cool at the same time
- neglects fan power
- dos not consider system properties and control
Variable Air Volume or Constant Air Volume

21. Plant Models: Chiller P electric () = COP () x Q cooling coil ()
TOA
What is COP for this
air cooled chiller ?
T Condensation = TOA+ ΔT
Evaporation at 1oC
TCWS=5oC
TCWR=11oC
water
Building users (cooling coil in AHU)
COP is changing with the change of TOA

22. HW3 Chiller model: COP= f(TOA , Qcooling , chiller properties)
Chiller data: QNOMINAL nominal cooling power,
PNOMINAL electric consumption for QNOMINAL
The consumed electric power [KW] under any condition
Available capacity as function of evaporator and condenser temperature
Cooling water supply
Outdoor 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: