1. Lecture Objectives: Discuss HW4 parts
Learn about modeling of HVAC systems

2. Which part of the building is the most responsible
Which part of the building is the most responsible? Building Envelope vs. HVAC System
(AHU and distribution systems)
Plant
(boiler
and/or
Chiller)
Building

3. Building Envelope vs. HVAC System
Load - System - Plant Model
Building
Qbuiolding
Heating/Cooling
System Q
including
Ventilation
and
Dehumidification
Plant
Electric
Energy
Gas

4. Building HVAC Systems (Primary and Secondary Building HVAC 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.
In many situation even more!
(or Gas)
Gas

5. eQUEST HVAC Models
Predefined configuration for typical systems (no change)
Divided according to the cooling and heating sources
Details in eQUEST help file:
For example:
DX Coils No 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 Coils Furnace
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.

6. Examples of HVAC System
Multizone Dual Duct System
Multi zone VAV with Re-heaters
55°F
90°F
55°F P C P C
Perimeter (P)
Core (C)

7. Dual Duct vs. VAV with Re-heaters for Different Weather Conditions
What happens
if outdoor air is
A, B, C A B C

8. Example of a Plant System (Chilled Water System)
Air cooled chiller
Chiller with a cooling tower
COP ~ 3
COP ~ 5
COP = Cooling Energy / Electric Energy ( same units)

9. Two Basic Approaches for Modeling of HVAC and Building Envelope
Load System Plant model
Building
Qbuiolding
Heating/Cooling
System Q
including
Ventilation
and
Dehumidification
Plant
Integrated models
Building
Heating/Cooling
System
Plant

10. Example of a HVAC Model 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]

11. Example of a 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

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

13. 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: