Lecture Objectives:

1
Lecture Objectives

• Discuss HW3 parts d) e)
• Learn about HVAC systems
• Role of HVAC system in the energy performance
• Differences between typical systems (examples)
• Modeling

2
Example of Energy Consumption in an Office
Building (Austin 20,000 sf)
Questions 1) How to put gas and electric
consumptions on the same graph 2) Which part of
the building is the most responsible for
the energy performance
3
Gas and Electric Consumptions
a) Use pricing
b) Convert gas to electricity
70 x106 Btu (76 x106 kJ or 21,000
kWh)
185,000 kWh
Gas is 4.5 of an energy bill
11.5
When we convert gas to electricity 3.8
4
Energy PrinciplesSite Energy vs. Primary Energy

• Site (End-use) energy is the energy directly
  consumed by end users
• Primary energy is site energy plus the energy
  consumed in the production and delivery of energy
  products

Primary Energy
Light
Thermal
Fresh air
HVAC System
Site energy (End use)
HVAC Heating, Ventilation and Air-Conditioning

Site Energy
Primary Energy
Distribution
Storage
Generation
5
Gas (Thermal) Energy vs. Electric Energy

• Two approaches for comparison
• Convert everything to electric energy
• Convert everything to primary energy
• General conversion factor
• 1kWh thermal energy 1/3 kWh electric energy

6
Which part of the building is the most
responsible?Building Envelope vs. HVAC System
(AHU and distribution systems)
Plant (boiler and/or Chiller)
Building
7
Building Envelope vs. HVAC System
Load - System - Plant Model
Building
Heating/Cooling System
Plant
Qbuiolding
Q including Ventilation
and Dehumidification
Gas
Electric Energy
8
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!
Gas
(or Gas)
9
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

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Examples of HVAC System
Multi zone VAV with Re-heaters
Multizone Dual Duct System
55F
90F
55F
P
C
P
C
Perimeter (P)
Core (C)
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Dual Duct vs. VAV with Re-heatersfor Different
Weather Conditions
What happens if outdoor air is A, B, C
A
B
C
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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)
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Two Basic Approaches for Modeling of HVAC and
Building Envelope
Load System Plant model
Building
Heating/Cooling System
Plant
Qbuiolding
Q including Ventilation
and Dehumidification
Integrated models
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Example of a HVAC ModelSchematic 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
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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 ?T
Evaporation at 1oC
TCWS5oC
TCWR11oC
water
Building users (cooling coil in AHU)
COP is changing with the change of TOA
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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)
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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
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