Tom LawrenceUniversity of Georgia

HVAC Overview - # 1

HVAC Systems Overview

Tom LawrenceUniversity of Georgia

HVAC Overview - # 2

Agenda

• Psychrometric questions?– Larger ‘psycho’ chart

• Email address list

• Project teams formed… topics?

• Overview of HVAC systems, types

Tom LawrenceUniversity of Georgia

HVAC Overview - # 3

HVAC Systems Overview

Equipment

External Factors• Ambient temperature, humidity• Solar radiation• Wind

Internal Factors• Occupants• Moisture gains• Acceptable environment (comfort, health and safety)• Internal air distribution

Tom LawrenceUniversity of Georgia

HVAC Overview - # 4

General Design Issues with HVAC

• Determine required indoor conditions – Temperature and humidity

levels

– Ventilation

• Determination of loads (cooling or heating)– Heat transmission through

building shell

– Heat gains from occupants

– Heat gains from lighting and equipment

– Ventilation and infiltration/exfiltration

• HVAC system type– Building size, # of subdivisions

– Local energy prices

– Local climate

– Initial cost versus life cycle cost

• Other considerations– Energy usage

– Indoor air quality

Tom LawrenceUniversity of Georgia

HVAC Overview - # 5

Type of Systems

• All air

• Water / air

• All water

• Centralized versus decentralized

Tom LawrenceUniversity of Georgia

HVAC Overview - # 6

Typical thermodynamic processes

Cooling and dehumidifying moist air

Evaporative cooling

Dry Bulb Temperature

Hu

mid

ity

Rat

io

(W)

AmbientNearly saturated supply,

Zone conditions,

Tom LawrenceUniversity of Georgia

HVAC Overview - # 7

Typical processes (Cont’d)

Heating

Ambient

Ambient, Zone conditions, Mixed zone/ambient, Heating to supply air,

Tom LawrenceUniversity of Georgia

HVAC Overview - # 8

Direct Expansion Air Conditioning

EVAP

Return Air

Outdoor Air

Mixed AirSupply Air

Outdoor AirCOND

Expansion Valve

Compressor

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HVAC Overview - # 9

Common System Types

Central systems, Variable Air Volume (VAV)

Supply Fan

Return Fan

Ventilation Air

VAV SupplyExhaust Air

Conditioning Coils

Tom LawrenceUniversity of Georgia

HVAC Overview - # 10

Common System Types

Central systems, Dual Duct

Supply Fan

Return Fan

Ventilation Air

Mixing BoxesExhaust Air

Cooling Coil (Cold Deck)

Filters

Heating Coil (Hot Deck)

Tom LawrenceUniversity of Georgia

HVAC Overview - # 11

Common System Types

Fan Coil Units (Unit Ventilator)

Supply Fan

Ventilation Air

Cooling Coil

Filters

Return Air

Heating Coil Drain Pan

Supply Air

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HVAC Overview - # 12

Common System Types

Packaged Unit (Rooftop or Sidewall)

Return AirSupply Air

Alternate Supply and Return Ductwork

Direct Expansion CoolingHeat Pump or Gas Fired Heating

Tom LawrenceUniversity of Georgia

HVAC Overview - # 13

Common System Types

Split-System

Return Air

Supply Air

Furnace

Evaporator

Condensing Unit

Refrigerant Lines

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HVAC Overview - # 14

Chilled Water Systems

Cooling Tower

Chiller

Various System Loads (Coils)

Chilled Water System

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HVAC Overview - # 15

Energy Recovery from Ventilation Air

• One common approach is enthalpy wheel

Exhaust

Intake

Cooling Mode

Return Air

Supply Air

Exhaust Air

Outdoor Air

Heating Mode

OA

Return AirSupply Air

Exhaust Air

Tom LawrenceUniversity of Georgia

HVAC Overview - # 16

Economizer Systems

Supply Air @ Mixed Conditions

Return Air

Recirculation Air

Exhaust Air

Outdoor Air

• Get ‘free cooling’ by using up to 100% outdoor air supply to room

• Controllers use enthalpy (T and H) or temperature only for control decision

Tom LawrenceUniversity of Georgia

HVAC Overview - # 17

Economizer Systems

Ambient

Ambient, Zone conditions, Mixed zone/ambient,

1h

2h 3h

1 1 3 32

1 3

m h + m hh

m m

Mixed air conditions:

supply air 3 2Q = m (h h )

Cooling provided to building: