Tom Lawrence University of Georgia HVAC Overview - # 1 HVAC Systems Overview.

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

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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

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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

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Type of Systems

• All air

• Water / air

• All water

• Centralized versus decentralized

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Typical thermodynamic processes

Cooling and dehumidifying moist air

Evaporative cooling

Dry Bulb Temperature

Hu

mid

ity

Rat

io

(W)

AmbientNearly saturated supply,

Zone conditions,

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Typical processes (Cont’d)

Heating

Ambient

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

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Direct Expansion Air Conditioning

EVAP

Return Air

Outdoor Air

Mixed AirSupply Air

Outdoor AirCOND

Expansion Valve

Compressor

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Common System Types

Central systems, Variable Air Volume (VAV)

Supply Fan

Return Fan

Ventilation Air

VAV SupplyExhaust Air

Conditioning Coils

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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)

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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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Common System Types

Packaged Unit (Rooftop or Sidewall)

Return AirSupply Air

Alternate Supply and Return Ductwork

Direct Expansion CoolingHeat Pump or Gas Fired Heating

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Common System Types

Split-System

Return Air

Supply Air

Furnace

Evaporator

Condensing Unit

Refrigerant Lines

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Chilled Water Systems

Cooling Tower

Chiller

Various System Loads (Coils)

Chilled Water System

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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

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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

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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: