cem 350 hvac air side systems 10-2016

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Air Conditioning & Refrigeration: CEM 350 Facility Systems Design Air-Side Systems

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Page 1: Cem 350 hvac air side systems 10-2016

Air Conditioning & Refrigeration:

CEM 350 Facility Systems DesignAir-Side Systems

Page 2: Cem 350 hvac air side systems 10-2016

Contents

• Fundamental HVAC Concepts• Air Handling Units• Air System Basics

• Fan-duct systems• Fan modulation & combinations• Year-round operation & economizers• Fan energy use & outdoor air

Page 3: Cem 350 hvac air side systems 10-2016

Fundamental HVAC Concepts

• Five subsystems or loops of HVAC• Air-side• Chilled water• Refrigeration equipment• Heat rejection• Controls

Page 4: Cem 350 hvac air side systems 10-2016

33 oC, 28 oC

27 oC33 oC

25 oC

Conditioned space

Page 5: Cem 350 hvac air side systems 10-2016

13 oC 13 oC

33 oC, 28 oC

27 oC33 oC

25 oC

Air side system

Page 6: Cem 350 hvac air side systems 10-2016

13 oC 13 oC

12 oC

7 oC

33 oC, 28 oC

7 oC

12 oC

27 oC33 oC

25 oC

Chilled watersystem

Page 7: Cem 350 hvac air side systems 10-2016

13 oC 13 oC

12 oC

7 oC 3 oC38 oC

49 oC10 oC

33 oC, 28 oC

7 oC

12 oC

27 oC33 oC

25 oC

Refrigerationequipment

Page 8: Cem 350 hvac air side systems 10-2016

13 oC 13 oC

12 oC

7 oC 3 oC38 oC

49 oC10 oC

35 oC

29 oC

33 oC, 28 oC

7 oC

12 oC

29 oC

35 oC

27 oC33 oC

25 oC

Heat rejection

Page 9: Cem 350 hvac air side systems 10-2016

13 oC 13 oC

12 oC

7 oC 3 oC38 oC

49 oC10 oC

35 oC

29 oC

33 oC, 28 oC

7 oC

12 oC

29 oC

35 oC

27 oC33 oC

25 oC

Control Loop

Page 10: Cem 350 hvac air side systems 10-2016

Individual room air-conditioning system

Page 11: Cem 350 hvac air side systems 10-2016

Primary air fan coil unit system

Page 12: Cem 350 hvac air side systems 10-2016

Dual duct system

What type of air conditioning system it is?

Page 13: Cem 350 hvac air side systems 10-2016
Page 14: Cem 350 hvac air side systems 10-2016

Air Handling Units

• Terminal unit or device• Such as fan coil units, VAV boxes

• Air handling unit (AHU)• Primary equipment of the air system• Handle & condition the air, control it to a required

state, and transport it• Basic components:

• Supply fan, water cooling coil, filters, mixing box, dampers, controls & outer casing

• A return or relief fan is optional, so as a humidifier

Page 15: Cem 350 hvac air side systems 10-2016

Air Handling Units

• Types of AHUs:• Horizontal or vertical• Draw-through or blow through• Factory-fabricated and field built-up• Rooftop and indoor• Make-up (primary) air • Recirculating

Page 16: Cem 350 hvac air side systems 10-2016
Page 17: Cem 350 hvac air side systems 10-2016
Page 18: Cem 350 hvac air side systems 10-2016

Air Handling Units

• Package units• A self-contained air conditioner• Equipped with a DX (direct expansion) coil• “Air handler”: the portion inside that handles air

• Rooftop package units• Gas heating / electric cooling• Electric heating / electric cooling• Heat pump system

Page 19: Cem 350 hvac air side systems 10-2016
Page 20: Cem 350 hvac air side systems 10-2016

Air Handling Units

• Indoor package units• Factory-assembly unit installed in a fan room or

machinery room• Floor-mounted or ceiling-mounted• Cooling, cooling/heating, heat pump• Heat rejection:

• Connected to an air-cooled condenser, OR• Water-cooled condenser

• Split package units• Indoor air handler + outdoor condensing unit

Page 21: Cem 350 hvac air side systems 10-2016

Air Handling Units

• Rating conditions & minimum performance• ARI and ASHRAE standards• Rating indices:

• Energy efficiency ratio (EER)• Seasonal EER• Integrated part-load value (IPLV)• Heating seasonal performance factor (HSPF)

Page 22: Cem 350 hvac air side systems 10-2016

Air Handling Units

• Coils• Indirect contact heat exchangers• Heat transfer between air flowing over the coil and

water, refrigerant, steam or brine insider the coil• Fins: extended (secondary) surfaces

• Fin spacing and density• Water circuits

• Number of water flow passages

Page 23: Cem 350 hvac air side systems 10-2016

Air Handling Units

• Direct expansion (DX) coil• Refrigerant is fed (e.g. R-22 and R-134a)• Air and refrigerant flow:

• Usually counterflow and cross flow• Typical evaporating temperature = 3-10 oC• Condensate drain pan (to collect condensation)• Performance factors:

• Face velocity, heat transfer coefficients, air-side pressure drop, physical size

Page 24: Cem 350 hvac air side systems 10-2016

Air Handling Units

• Water cooling coils - dry-wet coil• Chilled water flowing at 4-10 oC• Brine or glycol-water at 1-4 oC• Temperature rise (typical) = 7-14 oC

• Water cooling coils - dry coil• Sensible cooling (dry); no condensation• Poorer heat transfer coefficient

• Steam heating coil

Page 25: Cem 350 hvac air side systems 10-2016

Direct expansion (DX) coil

Water cooling coil

Page 26: Cem 350 hvac air side systems 10-2016

Water heating coil

Steam heating coil

Page 27: Cem 350 hvac air side systems 10-2016

Air Handling Units

• Air filters• Air cleaning and filtration• Operating performance:

• Efficiency or effectiveness of dust removal• Dust holding capacity• Initial & final pressure drop• Service life

• Types: low-, medium-, and high-efficiency filters + carbon activated filters

Page 28: Cem 350 hvac air side systems 10-2016

Air Handling Units

• Test methods of air filters• Weight arrestance test

• For low-efficiency air filters• Atmospheric dust spot efficiency

• For medium-efficiency air filters• DOP (dioctyl phthalate) penetration and efficiency

test• For high-efficiency air filters

• HEPA (high-efficiency particle air)• ULPA (ultra-low penetration air)

Page 29: Cem 350 hvac air side systems 10-2016

Low efficiency (panel-type) Medium efficiency (bag-type)

HEPA and ULPA filters Activated carbon filter

Page 30: Cem 350 hvac air side systems 10-2016

Air Handling Units

• Humidifiers• Steam humidifiers• Air washers

• Selection of AHUs• Face velocity < 3 m/s to prevent entrained droplets• Proper size of the equipment (energy efficiency)• Medium-efficiency filter >50% dust spot eff.:

improve IAQ, prevent smudging & discoloring• Air economizer: save energy

Page 31: Cem 350 hvac air side systems 10-2016

Steam grid humidifier

Page 32: Cem 350 hvac air side systems 10-2016

Air washer

Page 33: Cem 350 hvac air side systems 10-2016

Air-side Components

• EcoAdvisor: Energy Trainer for Energy Managers: HAVC Module 1 [AV 697 E19]• HVAC components

• Distribution equipment• Air-side components

• Dampers, filters, coils, fans, ducts and plenums, terminal units, diffusers, humidifiers, dehumidifiers

Page 34: Cem 350 hvac air side systems 10-2016
Page 35: Cem 350 hvac air side systems 10-2016

Air System Basics

• Fan-duct systems• Flow resistance R, pressure drop Δp and volume flow

rate V

• Duct sections in series:• Duct sections in parallel:

2VRp o

ns RRRR 21

np RRRR1111

21

Page 36: Cem 350 hvac air side systems 10-2016

Air System Basics

• Fan-duct systems• Terminology

• Primary air (conditioned air or makeup air)• Secondary air (induced space air, plenum air, or

recirculating air)• Transfer air (indoor air that moves from an adjacent

area)• System curve: volume flow vs pressure loss• System operating point

Page 37: Cem 350 hvac air side systems 10-2016

Air System Basics

• Fan Laws• Speed (n)• Volume flow (V)• Total pressure loss (Δp )• Air density (ρ)• For air systems that are

geometrically & dynamically similar: (D = impeller diameter)

Page 38: Cem 350 hvac air side systems 10-2016

Air System Basics

• System effect Δpts• Its additional total pressure loss caused by uneven

or non-uniform velocity profile at the fan inlet, or at duct fittings after fan outlet

• Due to the actual inlet and outlet connections as compared with the total pressure loss of the fan test unit during laboratory ratings

Inlet Outlet

Page 39: Cem 350 hvac air side systems 10-2016

Fan system operating point & system effect

Page 40: Cem 350 hvac air side systems 10-2016

Air System Basics

• Modulation of air systems• Constant volume system

• Volume flow rate remains constant; supply temperature is raised during part load

• Variable-air-volume (VAV) system• Volume flow rate is reduced to match part load

operation• Modulation curve

Page 41: Cem 350 hvac air side systems 10-2016

Fan modulation curve

Page 42: Cem 350 hvac air side systems 10-2016

Air System Basics

• Fan modulation methods• Damper (vary the opening of the air flow passage)

• Waste energy• Inlet vanes (opening & angle of inlet vanes)

• Low cost; less efficient than following types• Inlet cone (peripheral area of fan impeller)

• Inexpensive; for backward curved centrifugal fan• Blade pitch (blade angle of axial fan)• Fan speed (using adjustable frequency drives)

• Most energy-efficient; but more expensive

Page 43: Cem 350 hvac air side systems 10-2016

Damper, inlet vanes & fan speed modulation

Page 44: Cem 350 hvac air side systems 10-2016

Air System Basics

• Fan combinations in AHUs• Supply and exhaust fan/barometric damper

• Used when no return duct or low return pressure loss• Barometric relief damper: to prevent excessive high

space pressure• Suitable for systems w/ no air economizer mode & a

low pressure drop in return system

Page 45: Cem 350 hvac air side systems 10-2016

Supply and exhaust fans

Page 46: Cem 350 hvac air side systems 10-2016

Air System Basics

• Fan combinations in AHUs• Supply and relief fan

• Relief fan to prevent excessive high space pressure• Usually operated in air economizer mode• Outdoor air damper is fully opened; recirculating

damper closed• Suitable when pressure drop of return system < 75 Pa,

or there is a considerable pressure drop in relief or exhaust flow passage

Page 47: Cem 350 hvac air side systems 10-2016

Supply and relief fans

Page 48: Cem 350 hvac air side systems 10-2016

Air System Basics

• Fan combinations in AHUs• Supply and return fan

• Return fan at the upstream of the junction of return, recirculating and exhaust flow passage (ru)

• Has similar characteristics as supply+relief fan, but a higher total pressure at junction “ru”

• Careful selection of return fan is needed to avoid excessive pressure in the duct system

• Suitable when pressure drop of return system > 150 Pa, or those requiring a negative space pressure

Page 49: Cem 350 hvac air side systems 10-2016

Supply and return fans

Page 50: Cem 350 hvac air side systems 10-2016

Air System Basics

• Year-round operation of a VAV system• Region I: Refrigeration/evaporative cooling

• Enthalpy of outdoor > that of recirculating air• Region II: Free cooling & refrigeration

• Enthalpy of outdoor ≤ that of recirculating air• Region III: Free cooling, evaporative cooling &

refrigeration• Enthalpy of outdoor ≤ that of recirculating air

• Region VI: Winter heating

Page 51: Cem 350 hvac air side systems 10-2016

Control diagram of a VAV reheat system for year-round operation

Page 52: Cem 350 hvac air side systems 10-2016

Year-round operationRegion I: Refrigeration/evaporative coolingRegion II: Free cooling & refrigerationRegion III: Free cooling, evaporative cooling & refrigerationRegion VI: Winter heating

Page 53: Cem 350 hvac air side systems 10-2016

Air System Basics

• Economizer• A device consisting of dampers and control that

uses free cooling capacity of either outdoor air or evaporatively cooled water from cooling tower instead of mechanical refrigeration

• Air economizer:• Enthalpy-based• Temperature-based

• Water economizer

Page 54: Cem 350 hvac air side systems 10-2016

Air System Basics

• Fan energy use• For each l/s air

supplied:

• For system using separate outdoor ventilation:

mf

sypsl

W

1000/

mf

sySO

pR

slW

1000

)1(/ ,

Page 55: Cem 350 hvac air side systems 10-2016

Air System Basics

• Outdoor ventilation air supply• Aims

• Provide acceptable indoor air quality• Achieve energy efficiency in the system

• ASHRAE Standard 62-2001 (IAQ standard)• Demand-based outdoor ventilation air control using

CO2 as an indicator• CO2 concentration < 800-1,000 ppm

• A specific indoor air contaminant can also be used

Page 56: Cem 350 hvac air side systems 10-2016

Air System Basics

• Outdoor ventilation air supply• Minimum outdoor air control

• Type I: uses a CO2 or mixed gas sensor + DDC controller to control the volume flow rate of outdoor air

• The best one but can be expensive

• Type II: uses a CO2 or mixed gas sensor + DDC controller to control the ratio of the openings between outdoor and recirculating dampers

• Suitable for VAV system

Page 57: Cem 350 hvac air side systems 10-2016

Air System Basics

• Outdoor ventilation air supply• Minimum outdoor air control (cont’d)

• Type III: uses a flow sensor or a pressure sensor + DDC controller to control the dampers to provide nearly constant volume outdoor air intake

• More complicated & may cause energy waste

• Type IV: adjust the opening of outdoor damper manually to provide constant volume outdoor air

• Mainly used for constant-volume systems