ALFA LAVAL Compact Heat Exchangers in HVAC Systems

7/27/2019 ALFA LAVAL Compact Heat Exchangers in HVAC Systems

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Compact Heat Exchangersin HVAC systems

ASHRAE meeting in Mxico City 2009-01-13

Martin CronaAlfa Laval Lund AB


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Compact heat exchangers for HVAC

Heat transfer characteristics

Topics of the presentation

Content

Alfa Laval Slide 2

CHE in HVAC applications CHE Components

Design guidelines


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Compact heat exchangers

in HVAC systems

Enables high energy efficiency

Close temperature approach

Small temperature losses

Increased temperature drop

Fast response times at regulation Limited footprint

Compact design

High thermal efficiency

Easy service

Openable for mechanical cleaning

Expansion of capacity possible

Alfa Laval Slide 3


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Gasketed plate heat exchangers

Brazed Heat Exchan ers

Alfa Laval Slide 4

All-welded heat exchangers

Fusion bonded heat exchangers


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Compact heat exchanger

Alfa Laval Slide 5


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PHE basic components Carrying bar

Frame plate

Pressureplate

Plate packTightening bolts


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Gasketed plate heat exchanger

Pack of corrugated plates sealed by gaskets

Possible to open for cleaning and extension

Pressure range 0-30 barg

Alfa Laval Slide 7

Temperature range -25 C to 180 C Flexible connections sizes (20mm) to 500mm

Flexibility in plate and sealing material selection


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Brazed heat exchangers

BHE = Brazed Heat Exchanger

Compact design

Corru ated stainless steel

BHE - design

Frame plate

Connections

Alfa Laval Slide 8

plates Cupper as brazing material

Main use in heating andrefrigeration duties

Max temperature: 225C

Max pressure: 32 barg

Foil

Heat transferplate


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Fusion bonded heat exchanger

FHE = Fusion bonded Heat Exchanger Compact design

100% stainless steel

FHE - design

Alfa Laval Slide 9

n corruga es p a es

Stainless steel as bonding material

Max temperature: 550C

Max pressure 32 barg

Main use in ammonia and corrosivemedias


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All-welded heat exchanger Gasket free HE for high temperatures or

pressures

Many types exist

Plate types

Plate & Shell

Alfa Laval Slide 10

Openable block type

Spiral heat exchangers

Steam condensation is primaryapplication in HVAC

Welded HE main use is in chemicalindustry

Plate type

Plate & shell


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Compact heat exchangerCharacteristic

Feature PHE BHE FHE WHE

Flow / Capacity Connection size 20mm 500mm 20mm 100mm 20mm 100mm 50mm 250mm*

Temperature Max temperature 180C 225C 550C 300C*

Pressure Max designpressure

30barg 32barg 32 barg 60barg*

Serviceability Mechanical Yes No No No / partly*cleaning

Cost efficiency Cost ratio 3 1 2 4-5*

Risk of fatigue(only relevant in steamduties)

Fatigueresistance

Excellent OK OK OK*

Medias to use Corrosionresistance

Flexibility in plateor gasketmaterial

Limited bycupper

Limited bystainless steel

Flexible in platematerial

Primary HVAC applications -all duties withintemp andpressure range

-small capacities-clean medias-freon duties

-ammonia duties-tap water

-steamcondensation

Alfa Laval Slide 11

*depend on WHE type


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HVAC applications Cooling interchanger

Free cooling

Pressure breaker

Condensor protection

Ice stora e

District cooling

Heat recovery

Domestic hot water

Pool Solar heating

Alfa Laval Slide 12


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Efficient heat transfer

Cold fluid in at T2 In

Mass flowrate m2

Cold fluid out at T2 OutMass flowrate m2

Hot fluid in at T1 InMass flowrate m1

Definitions

Q = Heat load, kBTU/h (W)

(rate of heat transfer)

m = Mass flow rate, lb/s(kg/s)

Cp= Specific heat, J/kgC(the energy needed

1 Out

Mass flowrate m1

Heat released by the hot fluid: Q1=m1*Cp1*(T1 In-T1 Out)

Heat absorbed by the cold fluid: Q2=m2*Cp2*(T2 Out -T2 In)

No heat loss Q1 = Q2

Heat transfer equation Q=u*A*LMTD

Pressure drop P=k*v2

to heat 1 kg of the fluidwith 1C)


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Heat transferred in a HE

The temperature profile at one point of the plate wall

Wall

Flow direction

T1, Bulk temperature on hot side

Hot side

T

T3

T2, Bulk temperature on cold side

Flow direction

Cold side

More turbulence Thinner laminar film

Increased u-value

Better Heat Transfer

1/u = 1/hot + 1/cold + /


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Close temperature approach

Thermal definitions

Ex. T

Tcold,out

Cold water to chiller

Water to A/C in house

Thot,out

Water return from house

Thot,in

1

2

T,in

T,hot

Alfa Laval Slide 15

2

1ln

21

=LMTD

Cold water from chiller

,

LMTD

TTNTU

outcoldincold

coldcold

,,

==LMTD

TT=NTU

outhotinhot

hothot

,,

=

Higher NTU means more difficult heat transfer

LMTDs possible down to 1F

Normal NTU in HVAC Cooling 6-7

NTU in district cooling upto 9

Increased NTU means increased area


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Energy efficiency

Q = 1700 kBTU/h

47F

57F

45F

55F

47F

57FCOP = 3,4

80F

90F

78F

88F

Qcond = 2200 kBTU/h

50F

40F

Alfa Laval Slide 16

Qcool (kBTU/h)

LMTD (F)

Qchiller (kW)

Loss

Direct

1700

-

146-

PHE

1700

2

154-5%

S&T

1700

7

174-18%

High energy efficiency with PHE

Less loss on condensor side


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HE comparisonCompact heat exchangeradvantages

Smaller foot print

Less weight

Less fouling risk

6ft

5ft

Alfa Laval Slide 17

20ft

No fouling factor needed indesign

Small hold-up volume

Easier maintenance

Easier installation


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System optimization

47F

57F

45F

55F

58F 60F

46F

56F

Alfa Laval Slide 18

Q = u * A * LMTD

Smaller LMTD give larger heat exchanger

LMTD 2 down to 1 give A up 250%

Smaller pressure drop give larger heat exchanger

P down from 7 to 3,5 psig give A up 40%

Larger temperature drop enables smaller flow

3F larger T mean 25% smaller flow


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Energy savings with chiller by-pass

Q = 1700 kBTU/h

47F

60F

45F

58FCOP = 3,4

80F

90F

78F

88F

Qcond = 2200 kBTU/h

45F

58F

Alfa Laval Slide 19

Low temperatures in winter time for cooling source

Low wet bulb temperature in cooling towers

Low water temperature in water cooling

When cooling temperature go below A/C temperature

Chiller by-pass is possible

156 kW is saved

Pay-back often within 1-2 years


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Alfa Laval Slide 20


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PHE full serviceability Carrying bar

Frame plate

Pressureplate

Plate packTightening bolts


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Corrosion factorsIn cooling and heating there is with some water qualities riskof crevice corrosion and pitting corrosion.

Basic condition is that free oxygen and chlorides must bepresent and the corrosion risk depends on the factors below

Alfa Laval Slide 22

Factor Change Influence

Chloride content

Temperature

pH Level


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Plate - materials Standard materials and typical uses AISI 304

Typically in clean water-water duties

Example, up to 50 ppm chlorides at 50C

AISI 316

Typically in water-water duties

254 SMO (high-alloy stainless steel) Many uses including high-chloride water-water duties

Example, up to 6000 ppm chlorides at 50C

Titanium

Most frequent use is for sea water (3.5% chlorides) Example, up to 130C in sea water


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Gasket - materials The choice of rubber material depends on Temperature

Required lifetime

Media

Rubber materials change properties due to

Time - the rubber relaxes

-

Hardening by attack of oxidising agents (e.g., oxygen in air)

Swelling or softening by absorption of chemicals in the fluids

Common gasket types

Nitrile

EPDM

FKMT


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Fi l te r

A filter for industrial coolingsystems using low-quality water

Protecting the heat exchanger

The Filter operates as an integralpart of a cooling system to removedebris which can foul and clog aplate heat exchanger or a tubularcondenser.


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in HVAC systems

Enables high energy efficiency

Close temperature approach Small temperature losses

Increased temperature drop

Fast response times at regulation

Limited footprint

Compact design

High thermal efficiency

Easy service

Openable for mechanical cleaning

Expansion of capacity possible

Alfa Laval Slide 26


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Thank you!

Alfa Laval Slide 27

Questions?

ALFA LAVAL Compact Heat Exchangers in HVAC Systems

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