Waterside energy-recovery hourlong-chicago_ashrae

© 2011 Ingersoll Rand

WatersideEnergy RecoveryRequirements, Design and Application

WatersideEnergy RecoveryRequirements, Design and Application

Mick Schwedler, PEmanagerTrane applications engineering

reasons to useEnergy Recovery Required by code or standard

Availability of simultaneous heatingand cooling loads

Economically justified Reduces heating load Reduces ancillary power

Environmentally responsible Reduces emissions Eligible for “green” benefits (energy, water

usage)

ASHRAE 90.1-2010 (since 1999)Waterside Energy Recovery

Facility operates 24 hours per day Heat rejection exceeds 6 million Btu/hr

(~ 450 tons)

Design service water heating load exceeds 1 million Btu/hr

Required energy recovery is(smaller of): 60% of design heat rejection

Preheating water to 85°F

IF …

THEN

types ofHeat-Recovery Chillers Single condenser (“bundle”)

Dual condenserEqually sized

bundles

Auxiliary condenserUnequally sized

bundles

standardcondenser

heat-recovery

condenser=

standardcondenser

heat-recovery

condenser>

heat-recovery chillersSingle Condenser

centrifugal compressor

scroll compressor

helical-rotary (screw)compressor

heat-recovery chillersDual Condenser

heat-recoverycondenser

standardcondenser

evaporatorwater-cooled chiller withcentrifugal compressor

heat-recovery leaving capacity chillercondenser water control? efficiencyFull capacity hot yes decreasesPartial capacity warm no increases

heat-recovery chillersComparison of Options

Chiller condenser optionCharacteristic Dual Auxiliary “Heat pump”

Configuration Second, Second, No extrafull-size smaller condensercondenser condenser

Application Large Preheating Large base-heating loads heating loadsloads or continuous

operation

Leaving water Hot Warm Hot

Capacity control? Yes No Yes

Chiller efficiency Decreases Increases Acceptable

variable air volumeTempering Supply Air When required supply/primary airflow is less than minimum setting:

Reduce primary airflow to minimum

Let space temperature drift downward

Add heat to avoid overcooling105°F (40.6°C) water often is sufficient

Supply air is always dehumidifiedSupply air is always dehumidified

waterside heat recoveryTemperatures

Service-water 85°F to 95°Fpreheating (29.4°C to 35°C)

Space heating 105°F to 110F(40.6°C to 43.3C)

source: 2008 ASHRAE Systemsand Equipment Handbook

Effectively balancesheat-recovery temperaturesand system pressure drops

tempering VAV supply airHeating Coil Selectionselection parameter 1-row coil 2-row coilEntering water 113°F 105°FCoil flow rate 4.33 gpm 1.75 gpmFluid delta-T 6.02°F 14.91°FCoil fluid pressure drop 10.3 ft H2O 0.21 ft H2OAir pressure drop:

design cooling airflow 0.45 in. wg 0.79 in. wgminimum airflow (est) 0.04 in. wg 0.07 in. wg

Leaving-coil (primary) air 75°F 75°F

waterside heat recoveryEffect on Chillers Compressor work is proportional

to lift “Lift” is pressure difference between evaporator

and condenser

Warmer condenser water (for heat recovery)raises condenser pressure

Changes in lift affect different compressors differently Positive displacement

Centrifugal (full load vs. part load)

positive-displacement water chillerRefrigeration Cycle

enthalpy

pre

ssu

re

evaporator

compressorliquid/vaporseparator

expansiondevice

condenser

16

7

5

4 3

heat recovery

2

positive-displacement water chillerCapacity

temperature rise (leaving-condenser water)

100

0° 10° 20° 30° 40°

chill

er c

apac

ity,

%

80

60

40

20

0

compressortype:

scrollscrew

temperature rise (leaving-condenser water)

100

0° 10° 20° 30° 40°

pow

er in

crea

se,

% k

W/

ton

80

60

40

20

0

compressortype:

scrollscrew (S)

positive-displacement water chillerEfficiency

screw (M)screw (L)

centrifugal chiller performancePower Increase

condenser water temperature, °F

26

pow

er in

crea

se,

% k

W/

ton

10

imp

eller diam

eter, inch

es

20

30

40

085 87 89 91 93 95 97 99

28

30

32

power increase

impeller diameter

compressorchange

Heat recoveryChiller 85-105 F

centrifugal chiller comparisonEfficiency

Operating modeChiller type Cooling Heat recovery

Cooling only 0.57 kW/ton Not applicable(6.2 COP)

Heat recovery 0.60 kW/ton 0.69 kW/ton(5.9 COP) (5.1 COP)

Entering to leaving water temperatures:Evaporator 54°F to 44°F 54°F to 44°F

(12.2°C to 6.7°C) (12.2°C to 6.7°C)

Condenser 85°F to 95°F 85°F to 105°F(29.4°C to 35.0°C) (29.4°C to 40.6°C)

heat-recovery chiller controlCondensing Temperature

% load

% m

axim

um

pre

ssu

re d

iffe

ren

tial

B

CA

unloading with constantleaving hot-water temperature

unloading with constantentering hot-water temperature

Compressor type Acceptable basis of control

Positive displacement Entering-condenser water temperature

Leaving-condenser water temperature

• Provides less capacity• Uses more power

Centrifugal Entering-condenser water temperature

• Reduces likelihood of surge

heat-recovery chiller controlCondensing Temperature

Energy Recovery Topics Airside

Outdoor air Types Requirements Operation

Supply air tempering Requirements Operation

Waterside Requirements

Types

System configurations

Operation

system configurationPrimary–Secondary

Available heat= 150 × (52.6 – 40)= 1890 MBh

Auxiliary heat required= 2000 – 1890= 110 MBh

Available heat= 150 × (52.6 – 40)= 1890 MBh

Auxiliary heat required= 2000 – 1890= 110 MBh

heat-recoverychiller production

(supply)

distribution(demand)

40°F825 gpm56°F

40°F225 gpm

52.6°F

40°F

40°F

52.6°F

52.6°F

off

750 gpm

300 gpm

system configurationPreferential Loading

Available heat= 150 × (56 – 40)= 2400 MBh

Rejected heat= 2400 – 2000= 400 MBh

Available heat= 150 × (56 – 40)= 2400 MBh

Rejected heat= 2400 – 2000= 400 MBhproduction

(supply)

distribution(demand)

40°F825 gpm56°F

40°F225 gpm

51.2°F

40°F51.2°F

off

750 gpm

heat-recoverychiller

40°F56.0°F

300 gpm

525 gpm

system configurationsSidestream Loading

Available heat= 150 × (56 – 42.7)= 2000 MBh

No rejected heatNo auxiliary heat

Available heat= 150 × (56 – 42.7)= 2000 MBh

No rejected heatNo auxiliary heat

production(supply)

distribution(demand)

40°F825 gpm56°F

40°F75 gpm

50.2°F

40°F50.2°F

off

900 gpm

heat-recoverychiller

42.7°F56°F

300 gpm

51.2°F

system configurationsSidestream LoadingControl strategies:

Satisfy heating requirements

Maintain leaving-condenserwater temperature(positive-displacement compressors)

system configuration comparisonHeat Available/Required

System configurationPrimary–

Characteristic secondary Preferential Sidestream

Cooling load:cooling-only units 393 tons 350 tons 383 tonsheat-recovery unit 157 tons 200 tons 167 tons

Heat-recovery 40°F 40°F 42.7°Fsupply temperature

Available heat 1890 MBh 2400 MBh 2000 MBh

Auxiliary heat 110 MBh –400 MBh* 0 MBhrequired

*Surplus recovered heat must be rejected

system configurationsVariable Primary Flow

VFDmodulating control valvefor minimum chiller flow

Piping heat-recovery chillerin sidestream position maysimplify control

Piping heat-recovery chillerin sidestream position maysimplify control

controlvalve

bypass line

heat-recoverychiller

system configurationsDistributed SidestreamTypical application:

Remote heating requirement

Chilled water load

Small chiller (or water-to-water heat pump)

chilled watersupply or return

heatingload

heat-recovery chiller

airside system optionsLoad-shedding economizer

outdoor-airtemperature sensor

controller

chilled watersupply or return

heatingload

heat-recovery chiller

Control cooling load soheat rejection equals

heating load

airside system optionsLoading chiller with exhaust airstream

EAEA

RARAEAEA

spacespace

OAOA SASAMAMA CACA

CC

T

HH T HH

CC

Water to chillerWater to chiller

Water from chillerWater from chiller

single condenserHeat-Recovery Control

water-cooledchiller

condenser

evaporator

coolingtower

P P

P

coolingload

heatingload

V2heat

exchanger

T2

controller

T1

V1controller

Dual-Condenser Chillers

heat-recoverycondenser

standard condenserpiped to cooling tower

centrifugalheat-recovery chiller

dual condenserHeat-Recovery Control

water-cooledchillerevaporator

P

standardcondenser heat-

recoverycondenser

heatingload

P

coolingtower

P

coolingload

V2

T2

auxiliaryheat

PT1

Control based onentering-condenserwater temperature

Control based onentering-condenserwater temperature

controller

controller

Analysis ToolstoolSystem Analyzer™

TRACE™ Chiller PlantAnalyzer

EnergyPlus, HAP, TRACE

applicationHigh-level scoping (< 1 hr)

Simplified building entries

Full analysis of chilled water plant, economic rates

Full energy simulation

Hour-by-hour calculations of energy consumption, power demand, related costs

Waterside Energy Recovery Steps Simultaneous heating

and cooling loads

Chiller HR capacity = Design heat recovery load

Select lowest temperature that meets requirements

Select the proper chiller type

Analyze the system

Place the chiller(s) in the appropriate system location

Design the system with the proper connections and controls

Train the building operators

Operate the system properly

waterside heat recoveryReferencesFrom Trane:

Waterside Heat Recovery in HVAC SystemsSYS-APM005-EN

1991 Engineers Newsletter: “Two GoodOld Ideas Combine to Form One New Great Idea”http://www.trane.com/commercial/library/EN20-1.pdf

By others:2008 ASHRAE Handbook: HVAC Systems and Equipmentchapter 8

2003 ASHRAE Journal: “Energy Efficiency for Semiconductor Manufacturing Facilities”Ralph M. Cohen, PE (August issue)

waterside heat recoveryReferences

2008 ASHRAE Handbook: HVAC Systems and Equipmentchapter 8

2003 ASHRAE Journal: “Energy Efficiency for Semiconductor Manufacturing Facilities”Ralph M. Cohen, PE (August issue)