ashrae chiller course condenser water hr

Chiller Course - Condenser HR 1

Chiller Heat Recovery DesignChiller Heat Recovery Design

Julian de Bullet

Director of Industry Relations

McQuay International


Why Consider Heat Recovery?Why Consider Heat Recovery?

� Green Is Good (For Business)

– Conservation of Natural Resources

� Lower Annual Energy Usage

– Reduce Operating Cost

� Provide a Good Life Cycle Analysis



� Air Or Water Side Economizers Are Not Required If:

– “Systems That include A

Condenser Heat Recovery

System Complying With

6.3.6.2” (6.3.1)

� Simultaneous Heating And Cooling Is Allowed If:

– “At Least 75% Of Reheat

Energy Is Provided By Site

Recovered Energy Source” (6.3.2.1)



� Air Side Energy Recovery (MUAs) Not Required If:

– “60% or More of Outdoor Heat

Energy Is Provided From Site

Recovered Energy” (6.3.6.1)

� Condenser Heat Recovery Required For Domestic Hot Water Systems That:

– Operate 24 Hr/Day

– Total THR Is > 6 Million Btu/Hr

� (400 Ton System)

– DHW Load Is > 1 Million Btu/Hr



� LEED (Leadership in Energy & Environmental Design)

� Score Points For Reducing Energy Cost Below ASHRAE

Std 90.1


Heat Recovery RequirementsHeat Recovery Requirements

� The Potential Heat Recovery At Any Point In Time Is The Lesser Of The Heat Source Or The Heat Load

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

BT

U/f

t^2

Heating Cooling

Simultaneous Heating And CoolingSimultaneous Heating And Cooling


Heat Recovery RequirementsHeat Recovery Requirements

� Heat Recovery Can Be Used For Preheat Or Charge Mode

Domestic Hot WaterDomestic Hot Water

0 6 12 18 24

Hour Of The Day

BT

U/f

t^2

Domestic Hot Water Use Boiler Power


VAV With ReheatVAV With Reheat

� VAV Boxes Require Reheat When Minimum Flowrate Is Reached

� Generally Occurs In Mild Or Cold Weather (Winter)

� Can Happen During Morning Warm-up Any Season

� Airside Economizers Will Remove Source


Constant Volume With ReheatConstant Volume With Reheat

� Reheat Used To Warm (55°F) Supply Air As Required By Each Zone

� Required Even On A Design Day

� High Reheat Loads In Cold Weather


� Excellent Choice For Heat Recovery


FancoilsFancoils

� Hot Water Used Whenever A Zone Has A Heat Load

� Four Pipe System Only

� Most Buildings Require Hot Water And Chilled Water In Winter

� WaterSide Economizers Will Remove Source

� Excellent Choice For Heat Recovery


Unit VentilatorsUnit Ventilators

� Unit Ventilators Require Heat When There Is a Heat Load

� Dehumidification May Require Reheat





MultizoneMultizone

� Multizone Control Logic May Require Simultaneous Heating And Cooling

– Only Allowed By Std 90.1 If Reheat Is From Reclaimed Source




Single Condenser HR DesignSingle Condenser HR Design

Heat ExchangerPump

Heat Exchanger

Condenser WaterPump

Chilled WaterPump

Cooling Tower

3-Way BypassValve

Boiler Loop


Split Condenser HR DesignSplit Condenser HR Design

Boiler Loop

Heat RecoveryPump

3 Way BypassValve

Cooling Tower

Chilled WaterPump

Split CondenserHeat Recovery

Chiller


Heat Recovery DesignHeat Recovery Design

� Generally Design Boiler Load Greater Than Design Chiller THR (Total Heat of Rejection)

– Actual Design Heat Recovery Rate Requires Annual Energy Analysis

– Almost Never Boiler Or THR Design Capacity

– Load Will Be Met By Combination Of HR And Boiler

� THR = 1.25 x Chiller Capacity

� Only One Chiller Need Be HR Type In Multiple Chiller Plant

– Must Be First On, Last Off

– System Designs That Backload Chiller Improve HR


Heat Recovery DesignHeat Recovery Design

� Boiler Temperature Range Typically 20°F (180-160°F)

� Condenser Loop Temperature Range 10°F (95-105°F)

� Size Heat Recovery Loop For Design Load

– 3 gpm Per Design Ton At 10°F Range

– This Must Be Less Than The Boiler Flow Rate

� Two Control Schemes

– Maintain Boiler Supply Water Temperature

– Maintain Boiler Return Water Temperature


Maintain Boiler Supply W.T.Maintain Boiler Supply W.T.

� Load Water Temperature Range Proportional To THR

� If Boiler Load = 25% Then Range = 5°F (Based 20°F Range)

� Maintaining 105°F SWT Will Require 100°F Return Load Water

� Guarantees High Lift On Chiller

– Surging

– Hot Gas Bypass

� Still Need Boiler “Trim”

� Not Recommended

10 50 100

105

95

44Te

mp

era

ture

% Cooling Load

Leaving Chilled Water

Evaporator Refrigerant Temperature

Condenser Refrigerant Temperature

Heat Recovery Supply

H.R. Cond. Water Return


Maintain Boiler Return W.T.Maintain Boiler Return W.T.

� If Boiler Load = 25% Then Range = 5°F (Based 20°F Range)

� Maintaining 95°F RWT Will Provide 100°F Boiler Supply Temperature

� Minimizes Chiller Lift

� Boiler Will “Trim” to Meet Required Supply Temperature

� Recommended10 50 100

105

95

44Tem

pe

ratu

re

% Cooling Load

Leaving Chilled Water

Evaporator Refrigerant Temperature

Condenser Refrigerant Temperature

Heat Recovery Supply

H.R. Cond. Water Return


Heat Recovery ControlHeat Recovery Control

“During Heat Recovery Mode, Maintain Boiler “During Heat Recovery Mode, Maintain Boiler

Return Water Temperature At 95ºF”Return Water Temperature At 95ºF”– Boiler Supply Water Temperature Will “Float” Depending

On Actual Heating Load In Building

– 25% Boiler Load = 100°F SWT (5°F Temperature Range)

NotNot

“During Heat Recovery Mode, Maintain Boiler “During Heat Recovery Mode, Maintain Boiler

Supply Water Temperature At 105ºF”Supply Water Temperature At 105ºF”– 25% Boiler Load = 100°F RWT

– Entering Condenser WT will be 5°F Higher Than Above

– Boiler Will Still Be Required

– Same Amount Of Energy Will Be Recovered

– Chiller will Work A Lot (10%) Harder


Selecting HR ChillerSelecting HR Chiller

� HR Design Capacity Can Be All Or Part Of Chiller THR

– 100 Ton Chiller

– 125 Tons THR

– HR Can Be 0 to 125 Tons

� Chiller Size Should be Matched To Source Load During HR

– Keep The Chiller Loaded!


What Is A Heat Pump ChillerWhat Is A Heat Pump Chiller

� A Water To Water Heat Recovery Device

� A Heatpump

� Provides Hot Water At A Specified Temperature Using Waste Heat From A Low Temperature Loop


DesignDesign

3-Way BypassValve

Cooling Tower

Heat Pump

Chilled WaterPump

CondenserWater Pump

85 °F

85 °F95 °F

Std. Chiller

140 °F130 °F

Boiler Loop


DesignDesign

� Boiler Temperature Range Typically 20°F (180-160°F)

� Source Chiller Condenser Loop Temperature Range 10°F (65-75°F)

� If Source Chiller THR Larger Than Heat Pump Try To Use 5°F On Source Side To Improve Performance

� Bypass Balance Of Condenser Water Around Heat Pump

� Use 10°F Temperature Range On Load Side


Impact To Rest Of HVAC SystemImpact To Rest Of HVAC System

� 105°F Supply Water From HR Chillers Will

Require Different Size Reheat Coils

– Increased Capital Cost

– Fan BHP Penalty (Can Be Significant)

� 140-160°F Supply Water From Heat Pump Can

Use Same Size Coils In Most Cases

– The Small Loss In Performance From 180°F Design

Condition Is Acceptable Due To Smaller Loads


Sizing HR Chillers Sizing HR Chillers

� Airside Energy Recovery Systems Are Sized Based On Design Load Conditions

� Water Side Energy Recovery Must Be Sized During Part Load Conditions

� Requires Annual Energy Analysis


Sizing HR ChillersSizing HR Chillers

� Using the THR Of Chillers Rated Cooling Capacity For HR Design Is Not Recommended

– Undersized Chiller Will Miss HR Opportunity

– Oversized Chiller Will Waste Capital

– Possible Surge Issues

� Manual Method Described In ASHRAE Chiller Heat Recovery Application Guide


ExampleExample

� Acute Care Hospital In Chicago

– 480,000 ft², 3 Story

– 1600 ton Chiller Plant

– 22,000 MBH Boiler Plant

– Constant volume With Reheat

– 409,330 CFM Supply Air

– 192,000 CFM Ventilation Air


ExampleExample

� Option 1 - Base Building

– Two 800 Ton Centrifugals

� Option 2 -

– 472 Ton Heat Pump 4.4 COP

– Two 800 Ton Centrifugals

� Option 3 - Heat Recovery Chiller

– 400 Ton Split Condenser Heat Recovery Chiller 0.73 kW/ton

– 1200 Ton Centrifugal


Example Example -- Option 2 Heat PumpOption 2 Heat Pump

� 140°F Hot Water

� 70 °F Entering Source Water

– 5 °F Source Temperature Range

– 2200 US Gpm

� Source Chiller Condenser Pump Head Increased By 20 Ft

� Hot Water Tertiary Pump Added


Example Example -- Option 3 Heat RecoveryOption 3 Heat Recovery

� 400 Ton Chiller Size Optimized For Heat Recovery Load (5,324,226 Btu/hr)

� 105°F Hot Water

� Supply Fan Static Pressure Increased By 0.20 In. To Offset Deeper Heating Coils

� Hot Water Tertiary Pump Added


ResultsResults

0

2000000

4000000

6000000

8000000

10000000

12000000

14000000

Chillers Pumps Towers Fans Boiler HW Pumps

kW

h

Base Building Templifier HR Chiller


ResultsResults

� Chiller Work Increased

– 55% Due To Heat Pump

– 18% Due To HR Chiller

� Heat Pump Work Increased 15% Due To Condenser Pump

� HR Supply Fan Work Increased 4% Due To Higher Static Pressure

� Hot Water Pump Work Increased 25%Due to Additional Circulation Pump


ResultsResults

� Tower Work Decreased 21% Due To Reduced Rejection

� Boiler Work Reduced

– 34% Due To Heat Pump

– 28% Due To Heat Recovery Chiller

� Additional Savings Occur When Load > Source

– HR Option Only Has THR From HR Chiller

– Heat Pump Options Has Source Chiller THR + Heat Pump Compressor Work


ResultsResults

� Both Energy Recovery Options Saved Over 6 Million kBtu/yr

� Heat Pump Saved $108,000/yr

� Payback Less Than 2 years

� 80% IRR


ConclusionsConclusions

� Water Side Energy Recovery Good Option

� Requires Annual Energy Analysis To Optimize

� Heat Pump Provides 140 To 160°F Hot Water

– Domestic Hot Water Heating Possible

– Domestic Hot Water Preheat Only With HR Chillers

� Right Applications Energy Savings And Financial Savings Can Be Significant



� Green Is Good (For Business)

– Conservation of Natural Resources

� Lower Annual Energy Usage

– Reduce Operating Cost

� Provide a Good Life Cycle Analysis

THANK YOU!

ashrae chiller course condenser water hr

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