CHP, Waste Heat & District Energy CHP, Waste Heat & District Energy 

Module 8: CHP System Thermal DesignModule 8: CHP System Thermal Design

11/17/1011/17/10Slide Slide 22

Module 5 Topics  Module 5 Topics  

•• CHP System DesignCHP System Design

•• Thermally Activated Thermally Activated TechnologiesTechnologies

•• System OptimizationSystem Optimization Electricity Consumption & Cooling T/E Ratio

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11/17/1011/17/10Slide Slide 33

CHP Design Goals

• Integrate natural gas engine, electric generator, heat recovery equipment and thermally driven HVAC equipment with the building systems

• Maximize economic advantage

• Minimize project cost

11/17/1011/17/10Slide Slide 44

CHP System Design

• Maximize Economic Advantage• Match the CHP system Thermal/Electric Ratio with the 

facility requirements and Baseload the CHP system electric and thermal output

• Minimize Project Cost• Understand the electric, heating and cooling loads and 

select equipment for maximum load factor – Not necessarily maximum efficiency. 

Maximizing load factor is the way to maximize profit.Rule #1Rule #1Rule #1

11/17/1011/17/10Slide Slide 55

CHP System Design

Thermal Form Varies – Electric Form is Constant

Conventional Wisdom:• Select Generator on Electric Load Basis• Select Thermal Technology on Generator Basis• Fit Thermal Output to Building

CHP Wisdom:• Select Thermal Technology on Thermal Load Basis• Select Generator on Thermal Basis• Fit Electric Output to Building

‘Thermal First’ design is the way to maximize load factorRule #2Rule #2Rule #2

11/17/1011/17/10Slide Slide 66

CHP System Design

The heating and cooling Thermal/Electric Ratios are the key load characteristics required to ensure high CHP Load Factor. 

Heating T/E Ratio =  Heating Load in MBH / Electric Load in kW

Cooling T/E Ratio = Cooling Load in Tons / Electric Load in kW(The T/E Ratio is the inverse of the Power/Thermal Ratio)

The Load T/E Ratios define the CHP ConfigurationRule #3Rule #3Rule #3

11/17/1011/17/10Slide Slide 77

CHP System Design

Economics

Essentially the thermal revenue represents the annual cost savings. 

Without thermal revenue, the cost savings are significantly reduced and the payback is greatly increased. 0% 20% 40% 60% 80% 100%

Revenue

Profit

Revenue/Profit Share

ElectricThermal

11/17/1011/17/10Slide Slide 88

CHP System Design

Know your Loads:

Electric utilities usually provide 15 min interval data from which can be derived load duration curves. 

Thermal information should be measured and tabulated through summer, winter and shoulder season.

Thermal characteristics (flow, pressure, temp) need to be identified. 

Electric Load Factor, 2007 Jan - Apr

89%97%

0%

20%

40%

60%

80%

100%

120%

1,000 1,500 2,000 2,500 3,000 3,500 4,000

Power Demand (kW)

Tim

e ab

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Pow

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d va

lue

Average Mthly Steam Load Factor, 2003 - Apr 07

96%90%

0%

20%

40%

60%

80%

100%

120%

4 5 6 7 8 9 10 15 20 22

Average Steam Demand in MMlbs/hr

Tim

e ab

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team

Dem

and

valu

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11/17/1011/17/10Slide Slide 99

Averaged Cooling Load T/E Ratio

Electricity Consumption & Cooling T/E Ratio

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Source: 1995 EIA Buildings Survey

11/17/1011/17/10Slide Slide 1010

Typical CHP System Cooling T/E Ratio

0.6 ‐ 0.7Steam Turbine

2E Absorber> 1 MWGas Turbine

0.2 ‐ 0.4

0.4 ‐ 0.5

0.9 ‐ 1.0

T/E Ratio (Ton/kW)

2E Absorber

Desiccant<  1 MWMicroturbine

1E Absorber

2E Absorber

2E Absorber

Cooling TATRangeGenerator

.1 to 3 MWIC Engine

> .25 MWBiomass

11/17/1011/17/10Slide Slide 1111

CHP System Design

Aim for the highest thermal and electric load factor through all seasons – incorporate as many cooling and heating loads as possible.

Dom HW + cooling in summer     simultaneous heating and cooling.

Output has to be distributed so CHP system location is an important factor.

Building HVAC integration is a vital ingredient for new and retrofit CHP installations.

11/17/1011/17/10Slide Slide 1212

CHP System Design

Remember CHP cooling can reduce peak electric loads substantially

Series flow recommended on all thermal loops with the CHP system on the return line

Don’t forget O&M

25%

11/17/1011/17/10Slide Slide 1313

Thermally Activated Technologies

Technologies:Hot Water HEXBoilers/Steam GeneratorsOrganic Rankin CycleBackpressure TurbinesAbsorbersSteam TurbinesDesiccantsAdsorbers

Applications:Process HeatSpace HeatDomestic Hot WaterCoolingFreezingDehumidificationPower Generation

11/17/1011/17/10Slide Slide 1414

Cooling Technologies

• Cooling Technologies for CHP are HVAC devices that produce cooling from waste heat and include: 

• Steam Turbine Chillers

• Double Effect Absorbers

• Single Effect Absorbers

• Desiccants

• Adsorbers

• Cooling and Dehumidification Systems are available across a wide range of CHP configurations and sizes, from 50 kW to multi‐MW applications. 

Efficiency

11/17/1011/17/10Slide Slide 1515

Steam Turbine Chillers

• High Temperature Activation

• Moderate Cost at Large Tonnage

• High Pressure Steam System

• High Efficiency

700 to 5,000 Tons

High FL Efficiency – 1.2 COP, 10 lbs/ton, compact footprint

High IPLV Efficiency – 2 COP

High CHP Efficiency – FL at varying ambient

Condenser Water 3 to 4.5 GPM

11/17/1011/17/10Slide Slide 1616

Absorption Chillers

•Single Effect:•Low Temperature Activation, 200 F

•Low Cost•Simple

•Good Efficiency –0.7 COP

Wide range of models from <100 tons to >1,000 tons

Activated by Steam (15 psi - 125 psi), Hot Water and/or Exhaust

4 to 5 GPM Condenser Water, Large & Heavy, Slower Response

Double Effect:High Temperature Activation, 350 FModerate CostComplexHigh Efficiency –1.2 COP

11/17/1011/17/10Slide Slide 1717

Desiccants

• Liquid or Solid Desiccant• Low Temperature Activation ‐

Bottoming Cycle• Low Cost• Low Efficiency – 0.5 COP• Low Size

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150 160 170 180 190 200 210 220H W In let T em p era ture (F )

CO

P s im ple scaveng ing -a ir regene ra to r

1 .5 e ffec t regenera tor w ith uppe r s tage a t 300 F

11/17/1011/17/10Slide Slide 1818

Adsorption

• Low Temperature Activation

• Low Efficiency – 0.5 COP

• Refrigeration Capable

• Large & High Cost

• Requires Surge Tanks & Cooling Tower

11/17/1011/17/10Slide Slide 1919

System Optimization

Electric refrigeration chiller cost can be reduced and its efficiency doubled by using a heat recovery absorber.

Existing Refrigeration Chillers Power GeneratorChiller Output Tons 500 Electric Output kW 2,388

Chiller Efficiency kW/TR 2 LHV Elec Efficiency % 39.1%Chiller Input kW 1,000 Fuel In MBH 22,936

CT Fan Input kW Air Cooled Total HR 3 MBH 8,500Total Parasitics 1 kW 0 1E Absorber Output Tons 496

Abs/Cond Heat Rejection MBH 14,450

CHP Refrigeration ChillerElec Centri Chiller Output Tons 500

Elec Chiller Efficiency kW/TR 0.694New Refrigeration Chillers Elec Chiller Input kW 347

Chiller Screw Output Tons 500 YK Cd Output MBH 7,185Chiller Efficiency kW/TR 1.533

Chiller Input kW 766.5 CHP System ParasiticsCT Fan 2 HP 30 Electric Chiller CT Fan 2,4 HP -

Total Parasitics 1 kW 56 Absorber CT Fan 2 HP 50Total Parasitics 1 kW 101

Notes: 1 Parasitics include cooling tower, condenser pump and absorber2 Design wet bulb temperature = 73 F3 Includes Jacket + Exhaust, excludes 2nd Stage Intercooler4 CT not required when Abs operating or use Abs CT

Performance

Existing Chillers

Replacement Chillers

CHP System

11/17/1011/17/10Slide Slide 2020

System Optimization

System Integration for High Efficiency & Thermal Output

DumpCondenser

Chilled WaterSupply/Return

SteamTurbineChillers

Condensate Return

Steam Supply

CoolingTowers

Biomass Boiler

Steam HeatSupply/Return

Steam Turbine Efficiency

05,000

10,00015,000

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100125150200Steam Pressure (psig)

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CO

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Steam Flow COP

1.35

1.33

Condenser W: 80 FOutput: 2,000 Tons

Chilled W: 44 F

Steam Turbine Efficiency

05,00010,00015,00020,00025,00030,00035,00040,00045,00050,000

85807570656055

Condenser Water Temp (F)

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m F

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(lbs

/hr)

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1.0

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Steam Flow COP

1.661.49

1.21

Steam: 150 psigOutput: 2,000 Tons

Chilled W: 44 F

11/17/1011/17/10Slide Slide 2121

System Optimization

HR Surface Area/Size

CT & Pump ParasiticsCondenser Water Parasitic Load

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Wet Bulb Temperature

CT Size

11/17/1011/17/10Slide Slide 2222

Load Optimization

Some load profiles vary dramatically from peak to off‐peak hours.

In order to maximize return on investment the CHP system should operate 24 hours per day.

Mall Summer Electric Load Profile

0 Kw

5000 Kw

10000 Kw

15000 Kw

20000 Kw

25000 Kw

1 3 5 7 9 11 13 15 17 19 21 23

Hour of Day

Total Elec DmdNon-Cooling Elec DmdCool Elec Dmd

11/17/1011/17/10Slide Slide 2323

Load Optimization

Thermal Storage and Electric Chillers can be used to level CHP electric and thermal load profiles for high 24 hour Load Factor

August Chilling Profile

August Chilling Load

Total Chiller Output

Chilled Water Storage

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11/17/1011/17/10Slide Slide 2424

Load Factor vs Efficiency

• “No matter which basis is used to choose the prime mover, the degree of use of the available heat determines the overall system efficiency; this is the critical factor in economic feasibility. Therefore, the thermal/electric ratio of the prime mover and load must be analyzed as a first step towards making the best choice. Maximizing efficiency is generally not as important as thermal and electric utilization.”

• ………. ASHRAE Design Guide, Chapter 7 – CHP Systems

Gearoid FoleyGearoid FoleyNew Jersey New Jersey 

50 WASHINGTON ROAD50 WASHINGTON ROADPRINCETON JUNCTION, NJ 08550PRINCETON JUNCTION, NJ 08550

TEL: TEL: 609.799.2340 609.799.2340 EE‐‐MAIL: MAIL: ggfoley@foley@maceac.psu.edumaceac.psu.edu

Richard SweetserRichard SweetserVirginia, DC and MarylandVirginia, DC and Maryland12020 MEADOWVILLE COURT12020 MEADOWVILLE COURTHERNDON, VIRGINIA 20170HERNDON, VIRGINIA 20170TEL: 703.707.0293TEL: 703.707.0293EE‐‐MAIL:  MAIL:  rsweetser@maceac.psu.edursweetser@maceac.psu.edu

Bill ValentineBill ValentineDelawareDelaware

THE PHILADELPHIA NAVY YARDTHE PHILADELPHIA NAVY YARD4801 SOUTH BROAD STREET4801 SOUTH BROAD STREET

PHILADELPHIA, PA 19112 PHILADELPHIA, PA 19112 TEL: TEL: 609.799.2340609.799.2340

EE‐‐MAIL: MAIL: wjv3@psu.eduwjv3@psu.edu

Larry BurtonLarry BurtonPennsylvania and West VirginiaPennsylvania and West VirginiaPENN STATE UNIVERSITYPENN STATE UNIVERSITYUNIVERSITY PARK, PA 16802UNIVERSITY PARK, PA 16802TEL:  814.360.9868TEL:  814.360.9868EE‐‐MAIL: lcb2@psu.eduMAIL: lcb2@psu.edu

James Freihaut, DirectorJames Freihaut, DirectorMidMid‐‐Atlantic Clean Energy Application Atlantic Clean Energy Application 

CenterCenter104 ENGINEERING UNIT A104 ENGINEERING UNIT A

UNIVERSITY PARK, PA 16802UNIVERSITY PARK, PA 16802TEL: 814.863.0083TEL: 814.863.0083

EE‐‐MAIL: jdf11@psu.eduMAIL: jdf11@psu.edu