maximizing hydronic system design – the fundamentals...

MAXIMIZING HYDRONIC SYSTEM DESIGN –THE FUNDAMENTALS PART I

Presented by Cleaver Brooks’ Steve Connor& DCEs’ David Grassl

April 26, 2017

TODAY’S TOPICS

• Brief review of how hot water boilers have evolved and why• The need to know about what affects condensing in boilers• Some key insights about boiler efficiency• Key condensing boiler differences which impact the system • Understanding the load and calculating for it• System design and piping configurations• Control strategies• Summary• Questions & Answers

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HYDRONIC HEATING, THE EARLY YEARS…

FiretubeCast Iron Firebox

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OPEC & BMA

Oct. 1973 – November 1974

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OPEC & BMA

Oct. 1973 – November 1974

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Boiler No. 1

Return temp. gauge

Outlet temp. gauge

Three-way modulating valve

Standby pump

Boiler air vent(2) Pipe Primaryw/ parallel heating circuits& Reverse Return off theZones.

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• Firetube Boiler – hot flue gases pass through one (or multiple) tube passes through a pressure vessel that contains water (and/or steam)

• Watertube Boiler – tubes contain water that are externally heated by the boiler flue gases

• High Mass Condensing Boiler - more than 50 gallons of water volume per MMBTU

• Low Mass Condensing Boiler - less than 20 gallons of water volume per MMBTU

• Condensing Mode – boiler operating below the flue gas dew point

• Non-condensing Mode – boiler operating above the flue gas dew point

BOILER DEFINITIONS

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HYDRONIC HEATINGNON CONDENSING BOILER TYPES

• Firetube• Fire Box• Watertubes –

Flextube• Copper fin-tube• Cast Iron Sectional• Modular watertube

Cast iron Flextube

Modular watertube

Firetube

Fire Box Copper fin-tube

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• Firetube – large mass, steel• Effective heating surface, higher minimum flows and temperatures

required• Watertube – Flexible tubes, steel

• Thermal shock resistant, wide range of flow, minimum inlet temperature required, assemble on site

• Cast Iron – low water volume, sectional• High material/thermal mass, assemble on site, limited flow range, high

minimums• Watertube – mid mass, membrane wall, steel

• Smaller footprint, higher minimum flows and temperatures, subject to thermal shock

• Modular – low mass, copper fin-tube• Smallest footprint, less heat exchanger, lower water volume

HYDRONIC HEATINGNON CONDENSING BOILER TYPES

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Firetube – Long life, best efficiencies (84-85%)Flextube – Long life, 80-85% eff., wider Delta T,

thermal shock resistant

Cast Iron – Medium life, higher maintenance, primary-secondary pumping

H/M Modular – medium life, lower return temp, pumping flexibility

Low mass – Shorter life, high press. drop high minimum flow requirements, primary-secondary pumping, 80-85% eff.Atmospheric – Low efficiency (60-80%)

Quality Segmentation

Value

System Impact

HYDRONIC HEATINGNON CONDENSING BOILER TYPES

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HYDRONIC BOILERSNON-CONDENSING PROS AND CONS

Advantages• Most have Higher

Temperature Limit• Higher Pressure designs• Larger Capacities• Fuel oil and alternative fuel

back-up• Lower Initial Equipment

Cost

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HYDRONIC BOILERSNON-CONDENSING PROS AND CONS

Disadvantages• Larger footprint• Standard Efficiencies

• Less than 85%• Rust Corrosion

• Minimum operating/return temperatures

• Thermal Shock• Cast Iron / Firetube

• Piping/pumping limitations• For Boiler Protection

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THE SCIENCE BEHIND CONDENSING

Non-condensing boilersAvailable energy influe gas is lost80-87% eff. at very best

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If return water is too cold, condensation can form inside of the boiler

NON-CONDENSING BOILER LIMITATIONS

Corrosion

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Boiler Efficiency Improves Dramatically with Condensing

Available Energy is recovered before it is allowed to go up the stack

Efficiencies now: 90% to 99%

THE SCIENCE BEHIND CONDENSING

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• Operating at LOW Temperatures

• Consistent Fuel/Air Ratio Control

• Effective Heat Exchanger

Boiler Efficiency Improves Dramatically with Condensing

Condensing Efficiency Drivers

THE SCIENCE BEHIND CONDENSING

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Efficiency Characteristics with Condensing

THE SCIENCE BEHIND CONDENSING

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• Operating at LOW Temperatures

• Consistent Fuel/Air Ratio Control

• Effective Heat Exchanger

Boiler Efficiency Improves Dramatically with Condensing

Condensing Efficiency Drivers

% O2

% E

XCES

S AI

R

FLU

E GA

S DE

W P

OIN

T

THE SCIENCE BEHIND CONDENSING

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CORRELATION BETWEEN EXCESS AIR & EXCESS O2

Excess Air Excess O2

15% 3.0 %

25% 4.5 %

35% 5.8 %

45% 7.0 %

55% 7.9 %

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• Operating at LOW Temperatures

• Consistent Fuel/Air Ratio Control

• Effective Heat Exchanger

Boiler Efficiency Improves Dramatically with Condensing

Condensing Efficiency Drivers

Loss in boiler efficiency

% O2

% E

XCE

SS

AIR

FLU

E G

AS

DE

W P

OIN

T

THE SCIENCE BEHIND CONDENSING

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• Operating at LOW Temperatures

• Consistent Fuel/Air Ratio Control

• Effective Heat Exchanger

Boiler Efficiency Improves Dramatically with Condensing

Condensing Efficiency Drivers

Counter-flow Heat Exchanger

Cold water return/inlettemperature introducednear the coldest flue gases

Hot water supply/outlettemperature exitsnear the hottest flue gases

Effective Heating Surface to promote condensing

THE SCIENCE BEHIND CONDENSING

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CONDENSING TECHNOLOGYCONDENSING BOILER TYPES

Modified Firetube [SS] Cast Aluminum Cast iron w/ add-on HX Copperfin w/ add-on HXFiretube [SS]

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• Stainless Steel Firetube – larger mass • Most effective heating surface, better for condensing and variable flow

• Cast Aluminum – low mass• Good heat transfer material, potential waterside corrosion, prone to erosion

• Modified Firetube with add-on HX – mid mass• Less effective heating surface, subject to thermal stress

• Cast Iron with HX – low mass• Less effective heating surface; prone to short-cycling

• Copper Fin Water Tube with add-on HX – low mass• Prone to short cycling and possible erosion & plugging

CONDENSING TECHNOLOGYCONDENSING BOILER TYPES

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HYDRONIC BOILERS –CONDENSING BOILERS

High mass – Long life, high ∆T limit, large water volume, premium operational efficiencies

Designed for primary variable flow

Mid-mass – Medium life, 30-60 F ∆T limit, limited water volume, high efficiency

Capable of limited primary variable flow

Low mass– Shorter life, 20F-30F ∆T limit, little water volume

Primary-secondary ONLY

Quality Segmentation

Value

System Impact

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• Lower equipment cost• Quick response to load

variations• Compact footprint• High efficiency ratings

Advantages

CONDENSING BOILER TECHNOLOGYLOW MASS BOILER DESIGN

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Disadvantages• Needs minimum

circulation• Higher energy

requirement• Higher Pressure Drop• Erosion problems• More maintenance• Lower life expectancy• More frequent cycling

• Often needs buffering

CONDENSING BOILER TECHNOLOGYLOW MASS BOILER DESIGN

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• Rugged construction• Less cycling• Lower thermal stress on

the boiler• Stable temperature control• Minimal pump head• Low-flow or no-flow

tolerant• Compact• Excellent operational

efficiencies

Advantages

CONDENSING BOILER TECHNOLOGYHIGH MASS BOILER DESIGN

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• Higher equipment cost• Heavier• Somewhat larger than

low mass

Disadvantages

CONDENSING BOILER TECHNOLOGYHIGH MASS BOILER DESIGN

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HYDRONIC BOILERSCONDENSING CONSIDERATIONS

Why Condensing?

• Highest efficiencies• Thermal shock resistant• Lower temperature

designs • Venting flexibility• Smaller footprint• Modular system design

solutions• Often includes low

emission burner technology

Limitations?

• Limited alternative fuels• Category IV flue

requirement• Limited water side

inspection• Some designs

• Piping/pumping limitations

• Some designs

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DAVE GRASSL

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UNDERSTANDING THE LOAD

Building Loads Consist of:• Envelope Losses• Ventilation & Infiltration• System Losses• Pickup Factor

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• Loads Not Included in Calculations:• People• Lights • Equipment• Solar Radiation

• These loads are still present

UNDERSTANDING THE LOAD

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• Safety Factors:• Standard design practice is 10%-25%• Coil sizing overview

• Result:• System oversizing• Equipment cycling • Increased equipment wear & tear

• Recommendation:• Unnecessary due to safeties in loads

calculations and equipment selection

UNDERSTANDING THE LOAD

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SYSTEM DESIGN & APPLICATIONS –PUMPING CONFIGURATION

• Two sets of pumps • Primary pumps are for heat production • Secondary pumps are for distribution

• Common piping hydraulically decouples loops• Minimum flow bypass required to protect pump• Two-way control valves at terminal units• DPT transmitter to control pump speed

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Primary-Secondary Flow

SYSTEM DESIGN & APPLICATIONS –PUMPING CONFIGURATION

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• Single set of pumps handle all pumping• Minimum flow bypass required to protect equipment• Two-way, two-position isolation control valves at

boilers in parallel• Two-way, modulating control valves at terminal units• DPT transmitter to control pump speed

SYSTEM DESIGN & APPLICATIONS –PUMPING CONFIGURATION

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Variable Primary Flow

SYSTEM DESIGN & APPLICATIONS –PUMPING CONFIGURATION

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MINIMUM FLOW CALCULATIONS

• Minimum Flow Bypass Requirements:• Must protect pump or boilers from unstable conditions• Boiler may not be limiting factor

• Calculations:• Pump

• Typically 20%-25% best efficiency point• Boiler

• Based on minimum firing rate• Method

• Minimum flow bypass with flow meter and bypass valve• Three-way valves in the system to allow for minimum flow

• Application• Secondary loop on primary-secondary system• Variable flow primary system

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Three Way Control Valve

TABLE COMPARING VPF & PS

Variable Primary Flow Primary-Secondary

Piping Loop Quantity One loop with all equipment Two loops connected with a common pipe

Pumps Quantity One set Two sets

Pump Sizing Must support entire system pressure drop and flow

Primary – Sized for boiler flow and loop pressure dropSecondary – Sized for distribution flow and loop pressure drop

Pump Types Typical base mounted, end suctionPrimary – Typically inlineSecondary – Typically base mounted, end suction

Minimum Flow Bypass Required to protect pump and/or boiler Required to protect secondary (system) pump

Terminal Unit Control Valves Two-way, modulating Two-way, modulating

Boiler Control Valves Two-way, two-position Not required due to boiler primary pump

System Pump Speed Control Typically DP control Typically DP control

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SYSTEM DESIGN & APPLICATIONS –TRADITIONAL SYSTEMS

• One for one substitution• Must be in condensing mode• Utilize hot water reset

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Non-Condensing Condensing

180

160160

180

SYSTEM DESIGN & APPLICATIONS –PUMPING CONFIGURATION

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180

160160

180140 140

120 120

SYSTEM DESIGN & APPLICATIONS –PUMPING CONFIGURATION

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• Movement toward larger ΔTs• Q = 500 X GPM X ΔT

• Reduce pumping flow• Reduce piping sizes, pumps, &

accessories• Decrease hot water return to the boiler

• Dependent on boiler type• Higher mass allow for higher ΔT• Low mass are limited on ΔT• Recommend 30°F-50°F for ideal savings &

control

SYSTEM DESIGN & APPLICATIONS –HIGH ΔT SYSTEMS

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SYSTEM DESIGN & APPLICATIONS –HIGH ΔT SYSTEMS

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180160

160120

150110140100

• Hot Water Supply Temperature Reset• Pump Control

• Delta P• Delta T• Valve Position & Critical Zone

Reset

SYSTEM DESIGN & APPLICATIONS –SYSTEM CONTROL STRATEGIES

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• Hot Water Reset• Popular, proven

standard control strategy

• Most boilers have built-in logic already

• Load is proportional to the outside air temperature

• Water temperature can be decreased to meet load

SYSTEM DESIGN & APPLICATIONS –SYSTEM CONTROL STRATEGIES

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Non-Condensing Boiler Reset Curve

SYSTEM DESIGN & APPLICATIONS –SYSTEM CONTROL STRATEGIES

Condensing Boiler Reset Curve

150

140

130

120

110

100

90

80

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Hot

Wat

er T

empe

ratu

re (

o F)

SYSTEM DESIGN & APPLICATIONS –SYSTEM CONTROL STRATEGIES ΔP PUMP CONTROL• Most common method

• Used on VPF & P-S systems• Differential pressure transmitter • Located near remote coil • Can use multiple & control to worst case• Parallel pumps should use the same signal

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SYSTEM DESIGN & APPLICATIONS –SYSTEM CONTROL STRATEGIES ΔP PUMP CONTROL

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• Newer method with pump microprocessors• Built-in VFDs or EC motors

• Methodology:• Uses supply & return temperature sensors in system

piping • Flow rate varies to match required heat output• HWR is constant resulting in lower temperatures

• Results:• More time in condensing mode• Decreased boiler cycling• Increased system efficiency

• Uses:• Primary boiler pumps

SYSTEM DESIGN & APPLICATIONS –SYSTEM CONTROL STRATEGIES ΔT PUMP CONTROL

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SYSTEM DESIGN & APPLICATIONS –SYSTEM CONTROL STRATEGIES ΔT PUMP CONTROL

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SYSTEM DESIGN & APPLICATIONS –SYSTEM CONTROL STRATEGIES CRITICAL ZONE RESET

• Use of DDC system to monitor valve positions• Requires sequence to be programmed• Increased complexity & cost• Methodology:

• Keep one control valve fully open• Trim & respond setpoint

• Results:• Higher energy savings due to response

directly from the load• Uses:

• Variable primary flow• Primary secondary

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SUMMARY

• Non-condensing boilers have their place in hydronic heating systems• Condensing boilers can achieve over 90% efficiency given the right

conditions:• Return water temperature and firing rate• Consistent fuel/air ratio control• Effective heat exchanger design

• Boiler mass plays a critical role in providing excellent system efficiency and lowest cost of ownership.

• Building load calculations include the actual heating losses, but do not take into account heat gain items

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SUMMARY

• Primary-secondary systems include: • Constant speed primary (boiler) pumps • Variable speed secondary (system) pumps

• Variable primary flow systems include:• One set of pumps that pump through boilers and the system

• In new system designs, increasing the Delta T will:• Reduce flow rates, reducing pipe and pump size • Save on equipment cost & electrical energy

• Supply temperature reset allows water temperature to meet load demands • System control strategies include:

• Delta P Pump Control• Delta T Pump Control• Critical Zone Reset

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Catie Van Wormer cvanwormer@cleaverbrooks.com

Dave Grassldavid.grassl@dynamicmke.com

QUESTIONS?

5655