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MAXIMIZING HYDRONIC SYSTEM DESIGN – THE FUNDAMENTALS PART I Presented by Cleaver Brooks’ Steve Connor & DCEs’ David Grassl April 26, 2017
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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