Campus Energy 2016
Austin, TX
Effective Water Treatment for Chilled
and Heating Water Systems for
Thermal Distribution Systems
Jim Gleason
GE Water Senior Product Applications Engineer
February 9, 2016
GE Proprietary and Confidential
Definition of Closed Water System
Not Open to Atmosphere
No Water Evaporation
Designed for Minimal
(less than 1%) water
losses
Used to transport Chilled
or Heating Hot Water or
both with two pipe
systems
Typically treated with
higher dosage levels of
chemical treatment. Still subject to corrosion and scale despite
being “closed”
Closed System (typical assumptions)
• Extremely low water losses due to evaporation
or blowdown
To
• Cooling
High quality makeup (softened at minimum)
Tower
Heat Process
• High inhibitor Exchanger
levels (to
achieve lowest possible mpy)
Heat
Makeup
• Temperature ranges as high as 350°F Load
From
• Water, glycol, and brine systems
Cooling
What happens when we assume? Surge
Tower Tank
Closed Loop System Monitoring
• Iron (Ferrover Method/FerroMo if molybdate
inhibitor)- number one test to run
• Chemical residuals (NO2, NO3, NH3, MoO4, TTA)
• System parameters, such as pH and conductivity
• TAP analysis and verify that metals present reflect
the system metallurgy
• Water losses and leaks
• Microbiological activity, both sessile and planktonic
• Corrosion coupons
• Outlet water temperatures on critical exchangers
• Stagnant conditions
Condenser Approach Temperature
When Tubes Are Dirty
Insulation Effect – Scale, Fouling, Bio
More energy to raise water temp
Efficiency loss as high as 40%
Problem amplified with Enhanced Tubes
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The Water Treatment Triangle
Ranking the three legs of the triangle
Corrosion first among equals
Why? Because corrosion by-products inhibit heat transfer and promote MB
growth, which also inhibits heat transfer
Deposition easiest of three to treat- to stop scale, either remove calcium via
softening/demin/RO, or use scale inhibitors like phosphonate/AEC (acid for
closed loop pH control not usual)
SSF excellent to minimize deposition of suspended solids- minimize
“bleed/feed”
Biological easiest to get out of control
Biocides less lethal than in past
Biocides also either expensive or indiscriminate
Must rely on monitoring to avoid problems beforehand
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Corrosion by-products:
Disproportionate Volume
For 2000 yards standard weight pipe, 20 mpy
corrosion for 6” diameter pipe will generate 5
tons hydrated iron each year (40 ft3/year
volume)
20 mpy for 24” diameter pipe will generate
almost 25 tons hydrated iron each year (200
ft3/year volume)
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Biofilms
Biofouling
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The Tangible Impact
• Microbial films consist of water.
• Trapped water Stagnant water
Poor conductor of heat
Biofilm - great insulator
1 mm of biofilm = 83 mm Steel Exchanger
Tube
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Confidential
Effect of Condenser Scale
Thickness
On Power Consumption (Clean Tubes)
Power Consumption
Percent Added
Condenser Scale Inches
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Confidential
Key Performance Summary
Chillers - 40% to 60% of Building energy
consumption.
Chillers can operate inefficiently
without being obvious
Tube fouling - Main cause of efficiency
loss
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Basic Mild Steel Corrosion Cell
Water
(Electrolyte) O2
Fe(OH)3 Fe2+ OH-
FERRIC
H 2O
Electrical Potential e-
Fe(OH)2
FERROUS
Electron Flow
ANODE (-) Carbon Steel CATHODE
(+)
GALVANIC CORROSION BASICS:
concern for mixed metallurgy systems
Stainless Steel (Passive)
Titanium Cathodic -
More Easily
Bronze Protected
Copper (More Noble)
Brass
Stainless Steel (Active)
Cast Iron
Mild Steel
Anodic - Aluminum
More Easily
Corroded Zinc
(Less Noble)
Magnesium
GALVANIC CORROSION
(COPPER INDUCED)
Galvanic Corrosion
Example - Copper Plating on Steel
FeO + Cu+2 ----> Fe+2 + CuO
Fe+2 Cu+2
Cu0
Fe0 2e-
Corrosion Monitoring
Corrosion Coupon Assembly
•Corrosion coupon monitoring
remains the least expensive
method; insertion probe also
option
•Every closed system should be
equipped with multiple metallurgy
coupon sites
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Acceptable Corrosion Rate
Standards:
Closed Chilled Water Loops
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Biological Monitoring
ATP
Dip slides
Aerobic Count Plates
(Petri Dish)
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Confidential
Microbial Guidelines: Closed
Systems
MB count level within a Biocide treatment regimen
system (cfu/ml)
>107 Biocide failed to provide protection
105 - 106 Unsatisfactory biocide control
103 - 104 Biocide control satisfactory
<102 Excellent biocide control
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MB monitoring: bulk counts not
enough
Must look for sessile (surface) organisms;
filters/strainers perfect “host” structures
Bulk organisms in transit between surfaces
Organisms secrete biofilms to control
environment
Negative interplay between corrosion and bio-
loading (lots of free “housing”)
MB count 10-100x higher at surfaces than bulk
Bacteria and Bio-Fouling Inhibition
Bacteria of concern in closed systems:
• Sulfate reducing bacteria (SRB’s); damaging at very low cfu/ml counts,
generate little ATP
• Nitrite reducing bacteria- same concerns as SRB’s
• Pseudomonads
Pseudomonads biofilm
SRB induced corrosion
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Factors Affecting Biocide Choice
• Concentration
• Temperature
• pH
• Compatibility with other treatments present
• Cost effectiveness (usually better to feed more
less often)
• Resistance/Immunity
• Broad spectrum of activity
• Compliant with EPA End-Use Label Criteria
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Scale Inhibition
Solutions
• Ensure treatment formulation includes scale
control agents
• Monitor system chemistry closely
• In hard water areas soften the fill/makeup water
• If softened water used, review treatment chemistry
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Filtration of Closed Systems
Routine Filtration for Closed Systems
•Large systems system turnover of 1 to 4 days
• Variable speed pumps - Reduce velocity and
increase the tendency for deposition of debris—
Greatest Impact: Enhanced Tubes
•Filter selection is determined as follows:
Filter Ft3/h =System Volume
Days per turnover x 24)
Monitor Particle size (PSA)
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Filtration
Various
Types
• Strainers
• Dirt Separators
• Magnetic filtration
Cartridge filter
• Hydro-cyclones
• Disposable media filtration
• Cartridges or bags
• Auto filtration
• Multimedia (sand/anthracite)
• Membranes
• Reverse Osmosis
• Nano filtration
• Ultra filtration
Bag filter
Chemical Solution
Select program based on water
chemistry and application
Create/Replenish Passive Barrier
Special attention to copper inhibitor
and monitoring
Regular Water Testing and
Monitoring
Primary Closed System Inhibitors
• Nitrite (anodic inhibition)
• Molybdate (also anodic inhibition)
• Phosphonates (anodic inhibition)
• Alternative programs (cathodic inhibition)
Anodic vs. Cathodic Inhibition
Anodic inhibitors form gamma iron oxide film on metal surface
(usual iron oxide film not adherent). Can achieve lowest
possible mild steel corrosion rates. Must be maintained at
minimum residual at all times. Can be expensive program if
MU to system elevated.
Cathodic inhibitors form barrier film at cathodic sites, using
calcium hardness in water. Corrosion rates not as low as
anodic inhibition. Require antiscalant. However, can be much
less expensive if MU to system elevated.
. GE Proprietary and Confidential
Nitrite
Mechanism
• Anodic passivator
• Promotes passive iron oxide film
Advantages
• Low cost (compared to other anodic programs)
• Very effective on carbon steel
• Independent of oxygen
• Stable to 350ºF
Nitrite Challenges
• Effective only on carbon steel
• Oxidized to nitrate by MB, chlorine, and oxygen
• Passivation reaction produces ammonia
• Aquatic toxicity
• Brass stress corrosion cracking (O2 present)
• Aggressive to solder
• High dosages required
150- 1,200 ppm (500-700 ppm typical)
Molybdate
Mechanism
• Oxidizer
• Forms passive anodic film
Advantages
• Excellent MS corrosion inhibitor
• Mildly effective on Cu, Al, solder
• Excellent stability
• Compatible with oxidizers
Molybdate
Disadvantages
• Higher cost
• Slow passivation, especially in low D.O.
• Not allowed by some discharge permits
Dosage
• 150 - 500 ppm as MoO4
Molybdate / Nitrite Blends
Synergistic Combination
Provides Excellent MS Performance
• Low and high D.O.
• Stagnant conditions
Disadvantages
• Cost
• Still can be prone to MB reversion
Phosphonate
• All organic inhibitor blend w/dispersant
• Designed for low conductivity systems
• Low active concentration
• Excellent environmental profile
• Ideal for new or cleaned systems
– 0.05-0.07 mpy on mild steel
– 0.06-0.08 mpy on copper
May remove existing corrosion by-product if system not
clean
Copper Protection
Most used - azoles:
•Tolyltriazine (TTA) – most commonly used
•Benzotriazole (BZT) – commonly used
•Halogen Resistant Azole – unique properties
•Typically blended in with anodic inhibitor
• Increasing levels - sulfate and chlorides
• Chemically bonds with copper and copper alloys
to create film, stable for 5 - 7 days
• Complex with Cu+2 preventing copper plating of
Al and low carbon steel,
subsequent aggressive pitting
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High Makeup Systems
Closed System, But Has High Water
Losses (>5% System Volume Lost/Day)
• Sliding scale for ortho-PO4 residual
Inversely dependent on system pH and calcium level
• Can not use softened/demineralized/RO MU
• One drum blend should include pyro-PO4 to “toughen up”
cathodic barrier film
• Can not achieve lowest possible mild steel corrosion
control
• Requires antiscalant to prevent CaPO4 deposition
Chemical Solution
Program based on water chemistry
and application
Inhibitor Pros Cons
Effective with no High Cost, Heavy
Molybdate breakdown/Cl2 Metal
OK
Cost effective Breakdown,
Nitrite Works rapidly bacterial
food/conductivity
Low Cost Effectiveness,
Phosphate
Precipitation
Perceived as safe Effectiveness,
Silica
scale formation
Complex Iron and scale Breakdown,
phosphate removal bacterial food
Microbial Control
Non-oxidizers typically used in closed
systems rather than
oxidizers- why?
• Oxidizers (cheaper) are indiscriminate- may oxidize
corrosion inhibitor as well as organisms
• Non-oxidizers (more expensive) target specific organisms
with minimal collateral damage
• In order to be applied as infrequently as possible,
sessile monitoring maximizes results while
minimizing costs.
Biocide selection for closed systems
Best to perform either on site or off site toxicant evaluation,
incorporating sessile MB sample
Biocides can select out resistant MB strains over time
Toxicant evaluation allows optimization of existing
program/identification of new program with respect to dosing amount
Monitoring allows optimization of existing program with respect to
dosing frequency
Servicing a Closed Loop
Check Inhibitor Levels, Conductivity & pH
Once/Month
• Compare with make-up vs. inventory
• Check the draw down on the pump
Bioscan or ATP Analysis Monthly
Check For SRB Bacteria
Inspect Coupons Quarterly, Analyze Annually
• 0.1 mpy for the most critical systems
• Up to 0.5 mpy (“soft cap”) - 1 mpy (“hard cap”) for
less critical systems
Closed System Pre-Op Cleaning
Cleaning and Passivation of new piping surfaces
Acid cleaning not desirable vs. cleaning/passivation
together
Proper water treatment is essential for
Removing oils/slag from manufacturing and
construction
Protecting new pipe and creating a protective
passive layer.
The precautions taken on Pre –Op cleaning
Will add years to Heat Exchanger/Chiller life
HVAC Chiller/Closed System Lay-
up
Cleanliness of the heat transfer surfaces
Proper water treatment is essential for
maintaining top efficiency
minimizing corrosion.
The precautions taken on laying up (either wet or dry) will
add years to chiller life and prevent shutdowns
Wet layup: biocide/biodispersant/2-3x normal inhibitor
residual
Dry layup: vapor phase inhibitor
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Chiller Performance Optimization –
What is Measured can be improved
Mechanical and Chemical Performance
• Approach temps
• Evaporator
• Condenser and Chilled KPI’s monitored
• Routine Microbiological Monitoring
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Thank You for your Attention
Questions ?
