Energy Efficiency in
Wastewater
Treatment Facilities
Neal R. Forester P.E. LEED AP
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My Background
• 7 Years Testing, Adjusting and Balancing and
Commissioning of HVAC Systems
• 13 Years Consulting Engineering
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HVAC
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Odor Control
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Fire Protection
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Wastewater Process Design
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Wastewater Treatment Facilities
Two different worlds
• Non-Process Facilities
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The basic commercial type facilities, offices,
warehouses, shops etc.
The “standard” practices apply
• Process Facilities
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Designed solely to serve the process
Governed by a different set of codes and standards
Additional influences such as worker exposure,
environmental regulations and severe operational
conditions
The Non-Process Facilities
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The Non-Process Facilities
• The “standard” practices apply
• Access is readily available to the trades and
services for a successful project:
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Contractors
TAB
Cx Agents
• Cooperative authorities
• Processes such as LEED are understood
• Engaged Clients
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The Process Facilities
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The Process Facilities
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The “standard” practices may not apply
May require specialized contractors to execute
Authorities can be outside their comfort zone
LEED can be nearly impossible
All resources given to the process
Client pressure to make things stupidly simple
Cx is generally limited to the process
Severe service conditions
A Contradictory Result
• The LEED plaque or equivalent gained for the
non-process facilities is reduced to nothing
more than some sort of a badge of honor hung
at the front gate in a attempt to put a rubber
stamp of “Green” on the site as a whole.
• A single process decision in a single process
facility can eclipse the entirety of the energy
savings achieved in all of the non-process
buildings combined.
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What To Do?
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Identify the real requirements
Challenge the status quo
Check all assumptions
Use the resources at hand
Anticipate the unexpected
Finding Opportunities
The normal incentives for owner to choose greater
efficiency are not as available:
• Peak electrical demand reduction: HVAC related
electrical demand is usually not coincident with peak
process demand and is much smaller.
• Tax Credits: Many energy efficiency programs operate
in a tax credit structure not available to the wastewater
operation.
• Many times the incentives that are utilized focus on
the process due to the relative magnitude of energy
consumption.
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Finding Opportunities
The supporting services such as HVAC are
typically overlooked and can be places where
significant energy efficiency gains can be
realized. Let’s look at a few examples.
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Example #1
The Energy Code Myth
Intent
A.H.J.
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Energy Code Myth
• The perception is that the application of the
minimum prescriptive requirements always
saves energy.
• The AHJ may have little incentive to allow
deviations to the code.
• Enforcement can actually increase energy
consumption when the design conditions fall
outside of the normal conditions assumed
during the development of the codes.
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Energy Code Myth
• A wastewater process electrical room with high
heat gains in mild climate (Pacific Northwest).
• Space temperature setpoint set at 85°F to increase
the amount of time that outside air economizer can
operate and reduce mechanical cooling.
• Architectural analysis indicated that envelope
insulation was required to meet energy code.
• An in-depth analysis of this situation indicates an
increase in the energy budget due to increased
mechanical cooling.
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Energy Code Myth
• The energy savings associated with the elimination of
the envelope insulation was difficult to realize.
• The code enforcement entities were reluctant to allow
the exemption.
• Doing the “right thing” cost a lot of design budget
rarely available for this type of facility.
• Can get questioned at each stage of the process. The
Cx agent questioned the contractor about the
envelope construction.
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Example #2
A Large Thermal Source
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A Large Thermal Source
• Low quality thermal sources are usually disregarded
as “uneconomical”.
• With the high ventilation rates required at wastewater
facilities in extreme climactic conditions the “low”
quality sources can provide significant benefit.
• Wastewater treatment has a large amount of water
that can be used as a heat sink or source or both.
• Wastewater temperatures usually both less than
outside air during cooling and greater than outside air
during heating.
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A Large Thermal Source
• In a facility in Minnesota the outside air design
temperatures range from -25 to 88°F.
• A spray water system continuously pumped secondary
clarifier effluent for cleaning processes.
• Effluent temperatures ranged from 55 to 70°F.
• A headworks facility required continuous ventilation
with 100% outside air at 12 air changes per hour for
electrical classification and worker exposure control.
• Heating to be provided to maintain space temperature
at 50°F.
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A Large Thermal Source
• A “low temperature” glycol loop was installed to
exchange heat between the secondary effluent and
the makeup air.
• At the extreme low temperature the loop provided
outside air preheat from -25 to 25°F.
• The peak process demand occurs during the winter.
Therefore the peak electrical room cooling occurs
during the winter. The same loop that provides
makeup air preheat simultaneously provides electrical
room cooling. The electrical room heat is captured and
is available for makeup air heating.
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Example #3
A Simple Move
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A Simple Move
• Large electrical transformers are usually placed
outside for many reasons:
• Safety
• Required Cooling
• Building Footprint
• The electrical demand and associated heat rejection
associated with transformers may not be coincident
with the peak cooling.
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A Simple Move
• Generally the large substation transformers located
outside to avoid having to provide cooling. Heat is
simply rejected to the outside air.
• The transformer heat rejection is a function of the
electrical load.
• In non-process facilities the peak electrical load is
generally produced during the yearly peak cooling
period due to the dominance of HVAC cooling
demand.
• In process facilities the peak may occur at another
time. Wastewater peak demand may be during winter.
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A Simple Move
• In the same Minnesota facility with the electrical room
cooled by the low temperature glycol loop, the peak
electrical room heat rejection and therefore the peak
transformer heat rejection occurs during the winter.
• Moving the transformers into the electrical room allows
the energy normally lost to the outside to be captured
from the electrical room and made available for
makeup air preheating.
• Due to the size of the process demands the resulting
heating capture was approximately 70 kW (239,000
BTU/hr).
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Example 2 + Example 3
• The implementation of the low temperature loop for
makeup preheat and electrical room cooling coupled
with the move of the transformers inside the building
resulted in significant energy savings.
• Approximately $75,000/yr (2008) in avoided natural
gas costs.
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Example #4
Avoiding the Cooling Tower
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Avoiding a Cooling Tower
• A treatment plant in desert Southwest needs cooling
for electrical rooms and process spaces.
• A new central chiller plant is being provided to supply
the cooling need.
• Makeup water quality for cooling towers is an issue.
Potable water available has a hardness greater than
what most cooling towers blow down. Creates a
serious scaling issue.
• Owner was concerned about worker exposure to water
treatment chemicals.
• There was no thermal limit on the wastewater effluent.
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Avoiding A Cooling Tower
• Water was available from the chlorine contact basins
but had high levels of residual active chlorine. This
required the use of titanium tubes in the condenser.
• The peak effluent water temperature occurred 30 days
after the peak outside air temperature. During peak
cooling the condenser water temperature was less
than that available from a cooling tower.
• Fall conditions were difficult for chiller operation due to
high condenser water temperatures coincident with
low cooling loads. Supply water temperature had to be
reset upwards to reduce thermal lift that caused
compressor surging.
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Avoiding A Cooling Tower
• The unexpected heat
exchanger
• VFD cooling auxiliary heat
exchanger connected to the
condenser water and
constructed of conventional
materials.
• Not shown on any submittal
materials.
• Had to be reconnected to
chilled water and controls
added.
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Avoiding A Cooling Tower
• The unexpected “stuff”.
• Plastic debris that
passes through the
treatment process.
• Mostly fruit labels.
• Results in plugging of
the chiller inlet strainer.
• Additional strainers
added to system to
facilitate cleaning.
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Commissioning
What Have You Done For Me Lately?
Cx? Why?
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A Commissioning Culture
• With the historical treatment of HVAC and related
systems within wastewater, the industry had relied
upon the contractors to deliver systems with
acceptable performance.
• Given the simplicity of the systems, little to no
prescribed checkout, testing, or commissioning would
have been required.
• Today the over-reliance on third party commissioning
entities has incrementally changed the nature of the
trades and contractors.
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A Commissioning Culture
• The mentality has slowly shifted from one of “pride in
workmanship” to one of “we can fix it if we get caught”.
• Under the right circumstances the Cx Agent can
obstruct the process by being nothing more than just
another box to check.
• Now even with simple HVAC systems, the contractors
cannot be relied upon to deliver a functional system.
• The more complex systems necessary to achieve
greater levels of energy efficiency simply don’t work
under this new paradigm.
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A Commissioning Culture
• The result has been a shift away from the traditional
treatment of HVAC designs for non-process facilities.
• Owners are now requesting that the HVAC controls be
integrated into the industrial process controls to
eliminate the HVAC controls contractor and shift the
Cx process to the more formalized and rigorous
method utilized by the process engineer and controls
integrator.
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Questions?
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