At the Marriott LAX
Saving Energy, Improving Performance, and Having a Good
Time Doing It
The Los Angeles Airport Marriott is a
1977 high-rise, full service facility
encompassing a nominal 600,000 square
feet that include meeting rooms, ball
rooms, several restaurants, and 1,000
guest rooms. With annual utility bills in
approaching $1.5 million, the facilities
engineering group jumped at the
opportunity to participate as a pilot
project in the Western Region’s
Retrocommissioning program (
).
The program is based on a process
developed in the commissioning
industry. It is targeted at tuning up
existing buildings, potentially
transforming them from the equivalent
of a poorly running family sedan to a high performance Indy racecar. But, unlike the
Indy speedster, the improved performance frequently translates to a reduction in
energy consumption, typically in the range of 5-25% of the consumption before the
effort.1 The process targets low-cost/no-cost performance improvements and
paybacks of 2 years or less are common. Frequently, local utility programs have
incentives that will help support the process, either by funding the engineering effort,
the improvements, or both. Many times, capital improvements are also identified,
which while beyond the scope and concept of the retrocommissioning effort, will
merit consideration as a part of the facilities long term planning process.
The remainder of this article will focus on the results of the effort that was undertaken
at the LAX Marriott. Exploring all of the findings in detail is beyond the article’s
scope, but a summary of all of the findings has been included and the details behind
many of the key findings will be discussed.
An Overview of the LAX Project
The effort at the Marriott LAX was the outfall of a task force of Marriott Facilities
Engineers brought together by Rob Bahl, the Western Region Engineering Director
and E.J. Hilts the Western Regional Energy Manager. Other team members included
Tracy Tomasek, Doug Rath, Paul Beyer, Steve James, and Jake Cormier. The goal
of the task force was to develop a retrocommissioning program that could be
1
For some examples and case studies that illustrate the savings potential, visit www.peci.org and download RetroCommissioning’s Greatest Hit’s, a paper presented at the International Conference for Enhanced Building
Operations in 2001 by Tudi Haasl
Retrocommissioning the LAX Marriott
1
deployed and implemented in the region’s facilities by 2005. The project is seen as a
way to expand Marriott’s ongoing commitment to resource and energy efficiency.
Building their own experience and publicly available commissioning resources, the
task force developed a process that would allow them to implement
retrocommissioning on a system wide basis. The next step was to find a test facility
for a pilot project. Task force member Tracy Tomasek volunteered his facility in Los
Angeles, and the project was off and running. Portland Energy Conservation
Incorporated (PECI), a Portland Oregon based not-for-profit dedicated to energy
efficiency and responsible resource use and heavily involved in developing
infrastructure for the commissioning industry was retained to assist with the project.
The project was initiated by assembling
drawings, specifications, balance reports,
control diagrams, and utility bills for
review by PECI. This information was
used to develop a fundamental
understanding of the facility and
formulate an initial plan of attack. Next,
task force members met PECI at the site
for a field exercise in which the facility
was surveyed to further refine the areas
that would be targeted by the process.
Based on the initial survey work, trends
were set up in the Energy Management
System (EMS) to gather data for
analysis. Data loggers were deployed on
the systems that were not served by the
EMS (See Figure 1).
Figure 1 - A typical data logger. These
electronics packages can be deployed where
needed to gather record information, which can
later be retrieved for analysis and
troubleshooting. Sampling times of less than a
second are possible and the battery power packs
allow the loggers to operate unattended for
weeks at a time. Flexible input options allow
virtually any process parameter to be sampled.
After the initial visit, the LAX Facilities
engineers, led by Rizallion “RC” Cloma
retrieved and redeployed the data loggers, accumulating nearly a month of data from
numerous systems on the site. This data was forwarded to PECI, who did some
preliminary analysis, which resulted in a Findings List (see Figure 2). This
information was then used by the task for to focus their efforts on a subsequent site
visit during which savings and implementation cost projections were developed.
The bottom line is that the project identified improvements in Indoor Air Quality
(IAQ) and performance, which could be achieved via low cost/no cost efforts. These
measures, when implemented, are anticipated to yield gas and electricity savings in
the range of $130,000 to $153,000 annually with a simple pay back 0.5 to 1 year,
depending on exactly how the staff goes about implementing them.
The complete findings lists as well as the referenced notes are included as part of an
Appendix in the
manual. Potential capital improvement projects also were
identified with a projected annual savings potential of $35,000 and a simple payback
range of 3.5 to 5.5 years.
2
Figure 2 - The LAX Findings List (Part 1)
Retrocommissioning the LAX Marriott
3
Figure 2 Continued
4
Retrocommissioning the LAX Marriott
Getting Ahead of the Game
Prior to the initiation of the retrocommissioning effort, the LAX facilities staff had
already taken significant steps targeted at improving the performance of their systems
and paving the way for the retrocommissioning process. Specifically, the staff
worked through the facility performing O&M procedures like calibration and
adjustments to eliminate the obvious and allow the systems to be probed in greater
depth by the proce process.
They also had upgraded their filters in several units to utilize extended surface area
technology. In addition to improving IAQ, which is continuously challenged by
emissions from traffic at the near-by airport, the filters offered savings on several
other fronts. The lower pressure drops offered by the technology directly reduce
energy consumption. In addition the extra media surface increases the dust holding
capacity by a factor of 2 as compared to conventional filters. As a result, filter life
cycles are increased, reducing labor costs, reducing filter costs, and minimizing the
waste stream from the facility. A variety of options exist for employing the filters, as
is illustrated in Figure 3.2
Standard 30% Prefilters with 65% Standard
Final Filters - 24 hr/day, 7 day/week
Total Cost, Filters, Labor, and Energy
$12,000
$10,000
Standard 30% Prefilters with 75% Extended
Surface Area Final Filters - 24 hr/day, 7
day/week
$8,000
75% Extended Surface Area Final Filters Only
- 24 hr/day, 7 day/week
$6,000
$4,000
Standard 30% Prefilters with 65% Standard
Final Filters - 12 hr/day, 5 day/week
$2,000
$0
0
10
20
30
40
Month
50
60
Standard 30% Prefilters with 75% Extended
Surface Area Final Filters - 12 hr/day, 5
day/week
75% Extended Surface Area Final Filters Only
- 12 hr/day, 5 day/week
Figure 3 - Extended Surface Area Filter Life Cycle Costs: Extended surface area filters offer
many options for reducing costs. Success depends on performing filter changes based on pressure
drop, not time or visual appearance. Thus, providing pressure drop gauges on all filter bank is key to
success.
2
See Using Extended Surface Air Filters in Heating Ventilation and Air Conditioning Systems: Reducing Utility
and Maintenance Costs while Benefiting the Environment at www.PECI.org for a case study documenting
some of the benefits of this technology. A PowerPoint® presentation titled Extended Surface Area Filters, also
available at the site provides additional information on the technology.
Retrocommissioning the LAX Marriott
5
Double Duct Air Handling Systems Findings
The LAX facility
incorporates 5 large
double duct air handling
units to serve its ball
rooms, meeting rooms,
restaurants and public
spaces. A typical unit
configuration is
illustrated in Figure 4.
While this approach was
common for handling
large areas with multiple
zone requirements at the
time the LAX facility was
designed, it has its
drawbacks in terms of
efficiency. Specifically:
2
1
3
1
4
5
6
Figure 4 - A Typical Double Duct Air Handling Unit Typically,
the units include an economizer section and filters (1), a high
pressure supply fan with a diffusion plate in the discharge (2), and
a hot and cold deck (3 and 4) to create cold and hot air streams.
These airstreams are delivered by as high velocity duct system (5)
to constant volume mixing boxes (6), which mix the air streams as
necessary to match the requirements of the area served while
regulating flow at a constant volume.

The systems tended to be designed for large load handling capacities and high
flow rates. As a result, the fan energy associated with them can tend to be high
relative to the requirements of the load and other approaches.

The high velocity duct systems accentuate the friction losses associated with any
duct system and further elevate the system’s fan energy requirements.

The need to split the supply flow into two separate airstreams forces poor
discharge conditions on the supply fan, which further degrades the system
efficiency and increases the fan energy.

The parallel hot and cold air streams further compromise efficiency by setting the
stage for simultaneous heating and cooling. Even the best of mixing boxes will
waste some energy due to damper leakage as can be seen from Figure 5.

Serving a hot and cold air stream from a common supply stream that is served by
an economizer cycle compromises the economizer’s ability to deliver economy.
If the economizer is controlled to minimize the cold deck cooling requirements,
then the hot deck is burdened with an additional heating load as compared to what
would be achieved by recirculating more return air to provide a higher mixed air
temperature. But, elevating the mixed air temperature reduces the cooling
capacity of the cold deck with out using mechanical cooling.
6
Retrocommissioning the LAX Marriott
Lower Level Corridor Mixing Box Performance with a Set Point Change
80
Full Heat
Temperature, °F
75
Mixing Box Cold Deck
Temperature °F
Mixing Box Hot Deck
Temperature °F
70
Mixed (Leaving) Temperature
°F
Return Temperature °F
65
AC5 Imperial Ball Room Hot
Deck °F
60
AC5 Imperial Ball Room Cold
Deck °F
55
Full Cool
50
3/12/04
12:00 PM
3/12/04
12:28 PM
3/12/04
12:57 PM
3/12/04 1:26 3/12/04 1:55 3/12/04 2:24 3/12/04 2:52
PM
PM
PM
PM
Date and Time
Figure 5 - Recently Overhauled Mixing Boxes Still Show Evidence of Damper Leakage
For these reasons, double duct systems are ideal candidates for some focused
retrocommissioning effort. Figure 6 lists the findings associated with the LAX
double duct air handlers. The following paragraphs will discuss some of these
findings in greater detail.
Figure 6 - Double Duct Air Handling Unit Findings
Retrocommissioning the LAX Marriott
7
Reducing Air Flow Rates
Analysis of the drawings and other contract documents revealed that the LAX double
duct units were designed with flow rates that equated to 2.6 to 2.9 cfm/square foot.
However, many loads that exist in the areas served by the units can typically be
handled by 1.0 to 1.5 cfm/square foot. The conclusion reached from these
observations is obvious; in the general case, it should be possible to reduce the
airflow rates on the systems. Data loggers and field measurements revealed that:

Total flow for the systems was at 100% to 115% of design.

Cold deck flow and hot deck flow were nearly identical; i.e. the air handling unit
supply flow was evenly split between the hot and cold deck via the actions of the
mixing boxes, which in general, were mixing equal volumes of hot and cold air to
satisfy the loads they served.

Cold deck temperatures were running in the low to mid 50’s°F while hot deck
temperatures were running in the 75 to 95°F range. This fact, combined with the
previous bullet supported the excessive flow hypothesis.
The ability of an air stream to handle a cooling load is a function of the flow rate and
the difference in temperature between the air stream and the desired zone
temperature. The fact that the mixing boxes were blending hot and cold air to satisfy
the load indicated that a supply stream at the cold deck temperature would over cool
the space. The mixing process that was occurring in the system represents energy
waste due to simultaneous heating and cooling. Reducing the system flow rate would
force the mixing boxes to use more cold air and less hot air to handle their loads,
reducing the simultaneous heating and cooling in addition to saving energy at the fan
due to the reduced flow rate.
Further analysis revealed that implementing this measure could save $56,300 by
reducing fan energy and simultaneous heating and cooling. Implementing the change
can be accomplished in a variety of ways, ranging from a sheave change to installing
Variable Speed Drives (VFDs). Purchasing and installing new sheaves and belts is
the most straight-forward and cost effective approach and actually delivers the best
over-all efficiency since there would be none of the efficiency losses associated with
a VFD. However, while more costly, using a VFD to accomplish the speed change
has several advantages.

Improved Flexibility: Once the drives were installed making the experimental
changes necessary to determine the optimum flow rate would be very easy in
contrast to multiple sheave changes. It would also allow the operating staff to
return to the high flow rates for special situations that might occur such as a
function with unusually high cooling loads due to special lighting and equipment
or higher than normal occupant densities. Similarly, the staff could depress the
flow rates below what was required for functions that might involve filming the
proceedings where eliminating background noise may take precedence over
comfort.

Paving the Way for Future Improvements: Having VFDs in place would be a
major step towards making the conversion from constant volume double duct
operation to variable volume double duct operation as described in DD02.
8
Retrocommissioning the LAX Marriott

Improve AHU Start-up Reliability: The operating staff have experienced startup problems ranging from motor failures to AHU casing damage when the double
duct units are started and stopped due to the large flow rates and high static
pressures involved and the large motors required to operate the units (see DD03
and DD10). Variable speed drives would minimize the potential for damage by
providing a soft start. The facility typically looses one motor a year due to startup problems with a resulting cost of $1,500 to $2,500 depending on the exact
motor size and the rigging problems associated with getting a new motor in place.
Thus these avoided costs are included as part of the savings potential associated
with this finding.
The savings calculation was based on the assumption that on the average 0.5 cfm per
square foot could be eliminated. On the average, this is probably conservative and
the savings achievable might easily be 2 or even 3 times what is projected. However,
it will be important to bear several things in mind as implementation proceeds.

Even though the average flow rate is high, it is likely that there are zones that
need the capacity they are currently served with. Thus, carte-blanche reductions in
airflow at the central unit will need to be supplemented with minor rebalancing at
selected zones.

Determining the exact flow rate reduction can be accomplished in one of several
ways. One approach would be to have an engineer do a zone-by-zone load
analysis based on the real time loads. Another way would be to deploy data
loggers on all or nearly all of the double duct boxes and let them “tell you” what
the load is. Access may be an issue for this option since the majority of the boxes
are above high ceilings. A third approach would be via experimentation using
incremental reductions in flow during the cooling season until nearly all of the
flow on the hot deck is eliminated, which would indicate that all of the cooling
capacity was required to offset loads. This approach might be the most viable,
especially if the speed reductions are accomplished via VFDs rather than sheave
changes.

Making changes of this type will ripple out into the other systems in the building
and most likely require adjustments in other areas. For example, reducing flow
rates will probably change pressure relationships and some rebalancing or
verification of exhaust flows and ventilation rates may be necessary to contain
cooking odors and ensure good IAQ. Similarly, reducing flows will reduce the
potential to simultaneously heat and cool, thus saving energy on other systems.

It is important to not take credit for saving energy twice when assessing the
benefits of complementary features. For instance, reducing flows in the double
duct AHUs will minimize the potential to simultaneously heat and cool. Thus,
the benefits of energy recovery to handle the simultaneous heating and cooling
will be less than they would be if the flow rates at the double duct units had not
been reduced. The calculations used for this evaluation have endeavored to do
this to the extent possible given the time constraints and budget. Thus, it would
be desirable to implement the major findings first and then re-assess the savings
potential of related findings.
Retrocommissioning the LAX Marriott
9
Reducing Simultaneous Heating and Cooling
Optimizing deck temperatures minimizes simultaneous heating and cooling potential.
As a result, both reheat and cooling energy is saved. These savings ripple back to the
central plant because the pumping energy pumping energy associated with moving
the chilled and hot water to the loads is reduced.
This finding proposes automating and optimizing the manual resetting of deck
temperatures. The staff currently is accomplishing this manually. While diligent in
their efforts, other operational issues often will keep even the most dedicated operator
from making the ideal and timely set point changes associated with optimization.
Computers, on the other hand, are very good at this. Plus, the points added to allow
this to be implemented will provide other advantages in terms of diagnostics and
alarm capabilities. These features will add value in terms of improved performance,
improved guest satisfaction, and improved persistence of the RCx implementations.
Economizer Performance
The double duct air handling systems were a good
news/bad news situation. The good news was that
serving both the hot deck and cold deck in no way
compromised the operation of the economizer cycle.
The bad new is that this is because there are no
economizers. Three of the units simply do not have a
connection to outdoor air that would allow operation
above minimum outdoor air up to 100% outside air; the
fundamental component of economizer theory. Two of
the units have a return air connection and an outdoor air
connection, but there are no dampers on either
connection, thus no ability to modulate the outdoor air
flow. The configuration of the units is such that the
will operate as essentially 100% outdoor air units,
despite the return air connection. Testing during the
retrocommissioning process revealed that this was in
fact true.
Figure 7 - The lack of
dampers on the outdoor air
intake and its close
proximity to the supply fan
virtually guarantee that this
unit will operate as a 100%
outdoor air unit, despite the
return air connection
(bottom opening).
The three units lacking the outdoor air capability to
support an economizer cycle offered the greatest
opportunity for savings. This is because the lack of
economizer capability requires that the central chilled water plant operate on a year
round basis. But achieving the savings does not lend itself to the low cost/no cost
solutions associated with retrocommissioning and will require some sort of capital
expenditure. The conventional approach to the problem would involve extending a
large outdoor air duct from the units to the building exterior, a complicated and
expensive undertaking in the LAX facility. A more novel but proven approach
involves using the cooling towers to generate chilled water directly during cold
weather. This still requires the operation of the chilled water pumps and tower fans,
but eliminates the need for a very large outdoor air duct and some complex controls.
Thus, it additional study may reveal that this is the most viable option for the facility.
10
Retrocommissioning the LAX Marriott
Initial estimates indicate that this approach could save $21,400, but could easily
require an expenditure of $75,000 to $100,000.
The two units that are equipped with outdoor air connections but no control present a
much more easily implemented solution; i.e. simply add dampers and controls.
However, the characteristics of the climate in Los Angeles (see Figure 8), coupled
with the way that the double duct configuration compromises the economizer
performance, minimize the savings potential to approximately $4,400.
Annual LAX Outdoor Air Temperature Distribution
2500
2000
Hours
1500
1000
500
0
30
40
50
60
70
80
90
100
110
Temperature, °F
Average Bin Temperature vs. Hours in the Bin
Freezing
Space Condition
Figure 8 - A view of the Los Angeles Climate: The climate in Los Angeles is relatively cool and
dry most of the year. Thus, an economizer-equipped unit would tend to operate on 100% outdoor air
much of the time, just as the units do now. The only times that having the ability to modulate the
outdoor air flow would provide benefit are when the outdoor temperatures are above the typical space
temperature and during when the outdoor air temperatures are below the design cold deck temperatures
(typically 50-55°F). Subfreezing weather and the operational issues typically associated with it are
simply not an issue in Los Angeles.
Preliminary analysis indicates that the most cost effective approach to saving energy
with these systems involves removable blank-off plates that are opened and closed
seasonally based on outdoor air conditions and alarms generated by the EMS. The
plates should be sized to allow enough open louver area to provide the minimum
outdoor airflow necessary for maximum occupancy. Determining this will be most
easily accomplished via experimentation. Because implementing this measure will
increase the recirculation rate, the filters should last longer.
Retrocommissioning the LAX Marriott
11
Implementing Schedules
Trend analysis revealed thatAC-3, the largest air handling unit on the site, was not
being shut down at night when the area it served was unoccupied. This was not news
to the operating staff; there was a compelling reason for keeping it on line.
Specifically, the operating staff had discovered through painful experience that the
unit could be extremely difficult to restart, often resulting in motor failures and
damage to the AHU. Each motor failure costs approximately $1,500 dollars for the
motor itself and has the potential to cost tens of thousands of dollars in lost revenue
due to the inability to condition the ballroom area it serves. On the other hand,
solving the problems that prevent scheduled operation has the potential to save
$15,100 annually, mostly in the form of fan energy. There are several potential root
causes for the problem.
1 Overload Sizing: In theory, the overloads on the motor starter should take the
motor off line before the current flow through it is excessive enough to cause
damage. Overload sizes should be checked and adjusted to match the motor that
is installed. Implementing this recommendation will not solve the start-up
problem, but it will help minimize the potential for burning up the motor when it
does have to be restarted.
2 Loose Connections: Loose wiring connections can reduce the voltage to the
motor, making it difficult for the motor to accelerate up to speed. This prolongs
the inrush current, which, in turn, can lead to premature motor failures. There are
a variety of techniques that can be used to identify loose connections, ranging
from having a licensed electrician physically check them to making a
thermographic survey.
3 Fan Wheel Cleanliness: Over time, dirt can accumulate on a fan wheel, adding
a surprising amount of weight to the wheel. This added weight changes the
moment of inertia of the wheel, which means it will take the wheel longer to
accelerate, all other things being equal. If the wheel takes longer to accelerate,
the motor in-rush current will last longer and can result in premature motor failure
and/or nuisance overload trips that start to occur on a fan that previously has been
problem free. This scenario has, in the past, caused un-informed facilities staff to
increase the overload size beyond what should be installed for the motor, curing
the symptom and not the problem and leading to the issue discussed in 1 above.
4 Motor characteristics: All motors are not created equal; different motors from
different manufacturers or different product lines can have radically different
starting characteristics and moment of inertia capabilities. If the replacement
motors that have been installed did not take the fans starting torque requirements
into consideration, its not out of the question that the new motor simply is not
capable of starting the existing fan. Initially, this would probably show up as a
nuisance overload trip, leading to a solution similar to that described in 3 above
and a problem similar to that described in 1 above.
It is important to understand that even if the items listed above are not the root cause,
implementing other measures may eliminate the problem on this unit. Specifically, a
reduction in airflow will result in a significant load reduction on the fan motor since
fan power varies as the cube of the air flow. This particular unit has a design brake
12
Retrocommissioning the LAX Marriott
horsepower requirement that is very near to the motor horsepower capability, in
contrast to the other units. Unloading the motor via an airflow reduction may have a
significant impact on the current operating problems.
The implementation cost reflected in the findings list provides a VFD to allow the fan
to ramp up to speed, minimizing the loads on the power system and motor and the
shock to the AHU casing. Installing a VFD on a constant volume system as a
balancing device can be undesirable because of the added complexity and efficiency
losses represented by the drive (see Figure 9). However, in this situation, it may be a
viable way to allow the fan to be scheduled and the savings might outweigh the
efficiency losses and complexity issues. The drive also paves the way for the
recommendations of DD2. It is also important to understand that implementing the
recommendations of DD11 may address the start-up problem because it will
significantly unload the motor, and the implementation costs might drop to virtually 0
if the VFD is not required
Variable Speed Drive Efficiency
100%
90%
Model 40P4, 1 hp
80%
Model 43P7, 5 hp
Efficiency
70%
Model 47P5, 10 hp
60%
Model 4015, 25 hp
50%
Model 4030, 50 hp
Model 4055, 100 hp
40%
Model 4075, 150 hp
30%
20%
10%
0%
0%
10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110% 120%
Percent of full speed
Figure 9 - Drive Efficiency Varies with Speed and is never 100%. Notice how the efficiency
generally improves as motor size increases and starts to fall off rapidly below 50-6-% speed.
Finding Interactions
HVAC systems are extremely interactive, both with other systems in the building as
well as with the building itself. Thus it is not surprising that many of the findings
identified for the for the double duct units are interactive. For example:

Reducing air flow reduces over cooling.

Reducing over cooling reduces hot deck flow and increases cold deck flow.
Retrocommissioning the LAX Marriott
13

Increasing hot deck flow increases the velocity driven energy impact of poor
fitting designs.

Reduced hot deck flow reduce baseline gas consumption.

Reduced hot deck flow reduce parasitic cooling energy consumption
(simultaneous heating and cooling).

Reduced cooling load reduces central plant flow requirement at part load.

A reduced central plant flow requirement increases plant turn down requirement
at part load.

An increased turn down requirement demands a more robust central plant;
problems that were not evident before may become apparent.
This interactivity may sound discouraging; some may consider it a reason not to
move forward. However, this is not the case. They actually represent opportunities
to make improvements in other areas. Successful retrocommissioning leads to
continuous commissioning, a process whereby the buildings systems are continuously
monitored, adjusted, and optimized, as the operating team continuously adjusts and
tunes the systems to meet the constantly varying requirements of the loads they serve
and to compensate for wear and aging.
Other Air Handling Systems
The other air handling systems on the project exhibited similar findings to those
described for the double duct units as can be seen from Figure 10.
Figure 10 - Other Air Handling Unit Findings
Finding AHU08 merits some additional discussion. The project documents and
discussions with the operating staff indicate that many of the air handling units on the
project are equipped with electric reheat coils which are still active. Time constraints
prevented focusing any attention on these units during the project. However, electric
heat typically has high operating cost and less than desirable source energy
implications associated with using it. In general terms a btu of heat generated by
burning fossil fuel to make steam and hot water in the central plant will use 60-70%
14
Retrocommissioning the LAX Marriott
less source energy when contrasted with electricity generated with fossil fuels in a
conventional power plant. Costs for the steam/hot water approach will typically be
30-50% of the cost associated with using electricity for heat. Most of the efficiency
losses associated with using electricity for heat are related to the energy conversion
processes used to generate the power and losses associated with transmitting it long
distances.
Because of these factors, the LAX electric heating coils are worthy of some focused
attention as part of on-going O&M and capital planning. More detailed
recommendations are included in the notes pages associated with the findings list.
Past experience indicates that these efforts will result in energy savings, performance
improvements and improved safety.
The Marriott LAX Chilled Water Plant
The findings associated with the Marriott LAX chiller plant are illustrated in Figure
11.
Figure 11 - Findings for the Marriott LAX Chilled Water System
The Los Angeles Marriott features a recently upgraded variable flow central chilled
water plant. Figure 12 illustrates the plant in the form of a simplified schematic and
highlights some of its design features. An attachment to the Findings List Notes
included with the
manual provides additional details regarding variable flow
system operation for those who are interested.
This design, often termed a “primary-secondary arrangement” allows constant flow to
be maintained through the chillers in one flow circuit while the system load varies
with flow in a separated but interconnected flow circuit. Varying the flow with load
is the primary energy savings mechanism as contrasted to a constant volume system.
To get the flow to vary with the load, the loads served by the system must be
equipped with two-way valves instead of three-way valves, which typically would be
applied on a constant volume system.
Retrocommissioning the LAX Marriott
15
Figure 12 - The Marriott LAX Variable Flow Chilled Water Plant The plant incorporates a constant volume pumping
circuit through the chiller evaporators (the yellow highlighting on the drawing to the left) that is coupled with a variable flow
circuit through the loads (the lavender highlighting on the drawing on the right). Both circuits share a common section of
piping typically called the bypass line or decoupling line (the red oval on the drawing on the right). It is this section of pipe
that allows one circuit to function independently of the other. The flow rate in the decoupling line will vary and can be from
the return to the supply (often termed “forward flow”), from the supply to the return (often termed “reverse flow”) or under
some very specific load conditions, zero.
Excessive Chilled Water Distribution System Flow
A Direct Digital control (DDC) system was included as a part of the plant upgrade
project. During the first site visit, the trending capabilities of the system were set up
to monitor system performance parameters to allow problems to be identified and
diagnosed. Figure 13 illustrates some of the data that was captured. The calculated
load was based on chiller temperature and flow measurements taken by the DDC
system (also called the EMS). The theoretical flow line illustrates the flow that
should exist in the distribution system for the documented load conditions.
Unfortunately, the actual flow to the loads was significantly higher than the required
flow and showed no tendency to vary with load.
This sort of problem is actually quite endemic in variable flow chilled water plants
and has operating implications that ripple out to the loads and cause further
inefficiencies. For instance:

The high distribution flow rate relative to the chiller flow rate means that there is
forward flow in the bypass line; i.e. flow bypasses the chillers in the decoupling
line. As a result, the temperature to the loads is higher than the temperature
leaving the chillers because of the warm, bypassed water blending with the cooler
leaving water from the chillers. Most automated plant control strategies target
minimizing or preventing this situation.

The elevated supply temperatures to the loads cause the control valves at the loads
to open more than they would had the design supply temperature been delivered
to them.
16
Retrocommissioning the LAX Marriott
Chilled Water Base Chart, 03-04-04 11am - 03-05-04 11am
2,000
250
Calculated Load Tons
1,500
200
150
1,000
100
500
50
0
11:36
AM
2:36
PM
5:36
PM
8:36
PM
11:36
PM
2:36
AM
5:36
AM
8:36
AM
Flow, gpm
Load, tons; Temperature, °F
300
Outdoor Air Temperature
Theoritical Flow gpm
Total Flow to Loads gpm
0
11:36
AM
Date and Time
Figure 13 - Marriott LAX Chilled Water Plant Peformance Note the discrepancy between the
theoretical flow requirement and the measured flow.

Driving the control valves open further aggravates the excessive flow condition in
the distribution system, which further aggravates the forward flow in the bypass
condition at the central plant.

The aggravated forward flow condition drives the process into a viscous circle
until things somehow come into balance.
On low load days, the higher supply temperatures may actually satisfy the loads, but
the plant pays a penalty in terms of efficiency. At some point, some or all of the
loads begin to drift above set point due to the elevated supply water temperatures.
The retrocommissioning team saw evidence of this in several areas on the project
(see findings AHU03 and AHU08). Implementing some of the other findings like the
flow reductions at the double duct units will make the plant overflow condition a
bigger operational issue since the double duct systems will be less tolerant of high
chilled water supply temperatures as the mixing boxes shift more of the flow from the
hot deck to the cold deck.
The excess flow issues at the Marriott LAX plant can be attributed to three general
issues (see Figure 14):

Control loops that are out of control: Generally this is caused by the elevated
supply temperatures either directly because the valves are driven fully open in an
effort to meet a set point that simply can not be achieved with the available supply
temperatures. The out of control condition can also be generated by frustrated
operators setting the controllers for unachievable set-points (for instance, setting
the chilled water valve controller for 45°F which is below the plant design supply
temperature and well below the cold deck design temperature).
Retrocommissioning the LAX Marriott
17
AHU3, 03-04-04, 4-10 am
100
120
95
90
PCM-2-1 AI 1 AHU3 Cold Deck
100
Temperature, °F
80
75
70
80
Unachievable set
point; coil runs wild
60
65
60
40
Valve Command, %
85
AHU-3 Supply Air SP.
PCM-2-1 AO 1 AHU3 CHW Valve
55
50
20
45
40
4:00 AM
0
5:00 AM
6:00 AM
7:00 AM
8:00 AM
9:00 AM
10:00 AM
Date and Time
Figure 14 - The Three General Causes of Excess Flow at the Marriott LAX Chilled Water Plant Set points well below
what could be achieved by the current or design operating parameters drive valves fully open (left). Three way valves
applied on a system where the flow must vary to achieve design intent maintain nearly constant system flow rates regardless
of load condition (bottom right). The lack of a variable speed drive on the distribution pumps means that the pumps must be
pushed up their curve to vary flow (top right).

Three way valves at the variable flow loads: For a variable flow plant to
function, it is essential that the loads be equipped with a valve design that varies
flow as the load changes. Sadly, many of the largest loads on the system are still
equipped with three way valves. These valves do not contain a balancing valve in
the bypass line, which could further aggregate the problem. This is because the
bypass connection is relatively short and quite possibly represents much less
resistance to flow that the coil it the valve serves. As a result, when the valves
modulate to bypass, the flow tends to short circuit around the coil immediately
and at a rate in excess of design. This non-linear valve characteristic can also
make the valve control loops difficult to tune.

Lack of variable speed capability on the distribution pumps: The
distribution pumps at the central plant are not equipped with variable speed
drives. As a result, flow reductions must be accomplished by forcing the pump up
its operating curve rather than reducing its speed. This increases the head in the
system, which may over-power the close-off capabilities of the chilled water
valves, causing flow through the loads even if it is not required. There was some
evidence of this observed at the guest room fan coil units. This problem is
compounded by the fact that the pumping head on several of the distribution
pumps appears to be excessive for the system. The two larger pumps have nearly
twice the head of the smaller pump. Yet, the plant has always been able to serve
the loads by operating only the smaller pump. A quick field assessment of the
pumping head requirements for the system indicates that it is probably closer to
the smaller pumps rating than not. Further support is evidenced by the operating
18
Retrocommissioning the LAX Marriott
staff’s reluctance to operate the larger pumps because they know they have
problem with over-pressurizing the system and leaks when they do.
There is also a subtle but important detail associated with the current control
arrangement for the loads that do have two-way valves that prevent the valves from
being totally effective. Currently, there is no interlock available to close these valves
when the units are off. As a result, the valves tend to drive open when the fan stops.
This makes a bad situation worse by contributing to the excess flow condition and by
driving the system return temperature down because of the high volumes of supply
water that are mixed in with the return. The supply water is still cold since the
inactive coils transfer no heat from it. This creates additional operational problems
at the central plant, further degrading its efficiency.
Many of the issues associated with the chilled water plant actually have there roots in
the cancellation of the final phase of the chiller plant upgrade project due to budget
problems that were the outfall of the events of 9/11. Completing the following steps
associated with the final phase of the central plant project will go a long way towards
improving the performance of the central plant.

Convert all loads to 2-way valves: It may be possible to perform this work inhouse on the smaller valves by adding a balance valve to the bypass connection
associated with three-way valves and then throttling it nearly closed. The result
will be a valve that operates almost as if it were a three way valves. Outside
contractors will probably be required to modify the larger valves due to the need
to work with big pipe.

Install a variable speed drive on at least the lead pump in the central
plant: Adding a drive to one of the larger pumps would also be desirable in terms
of operating flexibility and redundancy. Another option to consider would be to
sell the existing oversized pumps and use the proceeds of the sale to help fund
replacement with variable speed pumps selected for the actual requirements of the
system. This approach will provide the best efficiency since the replacement
pumps could be optimized for the system’s requirements.

Tune control loops: Tuning the control loops to operate at the correct set point
and be stable under all load conditions will be a critical final step in the
improvement process. Otherwise, the benefits gained from the other steps will
not be realized.
All of these changes will undoubtedly raise other operational issues with the chilled
water system. This is because they will force the system to operate as a variable flow
system per its design intent, an operating contingency it has not had to face in the
past. This should not be viewed as a problem, but as an opportunity to further
improve the efficiency of the plant and maximize the benefits of the potential that the
recent upgrade investment represents.
Based on past experience, there are two issues that are likely to come to the forefront
as the plant is forced to work in the variable flow mode.
1 The loads served by the system need to be tailored to the differential temperature
capability of the plant both at design and as the load drops off. In other words,
the temperature rise across the loads should match the temperature drop produced
Retrocommissioning the LAX Marriott
19
by the chillers. Typically, this is a matter of coil circuiting and flow rates at the
loads and evaporator circuiting and flow rates at the chillers. Temperature rises at
the loads of 12 - 16°F are both achievable and common. But shallow coils (less
than 6 rows) such as those typically found with fan coil units often simply cannot
generate a temperature rise greater than 6 to 8°F. Thus, when a system with a
design temperature differential in excess of this value must serve a significant
quantity of fan coil units, particular attention needs to be paid to ensure that the
design differential is realized at the plant. One technique involves selecting some
loads for a temperature rise that is excess of the plant requirement to balance out
the lower temperature rise loads and deliver a mixed temperature that matches the
chillers. Design temperature differentials of 10 - 14°F are typical; the LAX plant
appears to be targeted at 12°F.
If this contingency is not addressed, the relatively cool return water from the low
temperature rise loads like fan coil units tends to drive the system temperature
differential down and the flow rate up relative to what might be expected on a
non-fan coil equipped system serving the same load. This, in turn creates
significant operating problems at the central plant that can cause it to be quite
inefficient due to excessive, unnecessary pumping rates and unnecessary auxiliary
energy.
At the Marriott LAX, the potentially low temperature rise associated with the fan
coil units, when coupled with their quantity (approximately 1,000) could mean
that the temperature difference of the fan coil unit circuit relative to the plant
design is an issue. There is some evidence to suggest that this had been
considered at one time in the LAX plant. Specifically, there is an abandon
pumping circuit that used to serve a compressor in the laundry area. The
configuration of the piping serving this load (now abandon in place) suggests that
the pump could be configured to elevate either the supply temperature to or return
temperature from some or all of the loads, thus helping to alleviate the low
temperature rise associated with the fan coil units. Since the laundry has been
decommissioned, this function is no longer provided and there is no indication
that the central plant upgrade addressed it directly via some other mechanism.
Budget for further analysis of this issue should be included in the engineering
support associated with the implementation effort.
 2
The bypass configuration in the central plant will tend to make starting the
2nd chiller difficult under some operating scenarios. Specifically, when a chiller
closer to the plant return connection than the operating machine is started, the
flow changes that occur place a nearly instantaneous load change on the operating
machine. Frequently, the capacity control system of the operating machine
cannot react quickly enough and the machine trips off line on a nuisance safety
trip. There are operating techniques that can be used to deal with this issue, but
since the staff’s experience has been that they only need to operate one machine,
they probably have not had to develop an operating strategy to deal with it. When
the loads on the system reach the point where it becomes necessary to bring a
second chiller on line, the operating staff may begin to experience this system
nuance. Its important to understand that this does not mean the system is
20
Retrocommissioning the LAX Marriott
unworkable; it just means that it needs to be operated with sensitivity to the
issue.3
Excessive Evaporator Pump Head
In a variable flow chiller plant, the evaporator pumps function to move water from
the return side of the bypass connection, through the chillers, to the supply side of the
bypass connection. As a result, their head requirements are typically modest since the
piping circuits they serve tend to be short relative to the distribution system.
Fredrick/Weinman Engineered Products 2-1/2 KH, 2-1/2 x 3 x 12
Serial Number 110188-1-96, 1 inch pattern 4586 impeller, 20 hp, 1750 rpm, Curve number 2-1/2KH-182
160.00
12 inch
140.00
11 inch
Head, ft. w.c.
120.00
10 inch
100.00
9 inch
80.00
15 bhp
60.00
10 bhp
7.5 bhp
40.00
Impeller Lines
Brake Horse Power Lines
Pump Efficiency Lines
System Curve
5 bhp
20.00
0.00
0
100
200
300
400
500
600
Flow, gallons per minute
The inf or mation on this pump cur ve was r epr oduced f r om the manuf actur er s cer tif ied per f or mance cur ves f or the pur pos es of analys is and illus tr ation. To ver if y cer tif ied per f or mance f or this pump, r ef er to the manuf actur er s cer tif ied per f or mance cur ve
Figure 15 - A Typical Centrifugal Pump Performance Curve The pump will operate at the point
where the system curve (the dashed red line) intersects the pump impeller curve ( the solid blue, green,
yellow and red lines). Most pumps can utilize a range of impeller sizes and the actual impeller
installed can be trimmed on a lathe to any size between the maximum and minimum impeller size to
match the performance to the system curve. Constant horsepower lines are also depicted on the curves
to allow power requirements to be assessed (the gray dash-dot lines). In this example, the system
curve intersects the 12” impeller curve at about 378 gpm requiring a little over 15 hp. (inside the red
circle). If the desired flow rate is 300 gpm, one way to achieve it would be to throttle the pump to 300
gpm. This would “push” the operating point up the pump curve to the blue circle, reducing the
horsepower slightly but not much since the horsepower lines and pump curve are nearly parallel in that
area. A more energy efficient option would be to reduce the impeller size to approximately 9-3/4” (the
green circle). This would reduce the power requirement to approximately 8 hp while still delivering
300 gpm of flow because the pump would not have to move water against a throttled discharge valve.
If the pump selections end up having more head than is necessary, the pumps will run
out their curves until the flow they produce comes into balance with the pressure
requirements of the system they serve at a higher flow rate. The balancing contractor
3
Explaining the details of this issue and what happens when the second chiller is started is complicated and
beyond the scope of this case study, but there is a document attached to the Findings List notes that PECI
prepared for another similar project which explains the issue in detail.
Retrocommissioning the LAX Marriott
21
typically will throttle the pumps back to the design flow, which often (but not always)
will save energy as compared to not throttling the pumps. Since the performance of
the chillers and chiller plant is related to running at the design flow conditions, the
pumps need to be throttled to design even if energy will not be saved. In any case,
the throttled pumps will use more energy than necessary because the pressure drop
taken by the water as it flows through the throttled discharge valve is dissipating
energy that was put into the system by the motor only seconds prior.
Trimming the pump impeller to match the pump performance to the system offers a
way to achieve design flow with out wasting energy at a throttled valve (see Figure
15). This can be a relatively inexpensive undertaking compared to the savings
potential. Typical costs for a 1,000 to 2,000 gpm pump are as follows:

$50 to $150 to turn down an existing impeller.

$500 to $1,000 for a new impeller if you don’t want to risk your existing impeller,
require a quick turn-around, or want to be able to go back to the original operating
point at some time in the future. Note that this may not be an option with older
pumps if the impellers are no longer stocked.

4 to 8 man-hours plus a gasket set to remove and replace the impeller.
Paybacks in the range of 6 months to 2 years are very
common.
This is a very common finding that can be assessed by a
very simple tests and yield significant savings. In
addition, there are usually some very obvious indicators
of the condition. Either the discharge valve will be
wide open and the pump will be rated for much more
head that a quick assessment of the system would
indicate is necessary4 or the discharge valve will be
very heavily throttled. The latter was the case with the
evaporator pumps at the LAX Marriott; actually the
throttled valves were on the discharge of the
evaporators rather than the evaporator pumps, but the
Figure 16 - A Throttled
effect was the same since the valves are in series with
Valve at the Evaporator
the pump discharge. Trimming the pump impeller to
Discharge at the LAX
eliminate the need to throttle the valve has the potential
Marriott The position
to save $6,500. Since there are actually three
indicator is inside the red
circle. Full open is straight up.
evaporator pumps piped in parallel and the plant
typically only needs one chiller, a variety of options
exist. Trimming only one impeller provides the fastest payback but introduces some
fairly minor operating issues that need to be contended with. Trimming all of the
impellers eliminates most of the operating issues, but increases the payback., although
it still is projected to be a year or less.
4
For an example of a technique that can be used to quickly assess pump head requirements in the field, go to the
Energy Design Resources web site at www.energydesignresources.com and download the design brief titled
Design Review, which is free of charge.
22
Retrocommissioning the LAX Marriott
The Marriott LAX
Condenser Water
System
Portland Energy Conservation Inc.
1400 SW 5th Avenue, Suite 700, Portland Oregon 97201, 503-248-4636, FAX - 503-295-0820, www.peci.org
Cooling
Tower
Cooling
Tower
Cooling
Tower
Cooling
Tower
Cooling
Tower
Cooling
Tower
The condenser water
system associated with
Chiller 1
Chiller 3
Chiller 2
the LAX Marriott chilled
Refrig.
Comp.
water plant is illustrated
as a simple schematic in
Pump
Pump
Figure 17. The condenser
Pump
Pump
Pump
PP1
PP3
PP2
pumps exhibit a potential
for energy savings via
impeller trims that is
similar in concept and
magnitude to that
Figure 17 - The LAX Marriott Condenser Water System
described in the
preceding section for the
evaporator pumps. In addition, there are several attributes of the system that can be
exploited to advantage to deliver additional energy savings for a relatively low level
of effort.
1 The installed tower
Condenser System Performance 3/4/04; 12:30 pm to 1:00 pm
capacity is quite
generous relative to
the installed chiller
capacity and is
provided as two banks
of three cells each.
Currently, the staff
operates off of one
bank while
performing
maintenance on the
other bank. If both
banks are utilized
Time
concurrently, the
evaporative surface
Figure 18 - Marriott LAX Condenser Water System
area is doubled. This
Performance
will allow the towers
to dissipate more heat before fan operation is required, thereby reducing fan
energy requirements.
110
200
100
180
Condenser Water from Tower 2
Condenser Water to Tower 2
90
160
70
120
60
100
50
80
40
VFD 2 Speed Command
Outdoor Air Temperature
VFD 1 Speed Command
VFD 3 Speed Command
60
30
40
20
20
10
0
12:30 PM
Condenser Water System Set Point
140
VFD Command, %
Temperature, °F
80
0
12:35 PM
12:40 PM
12:45 PM
12:50 PM
12:55 PM
1:00 PM
Implementing this operating strategy has the additional advantage of further
reducing pumping energy since it will split the condenser water flow between two
generously sized mains.
2 From an air handling standpoint, each tower cell is an independent air handling
system in parallel with the identical air handling systems represented by the other
Retrocommissioning the LAX Marriott
23
cells. The fan affinity laws state that the fan power varies as the cube of the flow.
Applying this to the tower cells reveals that running two cells at half speed will
consume 1/8 (1/2 cubed or 1/2 times 1/2 times 1/2) of the energy that one cell
would consume running at full speed. Currently, the system is programmed to
run one cell up to full speed before starting a second cell (see Figure 18). Energy
savings will be realized by reprogramming the system to start bring all fans on at
minimum speed and them ramp them up together rather than one at a time.
3 Chiller efficiency is improved by lowering condenser water temperatures. But,
lowering condenser water temperatures will generally require additional fan
energy, all other things being equal. In most plants, there is some potential to
optimize the condenser set points by experimenting to discover the optimum
balance between reduced chiller kW and increased tower fan energy. The kW
information available from the tower fan VFDs and the chiller control panels
make this a fairly simple undertaking. By adjusting the condenser water supply
set point gradually and observing the results in terms of a net kW increase or
decrease when the tower energy and chiller energy are added up, the operating
staff can optimize over-all efficiency. It may be necessary to determine the
optimum setpoint under a variety of conditions and then use the programming
power of the DDC system to implement a reset schedule that varies the set point
as a function of some parameter like outdoor air temperature to ensure
optimization under all conditions.
While the savings to be realized by this implementation are modest relative to some
of the others ($2,600) they are easily achieved and have the good potential to persist.
Since the LAX climate rarely if ever sees subfreezing weather, the limitations to these
approaches that would arise in that situation do not need to be considered, further
simplifying the implementation.
The Marriott LAX Heating Hot Water and Steam Systems
Figure 19 - Findings for the LAX Marriott Heating Hot Water and Steam Systems
A central hot water system serves the major heating loads at the Marriott LAX. The
guest room fan coil units are not served by this system and incorporate electric heat.
24
Retrocommissioning the LAX Marriott
A central steam system provides heat for the hot water system along with the pools
and Jacuzzi and the domestic water systems. The findings associated with the hot
water and steam systems are illustrated in Figure 20.
The heating water system
is illustrated as a
simplified schematic in
Figure 20. The plant is a
relatively simple constant
volume system with heat
provided via a steam heat
exchanger served by the
boilers. Several
conservation
opportunities exist in the
system. One was
implemented during the
course of the
retrocommissioning
process.
Portland Energy Conservation Inc.
1400 SW 5th Avenue, Suite 700, Portland Oregon 97201, 503-248-4636, FAX - 503-295-0820, www.peci.org
Heat Exchanger Pumps 1 and 2
Heat Exchanger
Pump
HWP1
Pump
HWP3
TDV
Pump
HWP 2
Past experience indicated
Figure 20 - The LAX Marriott Central Hot Water Plant The
that it might be possible
plant has undergone several modifications since it was first built.
to operate only one of the
The most recent added the secondary pumping circuits to the heat
parallel pumps serving
exchanger. Notice how the return from the heat exchanger (red
circle) connects to the main ahead of the supply connection (blue
the heat exchanger rather
circle), the reverse of what would normally be designed. While the
than both pumps as was
flow and temperature conditions that occur as the water flows
the practice. Rather than
through the series of tees that make up the secondary connections
do a lot of calculations to
are complex and theoretically interesting, the net effect on plant
assess the impacts of such
efficiency and operations is negligible.
a change, the team took
advantage of the forgiving nature of heating water systems, installed a data logger to
monitor temperatures and pump energy, and turned off one of the pumps. The result
was no detectable change in plant performance accompanied by a reduction in
pumping energy that equated to an annual savings of $500. While modest in the
context of the other opportunities, the savings was easily achieved with a nearly
instantaneous simple payback.
The steam system also has the potential for some quick, easily achieved, low risk
efficiency improvements. Many of the valves and specialties currently are uninsulated, probably because the insulation was removed for maintenance purposes.
Since the steam system operates at a relatively high temperature (approximately 240 260°F) the losses from the uninsulated fittings can be quite significant.5 Installing
removable insulation blankets has the potential to make a very significant reduction in
the losses from these fittings. The blankets can be quickly removed and reinstalled
by the maintenance staff as necessary to service the equipment. At the LAX Marriott,
5
A DOE funded study developed a handy tech sheet for quickly estimating losses from uninsulated fittings in
steam systems. It can be downloaded at no cost from
http://www.oit.doe.gov/bestpractices/technical_publications.shtml#technical.
Retrocommissioning the LAX Marriott
25
the estimated annual savings associated with installing the blankets is approximately
$12,500 with a payback of approximately 9 months.
Figure 21 - Uninsulated Valves and Specialties at the Marriott LAX Plant (left) and Removable
Insulation Blankets Installed on Another Project (Right)
Figure 22 - Other Marriott LAX Findings in Miscellaneous Categories
26
Retrocommissioning the LAX Marriott
Other Miscellaneous Findings
Guest Room Fan Coil Unit Performance
110
Temperature, °F; Relative Humidity, %
Figure 22 illustrates other
findings identified by the
study in a variety of
categories. Time
constraints precluded
analysis of many of these
issues, but the evidence
suggests they are worthy
of additional investigation
by the staff.
100
Possible simultaneous
heating and cooling
when strip heaters run
Temperature difference
may90 indicate valve leakby (sensors not in wells)
Return Air Temp., °F
80
Return Air RH
CHW Supply Temp., °F
70
CHW Return Temp., °F
60
50
One item worthy of
Tendency towards a high relative
attention in particular is
humidity may indicate inadequate
the guest room fan coil
make up air conditioning
Date and Time
units. While the savings
potential for any given
Figure 23 - Potential Guest Room Fan Coil Units
unit is small, the sheer
number of units makes
the net savings potential significant for any issue that is repeated from unit to unit to
unit. It is not at all uncommon to have a design error, operational error or failure
propagate through multiple similar units with significant implications in terms of
energy and performance.
40
Wed
3/24/04
3:00 PM
Wed
3/24/04
6:00 PM
Figure 23 Illustrates some potential
issues that showed up in several data sets
retrieved from the guest room units.
While the sample size was to small to
state that the potential deficiencies apply
to all units, the fact that these issues
showed up more than once means they
merit additional consideration. At a
minimum, add ional data logging and
analysis of a significant (5-10%) sample
of the guest rooms would be desirable.
Additional actions to be taken can be
based on the results of this effort.
Wed
3/24/04
9:00 PM
Thu
3/25/04
12:00 AM
Thu
3/25/04
3:00 AM
Thu
3/25/04
6:00 AM
Thu
3/25/04
9:00 AM
Thu
3/25/04
12:00 PM
Thu
3/25/04
3:00 PM
Figure 24 - Possible Indications of Errosion
Note how the pipe wall has been thinned in this
area down stream of reduced port ball valves.
Cavitation and erosion could be responsible for
this. Both phenomenon might be associated with
flow rates in excess of what is required.
The Marriott staff has suspected for
some time that the flows and pressures
in the domestic water system might be
excessive, based on the piping failures they have experienced, which appear to be
related to erosion. (see Figure 24). While some energy savings potential might exist
if the flows and pressures are reduced to eliminate the problem, the far more
significant benefit will be realized as reduced failures in the system.
Related to the preceding, the Marriott staff has also spent some time exploring the
possibility that the domestic water booster pumps could be shut down. The data set
illustrated in Figure 25 indicates that while this may not be viable all of the time, it
Retrocommissioning the LAX Marriott
27
may be possible some of the time, especially if low pressure shower heads are
installed in the upper floors and a high volume bypass with a check valve is installed
around the pump set. Shutting down the pump part of the time has the potential to
eliminates an 8kW load, saving $3,000 per year.
Domestic Water Booster Pump Performance
120
100
Incoming water pressure at pump
suction with the pump running
Pressure, psig
80
Building height in psi
60
Difference between incoming water
pressure and building height psi
40
20
0
3/23/04 3/23/04 3/24/04 3/24/04 3/24/04 3/24/04 3/25/04 3/25/04 3/25/04
12:00 PM 6:00 PM 12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM 6:00 AM 12:00 PM
Date and Time
Figure 25 - Marriott LAX City Water Pressure Note how the available city water pressure may
exceed the requirement to serve the upper floor of the facility some of the time.
Conclusion
The preceding paragraphs represent just a few of the details behind the results of the
Marriott LAX effort. And that’s only the beginning. Time constraints prevented
analysis of a significant amount of the data collected over the course of the project.
As the staff and their consultants spend additional time with the trends that have been
collected but have yet to be explored, they will more than likely discover additional
savings and performance improvements. In fact, the biggest problem most
experienced commissioning practitioners have with the data collected in this type of
project is making themselves stop playing with it before they blow their budgets. In
other words, they are saving energy and resources and having a good time doing it.
C:\Workspace\520 - Marriott RCx Project\Findings\LAX Case Study v2.doc
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Retrocommissioning the LAX Marriott