TECO: A deep dive into optimization data yields unexpected savings
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
TECO: A deep dive into optimization data
yields unexpected savings
Layered efficiencies drive down costs while maintaining reliability
By Michael P. Manoucheri and Ben Erpelding
TECO
Thermal Energy Corporation’s district energy system serves 51 buildings on the campus of Texas Medical Center.
three-phrase initiative to explore customer demand for chilled water con- ing the chiller plant’s electrical demand.
A and implement cost savings across
the largest district cooling sys-
tem in North America has paid off
handsomely – and quickly – bringing sig-
nificant system improvements even in
tinues to rise.
TECO, named IDEA's System of the
Year in 2019, provides chilled water
and steam to Texas Medical Center in
Houston, which – as the world's largest
In the first seven months of optimization
– from June to December 2020 – TECO
lowered peak demand by 2 MW, saving
nearly 10.5 million kWh, and reduced the
plant’s energy consumption by 6%. Now,
the midst of the COVID-19 pandemic. medical campus – requires reliable, TECO can avoid spot-purchasing power
Efficiency gains have been seen in con- economical heating and cooling and from the sometimes unreliable public grid
denser management, chiller operations has growing needs. and more easily keep up with customer
and thermal energy storage. Peak chilled water demand has demand. By reducing peak demand, TECO
The project’s genesis can be traced increased by 9,000 tons over the past four also bought time to develop a new mas-
to IDEA’s annual conference in June 2019, years and is expected to grow by an addi- ter plan, including how and when to add
when representatives from tional 9,000 tons over the next power production capacity.
Thermal Energy Corporation three years. TECO has found
(TECO) and Optimum Energy MAINTAINING that the most cost-effective PHASE 1: CONDENSER-SIDE
struck up a conversation about RELIABILITY, way to manage district growth OPTIMIZATION
the pitfalls of drawing electric- EVEN AS DEMAND while maintaining its histori- TECO has two interconnected plants
ity from the grid in the swelter- RISES, THROUGH cal reliability of 100%, with no housing 27 chillers, nine boilers and one
ing heat of a Texas summer. INNOVATIVE unplanned outages since 1992, TES tank, managed by a Toshiba distrib-
The TECO team wondered EFFICIENCY is to layer on new efficiency uted control system. System capacity is
if the company could decrease MEASURES. measures. 120,000 tons, with a peak load of 78,600
electrical consumption from Partnering with Opti- tons and 345 million ton-hours per year
its main site before June 2020, mum Energy, TECO’s engineer- of annual load. The system’s latest chilled
the start of the next peak demand sea- ing team developed a three-phase plan. water expansion, called the East Chiller
son. Customer chilled water demand was First, for the condenser water system to Building, consists of four 8,000-ton vari-
growing rapidly enough to soon exceed conserve more energy and reduce costs; able-speed York Titan chillers; four
on-site generation resources. second, to have the chiller staging pro- variable-speed, primary-only chilled
TECO needed a solution that would cedures better handle changing loads; water pumps (24,000 gallons per min-
maintain reliability, keep costs down and and third, to take advantage of real-time ute, or gpm, 1,000 horsepower (hp), 138
conserve resources. That initial conversa- electricity pricing for the thermal energy feet head; four fixed speed condenser
tion, in 2019, turned into a multiphase, storage (TES) tank dispatch. water pumps (16,300 gpm, 600 hp, 112
plant-wide optimization journey that Two years down the road, TECO has feet head) and six variable-speed cooling
now saves TECO $550,000 and 16.1 mil- improved control over the energy balance tower fans (16,300 gpm, 101-86 degrees
lion kWh of energy annually – even as of its CHP system and its TES tank, reduc- F, 80 F WB, 250 hp).
© 2022 International District Energy Association. ALL RIGHTS RESERVED. District Energy | Spring/Summer 2022 25
The East Chiller Building condenser
FIGURE 1. 2019 trends for variable speed chiller #4 efficiency (kW/ton) vs. lift (deg F). water system was considered a low-risk,
ECH B CH4- kW/Ton versus Lift
high-reward starting point. Improvements
1.00
1.00
focused on reducing chiller lift, which is
0.90
0.90 defined as the leaving condenser water
0.80
0.80 temperature minus the leaving chilled
0.70
0.70
• water supply temperature. (High chiller
0.60
0.60
lift reflects hot, humid ambient condi-
y = 0.0106x + 0.0242
0.50
::. 0.50 tions that are typical in the summer, when
kW/ton
>
>
� R2 = 0.9769
0.40
0.40 demand for low-temperature chilled
0.30
0.30 water is high. Conversely, in winter, lift is
0.20
0.20 lower.) For example, a chiller with a sup-
0.10
0.10 ply temperature of 40 F and a leaving
0.00
0.00
condenser water temperature of 95 F
10.0 20.0 30.0 40.0 50.0 60.0 7C would have a design lift of 55 F.
10.0 20.0 30.0 40.0 50.0 60.0 70.0
Chiller Lift (deg F)
Chiller lift Figure 1 shows one of the 8,000-ton
chiller’s trended data for efficiency
Source: TECO
(kW/ton) versus chiller lift. If TECO’s
chiller were operating at 6,500 tons, a
2 degree F reduction in lift would save
FIGURE 2. ECHB Cooling Tower Performance; leaving condenser water temperature vs. outdoor wet 137.8 kW of energy.
bulb temperature at different delta Ts. Conditions were ripe for optimiza-
SPX Cooling Technologies
TRACS Version 6-MAY-09
tion: The four 8,000-ton chillers in the
90 Model F4109-4.0-10B
Number of Cells
Motor Output
10
250 Hp
East Chiller Building were designed for a
Motor RPM 1800
85 Fan
Fan RPM
32 ft HP7 9
112
2 gpm/ton condenser water system. The
(Full Speed)
Design Conditions:
remaining 23 chillers in the two plants
Cold water (F)
Flow Rate 163000 gpm
80 Mass Flow
Hot Water
22509.5 lb/s
101 °F
were designed for a 3 gpm/ton system.
Cold Water 86 °F
Inlet Wet-Bulb
L/G
4 18 F range
80 °F
1.263
Automated balancing valves maintained
75
Curve Conditions:
Fan
3 Pitch
15 F range Constant
design flow through the condenser bun-
Flow Rate 163000 gpm
70
( 100% Design Flow )
2 12 F range
dle on each East Chiller Building running
10 cell, Fans Full
4 205.000017
1 9 F range
chiller. In general, the cooling tower fans
65 3
were often operating at 100%.
Design point
2
q 18 °F Range The Optimum Energy and TECO team
60 1 p 15 °F Range
o
n
12 °F Range
9 °F Range developed a consistent, real-time, digi-
45 50 55 60 65 70 75 80 85 X Design Point
45 50 55 60 65 (°F)
Wet Bulb 70 75 80 85 tal standard operating procedure that
Wet bulb (F) Time: 08:37:03 Date: 12-03-2009 Drawn By: BCS included automation, operator prompts
Source: TECO
and screens, and energy conservation
measures. The plan included increasing
FIGURE 3. 2019 trends for constant speed chiller #9 efficiency (kW/ton) vs. lift (deg F) and two setpoints so that all condenser water bal-
different loading bins. ancing valves were near 100%.
A deliberate commissioning pro-
0.70 cess ensured that condenser water pump
motors did not over-amp as they rode
0.65
down their pump curve, that there was
0.60
no excessive pump/motor vibration, that
header pressures stayed high enough for
kW/ton
6,500 - 7,500 tons
0.55
5,000 - 6,000 tons
other auxiliary equipment served by the
condenser water system, and that the
0.50
flow stayed below the maximum allow-
0.45 able for each chiller. The new operat-
ing procedure includes running as many
0.40 cooling towers as possible while staying
above minimum flow requirements and
10 15 20 25 30 35 40 45 50 55
Lift (F)
implementing power-based relational
control of the cooling tower fan variable
Source: TECO frequency devices (VFDs).
26 District Energy | Spring/Summer 2022 © 2022 International District Energy Association. ALL RIGHTS RESERVED.
Because of the interdependencies Finally, the engineering team PHASE 2: CHILLER-STAGE OPTIMIZATION
of the energy conservation measures improved tower fan speed control. While As the engineering team moved to
(ECMs) above, the energy savings are conventional cooling tower control involves the second phase of optimization, it real-
compounded. When the condenser delivering a specific condenser water tem- ized that TECO’s shift operators were
valves are opened to 100%, the 16,300 perature to the chillers, holistic optimiza- using different ways of staging and run-
gpm pumps produce 19,500 gpm with tion achieves the best overall total plant ning the chillers – adding or shedding
no amp or vibration issues. The extra efficiency when calculated relationships chillers by looking at the chiller amps,
3,200 gpm in flow results in a 16% between fan energy and chiller energy are chiller vanes and district chilled water
reduction in chiller lift and a smaller con- maintained. The TECO systems employ a end-of-line differential pressure (DP).
denser water delta T (differential). The patented speed control method for tower High amps, vanes near 100% or a low
smaller delta T improved the cooling fans that is based on chiller power (kW). DP could trigger the operator to initi-
tower’s performance. Figure 2 shows the This first phase, from programming to ate a chiller add; low amps, vanes near
cooling tower leaving condenser water commissioning, was completed in March 20% or a high DP could trigger the opera-
temperature versus outdoor wet bulb 2020. In just the first year of improved tor to initiate a chiller shed. They main-
(WB) temperature at 100% flow and operations, TECO saved 6,656,000 kWh. tained end-of-line differential pressure
100% fan speed.
At 70 degrees F WB, for exam- In just the
ple, the cooling tower approach with first year of
a 15-degree F range is 8.7 F, while the improved
approach with a 12 F range is 7.5 F. The efficiencies, the
company saved
cooling tower approach also improves 6,656,000 kWh.
as flow is reduced. Running more towers TECO can now
creates a larger surface area, and at 80% avoid spot-
flow, the approach at 70 F WB with a purchasing
power and
12-degree F range is 4.5 F. The improve- more easily
ment in lift in this example is 8.7 – 4.5 keep up with
= 4.2 F. Using the result from Figure 1 customer
yields a 0.0445 kW/ton improvement in demand.
efficiency. TECO
About TECO
Houston-based Thermal Energy
Corporation’s 48 MW combined heat
and power-based district energy system
provides chilled water and steam to 51
buildings totaling 24.3 million square feet
at Texas Medical Center. The chilled water
system consists of 27 chillers and an 8.8
million-gallon thermal energy storage
tank. The equipment is controlled by a
Toshiba distributed control system.
Cooling capacity is 120,000 tons at 40 F.
Annual chilled water production is 345.1 TECO
million ton-hours.
Benefits of optimization • Cost savings Texas Medical Center
• Improved plant efficiency - Annual operations: $550,000 • 10 million patient encounters annually
- 7% annually - Simple payback: 1.9 years • 180,000+ surgeries annually
• Energy savings • Lower CO2 emissions totaling • 9,200 patient beds
- Electrical: 16.1 million kWh/year 13,685,000 lbs/year • $2 billion of annual life science
- Demand reduction: 2,112 kW • Enhanced maintenance prioritization research
© 2022 International District Energy Association. ALL RIGHTS RESERVED. District Energy | Spring/Summer 2022 27
by increasing or decreasing the chillers’ foot, 8.8 million-gallon TES tank, the tall- TECO’s utility. It then calculates the com-
evaporator flow set points. est thermal energy storage tank in the parative cost of discharging the tank and
TECO employed several ECMs to world when it was installed. It has a using the stored water during the day. This
standardize procedures. First, the team capacity of 76,000 ton-hours, a maximum gives TECO the real price of the stored
began automating the chiller add/shed flow of 16,500 gpm and a maximum out- energy as it comes in every five minutes.
decision criteria – screen graphics in the put of approximately 8,250 tons (at a Done correctly, it is much like successful
Toshiba distributed control system inter- 12-degree F chilled water delta T). stock trading: buy low, sell high.
face now tell the operators the next chiller The TES tank allows TECO to serve If the real-time cost of electricity
to stage on or off, and the optimum flow its customers with absolute reliabil- is greater than the trigger cost and the
setpoints on chilled water and ity, even in the case of chiller time is within the appropriate window of
condenser water. TECO runs plant equipment failure, using operation, operators will receive a mes-
the older constant-speed chill- A NEW ALGORITHM stored energy when it’s less sage to discharge the tank at a specified
ers as close to full amps and OFFSETS expensive and reducing elec- flow rate.
full vanes as possible. These INCORRECT trical demand during peak
machines are served by 900 WEATHER chilled water usage. TECO CONTINUOUS IMPROVEMENT, ALWAYS
hp constant-speed condenser FORECASTS AND was surprised to discover As TECO has discovered, the result of
water pumps and 500 hp and KEEPS UP WITH that charging the tank every chiller plant optimization is not necessar-
600 hp constant-speed chilled ELECTRICITY night was much more expen- ily a one-time gain.
water pumps. Figure 3 trends RATE CHANGES. sive than expected – and the Lasting value often comes from
the 7,000-ton constant speed data showed that significant implementing standard operating proce-
York chiller efficiency (kW/ton) cost savings could be gained dures, maintaining consistent operations
versus lift (degrees F) at different load- by using real-time pricing information to across all shifts and accruing multiple
ing bins (6,500- to 7,500-ton bins and automatically charge and discharge the continuous savings, such as the daily trim-
5,000- to 6,000-ton bins). Also, TECO now tank at optimal times. ming of TECO’s electrical bill through pre-
allows the East Chiller Building to modu- TECO had been following the gen- dictive TES dispatch.
late chilled water flow to make up the dif- erally accepted practice of charging the Progress may start with a big bang –
ference and maintain the end-of-line DP tank at night when electricity prices are a revamped chiller plant that immediately
at 7 psi. The district chillers are staged by lower and discharging it during the day. In drops cooling costs – but continual data-
looking at the tons, amps and VFD speed Texas, real-time pricing can change every driven efficiencies can save hundreds of
of the East Chiller Building chillers. five minutes. The operations team was thousands of dollars annually as well.
Along with the ECMs, TECO inte- relying on weather forecasts, electricity
grated the Optimum Energy Plant Diag- market price predictions and manual cal-
nostics tool into its work to help maintain culations to estimate the most advanta- Michael P. Manoucheri,
business continuity. TECO engineers have geous times for charging and discharging. P.E., is TECO’s president and
traditionally collected monitoring data; Those methods couldn’t offset incorrect CEO. He holds a Master of
adding data rationalization and diagnos- forecasts or keep up with rapid changes – Science in mechanical engi-
tics allows the team to mine those assets but a clever algorithm could. neering from UT Austin and
and prioritize opportunities to increase Optimum Energy engineers rea- a Bachelor of Science in
reliability and efficiency and to track key soned that the tank could be even more mechanical engineering from Colorado
performance indicators and monitor each cost effective with an automated algo- State University.
piece of equipment in the plant. rithm, which would allow the Toshiba dis- mmanoucheri@tecothermalenergy.com
Even with Covid-19 restrictions in tributed control system to automate the
place, the second phase was completed TES charge/discharge decision criteria.
by June 2020 – in time to maintain oper- Optimization would also include graphics Ben Erpelding, P.E., chief
ational reliability and avoid the high screens in the Toshiba human-machine technology officer at
demand charges of a Texas summer. interface that could tell operators when, Optimum Energy, has over
TECO saved 9,491,000 kWh of how and why to use the tank. Called eco- 20 years of experience in
energy in the first year of chiller stage nomic dispatch, the solution uses histori- energy efficiency, chiller
optimization. After completing the first cal data and actual electric market pric- plant optimization, and
two phases, electrical demand was ing to calculate the true costs of charging combined heat and power. He received his
reduced by 2,112 kW. the tank at night with power from TECO’s Master of Science and a Bachelor of Sci-
local grid and using the stored chilled ence in mechanical engineering from San
PHASE 3: TES SYSTEM OPTIMIZATION water during the day. Diego State University and is a registered
A deep dive into data collected over The algorithm takes into account the professional mechanical engineer in the
the first year of operations revealed a kilowatts needed to charge the TES tank state of California.
source of additional savings: TECO’s 150- and the real-time electrical rate from ben.erpelding@optimumenergyco.com
28 District Energy | Spring/Summer 2022 © 2022 International District Energy Association. ALL RIGHTS RESERVED.
You can also read
