HomeMy WebLinkAboutSaint Point Electric Boiler Sizing and Specifications Report - May 2016 - REF Grant 7081163Sand Point Excess Wind Utilization
Grant # 7081163
Inclusion 1: Sand Point Wind to Heat Boiler Sizing
Page 4 of 4
nx
power
a tanadgusix company
Sand Point Wind to Heat
Boiler Sizing
Date 05/24/2016
Prepared by Dan L.enel
TDX Power
615 E. 82nd Ave, Suite 200
Anchorage, AK 99518
www.tdxpower.com
Contents
Contents..................................................................................................................................................................2
1 Summary..........................................................................................................................................................3
2 Boiler Sizing...................................................................................................................................................4
2.1 Boiler selection criteria......................................................................................... 4
2.2 Available data.. ....... 4
2.3 Calculations.................................................................................................................................................5
2.3.1 Calculating excess wind power.....................................................................................................5
2.3.2 Heat demand......................................................................................................................................5
2.3.3 Effective heat delivered................................................................ 5
2.3.4 Data Validation ............................. 6
2.4 Boiler selection...................................................................................................................... 8
2.4.1 Electrical Service ......................................... 8
2.4.2 Boiler specification.............................................................................................................................8
2.4.3 Boiler cost...........................................................................................................................................8
2.4.4 Boiler selection.................................................................................................................................10
3 Fuel Savings Projections..............................................................................................................................11
4 Appendix........................................................................................................................................................12
4.1 Detailed boiler specification.......................................................................................................................12
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1 Summa
Two Vestas V39 wind turbines rated at 500 kW each, are part of the generation system that powers the
public electricity grid in the remote Alaskan community of Sand Point.
At times of high wind, the wind turbines produce more power than can be safely absorbed by the electric
grid. Currently, the excess wind energy generated during these times is converted to heat in a load bank;
the hot air vented unused to the atmosphere.
In order to capture the excess wind energy, an electric boiler will be added to the existing heating system
at the local clinic and the school.
The following describes the process used to select the boilers and predict the annual fuel savings.
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2 Boiler Sizin
2.1 Boiler selection criteria
The following general criteria describe the ideal boiler:
➢ Large enough to be able to absorb as much excess energy as possible
➢ Small enough to fit in the existing boiler room
➢ Optimized cost
➢ Serviceable without removing entire boiler
➢ Integrated controls with remote command capabilities
➢ Long life
➢ Well insulated to minimize heat loss
Y Low water loop pressure drop
Self contained safety system that shuts down boiler in case of abnormalities
Some of these criteria are contradictory, so finding the best boiler size involves a trade-off between some
of the requirements.
A detailed boiler specification is attached.
2.2 Available data
The following data was available to determine the best boiler size:
➢ One year of hourly data for electric loads, diesel generator output, wind turbine output (WT1,
WT2), load bank power, wind speed- and temperature (anemometer data from each wind turbine)
➢ Two years (2014 and 2015) of daily data for electric loads, diesel generator output, wind turbine
output (WT1, WT2), load bank power, wind speed- and temperature (anemometer data from each
wind turbine)
➢ Heating fuel consumption of the Clinic for the year 2015
➢ Heating fuel consumption of the School for the years 2009 and 2010
➢ Heating degree days (min., max., average and annual sum) for the years 2000 to 2015 for Sand
Point
➢ Existing boiler data
y Wind turbine data
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2.3 Calculations
2.3.1 Calculating excess wind power
Using the daily data and the wind turbine power curve, the theoretically available wind power potential
was calculated based on the measured wind speed- and temperature for each hour. For each data point,
the excess wind power was calculated:
PEW PW - PD + PD(min) - PLD(min)
PEW ? 0 (negative values were set to zero)
PEW: Excess wind power
Pw: Potential wind power
PD: Diesel generation
PD(min): min. genset load
PLD(min): control margin for the load bank. PLD(mnn) = min(50 kW, PW)
The boiler control is not fast enough to cope with rapid power fluctuations due to wind gusts. The load
bank will still be required to shave -off short power peaks due to wind gusts. The control margin for the
load bank was assumed to be 50 kW (but no more than the potential wind power), the minimum genset
load 180 kW.
2.3.2 Heat demand
Based on the annual heating oil consumption and the cumulative heating -degree-days for the same year,
the relative heat demand (kWl°F) for both the school and the clinic were calculated. With this information,
the actual heat demand for each day of the daily data set was calculated using the measured ambient
temperature.
2.3.3 Effective heat delivered
The buildings will only accept heat until their heat demand is satisfied, even if there would be more
excess wind power available. The effective heat delivered can never exceed the combined heat demand
of the school and the clinic. The result of minimum(excess wind power, [heat demand school + heat
demand clinic]) represents the heat delivered, not limited by boiler size (infinite boiler capacity).
A similar calculation was done further limiting the heat demand of the school and the clinic by the
respective boiler size. This represents the heat effectively delivered. The average effective delivered heat
was calculated for the entire data set with an array of selected boiler sizes for the school and the clinic
and compared to the average heat delivered with infinite boiler size. The ratio (percentage) of these
numbers represent the capability of the boilers to supply the maximum excess heat possible.
Since the goal of the selection process is to maximize the effective delivered heat as a result of the
combined effect of both boiler sizes, we calculated the impact of one boiler size by setting the other boiler
size to 1000 kW (representing infinity). In reality, the boilers are controlled by supply temperature and
excess wind availability. With this, they may or may not operate at the same time or at the same relative
power setting. However, the boiler size should be large enough to be able to make use of the available
excess power, independent of the operation of the other boiler.
The results of the sizing calculation can be summarized in the following graph:
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350
300
250 —
200 }
L
a
0
0 150
0
V
N
100
50
0
75.00 %
Sand Point Boiler size selection
80.00%
85.00% 90.00% 95.00%
Total heat captured vs. available heat
140
120
100
3
Y
80 N
.y
d
0
60 -,0
40
20
0
100.004E
C
u
As can be seen, the heat captured approaches 99.8% of the available heat with 260 kW boiler size for the
school and 80 kW for the clinic. Increasing the boiler size beyond this will not result in a better use of the
available excess wind energy.
2.3.4 Data Validation
The daily data set was used to calculate the boiler size. Wind data is stochastic in nature-, during gusty
days, the power output of the wind turbines can change significantly from one hour to the next. Since we
had hourly data available (but with a limited set of data points)- we calculated the excess wind power for
each data point for both the hourly and the daily data sets. We then presented the data in the form of a
histogram to be able to visually compare the two data sets.
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500
450
400
c 350
0
.y
300
a
o 250
200
E
Z 150
100
50
0
0
8000
7000
6000
5000
0
7 4000
a
0 3000
2000
1000
0
0
Histogram Excess Wind Power (daily data)
100 200 300 400 500
Excess Wind Power [kW]
600 700
Histogram Excess Wind Power (hourly data)
200
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400 600
Bin size [kW]
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100.0%
90.0%
80.0% y
70.0%
60.0% c
0
50.0%
L
d
40.0%
0
30.0%
d
u
20.0% a
10.0 %
0.0%
800
100.0 %
87.5 %
75.0% y'
0
.Y
62.5% y
L
a
50.0% o
m
w
37.5
E- j
25.0% "
12.5 %
0.0%
800 j
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The histograms show that the hourly data is actually a bit more evenly distributed than the daily data. If
any accuracy was lost using the daily data, it would result in erring towards higher excess wind power and
therefore slightly larger boiler size.
2.4 Boiler selection
The above size calculation resulted in a utilization graph that gives an indication to the max. feasible
boiler size. However, the actually selected boiler size depends on other factors as mentioned in 2.1
above.
2.4.1 Electrical Service
Also considered was the feasibility of powering the electric boilers using the existing electric services in
place for the school and clinic, including existing service transformers.
Using the existing service transformer works well for the clinic, which has a 150kVA (120/208 V)service
transformer and draws on average approx. 15 kW, with peak demand of approximately 31 kW.
The conditions at the school are less favorable. The school has a 225kVA (277/480 V) transformer that is
reasonably loaded and would not support an additional 270 kW of load based on the nominal rating.
However, distribution transformers are typically and intentionally oversized and able to be overloaded on
a short term basis. Also, the kVA rating is based on a relatively high ambient temperature. Typically,
when there are heating demands and excess wind at Sand Point, ambient temperature is low and cooling
conditions are optimal. TDX is considering installing temperature monitoring on the existing school
transformer, such that the boiler power draw can be limited in the event of high transformer oil
temperature. We feel this is worth pursuing, in that installing and maintaining a large service transformer
is expensive, and incurs additional no load loss on a 365/24/7 basis. However, final selection is still
pending.
2.4.2 Boiler specification
Based on the above calculations, the site conditions and the control requirements, we developed a boiler
specifications for both boilers, see attached.
The boiler size target range specified:
Clinic: 65...75...85 kW
School: 240...270...300 kW
2.4.3 Boiler cost
Boiler prices vary widely between manufacturers, but follow generally along the following criteria:
r Vessel size.
Most manufacturers have a limited set of vessel sizes to facilitate production. A given vessel size
will accommodate a wide range of heating element power and arrangement. The vessel is the
most expensive part of the boiler.
Heating elements.
The number and rating of heating elements used is dependent on the voltage, the capability of
the controls (number of steps) and the power density. Higher number of elements cost more and
require more (costly) electrical control elements.
v Controls.
The capability and refinement of the controls range widely. From simple thermostats to
sophisticated PID controllers and multi -step controllers.
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While the cost of the boiler is a major cost contributor, the cost of the associated transformer and
disconnect also must be considered. Using RSMeans cost data, we did a simple cost calculation for
various boiler sizes to get an indication of the relative cost of the boiler and associated equipment:
$200
$180
$160
$140
$80
E
$60
$40
$20
$0
0
Relative Electric Boiler Equipment Cost
+Boiler
--tl—Transformer 12470 to 480 V
— - Fused disconnect 480 V �
—0—Total
Poly. (Total)
-
100 200 300 400 500 600 700 800
Boiler kW
As expected, the relative cost ($/kW boiler size) generally favors larger boilers. The resulting total
equipment cost is based on discreet values for boiler, transformer and disconnect. The up -tick at 370 kW
is due to unfavorable step size of the transformer and disconnect (500 kVA, 600 A).
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2.4.4 Boiler selection
We obtained boiler quotes from four man ufacturerslrepresentatives and are in the process of reviewing
them and make a final selection.
Selection criteria:
➢ Adherence to specification
➢ Cost, including transportation
➢ Dimensions, orientation (smaller size preferred)
Number and size of steps/elements
➢ Controllers used
➢ Ability to integrate into master control system
➢ Quality of documents and service received
➢ Previous experience with manufacturer/representative
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3 Fuel Savings Projections
Based on historical temperature and fuel consumption data for both buildings, for an average season
(Normalized to the past 15 year average of heating -degree-day data) we made the following fuel
consumption predictions:
v On a 15 year average, the school is projected to burn 35270 gal, if fuel oil is the sole source of
heat. The excess wind power is projected to save 16083 gal. This represents a fuel saving of
45.6%.
i- On a 15 year average, the clinic is projected to burn 11778 gal, if fuel oil is the sole source of
heat. The excess wind power is projected to save 5512 gal. This represents a fuel saving of
46.8%.
The savings projection is based on two years of City load data and daily average wind speed as
measured by the wind turbine anemometers, and boiler sizes of 270kW and 75kW respectively. It also
assumes power plant genset minimum load of 180KW and the need to absorb 50kW of excess wind at
the power plant for frequency regulation purposes.
The projections also assume the school and clinic divide the excess energy proportionally based on these
boiler sizes. Since the school and the clinic are powered from the same source, we can only make an
accurate prediction for the combined fuel savings; the actual split between school and clinic depends on
the actual heat demand, the existing boiler control modes and actual heating loop temperature variations
etc.. However, the proposed electric boiler controls will allow to measure and adjust the excess wind
power distribution if needed.
Actual cost savings will depend upon the cost of fuel and rate for excess electricity, and will be addressed
separately.
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4 Appendix
4.1 Detailed boiler specification
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TOX
power
a tanadgusix company
Sand Point Excess Wind Power Utilization
Electric Boiler Specification
Date 02/29/2016
Prepared by Dan Lenel
TDX Power
615 E. 82nd Ave, Suite 200
Anchorage, AK 99518
www.tdxpower.com
Contents
Contents..................................................................................................................................................................2
1 Electrically heated water boiler 75 M..........................................................................................................3
1.1 Standard specification.................................................................................................................................3
1.2 Optional equipment.........................................•---•.......................................................................................4
2 Electrically heated water boiler 270 M........................................................................................................5
2.1 Standard specification.................................................................................................................................5
2.2 Optional equipment.....................................................................................................................................6
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1 Electrically heated water boiler 75 kW
1.1 Standard specification
Project name:
Sand Point Excess Wind
Item:
Electric boiler for clinic
Location:
Sand Point, Alaska
Seismic zone:
4
Ambient conditions:
Indoor, 50...120 °F
Rated heat output:
65...75...85 kW
Electric power service:
3 phase 208 VAC
Max. step size:
20% of heat output
Working fluid:
50% Water150% ethylene glycol
Working pressure:
30 psig
Working temperature:
max. 200 °F
Pressure vessel:
Welded steel vessel according to ASME boiler and pressure
vessel code, section IV
Insulation:
Fiberglass or similar, minimum thickness 1.5"
Boiler enclosure:
Metal enclosure with easy access to heating- and control
elements, rustproof.
Controls enclosure:
Integral to boiler enclosure or NEMA class 1 or 12 enclosure
attached to boiler enclosure.
Fluid connections:
Flanged or threaded NPT
Drain with shut-off valve, 112" minimum size
Air vent:
Automatic air vent/vacuum breaker with shut-off valve
Safety valve:
Approved and sized according to ASME boiler and pressure
vessel code, section I.
Heating elements:
Individual heating elements rated for continuous duty, sheathed
with high temperature, nickel -based material (i.e. Inconel).
Elements shall be flanged or threaded and easily replaceable
with only minimal disassembly required.
Heating element switching:
By 3-pole magnetic contactors with at least 500,000 full load
cycles service life, or solid state relays with zero -crossover
switching, or a combination of these.
3-pole circuit breaker for each element.
Temperature controller:
Electronic multi -stage PI controller with independent temperature
sensor.
Instrumentation:
Pressure gauge with shut-off valve, dampened.
Supply temperature gauge
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Control panel: Operator control panel, integral to the boiler, with the following
control elements:
- Temperature controller
- ON/OFF switch with indicator light
- Indicator light for each heating element or stage
- Disable switch for each heating element or stage
- Alarm/trip indicator light
Safety controls Low water cut-off
Over -temperature limiter, self -resetting
Over -temperature limiter, manual reset
Control 110 Provide dry contact "boiler operating"
Provide dry contact "boiler alarm"
Provide dry contact "boiler trip"
Provide terminals for safety shutdown loop.
1.2 Optional equipment
Please quote all options as line items.
Stage disable contacts:
Power limit input:
Additional control 110
Sand Point boiler spec.docx
Wiring provision (terminal strip) for external in -line contacts that
can break the control loop to each step contactor.
Control input (4...20 mA or 0... 5...10VDC or ModBus) to the
boiler stage controller to limit the max. boiler electrical load.
Provide dry contact, opens on low water cut-out
Provide dry contact, opens on over -temperature (auto IRS)
Provide dry contact, opens on over -temperature (man IRS)
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2 Electrically heated water boiler 270 M
2.1 Standard specification
Project name:
Sand Point Excess Wind
Item:
Electric boiler for school
Location:
Sand Point, Alaska
Seismic zone:
4
Ambient conditions:
Indoor, 50...120 °F
Rated heat output:
240..270...300 kW
Electric power service:
3 phase 480 VAC
Max. step size:
20% of heat output
Working fluid:
50% Water150% ethylene glycol
Working pressure:
30 psig
Working temperature:
max. 200 °F
Pressure vessel:
Welded steel vessel according to ASME boiler and pressure
vessel code, section IV
Insulation:
Fiberglass or similar, minimum thickness 1.5"
Boiler enclosure:
Metal enclosure with easy access to heating- and control
elements, rustproof.
Controls enclosure:
Integral to boiler enclosure or NEMA class 1 or 12 enclosure
attached to boiler enclosure.
Fluid connections:
Flanged or threaded NPi
Drain with shut-off valve, 1/2" minimum size
Air vent:
Automatic air vent/vacuum breaker with shut-off valve
Safety valve:
Approved and sized according to ASME boiler and pressure
vessel code, section I.
Heating elements:
Individual heating elements rated for continuous duty, sheathed
with high temperature, nickel -based material (i.e. Inconel).
Elements shall be flanged or threaded and easily replaceable
with only minimal disassembly required.
Heating element switching:
By 3-pole magnetic contactors with at least 500,000 full load
cycles service life, or solid state relays with zero -crossover
switching, or a combination of these.
3-pole circuit breaker for each element.
Temperature controller:
Electronic multi -stage PI controller with independent temperature
sensor.
Instrumentation:
Pressure gauge with shut-off valve, dampened.
Supply temperature gauge
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Control panel: Operator control panel, integral to the boiler, with the following
control elements:
- Temperature controller
- ON/OFF switch with indicator light
- Indicator light for each heating element or stage
- Disable switch for each heating element or stage
- Alarm/trip indicator light
Safety controls Low water cut-off
Over -temperature limiter, self -resetting
Over -temperature limiter, manual reset
Control 1/0 Provide dry contact "boiler operating"
Provide dry contact "boiler alarm"
Provide dry contact 'boiler trip"
Provide terminals for safety shutdown loop.
2.2 Optional equipment
Please quote all options as line items.
Stage disable contacts:
Power limit input:
Additional control 1/0
Sand Point boiler spec.docx
Wiring provision (terminal strip) for external in -line contacts that
can break the control loop to each step contactor.
Control input (4...20 mA or 0...5...I OVDC or ModBus) to the
boiler stage controller to limit the max. boiler electrical load.
Provide dry contact, opens on low water cut-out
Provide dry contact, opens on over -temperature (auto RS)
Provide dry contact, opens on over -temperature (man IRS)
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