HomeMy WebLinkAboutChickaloon Pre feasibiityPRE-FEASIBILITY STUDY - WOOD-FIRED HEATING PROJECT Sustainability, Inc
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Table
of
Contents
EXECUTIVE
SUMMARY ............................................................................................................2
1.1
Acknowledgements ................................................................................................................2
1.3
Sources ...................................................................................................................................2
1.4
Scope ......................................................................................................................................3
1.5
Resource
Assumptions ............................................................................................................3
1.6
Summary
of
Findings ..............................................................................................................5
1.6
Next
steps ..............................................................................................................................9
2
TECHNICAL
SUMMARY ....................................................................................................10
2.1
Existing
Conditions ...............................................................................................................10
2.2
Wood
Fuels
/
Wood
Fired
Heating
Equipment:.....................................................................10
2.3
Proposed
Configuration ........................................................................................................12
2.4
Energy
Savings ......................................................................................................................14
2.5
Cost
Estimate ........................................................................................................................16
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EXECUTIVE
SUMMARY
1.1
Acknowledgements
This feasibility study was supported by the Alaska Wood Energy Task Group and administered by the
Fairbanks Economic Development Corporation.
1.2
Objective
The objective of this report, as the title suggests, is to document the results of a pre-feasibility study
performed for the Village of Chickaloon. Buildings in the Village are currently heated with oil or
propane, often with a wood stove as back-up. The subject of the study is the feasibility of converting two
buildings included in the study to utilize an automated wood-fired heat boiler as the primary source.
Feasibility studies are often classified as Level 1 (L1), Level 2 (L2), or Level 3 (L3). Level 1 studies
consist of very rough calculations on a small number of important metrics (unit fuel costs, etc). Some
refer to L1 studies as “back-of-the-envelope” calculations.
At the other end, L3 studies are commonly called “investment grade studies”; the level of detail and
calculation is so high that one could use the results of an L3 study to get an outside entity to fund the
implementation of the project.
Level 2, then, is the bridge between L1 and L3; it is a screening study done to determine if it is worth the
time and expense to initiate an L3 study. Level 3 studies are generally quite expensive and thus not
entered into lightly. The L2 study helps decision makers determine which aspects, if any, of a proposed
project are worth the expense of an L3 study.
An L1 study can be done remotely; an L2 study requires at least a minimum amount of site observation of
existing conditions, conversations with the affected parties, and research with second-order parties (local
foresters, vendors, local contractors, etc). This is a Level 2 study.
Sustainability, Inc (SI) and efour, PLLC (efour) perform L2 and L3 studies across the state of Alaska,
from cities to small rural villages. We use the same performance and economic models for each type of
study; for us, the primary difference between the two studies is the quality of the inputs, which is
generally a function of how much time has been spent gathering information and the depth of that
information.
1.3
Sources
The primary sources of information that inform this study are data collected on site by SI and data
provided by the Fairbanks Economic Development Corporation (FEDC). Data collected on site by SI
include existing site conditions, equipment name plate data, current energy cost data, and equally
important, information gathered by talking to the local stakeholders in the Village.
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In addition, the Village has been actively pursuing a renewable solutions for the Village buildings,
including not only biomass heating, but solar thermal heating, solar photovoltaic power, and so on. They
have published some of their results in a Renewable Energy Plan. In terms of biomass heating, SI and
efour performed all their own analysis without reference to the Renewable Plan. However, we did extract
information from the Plan regarding the use of solar thermal panels to supplement the biomass boilers,
and incorporated that information into our results. We have not attempted to validate the solar thermal
performance and cost estimate data used in the Plan; we incorporated the information as published.
In addition to the site knowledge gathered by SI, additional biomass boiler performance and cost data
have been accumulated over the past several years from working with local engineers and contractors, and
from performing multiple L2 and L3 wood-fired feasibility studies.
Hourly weather data for the performance model was taken data collected and reported by Palmer
Municipal Airport, which is located about 30 miles away from Chickaloon, in the same river valley.
1.4
Scope
In Chickaloon, the scope of this report is limited to two buildings; A building that includes both a Shop
and the Environmental Offices (the Shop), and the Village Administration Offices (Admin Offices).
Currently, each building has its own heating system. The Shop utilizes an oil-fired boiler, while a
propane-fired heater heats the Admin Offices.
Biomass heating systems can be expensive to install; the economics generally work better for larger
buildings, or where two or more smaller buildings can be grouped together and served by a single
biomass boiler, using buried piping between the buildings to distribute the heat.
Taken alone, neither of the two buildings in this study is large enough to justify a biomass boiler – the
first costs are so high that the project economics are unfavorable under the public grant economic
approach. Chickaloon recognized this, and proposed grouping these two buildings into a common
biomass heating plant – the buildings are roughly 120 feet apart, so piping costs between the buildings are
minimal. SI and efour have followed this concept; we present the result only for a common heating plant
that serves both buildings.
As noted above, Chickaloon has proposed supplementing the biomass heat to these two buildings with
solar thermal heating panels mounted on the wall of the Shop. We have therefore presented the economic
and energy results in two forms – first without utilizing solar thermal, and then a second time including
the solar thermal cost and performance data as presented in the Plan.
1.5
Resource
Assumptions
SI and efour often perform studies on villages in Bush Alaska; off the toad system. In these villages,
biomass boilers generally have only two possible forms of fuel, wood chips or stick wood, both of which
they must produce themselves from local forests. Villages on the road system, however, have a third
option; wood pellets produced elsewhere and trucked to the village. For small scale projects, pellets are
in almost every way the best option.
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The main reason is that the village need not invest in wood harvesting and processing equipment – they
simply buy the pellets. The cost per ton may be higher than chips, but the pellets are much drier, and
therefore have a significantly higher content per pound (BTU/lb) than wood chips. Pellets handle very
well, almost never fouling the material handling systems. They are not at risk of freezing as long as they
are kept dry; chips contain so much surface and internal moisture that freezing into clumps is an issue.
Equally important is that because of various issues, reliable chip-fired boiler can only be made so small;
we have not found any with an output capacity of less than 500,000 BTU/h (500 kBTU/h). Pellet boilers
can have capacities as low as 35 kBTU/h. The estimated combined peak-heating load of the Shop and
Admin Offices is 92.6 kBTU/h – so even the smallest chip-fired boiler is significantly too large. It can be
made to work, but the Village would be paying for a lot of boiler they were not using – this shows up in
the economic results.
Stick-fired boilers were not included in the discussion above. Stick wood is almost always the cheapest
in terms of $/BTU, and is always available in the Village (or can be collected locally). However, there
are no stick-fired boilers that have automated feed systems – they must be fed manually every few hours
(as often as every four hours in cold weather). If this labor is accounted for in the model, then this
generally reduces the economics of stick-wood boilers as an option.
Our model presents the results for all three fuel forms, but in Chickaloon, we would only recommend
pellet-fired boilers.
Figure 1.1 below shows the assumptions that have been made for the existing fuels in the Village (oil and
propane):
Figure 1.1
Figure 1.2 shows the assumptions made for the cost of wood fuel, in various forms.
Figure 1.2
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Because each form of fuel has different heat content and is sold in differing units, direct comparisons of
the data in Figures 1.1 and 1.2 are very difficult. To make the comparison simple, all these energy
sources are converted to a common unit, one million BTU (1 mmBTU).
To make the comparison even more relevant, the conversion efficiency of each source has been factored
in. In this case, the conversion efficiency is the boiler efficiency. It is different for each fuel – using drier
wood results in better boiler efficiency, and the oil and propane boilers have their own efficiencies as
well. In Figure 1.3 below, therefore, the mmBTUs references are those coming out of the boiler into the
space, not the gross heat content of the fuel going into the boiler.
Figure 1.3
As expected, stick wood is the least expensive, followed closely by wood chips and wood pellets. Oil is
half again as much as wood, and propane is more than twice as expensive as any wood source.
1.6
Summary
of
Findings
The following Figures summarize the performance and economic modeling that SI and efour performed.
As noted above, we show the results for pellet, chip and stick fired boilers, but we would only
recommend the use of pellet boilers in this case. The text of this section, therefore, deals only with the
pellet fired option.
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Figure 1.4 below shows the overall economic summary:
Figure 1.4
As footnote (1) indicates, we have not estimated any increase in annual maintenance with the installation
of the pellet-fired boiler. This is because the fuel consistency is so high, the material handling so smooth,
and the pellet boilers so reliable that in essence it is as close to being as automatic as an oil fired boiler
that a wood fired boiler can get. We would expect that whoever currently cares for the oil and propane
boiler will also take care of the pellet boiler, and that no significant additional time or parts expenses will
be incurred.
It was noted above that biomass boiler projects require a certain scale in order to be truly economical.
Even when the two buildings in Chickaloon are combined, they are quite small as biomass projects go.
This is reflected in the net simple payback of the project, roughly 17 years. Although the unit cost of oil
and propane are much higher than that of wood, the buildings are so small that the base fuel cost of fuel,
$12,488, is not large enough to offset the cost of the construction in a relatively short time frame, even if
all of the liquid fuel is displaced by wood energy (as is the case).
Note that the addition of the solar thermal option does not improve the project economics; the marginal
savings do not offset the marginal additional cost– thus the NSP get slightly longer with Solar included.
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Figure 1.4 is based on current fuel costs; these will not stay the same. Thus we present a 20 year cash
flow the project (pellets only). In this cash flow, the cost of all fuels is escalated, although not at the same
rate. Wood is assumed to increase in cost at a slower rate than oil or propane, because the resource is
local and renewable. The escalation rates used are shown in Figure 1.5:
Figure 1.5
Using these factors results in the following 20 year cash flows:
Figure 1.6
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Figure 1.7
In essence, the savings are projected to more than triple by year 20. For that reason, the high NSP of the
projects should not be enough to disqualify them. Renewable projects provide benefits beyond the
monetary ones. These decisions must be made at the Village level.
The final Figure of this subsection is a summary of the cost estimate. The complete construction estimate
is contained within Appendix B.
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Figure 1.8
1.6
Next
steps
Based on economics alone, the project is marginal. The real issue is the actual estimate of the Soft Costs
in the project. Our standard is around 24% of the total project to meet standards of a granting
organization. However, these costs are probably higher than necessary and should be considered by the
granting agency in the ranking process for the projects economic viability. Also, as noted above, the
project generates benefits to the Village beyond the obvious monetary ones. Among these are:
• Use of renewable resources
• Reliance on local, rather than remote energy sources
• Reduced carbon footprint
• Reduced secondary emissions (NOx, S, CO, etc)
• Increased fuel price stability (for future budget planning)
• Energy money spent remains in the local economy
There are no doubt others as well. As was noted above, a Level 2 study is a screening study, meant to
provide enough information to the stakeholders to A) determine how to proceed next, B) determine
whether to proceed, or C) halt the project until conditions improve. This study provides the information
needed for Chickaloon and other stakeholders to make these decisions; the next steps are up to them.
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2
TECHNICAL
SUMMARY
2.1
Existing
Conditions
The following statistics in Figure 2.1 summarize the existing conditions in the two buildings:
Figure 2.1
The proposed pellet-fired boiler would displace all of the liquid fuel consumption of the two buildings;
however, the existing systems would remain in place as back up. This is explained in more detail in 2.3.
2.2
Wood
Fuels
/
Wood
Fired
Heating
Equipment:
The model that SI / efour uses for these feasibility studies calculates the properties of wood fuels based
on: 1) species used (can be more than one), and 2) moisture content at time of burn. If more than one
species is selected, the model calculates a “composite” value for the fuel. For example, if one used 70
percent of a specie/moisture with 6,000 BTU/lb and the remaining 30 percent had a specie/moisture heat
content of 8,000 BTU/lb, the “composite fuel would have (0.7 * 6,00) + (0.3 * 8,000) = 6,600 BTU/lb.
Figure 2.2 shows the calculated properties for the pellets used in this analysis. The properties of chips
and stick wood are also calculated, but as noted above, the report is based on a pellet-fired boiler.
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Figure 2.2
The most pertinent value in the Figure is the net useable heat content, 8,017 BTU/lb. Because of the low
moisture content (4 percent), pellets are by far the most energy-dense form of wood fuel.
There are a number of manufacturers of pellet boilers; the basis of design boilers used in this study is the
P4 series of boiler made by Froling. There are eight sizes in the P4 series, ranging from 35.8 kBTU/h
output to 200 kBTU/h.
The basic system components include:
• A pellet bin, which holds bulk amounts of wood pellets.
o This bin is kept filled by periodic deliveries to the Village by truck
o Some trucks have an adjustable auger which can move the pellets from truck to bin
o Pellets can also be blown pneumatically, although that is more common in areas with
extensive pellet use
o Pellets can be “dumped” into a front loader, and then dumped in the bin
o There are a number of delivery and loading methods
• A means getting the pellets from the bin into the boiler (material handling)
o This can be an auger
o Froling offers an option that pneumatically conveys the pellets to the boiler (the pellets
are entrained in a moving stream of air)
• The boiler
o The boiler uses onboard controls to modulate the firing rate to meet heating demand
o Will remain on and operating as long as the bin is kept filled, and no fuel fouling occurs
o Is a “hands-off” unit
• A thermal storage tank
o This tank is basically a “wide spot in the pipe”
o It hold large amounts of water, thus large amounts of heat
o In essence, the boiler heats the tank, the tank heats the building
o Wood-fired boilers cannot change output as quickly as liquid fueled boilers; when
heating load is variable, the tank smoothes out the load and gives the boiler controls time
to react
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o When loads are very low, the boiler may shut down (it will automatically re-start when
needed); during these “OFF” periods, the tank provide a reserve of hot water
o By monitoring tank temperature, the boiler can “anticipate” when load starts to increase
or decrease, and thus provide more stable temperatures
• Solar Thermal Panels / pump / heat exchanger (if included)
o This system uses heat from the sun to supplement the wood-fired boiler
o The cooler return water from the buildings is routed to the heat exchanger before it gets
to the boiler
o In this way, the system always takes all of the available the free solar heat before using
the wood heat
o The tank even allows storage of solar heat if the available heat exceeds the heating load
• A vent or boiler stack
o This vents the products of combustion and boiler emissions into the air through an
elevated stack or vent pipe
o May or may not include additional emissions control equipment
Examples of the Froling boilers and accessories are included in Appendix A
2.3
Proposed
Configuration
The proposed final configuration, which has been modeled for this study, can be summarized as:
• A new 8 x 20 mechanical room is constructed on the back side of the Shop
• The new pellet boiler, pellet bin, and material handling accessories are installed in the
mechanical room
• The thermal storage tank is installed in the mechanical room
• The solar thermal panels, if used, are mounted on the south side of the shop; the remaining
system components are installed in the new mechanical room
• The heat from the wood fired boiler is piped into the existing Shop mechanical room using
copper pipe
• The heat from the wood fired boiler is also piped to the Admin Office mechanical room,
using a combination of insulated plastic pipe (direct buried) and copper pipe (once inside the
building
• The plastic pipe proposed is a system called Insulpex, by Rehau; details can be found in
Appendix B
• The new piping will be tied into the existing systems in such a way that will always take the
“wood heat” before taking oil/propane heat (see details below)
• However, if for any reason the wood fired system cannot meet load, the existing boilers will
automatically start and fire as required to meet load
Figure 2.3 below shows a typical configuration for an oil-fired boiler or boiler plant. In this example,
there are two boilers, but only one runs at a time. In Chickaloon, there is only one, but the integration of
the systems is the same. This would be the “existing” case.
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Figure 2.3
Figure 2.4 shows the proposed case (valves colored in solid are closed):
Figure 2.4
In this case, valve 1 is closed, which forces the hot water return water through the wood fired boiler
instead of the oil-fired boiler. Likewise, valve 4 is closed, so the hot water from the wood-fired boiler
bypasses the existing boilers and goes out to the building. If for any reason, the hot water supply
temperature falls below set point by a set amount, the valves reverse position, and the existing boiler start.
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In an even simpler version, there are no automatic valves – the cooler return water flow through the (solar
thermal heat exchanger, if installed), the wood-fired boiler, and then the oil / propane boilers. If the solar
system meets set point, no boiler fires. If the solar system cannot heat the water to the supply set point,
the wood-fired system fires as needed to provide the additional heat required. If for any reason the wood-
fired system still does not meet supply water set point, the existing boiler fires.
The system works because each successive set point is set 5 or more degrees below the previous one. Say
the three hot water supply set point was, in order, 185 deg F, 180 deg F, and 175 deg F. If we take a day
when the solar heat is meeting load, the system would be delivering 185 deg F water. Perhaps a cloud
goes by and the available solar energy dips. By having a 5 deg F spread in set points, this prevents the
wood-fired boiler from starting every time a cloud goes by. Likewise, it was noted above that wood-fired
boilers cannot modulate output as fast as a liquid-fired boiler. The set point spread prevents the existing
boilers from firing every time the wood fired boiler needs a bit of time to catch up (as does the thermal
storage tank). At the same time, the system requires no operator intervention or automated controls. If
the hot water temperature falls to 174 deg F, the oil-fired boiler does not know if the sun went down, or
the wood pellets fouled the material handling system – it simply fires because the supply temperature has
fallen below its set point.
2.4
Energy
Savings
Figure 2.5 below summarizes the energy consumption, existing and proposed, on a monthly basis:
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Figure 2.4
Note that the last two segments of Figure 2.4 show the savings with and without the solar thermal system.
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2.5
Cost
Estimate
The construction cost estimate is provided below. These what are commonly referred to as the “hard
costs”. The remaining soft costs, fees, permits, etc, are detailed in Section 1.