20150218 sbrsd boiler system sizing review final...feb 18, 2015 · beam’s study lists the...

Wilson Engineering Services 902 Market St.

Meadville, PA 16335

Office: (814) 337-8223

www.wilsonengineeringservices.com

M E M O R A N D U M

Date: 2/18/2015

To: Ingrid Borwick, SBRSD

From: Peter Oven, WES; Dan Wilson, PE, WES

CC:

Re: Boiler system sizing review for Southern Berkshire Regional School District

1.0 REPORT SCOPE

Southern Berkshire Regional School District (SBRSD) is in the design phase of a project to replace

the central boiler plant at Mt. Everett Regional School / Undermountain Elementary. Wilson

Engineering Services, PC (WES) has been contracted to perform an independent review of the

sizing of the boiler system. This report describes a heating demand model of the school

developed by WES, comments on two previous boiler replacement studies completed by BEAM

and Dietz, and compares the load coverage of those two previous studies based on WES’s

demand model. The following list summarizes the data and reports provided to WES by SBRSD:

• BEAM 8/29/2014 study

• BEAM 9/24/14 study

• Dietz 12/2/2014 study

• Spreadsheet with 5 years of fuel oil delivery records

2.0 EXISTING HEATING PLANT

The 220,000 ft2 school is heated by a central plant consisting of three identical oil-fired hot

water boilers which are described in Table 2-1. These boilers are in poor condition. One is

cracked and has been removed from service, and the other two are leaking.

SBRSD Boiler System Sizing Review Memorandum – 2/18/15

WES ● Wilson Engineering Services (814) 337-8223 902 Market St., Meadville, PA 16335


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Table 2-1: Boiler Specifications

Boiler Manufacturer Weil McLain

Boiler Model 2294

DOE Output Rating 6.1 mmBtu/hr

Fuel #2 Oil

Burner Manufacturer Power Flame

Fuel Input Rate 52 gallons/hr (35 gph nozzle)

Date Installed 1991

Notes: A 35 gph nozzle is used on the burner, but the pressure is higher

than the manufacturer’s rating for the nozzle’s rated value. Power Flame

states that the system will provide up to 52 gph (7.28 mmBtu/hr input).

Five distribution pumps in the boiler room serve the various heating zones in the building. The

boilers operate year-round in order to provide domestic hot water (DHW).

Previous studies have been inconsistent in specifying the rating of the Weil McLain 2294 boilers.

BEAM’s study lists the minimum relief valve capacity as 6.1 mmBtu/hr but never explicitly states

the boiler output. Dietz lists the boiler output as 5.304 mmBtu/hr, which is the IBR Net Output

rating. Since load modeling is based on actual demand met by the boiler system, WES

recommends use of the output rating of the boiler, which is 6.1 mmBtu/hr.

Dietz reports that the nozzle rating on the burners of the Weil McLain boilers is 35 gallons/hour.

This was confirmed by SBRSD staff. Based on the heating value of #2 oil, this would seem to

indicate a maximum heat input of 4.9 mmBtu/hr, which would result in an output of 3.9

mmBtu/hr at 80% boiler efficiency. That is well below the DOE output of 6.1 mmBtu/hr. Having

been provided the burner serial number by SBRSD staff, WES contacted Power Flame, the

burner manufacturer, and inquired about the 35 gph nozzle. Power Flame reviewed their

records and determined that this burner was actually built for operating at 52 gph using a 35 gph

nozzle. The reason for this is that nozzle ratings assume operation at 100 psi, and in this case

the burner provides an oil pressure of 245 psi, which results in a proportionally higher flow rate.

The 52 gph value is essentially equal to the oil input rating of 53 gph as identified by Weil McLain

for the 2294 boiler. Therefore the boilers should be able to operate at or near their rated output

capacity of 6.1 mmBtu/hr.

3.0 CURRENT OPERATIONS

SBRSD staff report that a single boiler is sufficient to heat the school on moderately cold days,

but on days when the temperature is consistently below 20oF, two boilers are used. This

practice is based on historical experience. Anecdotal information from school staff is that during

the coldest days, the two boilers cycle between firing rates and never remain on high fire for

more than about 20 minutes in an hour. Based on visual inspection of the tank gauge located in

the boiler room, the plant operator estimates that fuel consumption on the coldest days is

between 500-525 gallons/day. This is equivalent to an average fuel input during the 24-hr

period of 2.9 – 3.1 mmBtu/hr, and an average output of 2.3 - 2.45 mmBtu/hr.




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4.0 PAST FUEL USAGE AND DEMAND MODELS

SBRSD provided WES with fuel delivery dates and volumes for fiscal years 2010-2014. Oil is

delivered to a 15,000 gallon tank. The annual fuel usage and Heating Degree Day (Base 55oF)

data are presented in Table 4-1. Heating Degree Day values were developed based on weather

records from Pittsfield Municipal Airport, which is located approximately 25 miles north of the

school. For the purposes of this report, the average annual usage of 54,037 gallons over the 5

year period is used for developing potential annual fuel cost savings.

Table 4-1: Heating Degree Days and Oil Deliveries

Fiscal

Year HDD

#2 Oil

(gal) gal/HDD

2010 4,236 59,598 14.1

2011 4,922 55,153 11.2

2012 3,664 45,610 12.4

2013 4,450 45,905 10.3

2014 5,140 63,918 12.4

Average 4,482 54,037 12.1

Analysis using HDDs can provide insight into energy usage trends because it allows fuel usage

data to be normalized relative to the severity of the winter. Fiscal years 2012 and 2014 were

selected as representative years for the purpose of sizing the biomass boiler, since they

represent historically mild and severe winters.

4.1 Demand Models

The heating demand for each year was modeled based on the weather data from Pittsfield

Municipal Airport, annual fuel deliveries, and an estimate of DHW demand. The DHW was

estimated to be 2,100 Btu/ft2/year1. This results in a daily oil usage for DHW of 11.3 gallons/day,

which is approximately 8% of total fuel usage. Note that WES anticipates that summer fuel oil

usage for providing DHW is excessive due to the method of using the extremely oversized fuel oil

boilers for this purpose. Therefore, it is possible that the daily usage value is underestimated in

this modeling effort. Understating the fuel use for DHW has the effect of reducing the peaks

shown by the heating demand curves. Figure 4-1 presents the daily average system output over

the course of the 2012 and 2014 Fiscal Years.

1 This value was obtained from the 2011 DOE Building Energy Data Book, Table 3.9.11, “Secondary School Energy

Benchmarks by City,” for IECC Climate Zone 5A.




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Figure 4-1: 2012 and 2014 Heat Demand (daily average values)

Figure 4-2 presents load duration curves for 2012 and 2014 which are developed from the

demand models. This chart is sorted to present the daily heating loads in order from largest to

smallest, not the order in which they actually occurred in time. From this chart it is apparent

that the coldest day in 2012 required average heat output of 2.9 mmBtu/hr, while the coldest

day in 2014 required average heat output of 3.1 mmBtu/hr. These values are generally

consistent with the operator’s anecdotal information regarding daily fuel usage. The minimum

load days have a demand of 0.05 mmBtu/hr which represents solely DHW usage.




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Figure 4-2: 2012 and 2014 Load Duration Curves (daily average values)

4.2 Use of Demand Models and Identifying Peak Loads

The modeling done based on past fuel usage allows development of a daily average demand

value. This has been shown to be accurate on many past jobs where Btu metering or where fuel

usage metering data was also available. It is important to note how this curve can be used

appropriately. The curves shown in Figures 4-1 & 4-2 present the daily average demand. By

definition, over the course of a 24-hr period, the loads at a school will vary from the daily

average. Thus, the curves are useful for sizing a biomass boiler to ensure it will run efficiently

and cover significant portions of the system demand, but they do not provide the peak or low

demands seen by the school.

The peak demand stated by the BEAM report is 3.0 mmBtu/hr. The BEAM report load modeling

was done using RETScreen Method 2. This is a very useful program for a preliminary look at a

system, but should not be used for final system sizing. It develops a demand curve based on

average monthly temperature data, and average annual fuel input. Reaching the desired fuel

input for Method 2 requires the user to put in the square footage of the building and a per

square foot peak demand value (Btu/hr/ft2). Then the user iterates until the value they put in




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for Btu/hr/ft2 gives the annual fuel usage they are targeting. The problem with the curve

developed by this model is that it uses average temperature data on a monthly basis. This

flattens out the curve significantly. It is significantly more accurate to use real weather data with

higher frequency for a specific year in which fuel usage is known.

The Dietz report identifies the peak demand at 7,000,000 Btu/hr, and states this was developed

as an estimate at -5°F outside air temperature. It is not clear whether this was developed based

on building load modeling by hand, with TRACE or other comparable software, or by general rule

of thumb. The report states the load estimate was “.. derived using historical oil consumption

data, actual oil nozzle sizes, and other acceptable industry methods.” A typical rule of thumb

used to ensure conservatism in sizing of boilers for schools in the Northeast is 35 Btu/hr/ft2, and

the Dietz value is very close to this number.

WES has performed Btu metering at schools in the past to identity peak demand, tightly size the

boiler systems, and optimize the size of biomass boiler systems. WES has seen that the peak

hourly demand at the schools is approximately 70-90% above the daily average demand. This is

on a cold Monday morning when the school is coming off of a weekend setback. On typical

school days the peak is typically about 30-50% above the daily average demand, and this is in the

morning when the school is ramping up from its nighttime setbacks and the doors are being

opened and makeup air is needed as kids and teachers arrive.

Using the 2014 model and the values previously discussed, WES estimates the peak demand is

between 5.5 and 6.0 mmBtu/hr. It is important to note that these peaks can be mitigated by

managing how the school ramps up from nighttime and weekend setbacks.

Table 4-2 summarizes the peak demands as estimated by each report. For proper boiler system

sizing, it is critical to remember that these peaks are only seen for an hour in a specific 24-hr

period, and the absolute peak demand for the school occurs for an extremely limited period of

time. In fact, you typically have to have the design degree day show up on a Monday when the

school is coming off of the weekend setback to see the true peak demand of the school building.

Table 4-2 – Estimated Peak Demands

Report Estimated Peak, mmBtu/hr

BEAM 3.0

Dietz 7.0

WES 5.5-6.0

Notes: For proper boiler system sizing, it is critical to remember that these peaks are only seen for an hour in a

specific 24-hr period, and the absolute peak demand for the school occurs for an extremely limited period of time. In

fact, you typically have to have the design degree day show up on a Monday when the school is coming off of the

weekend setback to see the true peak demand of the school building.




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5.0 BOILER SIZING

The goal of the overall boiler system is to replace the function of the existing, aging central

plant. The school is also seeking to utilize wood pellet fuel to offset the use of fuel oil to save

annual funds. In addition, the school would like to ensure there is sufficient oil boiler capacity in

place to provide for back up of the wood pellet system. Given these goals, the targeted

approach is to first size an oil fired system that will be capable of providing the needs of the

school, and then to determine the optimum pellet boiler sizing approach that will minimize

capital costs while maximizing fossil fuel offset and optimizing system efficiency.

Additional considerations and constraints to the approach include the following:

• The entire system needs to be able to fit within the confines of the existing boiler plant.

• The school specifically does not want to size this system to cover any future expansions

at the school. Further, there will be hydronic distribution system upgrades and a roof

project occurring in conjunction with the boiler replacement that should reduce the

overall heating demand and improve system performance.

Note that the pellet system could be containerized to alleviate space issues in the boiler room.

This typically does not add significant cost to the project, and can even reduce costs depending

on the labor costs for the job. This is because the container comes with all biomass related

piping, electrical, control wiring, pumps, thermal storage, and boilers already installed. Thus,

there is less work for the mechanical, electrical, and plumbing contractors to complete onsite.

Currently, the boiler room size is limiting the number of oil boilers that can be specified to

provide full backup, and is potentially impacting the biomass system model selection.

5.1 OIL SYSTEM SIZING

Oil system sizes were not recommended by the BEAM study. The Dietz study recommended a

Weil-McLain 2294 oil boiler, which has an output rating of 6.1 mmBtu/hr. WES recommends

that an oil system capable of providing 5.5-6.0 mmBtu/hr be installed to serve as full back up to

the wood pellet system. The preference is to provide this backup over 2 boilers, but based on

space in the boiler room, this may not be possible. The school does not like their existing Weil-

McLain model 2294 boilers, and thus it is recommended that this be considered when specifying

the boilers for the project.




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5.2 WOOD PELLET SYSTEM SIZING

The recommendations of the previous studies are summarized in Table 5-1.

Table 5-1: Summary of Previous Studies

Study Pellet Boilers

Pellet

Firing

Range,

mmBtu/hr

Oil Boiler,

mmBtu/hr

Thermal

Storage

(gal)

Pellet

Silo

(tons)

BEAM 8/29/2014 (2) Pyrot 540 (3.7 mmBtu/hr) 0.46 - 3.68 Not Specified 4,000 80

BEAM 9/24/2014 (2) Pyrot 400 (2.7 mmBtu/hr) 0.34 - 2.73 Not Specified 2,000 44

Dietz 12/2/2014 (2) Pyrot 540 (3.7 mmBtu/hr) 0.46 - 3.68 *5.30 1,500 80

Notes: *The boiler model identified is actually rated for 6.1 mmBtu/hr of output, the report listed the NET IBR rating,

which is shown here.

Figures 5-1/2 and 5-3/4 show the coverage of both of these pellet options with regard to the

2012 and 2014 load models. Table 5-2 shows the coverage of the daily average demand by each

set of wood pellet boilers. This shows that the coverage of the existing daily average demand is

pretty similar by either sizing approach. Note that the curve shows daily average, and there will

be demands both above and below the curve each day. On the days where the biomass system

capacity is exceeded during a peak, control of the system should ensure that the oil boilers

would cover the peak, and the biomass system would continue to remain at full output. Thus,

only a portion of the peaks are not covered by the biomass system.

Table 5-2 – Summary of Modeled Fossil Fuel Coverage by Pellet System, and Recommended

Assumption for Annual Coverage

Sizing Option

Efficient Firing

Range,

mmBtu/hr

2012 Load

Coverage

2014 Load

Coverage

Recommended

Value for Assumed

Demand Coverage

(2) Pyrot 400 kW 0.34 - 2.73 92.5% 95.0% 92%

(2) Pyrot 540 kW 0.46 - 3.68 91.6% 94.0% 93%

Notes: While the coverage should be approximately equal, WES assumes that coverage of overall load will be

slightly higher with the two 540 kW units. This is because of the demand curve at the school, and the reasonably

minor difference in efficient operating range at the low-end. On the high side of the range, there is a difference of

almost 1 mmBtu/hr, and this will pick up some additional load on the higher demand days.

Table 5-2 indicates that the two 400 kW boilers would cover approximately 1% more load in

2014 than the two 540 kW boilers. At first, this might seem counter-intuitive, but the reason is

that the smaller boilers are theoretically able to turn down to a lower low-fire output compared

to the larger 540 kW boilers. This allows the smaller boilers to operate efficiently for more days

during the shoulder seasons. In the 2014 model, the two 400 kW boilers are able to run an

additional 18 days below the level that the 540 kW boilers would be able to run, supplying 118

mmBtu during that time. Although the two 400 kW boilers are not able to supply the average




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daily load on the 5 coldest days of 2014, this is only a difference of 23 mmBtu over those 5 days

compared to what the two 540 kW boilers would supply. Therefore the 400 kW boilers would

supply 95 mmBtu more than the two 540 kW boilers would during 2014, according to the

mathematical model. The situation in 2012 is similar.

The last column in Table 5-2, “Recommended Value for Assumed Demand Coverage,” takes into

account more than just the mathematical models. The models do not consider transitory peak

loads, which would be more effectively covered by the larger 540 kW boilers, thus increasing the

coverage ratio compared to what the two 400 kW boilers would cover. Furthermore, the auto-

ignition feature of these boilers which allows them to shut off completely and then start up

again automatically means that in reality both the 400’s and the 540’s would probably run for

the same length of time in the shoulder seasons. At ultra-low fire the efficiency would be

compromised, although this is true for fossil fuel fired boilers as well.




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Figures 5-1/2 – Coverage of 2012 Demand by Past Boiler Sizing Recommendations




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Figures 5-3/4 – Coverage of 2014 Demand by Past Boiler Sizing Recommendations




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5.3 DISCUSSION OF BIOMASS BOILER SIZING

When optimizing the size of a biomass boiler system it is critical to identify the goals with regard

to coverage. In this case, the goal is to offset as much oil use as possible with as little capital

investment as possible, while ensuring the system will operate as efficiently as possible. Table 5-

3 provides a list of options with regard to biomass boiler system sizing, and coverage of the

annual demand curve provided by each. In each case, the boilers are limited to run only when

there is adequate demand from the system. For the purposes of this report, the efficient

operating range is between 25% and 100% of the boiler’s rated capacity.

Table 5-3 – Coverage of Demand by Various Sizing Approaches

Sizing Option

Efficient

Firing Range,

mmBtu/hr

2012

Load

Coverage

2014 Load

Coverage

Assumed

Demand

Coverage

(2) Pyrot 400 kW 0.34 - 2.73 92% 95% 92%

(2) Pyrot 540 kW 0.46 - 3.68 92% 94% 93%

1000 kW and 250 kW 0.21 - 4.10 95% 97% 94%

600 kW 0.51 - 2.05 89% 87% 86%

Economics are generally the driver of the biomass system sizing. Thus, WES has developed an

estimate of annual energy cost savings in Table 5-4 for each of the sizing options based on the

coverage identified. The average annual fuel oil usage is assumed to be 54,037 gallons as

identified in Table 4-1.

Table 5-4 – Annual Energy Savings for Each Sizing Option

Sizing Option

Annual

Fuel Oil

Offset

Pellet

Usage,

tons

Oil

Usage

Projected

Annual

Cost

Current

Annual

Cost

Annual

Savings

(2) Pyrot 400 kW 49,714 424 4,323 $120,182 $170,756 $50,575

(2) Pyrot 540 kW 50,254 429 3,783 $119,632 $170,756 $51,124

1000 kW and 250 kW 50,726 433 3,311 $119,152 $170,756 $51,604

600 kW 46,490 397 7,546 $123,461 $170,756 $47,295

Notes: All assumptions regarding system efficiencies and fuel prices are listed in Table 5-6. The average

annual fuel oil demand is 54,037 gallons as shown in Table 4-1.

The load curve for the school is reasonably steep. Thus, to obtain the maximum coverage of the

demand, a wide range of boiler operating capacity is needed. To cover the maximum range of

load efficiently, two boilers, one large and one small would need to be used. However, this is

not necessarily the most cost effective way to proceed. To optimize upfront cost versus load

coverage, particularly for a school demand curve, a single boiler can often offer coverage of the

majority of the load with minimum capital costs. Previous sizing efforts for this project have

used twin units to cover the vast majority of the load. This is a good approach that provides

redundancy and flexibility of load coverage. It is not within the scope of WES’s contract to price

out all the potential options.




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It is WES’s understanding that the project will be bid competitively, and thus it is not known

which manufacturer’s models would be used for the system. There are differences among the

potential vendors in the models (sizes) offered, and thus, a performance specification is usually

required to allow competition.

5.4 THERMAL STORAGE SIZING

WES recommends that the thermal storage capacity be equivalent to 75 gallons per 100,000

Btu/hr of installed pellet boiler capacity. This is based on the system’s use of wood pellets, the

specific load curve for the school, and the known load fluctuations during a 24-hr period in a

school. Table 5-5 shows the storage recommendations and impact to system operations at the

low and high end of the demand curve. Please note that proper plumbing of the thermal

storage system is critical to it being a useful component of the system. A three-way mixing valve

blending return from the system with supply from the tank should be included to allow the tank

to be kept at a higher temperature than the distribution.

Table 5-5 – Thermal Storage Sizing Recommendations

Sizing Option

Efficient Firing

Range,

mmBtu/hr

Thermal

Storage

Recommended,

gallons

Peak Output

for 1-hr,

mmBtu/hr

Peak

Output for

15 min,

mmBtu/hr

Storage of

Low-Fire

Rate, hrs

(2) Pyrot 400 kW 0.34 - 2.73 2000 3.06 4.04 2.3

(2) Pyrot 540 kW 0.46 - 3.68 2750 4.13 5.45 2.4

1000 kW and 250 kW 0.21 - 4.27 3000 4.78 6.31 5.6

600 kW 0.51 - 2.05 1500 2.35 3.03 1.2

Notes: The outputs and storage times assume that the thermal storage tank is kept at 200°F and supply temperature

is 180°F. Depending on how the backup oil system is controlled, the storage benefit could be greater.

Table 5-6: Fuel Costs, Heating Values, and Key Assumptions

Item Value Units Source

Cost of #2 Oil $3.160 $/gal SBRSD

Cost of Wood Pellet Fuel $251 $/ton SBRSD

#2 Oil HHV 0.14 mmBtu/gal WES Assumption

Pellet Fuel HHV 16.4 mmBtu/ton WES Assumption

Convert kW to mmBtu 0.003413 mmBtu/kW WES Assumption

Oil Boiler Efficiency 80% Percent WES Assumption

Biomass Boiler Efficiency 80% Percent WES Assumption

HDD Base Temperature 55 °F WES Assumption




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6.0 SUMMARY

WES’s scope is to review the boiler system sizing for the project. The approach taken by the

school and design firms is to provide for school heating demands with a combination of fuel oil

and wood pellet systems. System configurations recommended by past reports are presented in

Table 6-1.

Table 6-1 – Recommendations by Past Reports

Biomass System System

Recommended

Biomass Efficient

Firing Range,

mmBtu/hr

Fuel Oil System

Recommended

Fuel Oil System Rated

Output, mmBtu/hr

(2) Pyrot 400 kW 0.34 - 2.73 not specified not specified

(2) Pyrot 540 kW 0.46 - 3.68 Weil-McLane 2294 6.1

The following are WES’s recommendations:

1) Given the approach taken for system operations, it is recommended the oil system be sized

to be capable of meeting the majority of the demand in its role as a backup fuel source. It is

preferable that this backup capacity be provided by two boilers instead of one. However, it

is assumed that space constraints are the reason one larger oil boiler has been identified.

a. WES assessed the peak demand for the school at approximately 5.5-6.0 mmBtu/hr,

and the existing boiler specified will provide 100% of this demand. This boiler

capacity could potentially be reduced. However, there is not likely much in the way

of project cost savings to be gained through a minor reduction in the size of this

boiler.

b. The school has had poor results with the existing Weil-McLain boilers. While the

source of the issues is not known, the school voiced opposition to installing the same

model of boiler in the new plant. It is recommended that this past experience be

taken into consideration by the designer, and the basis of design manufacturer for

the specifications be discussed with the owner.

2) Give consideration to installing a containerized biomass system for this application. The

following are the reasons this could be a good application for a containerized system:

a. This would alleviate the concerns with space in the existing boiler room, and alleviate

the impact of this spacing on the boiler sizing.

b. Given the labor costs and markups seen on mechanical install for past biomass

systems in MA with public schools, this could prove to be very cost effective. The

vendor would complete all mechanical, electrical, and controls work within the

container and then send it to the site complete. The connection would be extremely

simple onsite, reducing onsite labor.




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3) The oil system is capable of providing peaking and backup needs for the school. Thus, the

goal of the biomass system is to offset the use of fuel oil at the school in the most cost

effective and efficient manner possible. WES evaluated several biomass system sizing

options, and Table 6-2 summarizes the efficient operating range, WES estimated coverage of

annual demands, estimated annual savings, and thermal storage sizing recommendations.

The coverage estimates are done while ensuring that the biomass boilers identified are

running only when school demand falls in their efficient operating range (between 25% and

100% of their rated capacity). WES’s scope was not to price all of these options, however,

since all past studies were using Viessmann as the basis of design, WES asked Viessmann to

identify the cost difference between two Pyrot 400 kW and two Pyrot 540 kW units. This

cost difference for the Viessmann equipment between these two options is approximately

$35,000.

Table 6-2 – Summary of Biomass System Sizing Options

Sizing Option

Efficient

Firing

Range,

mmBtu/hr

Assumed

Demand

Coverage

Annual

Fuel Oil

Offset

Estimated

Annual

Savings

Thermal

Storage

Recommended,

gallons

(2) Pyrot 400 kW 0.34 - 2.73 92% 49,714 $50,575 2,000

(2) Pyrot 540 kW 0.46 - 3.68 93% 50,254 $51,124 2,750

1000 kW and 250 kW 0.21 - 4.27 94% 50,726 $51,604 3,000

600 kW 0.51 - 2.05 86% 46,490 $47,295 1,500

4) WES recommends careful consideration of the specification development for the biomass

system. A performance specification approach will encourage the most competition as the

system sizing options and boiler configurations from various vendors can vary.

5) WES recommends that a heat exchanger be included that will allow pre-heating of the

domestic hot water by the space heating loop in the boiler room. This will allow coverage of

the load by the biomass system with minimal installed costs, and provide redundancy for the

new propane-fired water heater.

6) The pellet storage silo is typically sized to be 1.5 – 2 full delivery vehicle loads. The reason

being that you want to have some fuel left when you place an order, and you want to be able

to accept a full delivery to minimize your delivery costs if possible. Larger sizing of the

storage doesn’t generally provide much in the way of added benefit. It is also important to

remember that the boilers will very rarely be firing at their combined maximum output

consistently over extended periods of time, and the load curves should be considered when

determining how long the storage will last.

20150218 sbrsd boiler system sizing review final...feb 18, 2015 · beam’s study lists the...

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