Thursday, June 18, 2009

Properly Sizing PEX Pipe for Remote Boiler Connection When Long Runs will be Necessary

Tarm USA recommends installing solid fuel boilers in the basements or utility areas of homes whenever possible. Heat losses from boilers located within the home are reduced. Furthermore, heat escaping the boiler will diffuse into the home rather than to the outdoors.
Recently, we have seen a trend toward locating boilers in locations remote from the buildings they will be heating. Outdoor water stoves, which demand remote locations due to their tendency to smoke profusely, have popularized the use of PEX tubing buried underground between the heat source and the heat load. While the use of PEX tubing for remote, underground applications has become commonplace, information about properly sizing the tubing to adequately meet heating demands is not readily available. We are concerned that many customers are burying tubing, at a sizeable expense that may be too small to carry an adequate volume of hot water to properly meet their heating needs. Undersized tubing can often be compensated for by very large circulators, but this can lead to piping noise, high electric bills, and premature erosion of plumbing components.
Anecdotal evidence suggests that most of the underground PEX tubing that is now being installed, whether pre-insulated or not, is 1” in diameter. It is not clear whether cost, availability, or marketing is more influential, but 1” underground PEX tubing has become “the pipe to use” despite its limitations. Tarm USA wants its customers to understand these limitations prior to installing the wrong size tubing.
In order to avoid complications due to undersized tubing when installing a Tarm USA wood burning boiler remotely, generally the following tubing sizes should be used between the boiler and the heat source:
CategoryTarm USA Boiler ModelsOne way Pipe LengthUse “X” Diameter Tubing
1Solo Plus 30/Excel 2000/Solo Innova 30/ FrÖling 20/30<50’1”
1Solo Plus 30/Excel 2000/Solo Innova 30/ FrÖling 20/30>50’/<100’1”
1Solo Plus 30/Excel 2000/Solo Innova 30/ FrÖling 20/30>100’/<150’1¼”
1Solo Plus 30/Excel 2000/Solo Innova 30/ FrÖling 20/30>150’/<200’1½”
1Solo Plus 30/Excel 2000/Solo Innova 30/ FrÖling 20/30>200’/<250’1½”
2Solo Plus 40/Excel 2200/FrÖling 40<50’1¼”
2Solo Plus 40/Excel 2200/FrÖling 40>50’/<100’1½”
2Solo Plus 40/Excel 2200/FrÖling 40>100’/<150’1½”
2Solo Plus 40/Excel 2200/FrÖling 40>150’AVOID
3Solo Innova 50/ FrÖling 50<50’1¼”
3Solo Innova 50/ FrÖling 50>50’/<100’1½”
3Solo Innova 50/ FrÖling 50>100’AVOID
4Solo Plus 60<50’1¼”
4Solo Plus 60>50’/<100’1½”
4Solo Plus 60>100’AVOID

These suggested tubing sizes are based on a 20 degree temperature drop using a 50/50 water/glycol blend. Flow rates are assumed to be 10 gpm for the category 1 boilers, 14 gpm for the category 2 boilers, 18 gpm for the category 3 boilers, and 20 gpm for the category 4 boilers (See the formula at the end of this document to see how these flow rates are derived). In all cases these recommendations enable the use of readily available and reasonably sized circulators such as the Grundfos 15-58 Superbrute (3 speed) or the Taco 0014 by keeping head losses below 20 feet through the tubing itself. Of course there are other sources for head loss such as flat plate heat exchangers, fittings, and/or fan coils. These other sources for head loss are not inconsequential and should always be considered when calculating head loss.
By increasing temperature drop to 40 degrees, flow rates can be cut in half, which reduces head loss by a power of 1.75. So if flow is cut from 20 gpm to 10 gpm head loss is found by multiplying the head loss at 20gpm X .5 1.75. Some applications will be acceptable with a 40 degree drop, others such as fan coils may not. When a larger temperature drop is not possible, it is possible to increase flow rates through undersized tubing to improve heat transfer, however, as flow rates increase past 20 gallons/ minute head loss begins to increase dramatically. Keep in mind that if a person is planning to connect a remote wood boiler to a storage tank in another location, high head losses may be encountered. As head losses increase, flows will decrease. When the temperature differential between the boiler and tank is high the tank will still absorb all of the heat the boiler can make. However, as boiler and tank temperatures get with 15 degrees of one another for instance, it may be impossible to add any more heat to the tank. Consider the following example:
A Solo Plus 60 is installed in a shed 100’ from a home and a 20 degree temperature drop is required. A 50/50 glycol/water mix will be used. A 20 gpm flow is required. One inch PEX is the tubing. Head loss is 47.94’ through the tubing alone. Two Grundfos UP 43-70 F circulators will almost provide the necessary performance, 44’ of head @ 20 gpm (by placing identical circulators in series we can double the head produced at each flow rate). There is simply not a good “single circulator” solution for this amount of head loss as circulators that can handle these head loss conditions provide enormously high flow rates. For demonstration purposes only, these circulators draw 6.8 amps together (800Watts). Assuming that electricity costs $0.10 per Kw/hr. and that the circulators will operate 3000 hours/year, total electrical costs not adding for inflation will be $4,800.00 over a 20 yr period.
If we took the same example, but now used 1 ½” tubing, we could use two Grundfos UP 26-64F circulators. These circulators draw a total of 3.4 amps (370 Watts). Electrical costs over 20 years with this arrangement would be $2,220.00. The larger pipe in this example saves only $2,580.00 over 20 years.
Below you will find similar electricity cost scenarios, but in table format. The following examples involve a 50/50 water/glycol mix and 20 degree temperature drop:
FlowPipe LengthPipe DiameterHead LossCirculator20Year Power $
14100’1”36.4UP 26-99F x 2$2,940.00
14100’1¼”10.36UP 26-64F$1,110.00
14100’1½”4.68UPS 15-58FC$522.00
10100’1”14.5UP 26-64F$1,110.00
10100’1¼”4.34UPS 15-42F$390.00
10100’1½”1.96UPS 15-42F$390.00

HEAD LOSSES AT VARIOUS FLOW RATES, PIPE LENGTHS, PIPE DIAMETERS, AND ANTIFREEZE MIXTURES
Flow (Gal/Min)TemperatureWater MixPipe Dia.Pipe LengthHead Loss
10180H201”100’11.72
10160H201”100’11.96
10180H201”50’5.86
10180H201¼”100’4.58
10160H201¼”100’4.56
14180H201¼”100’8.19
14160H201¼”100’8.35
14180H201½”100’3.69
14160H201½”100’3.77
20180H201½”100’7.03
20160H201½”100’7.17
1018050/501”100’14.64
1016050/501”100’15.25
1018050/501¼”100’5.85
1016050/501¼”100’6.81
1418050/501¼”100’10.22
1416050/501¼”100’10.63
1418050/501½”100’4.61
1416050/501½”100’4.80
2018050/501½”100’8.76
2016050/501½”100’9.11

Above data courtesy of Wirsbo, Inc. Pressure loss for hePEX and AQUAPEX were converted to head loss by multiplying by 2.37.
H= (144ΔP)/D
H= head added or lost from the liquid
ΔP= pressure change
D= density of the liquid at its current temperature (approximately 60.75lbs/ft3 @180deg.)
In piping, as flow rates increase, head loss increases by a factor of 1.75. This means that if we double flow rates, head loss increases by 3.36 times (H X 2 1.75). If we triple flow rates, head loss increases by 6.84 times (HX 3 1.75). Using the Solo Plus 60 example from above: We have a Solo Plus 60 installed in a shed 100’ from a home. A 20 degree temperature drop is necessary. A 50/50 water/glycol mix will be used to prevent freezing. One inch PEX will be used between the buildings. Because we have a supply and return we are faced with 200’ of tubing overall. Head loss for 1” pipe at 10gpm is 14.64. If we double the flow rate to 20 gpm head loss becomes 49.19. IT IS NOT A LINEAR RELATIONSHIP!
Flow requirements can be calculated with a simple formula:
f=q/(kXΔT)
f= flow
q= rate of heat output in BTUs
k= a constant based on the concentration of antifreeze
ΔT= temperature drop of the loop in degrees F.
k factors to be used in the above equation:
100% water = 500
70% water, 30% propylene glycol = 477
60% water, 40% propylene glycol = 465
50% water, 50% propylene glycol = 449
These k factors courtesy of Ipex “Manual of Modern Hydronics 3rd Edition”

Wednesday, June 17, 2009

European Union to North American Wood Boiler Efficiency Conversion

Background(for the technical savvy):

Thermal Efficiency

For an energy conversion device like a boiler the thermal efficiency is:

clip_image002[36]

So, for a boiler that produces 30KW (100,000 Btu/h) output for each 40KW (140,000 Btu/h) heat-equivalent input, its thermal efficiency (n) is 30/40=0.75, or 75%. This means that 25% of the energy is lost to the environment.

Fuel Heating Values and Efficiency

In Europe the usable energy content of fuel is typically calculated using lower heating value (LHV) of that fuel, i.e. the heat obtained by fuel combustion (oxidation), measured so that the water vapor produced remains gaseous, and is not condensed to liquid water. In North America, the higher heating value (HHV) is used, which includes the latent heat for condensing the water vapor.

Definition of Fuel Heating Values

The lower heating value (LHV) of a fuel is defined as the amount of heat released by combusting a specified quantity (initially at 25 degrees Celsius or another reference state) and returning the temperature of the combustion products to 150 degrees Celsius.

The LHV assumes that the latent heat of vaporization of water in the reaction products is not recovered. It is useful in comparing fuels where condensation of the combustion products is impractical, or heat at a temperature below 150 degrees Celsius cannot be put to use.

By contrast, the higher heating value (HHV) includes the heat of condensation of water in the combustion products but primarily not on the moisture content of the fuel.

Relation Between Higher and Lower Heating Value

The difference between the two heating values depends on the chemical composition of the fuel (dry basis).  For example, with hydrocarbons the difference depends on the hydrogen content of the fuel. For gasoline and diesel the higher heating value exceeds the lower heating value by about 10% and 7%, respectively, for natural gas about 11%.

The source of the text above was condensed from: http://en.wikipedia.org/wiki/energy_conversion_efficiency Wikipedia, the free encyclopedia.

Fuel Heating Values for Firewood

Chemically analyzed wood (dry mass) is a “hydrocarbon oxide”, as its major contents are carbon, oxygen and hydrogen with small variations of concentration. Higher concentrations of hydrogen content increases the heating values.

Typical heating values for wood fuel, based on dry mass (w=0%):

Hardwood (EU):                      LHV (dry) = 18 MJ/Kg (7756 Btu’s/lb)       HHV (dry) = 19.3 MJ/Kg (8316 Btu’s/lb)

Coniferous wood (EU):         LHV (dry) = 19 MJ/Kg (8187 Btu’s/lb)        HHV (dry) = 20.4 MJ/Kg (8790 Btu’s/lb)

Lower heating value LHV can be calculated from higher heating value HHV if hydrogen content of fuel is known, as follows:

                                                     LHV (dry mass) = HHV (dry mass) – 0.22 * h

where:    LHV, HHV =   Heating Values in MJ/Kg,  h = Hydrogen content in dry mass in %, 0.22 = Heat of vaporization of combustion products and stoichiometric factors in MJ/Kg

Water Content and Moisture Content in Fuel

Water content “w” is defined as amount of water mass in relation to total mass of fuel, given in %. Water content primarily is used in EU standards.

Moisture content “u” is defined as amount of water mass in relation to dry mass of fuel, given in %. Moisture content primarily is used in US standards.

clip_image002                           clip_image002[4]

Influence of water Content to Heating Values

Depending on water content “w” the both heating values are decreasing as follows:

clip_image002[8]

where:

  clip_image002[10]=Higher heating value in MJ/Kg, at water content W in % 

clip_image002[14]=Higher heating value in MJ/Kg, in dry mass (water content W = 0%)

clip_image002[16]=Water content of fuel (see above) in %

clip_image002[24]

where:

clip_image002[20]=Lower heating value in MJ/Kg, at water content W in %

clip_image002[22]=Lower heating value in MJ/Kg, in dry mass (water content W = 0%)

clip_image002[26] =Water content of fuel (se above) in %

clip_image002[28]=Heat of vaporization of water in MJ/Kg, based on 25 degrees Celsius

The source of the text above: European testing material standards, especially Austrian standard ÖNorm M 7132

Influence of Heating Values used to Boiler Efficiency

At same heat output Qout the figure Qin in efficiency quotation at top of this document is calculated differently between EU and US standards.

Efficiency calculation in Europe:

clip_image002[30]

Efficiency calculation in the United States:

clip_image002[32]

Ratio between US and European Boiler Efficiency:

clip_image002[34]

U.S. Efficiency Ratings Based on Moisture Content and Grain Derived from European Test Data

Efficiency Ratings conversion table Jun 09

PDF Version of the chart above

Monday, June 8, 2009

IRS Guidance on Tax Credit for Purchase of Biomass Stoves

On June 1, 2009, the Internal Revenue Service (IRS) finally issued its guidance for the 30% consumer tax credit (up to $1500) for the purchase and installation of a 75-percent efficient biomass-burning stove.

In a letter to the IRS in February 2009, HPBA asked for specific guidance on a number of issues, but we are confident that this minimal guidance is sufficient. We understand that the IRS is not asking for further testing if a stove manufacturer has already self-certified using valid test data.

Some important points of the tax credit are:

  • To be considered, a stove must use the burning of biomass fuel to heat a dwelling unit or to heat water for use in such a dwelling unit, and have a thermal efficiency rating of at least 75% as measured using a lower heating value;
  • Installation is covered, as long as it is a requirement for the stove's proper and safe functioning;
  • This consumer tax credit is 30% (up to $1500) for the purchase and installation of a 75% efficient stove, and is available in both 2009 and 2010;
  • The tax credit is an aggregate, i.e., the total $1500 can include other energy efficient items. For instance, if a consumer claims $900 on a new stove, then he will have $600 to purchase additional energy saving products in the same tax year;
  • If a taxpayer uses the entire $1500 tax credit on a competing product then they cannot use it for a biomass stove in that same tax year;
  • This credit applies only to existing principle residences;
  • Manufacturers must provide a certificate of qualification for each product as required in the guidance which can be obtained for the customer to use;
  • Taxpayers must retain the certification statement for tax recordkeeping purposes, but the certification is not required to be attached to the tax return;
  • Prior purchases made between January 1, 2009, and June 1, 2009 are covered if the manufacturer offers a certificate of qualification for the product;
  • If a manufacturer has documentation that a stove has already achieved the required efficiency rating, no further testing is required;
  • The IRS has not stated that inserts are covered, or are not covered, but based on EPA's practice of treating inserts and freestanding biomass stoves in a similar fashion, manufacturers may choose to include inserts.

If you would like to read the entire guidance, IRS Notice 2009-53, Non-business Energy Property, it can be found on www.hpba.org or at www.irs.gov/pub/irs-drop/n-09-53.pdf.

Overall, this tax credit is an outstanding achievement for the biomass stove industry and will clearly increase demand for the products. Please consult your tax advisor if you have ANY questions about how this measure applies to your particular circumstance. More information on this tax credit will be made available as it is learned. 

June 3, 2009

W. Allan Cagnoli
Director, Government Affairs
H P B A
Hearth, Patio &  Barbecue Association
1901 North Moore Street, Suite 600
Arlington, VA 22209-1728
(703) 522-0086 x138   fax (703) 522-0548
cagnoli@hpba.org   www.hpba.org

Which would you choose?