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Frequently Asked Questions
Several representatives from APPA member utilities with sustained, successful tree-planting programs tested the Tree Benefits Estimator. The questions below are based on their feedback. The answers provided come from Misha Sarkovich, Ph.D., project manager, SMUD. If you have a technical question that is not on this list, please contact him.
1. What if I do not see my tree on the list?
Since there are thousands of tree species, it is unrealistic
to expect that all tree species can be listed. Currently,
there are 188 trees listed in the estimator. If your
tree is not listed, please, select a tree species from
the list provided that is similar in terms of type (deciduous
or evergreen), and tree size (small tree, which grows
up to 25 ft in height, medium tree, which grows up to
45 ft in height, or large tree, which grows up to at
least 46 ft in height). You can get the tree size information
from any arboricultural resource, including the Internet.
This estimator uses the Western Garden Book, which is
published by Sunset Publishing Corporation, Menlo Park,
CA, which has 2,000 plant entries. You can check www.treelink.org
and www.arborday.org
for more specific information about types of trees.
To get a tree added to this estimator, contact TreePower.
2. What if my tree is less than 1-year-old?
A tree that is just planted (and thus it is less than 1 year old) is considered in this model to be 1-year-old tree. The benefits are rather small for 1-year-old tree. The methodology is based on the "standard" nursery raised trees which are typically sold in 5-gallon containers, and which are usually 1 inch in diameter at the tree base (1 foot above the ground). This methodology assumes that the standard (5 gallon) trees are "0" age, regardless how long the trees have been growing in the containers.
3. What if I plant trees in a forest or park, but not near buildings?
Then select "No cooling load (0%)" on the first question "Does your utility have a summer cooling load?" Regardless of whether your utility has any summer cooling load, the program will then continue estimating environmental benefits such as the estimates of carbon and CO2 sequestration for the specified tree species.
4. Can you calculate carbon sequestration for shrubs? If so, how can this be done with the estimator?
You could use small tree species (such as Japanese Maple) if you believe that the shrubbery is big enough to provide environmental benefits such as the carbon and CO2 sequestration.
5. What is the definition of a "Mature Tree"?
"Mature tree" means that the tree has a well-developed tree canopy (i.e. mature canopy). Smaller trees are usually considered "mature" at 20 years and for larger tress, 25 years. In other words, trees will continue to age but tree canopy will not get bigger (just like adults.)
6. How do I decide between 0, 50 and 100 percent for cooling load?
You could have any cooling load factor from 100 percent to zero. This methodology chooses two values (100 and 50) in order to simplify the presentation and calculations. A100 percent load is based on heavy summer air conditioning load (such as the case in California and in Southern states). A 50 percent load is based on more moderate climate, which has a smaller air conditioning load or shorter air conditioning season. Zero means no air conditioning load, or when trees are located too far from the buildings to provide any direct shading (such as park or street trees). Regardless of whether your utility has any summer cooling load, the program will then continue estimating environmental benefits such as the estimates of carbon and CO2 sequestration for the specified tree species.
7. Do I need to determine how many of the planted trees survived?
No, there is no need to inspect and ascertain tree survival
for any individual tree plantings. The age of the tree
from the planting date (from 1 to 30 years) will determine
automatically the tree survival rate factor and the
tree growth rate factor, which will then determine together
the level of benefits (for any year between 1 and 30).
In other words, the combination of the tree growth rate
and the tree survival rate will determine the final
multiplier factor that will estimate the appropriate
level of tree benefits for any year. To see the underlying
assumptions about the tree survival rate factor and
the tree growth rate factor, please check the following
link /treeben/data/growthmortalitygraph.asp
In order to estimate tree benefits for any tree age (between age 1 to 30 years), the program will automatically multiply the energy, capacity and carbon sequestration benefit values of MATURE trees with the appropriate Tree Growth and Survival Rate FACTOR. You do not need to make any adjustments or any additional calculations.
8. My utility has planted trees for the past 12 years, but never tracked the benefits. Is there a simple way to estimate past savings?
Yes. In order to dramatically reduce the required data inputting workload, it is possible to use a Random Sample of the past tree-plantings. A utility could randomly select at least 380 trees (or more trees) for a sample of its tree planting effort. That would provide +- 5 percent error term. Then the utility would collect the required tree-siting data (such as the year a tree was planted, tree species, tree distance from the building, tree orientation) and then use the estimator for the sample data. That would give the utility an AVERAGE benefits per tree - average energy savings (KWh saved), average capacity savings (KW saved) and average carbon and average CO2 sequestration (lbs) values resulting from trees planted individually in urban and suburban settings. The next step would be to multiply the AVERAGE tree benefits with the total number of trees planted to derive TOTAL benefits.
There is no need to measure or establish mortality rate for any particular utility tree-planting program because the estimator already takes that factor into account automatically through the application's tree survival rate (it is already embedded and part of the calculations). In other words, you do not need to go back and visit every tree planted to determine if tree(s) survived.
If there is no energy savings (kWh saved) or capacity savings (kW saved) because there is no air conditioning load or trees are planted in open space (such as parks and streets) then there will be no need to collect the tree distance and tree orientation data. You could input anything (i.e. any value) for tree distance and tree orientation data (since they are required fields) but you would select "No Cooling Load (0%)" at the top and the estimator will give you ZERO values for energy savings (KWh saved) and capacity savings (KW saved) and POSITIVE values for carbon and CO2 sequestration (lbs).
9. What is the difference between kW saved and kWh saved; and how can I explain to customers the benefits of kW and kWh savings?
Kilowatt (kW) represents a unit of electrical power equal to 1,000 Watts. It represents the measure of instantaneous demand for electrical power. If ten customers each have a light bulb with the 100-Watts rating, then it will require 1kW of electrical power demand to light up all ten light bulbs instantaneously. The utility is required to provide sufficient power in the grid with adequate voltage to provide enough power to light up all ten light bulbs. Kilowatts saved (kW saved) represents a measure of instantaneous demand for electrical power that is avoided or did not have to be generated as a result of the tree plantings.
Kilowatt-Hour (kWh) represents a common unit of electrical energy consumption or the basic unit of electrical energy. One kWh equals 1,000 Watts consumed for one hour. It equals the total energy consumption taken from an electric current steadily for one hour. If ten customers have each a light bulb with a 100-Watts rating, then it will require 1 KWh of electrical energy to light up all ten light bulbs steadily for one hour.
For instance, a utility would sell from its electrical grid sufficient energy with adequate voltage (1 KWh) to ten customers to provide enough energy to light up all ten light bulbs for one hour. Similarly, a 2-kW (2,000 Watts) air conditioner operating for 30 minutes uses 1 kWh of energy. Kilowatt- Hour savings (kWh saved) represents a measure of energy use avoided as a result of the tree plantings.
10. What if you plant two (or more) different trees in different areas? How do you calculate the benefit?
You would have to run two (or more) calculations (for example, one for a tree planted in the south; and one for a tree planted in the west) and then add the benefits. The total benefits are cumulative (1+1=2). If you have two trees planted in the same area, then simply input two (2) trees in the input form under the "Number of Trees" question and the program will calculate the total benefits for two trees automatically.
11. What if I plant trees that are not in a standard
5-gallon container?
The methodology is based on the "standard" nursery raised
trees which are typically sold in 5-gallon containers,
and which are usually 1 inch in diameter at the tree
base (1 foot above the ground). However, SMUD Shade
Tree program has experienced that 5-gallon container
trees will grow quickly and catch up with the larger
15-gallon container trees within the next couple years
and thus the methodology applies for both 5- and 15-gallon
container trees. Also, this methodology assumes that
the standard (5 gallon) trees are age "0" when planted.
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