Rainwater Collection Calculator: Difference between revisions

The Rainwater Collection Calculator was created to assist in building a rainwater catchment system. Instructions on how to use the tool as well as the basis for all calculations will be presented here.

Creators

Created by Daniel Cobb with Mike Despars and Lonny Grafman.

Instructions

1. Enter the address in the following format '55555 Rainwater Lane, City, State' and click CENTER MAP to show the structure.
2. Click on each corner of the structure's roof. This must either go in a counter-clockwise or clockwise order when selecting each corner.
3. Click the GO button to the rainwater catchment system specifications of this structure using default values.
4. Enter the optional information into the fields below the map in order to see more personalized data. All of these fields have default values and are therefore optional. When data is entered into these fields the output data will automatically adjust itself.
5. If a mistake is made click the RESET PAGE button to reset the map and all data fields.
6. In the list of specifications click the graph link to see a physical representation of the data.
7. To change the units from standard to metric simply click (units : US) found at the top of the list of outputs. This will change the units for all inputs and outputs to standard or metric.

Dynamic Map

The dynamic map was modified from the version found on http://save-the-rain.com/world-bank/. This map is coded using the GoogleMaps API. We chose to use a different data set for the rainfall data. We used the data provided by http://www.ncdc.noaa.gov/ghcnm/v2.php?.

Monthly Water Usage

Enter your monthly water usage. Clicking on the auto-fill link will let you enter different usage amounts for each month. With auto-fill on, it will assume that you use the same amount each month, this is the default setting. You can determine your monthly water usage by looking at your water bill or measuring the amount yourself. Estimate the flow rate of each water source in your structure using a stopwatch and a container with a known volume. Then estimate how long you use each source per day. Convert this into usage per month by multiplying by 30. Add up the usage for each source and you have your monthly water usage. We assumed that the average US person uses 3000 gallons per month. This assumption was made from data provided by http://www.epa.gov/WaterSense/pubs/indoor.html.

Tank Size

If you currently have a storage tank or know what size tank you will be using enter the volume of the tank.

Tank Distance

This is the distance from your First-flush device to the storage tank. This will help determine the pipe size required for your system.

Roof Material

Choose the roof material of your structure. If the material is not listed, choose the material that is the closest in comparison. This will help determine your collection potential as each material has an efficiency rating.

Rainfall

Enter the total rainfall per month of your region. This should be total rainfall and not rainfall per time. This data is automatically entered by choosing your structure on the map. You are welcome to change this data if you used another source to get your rainfall data.

Area

Enter the footprint of your structure if you would not like to use the map to calculate this or if your structure cannot be found on the map. The footprint of your structure is the area of a horizontal cross-section of your structure. This is not the surface area of your roof as we assume that rain will be falling straight-down most of the time.

Annual Rainfall

This represents the amount of rain that will fall in one year at your location. This data is gathered upon clicking the GO button after choosing your structure from the map. You can optionally enter your rainfall data and this will sum up every months rainfall.

Monthly Rainfall

Monthly rainfall is a graph which represents the rainfall data for each month. It is a physical representation of the data. It is pulled either from the map or from the data you provided.

Usage Profile

Your usage profile is represented as a graph. This is based upon the default value of 3000 gal per month or the values you manually enter yourself.

System Efficiency

The system efficiency is based on the rooftop material. Each material has a different efficiency rating based on its permeability. These values were gathered from research done by Tim Dower at http://www.harvesth2o.com/Capture_System.shtml. The values used are as follows.

Annual Collection Potential

This was calculated using the Collection Calculations from Basic rainwater collection calculations. This the total amount of rainfall you can collect annually assuming you have a place to store all the water.

Minimum Tank Size

If you have entered in your own storage tank size this will represent that value. Else after hitting the GO button our algorithm will determine what the minimum tank size should be so that you never have a month with less than 6 gallons. We recommend that you use the next highest standard tank size when planning your system. We calculated this using the formula:

End of month volume = (Previous end of month volume) - (Usage during month) + (Rain collected during month)

We have the maximum tank size set at 4,000,000 gallons. Our algorithm uses a modified binary search to find the minimum tank size, if it is possible with a storage container with a volume less then 4,000,000 gallons.

Monthly Tank Levels

The monthly tank levels represent how much water will be in your storage tank each month. This uses the minimum tank size and represents how much water will be in the tank each month after usage.

Full Tank Weight

The weight of the tank in lbs or kgs will be shown here. This is the weight when the tank is completely full and should be taken into account when constructing your system. It is using the minimum tank size or the tank size you entered.

Pipe Size

First Flush Size

Slow Sand Filter

Warnings