Executive Summary: The Objective of this project was to create a rainwater harvesting city for a restroom facility in Brownsville, Texas. This project team created a water balance that estimated the dimensions of the roof and the landscape to collect enough water to make a difference in the annual savings for the city of Brownsville. This design was made for clients to have ease of flexibility if they wanted to make any changes to the design, like increased roof dimensions or a material in the rainwater harvesting system, itself. Data for evapotranspiration and rainfall (inches) is from the Texas Water Development Board reports and other sources.
Problem: Design a rainwater harvesting system for a facility in the city of Brownsville, Texas.
Background
Brownsville, Texas, a city located around the United States/Mexican border, needs a rainwater harvesting system built for a restroom facility consisting of 6 stalls, in total (three for men and three for women). Brownsville acquires about 28 inches of rainfall every year, and the month of September has the heaviest rainfall, able to have almost up to 8 inches of rainfall, alone. Its location by the Gulf Coast allows the city to have heavier rainfall than northern states. Using the rainwater for irrigation is an option, but is not required. This report does, however, take in account that possibility. Also, a permeable parking lot is available for collection of rainwater, but that was not used in this design for the sake of simplicity.
The contact for this project was Joe Hinojosa of Brownsville’s Public Works. According to him, the restroom facility had yet to be built, so all the plans were open to be determined while creating a rainwater harvesting system. Electrical power, needed for the system’s pumps, were 600 feet away, next to a major highway. Brownsville needs a rainwater harvesting system that requires low maintenance, flexibility in design, is economical, and is able to last through dry seasons.
Water Balance
Assumptions: It was assumed that the restrooms would need about 600 gallons of water per day (according to the calculation of Dr. Jones “6 toilets x 2 gals trip x 50 visitors = 600 gals per day”). The tank was assumed to have varying amounts of supplemental water depending on the amount of rainfall. The vegetation is native to the area, so they will consume the least amount of water, if any. The landscape area is about 2,500 ft2 to allow enough space for irrigation, if decided upon. Roof dimensions are 2,760 ft3 in our design, allowing an optimum and realistic amount of rainfall inflow. An increase in the roof dimensions from 2,760 ft3 to 3,000 ft3 will increase the amount of rainwater by 4,000 gals.
Calculations: First to calculate water inflow (gals) it was essential to multiply the roof dimensions (ft3), the total amount on rainfall (in), divided by 12 to convert to feet, multiply by .62, .85, and 7.48 to convert feet into gallons . For the month of January 2,760 ft3 (roof dimension) was multiplied by the 1.36 inches of rainfall, .62, .85, and 7.48 to obtain 941 gallons of water inflow. Rainfall (in), evaporation loss (gals) and ET for vegetation (in/day) are all acquired via the research of others, as mentioned in the bibliography. To measure water outflow the ET for vegetation had to be divided by 12 (to be converted to unit feet), multiplied by the total landscape area, 31 (conversion factor) ,and then multiplied by 7.48 to convert the calculation to gallons. For example, for the month of September:
Water Outflow= (ET veg. /12) x 2500 ft2 x 31 x 7.48
= (.2/12) x 2500 ft2 x 7.48= 312 gals
When water outflow was calculated, it was seen that there was not a sufficient amount of rainwater harvested to run the system, and, therefore, supplemental water will have to be obtained from the city to sustain the project on a monthly basis depending on the varying weather conditions. To calculate water storage:
Water Storage (gals) = Supplemental Water + Water Input – Water Output – System Losses
Water storage (gals) January = 2,000 (gals) Supplemental Water + 1233 (gals) Water Inflow –
9662 (gals) Water Outflow (demand)- 3.53 (Evaporation Losses)
= -6432 (gals) of water stored
Cost Estimate:
Rain Water Harvesting Cost Estimates
Collection System
Material Quantity(ft) Price per foot Total Price
Vinyl Gutter System 472 $6 $2,832
Storage System
Material Quantity Price Total Price
Plastic 2,000 gals tank 2 $1,100 $2,200
Tank Level Sensors 1 $895 $895
Distribution System
Material Quantity Price Total Price
PVC Pipe(ft) 80 $2 $160
2" Ball Valve 5 $72 $360
2" PVC Tee 3 $8 $24
2" PVC 90 9 $8 $72
Water pump w/ pressure tank 1 $2,000 $2,000
2 hp Water Pump 1 $250 $250
Overall Total
$8,793
Diagram/Descriptions: Rainfall will be collected from the gutter system which runs along each two hundred and thirty foot side of the building. Water runoff from the metal roof will collect into a six inch vinyl gutter system. The reason for using vinyl gutter is to eliminate the possibility of rusting and pro-long the life of the system. After water collects into the gutters off the roof they will be channeled down to the distribution system. This distribution system will consist of two main collection tanks. The tanks will be two thousand gallons in size and made of plastic both for cost effectiveness and ease of maintenance. Each tank will have its own specific duty. The active tank will be the main tank sending water to the toilets inside. This tank will remain full at all times with the help of both city water and rain water. The collection tank, tank two, will have the purpose of collecting the water runoff from the gutters. From this tank water can be pumped into the active tank via a water pump. As for the active tank the city water added will be pumped in and regulated by an Ashcroft GC52 Differential Pressure Transmitter which measures pressure between two points to determine whether or not to pump water in. On the discharge side of the active tank water will be pressurized and pumped into the toilets. The line will be pressurized by an ABS2.4 - Variable Speed Water Pressure Booster Kit - 3HP which will mount outside the tank. With the entire system layout we have implemented a bypass water route which will bypass both tanks and pumps and feed directly into the discharge line in case of pump failure, pipe breakage, or down time needed to perform maintenance on the system.
Summary
This Rainwater Harvesting System is an economical design that allows flexibility as well as durability. A bypass from the city water line directly to the building allows for any malfunctions to be easily fixed without having to shut down the facility for repairs. Also, this system saves approximately 46,000 gallons of water, annually, that is usually bought from the city instead.
Partner Report:
Lucas Allen: Diagram of Rainwater Harvesting system and specific details about the system itself including cost and materials
Kai Williams: Writing of the report, research about the city, excel spreadsheets
References
1. Dr. Jones
2. Texas Water Development Board. "The Texas Manual on Rainwater Harvesting." 3
(2005): 1-88. Web.
3. Javier Guerrero
4. "Average Weather for Brownsville, TX - Temperature and Precipitation." National
and Local Weather Forecast, Hurricane, Radar and Report. The Weather Channel. Web. 27 Nov. 2010.
5. "Normal Monthly Precipitation (Inches)." NCDC: * National Climatic Data Center
(NCDC) *. National Oceanic and Atmospheric Administration. Web. 05 Dec.
2010. http://lwf.ncdc.noaa.gov/oa/climate/online/ccd/nrmlprcp.html.
*This Report was created by Lucas Allen and Kai Williams
No comments:
Post a Comment