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An investigation into new SUB rooftop garden irrigations systems Chow, Peter; Logawa, Banda; Chang, Michael 2011

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UBC Social Ecological Economic Development Studies (SEEDS) Student Report An Investigation into New SUB Rooftop Garden Irrigations Systems Peter Chow Banda Logawa Michael Chang University of British Columbia APSC 262 Spring, 2011 Disclaimer: “UBC SEEDS provides students with the opportunity to share the findings of their studies, as well as their opinions, conclusions and recommendations with the UBC community. The reader should bear in mind that this is a student project/report and is not an official document of UBC. Furthermore readers should bear in mind that these reports may not reflect the current status of activities at UBC. We urge you to contact the research persons mentioned in a report or the SEEDS Coordinator about the current status of the subject matter of a project/report”. 1An Investigation Into Rooftop Garden Irrigation SystemsPrepared By:Peter ChowBanda LogawaMichael Chang 2AbstractIn this report, the researchers investigated three different solutions for the rooftopgarden irrigation system in the new SUB at UBC. They included drip tape, soakerhose and sprinkler irrigation. The soaker hose was recommended. There are a fewrequirements that are to be met with the solutions. The goal of the new SUB is tohave the LEED Platinum Plus Certification so in order to do that, 90% waterefficiency should be achieved. The area of irrigation is 1866 m2 or 20085 sqft. Someconstraints includeAfter performing a triple bottom line analysis, the sprinklers were found to be theleast expensive in the initial and maintenance costs. The costs of soaker hose anddrip tape were close in long term period and since the SUB is designed to last 100years, that will be the comparison that is focused on. Sprinkler irrigation was foundto have the highest impact to the environment in the sense that its maximum waterefficiency was 51.56%. This eliminated the choice of using sprinklers because itwould not come close to the LEED Certification. Carbon footprint was thenexamined and the soaker hose was found to have the least footprint. In terms of thesocial impact, there was very little difference between the three solutions.After careful consideration, the soaker hose was selected because of its low carbonfootprint. In terms of its economical impact, it was similar to that of drip tape in longperiods of time. The sprinkler was very inexpensive; however, its water efficiencywas too low to be considered. 3Table of ContentsAbstract ..................................................................................................... ................ 2List of Figures ......................................................................................... ................ 4List of Tables ................................................................................................... ........ 4Glossary ......................................................................................................... ............ 5List of Abbreviations ............................................................................................ 51.0 INTRODUCTION ..................................................................................... ...... 61.1 REQUIREMENTS ............................................................................................ 61.1.1 LEED CERTIFICATION............................................................... 61.1.2 AREA OF IRRIGATION ................................................................72.0 SOLUTIONS...................................................................................................... 72.0.1 DRIP TAPE..........................................................................................72.0.2 SOAKER HOSE...................................................................................92.0.3 SPRINKLER SYSTEM.....................................................................123.0 TRIPLE BOTTOM LINE ANALYSIS..........................................................153.1 ECONOMICAL IMPACT................................................................................153.2 ENVIRONMENTAL IMPACT.....................................................................173.3 SOCIAL IMPACT............................................................................................19CONCLUSION........................................................................................................ 20REFERENCES ....................................................................................................... 20 4List of FiguresFigure 1: Area of Irrigation, p.7Figure 2: Soaker Hose, p.10Figure 3: Soaker Hose, p.11Figure 4: Soaker Hose, p.11 Figure 5: Components of sprinkler irrigation system, p.12Figure 6: Sprinklers, p.13Figure 7: Initial Cost of Sprinkler System, p.15Figure 8: Cost Vs. Spacing for Initial Implementation, p.16Figure 9: Cost Vs. Spacing for 20 Years, p.17Figure 10: Cost Vs. Spacing for 100 Years, p.17Figure 11. Material Carbon Footprint for the Initial Setup, p.18Figure 12. Material Carbon Footprint for 100 years, p.19 List of TablesTable 1: Initial Cost of Sprinkler System, p.13Table 2. Water Efficiency of Drip Tape, Soaker Hose, and Sprinkler, p.19 5Glossary Carbon Footprint: Total amount of Carbon Dioxide produced for manufacturing acertain material. It is usually represented in kg CO2/kg material Flow Regulator: A device which regulate the flow rate of a fluid passing through Mulch: A protective covering which is usually consist of plant residues Percolation: Seepage of water through a porous material Triple Bottom Line Analysis: Analysis based on the economic, environment, andsocial values of a product List of Abbbreviation SUB: Student Union Building LEED: Leadership in Energy and Environmental Design PE: Polyethylene 61.0 IntroductionIn this report, the researchers will outline three solutions for the rooftop gardenirrigation at the new SUB. They include drip tape, soaker hose and sprinklerirrigation. Throughout this report, the researchers will give a detailed description ofthe three solutions, including the economical, environmental, and social aspects ofeach product. The researchers will then use a triple bottom line analysis to compareand contrast the solutions, thereby recommending one solution. 2.0 Requirements 2.0.1 LEED CertificationIn the new SUB building, we are trying to achieve the LEED Platinum PlusCertification. It is the highest possible grade for a building designed to beenvironmentally friendly. Therefore, in proposing a solution to the rooftopirrigation, we can earn a possible ten points in the LEED Certification. In the WECredit 1: Water Efficient Landscaping, we can earn a possible 4 points for using onlycaptured rainwater, recycled wastewater, recycled graywater or water treated andconveyed by a public agency specifically for nonpotable uses. Since we have alreadydecided to use captured rainwater, we need to most efficiently use the limitedrainwater. However, the building project has not progressed to a point where weknow how much rainwater we have for irrigation; therefore we will attempt toachieve a 90% efficiency for the rooftop irrigation.WE Credit 2 deals with wastewater generation so it does not relate to therooftop irrigation. The intent of WE Credit 3 is to further increase water efficiencywithin buildings to reduce the burden on municipal water supply and wastewatersystems. This credit specifically says that it does not pertain to irrigation so it alsodoes not apply. 72.0.1 Area Of IrrigationFigure 1 below shoes the areas that need to be irrigated. The total area is 1866 m2 or20085 sqft. One note is that the areas are oddly shaped so irrigation efficiency maybe sacrificed. Figure 1: Area of Irrigation 2.0 Solutions 2.0.1 Drip Tape IrrigationDrip-tape is a thin-wall hose, usually made of polythene (PE) that has beenwidely used for irrigation system in the last few decades. Essentially, drip-tapeirrigation system uses a flexible tubing to deliver water effectively to the root areaof the plant with great flexibility. Emitters are placed along the drip-tape tubing. Theplants receive a precisely controlled amount of water, drop by drop, depending onthe rate of the flow and the choice of emitter size. This attribute of drip-tapeirrigation offers the highest efficiency among other commonly available systems onthe market.It has been reported that typical drip-tape irrigation system can achieve anirrigation efficiency of above 90% [1] [2] [3]. Other mechanisms causing the large 8difference in watering efficiency between conventional sprinkler and drip-tapeirrigation are surface runoff, evaporation. Surface runoff and evaporation occursimultaneously when the humidity of soil is over-saturated over a large surface area.The additional water is wasted to the drainage system via surface runoff and to theair via evaporation before it has a chance to penetrate the soil over one to twoinches, i.e. lack of deep percolation. This results in unbalanced irrigation along theroots. Unlike sprinkler’s planar irrigation pattern, drip-tape irrigation createsprecisely defined wetting zone at the designated locations and a teardrop shapedwetting pattern deeply down the plant roots through capillary and gravitationalforce, as reported by Haman and Izuno [4]. This precise wetting at the plant rootsavoids watering the foliage and reduces the risk of diseases [5]. The limited wettingzone also helps in removing and preventing weeds as only the designated plants areirrigated. Moreover, the ability of deep percolation allows effective irrigation at theend of the plant roots without any issues arise from over-watering, e.g. formation ofpuddles that submerge a major portion of plant roots, leading to displacement of airin the soil and, thus, drowning the plants. This deep percolation feature provides abetter alternative to sprinkler-based system as the new SUB’s rooftop garden has aspecified extensive green roof and raised planting area with 150mm-/600mm-depthgrowth medium [6].All of these properties make drip-tape system a superior irrigation efficiencythat places such system as a lower cost in operation and a more sustainable choiceas opposed other irrigation systems. The irrigation efficiency of drip-tape systemcan be more beneficial in the case of chemigation and integrated fertilizationrequirement where a large percentage of the total agricultural chemicals orfertilizers are conserved in contrast to sprinkler-based system. Another keyadvantage of drip-tape system is its ability to be highly customized to adopt a widerange of different layouts and irregular terrains and leads to a lowerimplementation cost and simplified planning process. In addition, drip-tape systemcan be operated under a relatively low pressure (5-30 psi) in contrast to sprinkler-based system that generally requires a higher pressure to pump the water into theair [4]. This would also make drip-tape systems more economically andenvironmentally beneficial than sprinkler system due to the energy conserved forthe pumping process.Besides these operational features of drip-tape system, the system has a fewadvantages over sprinkler system. One of the economical advantages of drip-tapesystem is the implementation cost. Typical drip tape costs about $.15 to $0.30CADper foot (15 mil drip-tapes) and it can last up to 3 years for 15 mil drip tapes [7-8].Depending on the types of plants in the rooftop garden, the inter-dripline spacingcan vary from tens of centimeter to a few meters, which can lead to a drasticvariation in the cost over the entire projected lifetime of the new SUB, i.e. 100 years.The environmental aspect of the trip-tape system’s operation is tightly coupled to itseconomical advantages. The conservation of water and energy(consumed by thepump) not only reduces the operation cost, but also helps in reducing the carbonfootprint of the entire system. As PE drip-tape is most commonly used, the carbonfootprint of PE must be taken into consideration for environmental assessment. Dueto the limited lifespan of drip-tap, it might have a substantial impact on the 9environment at the end of the product life cycle. Unfortunately, it has been reportedthat plastic (e.g. PE) recycling is not readily available in Point Grey, Vancouver, B.C.by Timothy Carter from UBC Farm. Thus, drip-tape system may potentially causeserious environmental issues if the reusability and end-of-life treatment of drip-tapehave not been carefully addressed.In terms of commercial availability, drip-tape system is commonlyimplemented around the globe and is readily available in North America. A widerange of drip-tapes with different emitter spacing and diameters, and tube-wallthickness (we use 15 mil rather than 8 mil as the standard drip-tape configurationused for later calculation, as it has a longer lifespan of 3 years) can be easilyobtained from various suppliers in North America, e.g. Irrigation Direct©(http://www.irrigationdirect.com/), The Drip Store©(http://www.dripirrigation.com/), and Drip Works©(http://www.dripworksusa.com/). 2.0.2 Soaker Hose IrrigationSoaker hose is a type of low- volume irrigation system which works similarly to driptape. However, instead of having equally spaced emitters to allow water out, such asin drip tape, soaker hose utilizes its porous material to “allow water to seep out theentire length of the hose” [9]. Mainly made out of recycled old tires, soaker hoses areconsiderably tougher and more environmentally friendly than drip tape. As a result,“it [soaker hose] is tough enough to survive being buried in the soil or under a layerof mulch, and is less likely than a drip line to be nibbled by rodents” [13].In terms of water efficiency, soaker hoses can save between 70% to 90% waterconsumption. Compared to the other irrigation systems studied in this researchproject, the performance of soaker hose lies in between the sprinkler and drip tapeirrigation. 10 Figure 2: Soaker HoseAccording to a study conducted by University of Rhode Island, soaker hoses requireless equipment and are generally easier to set up than drip tapes [10]. A typicalautomated soaker hose irrigation system simply consist of a programmable timer, aflow regulator (whenever it is required, considering that soaker hose works betterunder low pressure), hoses, pipes fittings and end caps.Another economical advantage of soaker hose is its relatively long lifespan. Thereare several ways to increase the life span of soaker hose, hence reducing itsmaintenance cost significantly, such as the following steps which are suggested bythe City of Bellevue[11]: Unscrewing the end caps and flushing out any accumulated sediment once or twicea year; otherwise, it may clog the system and affect the water distribution rate Covering the system with mulch to protect it from the sun. If left under the sun,soaker hose will deteriorate after 2 to 3 years Replacing small cuts and nicks with connectors and hose clamps which areavailable from garden centresUnder thorough care, soaker hose system will only need to be replaced after 6 to 7years.Despite its advantages in maintenance cost and ease of installation, soaker hosesystem has a high initial cost. A soaker hose with 90% efficiency cost $27.99 for 50 ftlength or approximately $1.85 per meter (refer to Commercially Available Productsection). Furthermore, soaker hose has certain limitations which need to beconsidered during installation. In order to get a uniform water delivery throughoutits length, each run should be kept short, never longer than 50-75 feet, and thegrounds must be reasonably levelled as well [10]. 11 Commercially Available Products Figure 3: Soaker HoseRetail Price: 27.99 for 50’ length from Amazon.com Figure 4: Soaker HoseRetail Price: $14.99 for 50’ length from Garden.com 12 2.0.3 Sprinkler Irrigation 2.0.3.0 Physical DescriptionBelow shows typical components of the sprinkler system. Figure 5: Components of sprinkler irrigation system This figure shows the typical components of a sprinkler system (i) A pump unit (ii) Tubings- main/submains and laterals (iii) Couplers (iv) Sprinker head (v) Other accessories such as valves, bends, plugs and risers. The rotating head sprinkler system has certain characteristics. The lateral pipes areusually placed on the ground. The riser pipes are attached to these lateral pipes. Onthe riser pipes are the nozzles placed evenly. The sprinkler heads will then berotated. 13 Figure 6: Sprinklers 2.0.3.1 Cost Initial CostsThe Social Garden is 242m2 or 2605 sqft whereas the Production Garden is to be1040 m2 or 11194 sqft. The typical water efficient sprinklers can have a radius of 25feet [14]. This means that we will need two sprinklers for the Social Garden and sixsprinklers for the Production Garden. From sprinkler.com, one sprinkler cost $8.45so the eight total sprinklers will cost $67.6.The total green roof area that needs to be irrigated is 1866 m2 or 20085 sqft. Thesprinklers have been laid out, needing 16 sprinklers according to figure 8. Product Price per item ($) Quantity Price of Quantity($)Sprinkler 8.45 16 135.2¾’’ x 25’ SteelPiping 20.90 [15] 25 522.5¾’’ Female TeeFitting 2.30 [16] 16 36.8¾’’ Couplers 0.56 [17] 13 7.28¾’’ Threaded Cap 0.53 [18] 6 3.18¾’’ Male to FemaleRiser Pipe 1.04 [19] 16 16.64Sprinkler SystemController 72.93 [20] 3 218.79Pump unit 582.92 [21] 3 1748.76 Total 2689.15 14 Table 1: Initial Cost of Sprinkler SystemThe initial installation costs are estimated to be around $4000 dollars [22]. Thisbrings the total initial costs up to $5542.86. Maintenance CostsThe pipes and fittings do not requirement much maintenance; however, the washerson the sprinkler heads could be worn out easily. This should be checked once aseason or every 6 months. In general, check all equipment at the end of a season tomake repairs and adjustments [23]. This takes approximately 2 to 5 hours. At $25dollars per hour, this ranges from $50 dollars to $125.The sprinklers are warranted for two years [24]so they may be replaced every twoyears. In the worst-case scenario, all 16 sprinklers could be replaced, costinganother $135.20. 2.0.3.2 EfficiencyThe efficiency of the sprinkler is at the maximum 75% [25]. This accounts for thewater evaporated. The sprinklers have a circle of wetted area so for square gardens,there will be some overlap, hence, a decrease in efficiency of water usage. Looking atFigure 8, the layout for the garden, there is quite a bit of overlap. If there were nooverlap, only 11 sprinkler heads would be needed; hence a further 68.75%efficiency would be multiplied to the evaporated water efficiency. This is alsoassuming that all the water goes to the soil; however, as it can be seen from Figure 8,the layout of the garden, this is not true. Therefore, the maximum efficiency at thislayout is 51.56%. On a hot summer day, 50% of the water can be evaporated fromthe sprinkler [26]. This would bring the total efficiency down to 34.375%. 15 Figure 7: Layout of Sprinklers Note: Circles are the wetted area of each sprinkler. 3.0 Triple Bottom Line Analysis 3.1 Economical ImpactIn order to compare the economics of the three systems (sprinkler, drip-tape andsoaker hose), we must derive a comprehensive analysis covering a wide range ofcosts including operation, maintenance and initial installation expenses. The cost ofsprinkler system is a flat-rate with respect to the layout of the plants while the costof drip-tape and soaker hose systems rely heavily on the inter-dripline spacing as itdetermines the required tubing length that takes the major portion of the systemcost. First, we determined the required length of the tubing required for specificspacing which will depend on how far apart the plants are placed: , where is the inter-dripline spacing, is the number of rows (thus,would be the width) and is the area of the entire rooftop garden. We did not takeinto account of the edge placement due to the high flexibility of the two systems.Next, we formulated the cost for drip-tape and soaker hose: 16 , where is the material cost ($0.656 per meter for drip tape and $1.85per meter for soaker hose). To calculate the labour cost for replacement over aspecific period, we derived the following equation:= / ×, where is the total labour cost and is the length of tubingthat can be replaced per hour of work at an hourly wage of . Thus, weobtained the following expense plot over different spacing based on the assumptionthat the labour cost is at $10 per hour and that 1400 meter of drip-tape/soaker-hose can be replaced within 1 hour of labour, and sprinkler can be replaced at a rateof 15 minutes per sprinkler head. The lifespan for the sprinkler, drip-tape andsoaker hose are 3, 7, and 2 years, respectively. The cost of sprinkler is calculatedwith the assumption that the metal pipe lasts longer than the lifespan of the SUBproject, i.e. a flat rate of $805 is used in the calculation for the installation of pipe.We have not taken into account of the cost of pump, filters, sensors and controllers,as these expenses do not deviate too much between different systems. In addition,we have not included the water expenses as it depends primarily on the type ofplants and the local weather. Figure 1 depicts the costs associated to different inter-dripline spacing for initial implementation cost, and total expense for 20 years and100 years. Figure 8: Cost Vs. Spacing for Initial Implementation 05 1015 2025 3035 0 0.5 1 1.5 2 2.5 Co st( $1 00 0) Spacing (m) Cost v.s. Spacing for Initial Implementation Drip TapeSoaker HoseSprinkler 17 Figure 9: Cost Vs. Spacing for 20 Years Figure 10: Cost Vs. Spacing for 100 Years Note. Total cost comparison between drip-tape, soaker hose and sprinkler systems over different excluding the cost of filter, pump and controller for (a) one year, (b) 20 years, and (c) 100 years.In summary, the cost of the different systems depends heavily on the spacingbetween the plants. The best approach in selecting the most economical irrigationsystem is to use a hybrid system that utilizes the advantages of drip-tape and soakerhose for areas with irregular shapes or edges. 3.2 Environmental ImpactIn conducting the environmental analysis, booth material carbon footprints andwater efficiency of the irrigation systems are evaluated and compared. 020 4060 80100 0 0.5 1 1.5 2 2.5 Co st( $1 00 0) Spacing (m) Cost v.s. Spacing for 20 Yr Drip TapeSoaker HoseSprinkler 0100 200300 400500 0 0.5 1 1.5 2 2.5 Co st( $1 00 0) Spacing (m) Cost v.s. Spacing for 100 YrDrip TapeSoaker HoseSprinkler 18 Figure 11. Material Carbon Footprint for the Initial Setup Note: *Carbon footprint of drip tape and sprinkler material (polyethylene) is considered to be 2kgCO2/kg material [25] * Carbon footprint of soaker hose material (recycled rubber) is considered to be 0.124kgCO2/kg material [26] * Carbon footprint of steel pipe material is considered to be 1.987kgCO2/kg material [27]From figure 12, it could be seen that total carbon footprints of sprinkler in the initialinstallation is the highest compared to the other two alternatives. More than 1200kgof CO2 needs to be produced to manufacture the materials used in the sprinklersystem. The high carbon footprint mainly comes from the steel pipes which are usedto supply water to the sprinklers. It should be noted that this value is even higher ifwe take into account the fabrication process and the long distance shipping of thematerials as most steel are currently produced in China.The carbon footprints for the entire project duration of 100 years, however, showsdifferent trend than the previous graph. In figure 12, we can see that for plantspacing less than 0.8m, sprinkler system has lower carbon footprints than drip tapesystem. However, the soaker hoses are still leading as the system with lowestcarbon footprint. The slight change in the trend of the two graphs is caused by thedifferent lifespan of each product. In conducting our analysis, we compare themaximum lifespan of drip tape, soaker hose, and sprinkler irrigation system. Themaximum lifespan of drip tape is 3 years, 7 years for soaker hose, 2 years for thesprinkler itself, and approximately 25 years for steel pipes. 0200 400600 8001000 12001400 0 0.5 1 1.5 2 2.5 3 Ca rb on  Em mi sio n ( kg CO 2) Plant Spacing (m) Material Carbon Footprint for 1st years Drip TapeSoaker HoseSprinkler 19 Figure 12. Material Carbon Footprint for 100 yearsIn addition to carbon footprint calculation, water efficiency is also one of ourdeciding factors in evaluating the environmental benefit of the three irrigationsystems. Water efficiency of each product is summarized in the following table: Table 2. Water Efficiency of Drip Tape, Soaker Hose, and SprinklerIrrigation System Water Efficiency Water Efficiency of the SpecificProductDrip Tape 90% and above 90%Soaker Hose 70% to 90% 90% (Dramm Soaker Hose)Sprinkler 34.4% to 51.56% 51.56%Note: Water efficiency accounts amount of water evaporatedBased on both carbon footprint and water efficiency analysis, soaker hose has thebest performance among the three irrigation systems. Social ImpactFor this particular problem, there are not many social impacts. One main one is thefact that we must look at where the product that we are buying comes from. Ifbought locally, we can create jobs inside the country. All three products that wehave chosen are made in the US. The pipes that are needed mostly come from China.We must then look if the products are made by employees who are underpaid ormistreated. 05000 1000015000 2000025000 3000035000 4000045000 50000 0 0.5 1 1.5 2 2.5 3 Ca rb on  Em mi sio n ( kg CO 2) Plant Spacing (m) Material Carbon Footprint for 100 years Drip TapeSoaker HoseSprinkler 20 Another social impact that we can look at is the comfort level in maintaining thesystems. The sprinkler system requires seasonal checkups while the soaker hoseand drip tape requires leveling the soil for each replacement. There is no advantagehere because it can be argued both ways: frequent smaller jobs or infrequent largejobs. ConclusionAfter the triple bottom line analysis, the soaker hose was recommended for a fewreasons. Compared to the drip tape, the long-term costs were very similar althougha little higher than the drip tape. At 20 years, if the spacing of the plants were 0.3m,cost for drip tape was $20,000 whereas for soaker hose, it was $23,000. In the 100years category, it is even closer. In terms of the carbon footprint, the impact of thesoaker hose is much less than that of drip tapes. If the spacing were again, 0.3m, at100 years, the carbon footprint for the soaker hose is 1608 kg CO2 whereas for driptape, it is 14635 kg CO2. In order to achieve the LEED Platinum Plus Certification, weneed to use environmentally friendly materials. The sprinkler system waseliminated because of its low water efficiency of 51.56% at maximum. References [1] Ma. “Drip Irrigation Tools”. [Online]. Available: http://www.gardenguides.com/129796-drip-irrigation-tools.html [March 29, 2011] [2] A.A Moezzi et.al. “Optimal application of irrigation water with drip-tape methodfor Pashmineh Zar croplands, Andimeshk, Southwest Iran”. [Online]. Available: http://cat.inist.fr/?aModele=afficheN&cpsidt=21531979,2009 [March 21, 2011] [3] A Handbook of Water Conservation Technologies and Practices.  [Online] . 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