Rainwater Automation. John Larrison

Transcription

1 Rainwater Automation John Larrison This paper discusses how the benefits of automation can help improve the quality of water collected while lowering both the installation and maintenance cost of the system compared to traditional rainwater collection systems. Apr 2017 White Paper Page 1

2 Contents Introduction... 2 Collection Basics... 3 Active System Advantages... 5 First Flush... 6 Accumulation Method... 7 Flow Rate Method... 7 Combination Method... 7 Cost Considerations... 8 Plumbing & Installation... 8 Industrial Applications... 8 Introduction This paper is intended to introduce our concepts about how to improve large scale rainwater collection systems. If you are new to rainwater harvesting, the Collection Basics section will help you get started. If you already understand the basics, this section will help orient you to the touch points we are addressing with automation. This paper focuses on staging and first flush. There are more automation features in the controller that are not covered in this brief paper. After we have covered how this automation benefits the system with better water quality while requiring less and simpler maintenance, we will show how adding automation to the system can usually be offset by lowering the cost. If you are a system professional, using this automation can allow you to provide your customers with a better system at a lower cost. If you are a DIY type person (and you are able to read basic wiring diagrams) our controller will allow you to install a world class water collection system. There is an associated spreadsheet on our web site that helps illuminate several of the concepts presented here. It also assists with sizing and planning your system and then determining suitable parameter values once your system is operational: Rainwater Collection System Controller U.S. Patent 9,633,532 Apr 2017 White Paper Page 2

3 Collection Basics Figure 1 depicts the key components of a wet system. It is possible to have a pipe that runs directly from the gutter into the top of the tank. These dry systems have several limitations that make them less common. However, most of the issues discussed here are also applicable to them. segment is never higher than any point in the plumbing where air can enter. So even if you have a 2 story house and several of your gutters are on the 2 nd story (say 25 feet up), it s the collection entry point of the lowest gutter that establishes the pressure that is available for the entire system. I ll start by describing the key parts of the system. The drop from the gutter to the wet line (item A) is the most critical part of the system. It is this tiny segment of plumbing that creates the differential pressure to move water through the rest of the catchment plumbing, including up the riser (item E) and into the cistern. This pressure If you place some kind of screen or filter in this section that is not air tight, you will further lower the pressure that will be created. It is for this reason that most systems forgo trying to filter below the gutter and instead install a screen (item D) into the entry of the tank. Gutter A Wet Line Screen D E Main Cistern B C Figure 1 - Basic "Wet" Collection System If your gutters are all very high or your site elevation allows the cistern to be placed downhill from the house this is much less of an issue. But most systems will have to address this very limited amount of pressure in one of 2 ways. The first is to use large pipe. Larger pipe does not create more pressure but it allows more water to move at the same pressure. This is why you typically see 4 or 6 pipe used for the catchment plumbing. The second factor is the distance water must move to get to the cistern (item B). Since every foot of pipe creates resistance to flow, and turns create even more resistance, this length is very limited in practical application. To get any significant distance from the house and still capture a heavy downfall, 6 is not uncommon. All plumbing below the wet line will hold water. PVC and other commonly used pipe is translucent, meaning that sunlight can penetrate it. This causes algae, bacteria, insects and other undesirable pollutants to accumulate in the water. It s not uncommon to smell a swamp White Paper Page 3

4 stench while standing near these pipes. New rain will push this brew into the tank and the quality of water in the tank slowly deteriorates. For this reason most systems are plumbed with a catchment drain valve (item C). This should be opened after the rain and remain open to allow dew & condensation from entering the main cistern as this is very low quality water. Having lived with such a valve for years, I can tell you that while this works in theory, remembering to close the valve when the rain starts does not. The tendency is to leave the valve closed to make sure you don t miss a big rain. But this also means you don t notice that slow build-up of dew and condensation (until it gets so bad that the swamp smell permeates). Leaving the valve closed just in case it rains negates most of the benefits of having the valve. Earlier I mentioned that item B required large pipe. Although this pipe is buried so it won t show, it requires a wide trench which requires a backhoe to dig. This is an expensive and disruptive process (unless the water system is being installed with new construction). This also takes installing a rainwater system out of the realm of a DIY project for all but the most ambitious homeowner. Finally, there is the screen filter (item D). No doubt you ll need it since everything that is on your roof and in your gutters will flow through the catchment and wind up in the tank without it. But there are 3 major problems with this screen. First, it s on top of a high cistern. You ll need a ladder to get to it and its likely going to be a bit precarious when you re up there moving things around to fish it out to clean it. It s very easy to spill some of the crap in the screen into the tank with all the jostling, negating the whole point of the screen. The second problem is that if it s working properly, it s like a tea basket. All the good water that flows to the tank later in the rain will have to wash past the dead bugs, bird poop, rotting leaves, fungus, algae and mold that s gathered in the screen since the last time you were on a ladder cleaning it out. Finally, there is just no screen that is perfect. Pollen, sediment and anything in solution will pass right through it. It will not keep sunlight and mosquitos from getting into your tank. There is no chlorine in rainwater so sunlight creates algae wherever it falls, and I bet you already know what mosquitos do. If the screen fails you might find a sizable rodent in your tank who though he had found a great swimming pool (it s happened). This seems like a lot of problems but they can all be solved with an active collection system and an automation controller. The rearrangement of these items on an active system completely changes the dynamics, cost and flexibility of a rainwater system. The next section will show how an active system can reduce and simplify the maintenance, provide more placement flexibility and vastly improve the quality of the water collected. White Paper Page 4

5 Figure 2 shows the same items as the passive system previously discussed. It adds a small staging tank, a pump with filter (these are the same type of pumps you see on back yard pools) and some additional plumbing. Since the smaller tank has a shorter riser (item E), the pressure differential (item A) has greatly increased. Since the tank is about the size of an air conditioning unit, it can be installed near the same area and tap power for the pump easily. The empty tank is very light and can easily be positioned by one person. Most people are already accustomed to this area of their house being utilitarian and won t object to a small 4 x4 Active System Advantages tank there. By placing it close we keep the catchment plumbing short. Even if this is not desirable, you ll still have much more flexibility about placement and large pipe can be minimized (or eliminated) from the plans. If it is placed close to the house, the increased pressure and shorter distance may even allow 3 pipe to be used for downspouts and plumbing to the staging tank (depending on roof size, number of staging tanks, etc. in the plan). Trenching for three inch pipe can be done with a trencher or rock saw so it s far less disruptive to the site and the equipment cost is far less. Gutter A 300 Gal Stage E Pump & Filter D Figure 2 - Active Collection System C B Main Storage It gets even better from here. Properly sized pumps can create 25+ ft. of head pressure and move upwards of 60 gal/min. You can use 2 pipe to move water from the staging tank to the main storage tank (item B). Even with smaller pipe you can achieve distances that are just not feasible with the passive approach. Since this line is pressurized, it doesn t need the vertical riser into the storage tank. Water in this line has already been flushed and is not subject to sunlight so it does not have to be drained. It s also much easier to protect from freezing. The pump s basket filter (item D) replaces the tank-top screen. Since it s in the pressurized path from the pump it has less impedance to the flow when it does get full. Because the filter basket is at ground level, the process to clean it is very simple, requires no ladders and eliminates the potential to drop accumulation into the storage tank while servicing. Now that it is easy to check and service it s more likely that the owner will perform this crucial maintenance. There is no longer any regular maintenance on the main cistern (which is now a closed system). White Paper Page 5

6 That s a lot of pros for active collection, so what are the cons? Probably the biggest is since there is some pumping involved, power does have to be available during rainfall for the staging system. It also requires some float switches and pump control. Even if you choose not to implement the active approach on a new system or you are looking for ways to improve a traditional system, an automated first flush will make a huge difference in water quality. only be used in 2 story or industrial systems. Some flush devices are inefficient (using some good water to flush off the debris) or ineffective (flush only a small portion of the first rainfall). There are some that do work but they are large, expensive and maintenance prone (eliminator tanks). Even these don t always provide complete separation from new water coming in and residual water from the previous flush. All of them require maintenance of some sort to keep them working. It s no surprise that many systems simply do not include a first flush. Traditional systems with long runs of large catchment plumbing can also benefit with the catchment drain pump option. This pumps the water remaining in the catchment after a rain to your cistern before opening the flush valve. First Flush The first flush is one of the most important functions for a rainwater collection system. Just consider that the roof you are going to collect from is exposed to the elements. Birds poop on it, dust, pollen and pollution settle on it. The sun may bake out chemicals from its surface. Gutters are shady places where residual moisture attracts mold, insects and all sorts of debris. All of this moves through your catchment when rain starts falling. So what we want to do is use the first part of the rain to wash all that stuff off the roof, out of the gutters and send it to a flush line somewhere. So the First part of the rain serves as the flush (thus first flush ). There are many challenges to create a good first flush and there are no shortage of products for this. However, these products tend to create as many new problems as they solve. Many are designed to be installed in the critical pressure differential section (item A). Since this space is generally so limited, many of these devices can The solution is to automate the drain valve (item C) and make sure that this valve is placed in the lowest point of the catchment system. The valve is normally open and closes only after conditions defined by an automation system have been met. Since this valve is automated and tied to the environment, it effectively converts a wet system into a dry one by eliminating standing water in the catchment. The valve does not affect the pressure in the catchment system as a screen or filter would, there is nothing to clean, once closed there is no lost water, new water never contacts old flush water, flush volumes proportional to the surface area are easily achieved and seasonal adjustments can be made with a push button instead of hiring a plumber. There is really no downside to this approach unless you are just not comfortable with some technology. Let s explore how the flush works in a little more detail. There are two approaches for determining when enough rainfall has occurred to start collection: accumulation or flow rate. Both use a rain sensor and each has its pros and cons. White Paper Page 6

7 Accumulation Method Flow Rate Method This method is a very simple concept. A sensor detects rainfall volume (in hundredths of inches). When the set amount is reached, the flush valve closes and collection begins. The user can change the volume setting to account for changing seasonal conditions (pollen) or environmental issues (pollution), taking into account the criticality of the need for water. More first flush always renders better water, less flush renders more water but lower quality. After no rain has been detected for a predetermined amount of time (usually 1 day), the flush valve is opened and the catchment is drained. Automation can adjust the flush to account for recent rain (less flush) or extended drought (more flush). The disadvantage of the accumulation method is that when it s raining very slowly (misty kind of stuff), there will not be enough flow to really clean the roof & gutters. Eventually though, enough rainfall will be measured to start the collection. When it starts raining harder some sediment can break loose and flow into the system which is now capturing. This is more likely to be an issue if the roof has overhanging trees such that leafs and twigs are prevalent. These conditions typically require sufficient flow to wash them through the catchment while the system is flushing. This method solves the just mentioned problem of leaves and twigs by timing the rainfall detections to determine the intensity of the rain. Only when the rain is occurring at or above a set threshold will it be counted. The user determines how long rainfall must be at this rate before collection will begin. This may require some trial and error along with awareness of existing conditions to find the best settings. The user can select a higher rainfall rate or more time for the set rate (or both). The downside of this method is that a very long but gentle rainfall may never close the flush valve. Combination Method To get the benefits of both methods the recommended approach is to first set the flow rate method as just described. Then determine what amount of flush this would be in terms of gallons flushed. Set the accumulation setting to be 3 to 4 times this amount. If hard rain comes early, collection begins sooner. If hard rain never happens then eventually enough gentle rain will wash the debris sufficiently to clean the water to an acceptable level. White Paper Page 7

8 Plumbing & Installation The staging tank, pump and associated plumbing will add about $700 to your materials for an active system. But being able to use 2 pipe to run to your main cistern has a huge savings. The cost of the pipe alone is significant. Typically 2 runs around $9 per 10 lengths whereas 4 is $17 and 6 is a whopping $42. Assuming you use the same size for all lateral runs, a modest house with a tank 100 away can easily use 300 of pipe. That s a $300 to $1,000 savings just on the pipe. Smaller fittings are similarly cheaper as well. Installing 2 pipe is a relatively easy job. Installing 6 (or even 4 ) is a much more difficult and expensive task. If you also consider the difference in installation equipment (a trencher vs. a backhoe) the cost savings for the stage approach becomes easy to justify. Cost Considerations gallons. Let s assume that you are considering a 30K gal tank when you might only need 10K gal. If you purchased a 24x36 storage building (usually less than $10K) with 4 PVC tanks hidden inside (about $4.8K), you could save around $15K. You would also have a nice building to house pumps, provide weather protection and space left over for other storage. Use a vertical roof style so you can add gutters to your building and you get another 864 sq./ft. to collect water from. You also won t have a large shiny tank dominating your view. Even if you do run out of water with the lower capacity, you can get 2K gal of water delivered for about $100 in most locations. You ll likely never make up this large difference in cost with the deliveries you might need during a few extended droughts over the years. Industrial Applications Knowing that the staging approach provides tremendous freedom with the main tank placement, you can move the tank far enough away that it can be placed completely out of sight. If you are willing to consider tanks that can be put it in a building, you can potentially collect more rainwater from the building you put them in. More roof surface means more collection, which means you may need less storage. An optimum system should be engineered to factor in roof size, usage, rainfall records & storage capacity. But few are. Since water consumers may not know their usage, contractors have an inclination to upsize the storage. But consider if you paid for a 20,000 gal tank and realized later that it never dropped below ½ full, didn t you essentially overspend on the tank? It s not unusual for a steel tank to cost about $1/Gal for anything larger than 10K Many of the same justifications come into play in an industrial application. But it s a rare business that would willingly sacrifice the valuable space close to the facility for a large tank. This area is much better used for business purposes (customer parking, display of goods for sale, etc.). Also, most of these buildings a quite large and therefore need to dispatch huge volumes of water for a good first flush. Even if the water is not for potable use, you don t want your facility to have the lingering swamp smell greeting customers. Excessive sediment either means maintenance on valves where the water will be used or frequent changing of filters in the plumbing system. Both cost time and money which could be minimized with approaches discussed in this paper. White Paper Page 8