Browse Forums Eco Living 1 Apr 08, 2013 10:13 am I've browsed through here and spent some time with Google but can't seem to find a good guide to sizing a rainwater system. If anyone could link to one I'd appreciate it, otherwise I thought it might be a good thread to have on here. I'm in Mildura VIC, and want to know if it's feasible to be self-sufficient for household water on a 16 acre rural block I'm looking at buying and building on. The block has untreated irrigation water but no town water, so I won't need water for gardens, it's just for use in the house. The block has a 135m2 shed, and my initial house plans will be about 210m2 roof area, for a total catchment of 345m2. Some ABS data http://www.abs.gov.au/ausstats/abs@.nsf ... n%20(6.3.3) suggests the average household uses 100kL per person per year, but other sites suggest half that is for the garden. This means I need to allocate 200kL per year for a 4 person household, or rounding up 17,000L per month. Using BOM mean data for Mildura http://www.bom.gov.au/climate/averages/ ... 6031.shtml, our driest month is April with a mean rainfall of 18mm, which will only supply about 6000L of water from my planned roof area. Jan-Mar aren't much better and even the wettest month (Oct) only returns about 10,000L. It seems I need to triple my catchment area to ensure year round water supply. I'm questioning that 50kL per person per year figure. I'm guessing we could do better than that but I'm only guessing. Water efficient shower heads (x2), clothes washer, dishwasher, grey water to toilets (x2). Minimal use of bath. Two adults, two teenagers. No evaporative cooler. Any ideas on what water usage would be reasonable to base calculations on? Re: Sizing a rainwater system for self-sufficiency 2Apr 08, 2013 5:12 pm We are fairly careful, don't water the garden and only have 3 minute showers and use around 75L/person/day say 28kL/year. The average usage in Melbourne with drought restrictions over the past few years has been about double that. There must have been lots of people taking 30 minute showers! The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Sizing a rainwater system for self-sufficiency 3Apr 08, 2013 7:49 pm bashworth We are fairly careful, don't water the garden and only have 3 minute showers and use around 75L/person/day say 28kL/year. The average usage in Melbourne with drought restrictions over the past few years has been about double that. There must have been lots of people taking 30 minute showers! Ok, thanks, so 50kL per year is not really that far off the mark for normal usage (teenagers in the house). Hmmm, better find a way to increase catchment area.... Re: Sizing a rainwater system for self-sufficiency 4Apr 09, 2013 8:56 am Three threads up in the sustainability links there are some links for doing exactly this viewtopic.php?f=35&t=51738 Third and fourth link down should give you what you need. This is how we worked out our requirements Calculating rainfall and tank size Using data from here... http://www.bom.gov.au/climate/data/ and selecting weather stations from here... ftp://ftp.bom.gov.au/anon2/home/ncc/met ... SW_139.txt Now you need to measure the roof horizontal area that will be drained to the tank/s in m2. Depending on the roof shape it may not be practical to drain the whole roof to a single tank. Multiply the area m2 by the rainfall in mm for each month and divide by 1,000 will give you the volume of rain in kilolitres Area of proposed roof ( Rev 15 ) = 210 sq m so... Site Name Lat Long 066153 MANLY VALE (MANLY DAM) -33.7822 151.2556 Jun 1906 Oct 2006 50.8 50 N Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Mean 115.9 113.8 126.3 138.6 119.7 102.6 98.4 72.7 70.9 73.1 86.0 85.9 1225.6 kL ave 21.1 --> 21.1 Average rainfall = 1225kl per year so each month averages out to approx 100kl So Revision 15 roof of 210 sq m can hope to collect each month 21.1 kilolitres of rainwater As a comparison; if you can keep to the water boards Target 155L per person per day that is the equivalent of 57kLper person per year. 155L x 30 days = 4650L per person per month 3 people should consume 13950L per month Going by the last three water bills we consume approx 20,000L per month Stewie Re: Sizing a rainwater system for self-sufficiency 5Apr 09, 2013 10:57 pm Your 345 sq m roof harvest area in an area with a mean annual rainfall of 290 mm means that you will need to do some major economising. The chart you linked has a column that shows the average number of days each month where rainfall was at least 1 mm. Unfortunately, it does not show the average number of days each month where rainfall is less than 1mm and 2mm as is found on the major city charts. This information is very important when determining rain harvesting yield. In Melbourne for example, about 30% of rain days have falls of less than 1mm and from memory about 40% of the rain days have falls of less than 2mm. If the fall is 1mm or less, very little will reach the tank and not much reaches the tank when it is 2mm or less unless it falls all at once. Mildura has low rainfall, high temperatures and few rain days. This reduces yield. First Flush diverters can kill it. I noticed in your post that you have not factored yield loss. Mildura's average rainfall x your catchment area will give you about 100,000 litres with a 100% yield. Expect 85,000 litres max or 58 litres per person per day for your 4 person household. You should budget for 50 lpd. You need to improvise and the first thing to do is use irrigation water for sanitary flushing. If you don't have a water efficient washing machine, then buy a good front loader. There is also a $150 rebate for eligible low energy and low water use machines. http://www.water.vic.gov.au/saving/home ... hinemodels Investigate the use of enviro friendly laundry products so that the washing machine water can be used outside. The shower will be the huge guzzler. If your teenagers are girls, then good luck! 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Sizing a rainwater system for self-sufficiency 6Apr 10, 2013 8:37 am Thanks for those links above Stewie, some good reading there. SaveH2O Your 345 sq m roof harvest area in an area with a mean annual rainfall of 290 mm means that you will need to do some major economising. <snip> Expect 85,000 litres max or 58 litres per person per day for your 4 person household. You should budget for 50 lpd. <snip> The shower will be the huge guzzler. If your teenagers are girls, then good luck! Since it will be a new build with low resource use a goal from the start, the new building will be set up for efficiency, so water efficient front loader, dishwasher, shower heads, toilets, grey water to toilet flush and reuse on garden. I grew up an a remote irrigation property and we showered, laundered etc in straight untreated Murray river water with no ill effects (rainwater for drinking) but that doesn't really pass muster these days. In any case I was hoping to avoid using the irrigation water for essential purposes so I can be independent (the water is from an irrigation scheme, not private pumping). I hadn't factored in the low yield from low rainfall events, thanks for pointing that out, very important out here. The key figure for me is that allocation of 50L/person/day you quoted. Punching that into my spreadsheet with our BOM data, and allowing for an 80% yield, only March and April fall short, although it's tight all year. Bashworth earlier specified 75L/day though, so there's some variation there. I'm about to buy a new dishwasher for my existing house, already have water efficient FL, Methven showerhead and dual flush toilet. Now that the weather is getting milder, if I turn the irrigation system off and flick the circuit breaker on the evap air-con for a week or two I should be able to get an idea of our current water usage. Will need to get everyone to count toilet flushes which will be a little awkward, maybe a small whiteboard and marker on the back of the door so it's anonymous.... Re: Sizing a rainwater system for self-sufficiency 7Apr 10, 2013 9:52 am Evap air cons moisturise the air and are great in a dry climate (like Mildura) but are obviously not the best in a humid climate like QLD. People worry about the water lost during the purge cycle but the latest units only discharge 3-4 litres per hour whereas the older ones would discharge 10-12 litres per hour. Purge loss is insignificant when compared to the average 60 lph used to moisturise the air. I remember that the water use calculations were discussed in detail on the ATA forums a few years ago and doing a search on that site might be worthwhile. Re the purge loss, some people get the idea that they should save the water and use it to water their favourite plants but it's not a good idea as the purge is done to remove the salts etc that remain from the evaporated water. SIZE OF TANK At some time, you will have a period of well above average monthly rainfall and you really need to be able to harvest all of this water. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Sizing a rainwater system for self-sufficiency 8Apr 10, 2013 2:07 pm Evap works up here, but not that well when it's 40+. I am looking into a r/c split system based on the following reasoning:
I plan on building a very well insulated and tight house with good summer shading and thermal mass. In hot weather we need to open up the house for evap to work - that means pumping 30 degree air though the house (since evap can only drop 10 degrees or so). It would seem more efficient to be well insulated from the outside environment during the heat of the day and keep the box cool with refrigeration, then open up for fresh air at night. We will be building on an acreage, so ground sourced heat pump (partial DIY) may be an option which is more energy efficient. I can create electricity with solar panels to run the refrigerated system, but I can't create water for the evap one. As to tank size, I'm thinking 6 months supply in storage so around 50,000L - maybe 2 x 25,000L? Re: Sizing a rainwater system for self-sufficiency 9Apr 10, 2013 2:39 pm It is always best to supply large settling tanks away from the house and feed decanted water to a smaller (it can be tall) tank at the house. The height of the larger settling tanks and the land contour is obviously important when designing the system. The 22,500 litre tanks are a popular size and popular sizes usually means cheaper unit costs. About 2-3 years ago, my manufacturing partner bought two poly tanks for less than $1,200 each. With the PV, sanitary flushing also occurs at night. If you wanted to reduce pump start ups and noise, you could consider a header tank fitted with a float to supply the cisterns if there was roof space. The average person flushes the toilet 6 times a day. With a 4 person household, having a header tank could save 8,000 start ups every year. A pump's start up energy demand is 3-4 times its run demand. You obviously have an impressive handle on things. It is commendable. NOTE that when feeding rainwater to a tank via a bottom inlet, you will need mosquito proof leaf diverters fitted to the downpipes and these cut back the head but this is compensated by not having to feed into the top meshed inlet. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Sizing a rainwater system for self-sufficiency 10Apr 10, 2013 4:38 pm TimH247 As to tank size, I'm thinking 6 months supply in storage so around 50,000L - maybe 2 x 25,000L? Don't forget to allow for a fire fighting reserve. - The council or the CFA should be able to advise you of the amount The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Sizing a rainwater system for self-sufficiency 11Apr 10, 2013 5:58 pm Thanks for all the info there H20, very useful. Most of the blocks around here are dead flat which leads to a wet system. I've read through your posts on other rainwater threads and gained some excellent insights into what's involved. I will have some questions when it comes time for an actual install At this point I'm only in the feasibility stage so just trying to work out if it's possible to be self-contained on one of these blocks. Looks promising so I'm going to push forward with some more accurate budgets... bashworth TimH247 As to tank size, I'm thinking 6 months supply in storage so around 50,000L - maybe 2 x 25,000L? Don't forget to allow for a fire fighting reserve. - The council or the CFA should be able to advise you of the amount Good point bashworth. My vision involves a small dam/large tank to store irrigation scheme water for reuse (horse water, plant nursery, garden establishment), so CFA could use that if it's ever required. Will check with them. Rainwater is just for potable water in the house. As an aside, I'm looking at an LG LD1452WFEN2 dishwasher to replace the dying F&P in my current house. Claimed water use per wash is only 11.5L! Re: Sizing a rainwater system for self-sufficiency 12Apr 10, 2013 6:47 pm Planning for water efficiency is important. More important is that you can attain that efficiency. If not all the planning goes out the window. We live in country Vic and some years ago just had tank water for everything, the garden coming off dams. Given the actual cost of tanks to hold the water are not really that expensive I would have more than you need. If you price what having to get water delivered to your house because you run out, it does not come cheap, and the cost of an extra tank will soon cross your mind. We had at that time we had about 800 sq metres of catchment area. That includes shedding as well as the house, and with good falls water was soon replenished. Our tank held 25000 gallons or about 113000 litres storage. We had one year of very low rainfall, where to keep a good margin we still had to purchase some water. Given Mildura is not the wettest environment, my advice would be similar to H20's, with a small difference, in that I would have a substantial volume in a tank or tanks, transferred to a smaller tank near the house for usage. The brand escapes me now but we had one similar to the Pioneer tanks. Also as Bashworth says access for fire use is very handy, especially if your house is burning! Perhaps an irroigated water tank could be used for this purpose. An alternative to header tanks in the roof is to go old fashioned. Place a 1000 litre tank on a stand, 6/7 metres up, to supply water to the house. This could be placed in the area where your tanks are located to "hide" it a bit. Water transfer would only occur occasionally then. Settlement 1/2/12 New Shed 23/3/12 Slab poured 27/3/12 Frame complete 4/5/12 Roof complete 1/6/12 LOCKUP 29/6/12 Our new build blog http://kareenhillsownerbuild.blogspot.com/ Re: Sizing a rainwater system for self-sufficiency 13Apr 11, 2013 7:18 am delatite13 An alternative to header tanks in the roof is to go old fashioned. Place a 1000 litre tank on a stand, 6/7 metres up, to supply water to the house I like this idea, mainly because the header tank can be filled during the day when the solar panels are at work and gravity supplies the water pressure at night, but to get reasonable pressure (say 30psi) it needs to be 21m high. 7m is only 10psi, which isn't much pressure. Enough to slowly fill a toilet plumbed to a separate grey water system, but not much else. My elderly parents have a header tank on their hot water system (for pressure relief - wood stove heated) which is only 5-6m high. Showering is absolutely painful, I don't know why they put up with it (it needs a pressure booster on the hot line). Other than the grey water toilet fill, I can't see the point in having a separate smaller tank near the house. Doesn't that mean you need to pump from the main tanks to the small tank, then pump again from the small tank when water is actually needed? It just seems like an extra capital expense that also halves water supply efficiency. Re: Sizing a rainwater system for self-sufficiency 14Apr 11, 2013 11:40 am Hi TimH247, That reminds me, are you also clued up on pump sizing and friction loss? Having a smaller but tall tank at the house as I suggested gives better pump efficiency than drawing from a remote tank. A lot of people unnecessarily buy big expensive pumps (after advice from plumbers and builders) when all they needed was a larger diameter garden hose or pipework. As an example, at 20 lpm an 18mm garden hose has 8 times less friction loss than a 12mm garden hose. It is easy to fit a couple of metres of 12mm garden hose to the end of an 18mm garden hose so that the standard 12mm fittings can be used. This info is mainly for the benefit of site visitors. Try not to use small pipes for internal plumbing (apart from a header tank to a cistern) as the friction loss kills a pump's dynamic head. Pex and compression fittings are mostly used these days. Some of the newer washing machines also have high pressure solenoids and this has to be considered when determining the dynamic head that a pump needs to deliver to the machine. Friction loss varies markedly with the flow rate. Rainwater is naturally acidic due to the CO2 in the air and this reacts against copper pipe. Many people on tank water see blue or green stains in a sink or basin but not realise what the cause is. Putting a retrievable bag of crushed limestone in a tank will help balance acidic water but it forms a protective barrier as it dissolves. The limestone chips need re-breaking every 4-6 months. The Fluidmaster 400UK063 cistern valve is very compact, costs about $20 and is available with an optional gravity feed very low pressure (red 242LP071) seal. Don't fall for the trap of gravity or pump feeding to a cistern fitted with a seal that is designed to handle mains pressures greater than 1,000 kPa. http://www.haron.com.au/fluidmaster_products.html I gravity feed my main use cistern from my main tank for about 8 months of the year and have done so for many years. I was initially very wary of switching to mains pressure during summer but there has never been a problem with the seal. Until recently, it was on mains feed for 6 months (Melbourne) as the tanks were kept for garden use during a very dry and hot period. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Sizing a rainwater system for self-sufficiency 15Apr 11, 2013 2:55 pm Thanks for the link to the cistern valve, I assumed there would be a specific unit for low head applications. Copied and pasted into my spreadsheet of "relevant data" which is constantly growing (and changing). I'm not a plumber nor an irrigation engineer, but after 25 years as a nurseryman and orchardist, including some time working for an irrigation company as a technical manager, I've picked up a few things. I am familiar with the smell of pipe glue and know how to read a pump curve, but no substitute for the day to day hands on experience of a full time professional. I've been using a program called dp to calculate pressure loss, but lately just use an online calculator like this http://www.freecalc.com/fricfram.htm. I agree, bigger pipe is cheaper than a bigger pump (both purchase and running costs). I understand that a tank by the house has less friction loss and possibly less head loss, but I can't work out how that is overall more efficient if you have to pump the water from the main tanks to this one. Friction losses from a remote tank (eg 50m away) would be comparatively small if the appropriate sized pipe was used. In my case the ground is relatively flat, so no head loss other than friction losses. One example I can see where a second tank would benefit would be if there was a large head difference from the tank to the house, and the house was running on solar. A smaller pump (ie lower flow/pressure than required for showers etc) could run during the day topping up the house tank using solar energy, then a second small pump would supply the house needs, negating the requirement for a single larger pump to run on demand (especially valuable if running off batteries). My ideal scenario would be a house near the bottom of a hill (30-40m of head), so that a header tank on top of the hill could be filled during the day using solar power, then gravity feed the house at night. We don't have many sites like that here though. Re: Sizing a rainwater system for self-sufficiency 16Apr 11, 2013 5:01 pm TimH247 I understand that a tank by the house has less friction loss and possibly less head loss, but I can't work out how that is overall more efficient if you have to pump the water from the main tanks to this one. ..... In my case the ground is relatively flat, so no head loss other than friction losses. Flat ground allows you to gravity feed from the bigger settling tank to a smaller but often tall tank (commonly 900 or 1,000 litre poly) at the house. The pipework between the two tanks does not need to be big and the water in the balance pipe will be turned over many times every day. A remote tank also needs to be supplied with a wet system but if you don't use a vertical riser, you will have more head and the pipes regularly flushed without yield loss plus many other benefits. The link below is a currently active discussion about a low yield pumped system and an alternative low level wet flow path is discussed in part. The block slopes but the same head/efficiency principles still apply. viewtopic.php?f=19&t=63937 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Sizing a rainwater system for self-sufficiency 17Apr 11, 2013 7:16 pm SaveH2O TimH247 I understand that a tank by the house has less friction loss and possibly less head loss, but I can't work out how that is overall more efficient if you have to pump the water from the main tanks to this one. ..... In my case the ground is relatively flat, so no head loss other than friction losses. Flat ground allows you to gravity feed from the bigger settling tank to a smaller but often tall tank (commonly 900 or 1,000 litre poly) at the house. The pipework between the two tanks does not need to be big and the water in the balance pipe will be turned over many times every day. A remote tank also needs to be supplied with a wet system but if you don't use a vertical riser, you will have more head and the pipes regularly flushed without yield loss plus many other benefits. The link below is a currently active discussion about a low yield pumped system and an alternative low level wet flow path is discussed in part. The block slopes but the same head/efficiency principles still apply. viewtopic.php?f=19&t=63937 Makes sense for flat site. Thanks for the link, more reading material Once you know the basics, the rest is easy. Read my post in the thread linked below. viewtopic.php?p=1919271#p1919271 2 19497 Hi guys, I want to do some floor levelling before laying the planks and am considering doing it with self-levelling or yellow tongue PB board. I am wondering which one… 0 6510 18 90420 |