Friday, 28 May 2010

Planning Our House Water Supply

“Ochre Arch” is not located near a town or town water supply and consequently it’s important to try and make sure we have sufficient drinking quality water captured on the farm. Given that we have a remote energy power supply system we also want to optimise available energy sources for moving and heating when needed the house water.

Not long after buying the farm we installed a 22,700 concrete tank at the shearing shed. This has been our primary house water supply since that time. About 12 months ago we installed a new 13,600 litre galvanised iron tank at the house to replace one of the same size that had rusted out but discovered during last winter that the water running off the house roof absorbed smoke from the wood fire making it taste ‘not-so-nice’. Having constructed the new shed for the solar panels last year we recently purchased but have yet to have installed a new 22,700 poly tank. Once this is in place we will then have 59,000 litres of tank storage connected to the main roof areas on the farm.

The location of the above roof areas is such that it is necessary to have some form of pumping in place in order to create sufficient pressure for the house water to run through the pipes producing the appropriate volumes for our needs. Most farms in our situation that are on mains power simply opt for pressure pump/s that run/s virtually every time demand for the water is created via the turning on of a tap. We are not keen on this type of set-up as with many of them the pressure varies to an uncomfortable extent whilst showering and if we had one of these pumps it would use a considerable amount of power.

Six months or so ago we had a visitor (Stafford W) who is an engineer by background and put to us the concept of locating a holding tank up on the hill to the south east of the house into which we could pump the house water … with it then gravity feeding back to the house. We were wrapped with this idea and have been pursuing it – one of the reasons being that we would always have constant water pressure – similar to what people in the towns and cities are used to. Hopefully in the next two months this will be in place via a contractor we have engaged. Another 22,700 poly tank has been purchased to be the holding tank. When this is in place and if it and the other tanks are full we will then have as much as 81,700 litres available to us at any one time. With only two of us living here it is highly unlikely (baring something unforeseen) that we would ever need to bring in water i.e. we should be comfortably self-sufficient.

We identified a suitable location for the holding tank – located approximately 700 metres from the house and sheds and some 29 metres higher in elevation above the house. 29 ‘metres of head’ would, leaving friction loss aside, create 284 kilopascals (kpa) of pressure … more than enough we thought.

The holding tank will have a capacity gauge that can be seen from the house. Whenever the holding tank level falls to, say, half full, we’d then fill it via an electric pump (to be located in to shed that houses the remote energy system) and connecting 50 mm outside diameter (ODI) poly pipe. Our intention was to also install a split solar hot water system at the house that had a LPG booster, meaning we would rarely run out of hot water.

All of the above ‘looked good’ so we had the tank manufacturer place the holding tank at the chosen location … still there at the moment pending the contractor calling to do the installation and connecting. It was then that we contacted a supplier of split solar hot water systems. He suggested that we purchase an electric (rather than gas) boost split system and also informed us that all split systems require a minimum of 375 kpa to function properly.

We are comfortable with the suggestion about the electric boost system as apparently they are extremely effective, our remote energy system can handle it AND it will mean that we will then not have to pay for gas for the booster; although on rare occasions the diesel back-up generator may be required. The need for 375 kpa was a potential problem, though. After a bit of a cooling off period, some lateral thinking and some GPS and other measurements we have managed to locate an alternate site for the holding tank. This will be 45 metres higher in elevation than the house (on the same hill as the one we were going to use but in a different paddock) but involve probably another 100 extra metres of poly pipe AND some very rugged terrain over which the ploy pipe will need to be laid. The contractor was contacted and is comfortable with the change, including relocating the holding tank.

What we needed to do, though, was reach a comfort level that the altered set-up would in fact deliver water at a minimum of 375 kpa. It was then that we contacted our ‘water guru’, Phil W, for advice. He did some calculations and advised us that:

* As a ‘Rule of thumb’ water flow rates for various outlets in houses are generally:

  • 0.25 litres per second for bath, basin or shower
  • 0.2 litres per second for a kitchen sink
  • 0.1 litres per second for a toilet

* Given the set-up of our house water / plumbing here the maximum flow required would be 0.5 litres per second, assuming that say the kitchen sink tap was running at the same time as the shower

* Friction loss, expressed in metres of head, through 800 metres of 50 mm outside diameter PN8 grade poly pipe from a gross height/head of 45 metres would be:

  • 2.96 (roughly 3) metres of head assuming a volume rate of 0.5 litres per second
  • 10 metres of head assuming a volume rate of 1.0 litres per second
  • 35 metres of head assuming a volume rate of 2.0 litres per second

This would then mean that we would have a clear 42 metres of head to work with (45 minus 3). 42 metres of head produces 411 kilopascals of pressure. This is well in excess of the required 375 kpa to run the split solar system.

The critical assumption we are making is that the requirement of 375 kpa is based on INFLOW to the hot water system and not OUTFLOW from the system. Under normal circumstances the outflow through a hot water system would be around 275 kpa where the inflow was 413 kpa.

The investigation process continues but the above provides an insight into factors to be considered. We have decided not to directly connect the tank at the house to the pump given the taste of the water and will only pump directly from the shearing and renewable energy shed tanks.

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