NOTE: Make sure you read the first three posts (in order!) before tackling the rest, or it could be confusing: Post 1 is Designing the future, Post 2 is Setting up the problem, and Post 3 is Estimating basic requirements.

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Thursday, August 10, 2006

Water, water everywhere...

Just to get the designer wheels in your head started spinning, Peak Energy posted a good link to a story about a successful ground heat pump.

I have a little bit more to say about basic requirements as discussed in the previous post. Looking at Objective 2.1 (“The community will provide indoor plumbing adequate for four people.”), I’m starting to think that the driving goal (Goal 2) should be changed so that we can use it to address all the water management needs. This type of modification is common as Systems Engineering solutions are developed and I hope it shows you how fluid the design process is.

So, instead of Goal 2 reading “The community will have indoor plumbing”, how about “The community will provide adequate water supplies.” We’ll leave Objective 2.1 as it is, but add Objective 2.2: “The community will provide enough water to sustain four people.” Now that we fixed our goals and objectives, let’s define some requirements.

Taking some liberties with the data, the average human needs approximately 5 liters per day (lpd) for drinking, 45 lpd for hygiene and bathing, 20 lpd for cooking activities, and 3500 lpd for food production according to the Pacific Institute. (Very good link by the way.) Bear in mind these numbers reflect only the water “at the tap” – they take into account moderate efficiency improvements over the average American’s lifestyle and say nothing about recycling or help from local rainfall.

I will put these numbers into two categories: personal and agricultural, with respective values of 70 lpd and 3500 lpd. For the four-person community, this comes to 280 lpd for personal water and 14,000 lpd for agricultural water. This leads naturally to two requirements – “The community shall provide no less than 280 lpd of indoor water.” (Requirement 2.1.1) and “The community shall provide no less than 14,000 lpd of water for food production.” (Requirement 2.2.1)

Notice two things about these requirements: 1) They are wild-ass estimates and will surely be modified as your design develops and 2) they are intertwined with each other and their parent objectives. I could just as easily put Req 2.1.1 under Objective 2.2. Assigning requirements often comes down to intuition or preference, but remember that in the end every objective (for any project) must have at least one requirement. This ensures that every objective is met.

In future posts I will talk about planning for changes in your local water allocation due to global warming effects, aquifer depletion, or upstream pollution.

4 Comments:

At 1:38 AM, Blogger James Samuel said...

If this blog is going to remain useful as a resource it is likely to need a certain functionality that doesnt come as an automatic feature of blogspot - categories.

An ability to categorise posts for easy searching and reference will be very hepful as it grows.

Searching for ways to do this will bring up lots of options, most of them quite complicated. I have used labelr.com in the past but took it off my blog as it was unreliable and added a big overhead to page load time, making it unworkable for anyone who was not on a fast connection.

Maybe another reader has found a solution to this.

 
At 3:12 PM, Blogger PeakEngineer said...

Thanks James. I do have plans to add functionality as the blog grows. In the meantime (before I find a permanent solution) do you think a google site search would suffice?

 
At 8:22 PM, Blogger Big Gav said...

I live with just Google site search though Technorati tags are better - if you can be bothered with the overhead of adding them (for short posts its fine, but it doesn't work for my sprawling post style).

 
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