It's all Plain to Sea

mrhobbithhnet

Here's a chart that shows RH, Dewpoint for different Air Temps in the UACT of a SHCS:

And a PDF here: How much water in pounds is in a 1000 cuft of air at any known temperature and Relative Humidity.

Knowing your inputs and outputs to a SHCS, you can calculate the pounds of water your system is condensing. From that, it's simple to use a figure of approximately 970 BTU's extracted for each pound of water left in the system ie: condensed. That should give you the energy exchange due to phase change in any one moment. Average a few readings for the day, and you have a starting point to knowing the whole picture...

But remember there is still the heat transfers due to direct conduction of heat right from the air to the soil. One day I hope to make that simple calculation too...
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Hex · Joined: 27 Dec 2006 Posts: 204

Hi John
Is there any way to convert the graph into an xls spreadsheet so it can be used as a calculator? It may be a very useful tool for figuring out how much water is lost from eg: 0.5 cubic feet of air for a given temperature and/or humidity change.
From that we may be able to figure how many btu`s are lost via phase change. My recent results imply that 75% of the heat transfer is not by conduction but i`m not having great success balancing the heat equations as i run into a math nightmare with "grains" of water and other weird and wonderful stuff lol..i`m no mathmatician.
It would be nice if we could somehow assemble a range of tools to do these sort of calculations so we could punch in the known variables and see how well it tallys with the real world collected data.

Just a thought Very Happy

This calculator may be just the ticket
http://www.uigi.com/WebPsycH.html

mrhobbithhnet · Posted: Sun Oct 04, 2009 6:18 am Post subject:

Hex · Joined: 27 Dec 2006 Posts: 204

Hi John
I`m not really sure if the psychrometric calc is as i envision it either Wink

Here`s what i did
Set the calculator input values to
F db
RH%
Set the calculator output values to
RH%
btu/lb

Set known shcs input temp (eg 86F) and RH (eg 48%) and record btu/lb from output
Now set input temp to known shcs output temp (62.6F i think) and RH at 100% and record btu/lb
Assume 1lb of air = 13.5cubic feet so subtract results and divide the result by 27 (2x13.5) for my 0.5 cubic feet of tube air volume, this hopefully results in the btu difference between inlet and outlet.. assuming the air is still at dewpoint as it exits the tube. which it should be for a fraction of a millisecond before hitting the greenhouse air Very Happy

It won`t give you the complete story as the whole trip through the tubing is dynamic from start to finish, when i used the calculator i was hoping to find 0.16btu of heat transfer (the amount missing from the total after accounting for conductive transfer) but it came up with 0.263btu.

Obviously the dynamics involved will modify the RH and air temperature along the tubelength so using fixed start and end values won`t be at all accurate (and its the same for conductive heat transfer)
I guess a "correction factor" might be one way but it would have to be geared to the individual install and based on real test results for that system..even then it could only be roughly in the ballpark LOL

so its still looking far easier to catch an eel with the spoon Wink

mrhobbithhnet · Posted: Mon Oct 05, 2009 6:10 am Post subject:

I get the drift of your madness. And you are on the right track for sure, but where it leads is still a question.

And another field factoid - I never see 100% RH on outputs using my Kestrel 4000. Usually more like 80% is the actual case for 90 deg F/90% RH input. I would have assumed 100% RH out, but this meter don't show that at all. Hmmmm could be the meter's off or the fact. No way of knowing without putting some time into a test calibration suite I feel comfortable with..

If all goes well for me I'll have a few months of free time coming down the pike up here in Edmonton [Moscow west] - hope to get some sunnyjohn site revamp started and more work open sourcing SHCS and the SunnyJohn Toilet. Supposed to just be a vacation, but I'm hoping they run out of cash and lay me off for the winter. Still don't have a home I can get into things at. The job is not where I want to [or could] set up a home [Oregon], so I am stuck in limbo for now. A couple of more years of living that way down there and I'll surely go nuts not having a home to call my own and to build as a showcase of all things hobbitty... but the money's good [famous last words], and my team [all dear friends with families] can use me to keep them fiscally effective as a company in the R&D business. Besides, our investor CEO is a Chemical Engineer who can do these kind of differential calculus work easily if he had a mind to and has a bunch of PhD's in his back pocket to boot. He's got the paperwork and has promised some sort of response wrt to a set of excel sheets that builders and SHCS designers can use .. but no dice so far. Keep your fingers crossed bro, we might hit paydirt with him some day. Especially if he sees the incredible business potential of an install and design Co. for SHCG's using state of the art SHCS's. You could get a call [assuming big bucks in a foreign land turns your crank...] if the lights go on for him. It could if I had the time to draw up a proper proposal in a form he's accustomed to. State of the art greenhouse builders are incredibly busy now that the fear of service collapse is sending shivers through all the progressive city planners and businessmen in the States and Canada and the world. Nothing like a few salvos across the dinner tables in America to get some money flowing into local all season growing solutions. Laughing

Hex · Joined: 27 Dec 2006 Posts: 204

I guess the rh falls fractionally towards the outlet as its likely influenced by the greenhouse temp (warms up a fraction)
I`ve a feeling there are no simple explainations due a million hidden but interactive processes at work.
Everyone seems to be running out of money these days so its probably looking good for your winter vacation. Your CEO sounds like a mathmatician.. tackle him in his lunchbreak and see if he can figure out the relationship between conductive and latent heatloss along a given length and diameter of pipe at X airflow with X temperature/RH difference and if possible put it all in an xls format...shouldn`t take long lol

I`m sure there must be some very bright academics out there that are up for a challenge..where can we throw down a gauntlet? Very Happy

mrhobbithhnet · Posted: Mon Oct 05, 2009 7:14 pm Post subject:

We are on the same page bro. I.ve got my feelers out. BTW, my CEO don't live here, only see him once month Crying or Very sad

Hex · Joined: 27 Dec 2006 Posts: 204