Allen Mulvey <allen <at> amulvey.com> writes:

>=20
> Thank you for your comments. I'll try to reply to several
> people all at once.
>=20
> First, misting is not a part of irrigation. I am
> experimenting with moisture sensors like the one below but
> that is a totally different, and much simpler project.
> Misting is primarily for new growth and cuttings. Their root
> system is small if existent at all so they cannot
> effectively process moisture from the soil. The misting
> keeps the vegetation (above ground) from drying out. A
> cutting with no root system can dry out very quickly, even
> with moist soil.=20
>=20
> It would seem that relative humidity would be the most
> significant factor but it is not. Temperature has a twofold
> effect. First, as air is heated it is able to hold more
> moisture so the relative humidity has a tendency to drop as
> the air is heated. Secondly higher temperatures (more
> energy) help bridge the latent heat of transition so warm
> water evaporates more quickly than cold. A 60 percent
> relative humidity at 40 degrees Fahrenheit has a very
> different effect than 60 percent at 105 degrees. Both of
> these are well within the operating parameters of a working
> greenhouse. There is not a linear relationship. Barometric
> pressure can also have an influence as partial pressures are
> also involved. I was hoping to find a table which would map
> the rate of evaporation, as closely as possible, to my
> measurable variables. I had expected that some research
> nursery somewhere must have already done this.
>=20
> Allen
>=20
> Moisture Sensor:
> http://www.vegetronix.com/Products/VG400/

Thanks for explanation.  As somebody suggested, look at hydorology.  Also,=
=20
evaporation rate is a physico-chemical problem, this might help:
http://en.wikipedia.org/wiki/Evaporation

If the goal is to keep evaporation from cuttings low, than with RH close to
100% (but non-condensing) one can achieve that.  This implies that
temperature control is decent (no sudden drop in temperature that would lea=
d
to condensation).   However, in real-world application this can be
counterbalanced by just as rapid drop in RH, e.g. by blowing fresh air. =20

Please keep us updated on your progress/design decisions, it is an
interesting topic.  Especially for me, since I am doing similar things
(although not on a commercial scale, just a hobby) for my wife
(http://imagiknitter.blogspot.com/).  Eventually I owuld like to have al
kinds of sensors and reporting for growing plants.=20

Sergey Dryga

http://beaglerobotics.com

--=20
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