Aquaponics Digest - Mon 10/25/99
Message 1: Re: Technical greenhouse question
from "Robert Claytor"
Message 2: Re: Technical greenhouse question
from "munser"
Message 3: Re: Technical greenhouse question
from "Robert Claytor"
Message 4: Re: Inflation Fans, In or Out?
from "Barry Thomas"
Message 5: Re: Technical greenhouse question
from Ronald Polka
Message 6: Re: Technical greenhouse question
from Adriana Gutierrez & Dennis LaGatta
Message 7: RE: Technical greenhouse question
from "Ronald W. Brooks"
Message 8: Re: Inflation Fans, In or Out?
from Marc & Marcy
Message 9: Re: Inflation Fans, In or Out?
from Ronald Polka
Message 10: Re: Technical greenhouse question
from atkindw@cwjamaica.com (david w atkinson)
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Subject: Re: Technical greenhouse question
From: "Robert Claytor"
Date: Mon, 25 Oct 1999 03:50:38 PDT
We have a small 10x20 ft. greebhouse we built 15 years ago by setting the
whole thing six feet into the ground. This gives the earth's "thermal
flywheel" effect and allows cooler summers and warmer winters. the walls
into the ground are built of 8" concrete block coated with "Surewall" which
is fiberglass reinforced grout . We had no skills in laying up concrete
blocks with mortar. Anyway, we built a hoop-like roof from aluminum conduit
over the top and cover the whole south-facing side with shade cloth in the
summer. The floor is lined with 55 gallon drums full of water, with
seedlings, etc. grown on top of the drums. It works beautifully. doesn't
freeze in the winter, doesn't cook in the summer. We live in North Georgia
and we KNOW what a hot summer is!
rclaytor@hotmail.com
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Subject: Re: Technical greenhouse question
From: "munser"
Date: Mon, 25 Oct 1999 06:53:21 -0500
Robert,
Where did you get the plans for your greenhouse? It sounds like one I could
use. I'm in Little Rock, AR (Zone 7) and I like the idea of the underground
portion taking advantage of "nature's insulation". Thanks in advance for
any info you can give me, Ginger Unser
-----Original Message-----
From: Robert Claytor
To: aquaponics@townsqr.com
Date: Monday, October 25, 1999 5:42 AM
Subject: Re: Technical greenhouse question
>
>We have a small 10x20 ft. greebhouse we built 15 years ago by setting the
>whole thing six feet into the ground. This gives the earth's "thermal
>flywheel" effect and allows cooler summers and warmer winters. the walls
>into the ground are built of 8" concrete block coated with "Surewall" which
>is fiberglass reinforced grout . We had no skills in laying up concrete
>blocks with mortar. Anyway, we built a hoop-like roof from aluminum
conduit
>over the top and cover the whole south-facing side with shade cloth in the
>summer. The floor is lined with 55 gallon drums full of water, with
>seedlings, etc. grown on top of the drums. It works beautifully. doesn't
>freeze in the winter, doesn't cook in the summer. We live in North Georgia
>and we KNOW what a hot summer is!
>
>rclaytor@hotmail.com
>
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Subject: Re: Technical greenhouse question
From: "Robert Claytor"
Date: Mon, 25 Oct 1999 05:25:09 PDT
Ginger
I got the ideas for our solar greenhouse from a number of books I bought
from Rodale press ( the "Organic Gardening " people ). They have several
books about solar greenhouse design. I have seen them at the local libraty,
maybe you could find them there. If not, I can look up and give you some
titles of the books I have. It really works. We have banana trees growing in
Half-barrels ("whiskey kegs") that have grown there for years. But no
banans... then a friend pointed out to me that all my trees were MALES. Oh
well they are still beautiful.......
bc
>From: "munser"
>Reply-To: aquaponics@townsqr.com
>To:
>Subject: Re: Technical greenhouse question
>Date: Mon, 25 Oct 1999 06:53:21 -0500
>
>Robert,
>Where did you get the plans for your greenhouse? It sounds like one I
>could
>use. I'm in Little Rock, AR (Zone 7) and I like the idea of the
>underground
>portion taking advantage of "nature's insulation". Thanks in advance for
>any info you can give me, Ginger Unser
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Subject: Re: Inflation Fans, In or Out?
From: "Barry Thomas"
Date: Mon, 25 Oct 1999 16:08:45 +0100
>. The roof heat loss due to outside blower inlet air
> amounts to just over 1 % of the total. The size of this loss becomes
> insignificant relative to other things such as infiltration of cold
outside
> air which is nearly always the largest single component in the
greenhouse
> heat balance equation. This is directly related to construction
practices
> and quality of weather stripping and sealing.
>
> Ron Polka
> Southwest Technology Development Institute
> New Mexico State University
> Box 30001, Dept 3SOL
> Las Cruces, NM 88003
> rpolka@nmsu.edu
>
Ron,
Many thanks for setting me right on this - the explanation of the answer
was especially appreciated.
It does raise a couple of points that (along with a few others) I have
been so far unable to resolve though. My knowledge of large
gutter-connected GHs is even sketchier than that of smaller single span
structures so if we could look at the simpler example of a twin-walled
poly tunnel about the same size as one of the bays you mention (approx.
30' x 100'), I'd be grateful. :)
This would use a high-pressure/low-volume fan to provide inflation only
and a low-pressure/high-volume exhaust fan for cooling and introduction
of fresh air, yes?
But, both inflation and internal air quality are dependent on a fairly
constant (or regular at least) inflow of outside air. Temperatures on
the other hand can fluctuate significantly over a wide range of
timescales. And yet it is air quality and temp control that are linked
rather than air quality and inflation. This seems to cause a number of
problems. Among the more pressing of these are:
1) During the day, you must put a lot of energy into your exhaust fans
in order to remove large amounts of heat energy from the GH - non of
this heat is recoverable for use during the night and more energy must
be input to maintain nighttime temps.
2) At intervals during the night (or any colder period), internal air
quality demands that the exhaust fans be used to pull in clean air -
this must result not only in unwelcome temp fluctuations but also
increased heating costs as warm internal air is exhausted direct to the
atmosphere and no heat exchange occurs with the incoming cold air.
3) Pulling air out of the GH is always going to encourage leakage of
outside air into the structure. This appears worse than the same
flowrate of warm air escaping outwards as the incoming cold air
increases in volume once inside, ie - although the actual rate of
leakage is the same in either direction, it's worse when cold air moves
in?
(I assume that infiltration of cold air is less of a problem in single
span
tunnels anyway as there are fewer joins to seal?)
4) High water use during hot weather. The large volumes of air involved
in cooling via exhaust fans makes recovery of useful amounts transpired
and evaporated water difficult at best. If additional evaporative
coolers are used...
Most of these problems would seem to be removed or reduced if the air
from the the envelope _is_ exhausted into the GH, the volume of air
introduced by the inflation fan increased to that needed to maintain air
quality and cooling/heating achieved/aided via an active heat sink - the
exhaust fan being removed or kept for emergencies only. The most obvious
benefit from doing this is removal (or softening) of the link between
temps and airflow. Such a structure should also allow some level of heat
exchange between incoming/outgoing air, a slight positive internal
pressure to the GH to prevent/reduce ingress of cold air (and other
things) via imperfect seals and the ability to reuse some of the energy
you've gone to such trouble to remove during the day etc etc. The
reduced airflow should also allow easier/better integration with other
processes such as water recovery etc.
So, although I would certainly take your advice and use standard exhaust
fans if I was setting up a large commercial system, do you think this
could be a worthwhile model to aim at for a small commercial or large
hobby/testbed system where a little experimentation is less costly in
the event of failure? Although the heat pumps required to shift energy
between GH and heat sink will require power, it might be less than that
used by the standard model and other benefits could easily outweigh
cost?
Does this hang together do you think? Are there any major problems you
(or anyone else) see with this approach or any ways it should be altered
for improvement? Anyone happen to know of info regarding attempts in
this direction?
Thanks again for the info so far - sorry my own is so vague. :)
Barry
barrythomas@crosswinds.net
PS While I am searching and reading these subjects, if anyone has URLs
to relevant info handy (esp. heat transfer calcs) to help narrow the
search, I'd be very happy to receive them
.
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Subject: Re: Technical greenhouse question
From: Ronald Polka
Date: Mon, 25 Oct 1999 10:34:59 -0600
At 03:12 PM 10/24/1999 -0400, you wrote:
>
>1. Can hoop structures be retrofitted to allow some passive convection
>ventilation, avoiding the need for fans and cooling for at least some of
>the year? I've seen some advertisements for commercial hoop structures
>with what appears to be a vented hoop which lifts up from one side,
>almost creating a sawtooth effect. Or can you put in some central ridge
>venting?
>
As Ron Brooks wrote a hoop gh can be retrofitted most easily by removing
the endwalls during the summer months.
The commercial houses that have ridge vents or large side vents are quite
expensive and may not be amenable to retrofitting. You would need to
contact the vendors regarding that.
>2. Is there a way to run fans with solar power? This requires some
>up-front capital investment but reduces operating costs. If so, what are
>the reliability issues related to this equipment? Will sea air and
>extreme sunlight lead to a short life for the equipment and lots of
>headaches down the road?
Exhaust fans can be run with power from photovoltaic panels. The
disadvantage is the cost and in most situations this is insurmountable. If
you have access to grid power it is very doubtful that PV powered fans can
be cost effective. Exhaust fans require a relatively large electric
service. If considering PV power you must examine some of the following
issues.
What is the required air flowrate for sizing the exhaust fan?
Will you then size the PV system to run directly from the panels, if so can
you find the right DC motor for your fan? This can be a problem.
If you decide to run your exhaust fan with an easily purchased AC motor
then you will need to size and purchase batteries, a charge controller, and
an invertor, all rather expensive system components.
A battery powered system will allow you to size the system with fewer PV
panels, itself a substantial savings, but offset by the balance of system
costs of the other components.
The beauty of a solely DC system with no controllers is that to a certain
degree it is self controlling. When the sun is the brightest and the need
for ventilation the greatest the PV system will supply the most power.
However, system component sizing is critical when this approach is
attempted and there will be times when the PV system is generating power
that is not being used.
To give you a real life for instance. A few years ago I sized and costed
out a PV system for a small commercial greenhouse that was to be built one
mile off the electric power grid. After detailed system sizing and
extensive analysis I determined that the most cost effective means of
operating this greenhouse was with a diesel generator. It wasn't what the
owner wanted to hear but wishful thinking is not conducive to running a
successful business.
To sum it up I would have to say that in light of the high capital cost of
PV systems versus the moderate operating costs of AC ventilation systems
you should carefully examine the economics of photovoltaic systems before
committing yourself.
Ron Polka
Southwest Technology Development Institute
New Mexico State University
Box 30001, Dept 3SOL
Las Cruces, NM 88003
rpolka@nmsu.edu
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Subject: Re: Technical greenhouse question
From: Adriana Gutierrez & Dennis LaGatta
Date: Mon, 25 Oct 1999 14:48:03 -0400
Thanks again Ron, I read you loud and clear. Removing the end panels
sounds like a very practical solution. I wish I had known about it last
June...
> As Ron Brooks wrote a hoop gh can be retrofitted most easily by removing
> the endwalls during the summer months
> It wasn't what the
> owner wanted to hear but wishful thinking is not conducive to running a
> successful business.
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Subject: RE: Technical greenhouse question
From: "Ronald W. Brooks"
Date: Mon, 25 Oct 1999 15:42:41 -0400
Well I have to disagree
there is no such thing as all male Banana's. Each Banana has female ,
hermaphrodite and male flowers in all the same stalk. I grow Banana's up
north in my greenhouse and do not have a big problem getting them to fruit.
They are very heavy feeders , I use a slow release granule ( 1 -3 pounds ) a
month. Plus mix 30-30-30 in the water , and water every day, even in the
winter. Also I keep them in my warm orchid section , the temps do not drop
below 70 at night. Also Banana's like to grow in "mats" ( groups of more
than 1 )
I can send you some growing FAQ's private if you want.
Ron
The One Who Walks Two Paths
ICQ 44271371
-> -----Original Message-----
-> From: aquaponics
-> [mailto:aquaponics]On Behalf Of Robert Claytor
-> Sent: Monday, October 25, 1999 8:25 AM
-> To: aquaponics@townsqr.com
-> Subject: Re: Technical greenhouse question
->
-> . We have banana
-> trees growing in
-> Half-barrels ("whiskey kegs") that have grown there for years. But no
-> banans... then a friend pointed out to me that all my trees were
-> MALES. Oh
-> well they are still beautiful.......
->
-> bc
->
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Subject: Re: Inflation Fans, In or Out?
From: Marc & Marcy
Date: Mon, 25 Oct 1999 15:19:54 -0600
> none of
> this heat is recoverable for use during the night and more energy must
> be input to maintain nighttime temps.
There are practical techniques available to store this heat
energy and recover it at night.
> this must result not only in unwelcome temp fluctuations but also
> increased heating costs as warm internal air is exhausted direct to the
> atmosphere and no heat exchange occurs with the incoming cold air.
The incoming cold air can be routed through the heat storage
and at least raise the temperature if not fully heat it.
There are ways of insuring heat is as constant as you want
it.
> Does this hang together do you think? Are there any major problems you
> (or anyone else) see with this approach or any ways it should be altered
> for improvement? Anyone happen to know of info regarding attempts in
> this direction?
As Ron Polka demonstrated, various motor/fan characteristics
are well defined and calculations may be made using
non-olympian mathematics so a system may be engineered using
common existing technology and talent to do things a big as
your pocketbook.
The same holds true for other environmental factors you may
want to manipulate.
A huge range of possibilities exist depending on your
capitalization, talent resources, local building and zoning
codes, time constraints, personal goals, etc.
Make environmental choices such as large or small temp
variations, humidity mins/maxs/variations, constant or
intermittent airflow, etc. etc. What environment do you
want? This will define the controls you need.
The main question to many is "what am I willing and/or able
to spend?". The technology, time, talent, money
calculation/compromise plan usually converges thing only
after several plan iterations are made. Previously
unimportant things become important and vice versa.
For most the main thing is money and/or profit.
I recently did a study on solar electricity for aquaponics
pumping purposes. It is a viable and economical idea for an
intermittent pumping system. We are implementing it here as
we use the S&S paradigm which has an intermittent pumping
system.
A continuous duty battery operated fan/pumping/charging
system cannot work unless you have photovoltaic capacity
that can charge batteries AND run the fans simultaneously.
This is a horrendously expensive system. I can operate on
the power grid or company owned generator more profitably
after amortization.
A intermittent fan/pumping system can work with batteries if
the photovoltaics can produce enough battery recharge to
power your fans between fan cycles. Significantly fewer
photovoltaics than the continuously run system.
Two possible scenarios using common technology. Both would
satisfy my needs. The price difference is a factor of around
5. The intermittent system with give me higher profits, less
initial cash outflow and the same quality end product,
plants and fish.
Marc S. Nameth
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Subject: Re: Inflation Fans, In or Out?
From: Ronald Polka
Date: Mon, 25 Oct 1999 16:19:56 -0600
Barry
At 04:08 PM 10/25/1999 +0100, you wrote:
>
>It does raise a couple of points that (along with a few others) I have
>been so far unable to resolve though. My knowledge of large
>gutter-connected GHs is even sketchier than that of smaller single span
>structures so if we could look at the simpler example of a twin-walled
>poly tunnel about the same size as one of the bays you mention (approx.
>30' x 100'), I'd be grateful. :)
>
>This would use a high-pressure/low-volume fan to provide inflation only
>and a low-pressure/high-volume exhaust fan for cooling and introduction
>of fresh air, yes?
>
>But, both inflation and internal air quality are dependent on a fairly
>constant (or regular at least) inflow of outside air. Temperatures on
>the other hand can fluctuate significantly over a wide range of
>timescales. And yet it is air quality and temp control that are linked
>rather than air quality and inflation. This seems to cause a number of
>problems. Among the more pressing of these are:
>
>1) During the day, you must put a lot of energy into your exhaust fans
>in order to remove large amounts of heat energy from the GH - non of
>this heat is recoverable for use during the night and more energy must
>be input to maintain nighttime temps.
For the hobby greenhouse this is frequently solved by the use of thermal
storage such as black 55 gal drums filled with water. This is not done
commercially because floor space occupied by anything but plants translates
into less income. Under most circumstances you will still have to exhaust
hot air during the day but with drums you can temper your night time temp
drops a bit.
>
>2) At intervals during the night (or any colder period), internal air
>quality demands that the exhaust fans be used to pull in clean air -
>this must result not only in unwelcome temp fluctuations but also
>increased heating costs as warm internal air is exhausted direct to the
>atmosphere and no heat exchange occurs with the incoming cold air.
This may happen if you are doing environmental control based on air quality
such as CO2 levels. This is usually done in the large commercial ranges.
And then if CO2 levels need augmentation it is usually done with combustion
of natural gas or propane that also heats the house at the same time rather
than pull in frigid outside air. The interior air is usually not exhausted
unless the temps require it.
>3) Pulling air out of the GH is always going to encourage leakage of
>outside air into the structure. This appears worse than the same
>flowrate of warm air escaping outwards as the incoming cold air
>increases in volume once inside, ie - although the actual rate of
>leakage is the same in either direction, it's worse when cold air moves
>in?
This is rather confusing, I'm not sure what you are saying here. Any air
that is exhausted whether by positive or negative pressure must be replaced
by outside air. These are very much identical scenarios thermodynamically.
Negative pressure ventilation allows cold exterior air to enter at multiple
locations. Positive pressure ventilation allows warm interior air to exit
at multiple locations. If venting is temperature controlled the end result
is nearly the same.
>(I assume that infiltration of cold air is less of a problem in single
>span
>tunnels anyway as there are fewer joins to seal?)
True, the contiguous span of poly houses have few joints that allow
infiltration.
>4) High water use during hot weather. The large volumes of air involved
>in cooling via exhaust fans makes recovery of useful amounts transpired
>and evaporated water difficult at best. If additional evaporative
>coolers are used...
Water use for cooling can be substantial but recovery is impossible from a
practical viewpoint. That technology is NASA stuff, way beyond our capability.
>Most of these problems would seem to be removed or reduced if the air
>from the the envelope _is_ exhausted into the GH, the volume of air
>introduced by the inflation fan increased to that needed to maintain air
>quality and cooling/heating achieved/aided via an active heat sink - the
>exhaust fan being removed or kept for emergencies only. The most obvious
>benefit from doing this is removal (or softening) of the link between
>temps and airflow. Such a structure should also allow some level of heat
>exchange between incoming/outgoing air, a slight positive internal
>pressure to the GH to prevent/reduce ingress of cold air (and other
>things) via imperfect seals and the ability to reuse some of the energy
>you've gone to such trouble to remove during the day etc etc. The
>reduced airflow should also allow easier/better integration with other
>processes such as water recovery etc.
Part of the problem here is mixing together two very different concepts.
One is the removal of excess heat during the day via mass transport of hot
air. The other is minimizing heat losses during the night. When the exhaust
fans are running the status of the inflated envelope is irrelevant. In fact
heat transfer to the outside would be more effective if the envelope were
deflated. This would increase the convective heat loss cofficient to the
environment. When the exhaust fans are off at night you would like to have
the inflation blower operate at as low a flowrate as possible to reduce the
mass flowrate into the envelope. This is acomplished by installing the poly
glazing with the fewest possible areas for leakage, either into or out of
the greenhouse.
Taking advantage of these two different energy flows is quite difficult in
practice. This is due mainly to the quality of the heat that you are
dealing with. The temperature differentials are rather small which in turn
reduces heat transfer efficiencies. Industrial processes that capture waste
heat streams typically work with much higher temps.
>So, although I would certainly take your advice and use standard exhaust
>fans if I was setting up a large commercial system, do you think this
>could be a worthwhile model to aim at for a small commercial or large
>hobby/testbed system where a little experimentation is less costly in
>the event of failure? Although the heat pumps required to shift energy
>between GH and heat sink will require power, it might be less than that
>used by the standard model and other benefits could easily outweigh
>cost?
I would look at heat pump costs very carefully. They are capital intensive.
If you are looking at the standard air coupled heat pumps the coefficient
of performance is not that great. The heat pumps that are set up as earth
coupled or water coupled will provide a much better coefficient of
performance but are more site specific and cost more. If you already have a
heat pump for your house and have excess capacity this may be a cost
effective approach, otherwise it may be questionable. Your local electric
rates will play an important part in this decision. Plus when you do have
to dump heat during the day you will have to dump a lot quickly, hence the
use of large volume fans for exhaust.
>Does this hang together do you think? Are there any major problems you
>(or anyone else) see with this approach or any ways it should be altered
>for improvement? Anyone happen to know of info regarding attempts in
>this direction?
>
Ron Polka
Southwest Technology Development Institute
New Mexico State University
Box 30001, Dept 3SOL
Las Cruces, NM 88003
rpolka@nmsu.edu
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Subject: Re: Technical greenhouse question
From: atkindw@cwjamaica.com (david w atkinson)
Date: Mon, 25 Oct 1999 20:32:17 -0700
Hey Robert,
Do not wait. Post a listing of those titles you spoke about. I am
interested to hear.
David A. (from Jamaica WI)
At 05:25 AM 10/25/1999 PDT, you wrote:
>Ginger
>
>I got the ideas for our solar greenhouse from a number of books I bought
>from Rodale press ( the "Organic Gardening " people ). They have several
>books about solar greenhouse design. ...snip... snip..
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