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April 2003
Ask the Experts
Greenhouse Questions and Answers
Need to update
some your
equipment
or replace
some
structures
Why not
consider leasing.
Easy to set up.
Easy on the
pocket book,
flexible,
reasonable.
/Installers
/Owners
Our structures are extremely easy to erect.
Our structures are extremely strong.
We sampled greenhouse construction without compromise to strength.
Contact us today for the real good reasons of save yourself a ton of installation costs.
E
x p e r t A d v i c e
To be linked our site improvement files. Click on here. See how our new site files shall be formated. Great new look. Lots of great new information.
We are constantly working to improve our products, and we keep your comments and questions in mind.
Please write or contact us at agropon@agroponic.com. We will respond as quickly as possible.
F
A Q s
Here
are some Frequently Asked Questions from our customers.
DIF
in cool climates can quickly turn into DRIP unless you
understand the relationship with temperature and relative
humidity. Agroponic's Greenhouse News Notes.
Click
on here.
Question
: From Michigan. I have a 30' X 96' freestanding
greenhouse with a 250,000 BTU input heater . During the cold
snaps this winter I could only get 53 deg. F indoors. I've
had the plumber change the propane gas lines to a larger
size. I've had to rent portable heaters. Now, I've been told
it could be the heat exchanger. I didn't have this problem
last year ?
The
winter of 2002/2003 in the continental east has been
considerably colder than what is preceived to be the norm.
It just might not be the heater. It could be that you just
don't have enough heat.
click on here.
Question
: What is the general rule of thumb for selecting and
sizing a high pressure fog cooling system.
The
actual amount of fog ( water evaporation ) for greenhouse
cooling takes into many considerations. Considerations
include : project elevation, project location, project
environmental information, greenhouse structure,
ventilation/cooling systems, type of crop and cultural
practices etc. We like to take into account all of these
when sizing up a system for a client, but for those that
like to use the "good old rule of thumb practices"
click
on here.
Question
: How do you calculate the solar loading and the cooling
required.
The
cooling required is primarily based on the solar loading of
your greenhouse. The factors that determine the solar load
is the exposed building areas, the project latitude, outdoor
design conditions, project elevation above sea level etc.
We've have put together some information and hand
calculations for you. For the serious grower these
considerations should be acknowledged. Click
here for further
information.
Question
: What at the tips and recommendations for roof venting
??
The
most common question is what size of vent do I need. This
naturally is an important question but there are several
other factors to consider other than how many sq. feet of
vent you require. Height differentials plays a very very
major role in the performance of your vent system.
Click
here for further
information.
To return to this page please use the return button on your
browser.
Question
: How much heat do I need for our greenhouse structure
?.
Heat
loss for our most common 96' and 144' long gutter connected
structures, are in tabular form. Click
here for review.
To return to this page please use the return button on your
browser.
Question
: Gutter Connected Gutter Vent Systems - Control System
Economics ?
For
those that require entrance level control for you
greenhouse, where control of up to two sets of vents, two
stages of heating , airflow circulation and dehumidification
control. It is hard to go wrong with a Ventmate Plus .
(
For specifications )
For
those that require entrance level control for you
greenhouse, where control of only the vent set is required.
It is hard to go wrong with a simple ventstat.
(
For information.)
Question
: Gutter Connected Gutter Vent Systems - Economics
?
In terms of venting efficiency gutter vents are an extremely
easy and efficient method to vent and cool gutter connected
structures. But many time during the course of the last year
many have asked about the capital cost economics.
Simply put ---- if the capital cost is the major
consideration and if the house length is less than 144 feet,
fan and shutter is the less expensive route to go. End of
story.
But if the house is longer than 144 feet you will find the
economics alone will start favoring the gutter vent
system.
Economics aside and the only consideration is for
ventilation and cooling .... gutter venting is the route to
go on double poly houses.
Question
: Gutter Connected Gutter Vent Systems - Gutter Load
Capacity ?
Gutter vents on the poly clad structures is a very accepted
practice for venting and cooling the structures. However,
there are a couple considerations that are often overlooked.
In locations, depending on construction limitations ( amount
of gutter slope ) and rain fall intensity, the gutter vent
system can propose some challenges in relation to the amount
of rain fall the gutter can handle. If depending on the site
and construction techniques lead s to a very small slope in
the gutter, this severely derates the load carrying capacity
of the gutter system, so without installing interior leaders
into the gutter, water in the gutter can back up into the
structure through the vent system.
For
locations and projects where gutter fall is less than 1 1/2"
per 12 feet, rain intensity over 4" per hour, over 260 foot
length houses, and where interior rainwater leads or
plumbing is not desired, consider this.
With our double poly vent system, instead of allowing the
vent to close on the gutter, simply move the vent system to
one foot off the gutter. Install our aluminum base plate to
act as the slam rail for the vent. This allows you to double
poly from the gutter to the slam rail. The extra cost is
virtually nothing and it magnified the load carrying
capacity of the gutter at the fraction of the cost as
compared to interior overflows and pluming leads.
Single
Poly/ Curtain / Double Poly
We get this question asked of us many times from growers in
warmer regions, where it is common to use single layer poly.
The question is, I'm
planning to use single poly, I'd like to use 10 mil poly and
since we do get cold periods I'm also considering installing
an energy curtain.
This
a bit of a loaded question and leads to controversy.
On our double poly systems we use two layers of 6 mil poly
inflated to approximately 0.3" water column pressure. There
are several primary benefits to this this method.
The first and most obvious is a substantial increase in the
thermal properties of the cladding system. As an example a
single layer of greenhouse poly will have a U value of
approximately 0.95 to 1. Whereas double inflated poly will
have a U value of 0.50 to 0.55. That's right, double poly
will save almost 50% on your heating requirements.
Secondly, and seldom considered by the grower. Since double
poly has a better U value, at the same outside air and
inside air temperature conditions, the double poly has a
higher dew point temperature. This means less condense
dripping and less fogging of the film. Less condense
dripping usually leads to increase crop quality and less
disease. And since double poly is less susceptible to
fogging, ... hm .... more light.
Thirdly when one considers the cost of one layer of 10 mil
poly verses two layer s of 6 mil poly the cost difference is
insignificant. So what's the point.
Fourthly. We ask the growers using single 10 mil poly, why
do you use 10 mil ? Well we find it last longer than 6 mil.
Less prone to tears and shifting. etc. Interesting. But
consider this. When a grower installs a double inflated poly
roofing/cladding system, the fact that it is inflated adds
to the life of the poly. As the poly expands and contracts
as a result of temperature differences the differential is
taken up thought the inflation process. The poly is always
held securely to the structure. As long as the structure is
stiff enough not to move in the wind, the double poly
doesn't not move. We commonly have growers getting 5 to 6
years ( some even longer ) service on their 4 year double
poly systems.
Energy curtain requirements ??? Energy curtain systems are
expensive and can be an costly ongoing maintenance item.
They are only effective when they are closed. We maybe
incorrect but we do see many periods of the day when it is
cold outside and cloudy, and the curtain must be in the open
position. Heat is simply going up through the single layer
of poly. So what's the point ?
It is an interesting discussion, but if you are looking a
capital costs, an inflated double doubly system is far far
less costly than single poly and energy curtain system.
Heres the numbers. Say you have a greenhouse in a location
where outside air temperatures drop to 25 deg. F and you
wish to maintain 65 deg. F inside of the greenhouse.
For every square foot of single poly, you will loose 40
BTU's per sq. foot of exposed area per hour of heat. (
Curtain open )
For
every square foot of double poly, you will loose 20 BTU's
per sq. foot of exposed area per hour of heat.
For every square foot of single poly plus with an energy
curtain system with a R value = 1.25 , you will loose 17
BTU's per sq. foot of exposed area per hour of heat and
that's
only when the curtain is
closed.
Really
not much improvement is it.
And that's only when the curtain is closed ( assuming it
closes completely, and is dry, and is in good order. )
Question
: Is it possible to get higher head room and side wall
heights on the freestanding and cold frame structures.
Yep
there sure is and its quite simple.
For those wishing to use our standard ground sleeve
foundations ( i.e. pounded into grade. Simple get the
optional 1' or 2' extensions that slip onto the ground
sleeve before you install the arches.
For those planning on using concrete piles at all the ground
sleeve location, simply project the sleeves up higher. Our
standard sleeve are 32" long. We would suggest a minimum of
18" penetration into the concrete .... so this can raise the
clearances form 0 to and extra 14" quite easily.
But anytime you wish to raise the height let us know cause
the standard cladding packages provided will end up being
short of material.
Question
: How much fertilizer / mixing rates.
We
get hit with this one everything we do an injector
installation.
Heres a simply easy little trick. It doesn't matter what
type of fertilizer that you are using ( pre formulated or
single source ). Heres a great tip. If you take 10 grams of
any fertilizer and throw it into 100 liters of water PPM =
percentage. Its quite simple. But..... because of the
fertilizers act, phosphorus content is expressed as
phosphoric acid and potassium is expressed as soluble potash
one has to divide the phosphorus ( phosphoric acid ) by
2.23, and the potassium ( soluble potash ) by 1.21 . Other
others PPM = percentage if 10 grams is added to 100
liters.
So lets say a grower is injecting at 1:100 ratio. He wants
150 PPM of Nitrogen and is using 20-20-20 fertilizer.
At 1:100 injection one liter of stock solution is equal to
100 liters of irrigation water.
150 PPM target/20 % Nitrogen = 7.5
Therefor for very liter of stock solution they should add 10
X 7.5 = 75 grams of 20-20-20. This will get the nitrogen
levels up to 150 PPM.
What about phosphorus .... well its 150/2.23 = 67
PPM
and
potassium ..... well its 150/1.21 = 123 PPM
and if furnished with a trace package --- simply multiply
the % of each by the factor 7.5 and you have it.
Please note though ---- generally 20-20-20 will not furnish
any magnesium or calcium. This is generally the rule of most
water soluble fertilizers.
its not that confusing if you think about it for a
while.
Question
: Fertilizer Injection. What the heck does A/B and acid
mean ?
Depending
the the crop, your water conditions and the crop
requirements a lot of growers are using multi head
injection. The primary reason for multi head injection is
basically to provide separation of the various fertilizer
types in the stock solution tanks.
As an example say, your fertilizer feed program calls for
the use of magnesium sulfate and calcium nitrate
supplementation. Well if these two products were mixed up in
high concentration in one stock tank basically you'll end up
with a nice powdery white colored sludge at the bottom of
the stock tanks. What happens is the calcium from the cal
nitrate is attracted to the sulfates from the magnesium
sulfates ..... so you end up with quite expensive insoluble
calcium sulfate in the bottom of the tanks. The same holds
true with calcium and phosphate. You end up creating mono
calcium phosphate in the bottom of the tank. So,hence the
expression A/B ( sulfates / phosphates ) in one tank,
calcium in the other.
Acid injection ..... well depending on your fertilizer and
water chemistry ( i.e. ph ) of water, if the pH of the final
fertilized water is above 6.5 or higher, you amy find
deficiencies in trace ( micro nutrients showing up ). That
doesn't mean that they are not there, but because the pH of
the fertilized water is on the high side they become
unusable for the plant. The solution is to use a bit of acid
to get the pH down ( typical range is 5.5 to 6.2 ) and
magically a lot of your plant deficiencies ( trace/micro )
will disappear.
So A/B
and acid means a three head system. One for phosphates /
nitrates / potassium / sulfates, another one for the calcium
/ potassium / nitrates and the last head for acid injection.
THREE HEAD SYSTEMS. On fertilizer feed programs we try to
encourage the growers to mix up their A and B tanks so that
the density of the fertilizer solutions are the same at the
same injection rate. The trace elements can be placed in
either tanks.
Question:
Price
Lists. Why do you quote structure only and then the cladding
price ?
There is very good reason for this. A lot of our structures
are sold to many other reasons other than for greenhouse
use. As an example many of our 36 foot and 40 foot wide
freestanding structures have been used as airplane hangers.
In these applications generally they simply order the
structure ( some with 2 foot ground sleeve extensions ) and
one gable end framing package. The owners of these packages
simply clad with metal siding or plywood and single. We have
been told they make excellent hangers are very affordable
prices. Another example but more related to the greenhouse
operations is the use of our 30 foot freestanding houses.
Purchased as a hard structure ( structure only ) and again
clad them with metal cladding. Many growers them will spray
the inside with an 1" of spray insulation with fire stop
lagging and they end up with a very useable, workable,
inexpensive header / work area. Again if additional head
room is required they simply order 1' or 2' extensions onto
the ground sleeves. The same holds true for the cold frame
structures, it simply amazes us how many we have sold a hard
clad structures without roof cladding, but with with gable
ends. They make ideal lawn and storage sheds.
Other applications include:
Machinery and car storage.
Light industrial process and storage facilities.
Livestock shelters.
This is
the reason why we quote the structure price ( structure as
in all structural metal ) and the cladding price.
Question: What
is a turnkey package?
Answer: A turnkey package is one that consists of the
greenhouse structure, any options that the structure may
require, the heating system and related equipment, the
cooling system and related equipment, fertilizer injection
and related irrigation products and the environmental
controls. On must must remember, the greenhouse is only the
envelope that contains the environment, with the exception
of gathering solar light. It is the equipment and controls
that create and maintain the environment. This is why we
prefer the turn key approach. The primary benefit for the
grower/client that is seeking a greenhouse package is the
savings, the convenience and the confidence from a turnkey
supply or construction proposal. During the last past three
years we have found that this trend is increasing and we
strongly agree with this trend.
Question:
What is carbon dioxide generation and what does it do?
Answer: One must remember that plant growth requires, heat,
light, water, nutrients, and carbon dioxide to grow. Any
shortage in any item can result in the limitation of growth.
In the winter time time in particular when the greenhouse is
sealed out quite tightly from the outside, carbon dioxide
levels can fall to very low levels. This provides the
limitation in growth and quality. Therefore, most growers
operating during this time will include carbon dioxide
generation into their environmental systems. Carbon dioxide
generators can burn natural gas or propane to create carbon
dioxide. Some growers that do not have access to natural gas
or propane use liquid carbon dioxide to add carbon dioxide
into the environment.
Question:
Why use high efficiency heating, it costs more to purchase
the equipment?
Answer: In Western Canada, for growers operating during the
winter months, the cost of heating is a very large portion
of their operating expenses. Generally, depending on
situation high efficiency heating equipment reduces heating
expenses 10 to 20%. Also, energy costs are only going to
increase in the future, so, really isn't it wise to consider
high efficiency heating. High efficiency heating is slightly
more expensive to purchase up front. But the increased cost
is rapidly paid back in terms of fuel savings ( For Alberta
about 1 1/4 years ) and installation. As an example we sell
our high efficiency gas fired unit heaters about $175.00
more than the conventional gravity ( standard efficiency )
heaters. When it comes time to install the conventional
gravity heater, a lot of the money you thought that you were
savings will be rapidly spent on the increased price in
venting materials. An an example a 400,000 BTU high
efficiency power vented unit heater has a flue size of only
6", whereas, a conventional gravity vent heater, has a flue
size of 12". If you price out the difference in vent pipes
and vent fittings you will see that the bulk of the $175.00
that you believed you saved has already disappeared even
before you connected the gas pipe and turned the heater on.
So when you consider the cost to install and the operational
cost savings, the payback is almost immediate.
Question: We have been pricing out fixed overhead sprays and overhead watering booms. The fixed spray system seems cheaper ? Your comments.
Answer:
Click
Here
Question: We are considering a hot water boiler plant (5,000,000 BTU's) for our greenhouse operation. Our consultant and contractor are providing a system based on a 20 deg. F delta T. What does this mean ?
Answer:
Click
Here
Have a questions for us ? You can contact us by mail, phone,
fax or e mail at:
908 Ranchview Cres. NW.
Calgary, Alberta, Canada, T3G 1P9
Ph (403) 241-8234, fax(403)241-8238, email: agropon@agroponic.com
This page shall be updated quarterly with commonly asked questions from the past three months.
HIGH PRESSURE FOG COOLING
ENVIRONMENTAL CONTROLS
GREENHOUSE STRUCTURES
Cold Frames
Freestanding
Gutter Connects
FERTILIZER INJECTION SYSTEMS
HEATING / COOLING PRODUCTS
CHEMILIZER
fertilizer
Injection
Reznor Heating Products
Gas Fired Unit
Heaters