Frequently Asked Questions

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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 perceived to be the norm. It just might not be the heater. It could be that you just don’t have enough heat.

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.

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.

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.

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 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.

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.

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