Off grid Greenhouse Inflation Fan Application

[mooselick7]

I am constructing a 22'x48' greenhouse that uses a 120V 0.42A inflation fan to force air between the layers of plastic film.  Fan runs constantly.  There is grid power within 100 ft of it but I want to run it offgrid.

There is about 4.5 avg hr of solar per day but down to 3 hr of solar per day in the winter.  Performing the calculations with 3 days of autonomy and pricing it out:

3 each batteries 12V 200Ah  $1065

1 each 85W solar panel      $ 475

1 ea Charge Controller      $  30

1 ea Inverter 153w surge    $ 240

Total                       $1810

What am I missing here?  That cost is high just to run a silly little fan.  

Any suggestions?  

I have considered wind which is intermittent here but noise in the neighborhood and cost will be an issue.

Thanks for any help!

[TomW]

moose;

Thats why grid is always cheaper if it is available.

Welcome to the RE reality.

And, if you are extremely lucky and careful the batteries need to be replaced after from 5 to 10 years. No guarantee your site can keep the system running, either.

Solar is great but only when the sun shines.

Tom

[hydrosun]

Homepower magazine did an article a few years ago about a greenhouse that used a what looked like a 20 watt solar panel to keep a battery charged to run a 12 volt inflation fan. I've experienced that small 12 volt fans of the same rating are always much more efficient.  I don't know what kind of 12 volt fan is needed for inflating a greenhouse but there must be something out there. The higher efficiency would really cut down on the cost.

Chris

[TomW]

moose;

For simply running a fan you might look into DC fans and eliminate the inverter, its cost and efficiency tax. One of Ghurds [long time member] controllers could easily handle the control aspect.

Your .42 anmp load at 120 volts will be about 50 watts plus efficiency losses 24/7 and no way a single 85 watt panel will stay ahead of that to start.

Just after thinking it over some.

Good luck sorting it out.

Tom

[ghurd]

I see a few things to cut the cost and improve the performance.

First, the inefficient AC fan has to go.  With it goes the inverter inefficiencies and cost.

(Inverter: Yikes!  A suitable 153W surge should be about $30)

Next is the batteries.

Should be able to get 660AH (6 x 220AH 6V) for about $450~500.

And they tend to last a LOT longer than 12V units (AKA: boat batteries)

Knocked off about $800 so far.

The DC fan will use a lot less power than an inverter and AC fan.  The AC fan is most probably an oversized/overpowered off-the-shelf fan.

Probably be fine to reduce the battery bank down to 440AH (2 pairs of 6V).

Knocks off another $150, for a total reduction of $950.

DC fan maybe costs $10 to $50.  I will ignore it.

Ready for the bad news?

I figure that's a bit skimpy in the solar area.

I would rethink it with the DC fan after you know the power requirements of a matching characteristic DC fan (flow and pressure, but mostly pressure), and seriously consider more solar power.

There was also an error in the original calculations.

I have it roughly figured as needing at least 500W of solar to keep up with the AC fan.

Guessing you did the 12V DC amps required the same as the 120V AC amps.

G-

[mooselick7]

Thanks for the tip! - I will do a search on the Homepower dvd's.

[mooselick7]

Thanks for the good news:  I will look into DC motor to switch out with the AC and the batteries.  

You are right.  Im way off on the array size should be 10 times.  Ouch that makes my wallet hurt.

BTW in thinking about this, I need to look at the inefficiency of the system in this kit.  It is going to depend on how airtight this big plastic air mattress is but one would think constant inflation may not be required.  I will probably set it up as is with an extension cord and determine actual amps used with a watt-meter and go from there.

Thanks for all the help!

[dnix71]

What happens if the fan quits? Does the greenhouse collapse? If so, then some kind of mechanical support makes more sense first. What will you lose (plants, money) if it fails?

A solar powered exhaust fan wouldn't cost much, but those are designed for ventilation, not inflation.

I have netting and cages around my veggies and citrus to keep pests away.

[ghurd]

Testing the AC fan really won't tell anything important.

Be better off...

Getting a few 12V fans similar to the size it came with.  I expect it came with a muffin fan, so 12V should be cheap and easy to get.

I would try at least a couple with "lots" of blades, and different amp ratings.  I figure the "lots" of blades type tend to make more pressure than flow.

Connect it to the mattress' fan port, with a car battery, and measure the 12V amps.

Try a few different fans.  Might find a 0.120A fan that is plenty.

Sure would cut down on the cost of everything!

Do you have the air mattress stuff already?

It may help to tell the exact size and shape, number of blades, and a couple pics of the fan.  A pick showing the end of the fan blades may help a little too.

I may shoot you an email after I see the fan info.

G-

[mooselick7]

I will take a couple of pics of the fan tonight and send.  It is a small squirrel cage fan.  Besides a shutter mechanism, it looks like an automobile heater fan.  

I was going to test it first because of the above unknowns and other unknowns such as changes in heat/cold which I believe will draw power differently.  The AC fan is already bought so Im not out anything.  

Thanks, again.

[mooselick7]

The fan just maintains a layer of air between the two sheets of plastic.  There is a steel structure holding it all up. If it isnt inflated then the film wears out faster and there is less insulation value.  So Im told.  But raises a good point.

[zeusmorg]

 Let's see a 22' x 48' structure,, wooden frame, covered in plastic, door,, hinges, rudimentary foundation.

 I'm betting that could be built for less than you would have to spend on all this for solar panels!

 Somehow that inflatable greenhouse doesn't sound like a good idea.

[scottsAI]

Mooselick7,

Yellowtail In-Line Blower 4" Fan 12v 5.5a max.

http://www.defender.com/product.jsp?path=-1|6880|46775|732133&id=570334

Specifications: http://www.pumpagents.com/pdf/ShurfloPumps/277-4100.pdf

Looks like it can do the job, even slow it down a bit?

Found it for $21 looking around, shows up on eBay (Shurflo Blower).

The Math:

Lets say the fan uses 5a to run, thus need 24 * 5a = 120aHr/day

Energy needed per day: 12v * 120ahr = 1440 wattHr/day

If the sun is shinning 3 hours you need 1440 wHr/3hr = 480 watt solar panel.

Except the battery is only 90% efficient so the panel must be bigger.

The voltage of the panel is 17v at peak power, where the battery is 13v. The watts the battery sees is less than the watts of the panels, 25% larger panels are required. MPPT controller can help $, near cost of replacement panels.

For back up need four 12v 110ah batteries to meet your three days, discharging to 25% which is on the low side, if this happens, the battery must be recharged ASAP. (not by solar panels). Batteries are made to be used yet long term discharging will kill them, as will over charging!

If the blower can run slower speed and meet your needs then the current will be lower, plug the number in and see.

Have fun,

Scott.

[frackers]

I'd agree with that - I built a wooden one that uses just 4x1 sawn lumber and 3" nails.

Here are a few pictures of it (and a shade house) - the design used to be on the 'net but the website disappeared about 4 years ago

   http://gilks.ath.cx/gallery/v/quonset/

I've got a write-up about it somewhere, I'll see if I can dig it out...

I'll be making 2 more this winter that I can pick up and move about with the tractor to keep the wind off the veggies so if anyone shows some interest I can document it as I go...

[divemaster1963]

hey I would like to get the info on the qounset hut greenhouse. I have been looking at making one but was not sure where to start. please let me know when you get the info up.

divemaster1963

[zeusmorg]

 Ahh, I originally thought this was an air supported structure. I'm wondering about the so called insulation value.

 Insulation is achieved by trapped pockets of dead air.

Air being re-circulated through the plastic wouldn't do this as well, as far as I know.

 I can see a cooling effect, and In greenhouses, there is usually fans or openable panels to keep the temperatures down in the summer.

 but i can't see an advantage of having moving air between two sheets of plastic holding heat in, I'd think you'd be better off with two sheets separated by the frames, and taut.

 Of course, this isn't my project, and you already have the greenhouse, and you just want to know the best way to use the fan.

 I'm agreeing with most that using an inverter, vs using a DC fan that is capable of the same CFM of air movement would be wasteful.

 Every step in conversion of energy looses something. Your battery bank will be the biggest loss, however the sun doesn't shine all the time, so you do need storage!

 Also is the total cost of all the equipment over using grid worth it? It looks like to me,, there would be a LONG payback period.

 Maybe you would be better off just using grid electricity, and putting your money into something that would give you a better payoff. (such as solar hot water)

 All I'm seeing here is the bragging rights to saying "See my GREEN Greenhouse?"

[hydrosun]

There are at least two reasons to use a blower. To keep the two layers of plastic apart for the insulation value, and to keep the plastic taunt so it doesn't degrade by abrasion in the wind.

There is a group in the Midwest trying to stuff layers of bubble wrap (solar pool heater material either between the two layer to accomplish the same as a blower with even more insulating value. Some other people are just putting the solar pool heater material over one layer of greenhouse plastic. I bought some of the material and will try it this winter as a layer over some of my cold frames. I came across the idea and connections on builditsolar.com  The material is UV resistant and 12 guage, so it should last longer than greenhouse plastic. Not sure about the cost for a large greenhouse but it would eliminate the cost for powering a blower fan.

Chris

[wooferhound]

Here is a write-up that describes how much solar it would take to power a desk lamp.

http://www.fieldlines.com/story/2008/2/7/171927/1689

This stuff really adds up and the Grid Power will almost always be cheaper. The reasons for using Renewable Energy is not for saving money, the reasons are for living remotely without the grid, to be earth friendly, or as a hobby.

[Madscientist267]

A point to be made here, is that some are using "fan" and "blower" interchangeably. They are not the same thing, and one is much better suited for certain things than others.

While they both will move air, one is designed with creating a positive (or negative) pressure, the other is designed to simply move air.

For inflation, a blower is much better suited, and is much more efficient, as when the blower can no longer move air, the power required to drive the rotor is somewhat reduced.

A fan would spin at the same rate until someone called bessie on her cell phone, not get anywhere near the work done, and waste plenty of energy in the process. It's not very likely that the first cow would even show up.

[mooselick7]

I was ignoring zeusmorg's and other's flying monkeys as non-constructive (ie sarcastic/cynical which seems to be a warning largely ignored) and, not to mention, off-topic.  Before someone takes this advice and runs with it, you need to consider a few things...

You can build a high tunnel using materials from Home Depot and Northern Greenhouse Supply on the cheap for about $500.  I helped build one in Casper, WY a month ago using this as a guide ( http://aces.nmsu.edu/pubs/_circulars/Cr-606.pdf )  You can lower that cost considerably by using scrap materials, lower grade greenhouse plastic and some ingenuity.

These greenhouses built on the cheap or others suggested do not have capacity to handle the snow loads or wind loads where I live. Also, these cheap high tunnels dont have the necessary ventilation or insulation to allow full year round use.  

The greenhouse I am building with the inflation fan etc is commercial grade.  It has roll up sides and built to handle 30" of wet snow load and 60 to 70 mph winds.  When you roll up the sides on a greenhouse of this sort it becomes a 22' wide and 48' long airplane wing with considerable aerodynamic lift.

We intend to sell greens, vegetables and cut flowers along with supplementing our food budget. Also, we are working to reduce my households's total net energy use as estimates consider that our nation's food supply accounts for 15% of our nation's total energy use.  (I think this is underestimated.)

As far as exploring solar energy to run the inflation fan...  I appreciate everyone's constructive comments but let me save some of you some time.  I know it is going to be more expensive to install solar vs running off the grid that is not my reasoning in looking at it.  100 times more expensive?  Aint gunna happen.  10 times more expensive?  Getting closer.  This is also a learning process for me.  

My thanks especially to ghurd for leading by example with the sound advice and consideration...

Now back to topic...

[mooselick7]

Ghurd:

Attached are pics of the fan in question.  If you know of a DC alternative, that would be great.

From another source, I am told there is a one way air valve that can be installed with a switch so that the silly thing isnt running all the time.  I need to dredge that up out of the net.  

Thanks for your help.  

http://www.otherpower.com/images/scimages/13166/P6110001.JPG

http://www.otherpower.com/images/scimages/13166/P6110002.JPG

http://www.otherpower.com/images/scimages/13166/P6110003.JPG

[mooselick7]

I have heard of this but I dont think it will keep the everything taut and while the insulation would be there to some extent, I dont think it will keep the plastic taunt.  

BTW the cost of the plastic is $787.  A users of greenhouses without the inflation fan replace plastic in 2 to 5 years whereas those that have the inflation fan replace plastic past 15 years.   Replacing the plastic takes considerable time as well.  

[ghurd]

It looks like high volume and low pressure to me.

The one way air valve means it does not need volume, just some pressure.

If the plastic mattress-thing is anything like I picture it in my mind, it does not need much pressure at all.

Leading me to believe a DC muffin fan would work just fine.

And I believe this is a case where solar would be worth the initial cost.

Mental math this morning (pre-coffee) looked like about $70 / year for the grid fan.

Solar with junk ("boat batteries") payback was about 8 years and soon to need the 3rd set of batteries.

With a pair of Sam's Club golf cart batteries was 9 years But that had new batteries figured before then that would last a lot longer than the 9 year mark, meaning golf cart batteries worked out to cheaper.

That sounds BAD?

It only included the cost of RE related items.

It did not include the cost of running the grid to the green house.

If the cost of running the grid to the green house (I used $200 total cost) is deducted from the RE related costs, then even was at 4 years 9 months.  

After than time you are coming out ahead.

If you have to pay someone to do the AC grid wiring, or the run is long, or it requires an excavator or renting a ditch-witch, then solar may work out cheaper the first time the fan is turned on.

The one way air valve has me wondering if the initial cost could be reduced even more.

To know what is what, need to try several DC muffin fans and be sure they are up to the task.

Before spending money.

G-

[Bruce S]

mooselick7:

 While hopefully being on topic, I looked very closely at the type of blower and its motor. Static air warmed by the sun, will insulate.

This design of motor/blower setup looks to be used to keep inflated rather than air movement.

Though I could not deteremine from the mfg's website the CFM needed, I can say that it very closely matches the newer imported car blower motors, as well as the AUX squirrel cage motors found on older A/C systems.

Straight 12Vdc and high volume, also built to be controlled.

If you have the time or possibly spare "stuff" I would give the aftermarket a look see for the 12V blower motors.

The one I used to replace the rear motor in 1990 Suburban's aux cooling system has the very same look, just not mounting bracket they use to make a very solid seal.

Best of luck!!

Bruce S

A little off topic, these inflatable types must have something going for them, the Red-Cross, and Mil's use them too.

[mooselick7]

Thanks, Bruce!  I will look into this idea - I have the equipment to build an adaptor if necessary.  

[mooselick7]

Sounds plumb reasonable - I will investigate this as well.  

[BigBreaker]

Why not just support the greenhouse film with static supports rather than the inflation scheme?  Seems like hoops or tensioned wires would make more sense and would cost less than the RE powered fan set up.

[GaryGary]

Hi,

Don't know a lot about this, but my understanding is that the blower on this type of GH is just there to pressurize the area between the two sheets of poly.  I would guess that the required flow rate is whatever is needed to offset the leakage.  So, maybe the first step is to take great care in sealing all the leaks?  If you get them sealed really well, maybe a much smaller blower would do it -- a blower with enough static pressure, but not a lot of flow.

I have seen one of these houses in a pretty stiff wind, and the inflation really does keep the poly tight, and it does not flap around.

A fan with a half an inch inch of water static pressure rating would give you about 2 lbs per sqft pressure on the poly -- seems like that might be enough?

The PC style axial flow fans are designed to move a lot of volume at a low pressure drop -- I think the squirrel cage type that are designed to produce more pressure drop would be a better way to go.

For example, this one produces some flow at 0.5 inch of water pressure, and only draws 0.23 amp at 115VAC:

http://www.grainger.com/Grainger/items/1TDN7

This is a 12VDC one that is (maybe) at bit big:

http://www.grainger.com/Grainger/items/2C646

Seems like something along this line with half the flow and half the current draw might be in the ball park?

Even more pressure, but still to heavy current draw:

http://www.grainger.com/Grainger/items/4C814

This type produces a lot of pressure at only about 25 watts:

http://www.grainger.com/Grainger/items/4YM43

Gary

[GaryGary]

Just one more thought.

If you could arrange things so the the inlet that supplies air to the fan ended in a scoop that could be faced into the wind (perhaps using a tail vane to rotate it toward the wind), then the ram air pressure of the wind would help pressurize the fan inlet during times of heavy wind, which is when you actually will need the higher inflation pressure.

The pressure head of a 12 mph wind is about 0.1 inches of water, but its about 4 times that for a 24 mph wind -- so it gets better with more wind, just as you would like.

Just not sure it would be worth the mechanical complexity to build this kind of inlet?

But, it would be easy if your heavy winds always come from the same direction.

Gary

[ghurd]

Guy on ebay has a bunch of Sunon 12V muffin fans.

Rated 0.76A, 84.1 CFM, static pressure 0.74" water (3.85 pounds per sq foot).

Free shipping, $4.98.

Seems worth a shot!

I figured the plastic was factory made and heat sealed.

G-

[GaryGary]

Yes -- that looks like it might work.  Did not realize that this kind of fan was capable of that much pressure.  Seems like it might be a good choice for a small solar air collector as well -- I'm going to pick up one

Only 9 watts!

Sunon has a nice pdf catalog:

http://www.sunon.com.tw/products/pdf/maglev.pdf

Gary

[Airstream]

Muffin fans hate 'stalled air' and go noisy when it happens. When the eight or ten stub fan blades get trapped in their own wake the fan motor speeds way up and amplifies the noise, the over speed also and makes it nearly impossible for airflow to catch up until the fan is shut off / restarted.

If you do use one, having the fan pushing air into a large non-restrictive plenum/box that distributes air into the confined inter-layer film gap might work best. Even at that the pneumatics of wild outdoor wind reverse the flow they will go nutso like a summertime house fan put in the wrong window.

I suspect a deep three blade shape more like a 'screw' propeller would work better pressurizing a container, but I've only seen them at a surplus store near here and not tried one intentionally trying to raise static air pressure.

I did use a metal fire alarm panel box to house HID lamp ballasts in an old carriage house that had sparrows nesting in it, I used remote ballasts to reduce fire risk and wanted to cool the ballast box - I had a 3" round intake into the 16x32x4" panel box tried exhausting it into a 1-1/2" deep airspace behind the panel box and only got stalled air and fan over-speed fan, in the end I had to put a lamp dimmer on the AC fan to get a tiny cooling airflow w/o noise.

[Billystack]

As I'm planning a some similar projects for my trip to Burning Man this year, I'd thought I'd add some links that may be of help:

12v .35a 94 cfm computer fans I'm using for cooling of the hexayurt:

http://www.surpluscenter.com/item.asp?UID=2009061318263798&item=16-1312&catname=electric  Suprising amount of air from such a small fan.

Here's a shade structure I've built that is very similar to the hoop house (my last name is Hooper, so if nobody cares, I'm going to steal that name  

http://www.chromatest.net/Lovemonkey/  It holds up to the wind quite well.

Doesn't really apply to this converstation, but its cool, so I though you guys would enjoy the hexayurt.  Made from 12 4x8 panels of DOW Tuff-R insulation taped together with 6" bi-filament tape:

http://www.appropedia.org/Hexayurt_Playa

I've also built up some 12v LED lights all of which will run off a 50 or 65 watt panel and 10a charge controller into a 110 ah marine battery.

good luck with your project!