All year greenhouse
 

I have been given an evacuated tube solar water heating system and am thinking of how to incorporate it into a climitized greenhouse system.

I'm planning to buy a 13M2 greenhouse so would like to try to get the whole thing built at the same time.

My idea is to use the solar water heater to collect heat during the day and to have it connected to an underfloor heaing system in the greenhouse to maintain the soil temperature overnight and during the morning. The heating panels would be covered with soil in raised beds.

I'm also thinking of using a temperature/humidity sensor coupled to a processor based control system and (if I can work out how to construct them) motorised roof windows. The controller will control the heating/watering/windows to maintain an optimum growing condition.

Has anyone done anything similar to this? Any pointers/suggestions; soil depth/optimum temperature/humidity?

Nigel

Sounds like it will should work depending how much solar collector area you have and your local climate. At the very least it will increase the growing season.

I'd also suggest at least insulating around the perimeter of the green house, and if you can insulate the bottom of it and then dump soil into the insulated box you've made.

It would be intersting to know how much of a storage tank you would require in order to heat the greenhouse in the coldest winter days.

My friend has a large greenhouse business and grows only part of the year. He said that he needs to always maintain about 70F in order for his plants to grow healthy. He grows strawberries, squash, tomatoes and some other vegtables. He said his major expense is heating.

After I explained about the ground source heat, his interest became apparent and wants to know more. But the idea of using evacuated tube solar heating and storage tanks may be less expensive?

Geo

Our neighbors have two greenhouses that are of fair size (not gigantic) on their 2 acre lot. They're made of two layers of plastic and they blow air between them creating a baloon effect and an air barrier for some insulation value. With this setup and some foam insulation around the perimeter they're able to grow year round. In winter they grow lettuce and spinach which can handle mildly freezing temperatures down to the high teens (degrees F).

Spinach is cold hardy to around 0F. The cold hardiness of lettuce varies greatly depending on the cultivar, but the cold hardier lettuce cultivars can take down to 5F.

I've even heard that adding digesting compost in this type of box surrounding the base, would additionally boost internal heat of the greenhouse.

getting greens to survive the winter isn't overly difficult. Getting them to grow through the winter can be hard. They need to warm up during the day to grow. A greenhouse can help with this.

For kicks last winter I planted lettuce, carrots and beats in a front garden where I knew they would be sheltered from the worst of the weather and should survive. The did survive but didn't grow a bit from mid october until late march. I think with a small poly tunnel they'd have kept growing at least another month probably right through.

Low Cost DIY greenhouse design
 

Low Cost DIY greenhouse design of similar construction:
http://userpages.bright.net/%7Efwo/g.../southwest.jpg
greenhouse

I was thinking of the same thing myself. I was going to DIY the collector and use an old 75 gallon water heater for storage and lay PEX under a 2' raised bed garden. Collector would be drain-back. I didn't think about insulating the sides of the bed though - good idea. Does the composting need a minimum temp to start breaking down? Anyway you might be able to get some 12v pumps to circulate though the collector and the radiant tubing and use a panel to charge the battery. You could EVEN get an 80 gallon electric water heater and just wire in the bottom element as a backup.

Besides low temps, the other main factor causing limited plant growth in the winter is the short day length. This is why a lot of overwintered veggies that just sit there through Dec and Jan, then start growing from Feb on, despite Feb temps that are just as low as Jan temps. The higher your latitude, the more this is a factor in your plant's growth. At my latitude (34 N), most veggies remain in the doldrums from late Nov through most of Jan, even under cover. The main exceptions to this being lettuce cultivars developed in Europe for winter cropping and many overwintered Chinese crops. Compared with European spinach cultivars, Chinese spinach cultivars are less cold hardy but will keep growing and producing through the shortest winter days where European spinach just sits there. But as the days start to lengthen in Jan-Feb, the Chinese spinach will bolt while the Europeans will start growing nicely before bolting in Apr.

I don't see why your ideas would not work. It will take some experimenting to get it right.
I think 1/2" PEX may fit the bill if you bury it in raised beds as long as you are out of the root and tool zones. There are plenty of hydronic valves and thermostats on the market.

You would have a large mass to heat, so I would think you need to start heating early. Also you'd need to store heated water for the days with no sun or make provisions for alternative heat sources. Lots of variables. Check Gary's site out for the tools and more ideas. BuildItSolar: Solar energy projects for Do It Yourselfers to save money and reduce pollution


I know of a few greenhouses in Kansas that have a one foot wide trench in the center of their greenhouses. I've been told they are 10 to 12 feet deep. They are concrete lined and water filled. That provides a tempering effect year round but limit growing in the winter.

Saw an article in Mother Earth News (i think) where someone made a greenhouse out of hog panels...very strong and able to withstand snow build-up. I have an old 75 gallon gas water heater and was thinking of DIY on the panel with PEX for the heat exchanger. It would be a drainback system. I also have some small circulator pumps, one for the panel (minimal head pressure) and one for the loop. I suppose I could run just one for the whole thing-though the loop then the panel-but I'm not sure the pumps I have could handle the friction though the loop then the panel w/o burning up.

If I REALLY wanted to do it right, I would also have a PV panel with a small wind turbine backup to power a bank of batteries, which would in turn power some grow lights set up with a photocell and a timer. The timer to turn on the lights at 6AM and off at 8PM and a photocell to turn them off when its daylight enough. (hmmm maybe even enough power to run some 12v pumps).

I'm not sure what temp the ground needs to be to encourage growth though...gotta look into that.

Excellent idea of using solar water heater. I really want to have a greenhouse someday too and I will since I love gardening. My only suggestion is to make sure you study and have knowledge of the temperature you need to maintain in order to grow different veggies.. good luck :)

The greenhouse is almost finished
 

I have now almost finished my all year greenhouse. The greenhouse is 13 square metres in size and (as we suffer from very strong winds where I live) it is fixed to a shed I had built. The shed also houses all the control system for the greenhouse.

I built a control system using a PIC16F877A development board I bought on ebay, along with a few extra bits - display, keyboard etc. and I'm using DS18B20 1-wire temperature sensors for both the greenhouse and solar hot water control system.

The controller has settings for lighting (to control growth lights) these have settings for morning and evening times and a photo resistor to detect the light level and so turn on/off the lights as necessary.

There are 2 watering programmes that turn on an electronic valve for watering - there are 8 watering nozzels (4 each side).

There is a day time and night time heating program, the heating controls the underfloor circulating pump. There is also the ability to cool (not yet implemented though).

There is a control program for the solar heating that circulates water through the water panel and storage tank. Temperatures of both are monitored by 1-wire thermometers.

In the attached photos you can see the inside with the growing lights and watering nozzels, the control system and the individual programs and the whole control system. Also there are photos of the underfloor heating.

I have a few things growing in there now as you can see. I had a slight accident with over-temperature which is why the tips of the leaves of the lettuices are a bit brown.

Acuario

Wow, that is quite the setup! I'd love to hear more about how you went about making/insulating and designing the system.

Acuario,
Very nice setup. How are you cooling down the greenhouse? Are you using the roof vents, or are you going to install a fan? Are you going to keep track of how much this costs to operate?

Again, great job! Thanks for the inspiration.

Geo

Cooling has still to be solved. I have the control circuit pretty much built and the controller can activate the necessary relay. I'm pretty sure I'm going to use 12V computer fans - I have a box of them I bought years ago. The problem I have with using the windows is the wind we have where I live. Should it suddenly get windy it would rip the windows off, this is why it's built behind a shed; the shed is in the path of the prevailing winds.

The cost to operate is zero :-). You can't see them in the photos but there are solar panels on the roof that are connected to the batteries. These supply enough power to run everything. They were salvaged from a house I was working on when the owners had a grid supply connected.

Acuario

Can you tell us a bit more about the constructino of the green house? It looks like you used aluminum structural members and I'm guessing twin wall polycarbonate sheeting for some insulation value. Is the ground insulated at all? How is the tubing run in the floor? Do you have any pictures of the progress of the construction?

I noticed the LED panels you have in the greenhouse, are they 200 watt panels ? have you grown with them before , i assume they will be lowered over the plants or are they strictly supplemental.

The greenhouse itself was bought as a kit (1000+ pieces, like a giant Meccano set!) so I can't claim any fame for that. It is an aluminium frame with 4mm polycarbonate windows so there is some insulation.

The base is only really insulated in a few spots as a result of the polystyrene mounting panels for the underfloor heating (the black panels in the photo). Apart from this there is no additional insulation. As the temperature here rarely drops to freezing it shouldn't need too much insulation as the sand and gravel floor shoud store some heat and the heated floor should (hopefully) do the rest.

The construction itself took about a day and a half. The instructions were in picture form with writing in German so a bit of guess work a couple of times!

The shed itself is concrete block - as I'm not a builder I employed someone to build it for me so it would have straight walls and not be dangerous....

The lamps are LED and are 15W each panel, total 60W. With the small solar system I have there isn't capacity for much more. They are fixed to the roof so we'll see... We are now harvesting food from there and have more vegetables on the way.

Acuario

I have heard that the amount of sunlight will also affect plant growth. Maybe get a PV panel to charge batteries to run some grow lights and have them on a timer so they come on at maybe 6AM and off at 8PM? Tie them into a photo-cell to turn off when the sun is up. BTW congrats on the free system. Evacuated tube panels are about the most expensive available!

?????
If you read my posting then you'll see that I already have pv cells and grow lights, plus the lighting is much more sophisticated than just a timer - it uses a photocell connected to an ADC plus has a time control for forced daylight hours all built into the controller. It also turns on the lights should it become dark as a result of a storm.
Acuario

What do you plan to grow in the greenhouse over winter?

It's a big experiment but we already have (and have been eating):

Lettuice
Salad leaves
Italian peppers
Raddish shoots

We also have growing (but not yet ready for harvest)

Runner beans
Cucumbers
Spaghetti Squash
Tomatoes
Rocket
Chives

It also will let us get an early start in the spring. This year I grew a 71Kg pumpkin. I'm hoping that if I start one off next year I'll break this record.

I'll take a photo soon so you can see how it's doing.

I did buy 4 x 70W second hand solar panels last week for 100 euros so my power system is a bit more capable for when the days get shorter.

Thermal lost estimate
 

Just for fun, I compute the standard thermal lost for a greenhouse of 13M2 (see attach drawing)... this is an example only but with enough detail so you might adjust it for your own configuration....

This is the formulas we use to estimate the need in heating for commercial greenhouses.

The formula is pretty accurate if:
a) the configuration of your greenhouse are the same has the one draw.
b) Toledo Spain -- Minimum temperature is 2C
c) Tomato lower recommended temperature 13C -- 55F
d) Pepper lower recommended temperature 15.5C -- 60F

This formula does not consider the "Insulation" of the shed "end Wall". This one is likely much more resistant to heat transfer then the 4mm polycarbonate panel. So, the real lost should be lower.

Step #1 – Compute areas, volume and length of perimeter. (all from the drawing)

Sidewall = 2( 1.5m x 5m) = 15 m2
End area = ( 2 x 1.5m x 2.6m) + (0.5m X 2.6m) = 9.1 m2
Roof area = 2(1.39m x 5m) = 13.9 m2
Curtain W. = 3 m2 ---- (This is your concrete block wall)
Volume = (1.5m x 2.6m x 5m ) + ½(2.6m x .5m x 5m) = 22.75 m3
Perimeter = 2 x 2.6m + 2 x 5m = 15.2m

Step #2 – List of U-Values

Polycarbonate 4mm: U = 3.9 W/(m2˚C)
Insulated perimeter: U = 1.39 W/(m˚C)
Your curtain wall (200mm Concrete Block U = 2.9 W/(m2˚C) )

Delta T -- Tomatoes don't like to go under 13C (55F) at night, For pepper, it is about 15.5C (60F). You live in Toledo, Spain -- Use 2C. Consequently, the DeltaT = 15.5C (pepper) - 2C = 13.5C


Step #3 Conductive heat loss for each identified items:

1. Sidewall =3.9W/(m2˚C) x 15 m2 x 13.5˚C = 790 watts
2. End area = 3.9 W/(m2˚C) x 9.1 m2 x 13.5˚C = 480 watts
3. Roof area = 3.9 W/(m2˚C) x 13.9 m2 x 13.5˚C = 732 watts
4. Perimeter = 1.39 W/(m˚C) x 15.2 m2 x 13.5˚C = 285 watts
5. Curtain wall = 2.9 W/(m2˚C) x 3 m2 x 13.5˚C = 118 watts

step #4 air infiltration heat loss,

Qa = 0.373 x 13.5˚C x 22.75m3 x (exchange hours == 2) = 229 watts

Between 1 to 4. 1 for well build polyethylene and 4 for badly build glasshouse

Step #5 Add everything

Qt = Qa + Qc = 229+ (790+480+732+285+118 ))
= 2674 W
= 9126 Btu/hr

Generally add 10%.
So, if your heating system is able to supply 3KW, this greenhouse might be operated 365 days a years with fancy vegetable such as Pepper.

It also means that if you have a night at 2C that last 10 hours, you need 30kw (102K BTU) of storage. (you likely need more since the sun is not always there.)

NOTE: Obviously, for December, January, February you may decide to growth crop that need much less heat at night -- like several green. For example, the deltaT might be reduce at 8C or even 6C for some crop.

NOTE2: since you are handling so many (almost pro) gadget, you might think to improve your greenhouse like the pro do by installing a "Thermal Curtain" that deploy automatically at night; You may save between 20 and 40% in energy requirement with this type of gadget.

SPAIN: I don't know much about your location, but I am told that in Spain, "Controlling the heat gain" at summer time is a much bigger problem then heating the greenhouse in the winter. You will need a pretty powerful fans to replace a roof vent when the outside temperature is in the 30C.

WIND: On my commercial unit, we open part of the roof on the opposite side of the dominant wind. The computer also use a special "mode" call "rain shedding" when it detect some water on the roof. Obviously, this is a little bit fancy and all controlled by computers.

I actually loved your idea of solar water heater. Its the best way to save electricity. However there is just investment cost nothing more than that.

It's been a few years since I posted anything about the greenhouse so here's an update.

In the part of Spain where I live we sometimes have very strong winds. When I bought the greenhouse I asked if it was suitable for windy areas and they told me it should be ok. Unfortunately it wasn't. The greenhouse lasted 2 storms. The first ripped the roof vents off and pushed in some of the side panels (which I then repaired and attempted to strengthen with silicon and wood). The second storm totally destroyed the greenhouse, I still don't know where the door ended up as I never found it. The majority of the wall and roof panels were just shredded into small pieces and the structure was left a twisted mass of aluminium and bits of polycarbonate on the floor. Pretty soul destroying.

So, several years later I have decided to try again - in the interim period I haven't had a greenhouse or the desire to try again but now I have decided to have another go but with a different style. Fortunately the base and surrounding wall are still intact so I'll re-use that. I'll start a new thread with version 2 rather than continue this thread.

For water or for electric?