Jared Van Denend

Dan Grubbs wrote:Here's a possible different approach.
I know running hot-water tubes through the planting beds may seem like a budget buster, but would be more efficient to focus on soil temperature than ambient temperature? One could collect solar heat in tubes in a panel or heat from a large compost pile and run the tubing through the bottom of planting beds so that you spend your energy only heating the places where the plants are and not all that cubic feet of air. In extreme low temperatures, use row covers to hold in heat and deter frost. A small solar powered pump can circulate your warm water through the system.

There are some other posts on permies.com that touch on this topic extensively.

Here is a video of a small high tunnel with double layer and small blower. The person in the video is showing about a 60 degree gain with the double layer. https://youtu.be/LlEczaE0-eg

Here are some interesting ideas presented here by Verge: https://www.youtube.com/watch?v=b1p-Dm1bUjs

I think you are 100% correct about focusing on soil temperature... this is why i was thinking about burying the barrels directly under the beds.

I have seen these air transfer systems and they look great.... we will likely do something similar when we build a permanent greenhouse.   For our high tunnel we are just looking for low cost semi-simple solutions to add some heat.   The tubing is a great idea and perhaps we will have that, but the biggest issue in my opinion is night time temps.   But perhaps I'm going the wrong direction and if we heat our beds enough in the daytime then they will hold that heat into the night?  

Mike Jay wrote:

Jared Van Denend wrote:I read that 55 gallon drums often do not fully heat in greenhouses due to their size/thermodynamics.   I figured the solar collector would circulate the water, fully heating it (and hopefully heating it more).
I'm not attempting to raise the daytime temperature of the greenhouse.  I would like to simply add thermal mass for nighttime temps.

I'm struggling with this in my mind as well.  I've read that if you use one gallon water jugs for thermal mass they heat up fast and cool off fast so you lose the heat back to the greenhouse before the night is over.  10-20 gallon jugs were suggested to hold and release heat in about a day which would be perfect to offset the lack of sun at night.  55 gallon drums sound like they are more of a 3 day gain/loss so they can help out over cloudy stretches.

In my mind, it makes sense that circulating water into the drum from an efficient solar collector would boost the temp of the water and give you more heat to release at night.  But "conservation of energy" is telling me that the amount of energy into the building is the same either way.  So I'm guessing that with the solar collector inside the GH it would reduce your daytime temps slightly (by hiding that energy in the drums) and increase your nighttime temps by allowing the extra energy in the drums to come out then.  Overall, average GH temp would be the same but it would help by leveling the daytime highs and nighttime lows.

Another thermal mass collection idea I had (and probably many others) is to put some black pvc pipe at the highest point of the greenhouse and circulate water from it to your tanks.  All day the sun would hit that pipe (solar collector).  Plus the rising heat of the greenhouse would thermally warm the pipe as well.  That would let you store that heat before it escapes through the thin greenhouse plastic.  At night you'd have to shut off that pipe so it doesn't work in reverse.

Insulation ideas:
If you do the double poly glazing with the blower, maybe you can insert some packaging peanuts between the layers on the North side.  Or fasten some 1" styrofoam to the ribs between the layers.
You could fasten styrofoam to the inside of the ribs on the North side and cover them with a white or reflective material to bounce light back down to the plants.
Concrete curing blankets are another possibility.  Just drape them over the GH on the North side and tie them down.

I think perhaps you're stuck on the potential energy of the greenhouse...  It is working by trapping some of that energy inside its structure.   If a cold frame inside a greenhouse preforms better it is logical that a solar hot water heater would preform better as well.   BUT what is the trade off as far as area?  

I like your idea of the black PVC pipe.   To go a step further perhaps bury those barrels in the ground to heat the actual soil.  

Vern Life wrote:Hi Jared,

how much space are you allocating for the solar water heater ( I guess the water storage/ transfer portion)? I'm moving towards the GH phase of our build and have been thinking of this as well. I've thinking of using the black barrel wall idea as a winter heat storage mass and summer drought water supply that will serve as a work bench of planter shelf (hoping the warmth will add additional seed germination awesomeness). For the water heat however I've been playing with two ideas, the solar gain ( basically the high pressure black hose on the roof, I already blew up the black garden hose) and the compost pile water coil. The compost pile heater coil has been on my mind for the past two years for emergency hot water and it's thermal properties while providing ample compost for the spring planting. I've seen compost piles in corners of greenhouses or in one section that keep the GH mild even in snow.  

I have not really come up with a number.   The greenhouse will be 30x18'.   I think barrel tray is a good idea... we will be doing something similar, or burying them.

I've also looked into the compost water coil.  From my research it takes a very large compost pile to make it feasible.  I plan on trying a smaller system in a barrel.  Hopefully with the ability to swap out the coil/barrel when it needs it.   The problem with this is if you run your pump too fast and pull too much heat from the compost it will stop composting  (which is why i'm doing it in a barrel).

For us the big thing will be having many options all which will slightly boost the heat till (hopefully) we can grow some fruiting plants.    I think if we set up a good barrel system and have a few ways to heat them that will be the best for thermal mass etc.

What i'm worried about is if you put a bunch of thermal mass in your greenhouse and it is not getting heated daily it will simply be cooling the greenhouse rather than heating it.

if that is the case we just have to drain the barrels.    My biggest questions now is if its worth it to bury the barrels in the ground (if they are being heated by compost/solar hot water/coil in the stove) and if the solar collector should live inside our outside the greenhouse.

Mike Jay wrote:Hi Jared, welcome to Permies!

So are you proposing a solar water heater collector inside the greenhouse to heat water tanks that are also inside the greenhouse?  That's interesting and I'm not sure how much it will do.  The greenhouse will only accept a given amount of sunlight (energy).  Whether it hits the collector and goes into the tanks OR if it just hits the tanks directly (or the floor or plants), the same amount of energy was transferred into the thermal mass of the greenhouse.  But, you may prefer it to be transferred to you tanks instead of the ground, since water is a better thermal mass.  So if you goal is just increasing thermal mass energy accumulation, it should help.  But day in and day out, the average temp of the greenhouse would remain the same (I think).

If the collector is outside the greenhouse and absorbing energy that wasn't going to hit the greenhouse, then I think you get a better boost.

Or if you want your thermal mass to be hidden on the North side of some banana trees where the sun can't hit it, this would be a way to transfer energy there without putting the tanks in the sun.

If your high tunnel runs E/W, you may want to consider making part of the North side of the tunnel out of an insulated material.  Holding heat in would really help.

I am suggesting that...  I read that 55 gallon drums often do not fully heat in greenhouses due to their size/thermodynamics.   I figured the solar collector would circulate the water, fully heating it (and hopefully heating it more).
I'm not attempting to raise the daytime temperature of the greenhouse.  I would like to simply add thermal mass for nighttime temps.
Makes sense to put it outside of the greenhouse now that you say this - never though of the fact that this adds area for the sun to hit.

Any easy (cheap) ways to insulate high tunnels?  

Walt Chase wrote:Is this going to be a NRCS high tunnel?  If so, I imagine that what your are proposing would be "out of contract".  If not, Look into solawrap covering.  It is like bubble wrap for greenhouses.  A bit spendy, but when we build our next house (already have the property) my GH will be covered with it instead of traditional GH poly.  Supposedly will last for 20 plus years.  If not that look at using a double layer of conventional GH poly and use a blower to inflate between the two layers.  That coupled with more thermal mass in the HT and maybe even a wood stove could let you grow several extra months and possibly all winter depending on you climate and winter severity.  I would suggest a RMH, but have no personal experience with them, especially in a GH.  Could be a viable option as well.

It is not.  I will look into the bubble wrap as well as the blower.  We are keeping costs as low as possible for this house as we have the windows to build a permanent green house... we are running the high tunnel as an experiment to see where/how/what to heat etc our 2nd greenhouse.   The high tunnel will then become a starting greenhouse and a nightshade machine (we hope!).

We plan to put an old woodstove we have in/in a connected shed outside the greenhouse with the stovepipe running under the entire thing.   We may build a RMH if we have time.  I would also like to incorporate as many "simple" systems such as compost/solar hot water to cut down on our wood and the amount we have to tend the fire.  

We are building a high tunnel in WA (zone 7b).  The main purpose of the high tunnel is to get a whole bunch of starts rocking early spring... however if it is there we would like to grow whatever we can in it all winter.   So we are looking at heating options.

We are going to build cold frames inside the greenhouse which we will remove and place over some beds in the spring.  This got me to thinking if every layer of greenhouse material bumps the zone up... how about a solar water heater inside of a greenhouse.. heating up our barrels.

Has anyone done this?  I know theoretically it should work, but I'm wondering if the juice is worth the squeeze.   I haven't found any info about this type of setup on the web.