The problem with passive solar is that the heat tends to not last throughout the night. It takes a big mass of water to hold heat all night. I put a link below to the water bags that FarmTek sells. You can make your own, but if I were you I'd copy their designs.

I'd also have a back-up source of heat if at all possible, like an electric soil heating cable or a small propane heater. But as soon as you start spending money, you will want to grow a more monetarily valuable crop like tomatoes or cukes to recoup your investment. Beans are typically not grown in greenhouses for that reason.

Here is a link that might be useful: FarmTek water bags

You might want to look into phase change materials. This blog talks about using PCMs in a greenhouse:

http://greenhousefashions.blogspot.com/

The benefit of PCMs is that they can absorb a ton more heat than water in much less space. The amount of water you would need to bank enough heat would almost fill the greenhouse. What little space you'd have for plants you could not really use because you don't want the plants shading the water.

I am currently designing a greenhouse that we are building this coming spring. We are primarily using a Subterranean Heating and Cooling System which sucks the hot, moist air and sends it underground where it condenses and releases its heat. You can cool your greenhouse all summer long this way and use the stored heat in the winter to heat your greenhouse. This system is used successfully with hoop houses so you might want to look into this as well. Our challenge is that we have a high water table which prevents us from putting in an appropriate-sized heat sink so we are looking into doing a hybrid between PCMs and SHCS.

Best of luck!

PCM is neat stuff.

That blog linked to this company selling PCM-filled PVC pipe lengths:
http://rgees.com/products_pcm-pipe.php

They don't list prices. Do you have any idea how much they cost? Is it feasible to make your own?

Here is an informative page I found from an Indian company hat manufactures PCMs:
http://pcmenergy.com/products/doctorsays.htm

I have read that you can and it is really inexpensive (if you are using Glauber's Salt) but you need to mix in other ingredients in order for it to work over time. Below is a link to a guy who mixed his own PCMs and used it (along with other strategies) to heat and cool his house:

http://www.allanstime.com/SolarHome/index.html

One thing you need to be careful of is handling the material during a time when it is optimal humidity because that, too, could affect performance.

I don't know about prices. I have stayed away from Indian companies because of shipping but I have been in touch with Rgees (they are in North Carolina). You can buy samples for $25 each but the minimum order is $150. After a certain volume, the price goes down considerably. They can also sell their PCMs in bulk and you can fill containers yourself but again, you have to be careful of humidity. Once Rgees comes up with an estimate of PCMs for my prospective greenhouse design I'll update you on price.

I am in the process of building a new greenhouse and need some help. I am planning on using barrels of water for heat storage, and would like to know if you can get too many?

I have a small greenhouse that works very well with just water for storage, but it is against my house and has an upstairs porch as its ceiling.

This one will be larger and freestanding, so I'm wondering if the barrels will be sufficient.

I had really wanted to try the SHCS system, but was discourged when I could find no uptodate info, and besides I am actually going to convert an existing building, and I would have had to remove it to dig the underground portion of the system.

I am not familiar with with the players on this forum, but have been very impressed with the expertize on the "Container Gardening" forum. I am hoping someone can help, as I have a number of ideas for enhancing the system, but would like some help.

Thanks in advance, I would really appreciate help.

John

Curly Girl: Thank you for the information. Do you happen to know the mass of PCMs per square foot or volume of space. Also, is PVC the only material you can safely store it in, or can I put PCMs in a simple plastic bag or something. Also, the PCM websites all have temperatures, what temp should I get for a hoophouse? Thanks! Kim

azjohn - I'd say that water barrels would not be enough heat by themselves...except you're zone 8 and in Arizona, I presume, so I doubt you need much heat. What are the outside day and nighttime temps that you expect?

The only problem with too much water is usually running out of space. For it to hold too much heat, you'd have to be having extremely warm temps in the first place, and probably would not be greenhouse growing anyway.

And thanks for the link, curlygirl. With some rough estimates using the math they give for a greenhouse sample, I would need a couple thousand pounds of the stuff to make a significant difference with just the sun as a heat source.

However, I am using a wood-burning forced air furnace right now, and I would probably be best off to use small amounts of PCM within and around my current ducting, so I won't give up on the idea just yet.

I just heard back some encouraging news from Rgees. They recommend my putting encapsulated PCMs within the heat sink of the SHCS -along with the soil and/or gravel. That way, I can have the dehumidifying benefits of the SHCS along with the extra heat storage of the PCMs. Please note that SHCS is a phase change system -it is just that my high water table has me pursuing this other avenue (if my heat sink was flooded, it would take away my heat and -if this happened enough times- would fill my tubing with dirt).

AZjohn -I know what you mean about SHCS! Have you been looking at Sunny John's site? He used to have great forums where people could discuss their plans and challenges. I used to read them all the time when I was renting and could only dream and research. Now that I have a house and could use the forums to ask for feedback on my particular challenges, the forums are gone! However, I have some good news. SHCS is alive and well! Check it out:

http://www.roperld.com/science/ymcasolargreenhouse.htm
http://www.roperld.com/science/SGHBackyardSHCS.htm
http://barrettstudio.wordpress.com/2011/12/22/the-practically-zero-energy-year-round-greenhouse/
http://permaculturenews.org/2010/08/16/clever-rocky-mountain-greenhouses-give-major-season-extension/

KimHat- I know you can store PCMs in other materials such as metal tubes but I am having trouble finding that information right now. I would just go on the greenhouse fashions blog and ask questions in the comments. The blogger, Nina Reinhart, works for Rgees and is interested in getting PCMs into greenhouses. I think primarily because it would help their company expand into a new market but also because PCMs are absolutely perfect for greenhouses. The large temperature swings, the limited space, the high cost of heating and cooling, etc. Anything you can do to reduce temperature swings passively is something that will pay you back every year. I say all this without knowing what they actually cost but I think if you are in the planning stages of your greenhouse then it would make sense to think about how to incorporate them into your design. You can add them later but for me, aesthetics are pretty important so I am working them into the design now.

Also, there is another PCM product made by another company called Bio-Based PCM which you can integrate nicely into your house and it actually acts as a moisture seal too:

http://www.treehugger.com/green-architecture/bio-based-phase-changing-material-adds-instant-thermal-mass.html

Cole Robbie (love the name, by the way!)- where do you live? What are you growing in your greenhouse?

Thanks. I'm in Illinois, zone 6. My greenhouse season is in the spring. I raise bedding plants, tomatoes, and cucumbers.

PCMs in a greenhouse should be in the floor or in the benches used to hold plants. PCM paver stones for a walkway would be great. I have a gravel floor right now. For something with tons of mass, it does not hold enough heat to make more than a few degrees difference at night. Even with my wood stove furnace going full blast (it's in a nearby shed, not the poly house itself), the best I can do is about 15 degrees over the outside temp. My double inflated layer of 6-mil poly has a very low r-value, 1.3 I think. Plus, I have roll-up sides, which are hard to seal around, especially on windy nights.

For next year, I am going to try to heat water or ideally PCM with the hot air from the wood stove. Radiant floor heat with hot water through PEX is the best setup I have seen.

Please forgive my ignorance as i am a grandmother and a medicine woman trying to care for my little lake side community and only educated enough to take advantage of the expertise of those with the education(LOL) but I have had these subjects of thermal mass and PCM's swimming in my head for weeks in the planning of a (Passive)4 season greenhouse here in Oklahoma...
honestly heating is not my problem as it is dec 1st and 72 degrees outside today. we are in a record drought and the summers are reaching 114 for more days than i care to remember. I live out in the country where our power is never reliable as we are always the last to be reached in a crises( after every thunderstorm)..LOL and as of this date i haven't the money for a solar set up...I need to "COOL" my green house... Im thinking of digging down 4 feet (a walipini style. Ive read that the ground temp is a little over 50 degrees at 4 ft deep( not including any solar warmth.. I'm wondering if You might have any advice about my plan...Please make it simple...LOL

Oh and BTW has anyone considered a encapsulated soy wax?..isnt this the Phase change material that is being considered for so many new building materials now? wall board and bubble cloth?
Ive seen something like this put in pvc tubes, caped on the end and applied to the north wall for temp consistency in one application and now they are making this available for a pretty penny Im sure....is this worth trying to do myself? any help or advice would be so appreciated!..

these are the sites i have found....

http://large.stanford.edu/courses/2010/ph240/reinhardt1/

http://www.fact-sheets.com/home-garden/energy/drywall/

! would like to make contact with anybody who has
installed a solar under ground water tube heating
system in their greehouse.

12/11/12
wayne
317 852 9232