Let's brain storm: thermal mass materials

18 years ago

What do you think are good thermal mass materials? (especially, readily available inexpensive ones) I am about to put up my first greenhouse.

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Comments (49)

stressbaby
18 years ago
Water. It is not even close.
Here is a chart by mass:

Material Specific Heat in BTU/lb-F
Water 1.0
Iron 0.1
Glass 0.2
Stone 0.2
Wood (Oak) 0.6
Brick 0.2
Concrete 0.15
Sand 0.2

These are some volumetric numbers:

Material Specific heat in BTU/cu.ft.-*F
Concrete 19-30
Brick 22-31
Water 62.4

Hey, at least it is readily available and inexpensive. SB
weebus
18 years ago
How aobut brainstorming how to use it (water) and how to store it?
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agardenstateof_mind
18 years ago
About the best method I saw was square, 5-gallon honey cans; but I'll be darned if I can find a source for the things ... they all seem to have gone over to plastic buckets.

BTW, that came from an article, a link to which was posted in a message somewhere here on GardenWeb; you'll find that article at: http://www.survivalplus.com/foods/page0009.htm

Diane
nathanhurst
18 years ago
Water is excellent for its specific heat (only ammonia comes close), but as I posted in another discussion, you can get even greater storage using phase change materials. The most common is calcium chloride hexahydrate. The only data point I can find is that you can store 10kW hr of heat in 0.2m^3 at 25C, this corresponds to 8.5 cubic metres of water if you want to hold the temp over 1 degree C (and more practically, 850L if you are willing to allow the temp to vary over 10 degrees say 15C to 25C). For comparison, CaCL2.6H20 has a density of 1.7 compared to 1 for water.

If you could use the boiling phase change of water you could store 500 times more energy for a give volume of water over 1 degree. This means that 1 L could have the regulating effect of 500L in a tank. Put another way, for the same storage space you could store a years worth of heat rather than a days worth. Working out how is left as an exercise for the reader (and you could make a lot of money :)

A good cheap metal container is to reuse the ice-cream drums (here bulk ice cream generally comes in 40cm x30 x30 thin walled drums). The local icecream shop gives them away. I use them as pots for plants without trouble. After a while they get a nice oxide coating.
chris_in_iowa
18 years ago
My way of thinking and working is.

"If you have a heater running at night and you have vents open and fans running during the day for cooling then you have the potential for some creative ways of saving energy"

Water is great for thermal storage and also a good heat sink for cooling a greenhouse. But, in my limited experience and my humble opinion you have to either move the water around, or you have to move hot/cold air around the water.

As I see it there are three main ways of utilising a thermal mass.

1, Passive. The mass is there and no effort is made to enhance the heat collected during the day and no attempt is made to regulate the heat output at night. No external energy is needed.

2, Active. Methods are used to deliberatly collect and store heat when it is in surplus, Trombe walls, solar closets, solar panels to collect heat. Solar chimneys drawing warm outside air into a greenhouse through a thermal mass which will heat up your thermal mass and at the same time cool the incoming air. You need to add energy in the form of pumps and fans, but no energy is used for direct heating. Done right the pumps and fans only operate when you need heat.

3, Agressive. The thermal mass is circulated, stored and heated as required. If the greenhouse is heated using water to air heat exchangers, and the seed germination and propagation soil heating is water based then you have a method of heat distribution that gives you an enormous range of heat sources. You are not generating all the "heat" you need, you are using some energy to move heat around and just generating heat where you need more.

There is a fourth and very important factor in using as large a thermal mass of just plain old water as you can realistically fit inside a greenhouse. Latent heat of fusion.

"""How aobut brainstorming how to use it (water) and how to store it?"""

Old plastic trash cans...... the ones that are split, have holes in them that people throw away. They are free.
weebus
18 years ago
How about plastic trashcans with the flat lids and using them for legs of your benches?
chris_in_iowa
18 years ago
""How about plastic trashcans with the flat lids and using them for legs of your benches?""

They buckle and, split.....
chris_in_iowa
18 years ago
Why do I do stupid things like go outside and find a "bench leg" to show what can happen to it when it is 2F outside?????

I don't know!!!! But this is what can happen to a Rubbermaid trash can used as a bench support, and it tends to happen easier if the trashcan is full of water. Empty they are great, if they are full the slightest offset of weight on them causes them to buckle....

Here is a link that might be useful: {{gwi:310686}}
virgo91967
18 years ago
I have one better than plastic trashcans.. I have a brother that works at a chemical supply storage warehouse .. can get all manner of 35 and 55 gallon HDPE storage drums with removable tops. Plenty thick enough to not split or collapse under weight of benchwork. Only use the ones that held NON-toxic materials and wash VERY well with hot soapy water JIC.

for small ghouses, how about reusing 2 litre soda bottles or gallon milk jugs... they wont bust if you dont fill them completely,leave about 3 inches or so for expansion. Besides free, I think that all the additional surface area may be beneficial... But I could be wrong about that
chris_in_iowa
18 years ago
Yes I agree. This winter I am building real benches that my trashcan collection will sit under.

The 2gallon water containers that I placed around the outside of the plywood benches on top of trashcans were the main culprit in causing the buckling....

Not changing my configuration by much this next season but putting legs on the benches.
nathanhurst
18 years ago
Do they sell something like these:

Rain Reviva

in the US? They would be great for under benchs with a chance of ice.
stressbaby
18 years ago
So far we're only talking about passive uses, to use Chris's terminology. But Nathan has an active, if not aggressive system in use with his rainwater. In what sounds like a rather elegant system of pumps, he moves water through black tubing during winter to store heat, and through a swamp cooler during summer as a cooling method.

I, for one, could use more detail, Nathan... How much black tubing is required? More details on the manifold or controller (I couldn't make much out of the link in the other thread, linked below). Pics would be great.

Here is a link that might be useful: Link to the rainwater thread
brian_kc0kfg
18 years ago
Just a thougnt on containers, deep fryer oil containers are nice square, look at mcDonalds thats where I get all mine.
steve421
18 years ago
I was initially thinking about using 5 lb coffee tins...the only down fall is they may rust....especially if salt is added to the equation...also the metal may be too good of a conductor of heat so at night it may release the heat too fast....Question...since CaCl6h2o will may the water denser plus lower the freezing pt...wont just plain ole NaCl do the same thing....Also I have considered putting black trash liners ontop of the bench and place the plants ontop of that....Maybe a layer of wet sand inside the liiner may work....just brainstorming on the moment....sounds crazy but may turn out interesting...

Steve
mountain_curmudgeon
18 years ago
I agree with Diane about the square metal cans. The popular 55 gallon drum works but has problems with passive heat gain, the main one being the stratification of warm water in the drums. Another is the inability to place them squarely alongside each other and also in stacking them. (The rims on top and bottom prevent direct contact.)

Smaller square cans eliminate all these problems.
agardenstateof_mind
18 years ago
Off-topic, but thank you, Nathan, for posting that link re the Rain Reviva - after enduring a nasty drought here this summer, I've been thinking about some kind of rainwater collection/storage system and I like the idea of installing this under a deck (a good excuse to get the deck project moving, too). Will have to research availability of similar products in the US.

FYI, the Audubon House in Key West, FL, has two cisterns beneath the back porch for storing rainwater ... it is reported the former ship captain who built the house incorporated these for his wife who loved gardening, but couldn't count on consistent rainfall. Some ideas just never go out of style.
chris_in_iowa
18 years ago
Water storage.

Free flow waterbed mattress (I say free flow because that is just a vinyl sack. no foam and all the other stuff inside)

84" x 72" is about $60

Normally they are filled so they are level at about 8" but as a bladder you can get more in there. (don't ask.... the thing was huge! never fill a waterbed without watching it all the time!!!!)

OK going on 84x72x8 inches that gives us 48384 cubic inches which is 209 US gallons.

And I would feel quite happy placing a 350 watt waterbed heater under it!

Protect it from sunlight and it should last years.....

As we are really into numbers now, if we assume 1 US gallon is 8lbs then 209 gallons of water is 1672 lbs.

One BTU is the heat required to heat 1 lb of water 1F
(one BTU is released when 1 lb of water cools 1F)

If your water is 70F at sunset, and the lowest you can allow your water temperature to go is 40F then you can release 50,160 BTU total, or 4180 BTU/h for 12 hrs.

The key to all this is to make sure that your water mass is back at 70F by the following sunset. That way you know you have a 4000 BTU/h heater all set up to go again.
nathanhurst
18 years ago
Regarding my 'active' heating system. I use 100m of 19mm black poly pipe on the roof for heating. It's not very efficient, when I rebuild it in my new house (moving in 11 days...) I'll either use swimming pool ribbons, or cover it in a layer of plastic to reduce wind cooling. It currently produces about 4000W of heating in winter on a sunny day. Swimming pool ribbons claim to get about 300W/m^2.

Although I currently use an electric blanket to heat my cutting bench, I'm pondering using pumped warm water when available.

Measuring the heat is done with 1-wire bus sensors (in particular ds18s20), levels are with mercury tilt switches and the 'famous' hurst/sheridan level meter in the tank. I use an i2c relay bank which in turn drives 240V contactors for the pumps.

Getting the logic right is tricky. In my new house I'm going to have a separate low power computer (planning to underclock an athalon down to around 16W) to control everything - greenhouse and house heating, watering, internet, terrariums, music-on-demand, backups, weather logging, perhaps even coded entry (I saw electronic door jambs on special recently). If the code is ever vaguely reusable I'll stick it up on sourceforge.net (indeed there is probably already a suitable project for me to join).

I'm not sure what you mean by manifold.
virgo91967
18 years ago
So how long would it take that mass of water with a surface area of 5,520 square inches to cool from 70F to 40F ( oh I would assume it would be sitting on an insulated base)
nathanhurst
18 years ago
virgo91967, your question is ill-posed: if those 5,520 square inches were only 1mm deep it would take seconds, if those 3.5m^2 were the top of a 1km deep well at 70F it would take all year. Perhaps you are after the cooling rate of 3.5m^2?

I am not sure how to compute this, if you knew the expected evaporation rate you can work out the cooling rate using the latent heat of boiling (220kJ/kg) to work it out. In melbourne the yearly evaporation rate is 3m, which works out to be 660MJ per year per square metre or 20W/m^2.

To be honest, these calcs are fairly meaningless :)
chris_in_iowa
18 years ago
Nathan, you got it. All the calculations are meaningless because we are missing out big chunks.

""So how long would it take that mass of water with a surface area of 5,520 square inches to cool from 70F to 40F"

If it was open to the atmosphere, what is the air temp and humidity? Is there an air flow over it?

If enclosed what is the R value of the covering....

You are focused on the latent heat of evaporation because of where you are. To me the latent heat of fusion is what saves my ass....
nathanhurst
18 years ago
Latent heat of evaporation is also vastly bigger than that of fusion (2250 kJ/kg vs 330kJ/kg - I note that I was out by a factor of 10 - the cooling rate of 1m^2 is 200W, which is far more believable).

Incidently, recalling my earlier thoughts about using the heat of vapourisation to buffer a greenhouse, operating at a lower pressure does not change the melting point of water significantly, so you still get the buffering at 0C.

The calcs aren't entirely meaningless, they give some numbers to play with to see what is and isn't feasible.
virgo91967
18 years ago
Okay, My question was ill-posed... I was refering to Chris-in_Iowa's waterbed mattress idea... Would be no evaporation from a waterbed matress...
nathanhurst
18 years ago
Ok, in that case it is simply newton's law of cooling: http://en.wikipedia.org/wiki/Newton%27s_law_of_cooling

the R-value of the surface layer is about 0.03 m^2K/W, perhaps another 0.12 for inner skin, giving 0.15, which is 6.6Wm^-2K^-1, you have (70-40)*5./9 dK = 17dK for a cooling rate of about 390W over the 3.5m^2.

I guess those number from R-value calculations for houses, so they may be a little off.
chris_in_iowa
18 years ago
My brain is frozen so I am not thinking as well as I should but...

From Nathan's numbers it seems like the water bed bladder would act like a 390W heater, which is about 1330 BTU/h.

But I said 4180 BTU/h would be available for 12 hrs.

Why the difference? I believe it is because you have to activly transfer that water through a heat exchanger to get the heat back out. Just relying on the heat passivly coming out of the bladder gives you one fourth of the potential.

I had to smile when I saw the 390W... and waterbed heaters are 350W. I guess they are designed to just about keep up with the loss from an uncovered mattress.

The reason my brain is frozen? I happen to have a waterbed mattress in the barn. I also happen to have a waterbed heater, pumps and a couple of heat exchangers ( fan/radiator units from large refrigerators) Todays high at 3pm -4F Current temp -12F

I would love to set my toys up to do tests, but at the moment it is way too cold to even set the stuff up.
garyfla_gw
18 years ago
Hi
Find this an interesting thread as I'm trying to accomplish something similar in my shadehouse Afraid I can't offer much as I'm completely ignorant of physics lol.
I'm remodeling my shadehouse ,hopefully to make it more
useful all the time .
I'm located in S. Florida so heat is much more of a problem than cold But maybe someone can give some ideas on how to go about this.
I keep a heated 150 gallon aquarium in the shadehouse and have noted that during cold spells it is sufficeint to heat the entire area but has several problems.
I want to connect the 1000 gallon lily pool to the 150
and the 800 gallon bog area. Would be wonderful to come up with a way to heat them so they would never fall below 65.
Obviously I can use a standard aquarium heater and either cover the areas with bubble wrap or shut down the circulation system. Haven't the foggiest idea what size heater(s) would be necessary or how to locate them. It occured to me that the escaping heat would make t the entire shadehouse frostproof. But I'm not certain how much energy would be needed.
I can give the weather particulars if someone could make a guess or tell me how to think about this.??
I've tried several methods in the past and all have had serious flaws on a year around basis .
Before you think I'm insane lol The low last year was 42 for 3 hours and the record low was 26 and that day set low
daytime high of 52. Normally the temp is 65x75 during winter.
Thanks very much for any help you can give me.
gary
sail
18 years ago
Just a quick question from a Greenhouse newbie...

Has anyone attempted to use the ground as a thermal moderator? I understand that it doesn't make a very good heat sink but it is a large geo-thermal source.

Any techinques that prove promising?
stressbaby
18 years ago
Irritating, I can't find the link...maybe it's at home...

Yes, if I understand your question correctly, it has been done. The plans called for 55 gallon drums with 4 or 6 inch pipes from the drum, running through the ground and through raised beds in the GH. The fans were on the drums. To make it work, they used hundreds of feet of pipes, way more than what I intuitively would have expected.

Kind of like a ground source heat pump circulating air. SB
mylu
18 years ago
Only have 12 min. and I hate to do this but....
OK 30x96 foot g/h 6mil poly covering single layer, steel frame, Gravel Floor 3 inches deep.
Day time temp (for fun) 45F full sun 9 hours
Night time temp drops to 20F

No formulas needed

How many gallons of water, in square feet, would it take to maintain the min. temp of 55F in the g/h?

The true question here is feasibility. Times up gotta go...
chris_in_iowa
18 years ago
Yeay!!!! Insufficient data. I love that type of problem.

No formulas needed because you have not given enough numbers to put into any formula have you?

And I have never measured gallons in square feet before, but I am sure going to give that one a try tomorrow.
chris_in_iowa
18 years ago
P.S what color is the gravel?
nathanhurst
18 years ago
I think mylu means how many gallons per square foot.
chris_in_iowa
18 years ago
Nathan,

Mylu's question is a sucker question...

An ordinary poly covered hoophouse is not DESIGNED to use any kind of thermal mass effectivly. We have been at this for months now and STILL some people are not getting the idea that SOLAR structures are designed and built as a system.

Ya know, I should really quit posting here and start planting seeds.
mylu
18 years ago
Chris. It's not a "sucker" question.
I clearly stated if you need more numbers to let me know. The items listed are industry standards with know properties like 6mil poly single layer. (as one example)

Rephrase. You said as an example using a water bed mattress.
Cleary the mattress contains gallons of water and also takes up x amount of square feet. So does a 55 gallon barrel.

The gravel is plain old granite and its whitish... Standard items people use to cover a large g/h floors.

The point with no formulas is that most folks don't want to break out their scientific calculator and follow along.
It's obvious that you and Nathan (with his degree) love to play with numbers. Most folks see them and read blah, blah, blah.

Now the question was an easy one. How much water would one need to fit the requirements. Please don't run from the conversation by starting a new thread.

As for my understanding that g/h are designed as a system I can assure you if I didn't we wouldn't be a profitable nursery/wholesaler. Visit us sometime.

The real question is all this practical, economical and even feasible. Believe me. For one that burns over 3000 gallons of propane each year, and more next year, if the practical, economical and feasibility criteria are met we may invest in such a system.

Remember we can't afford to loose any space in any g/h and the benches are all 24 inches tall. Walking paths are no more then 2 feet in between. All the space is devoted to growing. Now with that said once the benches are full there is not much sunlight that reaches under the benches.

So get to punching the numbers...
chris_in_iowa
18 years ago
The water would cover the whole 96x30 floor a foot deep.

Assuming at the start of a 24 hour period the water was 80F and you only allowed it to drop to 60F then that volume of water dropping 20F would release enough heat to keep your greenhouse at 55F

Roughly.
mylu
18 years ago
Cool,
Feasable it could be done if every bench was 2ft high. You would have to have every one, on the underside of the benches with water. Meaning there is enough sq ft of flooring.

So in the morning the temp of the water would be 60F and
it would need to be heated again back to 80 degrees.

Now if it's cloudy all day and the temp doesn't get above 30 that day I might have a problem... And how can we heat the water when they are in the shade under the benches?

Now were into practicality.
nathanhurst
18 years ago
simple, you need a controllable heat exchanger. We discussed earlier how to extract large amounts of heat from the air for cooling, the remaining problems are how to extract maximum heat from the air for heating the water, and how to return heat to the greenhouse on demand.

Chris already has a solution to the latter - use the water to heat the beds directly. If you have a stockpile of warm water and you want to heat the beds you pump the water under the benches through pipes. Ideally the pump is variable speed to give even heating throughout the length.

The second problem also has a cheap solution and indeed could increase the solar heating power of your greenhouse. The idea is to run water through solar pool heating tube attached to your north (south here in au) wall. Of course there is no reason to only collect sunlight inside the greenhouse - run the pipe over your house roof, or shed roof or whatever. If your area is cold or windy you will probably need to cover over the pipe with plastic, but normal greenhouse plastic would be fine. This arrangement often generates decent heat even in cloudy days.

If you have significant technical skill an almost ideal solution, avoiding many problems, is to keep the water isolated (in insulated tanks) and use a split-cycle system to move heat in and out on demand. I know of no economically viable commercial systems for this, but it is probably fairly easy to modify a commercial split cycle system ( take the heat exchanger out and use a water propellor to force the flow). A back of the envelop calc tells me I can store 1.4GJ (1.3 million btu) in my greenhouse water store this way.

The subterranian condenser system posted in another thread is a very elegant solution to the 3rd problem, although the earthworks put me off a little.

One concern I have with storing large quantities of warm water is the chance of legionaires bacteria. Does anyone know of the issues. If you are healthy lungwise legionaires is not a risk, but if you smoke, or have a weak immune system it can be fatal. I suspect that having a thriving ecosystem in the water with plants, fish, algae and other bio things is adequate to control this. Legionaires and related diseases can also grow in warm humid conditions, so avoiding water thermal storage probably doesn't make you safe.

(also worth mentioning is amoebic meningitis - I think you need to get the spores from already infected water for this, but don't go sticking you head in the tanks :)
stressbaby
18 years ago
I know about Legionnaires disease. You are correct, Nathan, about those who are vulnerable to disease (immune suppression, smoking, elderly). The attack rate is low, something like 5%.

A closed system for heating the water should not pose any problems with regard to Legionnaires. The side of the system with a swamp cooler or any sort of aerosolization of the water does present at least a theoretical risk. Legionella pneumophila, the causative organism, is present in not only man-made water systems but ponds, streams, and rivers as well. I don't see how things "bio" reduces the risk. SB
nathanhurst
18 years ago
yeah, I realised after posting that actually my solution to this problem has been the bare germicidal UV lamp in the water storage. A 10W lamp should be plenty strong enough to keep bacterium levels to a safe minimum.

A biologically active system will have other life that outcompetes, eats and poisons the legionella and keep things more balanced. Also, if everything in the pong(I meant pond honest!) dies it's probably a hint that you need to drop in a block of pool chlorine :)
chris_in_iowa
18 years ago
To be honest because we are dealing with theory my very rough calculations said about 19,000 gallons. That worked out to be 96ft by 26ft and a foot deep I think.

Also I cheated big time! Wait for it..... I totally ignored the sun. I ran the "numbers as if you had a 5000sqft surface area and took no account of any heat from the sun at all.

I used a figure of 3 million BTU per day heat loss which equates to 34 gallons of propane a day.

For the full picture in your example you needed 3 million BTU input per day from somewhere. In daylight hours the sun provides some heat energy for the system, how much depends on the time of year and your latitude and cloud cover.

Capturing that heat energy and storing it is another fascinating topic.

As we are moving from theory to real world systems, if you are using a water based heating system inside the greenhouse then you have a wide range of fuels available to you without changing anything inside. Imagine that instead of a propane line running into the greenhouse you had a hot water pipe. However you heat that water is external to the greenhouse and it could be oil, propane, natural gas, waste veggie oil, wood, straw bales, corn etc.... (or even a combination.)

Now for the light hearted side of the discussion in here.

Did you realise that by placing straw bales around the outside of your greenhouse to a height of 2ft you could shave 10% off your yearly propane bill?
chris_in_iowa
18 years ago
I just hate it when I post then remember I should have posted some more..

Reference my post of Dec 4th. ""If you have a heater running at night and you have vents open and fans running during the day for cooling then you have the potential for some creative ways of saving energy""

What I am trying to say is that on your test day, you had 9 hours of full sun. Even in January I would expect that in your zone the exhaust fans would have come on for cooling. If you can capture that heat then it adds to your night time storage. In January it is not much, bit in my zone in March and April I am well below freezing at night and venting 90 degree air from 11ish to 5ish..

I may be wrong about this but on any day your cooling system kicks in and then at night your heater fires up you have to ask yourself is there a better way.
mylu
18 years ago
Now we're getting somewhere..
We store the water outside the tank. Although I am opposed to running tubs over the greenhouse, it would be hard to fashion if you used a second inflated layer. I can see storing the water in a tank. So the next questions are how big would the tank need to be and how many BTU's (roughly) is it going to take to heat said tank to achieve the 80F water temp.

Seems to me is we may be switching our night time heating bill to a day time heating bill...

One other consideration. Large greenhouses are built on a grade of about 1 to 2ft per 100. Insuring the any water on the floor/ground will run out of the house. That may pose a issue with the tanks in the house.
gbrendemuehl
18 years ago
No formula needed? Am I just supposed to guess?

Anyway, here is a link to a publication from Purdue University for solar energy heat storage. To determine the size of the storage you need to know:

The heating requirements
Storage reserve for days that heat can not be collect.
The temperature range (max-min) of the storage material

I have taken the worksheet from this publication and put it into a spreadsheet. For a heating requirement of 200,000 BTUH for this sturcture (estimate from a greenhouse heat loss calculator from other websites), 3 day storage reserve and and 50 degree termperature range, the needed volume of water is about 4600 cubic ft. or 34,500 gallons.

Not really practical for this greenhouse.

Here is a link that might be useful: Solar Energy Heat Storage
chris_in_iowa
18 years ago
Did we come to an end on this thread?

""Let's brain storm: thermal mass materials""

I think we agree for all practical purposes then water is the best for thermal storage.

Several interesting issues emerged and I think they are important.

"Seems to me is we may be switching our night time heating bill to a day time heating bill..." Yes, that may be a bonus in an unconventially heated greenhouse. During the day it may involve stoking up a wood, corn, straw bale, oil fired furnace to build enough heat to get through the night. In gbrendemuehls scenario you just have to do the "burn" once every three days.

""3 day storage reserve and and 50 degree termperature range, the needed volume of water is about 4600 cubic ft. or 34,500 gallons""

In the test greenhouse that is just under 2 feet deep. Why is that not practical? I admit that retro fitting a 34,500 gallon under floor holding tank in this case is not possible bit in the next one......

""Large greenhouses are built on a grade of about 1 to 2ft per 100. Insuring the any water on the floor/ground will run out of the house."" You heard the latest the EPA are throwing at us? Greenhouse waste water is going to be classed as toxic waste. (as it should be.....) Don't ask me for a link to verify this because I have not looked. However I do know I am the only one in this area with a greenhouse because the other guy who ran a commercial setup quit when he got slapped with a $17,000 water treatment bill. Storing and re-using the run off may be a side benefit.

The most important issue for us may be the fact that this thermal mass, free heat concept does not scale up to large commercial operations. We all know it works down to the "Wall-O-Water" level and up as far as 150 gallons of water under a 4x8 bench but to take it past that point you are looking at some really big heat exchangers and pumps.

For Mylu,

For you, the only benefit a water based heating system with the water under the benches would be is that with a prolonged power failure you would not lose your crop.
mylu
18 years ago
Thanks Chris. That's what the generator and kerosene heaters are for.
As for the run off I'll look into it. We do use drip irrigation to help eliminate the run off.
On that point I would think you would have to classify farms the same way. I would think there would be some type of size requirement to fit the bill (so to speak)
So inconclusion:
feasible = Yes
practical = No
economical = No
chris_in_iowa
18 years ago
The farms are taxed a "drainage" tax, this year mine went up over 500% (well, from 5 bucks and change to over $30 a year!!!) This area is doing a 10 year plan to upgrade the drainage ditches. Hog and turkey farms pay a lot more.

Back to greenhouses. Your set-up works both practically and economically. The same system as yours in my back yard would give me a fuel cost of 20 cents per plant. Not economic for bedding plants. That is why I gave serious thought to any structure before I even attempted building one.

In fact one may wonder why my particular greenhouse is so tall. Well, if it didn't work out all I have to do is put a roof and siding on it and it is a garage. The East end wall is built differently, a standard garage door will fit in it.

Well I have done all my theory this year and now the pressure is on again. Already have some plug trays planted so in a week or so I will have to find somewhere to put them.

P.S the coconut is a bust....
mylu
18 years ago
You think you go pressure huh. Come on down I'll keep you busy till May... How many seeds you sowing this year?
chris_in_iowa
18 years ago
Well last year I sowed 14112 seeds one at a time using a pair of tweezers (49 plug trays x 288 cells. I lost a tray somewhere!) Several thousand free sown in flats because the seeds were too small to see.

This year about half that as I ran out of room big time when I transplanted to six packs.

Several thousand of the plants went sraight from plug tray into the dirt. Onions for example, also the later batches of Coleus and Marigolds.

First things I am planting at the moment are onion seed, pansys, allysum, aster, calendula, cosmos etc.. Also cabbage, cauli, brussels etc.

All the things that say "can tolerate slight frost" or that say things like "When to transplant to garden: 6 weeks before to 2 weeks after last spring frost"

As you can see for the next several weeks I will be trying to prevent a heavy frost in the greenhouse, but am expecting only light frosts in there.

So far 1152 seeds planted...... Cheating with heat pads for germination though, in the kitchen.

Yep I know it is a bit odd to hope for a lowest low of 28F at night but I think I can manage a "light frost" in there quite nicely.
KellyBell
11 years ago
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, 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!..

Let's brain storm: thermal mass materials

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