GHAT/compost heated greenhouse?

So I am planning to build a plastic covered hoop house for raising chicks.  The hoop house will be 20' x 52' x 8'.  I need an efficient way of keeping chicks warm and proper ventilation is key since they produce a lot of ammonia.  Since I am placing the hoop house on top of my drain field, digging down and installing a climate battery is not an option.   So my plan is to use a linear compost pile outside the house that runs the length of the greenhouse (40-50' long).  Then blow compost heated air into the house to provide both heat and fresh air.  This will also create a positive pressure in the house so ammonia filled air can escape.  The intake for the system will be outside drawing in cool fresh air in winter, circulating that air through the compost pile via pipes and heating it and discharging into the house using inline duct fans.  My question is

1.Do you think rigid metal 6" duct will hold up under the weight of the compost?

2. How much duct work would I need to effectively heat the air to reasonable temperature?  

I believe smaller diameter and longer duct work would work better but I can't find any calculators or articles illustrating how much is needed.  I have seen the compost heating designs using piped water but most of the designs show the water discharging into a large barrel to allow the heat to warm the greenhouse and I don't know if that would work on a larger scale.  Plus the circulated water doesn't give me air circulation.  Any thoughts would be appreciated.

Hi Jeff welcome to Permies!  I think some of the GHAT piping systems could be a good place to start.  I think they use 4" plastic corrugated drain tiles (perforated in that application) about 50' long.  And I'd presume they're trying to transfer 100 degree air into 50 degree soil.  Looks like you're in a warm area so maybe you could predict that your winter situation would be 140 degree compost and 40 degree input air.  So maybe you could handle 100' of pipe to get full heat transfer.  The issue though would be "freezing" the pile with the cold air...  Depending on the size of the pile of course...

So to answer your actual questions, I'm thinking metal pipe would possibly rust, crush and/or not be very easy to work around when you try to turn or add compost.  

I think 100' would work but only at slow flow (GHAT divides the air among many pipes 50' long).  So to heat a whole hoop overnight it may be impractical.

Side note, I've heard you don't want to build up the soil level over a drain field because it changes the conditions for the microbes in your drain field.  18" down there's X amount of air, 36" down it's a different amount of air and the bugs may get sad.  

Welcome to permies Jeff!

We have a small brooder with an attached run that we use for ~130 day old meat chicks until 2-3 weeks of age. (brooder maybe 10ft X10ft max). I'm concerned that you seem to accept that there will be ammonia-filled air as a given. My current system uses layers of jute coffee sacks I get really cheap from a local organic coffee company. I add an extra layer based on age, where they've pooped the most, and I try to do so *before* I start to smell anything. We have a fan for circulation and open a sliding window after 3-4 days as we're reducing the temperature, but the window's only ~10 inches square. By 2 weeks we're opening the pop-door first during the heat of the day and gradually longer. We usually move the largest chicks to a portable shelter on grass at about 2 1/2 weeks (weather dependent), which decreases the density in the brooder to accommodate chick growth. If things work out according to plan, I don't remove any sacking until the birds leave so that I don't put mold into the air. If the weather causes a problem, I'd chase all the chicks into the run, remove some sacking, put fresh sacking on top, let any dust settle for at least 1/2 an hour, and then let the chicks back in. If the birds are reticent to have "outdoor play time" I remove their indoor waterers to encourage them! I also have a hanging basket outside which I fill with greens from the garden to entice them out for exercise, fresh air, and sunshine.

The key things is that the birds need plenty of warmth for the first few days, but then you need to be able to reduce the temperature. We vaguely follow Joel Salatin's chick temp chart which starts them at 92F for days 0-4 then reduces about a degree F each day for the next 4 days, then 4-6 degree F each day for the next 5 days or so by which time their bedding and bodies are usually generating all the heat they need. That can be accomplished by having more enclosed areas for "nap time" and "bed time" when they need more warmth - when they're running around eating and looking for interesting things to peck at, they don't need as much warmth. If you watch a mother hen managing a gaggle of chicks, that's what she does - lets them run around then tucks them under her feathers for a nap.

So hopefully what you're getting out of this is that you need zones of warmer and cooler spaces, and a way to manage how much heat from your compost is going where you want it/need it the most, and some sort of back-up system if you don't get your pile hot enough for those critical first 4-8 days.

Jeff Siewicki wrote:

1.Do you think rigid metal 6" duct will hold up under the weight of the compost?

2. How much duct work would I need to effectively heat the air to reasonable temperature?  

This article should help you understand the heating power of a compost pile.
https://smallfarms.cornell.edu/2012/10/compost-power/

For a brooder house a reasonable size compost pile seems possible.
Using a closed loop water line also seems like it could be used effectively in the different heating zones you set up.