Thermal Mass

[Jeremiah Robinson]

Our last discussion sort-of veered in the direction of thermal mass, so I thought I'd start a new one in that vein.  

Beyond barrels of pressurized ammonia, how else can you harvest and store heat in your greenhouse?

[Max Gfx]

I got overwhelmed with notifications on the previous thread and missed the part on pressurized ammonia. Good grief, I guess I'm glad I did. Honestly, I can say that I've never heard of such a notion for thermal banking and I'd never even consider it. There is such a thing as "fixing it until it's broken" (a'la Michael Jackson's face)...Water gives off 1 BTU, per pound, per hour. Air conditioning is the process of heat removal. If you have weak insulative qualities, your heat removal process is going to be accelerated and that 1 BTU per pound, per hour, is gonna result in a boatload of BTUs being given up...No matter how you slice it, whether it's evaporation or heat loss, it's all about the insulative qualities.

[Jeremiah Robinson]

Hey Max,

I think that you could make the argument that there's a cost/benefit to any of these thermal management strategies.

You can insulate and air seal a ton, but there comes a point at which it's no longer cost effective to do more.

At that point, I think that things like thermal mass make a lot of sense.  Many of the options (such as barrels full of water) are very cost effective, perhaps more-so than greenhouse improvements.  

The ammonia comment was a joke initially, but the more I think on it the more I think it might have an appropriate application if you could guarantee safety.  I don't think anyhdrous ammonia is that expensive, though I could be wrong.

[Jeff S]

I'm re-engineering and enlarging my system this summer with retaining heat as priority one. I'm curious about as you said what is the practical limit to insulation? I'm running 2" pipe just underground and using IBCs for FTs and GBs. I plan to use Styrofoam insulation. What do you feel is a good thickness for this.

As soon as I can get my wife off the other computer I'll attach the plans for suggestions and constructive criticism. 

[Jeremiah Robinson]

Hey Jeff, 

If you haven't yet read through my blog, read up.  It's all about this stuff.  I'd be happy to help with questions that arise.

[Jeff S]

Finally got tired of waiting for wife's computer so I'm sending from my office. Please critique this plan.

[Jeremiah Robinson]

Hi Jeff.  

Great sketchup!

As a basic white-box design it makes sense.  What you have here is a CHOP system.  A CHOP 2 system would be more reliable.  Check out Practical Aquaponics for this.

Another way to kill more birds is to lower your raft bed (or raise your media beds) and use it as a sump tank. Having the water flow through the media beds before entering the raft bed/sump will help with filtration.  This could also make it so you don't have to bury your sump.

As a cold weather guy, I'll always encourage you to reduce the surface area in which to lose heat.  Using a flood-drain system would eliminate the need for a sump tank, thus saving energy.  Here's a link to a description of one trial that shows it giving faster growth.  

Here's a link to my post about the four types of systems.

[Jeff S]

I like the idea of not digging for the sump and using the raft bed makes good sense. I watched a video from MPHGardener where instead of a floating raft bed he just laid the styrofoam top on the edge of the bed and eliminated the air/light gaps but that would require constant water height so some sort of sump would be required. Chances are I can avoid the digging since the sump would only need to be about 100 gallons for the 2 GBs. Here's another idea to cut back heat loss: Can a media bed be totally flooded and covered with styrofoam like a raft setup and still function as a biofilter? It would eliminate all that surface area.

[Jeremiah Robinson]

Yep.  That's how I do.  See below.

If you do constantly flooded beds you could keep your same design and avoid a sump as well.

[Jeff S]

1. Is there media in your beds?

2. Is this a Sketchup drawing and if so how do you do the plumbing?

3. Can the indexing valve setup be added easily at a later time?

4. What temp do you keep the GH at in the winter?

[Jeremiah Robinson]

Hi Jeff,

1. Yes.  It's called rock bark - like hydroton but 1/10 the cost.

2. Look for "plumbing elbow" on you-tube.  There's a tool that makes it easy.  Making pipes is just about using the follow tool.  That's also easy to find on you-tube.

3. It can, but if that's where you're hoping to go you'll want to start with a beefy, reliable exterior pump like this one.  Also, one of the benefits of a system like this is no sump.  To reap that benefit you'll want to avoid making a sump in your initial design.

4. Ah, you fell into the trap that so many aquapons (even commercial aquapons) fall into that costs them so much energy.  Luckily you haven't bought or installed a heater yet.  Read through the posts on enthalpy (number 1 and number 2) and you'll hopefully see why (in my opinion) heating your greenhouse is unwise. The only air-heat source I would consider is one that's free, such as the output from your home's bathroom exhaust or ERV.

You're asking great questions.  It's awesome that you're thinking through this before you break ground.