Need feedback on a solar greenhouse - cold weather, low heating reqmt

[WookinPaNub]

Hi all,
I originally posted this in a aquaponics forum, but in retrospect the portion of the design I need help / feedback on truly relates to effectively the greenhouse portion of it. My intention is to have a good sustainable year round production, in cold weather, with minimal heating. Sounds challenging doesn't it I have a design that I believe will actually work, and would like to get other folks thoughts for sanity / potential improvements.

For the purposes of this discussion, assume this house will be in the Woodland Park, CO area at roughly 7500 to 8500ft elevation. Even on the shorter days of the year in December I can still get about 9 hours of daylight from sunrise to sunset. The back of the Solarium / greenhouse will be backed against my house and it will be facing due South.

I'm going to break this into a couple of posts given the amount of content. I'll be as concise as I can, so bear with me.

This design leverages a lot of super insulation / passive solar concepts that I am leveraging in other areas of my house design. My apologies to those already familiar, but I have to assume not everyone is just in case.

This solarium housing the AP system would now be brought into the thermal envelope of the house. The house itself is built on the concept of super-insulation or (similarly) the European PassivHaus approach that really started it all. This would be extended to the Solarium with some minor differences.

For background, the house is designed to have R15 insulation under the slab / Below grade walls. Above grade walls are R40. Roof is R60. This goes hand in hand with an extreme attention to air sealing. Ventilation is handled by an HRV (heat recovery ventilation) to preheat fresh air brought into the space given the 'tightness' of the house. The solarium would have all these characteristics minus the super tight air sealing and HRV - I need fresh air in that solarium to some extent and an HRV for that area would be overkill IMO. As an aside the house, if constructed properly, should require about 2 hair dryers worth of energy to heat. The solarium moreso given it's not as 'rigid' in its construction, but still significantly less than normal.

In conjunction with this is passive solar heating, both through knowledge of the angle of the sun at different times of the year, thermal masses to hold and release heat as needed, and supplemental hot water solar collectors to bring in additional heat. It sounds like a lot, but the work is really in the initial construction. Once done the operation is basically running pumps / fans (low energy cost).

These are the foundation concepts, now to apply them into this design. On to post #2.

 

[WookinPaNub]

Here's an updated layout picture: NOTE: The first picture says 'Side' and should say 'Front' - sorry 'bout that.

Design aspects:
1) R15 / R40 / R60 insulation as described in the prior post, except where windows are. Even Venting doors would be insulated.
2) Windows would be some form of double glazing, fixed to reduce air infiltration.
3) Venting doors positioned in the lower center to draw cooler air in and through natural thermodynamics vent hotter air out the sides at the top. A ceiling fan would supplement as needed.
4) Still retain 4 'Bays' and the number of GB (Growth Bed) stay the same. However the number of FT (Fish Tank) in each bay drops from 3 to 2 (per earlier recommendations on safer balance / ratio). Third tank is now used as a hot water tank for thermal mass and heating the other 2 FTs (and also therefore the GBs with the water).
5) Hot water solar collector is attached to the vertical face of the solarium. This orients optimally for a winter sun angle (as winter is the time I need to produce that heat) and maintains a low profile against the building aesthetically.

Positioning of the fixed windows is critical as explained in #3 to follow....

 

[WookinPaNub]

The windows in the pictures are not drawn to scale but hopefully the concepts will come through. The design of the locations of these windows is critical. I need to minimize the amount of window sq footage (given windows will be the most heat loss in the system) and yet optimize the amount of light getting to the plants. And yet protect them from the burning summer sun. It's a bit tricky, but this seems like it might work. Here's the picture for talking points:

(Assumes Woodland Park, CO for this example)
1) Highest 'summer' sun angle is 66 deg. Too strong for direct contact on GBs
2) Median 'fall' and 'spring' sun angle is 45 deg
3) Lowest 'winter' sun angle is 20 deg

I think with proper window sizing / positioning, and a lot of high school math I've forgotten, this would work as reflected in the above image.

For summer, the sun comes into the solarium and shines primarily on the walkway between all the growbeds (not directly on them). The front window also allows indirect lighting in. Vents are open as needed, same with fan. HWSC is shut down.

In Spring / Fall as the sun moves a bit lower, the softer direct light hits both beds through both windows. Vents are opened as needed, HWSC still shut down.

In winter, the upper window has an insulation 'block' put in place from the inside of the solarium. There is limited sunlight through that area at that time of year, and most of the heat is lost through the ceiling of any structure. EPS comes in 6" thicknesses and could be used to fill in that space and give an addtl R-22 to the window area. Not a R60 like the rest of the solarium roof, but still much better. Vents are closed. HWSC are running during the daylight hours and heating the HWT in each Bay. This dedicated thermal mass heated daily may / should be enough to keep the overall Solarium in a productive temperature. Front windows could have simply heavy insulated curtains drawn at night, or at the upper end a louvered insulated shutter system. R value not as good as what is done with the upper windows, but wall areas lose less heat than ceilings so probably proportional am guessing?....

And finally what each 'Bay' looks like in more detail in #4....

 

[WookinPaNub]

Each Bay then looks like this:

Each bay then has 3GB and 2 FT. The middle tank remains, and is connected to the other two fish tank with a screened pass through pipe both high and low (there is a reason for this). The middle tank now takes on the role of a hot water tank in winter and general extra overall thermal mass to the system.

In wintertime the hot water solar collector (closed system) takes heat water and through a simple pex coil in the HWT performs a heat exchange into that tank. This will heat that tank more rapidly than would be desireable with the fishies I am guessing, so there are no fish in this tank. That heat is then shared with the adjoining tanks passively via natural convection (hence the upper and lower pipes). As the HWT heats, that heat rises in that tank, pulls in cold water from the adjoining tanks via the lower pipe, and as a result starts pushing warmed water into those adjoining tanks through the upper connecting pipes. Natural convection, doesn't cost a thing, and will end up gradually heating the FT without such a dramatic temp increase.

All 3 IBC drain pipes will be connected and will lead to a single pump. Pump then feeds and index valve and will F&D each GB individually. Plenty of water to prevent draining any FT, and water warmed in the HWT now feeds into the grow bed in addition to just the natural heat radiation to the air. Hopefully this keeps the air and water temps close enough to prevent undue condensation, especially given the super insulation of the room.

Some closing thoughts in #5....

 

[WookinPaNub]

So summary thoughts / perspectives:

- Up front cost certainly more, however these are concepts / materials used in the remainder of the house. I would consider it an extension of the investment
- Manually adding / removing insulation to the windows not overly ideal, but realistically only required during winter season
- System, if properly designed and constructed, actually seems to be fairly low maintenance. Again, looks like addtl pumps and plumbing as the primary additions
- With the thermal masses in the system, substantial insulation, and passive solar supplemental heating(winter only) this design seems like it should keep a pretty good temp in the system overall. I believe warm enough even in the winter for continued veggie / fish production. There's a lot of concrete, a lot of water thermal mass, and with the walls painted white it should reflect any light I get through the windows.


So......... all that being said, it's all still design in my head. The concepts have been around for quite awhile and seem to be quite effective, just a different way of applying them all together. With that being said, I'd love to get some feedback on the feasibility of the system or potential optimizations. Think this will work? Is it overkill and can be reduced in some fashion? Specifics are good, alternate ideas appreciated!

 

[lighthawk]

Wow. Looks to me like there is going to be a HUGE investment in time and money involved in this project. Trust me I am no engineer and I don't know where Woodland Park is but I live in Michigan and I couldn't even think about a similar project without a back up heat source that might have to keep things warm weeks at a time. Cold as it gets here I couldn't even consider going overnight without backup heat or I would have frozen and busted pipes.
One thing I do know is that when you think you have thought of everything put the plans away for a week. Drag them back out later and look them over again and ask yourself... What can go wrong here?
I changed my chicken coop design 9 times before I built it and there are still some things I would do differently.
Good luck to you and again welcome to TEG.

 

[WookinPaNub]

I was born and raised a little south of you in Ohio

It will be a big investment, no arguments here - and I don't want to get it wrong! My rationale for this design is twofold: First is that the remainder of the house is of a superinsulated / passive solar design so building this extra addition to that will be straightforward for the builders in labor and materials. Second is that I am more willing to put a large initial investment for long term minor cost / maintenance.

The heat source, outside of the thermal mass inherent in the solarium / greenhouse, is the hot water solar collector hydronically heating the space. The backup heat source (as this house will most likely be off grid) will be a diesel generator that will generate the electricity (for the whole house) and the engine heat will be captured for heating the house hot water storage tanks. I don't want to take the chance of losing what's in there either

What I am concerned about is
a) that I can get enough light to my plants all throughout the seasons (maybe diffusers or reflectors) with the limited window space
b) that I have enough ventilation to keep it from overheating in the hotter months

Any other ideas / revisions please let me know. I had also looked into SCHS when I started this design, but that is also a decent investment and still requires more active heating solutions in the coldest months. If there are other ideas that will meet my needs and goals, I'd love to hear them! I've gone through a number of revisions to get to this point and welcome further optimizations! Thanks!

 

[chris09]

WookinPaNub,

What is your glazing (roof) angle going to be, have you figured that up yet?
Your wanting maximum winter sun, correct?

Chris

 

[WookinPaNub]

Soprry for the late response, was remote out of town.

Winter sun is important, yes. I have not done the math on the roof but was initially thinking the following:
1) Shallow pitch
- Allows greatest headroom in the space
- Need to ensure the front overhang blocks direct summer sun but allowing other season lighting in as needed
- Accomodate the larger wall windows (see next bullet)
2) Windows on the walls to be larger than those on the roof
- Allow more winter sunlight in for both front and rear bays in the space
- Less heat lost through walls vs ceilings, so safer to have larger windows on the walls

What were your thoughts?

 

[chris09]

Soprry for the late response, was remote out of town.

Winter sun is important, yes. I have not done the math on the roof but was initially thinking the following:
1) Shallow pitch
- Allows greatest headroom in the space
- Need to ensure the front overhang blocks direct summer sun but allowing other season lighting in as needed
- Accomodate the larger wall windows (see next bullet)
2) Windows on the walls to be larger than those on the roof
- Allow more winter sunlight in for both front and rear bays in the space
- Less heat lost through walls vs ceilings, so safer to have larger windows on the walls

What were your thoughts?

Lets start with this,

If you have to little or to much angle you can reflect more winter solar energy than you would be adsorbing.

The greenhouse glazing (roof) should be properly sloped to absorb the greatest amount of the sun's heat in the winter. A good rule of thumb is to add 10 or 15 to the site latitude to get the proper angle. For example,I am in Hartville, Ohio at latitude 40.99 north, the glazing should be sloped at a 50 to 55 angle.

Also by having larger glazing on the side walls than on the roof you will have plants growing more toward the glazing on the side walls than the glazing on the roof and then you will be turning your plants more often.

Chris