I have a HFGH 10x12 that has 500 gallons of water storage and a section of radiator to extract heat from the ceiling and pump it into the tanks during the day. I hate to sound like gloom and doom, but even this is not enough storage to maintain the temps in there....it does help to keep the temps from fluctuating too quickly. Items with a higher density may help, but you still need a way to actively transfer heat to/from them.

I have 2 1500 watt heaters running at night in there to keep everything from freezing. They are set at 36 degrees and will run for most of the night when the temps go into the low 20's. (That's about $8/day in electricity!!!) I can't imaging how much it would cost to keep it at 50!!!! During the winter days, on a good sunny afternoon, when it's in the 30's out, I'm lucky to get the inside temps to be in the low 50's...it just isn't enough of a temp delta to get the tank to absorb any heat. Currently, the water temp is around 37-39 degrees....

Don't get me wrong, I love my HFGH, but it's is not energy efficient. I insulated the north wall and ceiling and it has helped a bit. If you're in a fairly cold zone like I am, my personal opinion is to not go through the expense of keeping one of these heated over the winter.

Here is a link that might be useful: my HFGH 10x12

Hi lori lee,
The one in the link is almost worthless to be honest,there just isn`t enough mass or enough flowrate to produce useful results.

yeah, that's what I thought. Probably why no one has done it. My greenhouse is also the hfgh 10x12, a Christmas surprise from my husband. I know he didn't count on doing all the modifications I am learning about here, but it sounds like they are necessary. Last year I experimented with self irrigating planters made with 5 gallon buckets, and an Autopot that did remarkably well, but I wanted to extend the growing season, so now I guess I get to. I always thought it would be nice to grow my own bedding plants, so I imagine I will be doing that as well.
I think I will take web4debs advice and not try to heat it during the winter. I have Eliot Coleman's book "Four Season Harvest" coming, so maybe I can implement some of his teachings in my new greenhouse.

A heatsink will work quite well if you make it large enough and have sufficient airflow to drive it. If you get a few hours of winter sun its worth the investment. It also works as a cooling system during the summer months.

I put 400 litres of water in my green house 15'*8' maybe. I found it lost heat in parallel with the outside temperature until it hit freezing. Then the inside temp held at 0C. Well on a bad day -0.5c. That was good enough for tomatoes, geraniums, minature roses, and a variety of wintersown starts. The only loss to freezing was some sub arctic plentys that sprouted just before a cold snap. I could tell some plants weren't happy; but, they lived.

I started wintersowing as my potting mix thawed and put the water in when the warm days out numbered the cold. (I didn't want to split my rain barrel.)

My floor area is about the same as a 15x8. I have around 28 tons of clay soil for thermal mass. Its beneath the floor so it doesn`t need any greenhouse space and makes quite a difference.

{{gwi:286476}}

hex2006,
Now that certainly peaks my interest. From what little is shown of the perimeter framework on your greenhouse, it appears to be a geodesic dome design. Would you care to share more construction images of how the passive solar air collection system is constructed and an explanation of it's operation?

Does the collection system rely upon any mechanical means for distributing warmed air - to be effective during the colder months? Does the central air plenum shown in your photo, serve as the primary air exhaust and if so, how are the ends of buried hose treated? Or, do they simply bend into loops and return back to the hub?

What did you use for the glazing panels and how are they attached to the metal framework? What flooring material did you select for use as a conductor? How is the foundation perimeter insulated and how deep does it extend below grade?

Sorry for all the questions, ;)

It would seem to me that a workable "heat sink system" is expensive, complex and time consuming to build, especially in zones colder than 7.

It would seem to me that the same investment should be in insulation (triple glaze?). The payback may be greater.

I have great doubts of any system which involves air movement inside a greenhouse because that will increase heat lost significantly.

dcarch

Hi Archdiver,
Its a geodesic of my own design,a small version of the Eden Project. Its glazed with air inflated "pillows". The perimeter insulation (2" xps) extends to 2ft deep.
The plenum serves as both inlet and outlet and has an addition feature that allows some or all of the air to be looped underground without being released back into the greenhouse. It increases the efficiency for a fixed amount of tubing, 172ft in this case.
Hi Dcarch,
Ideally any greenhouse should be thermally efficient no matter what heating solution is used ;)
It want expensive to install the heatsink but it did entail a fair amount of digging. The fan only runs during the day when there is surplus heat available. The heat is stored and released passively at night. The mass acts as an insulated 28 ton brick thats warmer than the air.
Heat is transferred evenly into the brick using this buried subsoil monster.

{{gwi:286477}}

Fascinating!

So, as I understand it, the 16 (+-) holes along the top perimeter of the hub, serve as air intakes - drawing cooler air off the floor by convection. This cool air would then sink and flow through each looped hose, where it (theoretically) collects warmth from the soil heat sink, or "brick" as you put it. The heated air then rises through the central chimney, is circulated throughout the greenhouse and drops to the floor when cooled, to repeat the process.

This following statement however, implies that the air is not recirculated:

"The plenum serves as both inlet and outlet and has an addition feature that allows some or all of the air to be looped underground without being released back into the greenhouse. It increases the efficiency for a fixed amount of tubing, 172ft in this case." Please clarify.

How cold does it get in your area of the UK and do you maintain plants over the winter? If so how effective is it?

we`ve been down to -8C this winter so not as cold as some places. The driving force is the sun so air tempering is probably a better term than "heating", it tends to conjure up images of propane heaters and the like :)
Air is drawn down the center of the plenum where it meets a cone deflector which directs it into the 15 lower tubes.
The air travels through the lower tubes and back towards the plenum.
The recirculation feature is located at the point they reach the plenum and the air is either drawn back into the intake or directed to the outlets which are the holes at the top.
The heat collection (and cooling)process is driven by a 700cfm 10" duct fan, variable speed controller and a differential thermostat. I sized the fan to provide upto 45 complete airchanges per hour for experimenting but 10-20 would be quite reasonable. The greenhouse is 9.5ft high with a volume of about 900cubic feet.
These were the results of some tests i did using different fan speeds,the soilmass temperature was 13CF (55.4F)at 3.5ft deep.
200cfm intake temp: 28C (82.4F) Outlet temp: 13C (55.4F)
400cfm intake temp: 30C (86F) Outlet temp: 15C (59F)
677cfm intake temp: 30C (86F) Outlet temp: 17C (62.6F)

This is how I am doing it this year.

I only have enough room on my McSuburb parcel to have small-scale structures, so this year for experimentation one of the things I have is a 4 x 6 coldframe (walls insulated at ~R-5) with a below-ground insulated structure, a water-tubing subsoil heating system and ~30 liters of water for thermal mass. The glazing is 8mm twinwall polycarb at a 30º angle and at night I cover the glazing with an old sleeping bag.

Further, I take some of the heated water and put it in the soil, which is insulated @ R-6 - down to 10" in a raised bed next to the house. Despite numerous days with highs in the single digits F (-15ºC ) and several lows well below 0ºF (-25ºC), last time I checked my soil was 64ºF in the sun and 58ºF in the shade (~18ºC and ~14ºC). Air temps during the day always need to be vented on sunny days and at night I have never dropped below 35ºF (2ºC), even on the night we hit -14F (-26C). So my dark-colored water and soil are my thermal masses.

So, to reinforce anecdotally what is above, IMHO the original link had inadequate mass to keep from freezing for that volume. The glazing insulation is important. Any text on solar houses or solar greenhouses spend considerable time on solar access and solar mass, as well as insulating the glazing at night and opening the glazing to the sky as soon as the sun is up. For example, right now the coldframe has heated up ~4ºF in 3/4 of an hour's exposure despite cloud cover allowing only ~40% of the expected cloud-free solar radiation through. The sun is free energy. We must do more than just collect it to make it work for us. We must store it, distribute it, and insulate our glazing.

Dan

Interesting looking "UFO" thing :-).

Do you have a way of evacuating water if the tubes get flooded?

dcarch

Hi Dcarch
It was strange looking beast before i buried it :)
To avert any potential flooding disaster i installed a 9000LPH (~2400gal)automatic sub pump with float switch in a sump below the plenum (more digging). The water will never make it up to the lowest tubes as the float switch kicks the pump in when the sump is half full.
It only runs once in a blue moon :)

{{gwi:286479}}

I am just finishing my 10'x20' solar greenhouse which I have previously talked about on this website. I buried 100' of equal length perforated ADS pipes on top of the rock and clay and covered them with 14" of 1" clean rock. They begin in a barrel plenum which has a fan mounted on top and inside a 6" galvanized duct that extends nearly to the ceiling. The north wall is buried in the hillside and insulated, constructed of concrete filled block and painted black.

I intend to add 1,000 gallons of water storage to collect my daytime BTU's as well as to even out the temperatures. I'm going to either build beds on top of the water containers or go to hydroponics.

I'm at 7400' elevation in SW Colorado and the sun's intensity is incredible. Without that fan running the temperatures are 100+ degrees but when it's operating the building is at 80-82.

This morning, the outside temperature was 12 and the greenhouse, 40. With water thermal storage and doubling of the plastic glazing, I'm confident it'll never freeze with the exception of one scenario: a 3 or 4 day snowstorm with little sun followed by the evil evening when it clears and the temps drop to well below zero, a twice or thrice a year occurrence here. Thus, I've provided wiring for a thermostat and heater.

I'm going out right now to plant a few things in pots. I have one 65 gallon container of water in place and will use left over polyethylene to envelope these new plantings within the greenhouse. This should even out highs and lows the seedlings will be exposed to.

Mark Mahlum