At about 48 degrees North latitude, I'm about 8 degrees further north than Denver.

I am at 2,000 feet elevation. Since 1 degrees of latitude = 69 miles or 364,320 feet), I am 2,914,560 feet north and at an equivalent elevation of 5,643 feet (2914560/800 = 3643 + 2000 = 5643).

What was the question?

Oh! When I built my 180 square foot backyard greenhouse 20 years ago it was with the intention of running it thru the winter months. The greenhouse could be called by some, a "sunshed." It has an insulated north wall and roof, half of both the east and west wall are insulated. The south wall is UV-resistant plastic film set at an angle to best admit mid-winter sunlight.

I had a natural gas ceiling heater installed. This kind of heater is often found in heated garages. Before I did this, I checked with the engineers at the local utility and talked about solar-gain. They told me that heating costs should average about $20/month thru the winter. That was 20 years ago.

Plans change. I have never run the heater thru the winter and don't know if the engineers' estimate was accurate or not. It doesn't seem to burn much gas during March and April when I do run the furnace.

I forget what the angle of the south wall is. It would be different for a place 8 degrees south of here. Your hours of winter sun in Colorado are a good deal greater than here not only because of more hours of daylight but because of greater chance of cloudless days thru the winter.

I purchased 6, double-tube, 8' fluorescent fixtures for supplemental lighting. You may not feel that this is necessary.

Somewhere, I found information about sunlight at various locations throughout the US. The solar power advocates use that info to assess the value of solar power. Sunlight is very important to someone who has a greenhouse. I will see if I can come across that again. One thing I learned is that this area is abysmal in this regard. Colorado fairs better.

Nevertheless, leaving aside ideas about heat sinks etc., etc. - greenhouse glazing of any sort has little insulation value. And yet, sunlight cannot enter the greenhouse at a high angle nor from the north during the winter months.

Maybe there will be more thoughts later. The math may have sprained a brain cell, for no good apparent purpose.

Steve

I have a similar greenhouse set up as Steve, mine is 20 x 25. On the north side its a regular, insulated stud-wall, with siding and sheet rock. The east end is my garage, the west being an 8ft glass door in the middle of a 20' wall. The south wall is windows, and the south roof a double wall poly-something. A concrete floor.

Over the winter, I just try to keep the thing from freezing - I have a couple of small space heaters hooked up to control switches that turn on when the temp is 40F. They only go on when the outside temp is below 10F. The rest of the time, there is enough solar gain to heat the concrete floor, walls, etc.

In the summer, the room needs a 50% shade cloth, or its unbearably hot.

Which is a point the poly-something roofing supplier told me - in Colorado, with the altitude and amount of sunlight, the problem is cooling the things in the spring/summer/fall, not so much heating it in the winter.

I heard, via the farmers' gossip network, that there are available Federal loans to set up greenhouses - I dunno if there is any truth to that, but they do seem to be popping up all over the place out here.

Solar Energy, January

Here is a link that might be useful: Solar Maps - National Renewable Energy Laboratory