100% Solar Heated Greenhouse

 Passive Solar, Solar Greenhouse, Sustainable  Comments Off on 100% Solar Heated Greenhouse
Feb 102016
 

Where can you find a free-standing frost-free solar greenhouse winter design?

In these days of peak oil, resource depletion and wars, and worries about the economy a community needs to learn how to grow its own food, especially in winter. 

The San Luis Valley is an agricultural community that exports and sells elsewhere most of the food  grown here. Mosca and Crestone and a few other areas have organic food growing operations, and some families have successful food gardens in summertime.

We in the Crestone community are located at the end of a long highway and may be vulnerable to interruptions in food supplies, especially low-priced, good quality organic vegetables in the winter season. For this reason I have taken  an interest in finding how we can grow our own fresh vegetables in the winter. Naturally, you think of a solar greenhouse to serve this purpose.

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Photo by Paul Shippee

Cheyenne Botanic Gardens shows tall plastic columns of water employed as thermal mass that stores solar heat for long winter nights, allowing flowers to bloom in mid-winter.                                        

Therefore, in December and January I traveled around the northern valley visiting solar greenhouses that might qualify as models for a good frost-free winter design. I didn’t find much that was impressive or successful in this regard.

Yes, the commercial greenhouses at the Sand Dunes swimming pool in Hooper, the solar greenhouse dome at Joyful Journey Hot Springs, and Erwin Young’s greenhouse building at the Alligator Farm all sport exotic plants and flowers and vegetables in winter. But these free-standing solar structures are mainly heated by warm geothermal water flowing up from deep in the ground and piped under the growing beds or into the tilapia fish ponds. While the sun provides light for the plants to grow, these designs are not adequate to provide enough solar heat to support survival through the winter.

Observations I made at other free-standing solar greenhouses, such as the various grow domes and Hanna’s greenhouse in the Baca, Lillian’s Green Earth Farm solar greenhouse in Saguache, and the Haidakandi ashram greenhouse all are vulnerable to below freezing temperatures in winter.

Although these types of free-standing solar greenhouses are great for extending the growing season for all plants, they are not adequate for growing a variety of vegetables through the winter unless supplied with an auxiliary source of heat. In other words, they are not designed properly for a frost-free 100% solar winter operation in our climate. In technical terms these solar structures have too much heat loss (due to their shape), do not have nearly enough thermal mass, and their glass is not at the correct angle or high enough R-value. Also in technical terms, in contrast to this, it definitely is possible to make a 100% solar-heated greenhouse for winter vegetables.

It is worth mentioning that the type of solar greenhouse that is attached to the south side of a private home is quite capable of producing winter vegetables when designed correctly. This is mainly because the north side is coupled to the home and loses no heat, but rather can gain heat from the house when needed to keep temperatures above 40F.

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Photo by Paul Shippee

Bill and Chinle’s grow-dome showing wilted kale plants 
after deep freeze in December 2007.                                              

However, having exhausted the available resources for a free-standing frost-free solar greenhouse winter design in our northern valley I did not stop there. By some good fortune I remembered hearing about a successful model of such a greenhouse built in 1977 in Wyoming. When a solar friend in Alamosa mentioned that the Cheyenne Community Solar Greenhouse was still thriving, and was still operated under the original designer/director, I called Shane Smith and arranged a tour in early January.

Arriving in Cheyenne on a sunny Monday morning I was at last introduced to a frost-free, free-standing, 100% solar-heated greenhouse that was blooming with orchids, bougainvilla flowers and many green vegetables. The building, which also gets 50% of its electricity from the sun, is now called the Cheyenne Botanic Gardens  (http://www.botanic.org ) and is run by the city. There are six employees including a horticulturist, a development officer the managing director, Shane Smith, and many  volunteers composed of seniors, disabled folks, and troubled youth who help care for, harvest and distribute the yield.

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Photo by CBG staff

Exterior of Cheyenne Botanic Gardens in Wyoming, a 100% solar heated greenhouse showing transparent plastic glazing at 45-degree tilt angle with two long, narrow photovoltaic panels dividing the three sections.

I asked Shane Smith many questions about the design and performance of this wonderful solar asset. Heated 100% only by the sun in the harsh Wyoming climate, the greenhouse never gets below 40F (except for a very occasional 38F) in any windy winter weather, cloudy or not. I had finally found what I was looking for: a model winter solar greenhouse that really works! The transparent south roof angle is 45 degrees and Shane confirmed that he has never found a reason to modify or change it. This critical shape lets maximum full sun into the greenhouse in winter, but not too much in summer while providing enough sunlight for year-round growing. The north roof is also 45 degrees and covers an interior north walkway, two stories of office and library space as well as access to a full basement under the middle third of the building.

The key to the superior winter performance of this solar gem is the very large amount of thermal mass arranged along all of the north walls and also the lower portion of the south glass wall. These are 55-gallon barrels full of water stacked three-high and also many tall plastic columns of colored water as well. In a quick eyeball observation I estimated the thermal mass volume to be at least two cubic feet of water for every square foot of south glass. The east and west walls are solid with no windows. Two large fans high up on the north wall are necessary to exhaust warm air in summer.

Photo by Paul Shippee

Photo by Paul Shippee

Cheyenne Botanic Gardens frost-free solar greenhouse showing many barrels of water that store daytime solar heat for night distribution (thermal mass).

This free-standing solar model would certainly lend much confidence to the design, financing and construction of a frost-free 100% solar, winter food-producing greenhouse for our Crestone community, as well as demonstrate the necessary details required for surrounding San Luis Valley communities. Toward this end I have been advocating such a project to potential stakeholders such as Shumei International and other interested parties who will join together and help make this vision a reality.

Passive & Active Solar – What’s the Difference?

 Active Solar, Passive Solar, Solar Greenhouse, Sustainable  Comments Off on Passive & Active Solar – What’s the Difference?
Feb 072016
 

Passive solar heating is a name that refers to sunshine streaming through south-facing windows on winter days when the sun is low in the sky. If the long side of the house faces south and is not shaded, and the windows are large, a substantial portion of the home’s winter daytime heating may be supplied by the passive solar gain effect.

Passive solar is so called because solar heating directly through south windows in winter does not need any mechanical devices – electric fans or pumps – to deliver the solar warmth into the house space.

Of course, larger south windows will deliver more sunshine to the home’s interior rooms. As larger windows are deployed, two problems arise that need attention. First, in a well-insulated conventional home, larger south windows will cause the rooms to overheat. Second, during long cold winter nights these large double-glass windows will lose a substantial amount of heat to the outdoors.

Passive Solar Homes
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However, these situations have practical solutions. The problem of daytime overheating can be mitigated by adding thermal mass  – earth materials, concrete, or large containers of water – to the interior spaces or solar greenhouse areas. And the problem of nighttime heat loss may be mitigated by adding moveable nighttime insulation to the large window areas. Both of these solutions cost money and they involve aesthetic and architectural concerns.

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Active solar heating is a term that refers to the use of electric pumps or fans to move the sun’s heat to the interior of the home or building. The sun’s heat is collected by solar heating panels mounted on the roof or on the ground, then transferred to a thermal storage tank of water or to a thick radiant concrete floor slab. This is achieved by circulating liquid or air heat-transfer fluids from the collectors through copper pipes or air ducts to thermal storage. In air systems large bins of potato-size rocks have also been used to store solar heat for later delivery to the heated spaces in the home.

Active solar heating systems fulfill the four system functions of:

  1. solar heat collection
  2. transport of heated water (or air) to the interior of the home
  3. storage of the solar heat, and
  4. distribution of the solar heat on demand to areas that need it

 

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These solar thermal collector panels (used to gather the sun’s heat) are typically 4’ x 8’ insulated flat boxes with a single glass cover and a blackened copper tube and fin absorber plate inside.

Active solar heating systems are popular for heating domestic hot water as well as for space heating. The many possible configurations of active solar installations require a skilled designer to size and integrate all the components – collectors, pipes, pumps, tanks, automatic controls – into a smooth, efficient, reliable, and durable home heating system. To achieve optimal performance and cost, a skilled installer trained in solar system options and behavior is also required. Solar training classes, solar home workshops and ebooks are available at http://crestonesolarschool.com or http://coloradosunworks.com for more in depth information.