Chena Hot Springs is working toward becoming a self-sustaining community, and an important part of making this vision a reality is to strive for greater independence in food production. Chena installed a small test greenhouse in 2004, which has operated year round and is heated entirely with water from our geothermal resource. One January, we were able to maintain the standard greenhouse temperature of 78°F while outside temperatures dropped to -56°F, which is typical for Interior Alaskan winters. This 134°F temperature differential was the largest recorded for any controlled environment production facility in the U.S.
Chena has recently added to its controlled environment facilities with the construction of a new 4320 ft2 greenhouse to provide our restaurant with a greater variety of fresh produce on a year round basis. Crops planned for the greenhouse include tomatoes, lettuce, green beans, peppers, cucumbers, and numerous other greens and herbs. Chena Hot Springs is also working in partnership with the University of Alaska Forestry and Agriculture Experiment Station on a controlled environment research project for investigating the opportunities of establishing similar projects throughout the State of Alaska, using geothermal or other waste heat streams.
To download the Chena Fresh fact sheet click here.
To download a document discussing the economics of greenhouse gardens in Alaska click here.
Original Greenhouse Project:
Chena erected its first greenhouse, a converted hoop house located next to the outdoor Rock Lake in the summer of 2004. This 1000 ft2 structure was a test installation to determine if growing conditions could be maintained year round utilizing the geothermal resources here at Chena Hot Springs. During the winter of 2005, we experienced outside temperatures as low as -56°F. At the same time, we were able to maintain an interior greenhouse temperature of 78°F. The hoop house is divided into two areas; an 800ft2 grow area and a 200ft2 air-mixing area. A 2" radiant fin tube is used around the perimeter of the grow area. 165°F water is pumped from one of the geothermal production wells through the fin tube. The same water is also pumped through a radiant air exchanger in the air-mixing area. The water from both heat sources is then returned into the outdoor Rock Lake. The exterior of the hoop house is 6 mil greenhouse poly-film. A second layer is added on during the winter season. Warm air from inside is then blown in between the layers to inflate the roof and end walls creating an insulation of warm air. Cold air in the winter season is drawn into the air-mixing area and mixed with the warm air from the radiant air exchanger. The warm air is then transferred into the grow area via a ventilation tube. This method prevents any cold air from coming into contact with the plants. A heated arctic entry is also used to prevent large amounts of heat loss or too much cold air from entering at once.
New Greenhouse Project:
In our new greenhouses, the concept of the hoop house was taken one step further once we had demonstrated successful results in the original house. Two Poly-Tex, XA-300, gutter-connected greenhouses, with a total area of 4,320ft2, were erected on a radiant heated concrete slab. The same 165°F water is pumped through the concrete slab. Each 30' x 72' greenhouse has its own environment controller and is maintained at different temperatures. One greenhouse is used for growing hydroponic tomatoes. There are approximately 450 tomatoes consisting of six Dutch varieties; one cherry tomato variety, one grape tomato variety, one beefsteak tomato variety, and three intermediate cluster tomato varieties. These tomatoes are grown using a Dutch technique in Dutch buckets with perlite and drip irrigation. The other greenhouse is used for growing hydroponic lettuce using a NFT (Nutrient Film Technique) bench system. This bench system is capable of growing approximately 2,000 head of lettuce on a rotating schedule, producing approximately 100 head of lettuce per week. The nutrient solution is monitored and adjusted by its own controller also. We are currently growing four different varieties of lettuce and plan to add a few more varieties and some herbs. We recently completed Phase II of the new greenhouse project. This phase includes two aspects; additional heating for the winter season and a 28' extension to both greenhouses. Radiant fin tubes will be added along the perimeter of each greenhouse. The 28' extension will work in the same way as the air-mixing area of the hoop house. This extension will also be utilized as a work area, display the current projects in the greenhouse, and offer public viewing into the grow area.
REVISED DEC 18, 2015 3PM DF