Sunday, February 22, 2009
I find something satisfactory about receiving 2 feet of snow yesterday and then entering our new greenhouse today only to find all our plants thriving. Outside the temperature was hovering around 29 degrees, but inside the greenhouse this afternoon the temperature was over 70 degrees. This is the first year with our greenhouse in operation. We have been outfitting it to grow an abundance of edible food and remain above freezing without additional heat all during the winter.
To grow food we have a couple of planters that we filled with cold hardy crops. So far we have been eating radishes, salad greens, chard, mountain spinach, broccoli raab, and a few herbs like mint and cilantro. To keep things going we have been starting a bunch of new seeds of kale, lettuce, arugala, mtn. spinach, and more fresh cooking herbs. Soon we will begin starts for the ourdoor garden.
Without extra heat we have been choosing crops that can handle the cooler night time temperatures. But to moderate the extreme cold of the night we have added a few extra features into the greenhouse. First off, the greenhouse is insulated on the east, west, and north sides to buffer the cold and keep the warmth in. In addition to the insulation we have added a lot of thermal mass. The walls have a thick layer of adobe mud over the insulation to heat up during the day and radiate the heat back at night. Along with the adobe walls we have added a lot of water storage: (2) 40 gallon barrels and (4) 20 gallon plastic totes. Together this worked well to passively heat our greenhouse at night, but we found we could still improve upon it.
During the day the temperatures were heating up to over a 100 degrees on a sunny day. So we added a cheap bathroom vent fan connected to a cheap thermostat. Now when the temperature gets over 65 degrees we suck the hot air from the top of the greenhouse through some coils in the 40 gallon water barrels. This acts to both cool the inside temperature and store the heat in the water to be released at night. With the vent system, I have found that the water barrels can heat up to 60-70 degrees on sunny day even when the outside temperature is close to freezing.