Passive Solar Gain From Attached Greenhouse

Yesterday we gained some heat from our attached greenhouse. When the sun shines, the greenhouse gains heat, and when it is warmer in there than in the house, we open the door and let the excess heat rise into the house.

This works because the interior door to the greenhouse is in our basement. When it is opened, heat thermosiphons into our house, in a manner of speaking.

The benches in the greenhouse are at grade level, which explains why from the exterior the greenhouse seems like it is built for very short people. When you enter the greenhouse from the basement you have to climb a couple of steps.

There is no need for illuminating underneath the benches, and that part of the greenhouse is underground, unexposed to the elements.

The insulated roof keeps heat in during the winter and the sun’s rays out in summer. The vertical glazing wall reflects the steeper rays of summer sun and admits winter rays. Plus the overhang blocks rays in the summer but not at the lower elevation of the sun in winter. We don’t use the greenhouse in the summer except sometimes Vidya seals gourds in there when it is raining. It has openings at both ends for natural ventilation.

The minor tradeoff on preserving heat and helping cooling, the two energy hogs of greenhousing, by using vertical glazing, is that new seedlings in flats will lean toward the light source and need to be turned occasionally.

When the greenhouse is cooler than the house in the winter, we leave it closed but it has never frozen. Being half in the ground, it tends to go to 55 F (15 C) as that is the steady temperature of the earth.

The floor of the greenhouse is almost a meter thick of gravel, which acts as a heat sink. It absorbs excess heat when air temperature is warmer and radiates it when air temperature cools. There is drain tile below the footer of the house so drainage is no problem.

We built the retaining wall for the greenhouse using rammed earth in tires.

We could have stuccoed over the tires but that is only for cosmetics and not necessary for function in this greenhouse as it would be in a structure built to live in. Plus, I think seeing the tires is more interesting.

The tire idea is based on the principle of the Earthship project. Taking shelter of Bhumi.