Glazing

Winter sun rays being captured and for photosynthesis and heat

Glazing (the clear surfaces) uses optimal angles and materials to manage Solar Gain. Solar Gain is the incoming sun rays that enter the SunCatcher, used for photosynthesis by the plants and to heat the structure. The most effective angle of the SunCatcher’s glazing to maximize solar gain for locations in the northern hemisphere is 60° up from horizontal. At this angle we maximize winter solar gain and conversely minimizes solar gain during summer months.

Summer sun rays being reflected to reduce overheating

For even better performance, the SunCatcher interior can include light color reflective surfaces, which reflect incoming solar radiation in the winter months back toward the plant growing space and thermal mass. These two features increase the amount of natural light reaching the plants compared to the amount of light that same footprint outside of the structure would normally receive during winter months.

Insulation

Insulation reduces heat loss through surfaces like the walls, floor, roof, and glazing. Like all energy efficient structures, SunCatchers are well insulated and designed to trap and store heat for as long as possible. Unlike a conventional greenhouse, this means we insulate the north wall, roof, and (to some extent) the sides which are not a source of significant solar gain. In colder climates, a reflective insulation “blanket” may be used to cover the glazing at night to further reduce the SunCatcher’s heat loss.

Thermal Mass

55 gallon barrels filled with water used as thermal mass.

The SunCatcher is a highly insulated structure that captures sunlight and converts most of that light to heat. The heat is stored in the SunCatcher’s thermal mass. During a sunny day, the thermal mass prevents the SunCatcher from overheating by absorbing most of the heat while venting excess heat and moisture. During the night or cloudy days, when the interior temperature drops, the thermal mass radiates this heat and helps maintain a suitable plant environment inside the SunCatcher. This thermal mass reduces temperature fluctuations inside the SunCatcher and maintains it above the outside temperature, greatly reducing the need for daytime venting and nighttime heating.

In larger models we use water-filled metal containers or phase change materials (PCM) as highly efficient thermal mass. In the evening when the SunCatcher cools down the PCM provides heat, much like an extra heater coming on when it is needed most. Integrating more thermal mass in your SunCatcher will reduce the temperature swings and increase stored heat for night and cloudy days. We encourage you to fill your smaller model with soil, plants and other mass that will help absorb and hold heat. If you have extra space, you may be surprised at the powerful effect of a simple container full of water to help regulate the temperature.

Ventilation

Ventilation allows temperature control while bringing in fresh air with renewed CO2 levels for the plants. The lower air intake vents are opened in conjunction with the upper exhaust vents to create a natural convective air flow. This releases excess heat and humidity out of the upper exhaust vents while drawing in fresh drier, CO2 rich air through the lower vents when needed during active photosynthetic periods. The rate of air exchanges is controlled with temperature sensitive vents. During the warmer summer months, you may want to leave your vents/sides open full time or even take off the sides of your smaller model to prevent overheating.