Heat sinks need to be exposed to a source of heat, such as solar or geothermal, that it can absorb and store until it releases when the ambient temperature drops. If your heat sink is supplied by solar energy, it should be placed where it gets maximum sunlight, keeping in mind that your plants need that sunlight too! When cooler nighttime temperatures arrive, it's important that the heat spreads to all corners of the greenhouse, so a central location is ideal - the further the warmth needs to travel, the less will reach the extremities.
Heat sinks are typically found within a sumberged or excavated location in the center of the greenhouse. This way, heat is absorbed not only from the sun, but additionally from the ambient soil around the sink itself.
