Isotonic exercises involve moving your joints and muscles rhythmically and repetitively through their ranges of motion using low resistance, while isometric exercises are static and require you to contract your muscles without joint motion.
Substations are normally outdoors and are enclosed by a wire fence. However in residential or high density areas, the substation may be indoors and housed inside a building to restrict the humming noise of the huge transformers. slide 2 of 6 View of a Substation
The two main types of supply systems are extended plenum and central plenum. A central plenum system is a system where all of the branch ducts start at the same location called a plenum. The extended plenum system consists of a supply air plenum which is connected to the outlet of the hvac equipment. The main supply ducts are attached to this and typically run to the end of the home. The size of them is reduced as necessary to maintain adequate air flow. The branch ducts attach to the main ducts and carry the conditioned air to the individual registers. That is the basics of how a system works.