Some hydronic systems use a separate reset-controlled mixing device for each water temperature required. It works, but
it's not always necessary.
We've discussed the theory and benefits of outdoor reset control in several past columns. You'll recall the basic idea is
to reduce water temperature to the heat emitters as the outdoor temperature increases. This helps balance system heat
output with building heat loss so interior temperatures remain stable. It minimizes on/off cycling of heat delivery. In
effect, the heat is always "on," but at just the right delivery rate to match the existing load.
Outdoor reset control is usually implemented one of two ways: