Hydronic heating and cooling
also: hydronics · radiant heating · boiler loop · air-to-water heat pump · outdoor reset
Systems that move heat with water or a water-glycol mix through pipes to radiators, radiant floors or fan coils, instead of moving air through ducts.
A heat source (a boiler, an air-to-water heat pump or a chiller) heats or cools water that pumps circulate to terminal units: baseboards, radiators, radiant floor tubing or fan coils. Water carries far more heat than the same volume of air, so pipes are much smaller than ducts, and hydronic systems zone naturally with valves and circulators.
Supply water temperature is the key control variable. Heat pumps are most efficient at low supply temperatures, which suit radiant floors and generously sized emitters, and outdoor-reset control lowers the supply temperature on milder days.
Where it bites: trapped air, poorly balanced loops, pump and valve sizing, freeze protection, and controls that run water hotter than necessary, which wastes efficiency, especially with heat pumps.
Founder takeaway
When designing hydronic controls, keep supply water temperature as low as comfort allows using outdoor reset and good balancing, especially with a heat pump source.
sources
engineer review pending