With regards to centralised HVAC heating and cooling systems, you will usually hear the terms Primary and Secondary circuits. This refers to particular parts of the system which have a unique purpose. The primary water flows into this to provide heated or chilled water to the secondary circuits.Click to see full answer. People also ask, what is a primary heating circuit?Primary circuit. An assembly of water fittings in which water circulates between a boiler or other source of heat and a primary heat exchange inside a hot water storage vessel, and includes any space heating system.One may also ask, what is a primary and secondary loop? The primary loop simply becomes the source of hot water (as opposed to a direct connection to the boiler or a holding tank). The primary loop also becomes the pressure reference point for the secondary circuit. In effect it acts like an expansion tank for the secondary circuit. Likewise, people ask, what is a secondary heating system? Secondary heating systems are those that provide space heating which is in addition to that provided by the main heating. This report considers two types of secondary heating: § Alternative heating: defined as heating that is used instead of the main heating in a room.What is primary and secondary chilled water system?The primary loop uses a constant speed pump to circulate the working fluid (water). The secondary loop uses a variable speed pump to manipulate the flow of the fluid such that the cooling coil demand is satisfied.