Variable-Speed Circulators: Delta-T and Delta-P Explained

Neither source below mentions heat pumps, so nothing here is heat-pump-specific. Not verified: heat pump flow-rate and delta-T requirements; follow the heat pump manufacturer's data and ask an HVAC contractor.

Delta-T circulators (ACHR News)

They hold a set temperature drop between supply and return, typically 20 F, speeding up or slowing as zones open or outdoor temperature changes. Installers can change the 20 F factory setting and must place the supply and return sensors. The article says this returns cooler water to the boiler, reducing short-cycling.

Delta-P circulators (ACHR News)

Developed in Europe for panel radiators with thermostatic valves. In North American on/off zoned systems the article says they run at a single fixed speed.

Why flow follows load (HPAC)

The article uses gpm = Btuh / (delta-T x 500). Typical design delta-T is about 20 F for heating and about 10 F for radiant floor and chilled water. In its example a fixed-speed pump let delta-T fall to about 7 F with two zones calling and about 3 F with one.

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General information only. Not HVAC, legal or code advice. Confirm sizing with the equipment manufacturer and a licensed contractor.