Taco 0012-VDTF4 Variable Speed Circulator Pump Cast Iron Differential Temperature with Flange.The Variable Speed Delta T 0012-VDTF4 Cartridge Circulator (00-VDT) is a microprocessor-based pump which automatically adjusts its performance to deliver the optimal heat transfer based on the actual operation of the system. The 00-VDT regulates the temperature to provide a fixed temperature difference of between 5 - 50 Degrees between two field installed sensors. Variable speed pumping to maintain a set differential temperature (delta T) between two sensors allows for automatic adjustment of the pump's performance to match the load of the system or zone, eliminate velocity noise in zone valve systems and conserve energy. Since delta T is directly related to flow rate, the pump's speed continually adjusts to the required BTU per hour. In almost all applications the design of the system was based on being able to maintain a certain delta T and figured by using the universal hydronics equation of BTU/hr = GPM x 500 x Delta T. Given that, any time there is a change to the heat load (i.e. warmer day or greater heat loss from a structure) then the GPM should change to match the required BTU/hr. This is achieved when the variable speed 00-VDT Circulators automatically and continually adjust their GPM output (by varying speed) to match the required BTU/hr output of the system, no matter the changes in heat load, while always maintaining the designed delta T between a supply and return sensor. .Find more e-Smart Products