closely spaced tees . The operating trick to P-S ( Primary-Secondary ) systems is the use of closely spaced tees . There ’ s nothing complicated about Primary-Secondary pumping . It is really not that difficult to understand . It is all about the ‘ path of least resistance ’ and is also nothing but a modified diverter system as I described earlier . The trick is to place the tees no more than 12 inches apart and with a fitting like that shown in Figure 2 , you just can ’ t go wrong .
One thing that should be noted is that the expansion tank , air separator and the fill valve all belong in the Primary loop . Make sure you install your Primary circulator so that it is pumping away from the expansion tank like in Figure 5 . That way , you can take advantage of the Primary loop circulator ’ s full differential pressure . If you put a fitting in like Figure 2 , you ’ ll gain a full-port ball valve in the common piping between the primary and secondary circuits , and that will allow you to be able to get the air out of the system a lot quicker as well . Pumping away also allows you to get rid of any system air that works its way into the piping .
requirements of the heating equipment . This allows the Secondary pump ( s ) and loop ( s ) to be sized and controlled to provide the design flow rate and temperature differential required to satisfy the heating load ( s ).
The most important thing to remember as we go from using a diverter tee system to a P-S system is that in the diverter system the diverter tees direct the flow of water and act as the ‘ flow boss ’ where in the P-S system , the circulators are in charge and act as the ‘ flow bosses ’. Figure 5
Another way to think of these systems is that Primary and Secondary loops end up becoming separate , with neither having an effect on the pumping head of the other . The Primary loop actually serves the heat source , ( boiler or heat exchanger ), while the Secondary loop serves the load ( s ). Primary- Secondary pumping arrangements allow for increased system temperature design drops , decreased pumping sizes and increased system control . The Primary loop and its pump are dedicated and sized to serve the flow and temperature differential www . fueloilnews . com | FUEL OIL NEWS | SEPTEMBER 2023 35