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Designer’s Guide / SYNC Boiler Reminder: the flow rates and other values listed on the preceding page are for each heat exchanger. When combined in common water piping, the flow rates will double. Increase pipe size accordingly. Use 2-1/2” minimum common manifold pipe size. ADDITIONAL CIRCULATOR PUMP SPECIFICATIONS 1. Maximum operating pressure for the pump must exceed system operating pressure. 2. Maximum water temperature should not exceed the nameplate rating. 3. Cast iron circulators may be used in closed loop systems. Important THE BOILER PUMP MUST BE A CONTINUOUS SPEED PUMP THAT KEEPS A CONSTANT FLOW THROUGH THE BOILER. WATER FLOW Is the minimum planned flow rate for the system loop below that of the minimum allowable flow rate through the boiler The lowest potential System Loop Flow Rate MUST be ~10% greater than the Boiler Loop flow rate. 18
Designer’s Guide / SYNC Boiler LOW SYSTEM FLOW RATE In situations where the boiler loop flow is less than the system flow, heated water from the boiler will backfeed down the System line and recirculate back into the boiler taking the path of least resistance. This means the boiler is recirculating already heated water in a very small volume which will cause the inlet water temperature to heat up quickly and cycle the boiler off. The result is the building will not receive the heat and the boiler will short cycle. Many modern hydronic heating systems are designed to vary the flow rate in the system loop as an energy efficiency measure. The system pumps can provide proper flow for the heat distribution system by measuring the pressure differential on the system and providing just enough flow to march the requirements of the heat emitters that are calling for heat at that specific time. When a system is designed with a Variable Frequency Drive for the system loop pumps, precautions must be taken to verify that the boiler loop flow rate will not be greater than the system loop flow rate. Additionally, the use of 3-way valves on the heating system to reset the system loop temperature will cause the flow rate to vary through the boiler. When using a low mass boiler such as the SYNC, a 3-way valve used for system loop temperature reset must be avoided or the boiler should be decoupled from the system loop with the use of a Buffer Tank or a Low Loss Header. A Buffer Tank is preferred. BUFFER TANK OR LOW LOSS HEADER A Buffer Tank or Low Loss Header solves this problem. These devices add water volume at the point where the System Loop and the Boiler Loop meet. Classic System / Boiler Loop piping isolates the flow rates well but a Buffer Tank or Low Loss Header will isolate the flow rates completely and add water volume to provide a more effective “decoupler” for the boiler. WATER TEMPERATURE Water temperature also needs to be taken into consideration. What is the return water temperature from the System Loop The minimum return water temperature to the SYNC boiler is 40°F (4.44°C). The SYNC operates more efficiently the lower the return water temperature is as it enters the boiler. Therefore, ideal condensing operation will be achieved at temperatures below 140°F, the colder the better. Temperatures below 100°F will deliver thermal efficiencies at 98% and above. 19
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