Burnham 8H manual

a.A boiler by-pass is recommended for any installation for improved system temperature balance, while serving to protect the boiler from sustained condensing operation. The by-pass also provides some measure of low return water temperature protection by reducing flow through the boiler. See Figure 23.

b.A blend pump is recommended to divert hot supply water into the return when system return temperatures can periodically dip below 135°F or when delta T’s rise beyond 40°F because of control schemes that shut off zone pumps for extended periods. See Figure 23, Detail “A”.

c.Primary/secondary piping with a by-pass is recommended to provide two points of mixing when dual temperature systems are used (i.e. baseboard and radiant heat, outdoor reset and domestic hot water production, systems incorporating night setback or multiple zone pumps on clock schedules). See Figure 23, Detail “B”.

d.If system three-way valves are used for temperature modulation, or if the system will

continuously run below 135°F for extended periods (due to low temperature applications like snowmelt, heat pump systems or others), primary/secondary boiler piping with a three- way valve and return temperature sensor is recommended. Refer to Burnham RTC Return Temperature Control Manual and Tekmar Essay #021 “Mixing Methods and Sizing of Variable Speed Injection Pumps” for more information on mixing devices and boiler protection from low return water temperature.

4.A hot water boiler installed above radiation level must be provided with a low water cutoff device as part of installation.

5.A start-up strainer is recommended for all installations (new and replacement alike) to prevent system debris and sediment from ending up in the boilers where it will inhibit heat transfer and may eventually cause a cast iron section to crack from overheating.

G.Alliance SL™ Water Heater (if used). Refer to Alliance SL™ Installation, Operating and Service Instructions for additional information. Install in same manner as space heating zone.

WARNING

Burnham Commercial recommends maintaining temperature differential (drop) across the system at 40°F or less and return water temperature at minimum of 135°F.

Continued boiler operation for prolonged periods of time under conditions when temperature differential across the system exceeds 40°F and/or return water temperature stays below 135°F, may result in premature boiler failure due to flue gas condensation and/or thermal shock.

If the above conditions exist, to protect a boiler from sustained flue gas condensation and/or thermal shock, the above-recommended temperatures may be maintained by employing common industry-accepted mixing methods to provide boiler protection.

Some common methods are boiler by-pass piping, blend pumps, primary secondary piping with a by- pass, mixing valves and/or variable speed injection pumps.

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