Are the Endurance models "Energy Star" compliant?
Yes, the Endurance units are "Energy Star" compliant.
Can the Endurance unit be vented with b-vent, or into a masonry chimney?
No. The Endurance units must never be vented into a b-vent or masonry chimney. They must be vented with stainless steel, certified to UL1738 standard. These are Category IV vented appliances. They are positive pressure, and may condense inside the vent because of their high efficiency.
How can a boiler with 87% AFUE be approved for chimney (Category I) venting without condensing?
A gas boiler with 87% AFUE can not be approved as a Category I boiler or be chimney vented. Chimney spaces may be used as "chases", but too much con- densation would occur if a regular chimney were used.
How does the combustion system work in the Endurance, compared to standard boilers?
Standard atmospheric boilers have combustion systems that require both primary air and secondary air for operation. The primary air is introduced through the air shutters and mixed with the gas from the gas orifices. The rich gas/air mixture is then introduced into the combustion chamber through the burners and is ignited by an ignitor of some type (standing pilot, interrupted pilot or hot surface ignitor, HSI). Upon ignition, the flame has an insufficient supply of air (primary air) provided with the gas and obtains the additional air (secondary air) required for proper combustion from the area immediately adjacent to the flame. The primary and secondary air are draft induced by a chimney or in the case of side wall vented boilers by a draft inducer or power venter. The Endurance boiler differs from that type of system and has a premixed combustion system that injects all of the air required for proper combustion with the gas and requires no secondary air. A combustion air blower forces the air for combustion into the combustion chamber with the gas. The speed of this blower, which is automatically adjusted by the heating requirements, determines the firing rate. The gas/air mixture at any time is properly proportioned by a ratio gas valve, which senses airflow and adjusts gas flow accordingly. A hot surface ignitor (HSI) ignites the gas/air mixture that is forced into the combustion chamber through a cylindrical burner. This type of system is insensitive to atmospheric conditions and site-related variables.
How does the DHW system in Endurance protect against differential pressures between hot & cold supplies to valves such as T/S valves?
The flow restrictors shipped with the Endurance EBP boilers are to be installed upstream of the cold water.
How does the modulation system in Endurance work?
The Endurance modulation system senses the boiler return water temperature indirectly and adjusts the input by varying the combustion air blower speed. Proper combustion is maintained by the ratio gas valve, which senses blower suction pressure and adjusts gas flow accordingly. The full output is provided when the return water temperature is low. As the return water temperature increases, the firing rate modulates downward and is a minimum just prior to limit operation. This type of modulating system is ideal for low mass boilers.
How much pressure drop does the tempering valve add to the DHW system?
The fitting size and design of tempering valves determines their pressure drop and there are so many different manufacturers and valve designs available that it is difficult to test all of them and provide pressure drop information. However, the passages in most tempering valves are large enough that they do not contribute significantly to the overall DHW system pressure drop.
What is the pressure drop through the brazed plate heat exchanger (both for the DHW side and for the boiler side)?
The design pressure drop through the brazed plate heat exchanger is the same for both the boiler side and the DHW side for any given flow rate. The DHW side flow rate is a maximum of 5 GPM and the pressure drop at that flow rate is 1.82 PSI (4.2 FT. W.C.). The boiler side flow rate and pressure drop are approximately the same.
What rate flow restrictors are used, and how much do they alter pressure drop?
The EBP 110 is shipped with a 4 GPM flow restrictor. It has a pressure drop of 15 PSI. The EBP 175 is shipped with a 5 GPM flow restrictor. It has a pressure drop of 13 PSI.