Designer Guide

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LOCHINVAR, LLC
300 MADDOX SIMPSON PKWY
LEBANON, TN 37090
www.lochinvar.com
Designer’s Guide / Knight XL Boiler
Therefore, cooler inlet water means higher efficiency. See the chart on the following page.
With low return water temperatures, the efficiency rating is high, up to 98%. As the return water
temperature rises, the heat transfer from the flue products is reduced and efficiency drops.
Do not exceed the maximum outlet water temperature of 195°F. By exceeding this value, the
heat exchanger coils may overheat and be damaged.
WATER VOLUME
The idea is to keep an amount of water in the system to support the heating capacity of the boiler
during the lowest possible demand.
What is the minimum Btu/hr system demand?
The minimum system demand must be GREATER than the minimum boiler
output.
The standard model Knight XL “M9” boiler has a 5:1 Turndown ratio. Or a minimum Btu/hr output
rate down to 20% of the heater’s total output rate. Having a low turndown will increase our
chances of the boiler’s Btu/hr output rate being below the system demand.
Example:
Imagine an installation consisting of three air handlers with 400,000 Btu/hr rated heating coils for
a total demand of 1,200,000 Btu/hr system demand. The system is heated by two Knight XL 700
boilers for a total input of 1,400,000 Btu/hr and total output of up to 1,176,000 Btu/hr. Each boiler
is the standard “M9” model that fires at 5:1 Turndown.