Designer Guide

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LOCHINVAR, LLC
300 MADDOX SIMPSON PKWY
LEBANON, TN 37090
www.lochinvar.com
Designer’s Guide / Knight XL Boiler
Chapter 4 – Water
We are no longer designing the gigantic, lumbering, gravity-feed boiler systems of our
grandfathers. Buildings are bigger and more complex. Energy efficiency and “green” building
demands have requirements for precise flow, for targeted temperatures, for low water volume and
more. The water piping system must not only meet the demands of the building but also match
the operational characteristics of the boiler.
There are three major concepts to consider when
designing the near boiler piping system. They are…
WATER FLOW
WATER TEMPERATURE
WATER VOLUME
Basically, a boiler or bank of boilers has a given range of operation under these three concepts.
A boiler has a water flow rate range. A boiler has a water temperature range. A boiler has a
water volume range. If you design a system that lets the boiler operate within its comfort zone, it
lives a long and prosperous life. If the system forces the boiler to operate outside any one of the
three comfort zones; the boiler suffers.
WATER FLOW
There are an infinite variety of system piping which will vary based on the system’s components
and operational design. The focus of this guide is to provide the Knight XL boiler with the flow
rate that will allow it to operate at maximum efficiency without damage. To that end, Lochinvar
requires Primary / Secondary piping.
Typically, system flow rates and boiler flow rates need to be controlled separately, that’s why a
Primary / Secondary piping loop is best. The Primary Loop, hereafter referred to as the “System
Loop” flows water around the building. The Secondary Loop, hereafter referred to as the “Boiler
Loop” branches off the system loop to flow water into and out of the boiler.
IMPORTANT BULLET POINTS FOR WATER PIPING
1. Water Connections
Knight 400-501 models have 1 ½” NPT and Knight 601-801 models have 2” NPT
threaded pipe inlet and outlet connections. Installed piping to the boiler must match the
1 ½” or 2” diameter, minimum.
2. Working Pressure
The boiler should not be operated at less than 12 PSIG.
3. Minimum & Maximum Water Temperatures
The minimum inlet water temperature entering the boiler is 0°F (-18°C).
The maximum outlet water temperature leaving the boiler is 185°F (91°C).
4. Flow Rate
The boiler works best with a constant flow rate through the heat exchanger. However,
recent changes to the SMART SYSTEM control allow the use of variable flow pumps.
5. Unions and Ball Valves
The water piping to the boiler should have unions and ball valves at the inlet and outlet
of the boiler to isolate the boiler for service. Use only full port ball valves.
Water