Designer Guide

22
LOCHINVAR, LLC
300 MADDOX SIMPSON PKWY
LEBANON, TN 37090
www.lochinvar.com
Designer’s Guide / Knight XL Boiler
On a very cold winter day, all three air handlers will call for heat and the two Knight XL will fire at
100% input rate to meet the demand. On a comparatively cool autumn day, only one 400,000
Btu/hr air handler might be calling for heat. The boilers, connected together with their Smart
System controls will fire only one boiler at its reduced input and output rate. The minimum 20%
input rate of a single Knight XL 701 is 140,000 Btu/hr with an output of up to 137,200 Btu/hr. Well
below the 400,000 Btu/hr minimum system demand. The Knight XL 701 will actually fire closer to
63% of its potential modulation rate to meet this minimum system demand.
The following table shows the maximum and minimum input and output rates for every Knight XL
with all of the available Firing Codes. Calculate the minimum load of your design to make sure
the system demand or system volume is larger than the minimum boiler output rate.
Model Number
Maximum Input
Rate
Maximum Output
Rate
Minimum Input
Rate
Minimum Output
Rate
KBN 400
399,999
391,999
80,000
78,400
KBN 501
500,000
490,000
100,000
98,000
KBN 601
600,000
588,000
120,000
117,600
KBN 701
700,000
686,000
140,000
137,200
KBN 801
800,000
784,000
160,000
156,800
If the minimum Btu/hr system demand is SMALLER than the boiler’s
minimum Btu/hr output then there may be insufficient water volume. If that
is the case, then a Buffer tank is your solution.
BUFFER TANK
The buffer tank adds water volume to the system providing the volume
needed to support the minimum output rate of the boiler if the minimum
system load can’t.
Refer to Lochinvar’s “Buffer Tank / Air Eliminator” product brochure for a
tank selection chart or visit the Lochinvar website for a fully automated tank
sizing program.
INDIRECT DOMESTIC WATER HEATING WITH THE BOILER SYSTEM
The Knight XL boiler system can be configured to provide Domestic Hot
Water with the addition of Lochinvar’s Squire Indirect or Hot Water Generator
Systems. Indirect water heaters area storage tanks fitted with a heating coil.
A sufficiently sized boiler will heat both the potable hot water demand and
provide source water for the hydronic heating systems. Indirect water heaters
use the boiler water as an energy source and can provide high recovery rates,
making them an economical water heating system.