Sizing The Electric Boiler; Designed Temperature Differential; Circulating Pump Information - Viessmann VITOTRON 100 Installation And Service Instructions Manual

Vitotron 100 Electric Boiler Installation/Service
Sizing of the Boiler

Designed Temperature Differential

Circulating Pump Information

Instructions for the Installer
It is very important to conduct a heatloss analysis of
the intended heated space. Select the electric boiler size
in kW based on its Btu/hr. rating that best meets the
designed heatloss.
It is important not to overly exceed the kW sizing as
this will lead to unnecessary costs of electric boiler, wiring
and materials. Consequentially it is extremely imperative
NOT to undersize the electric boiler.
How to choose the correct electric boiler size? Convert
BTU to kW by dividing the BTU load by 3,413.
(Ex. 33,513 BTU / 3,413 = 9.81kW). Choose a electric
boiler that slightly exceeds this kW requirement by no
more than 20%.
For larger BTU loads consider cascading the electric
boilers together and pipe the system in a parallel
configuration as described in the piping arrangement
section.
Note: that utilizing propylene glycol freeze protection will
reduce the heat transfer and cause the system to
be less efficient. Under no circumstance should
more than a 50/50 ratio of water to propylene
glycol be used. Consult with radiant system
designers for required freeze protection guidelines.
Radiant floor heating systems are typically designed for a
10°- 20°F temperature differential determined by when
the heating fluid leaves the electric boiler and where it
enters the radiant heat source. i.e. radiant PEX/tubing.
This electric boiler is equipped with a Wilo Star S 21 U
15, 3 speed circulating pump. To determine the speed or
setting of the pump, confirm with radiant design completed
by others and or complete a pressure-loss calculation.
Refer to calculations of loop lengths to determine proper
speed. The pump will automatically operate based on a
thermostat call for heat. After the thermostat temperature
set point has been reached, the pump will continue to
circulate water for 3 additional minutes as part of a post
purge operation to push heated water away from the heat
exchanger.
This electric boiler is also equipped with an additional
pump relay. This will aid the installer if there is any need
to pipe the systems with a secondary circulating pump to
overcome pressure drop due to piping or hydronic tubing
design. This is commonly referred to as primary/secondary
applications described in the piping arrangement section.
7