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5472 726 - 02
Vitotron 100 Electric Space Heating Hot Water Heater Installation/Service
Sizing of the Space Heating Hot Water Heater
Instructions for the Installer
It is very important to conduct a heatloss analysis of
the intended heated space. Select the space heating hot
water heater 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 space heating hot
water heater, wiring and materials. Consequentially it is
extremely imperative NOT to undersize the space heating
hot water heater.
How to choose the correct space heating hot water heater
size? Convert BTU to kW by dividing the BTU load by
3,413.
(Ex. 33,513 BTU / 3,413 = 9.81kW). Choose a space
heating hot water heater that slightly exceeds this kW
requirement by no more than 20%.
For larger BTU loads consider cascading the space
heating hot water heaters 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.
Designed Temperature Differential
Radiant floor heating systems are typically designed for a
10°- 20°F temperature differential determined by when
the heating fluid leaves the space heating hot water
heater and where it enters the radiant heat source. i.e.
radiant PEX/tubing.
Circulating Pump Information
This space heating hot water heater 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 space heating hot water heater 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.
