85
APPENDIX I
APPENDIX I - Variable Speed Injection Mixing
Variable Speed Injection Mixing
For Hydronic Heating Systems
The purpose of this section is to discuss the use of variable
speed injection mixing to precisely transfer heat from the high
temperature boiler (primary) loop to the lower temperature
radiant (secondary) loop in hydronic heating systems.
Various devices and plumbing arrangements can be used to
accomplish this transfer. In the past, it was common to use a
mixing valve in order to temper the water between the
primary and secondary loops in a system. In some instances,
the heat source (condensing or electric boiler, geo-thermal
heat pump, etc.) can be operated at lower temperatures and
dedicated solely to operating a low temperature radiant
heating system. In the vast majority of systems, mixing is
required because:
• A boiler minimum operating temperature is required
• High temperature water is required for other system needs
• Water temperatures vary over a wide range (e.g. solar heat
sources, waste heat utilization, wood fired boilers, etc.)
When the available heat source produces higher water
temperatures than is required by the radiant heating system,
a tempering device is required. To achieve the lower water
temperature required for the radiant system, the high
temperature boiler water must be blended or injected into the
return side of the radiant system to a level that meets the
required supply water temperature for the radiant side.
Technologies have evolved to the point of using small "wet
rotor" pumps to accurately adjust the secondary radiant
supply water temperature regardless of the flow activities on
either primary or secondary loops.
(See fig. a)
The speed of the injection pump
is automatically adjusted to
deliver the desired volume of
hot boiler water to the lower
temperature radiant loop. The
injection pump speed is
constantly adjusted as the
radiant heating system demand
and the supply water
temperature change. If the
boiler return temperature
becomes too cold, the injection
pump can be slowed down to
reduce the heat injection rate,
resulting in an increased boiler
return temperature.
Wirsbo offers a variety of controls that utilizes variable speed
injection pump output. This output modulates the power
supply to the circulator to vary its rotational speed. For
residential and many commercial systems, the controls have
a 120 VAC 50/60Hz output to directly power small circulators.
Radiant
System
a
Mixing with variable speed pump
System
Pump
High
Temperature
(Primary)
Loop
Valve
Injection
Point
Primary
Pump
Boiler
Summary of Contents for SYSTEMpro 311
Page 1: ...SYSTEMpro 311 Installation Manual...
Page 90: ...88 APPENDIX II APPENDIX II SYSTEMpro 311 Menu Tree...
Page 91: ...89 APPENDIX II APPENDIX II SYSTEMpro 311 Menu Tree...
Page 92: ...90 APPENDIX III APPENDIX III Application Drawings...
Page 93: ...91 APPENDIX III APPENDIX III Application Drawings...
Page 94: ...92 APPENDIX III APPENDIX III Application Drawings...
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