Modular Climate Changer - Page 24

Table A-3 — Recommended Bypass Duct Sizes (Inches)

Face-and-Bypass Damper Module

Designed to divert airflow around a coil, the face-and-bypass module can be used to control humidity or provide freeze protection for hydronic coils. Choose from the following damper module configurations:

Internal Face-and-Bypass Dampers.

(Figure A-21) Typically used immediately upstream of a modified- size (i.e., less than 100-percent airflow) coil, this option enables temperature control while operating the preheat coil at full flow. The dampers modulate to bypass air around the heating coil when the outdoor air temperature is warm enough to preclude freezing.

Application considerations:

• To ensure full airflow coverage across downstream coil banks, provide extra distance after the modified-size coil module, see Table A-2.

Table A-2 — Recommended Distance Between Coils (Inches)

• Internal face-and-bypass configurations that require 100-percent bypass, should be designed taking into consideration the reduced bypass area, higher velocities and higher pressure drops. External face-and-bypass may be considered for these systems.

External Face-and-Bypass Dampers. (Figure A-22, Table A-3) External face- and-bypass dampers perform the same function as their internal counterpart. However, they’re used upstream of a full-face (rather than modified-size) coil, and route air around the coil through an external bypass duct. See Table A-3 for recommended duct sizes that permit 100-percent bypass.

Application considerations:

• Unlike internal or integral configurations, no extra distance is required to achieve full airflow coverage across downstream coils (i.e., reducing the air handler’s length). •
  
• Duct placement varies with air handler arrangement. Ensure that the external bypass duct doesn’t interfere with stacked modules.