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Air Handling Units (AHU) Software Overview • 11-21
11.6 Air Handling Units
(AHU)
11.6.1 Overview
The E2 BX supports the simultaneous control of up to
six air handling units (AHU). AHU Control applications
govern all aspects of an AHU’s operations, including heat-
ing and cooling, dehumidification, fans, and economizer
control.
Unlike rooftop control units (RTUs), AHUs are con-
trolled directly by the E2 itself and not by a separate unit
control board.
An AHU Control application actually consists of three
separate control algorithms. The main control algorithm
monitors the indoor temperature and activates heating and
cooling stages when necessary to maintain the user-
defined temperature setpoint. Another algorithm monitors
the indoor humidity and uses a desiccant wheel or addi-
tional AHU cool stages to reduce the humidity level. The
third loop controls either a two-position (digital) or vari-
able-position (analog) economizer damper based on the
outside air conditions.
11.6.2 Temperature Control
In its most basic form, Temperature Control simply
reads a control input value, compares it to the active tem-
perature setpoint, and activates or deactivates heating or
cooling stages in an effort to satisfy the setpoint. The
majority of user setup that must be done in Temperature
Control involves specifying which input is to be used as
the control source, defining different setpoints for use in
occupied, unoccupied, summer, and winter modes, and
setting up the operating characteristics of the heating and
cooling stages.
11.6.3 Alternate Setpoints
For both the heating and cooling setpoints, you may
choose to use different setpoints during occupied or unoc-
cupied building times, and different setpoints for summer
and winter seasons. In other words, AHU Control may
have four different pairs of heating and cooling setpoints,
as shown in Table 11-9.
AHU Control looks at the E2’s Global Data parameters
to determine whether it should run in summer or winter
mode. Refer to Section 10.17, Set Up Global Data, for
information on how to set up summer/winter control
parameters.
The AHU chooses occupied or unoccupied mode by
reading an occupied state input, which is most commonly
tied to the output of a Time Schedule application.
11.6.4 Fan Control
The E2 BX can control three different types of AHU
fans. However, only one fan can be controlled per AHU.
The fan types include: single-speed, two-speed, and vari-
able-speed. Controls for all fans are similar in that they
operate in either of three modes:
• Continuous - The fan is always on, even
when the AHU is not in heating, cooling, or
dehumidification mode.
• Auto - The fan is only on when the AHU is
in heating, cooling, or dehumidification
mode.
• Summer ON, Winter Auto - This mode
allows the AHU fan to operate in Continuous
mode during the summer months and in
Auto mode during the winter months.
The operation of the fans during Continuous and Auto
modes is largely dependent on the fan type.
11.6.4.1 Single-Speed Fans
Single-speed fans require no advanced control parame-
Figure 11-14
- System Log Report Example
Cooling Heating
SUMMER COOL OCC SUMMER HEAT OCC
SUMMER COOL UOC SUMMER HEAT UOC
WINTER COOL OCC WINTER HEAT OCC
WINTER COOL UOC WINTER HEAT UOC
Table 11-9
- Possible Heating/Cooling Setpoints