Powered Induction units (also known as fan-assisted terminal units) ensure that dumping of the supply air will not occur. They contain a small fan which mixes the supply air with re-circulated room air to provide a constant volume supply to the space. The mixing of the two streams is controlled to achieve an air temperature that satisfies the cooling load for the zone being served. Induction units generally have higher capital and maintenance costs and also the potential for increased noise levels.
The EnergyPlus series powered induction unit (PIU) is an air system terminal unit that mixes varying amounts of secondary (re-circulated) air and primary (conditioned supply) air to produce a fixed flow of air to a zone. The unit contains a small fan that acts to induce the secondary air and a heating coil for heating the mixed secondary and primary air. The fan runs at a constant volume flow rate whenever the unit is on. The fan is downstream of the primary and secondary air inlets. The variable mixing is accomplished by a damper in the unit’s primary air supply inlet duct. This damper can move from fully open (100% primary air, 0% secondary air) to a minimum stop that is specified in the input description. At full cooling the damper will be fully open. At minimum cooling and for heating the damper will be at the minimum stop and the secondary air flow will be at its maximum.
The EnergyPlus model of the series PIU terminal unit is composed of three components: a zone mixer, a constant volume fan, and a heating coil (water, electric, or gas).
This is a read-only label that is automatically generated by the software and which incorporates the name of the zone in which the ADU is located.
This is the maximum volumetric air flow rate through the unit (in m3/s or ft3/min). Since this is a constant air volume unit, this is also the design, rated air flow rate of the unit.
This is the maximum volumetric air flow rate of primary air through the unit (in m3/s or ft3/min). This is the primary air flow rate at full cooling load when the primary air damper is fully open. Usually this quantity is the same as the total unit flow rate, but it can be less.
The minimum volumetric air flow rate of primary air through the unit expressed as a fraction of the maximum volumetric air flow rate of primary air. This input can be 0.0.
This section is visible only if the heating coil sub-component of this ADU has Type 1-Water.
The maximum hot water volumetric flow rate in (m3/s or gal/min) through the unit’s heating coil if a water coil has been selected. This value may be auto-sized.
The minimum hot water volumetric flow rate in (m3/s or gal/min) through the unit’s heating coil if a water coil has been selected. This value may be auto-sized.
This is the schedule that determines whether or not the unit is available for each timestep of the simulation. A schedule value greater than 0 (usually 1 is used) indicates that the unit can be on during the timestep . A value less than or equal to 0 (usually 0 is used) denotes that the unit must be off for the timestep.
This is the control tolerance for the unit heating output. The unit is controlled by matching the unit output to the zone demand. For units with water coils, the model must be numerically inverted to obtain a specified output. The convergence tolerance is the error tolerance used to terminate the numerical inversion procedure. Basically this is the fraction:
