Bryant 581A/B manual 265

APPLICATION DATA (cont)

b.CONTROL FEATURES — The EconoMi$er IV controller provides superior functionality for rooftop unit operation. EconoMi$er IV control features are included as follows:

Remote Minimum Position — The EconoMi$er IV con- troller can be used with a field-supplied and field- installed remote minimum position control switch that will enable and disable the EconoMi$er IV to open or close the damper beyond the minimum position for modified ventilation, providing 2 to 10 vdc output.

NOTE: Minimum position signal takes priority over the DCV (demand control ventilation) maximum position signal.

Demand Control Ventilation (DCV) — The EconoMi$er IV has DCV capability when using an IAQ sensor. This sensor is typically installed in the return duct or occupied space. When implementing a DCV control scheme with the EconoMi$er IV, the control algorithm will modulate the position of the damper between two user-configured damper positions, Maximum DCV Position and Minimum Occupied position. Design airflow rates for these two damper positions should be such that when the damper is at the Maximum DCV position, enough fresh ventila- tion air will be brought in to remove contaminants and

CO2 generated by sources other than people (i.e., since in unoccupied mode). The Maximum DCV position is intended to satisfy the IAQ “Base Ventilation Rate.” The Minimum Occupied position design airflow rate should be sufficient to satisfy ventilation requirements for

removing CO2 from all sources including people at the maximum occupancy.

IAQ Sensors — EconoMi$er IV can be utilized with any

IAQ (CO2) sensor that provides a 2 to 10 vdc output. The controller will modulate the outdoor air damper to pro- vide ventilation based on the sensor output and the IAQ setting of the controller. When used, an IAQ sensor will modulate the damper from the minimum position (base

ventilation rate based on CO2 levels) to maximum posi- tion (full occupancy ventilation rate).

Damper Operation — The EconoMi$er IV allows the damper to be configured for two adjustable damper posi- tions including maximum position and occupied mini- mum positions. The two (2) position damper capability is a unique feature of EconoMi$er IV and includes opera- tion flexibility as follows:

1.Minimum Occupied Position: This adjustable position allows a minimum ventilation (base ventilation rate) airflow rate through the unit during occupied periods.

2.Demand Control Ventilation (DCV) Maximum Posi- tion: A DCV maximum occupied position is provided when using an IAQ sensor for DCV. See DCV and Control sections for sequence. The DCV Maximum Position limits outdoor airflow into the rooftop when the DCV routine overrides the mixed air sensor. Set- ting the DCV Maximum Position of the outdoor air damper prevents large amounts of hot or cold air into the space.

IMPORTANT: When the DCV Maximum Position is set below the minimum position, the minimum position overrides the maximum position, negating most DCV functions.

Power Exhaust — The EconoMi$er IV has the capability to control one stage of power exhaust for maintaining air balance and pressurization. Control is activated based on outdoor air damper position (adjustable); factory-set at the “middle” position (dampers halfway open).

Compressor Staging — The EconoMi$er IV is an inte- grated economizer and has the ability to utilize simulta- neous outdoor air and compressors. The EconoMi$er IV can be configured to support economizer and compres- sor operation. Only one or two compressor operation is available with 3 to 121/2 ton units.

c. CHANGEOVER STRATEGIES — The EconoMi$er IV controller can be configured to accommodate all avail- able economizer control strategies that place the rooftop unit in economizer mode including:

Remote Minimum Position — Used when a remote sig- nal from a remote minimum position control will enable and disable the EconoMi$er IV (remote enable control).

Outdoor Dry Bulb — EconoMi$er IV will be enabled based on the outdoor-air temperature. This is provided standard with the EconoMi$er IV.

Differential Dry Bulb — EconoMi$er IV will be enabled whenever the outdoor-air temperature is lower than the return-air temperature.

Outside Air Enthalpy — EconoMi$er IV will be enabled based on the outside air enthalpy curves as shown in the EconoMi$er IV Changeover diagram below. The A, B, C, and D curves shown have been in use for many years and have been included as part of the latest ASHRAE 90.1 energy efficiency code. The curves are designed to take into consideration both outdoor temper- ature and humidity. These curves are used to set up the EconoMi$er IV controller to use the EconoMi$er IV for free cooling when the conditions to the left of the curve exist. When the conditions are to the right of the curve, then outdoor air cooling will not be used and the outdoor air damper position will be set at the minimum position.

Deciding which curve is used is a function of the outdoor climate and the type of economizer utilized. Since EconoMi$er IV is a fully integrated economizer, the range where outdoor air can be utilized for free cooling is expanded and the A and B curves may be used. The control point table in the EconoMi$er IV Changeover dia- gram below provides assistance for whether the A and B curves will be suitable. In general terms, a hot and humid climate may be a reason not to use the A curve, while a cooler climate might be more applicable for using the A or B curve.

The EconoMi$er IV has expanded outdoor air capability. For a changeover economizer which cannot utilize simul- taneous economizer and compression, both A and B curves would potentially be undesirable since the tem- perature and humidity levels are too high without com- pression assistance to provide effective cooling. Therefore, most changeover economizers utilize the D curve.

Differential Enthalpy — The EconoMi$er IV will be enabled based on the comparison of the enthalpy of the return air and outside air. When the outside air enthalpy is lower than he return side, the unit will be in econo- mizer mode.

Using the EconoMi$er IV controller for implementing different control changeover strategies requires the use of different combinations of dry bulb and humidity sensors as outlined in the EconoMi$er IV Sensor Usage table.

265