Economizer controls

Economizer controls

HVAC system controls that operate mixed air dampers to mix return and outdoor air to obtain air of a temperature appropriate for free cooling. Economizer controls are used during periods when outdoor air requires less cooling energy input than return air.
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In addition, in order to find an alternative solution for optimal economizer controls, it is necessary to understand how the optimal high-limit curves are created.
Differential enthalpy controls are theoretically considered as the most energy-efficient economizer controls (CEC 2003; ASHRAE 2009a).
Finally, a practical engineering approach for economizer control for replacement of physical humidity sensors is discussed based on the results of the sensitivity analysis.
The following is the schematic/ physical layout of the proposed HERV system--Most of the heat recovery systems available on market are either HRV or ERV or ERV without economizer controls.
The reasoning is due to the HERV's functionality, where it has the capability to switch between different modes; sensible recovery (when there is a minor difference in the relative humidities between indoors and outdoors), latent recovery (when there is a minor difference in the temperatures between indoors and outdoors); Sensible & Latent (when there is a significant difference in both temperatures and relative humidities between indoors and outdoors); and the economizer control (when both temperature and relative humidity variations are minor).
Desirable economizer controls use a dry bulb high limit to enable economizer use only when the OAT is appropriate.
Since outside air temperature (OAT) is needed by the advanced control system for economizer control, it can be used for the optimum start sequence as well.
Since connections for outside air, discharge air, and economizer control need to connect to the controller, the number of wires from an existing thermostat wire are typically not adequate.
DCV systems can be incorporated into existing HVAC equipment and often times operate in conjunction with existing economizer controls, sharing the same outdoor air damper (OAD).
Items like optimum start thermostats, economizer controls, and demand controlled ventilation can be independently prescribed, but a package of measures provides the synergy of addressing common problems together and building installer expertise and efficiency.
However, over-reliance on the added factory quality control and assumptions that all economizer control sequences are alike, can lead to failure conditions as explained later in this paper.
Use enthalpy economizer control in order to avoid high-humidity conditions in the datacom environment (use of dry-bulb economizer control can lead to humidity control problems in most parts of the country)