Methods and apparatus for differential energy based airside economizer changeover

1. A method of controlling an economizer in a ventilation system, comprising:

measuring a moisture related property of the first input air source to determine if conditioning of the first air source to a desired output air temperature results in a wet-coil or a dry-coil condition;

measuring a moisture related property of the second input air source to determine if conditioning of the second air source to the desired output air temperature results in a wet-coil or a dry-coil condition;

determining a measure indicative of energy associated with the conditioning of the first input air source for the wet-coil condition and for the dry-coil condition;

determining a measure indicative of energy associated with the conditioning of the second input air source for the wet-coil condition and for the dry-coil condition,

wherein the measure indicative of energy for the first and second input air sources includes sensible energy change associated with the conditioning of the first and second air sources when the dry-coil condition is determined and, includes sensible and latent energy change associated with the conditioning of the first and second air sources when the wet-coil condition is determined, wherein the measure indicative of energy for the first and second air sources has the same units for both the wet-coil condition and the dry-coil condition;

comparing the measure indicative of energy associated with the conditioning of the first air source and the measure indicative of energy associated with the conditioning of the second air source to determine which of the first and second input air sources applied to an air handler requires the least amount of energy for the conditioning; and

selectively enabling the economizer based upon the comparison of which of the first and second input air sources applied to an air handler requires the least amount of energy for the conditioning.

2. The method according to claim 1 , wherein the measure indicative of energy comprises energy rate as a function of volumetric flow rate.

3. The method according to claim 1 , wherein the first input air source includes return air and the second input air source includes outside air.

4. The method according to claim 1 , wherein the moisture related property comprises dewpoint temperature.

5. The method according to claim 1 , wherein the moisture related property comprises humidity ratio.

6. The method according to claim 1 , wherein the desired output temperature is determined as supply temperature setpoint.

7. The method according to claim 1 , wherein the desired output temperature is determined as measured supply dry-bulb temperature.

8. An article, comprising:

a computer readable medium comprising non-transitory stored instructions that enable a machine to control an economizer in a ventilation system, by:

receiving a measurement of a moisture related property of the first input air source to determine if conditioning of the first air source to a desired output air temperature results in a wet-coil or a dry-coil condition;

receiving a measurement of a moisture related property of the second input air source to determine if conditioning of the second air source to the desired output air temperature results in a wet-coil or a dry-coil condition;

determining a measure indicative of energy associated with the conditioning of the first input air source for the wet-coil condition and for the dry-coil condition;

determining a measure indicative of energy associated with the conditioning of the second input air source for the wet-coil condition and for the dry-coil condition,

wherein the measure indicative of energy for the first and second input air sources includes sensible energy change associated with the conditioning of the first and second air sources when the dry-coil condition is determined and, includes sensible and latent energy change associated with the conditioning of the first and second air sources when the wet-coil condition is determined, wherein the measure indicative of energy for the first and second air sources has the same units for both the wet-coil condition and the dry-coil condition;

comparing the measure indicative of energy associated with the conditioning of the first air source and the measure indicative of energy associated with the conditioning of the second air source to determine which of the first and second input air sources applied to an air handler requires the least amount of energy for the conditioning; and

generating an enable signal to selectively enable the economizer based upon the comparison of which of the first and second input air sources applied to an air handler requires the least amount of energy for the conditioning.

9. A system, comprising:

an economizer;

a first sensor to measure a moisture related property of the first input air source;

a control module to determine, from the moisture related property of the first input air source, if conditioning of the first air source to a desired output air temperature results in a wet-coil or a dry-coil condition;

a second sensor to measure a moisture related property of the second input air source to enable the control module to determine if conditioning of the second air source to the desired output air temperature results in a wet-coil or a dry-coil condition, wherein the control module includes a processor and circuitry to:

determine a measure indicative of energy associated with the conditioning of the first input air source for the wet-coil condition and for the dry-coil condition, and to determine a measure indicative of energy associated with the conditioning of the second input air source for the wet-coil condition and for the dry-coil condition,

wherein the measure indicative of energy for the first and second input air sources includes sensible energy change associated with the conditioning of the first and second air sources when the dry-coil condition is determined and, includes sensible and latent energy change associated with the conditioning of the first and second air sources when the wet-coil condition is determined, wherein the measure indicative of energy for the first and second air sources has the same units for both the wet-coil condition and the dry-coil condition;

compare the measure indicative of energy associated with the conditioning of the first air source and the measure indicative of energy associated with the conditioning of the second air source to determine which of the first and second input air sources applied to an air handler requires the least amount of energy for the conditioning; and

selectively enable the economizer based upon the comparison of which of the first and second input air sources applied to an air handler requires the least amount of energy for the conditioning.