.Buildings.Controls.OBC.ASHRAE.G36.Generic.AirEconomizerHighLimits .Buildings.Controls.OBC.ASHRAE.G36.Generic.AirEconomizerHighLimitsThis block outputs the air economizer high limits according to the energy standard, device type and climate zone. The implementation is according to the Section 5.1.17 of ASHRAE Guideline 36, May 2020.
When ASHRAE 90.1-2016 is used.
| Device type | Allowed only in these ASHRAE Climate Zones | Required High Limit (Economizer OFF when) |
|---|---|---|
| Fixed dry bulb | 1b, 2b, 3b, 3c, 4b, 4c, 5b, 5c, 6b, 7, 8 | outdoor air temperature is higher than 24 °C (TCut=24°C) |
| 5a, 6a | outdoor air temperature is higher than 21 °C (TCut=21°C) |
|
| 1a, 2a, 3a, 4a | outdoor air temperature is higher than 18 °C (TCut=18°C) |
|
| Differential dry bulb | 1b, 2b, 3b, 3c, 4b, 4c, 5a, 5b, 5c, 6a, 6b, 7, 8 | outdoor air temperature is higher than the return air temperature (TCut=TRet) |
| Fixed enthalpy with fixed dry bulb | All | outdoor air temperature is higher than 24 °C or the enthalpy is higher than 66 kJ/kg (TCut=24°C or hCut=66kJ/kg) |
| Differential enthalpy with fixed dry bulb | All | outdoor air temperature is higher than 24 °C or the outdoor air enthalpy is higher than the return air enthalpy (TCut=24°C or hCut=hRet) |
| Fixed dry bulb with differential dry bulb | 1b, 2b, 3b, 3c, 4b, 4c, 5b, 5c, 6b, 7, 8 | outdoor air temperature is higher than 24 °C or the return air temperature (TCut=min(24°C, TRet)) |
| 5a, 6a | outdoor air temperature is higher than 21 °C or the return air temperature (TCut=min(21°C, TRet)) |
When California Title 24-2016 is used.
| Device type | California Climate Zones | Required High Limit (Economizer OFF when) |
|---|---|---|
| Fixed dry bulb | 1, 3, 5, 11 to 16 | outdoor air temperature is higher than 24 °C (TCut=24°C) |
| 2, 4, 10 | outdoor air temperature is higher than 23 °C (TCut=23°C) |
|
| 6, 8, 9 | outdoor air temperature is higher than 22 °C (TCut=22°C) |
|
| 7 | outdoor air temperature is higher than 21 °C (TCut=21°C) |
|
| Differential dry bulb | 1, 3, 5, 11 to 16 | outdoor air temperature is higher than the return air temperature (TCut=TRet) |
| 2, 4, 10 | outdoor air temperature is higher than the return air temperature minus 1 °C (TCut=TRet-1°C) |
|
| 6, 8, 9 | outdoor air temperature is higher than the return air temperature minus 2 °C (TCut=TRet-2°C) |
|
| 7 | outdoor air temperature is higher than the return air temperature minus 3 °C (TCut=TRet-3°C) |
|
| Fixed enthalpy with fixed dry bulb | All | outdoor air temperature is higher than 24 °C or the enthalpy is higher than 66 kJ/kg (TCut=24°C or hCut=66kJ/kg) |
| Fixed dry bulb with differential dry bulb | 1, 3, 5, 11 to 16 | outdoor air temperature is higher than 24 °C or the return air temperature (TCut=24°C or TCut=TRet) |
| 2, 4, 10 | outdoor air temperature is higher than 23 °C or the return air temperature minus 1 °C (TCut=min(23°C, TRet-1°C)) |
|
| 6, 8, 9 | outdoor air temperature is higher than 22 °C or the return air temperature minus 2 °C (TCut=min(22°C, TRet-2°C)) |
|
| 7 | outdoor air temperature is higher than 21 °C or the return air temperature minus 3 °C (TCut=min(21°C, TRet-3°C)) |
Note that the device type Fixed dry bulb with differential dry bulb is not listed in either ASHRAE 90.1 or Title 24 standard. But it is possible to use in practice. See Section 3.1.6.2 in Guideline 36.