Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
I would suggest that the ProportionalMinimum represents a cycling fan system where the average outdoor air over the time step is reduced. FixedMinimum is better in this case and would represent an increase in outdoor air during the fan on cycle where the average over the time step is higher than the ProportionalMinimum case. And VRP is of course a better calculation and IMHO should be used with a constant volume system. I'm not sure what happens with VRP if the fan cycles.
The FixedMinimum input will maintain a minimum outdoor air flow rate (multiplied by the Min OA schedule if one exists) regardless of economizer. There is also a hierarchy, FixeMimimum is higher than exhaust air flow rate is higher than Ventilation:Mechanical.
Your last question "ASHRAE 62.1 includes a component that varies with occupant count" and then say "should not the ASHRAE 62.1 minimum OA flow rate change throughout the day", that sounds like DCV to me. If you don't use DCV, you can use FixedMinimum and the Min OA schedule (or occupancy schedule as a surrogate) to get this response.
| | 2 | No.2 Revision |
I would suggest that the ProportionalMinimum represents a cycling fan system where the average outdoor air over the time step is reduced. FixedMinimum is better in this case and would represent an increase in outdoor air during the fan on cycle where the average over the time step is higher than the ProportionalMinimum case. And VRP is of course a better calculation and IMHO should be used with a constant volume non-cycling fan system. I'm not sure what happens with VRP if the fan cycles.
The FixedMinimum input will maintain a minimum outdoor air flow rate (multiplied by the Min OA schedule if one exists) regardless of economizer. There is also a hierarchy, FixeMimimum is higher than exhaust air flow rate is higher than Ventilation:Mechanical.
Your last question "ASHRAE 62.1 includes a component that varies with occupant count" and then say "should not the ASHRAE 62.1 minimum OA flow rate change throughout the day", that sounds like DCV to me. If you don't use DCV, you can use FixedMinimum and the Min OA schedule (or occupancy schedule as a surrogate) to get this response.
| | 3 | No.3 Revision |
I would suggest that the ProportionalMinimum represents a cycling fan system where the average outdoor air over the time step is reduced. FixedMinimum is better in this case and would represent an increase in outdoor air during the fan on cycle where the average over the time step is higher than the ProportionalMinimum case. And VRP is of course a better calculation and IMHO should be used with a non-cycling fan system. I'm not sure what happens with VRP if the fan cycles.
The FixedMinimum input will maintain a minimum outdoor air flow rate (multiplied by the Min OA schedule if one exists) regardless of economizer. There is also a hierarchy, FixeMimimum FixedMimimum is higher than exhaust air flow rate is higher than Ventilation:Mechanical.
Your last question "ASHRAE 62.1 includes a component that varies with occupant count" and then say "should not the ASHRAE 62.1 minimum OA flow rate change throughout the day", that sounds like DCV to me. If you don't use DCV, you can use FixedMinimum and the Min OA schedule (or occupancy schedule as a surrogate) to get this response.
