G3.1.2.4 is unclear. First it states that the supply fan shall run continuously
during the occupied hours and shall be cycled to meet heating and cooling loads
during unoccupied hours. Ok , I get that.
Then it states that if the supply fan is modeled as cycling and the fan energy
is included in the EER, then the fan energy shall not be modeled explicitly.
That is confusing. When is it permissible to model the supply fan as cycling.
Is AHSRAE talking a supply fan serving a space that is never occupied?
Obviously, there is no such thing, someone will sometime do something in the
room.
Then G3.1.2.4 goes on to state that the supply, return or exhaust fans will
remain on during occupied and unoccupied hours in spaces that have heath and
safety mandated minimum ventilation requirements during unoccupied hours.
This requirement does not cover many of the scenarios that I model. For
example, natural ventilation provided by operable windows. It does not make
sense to keep the fan running if it not supplying ventilation air. I am
presently modeling a residential high-rise. No one keeps their apartment supply
fan running 24X7. Especially if there are operable windows.
Another example is a commercial property that has a DOAS supplying minimum air
directly to the zone HVAC system or supplying minimum directly to the zone
without isolation dampers. If I supply the 62.1 minimum air required by the
DOAS, then why run the supply fan?
I would be interested to hear other interpretations. Perhaps Jason Glazer can
give us his unofficial opinion.
I apologize for the blank email I previously sent, I meant to hit save, not send (Paul was quick to respond, thank you). I am modeling a dormitory of System Type 1. Appendix G Section G3.1.2.4 states, "Supply and return fans shall operate continuously whenever spaces are occupied and shall be cycled to meet heating and cooling loads during unoccupied hours." If the building occupancy schedule is fractionally loaded 24/7, am I over exaggerating fan energy consumption of the PTAC units by operating the fans continuously 24/7? Has anyone received review comments from LEED on the issue?
Thank you,
Brad
Brad Huff, E.I.T., LEED Green Associate
The message I wanted to post originally is pasted below. I should go on to further state that the PTAC units are naturally ventilated spaces. In your experience with these systems did you model them as operating 24/7 and if you did, did problems arise from a LEED review?
Modelers,
I apologize for the blank email I previously sent, I meant to hit save, not send (Paul was quick to respond, thank you). I am modeling a dormitory of System Type 1. Appendix G Section G3.1.2.4 states, "Supply and return fans shall operate continuously whenever spaces are occupied and shall be cycled to meet heating and cooling loads during unoccupied hours." If the building occupancy schedule is fractionally loaded 24/7, am I over exaggerating fan energy consumption of the PTAC units by operating the fans continuously 24/7? Has anyone received review comments from LEED on the issue?
Sorry, I have not submitted a project with PTAC units to LEED yet. I am
modeling two buildings right now that use a VRV system with a DOAS that supplies
ventilation air directly to the space. One is a commercial property in
Middletown, CT and the other is a high rise residential in Waterbury, CT.
I am preparing an requested for an official interpretation of this section to
ASHRAE right now.
I think it takes several months to receive an answer. I will post the answer on
the forum once I receive it.
Brad:
Did you intended to post a message?
G3.1.2.4 is unclear. First it states that the supply fan shall run continuously
during the occupied hours and shall be cycled to meet heating and cooling loads
during unoccupied hours. Ok , I get that.
Then it states that if the supply fan is modeled as cycling and the fan energy
is included in the EER, then the fan energy shall not be modeled explicitly.
That is confusing. When is it permissible to model the supply fan as cycling.
Is AHSRAE talking a supply fan serving a space that is never occupied?
Obviously, there is no such thing, someone will sometime do something in the
room.
Then G3.1.2.4 goes on to state that the supply, return or exhaust fans will
remain on during occupied and unoccupied hours in spaces that have heath and
safety mandated minimum ventilation requirements during unoccupied hours.
This requirement does not cover many of the scenarios that I model. For
example, natural ventilation provided by operable windows. It does not make
sense to keep the fan running if it not supplying ventilation air. I am
presently modeling a residential high-rise. No one keeps their apartment supply
fan running 24X7. Especially if there are operable windows.
Another example is a commercial property that has a DOAS supplying minimum air
directly to the zone HVAC system or supplying minimum directly to the zone
without isolation dampers. If I supply the 62.1 minimum air required by the
DOAS, then why run the supply fan?
I would be interested to hear other interpretations. Perhaps Jason Glazer can
give us his unofficial opinion.
Paul Diglio
Modelers,
I apologize for the blank email I previously sent, I meant to hit save, not send (Paul was quick to respond, thank you). I am modeling a dormitory of System Type 1. Appendix G Section G3.1.2.4 states, "Supply and return fans shall operate continuously whenever spaces are occupied and shall be cycled to meet heating and cooling loads during unoccupied hours." If the building occupancy schedule is fractionally loaded 24/7, am I over exaggerating fan energy consumption of the PTAC units by operating the fans continuously 24/7? Has anyone received review comments from LEED on the issue?
Thank you,
Brad
Brad Huff, E.I.T., LEED Green Associate
Paul:
The message I wanted to post originally is pasted below. I should go on to further state that the PTAC units are naturally ventilated spaces. In your experience with these systems did you model them as operating 24/7 and if you did, did problems arise from a LEED review?
Modelers,
I apologize for the blank email I previously sent, I meant to hit save, not send (Paul was quick to respond, thank you). I am modeling a dormitory of System Type 1. Appendix G Section G3.1.2.4 states, "Supply and return fans shall operate continuously whenever spaces are occupied and shall be cycled to meet heating and cooling loads during unoccupied hours." If the building occupancy schedule is fractionally loaded 24/7, am I over exaggerating fan energy consumption of the PTAC units by operating the fans continuously 24/7? Has anyone received review comments from LEED on the issue?
Thank you,
Brad
Brad Huff, E.I.T.
Brad:
Sorry, I have not submitted a project with PTAC units to LEED yet. I am
modeling two buildings right now that use a VRV system with a DOAS that supplies
ventilation air directly to the space. One is a commercial property in
Middletown, CT and the other is a high rise residential in Waterbury, CT.
I am preparing an requested for an official interpretation of this section to
ASHRAE right now.
I think it takes several months to receive an answer. I will post the answer on
the forum once I receive it.
Paul Diglio