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What is the ventilation fan standard for unconditioned zones according to ASHRAE 90.1?

asked 2021-08-01 09:26:28 -0500

Keigo's avatar

updated 2021-08-24 00:06:49 -0500

I think this post asked something similar, but let me ask again.

What is the ventilation fan standard for unconditioned zones according to ASHRAE 90.1?

For conditioned zones, Appendix G sets standards for baseline models according to HVAC system, but I can't find the standard for unconditioned zones such as storage, plant room, restroom, etc. If there is no standard, how should we set the fan delta pressures of the baseline ventilation fans in such unconditioned zones? The answer to this question, i.e. to model it as system 3 or system 4, does not seem reasonable to me.


G3.1.1-e in 90.1-2016 and 2019 states as follows:

image description

Can I apply this requirement to storage rooms, electrical/mechanical rooms and restrooms without cooling and heating? If so, the system fan power can be calculated by the following formula: image description

Fan Pressure Rise[Pa] results in 656.664 x Fan Total Efficiency. image description

If this Fan Pressure Rise represents the System Fan Pressure Rise including both supply fan and exhaust fan, it seems to be a strict standard compared to other HVAC Systems such as Systems 3 through 8. For example, when the proposed case has a supply fan and an exhaust fan in a mechanical room, each with 300Pa, the System Fan Pressure Rise can easily reach 600Pa. We cannot expect energy reduction of fan power in mechanical rooms.

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I haven’t done an ASHRAE 90.1 simulation for a while but I used to simulate unconditioned fans in the baseline equal to the proposed case (same kW). I never had a comment about that. In Trace700 you can input the fans as plan utility. Once the reviewer ask me to simulated it as process load in the space since it generates heat.

obuchely's avatar obuchely  ( 2021-08-24 16:11:43 -0500 )edit

Thank you for your comment! Your experience is very informative. But if that is correct, we cannot expect energy saving with fan power of unconditioned zones, which is disappointing.

Keigo's avatar Keigo  ( 2021-08-24 20:08:09 -0500 )edit

you can have saving for unconditioned fans, but you must do an exceptional calculation.

obuchely's avatar obuchely  ( 2021-08-24 21:23:30 -0500 )edit

I see, but it seems that I need some special energy saving methods such as on/off control by thermostat. Simply a low fan power would be unacceptable since there is no standard of fan power for the baseline case.

Keigo's avatar Keigo  ( 2021-08-24 21:35:46 -0500 )edit

In ASHRAE 90.1 and below you can have DCV with CO2 in parking fans. ASHRAE 90.1 above 2007 doesn't allow to claim savings due to DCV with CO2 since it is a standard practice.

obuchely's avatar obuchely  ( 2021-08-24 21:40:10 -0500 )edit

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answered 2021-08-24 23:33:40 -0500

Keigo's avatar

updated 2021-08-24 23:38:21 -0500

I couldn't find any official documentation, but I did find that this topic was often mentioned in LEEDuser:

According to them, the ventilation fan power in unconditioned zones should be treated as a process load and the ventilation fan power in the baseline case should be the same as the proposed case.

Any load not defined in ASHRAE 90.1 Appendix G appears to be treated as a process load.

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Asked: 2021-08-01 09:26:28 -0500

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Last updated: Aug 24 '21