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Appendix G VAV Box Type

asked 2019-08-19 08:05:43 -0600

updated 2020-01-13 16:39:23 -0600

90.1-2010 Appendix G - Systems Type 5-8. Based on G3.1.3.13 and G3.1.3.14 I have interpreted this as A Single Max - Single Min VAV Box control strategy. This is reinforced by the 90.1 PRM - Guide from PNNL (PNNL-25130), Section, which explicitly states Single Max at 30% minimum. I am getting push back from a Peer Review that this is wrong and since my Proposed has a mix of Single Max and Dual Max boxes, the Baseline Boxes should be the same control logic. They (properly) points out that the PNNL Guide isnt officially part of 90.1-2010. Which, while accurate, is pretty poor since IMO its a pretty good guide and appears to have been coordinated with ASHRAE and GBCI.

So - VAV Box Type & Controls in the Baseline - Single Max Single Min? Single Max dual Min? Dual Max Single Min? dual Max Dual Min?

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answered 2019-08-20 22:51:12 -0600

updated 2019-08-20 22:55:25 -0600

Could you use the reviewer's logic as a response? Ask them to support their comment with a reference. Since 90.1 doesn't explicitly state that the baseline should match the proposed their position is just as credible as yours.

I set the baseline VAV terminal control to single max/min prior to the availability of OpenStudio Standards' baseline automation, which sets the VAV dampers to Reverse acting (dual maximum). The reason is not well documented in the OS Standards code, but perhaps @aparker can elaborate.

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His logic is based on using the same/similar VAV box control logic between the Baseline and Proposed. which is a viable argument, especially since Appendix G is not explicit. So its a support by omission...? coworker here had a great point in that a Parallel Box by nature is typically a Dual Max Single Min, since the Fan would increase the airflow in heating. Though, this depends if one is looking at airflow from the Damper Point of view or the Box Point of View. If looking from main damper, its still a single max single min; from a box airflow is it dual max single min.

dradair gravatar image dradair  ( 2019-08-21 09:44:12 -0600 )edit

rechecking the PNNL guide, for PFB; it calls out single max single min; but the verbiage is written from primary damper point of view.

dradair gravatar image dradair  ( 2019-08-21 09:47:45 -0600 )edit

For VAV with reheat terminals the 90.1 PRM does explicitly state requirements for minimum and maximum flow rates (single min and max) but not in between.

MatthewSteen gravatar image MatthewSteen  ( 2019-08-22 23:22:31 -0600 )edit

PRM G3.1.3.13 and G3.1.3.14 contain requirements related to VAV Box Minimums (Sys 5/7) and FPB Fan air flows and airflow minimums (Sys 6/8) respectfully. Is that what you were referencing @MatthewSteen ?

Knowing the min setpoint(s) does not define the controls logic; thus the question. The absence of a 'heating maximum xx%' requirements implies a Single Max/Single Min control of the Primary damper; but that is support by omission not explicit wording. Its possible (Baseline Htg Max) = (Proposed Htg max) and still comply with min %s; making it reverse return. Not a fan of that tho...

dradair gravatar image dradair  ( 2019-08-23 09:02:52 -0600 )edit

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Asked: 2019-08-19 08:05:43 -0600

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Last updated: Aug 20 '19