5.6.4.4 OA Ventilation Rates for CBECC are too high compared to CBC req (Martyn)

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What NACM Section(s) are relevant to this issue?

5.6.5.4 and ACM Appendix 5.4A

Explanation of issue:

Martyn claims that the design OA ventilation rates are too high for retail (0.5 
cfm/ft2 vs. 0.25 cfm/ft2 per the CBC egress requirements).

See attached pdf file of email thread covering this issue.

Proposed resolution:

In progress, for v3b release

Please provide any additional information below.

Original issue reported on code.google.com by JohnJArent on 20 Nov 2014 at 9:24

Attachments:

• [Gmail - RE [External] Re FW CBECC Ventilation.pdf](https://storage.googleapis.com/google-code-attachments/cbecc/issue-856/comment-0/Gmail - RE [External] Re FW CBECC Ventilation.pdf)

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One comment before I describe the rules logic:

Should the occupancy level (ppl/1000 ft2) be user-defined for the proposed 
design for all spaces?

I believe we will need to have occupancy entered and ventilation level (cfm) 
entered as two separate inputs, if the user is allowed to exceed the minimum 
required design outside air ventilation rate.

Original comment by JohnJArent on 21 Nov 2014 at 3:02

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Occupancy level will normally be defaulted for all spaces.  Only when the 
designer needs to specify an increased occupant density will the occupancy be 
user specified.  Occupancy and ventilation rates are already separate inputs.  

Original comment by rhedr...@archenergy.com on 21 Nov 2014 at 5:52

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Yes, my understanding is that proposed occ density will now be user-defined.  
It is also my understanding that the default value, and the minimum allowable 
value will be 1/2 the CBC occupant density for all spaces types. 

Unless other rules or additional properties are are defined, this change is 
expected to have an impact on most proposed and baseline models if new default 
occupancy values are used:

- Reduced ventilation rates
- Reduced occupancy gains to the space
- Reduced hot water heating energy 
- Reduced impact of DCV controls.
- Generally smaller baseline fan sizes, and therefore, less fan energy use for 
constant volume systems.

Original comment by da...@360-analytics.com on 21 Nov 2014 at 6:49

• Changed state: Discussion

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Rules to reflect the the changes to detfault ventilation merged to trunk @ r2970
Revised Appendix 5.4a to include 0.5 ventilation multiplier committed @ r2976

Original comment by da...@360-analytics.com on 24 Jan 2015 at 9:04

• Changed state: Fixed

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A related change not noted in the original issue is an increase in the 
default/minimum occupancy density specified in Appendix 5.4A for the following 
SpaceFunctions:

Civic Meeting Place Area
Hotel Function Area
Housing, Public and Common Areas: Multi-family, Dormitory
*Lobby, Hotel
*Lobby, Main Entry

Those noted with a '*' had an increase from 10 to 67 people/1000ft2, so now 
will be required to have DCV controls in the proposed and baseline designs.

Original comment by da...@360-analytics.com on 25 Jan 2015 at 10:53