PVAV - Number of cooling stages

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What 90.1 PRM Section(s) are relevant to this issue?
3.7.5.2 Direct Expansion - Number of cooling stages

Explanation of issue:
In the last T-24 CBECC-Com (v3), the baseline assumption for PVAV was that 
these systems had 2 stages of cooling capacity. Do you want to adopt this 
assumption for 90.1?  To my knowledge, there is no explicit requirement for 
this in 90.1-2010, though there are IEER rating requirements stated in Table 
6.8.1A.

Proposed resolution:
Confirm and if the decision is to use 2 stage compressors for baseline systems 
5 and 6, update PRMRM.

Original issue reported on code.google.com by da...@360-analytics.com on 9 Oct 2014 at 12:47

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David, We'll use 90.1 2013 requirements for this. Table 6.5.1.4 of 90.1 2013 
specifies DX cooling stage requirements for systems that control space 
temperature by modulating air flow. 
Systems with rated capacity >=65,000 btu/h and <240,000 btu/hr would be modeled 
with 3 cooling stages.
Systems with rated capacity >=240,000 btu/h would be modeled with 4 cooling 
stages

Does this work?

Original comment by supriya....@pnnl.gov on 9 Oct 2014 at 6:35

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We currently only support the E+ DX:SingleSpeed and DX:TwoSpeed E+ objects. I 
suppose we could add another set of curves to try and approximate the 3 and 4 
stage cooling systems, but we don't currently have those curves prepared.

Original comment by da...@360-analytics.com on 9 Oct 2014 at 7:51

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David, 
We discussed this internally and 2 stage of control would work fine for DX 
systems.
90.1 2013 section 6.5.1.3 on integrated economizer control specifies that units 
that include an integrated air side economizer are required to have 2 stages of 
cooling. All other units (without integrated economizer control) are required 
to have 3 or 4 stages of cooling.

for App G we can stick to 2 stages of cooling for rated cap >75,000 Btu/h 
according to 90.1 2013 and ignore the requirement for 3 or 4 stage cooling for 
systems without economizer.

Does this work better?

Original comment by supriya....@pnnl.gov on 9 Oct 2014 at 10:00

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Yes, this works. Do you want this capacity threshold to apply all the Phase 1 
baseline HVAC system types with DX coils (#5/6-Multi-zone, #3/4-Single-zone), 
or just #5/6?

Original comment by da...@360-analytics.com on 9 Oct 2014 at 10:33

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Just 5/6.

Since 3/4 have CAV fans the capacity control requirements wouldn't apply to 
those.
I'll go ahead and make the required revisions to the PRM

Original comment by supriya....@pnnl.gov on 9 Oct 2014 at 10:50

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Original comment by da...@360-analytics.com on 14 Oct 2014 at 4:57

• Changed state: Fixed