[Bldg-sim] PTHP OA requirements

Chris Yates chris.malcolm.yates at gmail.com
Thu Sep 27 14:50:41 PDT 2012


Dear all,

This is a little embarrassing but I'm having a difficultly understanding 
the requirements for 90.1's system 2 (PTHP) with respect to fresh air. I 
used the E+ example file generator 
<http://apps1.eere.energy.gov/buildings/energyplus/cfm/inputs/> to 
create a simple 90.1 compliant "baseline" model for a dwelling (to use 
it as a template for a more detailed model). In the model from the file 
generator the PTHP operates 100% recirc, no OA. Checking CO2 levels, the 
air quality is fine (rarely exceeding 1200ppm). However, the only 
outdoor air entering the model is via infiltration. To compound the 
mystery, there are sizing parameters in the model that suggest OA should 
be delivered by the PTHP. I've also looked up some product specs and it 
appears that the units typically do do OA.

I feel like I've only got about as far as understanding that System 2 
shouldn't have an economiser! Does anybody know if there are any rules 
with respect to anything like OA fraction?

Also, in terms of system architecture E+ creates most models (including 
PTHP) with a mixing box, however would such a device physically have a 
mixing box? I'm sure that there is very little difference 
computationally, but it would be interesting to know.

I guess this query is also relevant to PTAC as well.

Many thanks

Chris
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