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
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