[Bldg-rate] [Bldg-sim] PSZ-AC
Eric Youngson
ericy at pae-engineers.com
Fri Sep 5 10:50:25 PDT 2008
Carol,
I believe that this confusion arises, for me at least, in the
fact that eQUEST only allows each zone to be assigned to one space as
described in the geometry. This also seems like it would reduce the
flexibility to rezone for different systems when doing design phase
modeling. Though I don't have enough experience to think of a good
example, it seems that this subtle point may have some important
consequences for accurate early design phase modeling.
As for the slave zones with hours not met-I'd like to add that
I'm having trouble getting the eQUEST design airflows to match the
actual designed values as well. OA is Specified and matches closely in
both the proposed & baseline but the design airflow in the baseline is
around 10,000 CFM short! Could this be caused by a the difference in
multi & single zone systems?
Thanks
Eric
-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Carol
Gardner
Sent: Sunday, September 21, 2008 9:39 AM
To: Paul Riemer
Cc: bldg-sim at lists.onebuilding.org; bldg-rate at lists.onebuilding.org
Subject: Re: [Bldg-sim] PSZ-AC
I think there's some confusion about spaces vs zones. A thermal zone can
have many spaces and be served by one packaged single zone system (PSZ).
A multizone system is one system serves each space/zone. While you can
attach more than one thermal zone to a PSZ system and not be technically
wrong to do so you will have the devil to pay because of the Control
Zone that you have to specify in eQUEST. It is almost impossible to
specify a control zone that won't create hours loads not met for the
other spaces in your output. There is a way around that, only specify a
heating/cooling schedule for the control zone and leave the others
blank, but it is far better to just create one thermal zone for each
PSZ: that meets all the requirements related to ASHRAE, LEED, god, etc.
I hope this helps. Many years and much pain have been a great teacher.
Carol
Paul Riemer wrote:
> I would be leery about combining zones as the baseline cooling
> efficiency, fan power, and economizer should be set by each unit's
> tonnage, cfm, and sf respectively. Further it is not your design cfm &
> tonnage but rather the baseline autosized cfm & tonnage.
> Also be sure you know your software because some programs will allow
> you to but more than one zone on a "single zone system" and then model
> no control or reheat on the secondary zones, either of which be
> outside the intent of Appendix G's system 3.
>
>
------------------------------------------------------------------------
> *From:* bldg-sim-bounces at lists.onebuilding.org
> [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of
> *Kendra Tupper
> *Sent:* Friday, September 05, 2008 9:34 AM
> *To:* Dan Russell; Eric Youngson; bldg-sim at lists.onebuilding.org
> *Cc:* bldg-rate at lists.onebuilding.org
> *Subject:* Re: [Bldg-sim] PSZ-AC
>
> I agree with Dan. The 90.1 User's Manual is a bit more clear on
> this subject, and references that a PSZ unit is created for each
> thermal zone.
>
>
------------------------------------------------------------------------
>
> *From:* bldg-sim-bounces at lists.onebuilding.org
> [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Dan
> Russell
> *Sent:* Thursday, September 04, 2008 4:12 PM
> *To:* Eric Youngson; bldg-sim at lists.onebuilding.org
> *Cc:* bldg-rate at lists.onebuilding.org
> *Subject:* Re: [Bldg-sim] PSZ-AC
>
> Eric,
>
> I understand System 3 (PSZ-AC) to be a standard packaged rooftop
> that may serve multiple "spaces", but only serves a single
> "thermal zone". In other words, there is only one thermostat that
> controls the entire unit.
>
> Your baseline should have a separate PSZ-AC for each thermal zone
> depicted by your HVAC drawings. Note that adjacent thermal zones
> with similar load characteristics (light/equip gain, people count,
> exterior exposure, etc.) may be lumped into a single thermal zone
> for modeling purposes (i.e. less zones = simpler model).
>
> Hope that helps.
>
> Dan Russell, EIT
>
> cid:image001.jpg at 01C840A4.E711B250
>
> *From:* bldg-sim-bounces at lists.onebuilding.org
> [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of
> *Eric Youngson
> *Sent:* Thursday, September 04, 2008 3:33 PM
> *To:* bldg-sim at lists.onebuilding.org
> *Cc:* bldg-rate at lists.onebuilding.org
> *Subject:* [Bldg-sim] PSZ-AC
>
> Sim List,
>
> ASHRAE system 3 is, Packaged Single Zone Air Conditioner (PSZ-AC).
> The description of PSZ-AC says, "Packaged rooftop air
> conditioner". I assume that this means a single unit serving
> multiple zones. This doesn't seem to make sense since the name
> contains the phrase 'single zone'.
>
> I have a building with baseline system 3, PSZ-AC and I'm not sure
> how to apply this system. The proposed building has a variety of
> systems. Should I have a system per zone or a single unit for the
> building?
>
> Thanks
>
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> *Eric Youngson *
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