[Equest-users] Fan usage - PTHP vs PSZ

David Reddy david at 360-analytics.com
Mon Mar 16 08:07:06 PDT 2015

Hi Harshul,
If you specify some small of outside air at the zone, say 
ZONE=OUTSIDE-AIR-FLOW = 0.001 cfm, the system (TYPE = PTAC, right?) fans 
should run 24/7 if your SYSTEM:FAN-SCHEDULE is set to 1 for all hours.  
As for the modeling the system as TYPE= PSZ, it sounds like you made 
sure that SYSTEM:INDOOR-FAN-MODE = Continuous, which is correct if you 
want the fan to run continuous regardless of heating/cooling demand.
- David

On 3/16/2015 7:19 AM, Singhal, Harshul wrote:
> Hello forum,
> Our team received a note from our LEED reviewers that our equivalent 
> full load hours (EFLH) in our baseline model were less than 8760, 
> despite the ASHRAE 90.1 requirements that fans be run at constant 
> speed 24 hours per day for multifamily occupancy type.  Our baseline 
> system type is PTHP.  When we plot hourly fan energy usage for the 
> building, usage varies hourly and loosely follows the profile of the 
> outside air temperature.  The EFLH is approximately 7517 hours (88%). 
>   When we switch the system to ‘packaged single-zone heat pump’ from 
> ‘packaged terminal heat pump’ EFLH becomes 8760.  This seems to 
> indicate that the lower EFLH of our baseline model is somehow 
> associated with the system type, however our team can’t seem to figure 
> out what characteristic of a PTHP causes fan energy to change hourly 
> despite the ‘constant speed’ designation. Does anyone have any insight 
> as to why PTHP EFLH would be below 8760 while packaged single-zone 
> heat pump would not be?  Thanks for any insight you might have.
> Cheers,
> cid:image002.jpg at 01D05CF2.73106640
> *Harshul Singhal, LEED AP BD+C*
> Project Consultant
> Thornton Tomasetti
> 386 Fore Street, Suite 401
> Portland, ME  04101
> *T* + *F* +
> *D* +
> HSinghal at ThorntonTomasetti.com
> www.ThorntonTomasetti.com
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