# PTAC(H) units



## Bryant (Sep 26, 2019)

Curious how others digest the fact these type of window units commonly found in hotels are not capable of providing the necessary ventilation air rates without a dedicated OA ventilation system, but rather rely on the equipment itself or worse case around the unit itself (that's a question for the thermal envelope another day).

These are the conditions that must be maintained to be compliant.

The PTAC unit indoor supply air fan must continuously introduce the required air quantity.
The PTAC vent door must be open.
The PTAC indoor fan must run continuously.
The outdoor air quantity must be measurable and verifiable (ANSI/ASHRAE Standard 62.1).
How is this possible when no one is in the room, the unit is off, the occupants leave it off intermit, and unless the bathroom exhaust fan is running in concert with the unit, no air movement, other than going in and out of the room into the corridor, of which is rated.

seems this is a cheap out of meeting the energy requirements and escaping the ventilation requirements.
Apologize for not putting the code sections out, in a pinch on this.   

Thanks in advance


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## ADAguy (Sep 26, 2019)

Ouch, you find these often turned off in older motels till occupied.


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## classicT (Sep 26, 2019)

I have recently dealt with a similar issue wherein we have a change in use from a dormitory to offices. Existing dormitory units each had a wall insert PTAC similar to a hotel.

End solution was to add several HRV units.


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## steveray (Sep 26, 2019)

401.3 When required. Ventilation shall be provided during the periods that the room or space is occupied.


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## Bryant (Sep 26, 2019)

Fresh air Fresh air what to do? Thanks for the input so far. The one question I'm trying to wrap my head around is when it is occupied, how is the PTAC unit able to provide the required amount of ventilation air if there is negative pressure in the room, equal in, equal out ? If the bath exhaust fan is not running, then there is not exchange of air in the room, can't count on the corridor or under cut door, rated corridor. And if the bath exhaust fan is undersized, then what, negative pressure. If the intent is to exchange airflow rate, (stale/fresh), seems it will never work unless there is another method such OAU to each room. We know that want happen on a majority of hotels, cheap is better in that mindset.


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## classicT (Sep 26, 2019)

Bryant said:


> Fresh air Fresh air what to do? Thanks for the input so far. The one question I'm trying to wrap my head around is when it is occupied how is the PTAC unit able to provide the required amount of ventilation air  is there is negative pressure in the room, equal in, equal out ? If the bath exhaust fan is not running, then there is not exchange of air in the room, can't count on the corridor or under cut door, rated corridor. And if the bath exhaust fan is undersized, then what, negative pressure. If the intent is to exchange airflow rate, (stale/fresh), seems it will never work unless there is another method such OAU to each room. We know that want happen on a majority of hotels, cheap is better in that mindset.


PTAC's cannot provide the required ventilation air unless they include an OAU function (atypical). 


*403.3 Outdoor Air and Local Exhaust Airflow Rates*
Group R-2, R-3 and R-4 occupancies three stories and less in height above grade plane shall be provided with outdoor air and local exhaust in accordance with Section 403.3.2. All other buildings intended to be occupied shall be provided with outdoor air and local exhaust in accordance with Section 403.3.1.


*403.3.2.1 Outdoor Air for Dwelling Units*
An outdoor air ventilation system consisting of a mechanical exhaust system, supply system or combination thereof shall be installed for each dwelling unit. Local exhaust or supply systems, including outdoor air ducts connected to the return side of an air handler, are permitted to serve as such a system. The outdoor air ventilation system shall be designed to provide the required rate of outdoor air continuously during the period that the building is occupied. The minimum continuous outdoor airflow rate shall be determined in accordance with Equation 4-9.

QOA = 0.01 Afloor + 7.5(Nbr + 1) (Equation 4-9)

where:

QOA = outdoor airflow rate, cfm
Afloor = floor area, ft2
Nbr = number of bedrooms; not to be less than one​
*Exception: *The outdoor air ventilation system is not required to operate continuously where the system has controls that enable operation for not less than 1 hour of each 4-hour period. The average outdoor air flow rate over the 4-hour period shall be not less than that prescribed by Equation 4-9.​


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## Bryant (Sep 26, 2019)

Ty J. said:


> PTAC's cannot provide the required ventilation air unless they include an OAU function (atypical).
> 
> 
> *403.3 Outdoor Air and Local Exhaust Airflow Rates*
> ...



I should have clarified with use group & Const type, R1 VA, burned out today will dive into the commentary tomorrow 2015 403..3.1
thanks


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