# Fresh air only HVAC



## cda (Sep 21, 2018)

So always something never seen before.

HVAC on the roof

Over 2000 cfm

Fresh air taken from the outside

No Return

Does it require a duct detector ???

If so where do you put it???


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## mtlogcabin (Sep 21, 2018)

there has to be a return or a way to provide relief to control the temperature within each room


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## cda (Sep 21, 2018)

Not into hvac

But it is fresh air only ducted to each room

No return

Each hotel room will have its own a/c unit.


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## mtlogcabin (Sep 21, 2018)

So the roof top unit supply's the common area only?


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## cda (Sep 21, 2018)

Rooms and common


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## chris kennedy (Sep 21, 2018)

cda said:


> Rooms and common



Link to M pages? Seen many OAHU's but never like your describing.


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## mtlogcabin (Sep 21, 2018)

cda said:


> Each hotel room will have its own a/c unit.


i am confused. what specifically does the roof top unit serve and how many floors


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## mtlogcabin (Sep 21, 2018)

pick one that works with what you have
2012 IMC
606.2 Where required.
Smoke detectors shall be installed where indicated in Sections 606.2.1 through 606.2.3.

Exception: Smoke detectors shall not be required where air distribution systems are incapable of spreading smoke beyond the enclosing walls, floors and ceilings of the room or space in which the smoke is generated.

606.2.1 Return air systems.
Smoke detectors shall be installed in return air systems with a design capacity greater than 2,000 cfm (0.9 m3/s), in the return air duct or plenum upstream of any filters, exhaust air connections, outdoor air connections, or decontamination equipment and appliances.

Exception: Smoke detectors are not required in the return air system where all portions of the building served by the air distribution system are protected by area smoke detectors connected to a fire alarm system in accordance with the International Fire Code. The area smoke detection system shall comply with Section 606.4.

606.2.2 Common supply and return air systems.
Where multiple air-handling systems share common supply or return air ducts or plenums with a combined design capacity greater than 2,000 cfm (0.9 m3/s), the return air system shall be provided with smoke detectors in accordance with Section 606.2.1.

Exception: Individual smoke detectors shall not be required for each fan-powered terminal unit, provided that such units do not have an individual design capacity greater than 2,000 cfm (0.9 m3/s) and will be shut down by activation of one of the following:

1.    Smoke detectors required by Sections 606.2.1 and 606.2.3.

2.    An approved area smoke detector system located in the return air plenum serving such units.

3.    An area smoke detector system as prescribed in the exception to Section 606.2.1.

In all cases, the smoke detectors shall comply with Sections 606.4 and 606.4.1.

606.2.3 Return air risers.
Where return air risers serve two or more stories and serve any portion of a return air system having a design capacity greater than 15,000 cfm (7.1 m3/s), smoke detectors shall be installed at each story. Such smoke detectors shall be located upstream of the connection between the return air riser and any air ducts or plenums.

[F] 606.3 Installation.
Smoke detectors required by this section* shall be installed in accordance with NFPA 72.* The required smoke detectors shall be installed to monitor the entire airflow conveyed by the system including return air and exhaust or relief air. Access shall be provided to smoke detectors for inspection and maintenance.

NFPA 72 2013 Section  17.1.5.3.1 requires a detector on the supply side as required by NFPA 90A


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## chris kennedy (Sep 21, 2018)

mtlogcabin said:


> 606.2.1 Return air systems.
> Smoke detectors shall be installed in return air systems with a design capacity greater than 2,000 cfm (0.9 m3/s), in the return air duct or plenum upstream of any filters, exhaust air connections, outdoor air connections, or decontamination equipment and appliances.



No return, no smoke detector. Just have to wonder how you balance such a system.


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## cda (Sep 21, 2018)

mtlogcabin said:


> i am confused. what specifically does the roof top unit serve and how many floors



It serves a five story hotel

There is a main duct running roof to 1st floor.

At each floor, it tees and runs a large duct into the corridor. Off of the large duct, is a small duct that goes into each guest room.

Each guest room will have a window unit type a/c


They say the roof unit is only bringing in fresh conditioned air

There are no return ducts


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## cda (Sep 21, 2018)

chris kennedy said:


> No return, no smoke detector. Just have to wonder how you balance such a system.




Why not put the duct detector on the supply side ??

If the hvac produces smoke, it can still shut down the unit, instead of pumping it into the rooms??


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## cda (Sep 21, 2018)

mtlogcabin said:


> pick one that works with what you have
> 2012 IMC
> 606.2 Where required.
> Smoke detectors shall be installed where indicated in Sections 606.2.1 through 606.2.3.
> ...






They do not meet an exception

72 is why I thought put it on the supply side


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## linnrg (Sep 21, 2018)

this is not uncommon for hotel, dormitory or apartment type occupancy
the missing return air that you are looking for is exhaust air from bathrooms.  In some instances the combined exhaust may be equipped with a heat exchange that might be in common with the supply unit but the air streams are independent.

for a supply only ventilation system you could put a smoke detector on the supply duct and it could tell you if the motor in the unit is burning up but it is not required.


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## mtlogcabin (Sep 21, 2018)

If something happens on the roof this should take care of providing smoke detection and you can still require the unit to shut down when the detection system goes off

Group R-1
[F] 907.2.8.2 Automatic smoke detection system.
An automatic smoke detection system that activates the occupant notification system in accordance with Section 907.5 shall be installed throughout all interior corridors serving sleeping units.

Exception: An automatic smoke detection system is not required in buildings that do not have interior corridors serving sleeping units and where each sleeping unit has a means of egress door opening directly to an exit or to an exterior exit access that leads directly to an exit.


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## chris kennedy (Sep 21, 2018)

linnrg said:


> for a supply only ventilation system you could put a smoke detector on the supply duct and it could tell you if the motor in the unit is burning up but it is not required.


Could also tell you if the bldg next door is on fire.


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## Builder Bob (Sep 26, 2018)

Problematic with any type of smoke/duct detector in hot humid locations - be more of a nuisance than a help - besides, it would be jumped out in a few months especially if along a coastal salt air region. Best advice, do a global shutdown when Fire Alarm is activated and move on......

Had more than one elevator shaft with troubles or supervisory issues in our coastal town. 

Technology is great for laboratory conditions, field conditions will give you headaches and heartaches to the point you eliminate the technology and have wasted the owner's monies with excessive maintenance cost and creating a divine public hatred for Fire Marshals everywhere.


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## linnrg (Sep 26, 2018)

Builder Bob said:


> Problematic with any type of smoke/duct detector in hot humid locations - be more of a nuisance than a help - besides, it would be jumped out in a few months especially if along a coastal salt air region. Best advice, do a global shutdown when Fire Alarm is activated and move on......
> 
> Had more than one elevator shaft with troubles or supervisory issues in our coastal town.
> 
> Technology is great for laboratory conditions, field conditions will give you headaches and heartaches to the point you eliminate the technology and have wasted the owner's monies with excessive maintenance cost and creating a divine public hatred for Fire Marshals everywhere.




This is so true


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## north star (Sep 28, 2018)

*# ~ #*

Amen ***Builder Bob***, ...Amen !.......We have been and are experiencing this
with the "All Powerful Energy Codes".........What a sham, and waste of
resources.......In some instances though like lighting, the energy reduction is
a true benefit [  i.e. - high pressure sodium or metal halide lights to LED's  ].

*# ~ #*


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