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Tempering natural ventilation

Sifu

Sifu

SAWHORSE
Joined
Sep 3, 2011
Messages
2,830
I have a designer proposing a T/I in a high rise without enough outside air. The space has a patio and he asked if he could use natural ventilation. Code allows either natural or mechanical, I assume a combination is also acceptable. However, some are telling me that the outside air needs to be tempered, and the IECC does require energy recovery ventilation systems in some situations. I think this would only apply to mechanical ventilation but those same people are basically saying you can't use natural ventilation anymore because you have to temper it. I have concerns with that, does the energy code now dis-allow the opening of a window or door to provide natural ventilation?
 
I think perhaps, you are getting confused by using two different code requirements that cause conflict with each other.

In my simple mind -

Does it meet the mechanical code? Yes or No?

and in times of harsh weather, does it meet the energy code. ( Yes or No)

Point being, the inhabitants are not going to open the window in times of harsh weather, hot days, or extremely code days thus meet the energy code requirements on the worse climate days.

Natural ventilation is the prerogative of the inhabitants - 402.1 Natural ventilation.
Natural ventilation of an occupied space shall be through windows, doors, louvers or other openings to the outdoors. The operating mechanism for such openings shall be provided with ready access so that the openings are readily controllable by the building occupants.

The tempered air requirement is only if you are mechanically providing make up air.........this requirement does not apply to natural ventilation.
 
The tempered air requirement is only if you are mechanically providing make up air.........this requirement does not apply to natural ventilation.[/QUOTE]

That is my opinion too, but others don't agree so looking for additional opinions. In this case they are providing both natural and mechanical outdoor air. It is my opinion that the mechanical air would be subject to the code, but the natural is not (how could it be?) but others believe the code essentially prohibits the use of natural ventilation.

BUT, speaking of the code to which I am referring: I am looking at the code for energy recovery ventilation systems. It is at 2012 IECC 403.2.6, 2009 IECC 503.2.6 (I don't have the 15 commentary). In trying to figure out what it means I went to the commentaries for 2009 and 2012, and they are different. The 2009 refers to the exhausted air, but the 2012 refers to the incoming air. Can someone explain that to me?
 
IECC
R403.5 Mechanical ventilation (Mandatory).
The building shall be provided with ventilation that meets the requirements of the International Residential Code or International Mechanical Code, as applicable, or with other approved means of ventilation. Outdoor air intakes and exhausts shall have automatic or gravity dampers that close when the ventilation system is not operating.

R403.5.1 Whole-house mechanical ventilation system fan efficacy.
Mechanical ventilation system fans shall meet the efficacy requirements of Table R403.5.1.

Exception: Where mechanical ventilation fans are integral to tested and listed HVAC equipment, they shall be powered by an electronically commutated motor.

IRC M1507 Mechanical Ventilation

M1507.3.1 System design.
The whole-house ventilation system shall consist of one or more supply or exhaust fans, or a combination of such, and associated ducts and controls. Local exhaust or supply fans are permitted to serve as such a system. Outdoor air ducts connected to the return side of an air handler shall be considered to provide supply ventilation.

That is all we require
 
This is a commercial T/I, in a high-rise, 2012 code. Apparently the building was designed and built without the outdoor air ventilation required today. In this case the space has a patio which allows the introduction of outdoor air through natural ventilation. The question is whether IECC 403.2.6 requires tempering of any outdoor air supply, effectively eliminating the use of natural ventilation allowed by IMC, through doors or windows. Something I do not believe.
 
# ~ # ~ #


SiFu,

I believe that **Builder Bob** has stated the correct
interpretation of your application in Post # 2.

In Section 403.2.6, `12 IECC, ...it says that the airflow
rate of a fan system [ read - mechanical system ] shall
have the capability to provide a change in the enthalpy
of the outdoor air supply......IMO, this would not \ does
not apply to natural ventilation in to a space.......If
natural ventilation [ air ] is supplied to a space, then
it is not mechanically supplied, ...conversely, mechanically
supplied air is not naturally supplied air........Does this
help your case ?


# ~ # ~ #
 
Last edited:
Sifu said:
The question is whether IECC 403.2.6 requires tempering of any outdoor air supply, effectively eliminating the use of natural ventilation allowed by IMC, through doors or windows.
Click to expand...

No

C403.2.5 Ventilation.
Ventilation, either natural or mechanical, shall be provided in accordance with Chapter 4 of the International Mechanical Code. Where mechanical ventilation is provided, the system shall provide the capability to reduce the outdoor air supply to the minimum required by Chapter 4 of the International Mechanical Code.

C403.2.6 Energy recovery ventilation systems.
Where the supply airflow rate of a fan system exceeds the values specified in Table C403.2.6, the system shall include an energy recovery system

[M] ENERGY RECOVERY VENTILATION SYSTEM. Systems that employ air-to-air heat exchangers to recover energy from exhaust air for the purpose of preheating, precooling, humidifying or dehumidifying outdoor ventilation air prior to supplying the air to a space, either directly or as part of an HVAC system.
 
Looks like you are all on the same page as I am. I understand it seems like a silly thing to ask if "natural" outdoor air has to be tempered but the boss thinks it does so I wanted other viewpoints before I push back.
Thanks.
 
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