What is the required fresh air supply temp?

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By default, the central cooling(from air system properties--system component tab) supply temp is 58 F which is the desired supply temp for just cooling. My question is, what should the temp be if the system is to be designed to temper outdoor air i.e what is the fresh air supply temp?

dele omotayo's picture
Joined: 2016-05-18
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If you're talking about a Dedicated Outdoor Air Supply (DOAS) of system,
where there is additional equipment that is able to heat and cool and
controls the individual zone temperatures, then I usually try to select a
supply air temperature setpoint that will minimize the amount of reheat or
recooling required. A precise answer would have to take into account the
specific building (how many zones are in heating verses cooling at the same
time), the climate (whether predominately heating or cooling) and the
efficiency of the DOAS and zone equipment. The goal would be to select a
temperature that will be the most efficient given all the different
variables that go into each project.

For me, where most of my projects are in a heating-dominated climate
(northwest US) and there aren't very many annual hours where pre-cooling is
necessary, I usually keep my temperature close to my cooling setpoint (58 F
in your example). This way, I'm preheating up to 58 F, then the zone
equipment can continue heating, but there is very little cooling necessary.
If my projects are in a predominately cooling dominated climate (CA and HI),
where there is very little need for heating, then the same 58 F supply air
setpoint works without much reheating.

If you are talking about make-up air systems WITHUOT additional equipment to
provide zone temperature controls, then my make-up air temperature setpoints
are all over the map depending on things like what is the acceptable room
temperature range (45 - 95 F??), how much internal load is generated (ovens,
equipment, etc??) and again, whether the project is located I a
predominately heating or cooling climate.

If HAP could add a supply air temperature reset schedule similar to the
Hot/Cold water reset schedules for Plants, then we could get more realistic
results from our air systems.

Good luck!

Michael L. Hardy, PE, F.NSPE
Black Oak Engineering, Inc.
Cell 503.314.5244

MLHardy's picture
Joined: 2010-12-08
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95F DBT / 78F WBT

Sent via DroidX2 on Verizon Wireless?

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Enrique Chavez-Castro3's picture
Joined: 2011-11-12
Reputation: 0

I take no exceptions to Michael's answer. But I wonder if you noticed there is a "CAV - Tempering Ventilation" air system type? Then the HAP defaults are 75 F for cooling and 70 F for heating.

Similarly, if you choose equipment type "Terminal Units" and "Common Ventilation System" you will have the options of pre-cooling and pre-heating coils. Again the defaults are 75 F for cooling and 70 F for heating.

Reba Schaber's picture
Joined: 2011-09-30
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