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Re: [EnergyPlus_Support] purchase air with outside air

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] purchase air with outside air
From: teklay Weldeabzgi <teklay1979@xxxxxxxxx>
Date: Thu, 2 Sep 2004 00:33:10 -0700 (PDT)
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i have one question about the purchased air model. my
work is to see the annual saviving in energy from
using roof and wall insulations. when i perform this i
get a result which is difficult to consider. i make
the program to report the Zone/Sys Sensible Cooling
Energy[J], Purchased Air Sensible Cooling
Energy[J],and Purchased Air Total Cooling Energy[J].
and while using roof insulation the annual saving
reported from Zone/Sys Sensible Cooling Energy[J]
ecceeds that of the annual saving from Purchased Air
Total Cooling Energy[J]. but i can't understand why
this happen. and the saving from the total cooling is
still less than that of the saving from the purchased
air sensible cooling. but it should be equal or
greater than. so why is this happen.
tek


--- Rahul Chillar <chillarrahul@xxxxxxxxx> wrote:

> here is an earlier reply to a some what related
> query for puchased air.
>
> The purchased air model is very simple but it can
> produce confusing results when the outside air
> option is used. The purchased air model takes return
> air from the zone and mixes it with the specified
> outside air volume. If the purchased air flow rate
> is less than the outside air flow rate, then the
> purchased air flow rate is used and is 100% outside
> air. It then takes this mixed air condition (dry
> bulb temperature and humidity ratio) and calculates
> the enthalpy change required to condition this air
> to the specified supply air temperature and humidity
> ratio. This is the total cooling reported. It also
> determines the sensible change required, and this is
> the sensible cooling reported. If the mixed air is
> drier than the specified supply air humidity ratio,
> then the total cooling will be less than the
> sensible cooling. Purchased air with the outside air
> option is useful for determining peak loads. If you
> are using purchased air for an annual load, it is
> better to introduce the outside
>  air directly to the space using ventilation or
> infiltration.
>
> Thanks
>
> Rahul Chillar
>
>
> Ian Doebber <idoebber@xxxxxx> wrote:
> I have specified a flow rate for say 0.027 m3/s of
> outside air to be mixed
> with some of the return air from my conditioned
> zone.  What I am wondering
> is how the purchased air option will controll this.
>
> 1.  Will the purchased air component continually
> bring in 0.027 m3/s of
> outside air irregardless if the purchased air
> component is needed to
> condition the zone.  Therefor, the annual amount of
> energy to condition the
> inflow of outside air to the setpoint temperature
> condition is essentially
> just added onto the annual amount of energy
> necessary to condition the zone
> when no outside air was specified.
>
> or
>
> 2.  Based on the heating and cooling inlet
> temperatures into the zone
> specified in the purchased air feature, for a given
> load in the zone, the
> purchased air component will determine the "exact
> needed flow rate" of air
> to condition that zone load.    Then based upon the
> flow rate, the purchase
> air component will determine the energy to condition
> the 0.027 m3/s of
> outside air and the return flow rate ("exact needed
> flow rate" - 0.027 m3/s)
> to the inlet zone temperatures. This way the outside
> air is only brought in
> when there is a zone load and the purchased air
> component needs to condition
> it.
>
> Which process happens and do I need to specify an
> "exhaust node" in my
> CONTROLLED ZONE EQUIP CONFIGURATION so that air in
> the zone can be released
> to make room for the incoming outside air.
>
> Thanks in advance
> Ian Doebber
>
>
>
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
>
> The group web site is:
> http://groups.yahoo.com/group/EnergyPlus_Support/
>
> Attachments are not allowed -- please post any files
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>
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>
> Thanks
> Rahul Chillar
> Grad Student
> Building Systems lab
> Univ Of Illinois Urbana Champaign
>
>
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References:
- Re: [EnergyPlus_Support] purchase air with outside air
  - From: Rahul Chillar

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