[EnergyPlus_Support] Re: Adaptation to sensible load variation of the object Coil:Cooling:DX:singleSpeed

["JV Dirkes II" <jvd2pe@xxxxxxx>]

Dear Aymeric,

I cannot look it up to confirm this, but I think that there  are two
variables which affect the discharge air temperature.

One of them is in SET POINT MANAGER:SINGLE ZONE COOLING:  the "minimum
supply air temperature" field.
The other is in SYSTEM SIZING:  the "Central cooling design supply air
temperature"  field.

Sometimes, I set these to different values, then report the node
temperature value and airflow rate to see which one is in use.  I recall
that E+ does not use the one I expect, so it's worth checking.

I hope this helps!

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "aymericnovel"
<aymericnovel@...> wrote:
>
> Thank you for quickly answering. It is already some considerations I
> will take care of.
> Now, I know the cooling coil is sized by E+ based on sensible load.
> My technical question is more about: Can it be sized by changing the
> blown air temperature instead of the airflow rate? or does the E+
> code leave no choice for that?
> I mean now it keeps blowing air at 13.5°C in the zone but it
reduces
> airflow rate from 0.08kg/s to 0.05kg/s to reduce cooling capacity.
> Could it be more like keeping airflow rate at 0.08kg/s and blowing
> air at 15°C or 16°C?
>
> Regards,
> Aymeric
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "JV Dirkes II"
> jvd2pe@ wrote:
> >
> > Dear Aymeric,
> >
> > Some general considerations:
> >
> > Split system DX systems always have difficulty controlling
> humidity; the
> > thermostat senses only temperature in most cases.  In addition, the
> > cooling coil is not designed or intended for high latent loads
> > (generally a sensible heat ratio of ~0.7 is expected).  The fact
> that
> > the compressor cycles on and off compounds the humidity control
> > problems, since no humidity gets removed during an "off" cycle.  In
> > fact, moisture on the cooling coil can even get re-absorbed if the
> fan
> > continues to operate while the compressor is off.
> >
> > Your system gets sized by E+ according to sensible load, not latent
> > load. When you reduce the sensible load, but latent loads remain
> > unchanged, the space humidity will rise because the DX coil
> > (correctly) canot handle the higher sensible heat ratio.
> >
> > If a split system is a logical choice for your application, then the
> > savings  you are seeing may be realistic.  If you want to deterime
> the
> > "maximum possible" savings in your      , I think you should
> consider a
> > cooling system which modulates the cooling (no compressor cycling
> on and
> > off).  That should control humidity much better.
> >
> >
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "aymericnovel"
> > <aymericnovel@> wrote:
> > >
> > > Hi,
> > > I have simulated a 90m² apartment in HoChiMin, vietnam. This is
my
> > > first study in such a humid climate so I apologize if my question
> is
> > > trivial. Here is my problem:
> > >
> > > I use the SingleSpeed DX coil in each cooled zone to simulate a
> split
> > > system.
> > > It recirculates only room air. The temperature setpoint for zone
> is
> > > 26°C.
> > > My study aimed to quantify benefits on cooling energy consumption
> of
> > > actions on the envelope (use of insulating concrete, low SµHGC
> > > windows) and reduction of lighting related internal loads. So far,
> > > very logical.
> > >
> > > And logically, I found that my sensible loads are reduced (about
> 30%).
> > >
> > > But, the DXCoil adapts to a lower sensible load by blowing less
> air
> > > at the same temperature. For an idea here are the 2 configuration
> at
> > > the air outlet of the coil:
> > > High sensible load => 0.08kg/s at about 13.5°C
> > > Low sensible load => 0.05kg/s at 13.5°C
> > >
> > > Logically, in the second case, the sensible cooling rate
> delivered is
> > > smaller, according to the fact sensible load is indeed smaller.
> > > BUT, the latent load increases accordingly. The SHR (Sensible Heat
> > > Ratio) decreases in the second case, making the latent part
> bigger:
> > > High sensible load => SHR = 0.7
> > > Low sensible load => SHR = 0.6
> > >
> > > So, when looking at the result on the total cooling rate, it is
> not
> > > as fruitful as expected...I guess it is a known fact for engineers
> > > who are used to work with high outdoor humidity ratio
> > >
> > > Is it because the coil is "single speed" that the regulation is
> > > automatically made by airflowrate? Is there a way to modify the
> blown
> > > air temperature instead? Indeed, that would create energy savings
> > > also on the latent part to blow the same airflow rate at a higher
> > > temperature if sensible load is increased? Isn't that the tendency
> > > of current evaporator to increase SHR? Should I change the object
> I
> > > use? I guess it is all related to "how the object calculates the
> > > blown air temperature"...
> > >
> > > If somebody could help me clear my mind on this topic, I would be
> > > grateful!
> > >
> > > Tnaks a lot,
> > > Aymeric
> > >
> >
>




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