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



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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