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Re: [EnergyPlus_Support] heat gains in E+
See responses below. Mike
On 5 Sep 2003, at 0:03, Helen Xing wrote:
> Hello, Mike,
>
> Thanks a lot for this. I have couple of related questions as below,
> and appreciate your taking time to help. - Helen
>
>
> At 01:05 PM 8/22/2003 -0500, you wrote:
>
> >Surfaces interact with the zone air heat balance by convection. So,
> >the value of most interest is (SurfaceInsideTemperature - ZoneAir
> >Temperature) * SurfaceArea * SurfaceInsideConvectionCoefficient
> >
> >The best way to calculate the contribution from the envelope is to
> >take the total load and subtract off the gains from windows, internal
> >loads, infiltration, and ventilation. The remainder will be the
> >impact of the envelope.
>
>
> Does Energyplus have an output which gives the total load of a
> building? I saw "zone/sys sensible load predicted" and "zone/sys
> moisture load rate predicted" and a grand total would help if it is
> available.
>
> Alternatively, can we get the total load using several E+ outputs as
> follows? total load = Window Heat Gain + Window Heat Loss (Loss has a
> negative sign) + SUMHAT - ZoneAirTemperature * SurfaceArea *
> SurfaceInsideConvectionCoefficient + People (Lights, Electric-Eq) -
> Total Heat Gain + Ventilation Heat Gain + Infiltration Heat Gain
Unless you are running a steady-state case, it is very difficult to
try to add up components. You should be able to come close if you
total things across a whole day, but you will not be able to match
things exactly on an hour-by-hour basis. For example, the heat gain
from lights, people, and equipment is partially radiant, so it is
first absorbed by a surface and later becomes a cooling load. There
are other time-lag issues as well which make it difficult. The
equipment load is where it all comes together in one place, such as
in the cooling load.
>
> My model seemed to have problems with this, though.
>
>
>
> >"Plant Loop Cooling Demand" is the required load on the chillers to
> >meet the chiller water loop setpoint. In your energy balance, you
> >would also need to add in fan power and chilled water pump heat to
> >fluid.
> >
> >Mike
>
>
> So this specific output "Plant Loop Cooling Demand" minus the fan
> power and chilled water pump heat to fluid is the effective cooling
> provided by the plant, which should equal the total cooling load we
> tried to compute above?
Not always. "Plant loop cooling demand" is the cooling required to
return the chilled water loop to its setpoint in the current
timestep. If the loop is always maintained at its setpoint, then
this should be a valid calculation. But if the loop does not reach
setpoint in a given timestep (because equipment was scheduled off or
below its minimum part load ratio) then the plant loop cooling demand
in the next time step will include the unmet load from the previous
timestep as well as any new load in the current timestep.
>
>
>
> >On 20 Aug 2003, at 22:23, Helen Xing wrote:
> >
> > > Hello,
> > >
> > > To itemize the hourly heat gains through a buliding's envelope -
> > >
> > > Is there a zone output for "Zone Opaque Surface Inside Face Beam
> > > Solar Absorbed"? This output is available for single surfaces
> > > from the E+ results, but the zone sum doesn't seem so.
> > >
> > > For window heat transfer and opaque surface inside face conduction
> > > (maybe something else as well), E+ gives both heat gain and loss.
> > > Is there a zone output for the net value to reduce the data
> > > volume?
> > >
> > > One step further, wonder if there is a direct output that gives
> > > the total net heat gain for a zone through the envelope?
> > >
> > > Is there a manual or something that explains the available output
> > > names in .RDD files?
> > >
> > >
> > What is "Plant
> > > Loop Cooling Demand"? According to the input-output reference, it
> > > is the demand provided by the plant equipment to meet the cooling
> > > setting point. So is it equal to the total cooling load (sum of
> > > Qenvelope + Qwindows + Qinternal + Q infiltration&ventilation ) as
> > > a plant-building balance check? In two cases of mine, this
> > > "balance" didn't hold though. What gives the cooling capacity
> > > value provided by the plant if Plant Loop Cooling Demand is not
> > > the one?
> > >
> > > Thanks a lot,
> > > Helen Xing
> > >
> > >
>
>
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