Dear forum,
I just had a new thought as I re-read this.
The “unmet load hour” hinges on the “throttling
range” definition. Back in the day when commercial controls were
pneumatically based, there was such a thing as “throttling range”
and it was easily defined since almost all control systems used proportional
(only) control loops.
Today, almost all control systems are digital and employ both
proportional and integral gains. By definition, if an integral gain is used,
the room might be .01 degrees from setpoint and eventually will drive
the actuator to 100% cooling (or heating). So, I’m wondering what I
might be missing…
The Building Performance Team
James V. Dirkes II, P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of jeannieboef
Sent: Friday, October 01, 2010 3:11 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: Time Set Point Not Met - Radiant Floor
Heating System
The following has come to my attention:
This area will be clarified when the new version of 90.1 is released next
month. New for the 2010 version of 90.1 are the following definitions and
addition to Table G3.1
****************************************
unmet load hour: an hour in which one or more zones is
outside of the thermostat setpoint plus or minus one half of the
temperature control throttling range. Any hour with one or
more zones with an unmet cooling load or unmet heating load
is defined as an unmet load hour.
temperature control throttling range: The number of degrees
that room temperature must change in order to go from full
heating to no heating or from full cooling to no cooling.
Temperature and humidity control setpoints and schedules as well as temperature
control throttling
range shall be the same for proposed and baseline building designs.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx,
"jeannieboef" <jeannieboef@...> wrote:
>
> Thanks, James. In my system it's not much, but when a window opens and the
air temperature changes by 1.5 Kelvin, the Radiant Floor System just can't keep
up because of it's huge thermal capacity. I don't have start up problems
because the system is always on (actually read a study on this, which shows
very small savings by ramping up and down overnight). Obviously, increasing the
capacity of the system can only improve things by a negligable degree. The as
designed system is also AS DESIGNED and thereby has this inherent property.
It's not so much I'm taking about in any case. 1 Kelvin tolerance instead of
0.2 would probably cut it.
>
> I've posted this question on some diverse blogs to see what people say and
will keep you posted.
>
> Thanks again for the input.
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx,
"James V Dirkes II, PE" <jim@> wrote:
> >
> > Dear Jeannie,
> >
> >
> >
> > This criteria comes from ASHRAE 90.1 ,as you probably know. ASHRAE
90.1
> > does not define this value, although I think perhaps they should.
Since
> > they do not, I suspect that it�s up to some interpretation.
> >
> >
> >
> > Normally, my �unmet loads� are at startup periods and do not last
for more
> > than an hour or so. In my opinion, this is not too important, since
you can
> > always start the system a bit earlier on the coldest or hottest days.
I
> > suspect that ASHRAE�s underlying rationale for not having too many
unmet
> > load hours was that they did not want the system deliberately
undersized.
> > If you can justify that it�s not (deliberately undersized), you may
be OK.
> >
> >
> >
> > p.s., This is my opinion only. I have not debated the issue on a LEED
> > certification!
> >
> >
> >
> > The Building Performance Team
> > James V. Dirkes II, P.E., LEED AP
> > 1631 Acacia Drive NW
> > Grand Rapids, MI 49504
> > 616 450 8653
> >
> >
> >
> > From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> > [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
On Behalf Of jeannieboef
> > Sent: Wednesday, September 29, 2010 2:25 AM
> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> > Subject: [EnergyPlus_Support] Time Set Point Not Met - Radiant Floor
Heating
> > System
> >
> >
> >
> >
> >
> > Time Set Point Not Met Tolerance is 0.2�C ( ... DOE had specified a
> > tolerance of +-0.5F for this...energyplus has a default of 0.2 degC).
Am I
> > justified in relaxing this tolerance on a system that obviously
cannot
> > respond to fast and so accurately to flux in room temperature?
Increasing
> > the "Capacity" of the system will not fix this.
> >
> > Should I then relax the tolerance on the baseline heating system
also?
> >
>
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