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Re: [EnergyPlus_Support] A question with baseboard heating
> The heating setpoint not-met hours largely decreased, but in the
> meantime the heating energy use was largely REDUCED compared with
> autosised results! Based on my understanding, the heating energy use
> should increase with much less heating un-met hours.
1. Comparing the two input files shows that the autosized version is missing
the priority fields for the baseboard heat in several of the ZONE EQUIPMENT
LIST OBJECTS. Adding the priority 2 fields helps reduce the number of hours
the setpoint is not met. I will refer to this as the "autosized-fixed"
version. (There should be an error message when the priority fields are not
present - this will be fixed.)
2. In the autosized-fixed version, the heating gas consumption is now 328 GJ,
and the total pump electricity is 5.34 GJ. In the non-autosized version, the
heating gas is 322GJ, and the pump electricity is 28 GJ. Even though the
heating gas consumption has dropped by 6GJ, the pump energy has increased by
nearly 25GJ. So the total heating energy input is higher by 19GJ in the non-
autosized version. This is consistent with less hours of setpoint not met.
3. So the questions remains - why does the autosized-fixed version still have
a large number of hours with setpoint not met? The VAV system is set to supply
ventilation air tempered to 17.2 C. With a zone heating setpoint of 22C, the
ventilation air adds additional load. The baseboard heaters are autosized to
meet the zone sensible heating load, with no allowance for the ventilation air
load. This is why they are undersized. I cannot think of an easy workaround
for this so that the baseboards will autosize to an adequate size.
Mike
On 9 Oct 2007 at 17:00, Zhen Tian wrote:
> Dear All,
>
> I experienced an interesting issue when I used baseboard heating system in E+.
> The building I am modelling has VAV system and baseboard heaing for perimter
> zones. The systems were autosized. But I found that there are too many hours
> that the heating setpoint were not met, using the Compact HVAC generated inputs.
> So I input the UA vaue and Maximum water fow rate for the baseboard using
> reference values from previous projects.
>
> The heating setpoint not-met hours largely decreased, but in the meantime the
> heating energy use was largely REDUCED compared with autosised results! Based on
> my understanding, the heating energy use should increase with much less heating
> un-met hours.
>
> My fellow tested on his mode and found the same phenmenon. Does anyone who what
> is the problem? We use the newest version of E+ with interm update.
>
> Thanks a lot.
>
> Regards,
>
> David
>
>
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========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
EnergyPlus-Support@xxxxxxxx
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