FW: Including internal loads in space heating energy summary

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Heating design in the library schedules I am using (*-Midrise Bldg) ignores internal loads for heating design purposes. I am performing a LEED energy performance analysis, and I want to be sure I am including the internal loads in the space heating calculations. The assurances I got from the Trace help was not overwhelming, and the space heating requirements of the model seem intuitively too high.
As a check, I created my own custom schedules for people, lighting, and process loads, with a heating design schedule which matched the cooling design schedule. The results showed increased receptacle and lighting loads (people loads were not listed in the report) as if the program were somehow double accounting for the two schedules. The space cooling energy use increased, as would be expected if the loads were counted twice. Surprisingly, the space heating energy use also increased. This has me concerned.
Does someone out there have knowledge about how Trace handles internal heat loads when calculating space heating energy use?

Tom Ferrel's picture
Joined: 2014-06-24
Reputation: 0

Hi Tom-

Design schedules are a common confusion point for new (and intermediate)
TRACE users.

It is wise to consider that TRACE is essentially two programs packaged as
1. First, it is a load design program. Then, it is an energy-simulation

The heating design schedule is only used to size heating equipment. If you
run the "Design" portion of the program, it only uses the "Cooling Design,
and Heating Design Schedules". Then, when you run the rest of the program
"system, energy, economics", it incorporates the weekdays schedules, etc.
It would be very difficult for non-advanced users to "spin the meter" with
lights or receptacles and ignore the impact on heating the load.

I would recommend looking at a checksums report to more clearly see the
impact when changing design schedules. Any of the checksum reports would
certainly show lights, misc, and people. I'm guessing you are looking at an
energy report? It would help to know the specific reports.

As to why the heating energy increased with the change in schedules, that
would depend on what you changed in the schedules.. Seeing that the cooling
energy increased tells me that you changed more than just the heating
design schedule. (when experimenting with schedules, it's best to change 1
thing at a time - i.e. just set change the heating design schedule)

Taking a stab in the dark, are you running a VAV system with Std 62
enabled? The load design troubles you are encountering may actually be a
result of something other than internal heat gains.

Let's start there and see what else we can find out,

Bob Fassbender

Bob's picture
Joined: 2010-06-30
Reputation: 475