proposed & baseline design energy use

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Hi,

In my model, I have to storage rooms with no cooling and just heating. One of them is gas infra radiant heater and the other one gas unit heater.
I modeled both of them as a unit heater (system type), 0 design kw/cfm, Furnace (heat source) and entered heating capacity (-400000 btu/h for infra and -120000 for UH).
When I run the LEED results (CSV), my gas cost is about $22/y.

I do not know, how to fix this problem.

Thanks in advance for your help.

Arash Pasgar

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Hi Arash,

I don't often do pictorial breakdowns like this, but this seems a particularly well-suited example to illustrate some common investigative procedures.

First observing your unmet heating hours are in check, I see a uniform rate of $0.776500/therm, then turning to your consumption reports after simulating: [cid:image004.png at 01CD3E75.4289DF40]
[cid:image005.png at 01CD3E75.4289DF40]
Annual gas consumption here is 2.49 MBtu. The simple math with the above rate works out to $19.33/yr by hand (acknowledging there's some rounding with that 2.49 figure, this checks out).

The rate seems a bit cheap to me, but then hey it's Texas. Don't mess with Texas =)! If there's a problem to fix, I expect it's with consumptions.

Your SS-R reports are a clue: These systems (1) do not run often, and (2) when they do, the load rings in well below the specified capacity (between zero and 10% mostly).
[cid:image006.png at 01CD3E77.0BB27ED0]

There may be some disconnect to resolve between the load calcs used to size your equipment and the loads being addressed in the energy model. Resolving such a disconnect may correct the amount of heating being done and thus bring your consumptions up. I suggest reviewing your constructions and other inputs affecting your model's heating loads for those zones (ex: internals like lighting, occupancies, and associated scheduling) against the load calcs. Perspective check: keep an open mind as the "problem" may not be with the model - load calcs can make mistakes.

Before turning your attentions to the load calcs however, consider whether all the associated envelope heating loads are even being seen by your gas heating systems. Looking to your geometries, I notice you have both plenum and under-roof zones defined. Closely review how those zones are tied (or not) thermally to the zones with the thermostats. Also consider whether the under-roof zone - which aggregates all the roof skin loads - (1) should not be broken up, (2) should be assigned to electric heating systems, and (3) is itself conditioned.
[cid:image007.png at 01CD3E77.5F83DCC0]

Playing around a bit with thermal ties and zone assignments as suggested, I arrived at a ~30 MBtu annual draw, bumping the annual gas costs into the hundreds... This may or may not be in the right ballpark for where you're headed, but illustrates the potential effects (>10x here) when your loads do not get to the correct thermostats:
[cid:image003.png at 01CD3E70.D353DBC0]
~Nick
[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.

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Nick, I have a follow-up question. How does one define the "thermal ties" between plenum and conditioned space zones?

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Hi Cole,

Apologies - "thermal ties" isn't an official DOE2/eQuest term - it probably isn't in the help files...

Zones have internal partitions (walls, ceilings, floors) and those interior surfaces have a property called "next to," which you can examine by double clicking the interior surface in the component tree. For two zones to be "thermally tied," one needs to have a (non-adiabatic) interior surface with the "next to" property calling out the other zone.

Here's a typical example of an office space which is tied thermally to a corresponding plenum space by a 131.8 ft2 interior surface using a defined ceiling construction:
[cid:image009.png at 01CD3F15.3CABD650]

Two spaces which do not have an interior surface linking them in this way will not transfer heat to one another. When I advise to investigate and define thermal ties - I mean to review whether the spaces in context (1) have the expected interconnecting interior surfaces (if not - define them), and (2) review what that "next to" property says, and correct if necessary.

~Nick
[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.

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