Hello eQuest users;
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I have 3 questions that are all related to each other. I am fairly new to energy
modeling, so please help me resolve these issues that I have been struggling
with for quite some time now:
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?Our project is a 17-story residential condo building in Monterrey, Mexico. The
HVAC system for each of the living units consists of a mini-split heat pump
system with 3 zones sharing an exterior condenser.
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1) I don?t think I am specifying the proper HVAC system type:
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In Wizard mode under the HVAC system definition, if I select the system type to
?Split System Single-Zone Heat Pump (residential)?, system per zone, and cooling
& heating sources both as ?DX coils? with heat pump source ?Air? ? in DDedit
mode, the HVAC system defaults to a PVVT system. Is this really the same thing?
Similarly, when I model the baseline building as a ?Packaged Terminal Heat Pump?
in Wizard mode, the HVAC system defaults to a PTAC system in DDedit mode, which
according to ASHRAE 90.1 is a completely different (an incorrect) system type.
When I attempt to change either of these types manually in DDedit mode, none of
the desired systems are available in pull-down options. How then can I
appropriately set the correct HVAC system types?
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2) There is no Space Heating occurring in my simulation:
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Every time I run a simulation, no matter how many options I seem to vary, no
Space Heating occurs for any of the HVAC system zones.? I have input the
manufacturers specified heating & cooling capacities for each zone and have even
tried varying the HVAC system types and capacities, but I simply cannot get any
heating to occur. Allowing eQuest to autosize the capacities yields slightly
more success, but if I know the actual capacities, shouldn?t I model them as
such? However, I can get different results if I vary the inputs related to my
last question:
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3) Lower input U-values indicate more energy use while higher input U-values
indicate less energy use. This same result consistently keeps happening for
windows, walls, anything. Shouldn?t the exact opposite result occur? In regards
to question 2, if I input a ridiculously high U-value for the exterior walls,
say 13.7 (the R value equivalent of the actual 0.073 U value), I finally get
some Space Heating results...
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In DDedit mode, under the ?Constructions? component, I have set up inputs for
the building?s U Values using the ?Layers input? as the Specification Method;
and for the layers/materials I basically just set up 1 layer that corresponds to
the entire assembly thickness and total U-value. I originally set up the
proposed design with several different layers, but I later changed it so that it
could more closely relate to the baseline input because I was not sure how to
set up the baseline assembly layers only knowing the required minimum R Value as
per ASHRAE 90.1. Honestly I get the same result whether I use the U-value input
or Layers input, but I assumed the Layers Input would be more accurate as it
accounts for wall thickness.
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I sincerely thank you in advance for any help that anyone can provide. I am not
an engineer, so I greatly appreciate any advice that I can get. Attached are the
.inp, .pd2, and weather.bin files.
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Chris Toothaker
See embedded comments.
Some additional thoughts...
If you always have zero heating no matter what, then just as Carol said it's likely a missing or incorrect thermostat schedule for one or more systems. A coincident symptom of missing thermostats would be having 0 unmet heating hours while simultaneously having zero heating energy consumption when you know you should have some heating loads. You can't have an unmet hour in a zone without a thermostat to define it first.
More than once I've taken a first look at the visual consumption/cost reports, and too quickly drew the wrong conclusion also... If the heating cost/consumption bars are tiny in magnitude, is it because the others are astronomical? Entering a utility rate with the decimal one figure off will do that very sneakily =).
The layers method of defining constructions is pretty much something I personally always do, even when I have limited information. The U-Value method of defining constructions, if I'm not mistaken, is intended only for lightweight constructions with effectively zero heat retention / thermal mass (i.e. a metal shed). If you tried to model any masonry or wood-framed wall using the U-value method, I'd expect a pretty inaccurate simulation because you won't be modeling the realistic "buffer" over time for external envelope loads. With regard to what layers to use for 90.1 baselines, import the attached reference file for all above-ground wall and roof constructions for all climate zones (get to detailed mode ? file ? input file... ? navigate to this .inp file). Kudos and Credits for the original file to Adam Boyd by the way. Open the file with a text editor (notepad) to learn in detail where the layers were derived from.
Alternatively if you're using eQuest 3.64, you could dabble with the LEED compliance tool to have it generate layered constructions similar to the attached. I've not looked hard to verify the accuracy but I found good numbers were generated for a single project/climate zone.
It's probably worth noting that Monterrey Mexico on a cursory google search doesn't appear to drop below freezing temperatures much. If you have a building with significant internal heat loads and good insulation it may be perfectly normal to have heating consumptions of a low magnitude, as your occupants/lights/equipment are 'self-heating.'
NICK CATON, E.I.T.
Thank you very much for your help I will try both of your suggestions
Chris Toothaker