[Equest-users] No Space Heating & U-values showing opposite results

[Carol Gardner]

See embedded comments.

On Mon, Oct 11, 2010 at 6:25 PM, Chris Toothaker <crtooth2000 at yahoo.com>wrote:

> Hello eQuest users;
>
> 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:
>
>  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.
>
>
> 1) I don’t think I am specifying the proper HVAC system type:
>
> 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?
>

*These systems are correct. You will notice that they will both default to
heat pump rather than dx w/ electric cooling. The PVVT & PTAC just refer to
the type of air delivery system not the heat/cool source.*

>
>
> 2) There is no Space Heating occurring in my simulation:
>
> 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:
>

*Check your thermostat schedule, if you have one. If you don't you need one.
*

>
> 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...
>

*It depends on if your building load is internally dominated or skin
dominated and if you are in a heating dominated or cooling dominated
building. There was a very good discussion about just this subject within
the last few weeks. Search the archive.*

>
> 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.
>

*You shouldn't/can't use layers if you only have the R-value. You should use
the U-value input in this case.*

>
> 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.
>
>
> Chris Toothaker
> Assoc. AIA
>
> SIMBIOSIS
> P.O. Box 132155
> Dallas TX 75313
> www.simbiosislab.com
>
>
>
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>


-- 
Carol Gardner PE
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