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

[Chris Toothaker]

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? 

 
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:
 
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...
 
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.
 
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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