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thermal zone for multiple spaces

asked 2016-02-02 10:27:55 -0500

Morteza's avatar

It seems OS is not capable of assuming single thermal zone for multiple spaces of different space types. I am trying to use OS for one of my LEED projects, when I select different space types (i.e. five spaces) and assign a thermal zone for them the simulation results (as shown in lighting summary table) indicates the program assumes five thermal zones, one for each space, with the same area, LPD and total power. However, there would be no problem if the selected spaces were with similar space type. Am I missing something or this is a problem with the software? Thank you for your time,

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Are you sure there are five thermal zones? I would think you would get one thermal zone with five lights objects. Can you post a picture of the output you are concerned about?

macumber's avatar macumber  ( 2016-02-02 11:12:16 -0500 )edit

Thanks for your prompt response, yes there are multiple thermal zones with identical floor area and lighting power. At first, I noticed from the annual interior lighting load that was almost triple the actual load. Please see the "Interior Lighting" table in the following link. Thanks,

Morteza's avatar Morteza  ( 2016-02-02 12:23:19 -0500 )edit

That's a fairly complicated model, I can't really tell what problem zones are. Can you make a smaller test model and post a link to the OSM?

macumber's avatar macumber  ( 2016-02-02 13:09:17 -0500 )edit

I just prepared a simple school-test model consisting 15 spaces with 4 thermal zones. Each thermal zone has 3 or 4 different spaces. For example, thermal zone 1 has 4 spaces with total area of 1500.83 sf. As you can see in the “lighting summary” table the total area of this zone is assumed for all the spaces within the zone. Total space area of the model is 6,786.07 sf (Table EAp2.2) but in lighting summary table, interior lighting total area is 25,860.48! Thanks,

Morteza's avatar Morteza  ( 2016-02-02 16:58:46 -0500 )edit

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answered 2016-02-02 18:01:34 -0500

updated 2016-02-02 18:11:45 -0500

I think this is a misunderstanding about that table. If you look in the Input Verification and Results Summary: Zone Summary table there are only 4 zones in the model for 630.39 m^2 of conditioned floor area.

What you are seeing in the Lighting Summary is that there are multiple lights objects in each zone. For example, THERMAL ZONE 1 has four lights objects in it. The first of these is '90.1-2007 - PRISCHL - CAFETERIA LIGHTS 2'. In the OSM, this was associated with Space 105 through Space Type '90.1-2007 - PriSchl - Cafeteria'; the load had a density of 0.9 W/ft^2. Space 105 has a floor area of 425.9902 ft^2, so in your final EnergyPlus model this is converted to a lights object with fixed wattage of 0.9*425.9902 = 383.39 W which is assigned to THERMAL ZONE 1. Does that make sense?

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However, I don't know why that table sums up zone area for the same zone multiple times. It seems to use that to compute it's summed lighting power density but that is not correct. The report shows a total of 7863.42 W for lighting. As mentioned above, your model has 630.39 m^2 of conditioned floor area, not 2402.28 m^2 as shown in the report. So your total LPD is 7863.42/630.39 = 12.47 W/m^2 = 1.16 W/ft^2 and not 3.2733 W/m^2 as shown in the Lighting Summary. The correct LPD is shown in the Zone Summary table, seems like the Lighting Summary is confusing at best, wrong at worst.

macumber's avatar macumber  ( 2016-02-02 18:10:27 -0500 )edit

Thank you for your time and all the feedback. As you have mentioned there are some confusions in the lighting table. Based on simulation results of the actual models consisting of thermal zones of multiple spaces, in both cases the calculated LPDs are the same however, the annual electric consumption related to the interior lighting of models are quite different. Following are the links to these models. Total gross floor area of these models is 19,205.36 sf and all components and assumptions in these two models are the same.

Morteza's avatar Morteza  ( 2016-02-03 18:28:28 -0500 )edit

Each model has 22 thermal zones; the only difference between these models is similarity and dissimilarity of spaces within some of the thermal zones. In “Simi-Spac-TZ.osm” model, there are six thermal zones with multiple spaces. The spaces that are in each of these thermal zones are of similar space type. In “Diff-Spac-TZ.osm” model, the spaces within each of the six thermal zones are not the same type. Following values are from Result Summary tables:

Morteza's avatar Morteza  ( 2016-02-03 18:31:40 -0500 )edit


Total LPD = 4.0887 Btuh/sf = 1.2 W/sf, Annual interior lighting from meter and from LEED Summary table EAp2-4/5 = 90,195 KWh, Total annual energy cost = $32,076.77


Total LPD = 4.0887 Btuh/sf = 1.2 W/sf, Annual interior lighting from meter and from LEED Summary table EAp2-4/5 = 157,040 KWh, Total annual energy cost = $40,254.08

Morteza's avatar Morteza  ( 2016-02-03 18:32:23 -0500 )edit

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Asked: 2016-02-02 10:27:55 -0500

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Last updated: Feb 02 '16