[Bldg-sim] Residential System Sizing

[Ellen Franconi]

Another reason that the results are different is that the space temperature may be different in the "loads" part of the DOE-2 program than in the "systems" part of the program. In "loads", the space temperatures are set equal to the space design temperate. In "systems", the space temperature is based on the zone setpoint schedule and whatever temperature is actually achieved in the space. Thus, if you have a set up or a setback from the design space temperature, it will be different. 
Ellen
 
Ellen Franconi, Ph.D., LEED AP
Energy Analysis Group Manager
Architectural Energy Corporation
2540 Frontier Avenue
Boulder, CO 80301
tel. 303-444-4149
fax 303-444-4303
efranconi at archenergy.com 
http://www.archenergy.com/ 


>>> Jeff Haberl <jeffhaberl at tees.tamus.edu> 2/2/2009 8:40 PM >>>
Bereket:

I would not expect the values in SV-A and LS-B to agree for most buildings. There are many reasons for this.

First, peak loads from LOADS do not include ventilation loads as would be the case in SYSTEMS, only infiltration. 
Second, you may be looking at different days on the weather file between LOADS and SYSTEMS, so this would 
need to be checked. 

In addition, DOE-2 sizes for the absolute peak, whereas other methods, such as Manual J, have some undersizing
built into the procedures, hence you'll almost always get a much larger system size in DOE-2. 

Both the SV-A and LS-B lists you show seem reasonable, with the exception of the MN #s, which I suspect that you
may have a fair bit of 24 hour infiltration in your input file...(i.e., low night time temps in MN?) 
However, without looking at the file I can only guess. 

There are 100s of reasons for the funny little differences you show.  You're probabloy better off running a Manual J 
calculation on the house if it is residential. DOE-2 is known for doing a very bad job of sizing for residential.

Jeff

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Jeff S. Haberl, Ph.D., P.E.............................jhaberl at esl.tamu.edu 
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________________________________

From: bldg-sim-bounces at lists.onebuilding.org on behalf of Bereket Nigusse
Sent: Mon 2/2/2009 5:59 PM
To: bldg-sim at lists.onebuilding.org 
Subject: [Bldg-sim] Residential System Sizing



Hello All,

I have a problem with DOE2.1E cooling system sizing.  The cooling capacity reported by DOE2.1e in SV-A and LS-B reports are quite different and shows different sensitivity trends depending locations.  

Question 1
For the case with out door air flow ratio input set to zero DOE2.1E calculated cooling capacity and the peak coolig load are shown below.   I assume that the out door air contribution to the system load is zero for zero out door air fraction and with this assumption the system cooling capacity will be different from the peak cooling load only due to difference in ARI and the peak cooling load hour weather conditions.  What else could cause the cooling capacity to be different from the peak load for zero out door air flow rate case?  I have looked into to DOE2.1E manual but wasn't able connect the steps from the peak cooling load to the system capacity?  

Question 2
Does the change from the peak cooling load to the  system cooling capacity seem a reasonable for the different loacations given below? 
The building is 2100 sqft conditioned floor area, two story, single family house.  Each floor is modeled as a single zone.


  Report AV-A Report LS-B    
Locations Supply Flow, CFM Cooling Capacity, kBtu/hr Peak Cooling Load, kBtu/hr Outdoor DB Temp at Peak Load, oF Outdoor WB Temp at Peak Load, oF
Baltimore, MD 850.0 25.7 22.1 93 73
Houston, TX 813.0 27.0 20.2 93 78
Chicago, IL 1054.0 29.3 20.3 89 72
Minneapolis, MN 1226.0 33.5 20.3 89 79
Duluth, MN 1258.0 34.8 18.1 87 72
Phoenix, AZ 1281.0 37.4 31.6 114 71


Thank you in advance for the help,


Bereket

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