[Bldg-sim] Residential System Sizing

[Jeff Haberl]

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
 
8=! 8=) :=) 8=) ;=) 8=) 8=( 8=) :=') 8=) 8=) 8=?
Jeff S. Haberl, Ph.D., P.E.............................jhaberl at esl.tamu.edu
Professor......................................................Office Ph: 979-845-6507
Department of Architecture.......................Lab Ph: 979-845-6065 
Energy Systems Laboratory.......................FAX: 979-862-2457 
Texas A&M University..............................77843-3581
College Station, Texas, USA.......................URL: www-esl.tamu.edu
8=/ 8=) :=) 8=) ;=) 8=) 8=() 8=) 8=? 8=) 8=) 8=) 

________________________________

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