[Bldg-sim] Residential System for High Ceiling house

[Abaza Hussein]

Hi all;

Can any one advice on the best HVAC system configuration for a house with a
high ceiling in the great room (other than installing a fan in the ceiling).
I have faced this problem many times. The way I was doing it is by over
sizing the AC unit for the second floor, and over sizing the furnace for the
first floor. But still, the thermostat in the second floor will not help in
making the lobby of the first floor much cooler that what it should be. The
same thing applies for the heating. Another way I was doing it is by having
one system for the entire house and run the fan continuously, but this
system is also in efficient, because I can not zone the house. Is there a
better way to do it and is there any research in this area?

Thank you.

H. Abaza

  _____  

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Xiaobing Liu
Sent: Tuesday, February 03, 2009 11:41 AM
To: 'Bereket Nigusse'; bldg-sim at lists.onebuilding.org; Jeff Haberl
Subject: Re: [Bldg-sim] Residential System Sizing

 

Bereket:

 

There are many other reasons could explain the differences:

 

1. "System-Sizing-Ratio". For many system, eQUEST uses 1.15
"System-Sizing-Ratio". 

2. Fan power. Different from space load calc, the system cooling capacity
has to account for fan power heat as part of the cooling loads.

3. How about latent cooling? Have you accounted for latent cooling in your
comparison?

4. Make sure the zones in LS-B and SV-A report are exactly the same. Has the
loads from roof/ceiling be accounted for in the LS-B report?

 

I am surprised to see in your results that Minneapolis, MN has slightly
higher cooling loads (20.3 kBtu/hr in LS-B) than Houston, TX (20.2 kBtu/hr
in LS-B).

 

Jeff:

 

In your e-mail, you mentioned that "DOE-2 is known for doing a very bad job
of sizing for residential". Is there any report/paper detailing this?

 

Xiaobing

-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org]On Behalf Of Bereket Nigusse
Sent: Tuesday, February 03, 2009 5:32 AM
To: Joe Huang; Ellen Franconi; bldg-sim at lists.onebuilding.org; Jeff Haberl
Subject: Re: [Bldg-sim] Residential System Sizing


Hi All,

I am modeling a residential building with RESYS as a system, and using auto
sizing for system sizing.

The space temperature (space design temperature) for load calculation is set
at 75 oF while the Design-Cool-T is set at 78 oF.  I believe that this has
the effect of decreasing the system cooling capacity. There is no set-back
or set-up applied.    No ventilation outdoor air is specified.
Infiltration, which is already captured in the building load calculation, is
part of the building load.  

How does the system cooling capacity increases by more than 50% (in the case
of Minneapolis and Duluth, Minnesota) compared to the building peak load in
the absence of any out door air load for ventilation?  

Thanks,
 
Bereket

 

 


  _____  


From: Joe Huang <joe at drawbdl.com>
To: Ellen Franconi <EFranconi at archenergy.com>;
bldg-sim at lists.onebuilding.org; Jeff Haberl <jeffhaberl at tees.tamus.edu>;
Bereket Nigusse <nigusse_ba at yahoo.com>
Sent: Tuesday, February 3, 2009 2:16:32 AM
Subject: Re: [Bldg-sim] Residential System Sizing

Ellen, 

 

Not exactly. What you wrote is definitely true during the SYSTEMS simulation
and peak loads reported in SS-F (?), but Bereket was referring to the SV-A,
which is the systems sizing report. Assuming that he's doing "auto-sizing",
the DOE-2 sizing routine will take the peak loads from LOADS and compute the
design cooling capacity at the COOLING-DESIGN-TEMPERATURE. (I may have the
keyword wrong, since I don't have a DOE-2 manual handy).  Thus, the
termperature discrepancy between the single LOADS temperature and the
COOLING-DESIGN-TEMPERATURE does exist, as you've mentioned, but transient
loads due to tempeature set-up or set-back or interzone heat flows are not
reflected. That's why an autosized SYSTEM will often still result in a few
undercooled or underheated hours.

 

My suggestion to Bereket in making sense of the numbers is to compare the
TEMPERATURE under SPACE-CONDITIONS for the LOADS reference temperature, to
the COOLING-DESIGN-TEMPERATURE (I may have this keyword wrong) is
ZONE-CONDITIONS in SYSTEMS. What kind of HVAC are you modeling?  It sounds
like a residential system (RESYS), but that system doesn't have any
OUTSIDE-AIR, does it ? 

 

Joe Huang

White Box Technologies, Inc.

 

----- Original Message ----- 

From: Ellen <mailto:EFranconi at archenergy.com>  Franconi 

To: bldg-sim at lists.onebuilding.org ; Jeff <mailto:jeffhaberl at tees.tamus.edu>
Haberl ; Bereket <mailto:nigusse_ba at yahoo.com>  Nigusse 

Sent: Monday, February 02, 2009 7:50 PM

Subject: Re: [Bldg-sim] Residential System Sizing

 

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

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

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