[Equest-users] Confirmation for finding the Baseline Energy Model Supply Airflow

[Otto Schwieterman]

Appendix ASHRAE 90.1 2007 Appendix G3.1.3.13 VAV Minimum Flow Setpoints
(System 5 and 7) states:

 

"Minimum volume setpoints for VAV reheat boxes shall be 0.4 cfm/sf of
floor area served or the minimum ventilation rate, whichever is larger."

 

For systems 5 & 7, I will set the minimum flow rate to 0.4 CFM/SF. If I
have high unmet hours due to the small amount of CFM, I will increase
the value on a room by room basis. The baseline's flow rates are
typically 30% less than my proposed model. The fans typically run more
often in the baseline model. 

 

Does anyone else have a different way to model the flow rates for the
LEED Baseline model?

 

From: Carol Gardner [mailto:cmg750 at gmail.com] 
Sent: Tuesday, September 07, 2010 9:02 PM
To: Kathryn Kerns
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Confirmation for finding the Baseline Energy
Model Supply Airfllow

 

You must use the 1.15 and 1.25 multipliers to meet LEED requirements. I
would look at the throttling range that eQ is defaulting to. if it's .5
F, which is I think what it is for PSZ, I would raise that to1 or 2 F,
which is reasonable. Then I would look at the space loads, equipment
especially and make sure all that looks good, then I'd look at the
schedules, make sure they are good, and then I'd look at the cfm/sf.
It's not unreasonable to match it to your proposed building and I don't
know of any issue LEED has with doing that.

Carol

On Tue, Sep 7, 2010 at 4:23 PM, Kathryn Kerns
<kathryn.kerns at bceengineers.com> wrote:

 

Yes, Carol I know the default airflow value is very low. Usually the
eQuest airflow auto sizing routine will select larger values than the
default. The problem is: what if the eQuest baseline energy model
selects airflows larger than the default cfm/sqft airflow values but the
baseline energy model still ends up with greater than 300 unmet hours or
the baseline energy model has more than 50 unmet hours greater than the
proposed energy model? 

 

Do you start increasing the baseline energy model airflows above the
auto sized airflow value in the thermal blocks that are having unmet
hours issues, or do you retain the auto sized airflow value and start
manually increasing the baseline heating and cooling capacities that
were also auto sized by eQuest using the 1.15 and 1.25 oversized
coefficients?

 

 

Kathryn Kerns

Systems Specialist

BCE Engineers, Inc.

| Ph: 253.922.0446 | Fx: 253.922.0896 | 

 

 

________________________________

From: Carol Gardner [mailto:cmg750 at gmail.com] 
Sent: Tuesday, September 07, 2010 2:22 PM
To: Kathryn Kerns


Cc: equest-users at lists.onebuilding.org

Subject: Re: [Equest-users] Confirmation for finding the Baseline Energy
Model Supply Airfllow

 

Kathryn,



I think that .5 cfm/sf is too low. I never saw it used when I was
designing HVAC systems except for an occasionally used interior space. I
immediately change it to1.0 cfm/sf which I feel is a good place to
start. For highly loaded rooms with lots of internal gain I sometimes up
that amount after I have checked the other possible inputs.

Carol

On Tue, Sep 7, 2010 at 1:55 PM, Kathryn Kerns
<kathryn.kerns at bceengineers.com> wrote:

 

Everyone, 

 

We are having a discussion at the office about how to define the supply
airflow and energy model baseline. I pick the baseline system type per
Appendix G (packaged single zone, packaged VAV, etc., set the heating
sizing ratio to 1.25 and the cooling sizing ratio to 1.15, leave the
heating and cooling capacities blank so the model will auto-size, and
then set the default airflow to 0.5 cfm/sqft and let eQuest run. I then
check to see if the baseline energy model unmet hours are less than 300
and are within 50 hours of the proposed model. If the baseline energy
model is above 300 unmet hours or isn't within 50 hours of the proposed
model, I will then start tweaking the airflow in the baseline energy
model thermal blocks that are causing the unmet hour issues to solve the
problem. 

 

Is this what everyone else is doing or do leave the airflow with the
default values it calculated with the 0,5 cfm/sqft limit and enter
capacity values in the previously blank HVAC cooling and heating
capacities slots so the baseline energy model stops auto-sizing? 

 

Thanks.

 

 

Kathryn Kerns

Systems Specialist

BCE Engineers, Inc.

| Ph: 253.922.0446 | Fx: 253.922.0896 | 

 

 


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-- 
Carol Gardner PE




-- 
Carol Gardner PE


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