EER to EIR Conversion for LEED Baseline

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All,

When you Calc your EIRs for baseline, do you use design capacities or oversized baseline capacities?

Thank you.

Kevin

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Kevin:

I believe it is 15% oversize for cooling and 25% for heating (Page 176 -
Appendix G - ASHRAE-90.1-2004 - I don't have 2007 yet). This is aside
from fan calculations.

This would apply to either package units or central plant equipment,
whichever is specified as baseline.

John R. Aulbach, PE, CEM

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And the baseline EIR should include the wattage calc'd from G.3.1.2.9?

Backing up for a moment, there is a funny way to determine the oversizing capacities, especially for PSZs. Here goes:

Run the design model with design capacity, run the design model autosized, find the ratio.
Run the baseline model autosized, apply the ratio. Now oversize for 15% cooling and 25% for heating.

Does anybody do this differently, because the fine print doesn't exactly say that much.

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OK, I read it again. Autosize the baseline and run four orientations to obtain the capacities (assuming an average of the four). These capacities will be oversized. I understand. Thank you.

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Kevin,

This is an important question. I am not aware of a definitive answer. I
just looked at 90.1-2004, 90.1-2007 and the User's Manuals for both. I
see no change in 2007 specific to how to determine the equipment
efficiencies.

I agree that if you determine efficiency by the baseline equipment size,
you generally end up using better efficiencies for the baseline
equipment. As you mentioned, this is because you are required to model
one system per zone. At the same time, when you determine fan power
based on the baseline equipment size, you use higher kW/cfm. I am
finding that, because of this, my models rarely show cooling energy
savings, and usually show huge amounts of heating energy savings.
(Baseline furnaces are 80% efficient and my proposed systems approach
95%. Also, the buildings I model are mostly in NY - high heating hours.
I often have heat recovery systems, which also help with the heating but
not much with cooling.)

So, for know, it makes sense to me to determine the baseline
efficiencies and fan energies from the oversized (10%/25%) baseline
capacities. Knowing this, I have to avoid the tendency to model every
single space on the architectural drawings, and try bundling them better
into zones. (Make all the spaces served by one VAV box a single zone.
Make all the spaces served by a single-zone system one large zone,
unless the uses and orientations differ greatly. Etc.)

That's my $0.02.

William Bishop, EIT, LEED(r) AP

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May I ask how a gas-fired device can be 95% efficient when the limit
based on the chemical equation for combustion is 93%? (7% of the
byproducts of combustion being water vapor)

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You have to capture some of that 7% somehow by condensing, such as with
a second heat exchanger.

William Bishop, EIT, LEED(r) AP

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