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CS-2009 EAp2:Minimum Energy Performance

System 5. Two boilers

In a review, the reviewer told me that as a system type 5, I should model 2 identical boilers. With that change (without defining capacity, I guess eQuest do it by demand) the baseline energy use decrease from 9 005 therms to 7 211 therms. As you can understand, this does not help in my purpose... and I cannot find a physical meaning. Anybody have a reasonable explanation? Thank you in advance

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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Tue, 09/09/2014 - 14:58

It makes perfect sense. The single boiler would operate many hours at well under it rated capacity. It is even exaggerated by the required 25% over-sizing. Two boilers which are staged as required would more closely match the loads throughout the year. Since the boiler efficiency is lower when the loads are lower the energy use would be greater. This is why modular boilers often make sense from an energy perspective.

Tue, 09/09/2014 - 18:56

Thank you Marcus, I thought the boiler capacity was modulating under demand already with just one boiler. I have no defined any capacity for the baseline boiler, so I guess it was defined automatically by the eQUEST. Where can I find an explanation about how have to be defined this boiler? (more detailed than G3 reference to the two boilers). Thank you in advance.
Profile picture for user sheffer
Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Tue, 09/09/2014 - 19:05

The boiler must be auto-sized and a 1.25 multiplier applied to the capacity (see G3.1.2.2). The modeling of the boilers for the Baseline is described in several sections of Appendix G (see G3.1.3.2 to G3.1.3.6).

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