I´m not sure if we have modeled the HVAC baseline system correctly. We are in a climate zone 2a (São Paulo - Brazil). And we are using in the project building a single mini split system 9.000 BTU, with CFMs of 620m3/h. According to Table G3.1.1A (ASHRAE 90.1), we have used System nº 2- PTHP for baseline moleding. We though that for this scenario, we would not need an Ecnomonizes High-Limit shut-off, but USGBC is asking us to model baseline with an economizer and a supply-air-to-room-air cooling temperature difference of 11ºC. Not sure where to plot this 11ºC temperature difference, and how to demonstrate that this HVAC is meant for cooling. why a high-limit shut-off is needed? We are really lost in this one. Can anyone help with this issue?

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Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Tue, 09/25/2012 - 17:02

I am confused as well. Climate zone 2a never should have an economizer in the baseline. Is your project residential? Systems 1 and 2 are for residential buildings only. If your baseline is indeed a system 2 then you do not have an economizer in the baseline (see G3.1.2.6). If your baseline is a system 3 to 8 instead of system 2 and you are in climate zone 2a you would still not have an economizer in the baseline (see Table G3.1.2.6A).

Henrique Mendes

Mr.

Green Domus | Desenvolvimento Sustentável

LEEDuser Basic Member

13 thumbs up

Tue, 09/25/2012 - 17:52

Hey Marcus, thank you for all your attention. Our project is not residential, it´s a small building which will be used for employees as a breakroom. in the project building we only have a small room (14 m2) which will have this mechanincal ventilation system. So what we should do is to run the baseline model again, considering system 4 I believe, I have to check is rooftop heat pump aplies. Then, I´ll need to calculate our fan power again right? Using the formula: CFMs * 0.00094 +A?

Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Tue, 09/25/2012 - 18:29

Sounds like system 4 and yes you would need to redo the baseline fan power calculations since the formulas are different for a system 4 than a system 2. See G3.1.2.9

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