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Ashrae sizing: Zone Sensible Cooling and ZoneHVAC:IdealLoadsAirSystem

asked 2018-11-02 12:33:38 -0600

Gio gravatar image

Hi, I'm studying ASHRAE 2009 cooling sizing (RESIDENTIAL COOLING AND HEATING LOAD CALCULATIONS Chapter 17) and in my model I'm using an IdealLoad system.

Can I get the sizing results from EnergyPlus? I see two tables that could be useful (in the html file): Zone Sensible Cooling and ZoneHVAC:IdealLoadsAirSystem tables. Is one of these the ASHRAE sizing result?

Referring to the html tables, if I read the table Zone Sensible Cooling it misses the ventilation losses. On the other hand, the ZoneHVAC:IdealLoadsAirSystem gives me very high values (much more than the Zone Sensible Cooling plus the ventilation loss) and I can't find an E+ document where the sizing method is described.

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answered 2018-11-06 17:44:39 -0600

See Engineering Reference section "Zone Design Load Calculation" for a description of the zone sizing methodology. ASHRAE sizing starts with a pure zone sensible load, then adds ventilation, and then can determine equipment sizes. The design loads reported in the HVAC Sizing Summary table output are equivalent to the pure zone load with no ventilation. One must be careful with the assumptions that go into this (internal gain and thermostat schedules for the sizing day types, and more).

The difference in the ideal loads results compared to the peak zone sensible load is likely due to latent cooling. Either turn off dehumidication in the ideal loads object, or report the ideal loads components to break out the components. Output:Variable "Zone Ideal Loads Zone Sensible Cooling Rate" is equivalent to the load reported in the HVAC Sizing Summary table. If you run a simulation for the sizing periods, you should see the same number show up. "Zone Ideal Loads Supply Air Sensible Cooling Rate" includes the ventilation load. And there are similar latent and total outputs as well.

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Asked: 2018-11-02 12:33:38 -0600

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Last updated: Nov 06