Determination of thermal zones in one multi-story building in EnergyPlus

According to Help Reference-Getting started, "The general rule is to use the number of fan systems (and radiant systems) not the number of rooms to determine the number of zones in the building. ". The case i have at hand is one simple building with 10 stories and i am going to assign 10 thermal zones and one single thermal zone for it, respectively and make comparison in terms of total energy consumption of assigned VRF hvac system.

However, when i run simulations in Energyplus, the energy consumption of HVAC system under two situations differ greatly. It is out of my expectations because the Reference said "the total building load calculated using a one-zone model of the Education Center (Figure 5.2) will NOT be significantly different from the total building load calculated using a more detailed model."

The simulation results are pasted below for two situations. If the building is separated into 10 thermal zones: Heating: 0 Cooling:836.85 Interior Lighting:12411.44 Interior Equipment:13053.06 Fans:31.40 if the building is modeled by only one thermal zone: Heating: 42.59 Cooling:1530.88 Interior Lighting:12411.44 Interior Equipment:13053.06 Fans: 75.80

zhuazheng3

asked 2018-10-17 22:35:50 -0500

11.8k

shorowit

updated 2018-10-18 09:30:30 -0500

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Some of the zoning discussion in Getting Started was written back when graphical tools to draw the building envelope were not available or were rudimentary (this document is schedules for a rewrite soon). In that example, even the detailed zoning model has single-zone HVAC systems. For a 10-story building, assuming a rectangular footprint, a commonly used current approach is five zones per floor - four perimeter zone for each facade direction and one core zone. Other considerations that would prompt additional zones would be areas with significantly different thermostat setpoints, different schedules, or different internal gain densities. For a highly-glazed 10-story building I would not expect a single-zone model to give a good result, or even a 1-zone-per-floor model. For comparisons like this, always check the "thermostat setpoint not met" results in the ABUPS report to be sure that each model has controlled the zone space temperatures as specified.

There are many general building energy modeling resources available, including two books published or endorsed by IBSPA that have far better information about accepted modeling practice.