EnergyPlus Air-Chiller Heat Balance Query

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Hello Community,

I am seeking help with an issue I’ve found while modeling evaporators for a refrigerated warehouse using the AirChiller object. I am working with the European Wet Standard Condition 2, which includes both sensible and latent heat in the cooling process. My problem is that the heat balance in my simulation seems to use only the sensible cooling capacity instead of the total cooling capacity (sensible + latent), and I’d like to understand why.

What I Did

I set up output variables for the AirChiller object to check its cooling capacities: total, sensible, and latent. I confirmed that total cooling capacity = sensible + latent, which is correct.

To check the zone air heat balance, I used this equation from EnergyPlus:

Here’s how I matched the terms in the equation to EnergyPlus output variables:

C_z*dT_z/dt​​: Zone Air Heat Balance Air Energy Storage Rate This is the heat stored in the zone air (in watts) when the air temperature changes over time.

∑Q_i: Zone Air Heat Balance Internal Convective Heat Gain Rate This is the total heat (in watts) added to the zone air from internal sources like people, lights, or equipment.

∑h_iA_i(T_si−T_z): Zone Air Heat Balance Surface Convection Rate This is the total heat (in watts) transferred to the zone air from all surfaces in the zone.

∑m_iC_p(T_zi−T_z): Zone Air Heat Balance Interzone Air Transfer Rate This is the heat (in watts) from air moving between different thermal zones.

m_infC_p(T_∞−T_z): Zone Air Heat Balance Outdoor Air Transfer Rate This is the heat (in watts) from outdoor air entering the zone, like infiltration.

Q_sys: The heat added or removed by the air system (like HVAC or the AirChiller).

My Findings

After checking the outputs, and source code, I noticed that Q​sys​ (the system heat term) equals:

Q_​sys​=Zone Air Heat Balance System Convective Heat Gain Rate − Refrigeration Zone Air Chiller Fan Electricity Rate (Q_​sys​ < 0)

This value is exactly the same as the absolute value of the Refrigeration Zone Air Chiller Sensible Cooling Rate, which is the sensible cooling delivered to the zone (in watts).

My Question

Why does the heat balance in EnergyPlus use the sensible cooling capacity in Q​_sys​ instead of the total cooling capacity (sensible + latent)? Since the AirChiller under the European Wet Standard Condition 2 handles both sensible and latent heat, I expected Q_sys​ to reflect the total cooling capacity. However, it only matches the sensible part. Is this how EnergyPlus is supposed to work, or am I missing something about how latent heat is included in the heat balance?

I’d really appreciate any explanations or insights from the community to help me understand this!

Thank you so much for your help!