The difference of Honeybee Energy Balance and the EnergyPlus Zone Component load Summary

Dear Ladybug Tools user:

Recently, I am studying the difference envelope for load analysis. There is one question which bothered me several days.

It is the difference of Honeybee Energy Balance and the EnergyPlus Facility Component load Summary.

Question 1:
Th sum of Solar+Equipment+Lighting+People+Infiltration+Mechanical Ventilation+Opaque Conduction+Glazing Conduction is 4258.745128.The Cooling energy is 4025.519152. The two value is not equal.

Question 2: The compotent of Honeybee Energy Balance is not equal to the EnergyPlus Facility Component load Summary
The Peak Cooling energy of Honeybee output is 4025.519152. The EnergyPlus Zone Component load is 3582.75.The two value is not equal.

Question 3
The peak load time is not difference.
The Peak time of Honeybee output is 14:00. The EnergyPlus Zone Component load is 16:00.

Here is the related files.

Honeybee load VS Energyplus load.xlsx (13.0 KB)
Window U Value energy simulation.gh (617.9 KB)

inTable.html (324.2 KB)

@minggangyin ,

I think all of your questions can be explained by noting the difference between instantaneous loads in the zone and the cooling load that must be removed from the space to keep the air temperature set point met. The latter of these two metrics accounts for thermal lag of the space and this is why the maximum cooling load tends to come after the peak sum of instantaneous load (hence the use of the term “lag”). It also explains why the maximum cooling load is generally lower than the peak sum of instantaneous load. These two images help illustrate this difference over the course of a cooling design day (used to size HVAC systems):

Instantaneous Load in the Space:

Cooling load intensity:

From these two graphs, you can see that the peak instantaneous load occurs somewhere around 9 AM when the sun is streaming into the space. This sun energy does not get immediately sucked up by the cooling system, though, since it soaks into the thermal mass of the floor slab, heating up the floor before the heat is eventually transferred to the room air and then is sucked up by the cooling system. Somewhere around 11 AM, the space hits the peak cooling load.

The principle that you note about energy balances holds true over longer periods of time (that the energy into the space equals the energy leaving the space). In other words the “area under the curve” of the two plots above should be roughly equal such that, over the whole design day, the heat in the space equals the heat leaving the space. But, on an hour-by-hour basis, this equation is rarely balanced. Heat is constantly getting stored and released from the thermal mass of the space.