loadmodeling.tool utilizes the full featured EnergyPlus whole building energy simulation engine for calculation of all building load results. EnergyPlus utilizes the industry standard Heat Balance method defined in the ASHRAE Handbook Fundamentals. The Heat Balance method calculates heat gains and losses for each surface of a room, along with the instantaneous internal loads. By using sub-hourly time steps complex interactions between the environment and rooms, and rooms to neighboring rooms is captured.

The primary inputs into room load calculation for both heating and cooling are

  • Accurate building geometry captured via drawing.tool

  • Detailed construction performance for all surfaces

  • Internal loads, including daily variability via schedules assigned via Room Templates

  • External environment defined by standard or user specified .epw weather file

EnergyPlus runs several levels of calculations for each zone, system and plant within a model producing design heating and cooling loads along with flow rates for air and other fluids. In loadmodeling.tool version 1.0 only the zone level calculations are performance producing cooling, heating and air flow results for every room in the model. Load is calculated for each time step of the design days specified and the peak value total cooling or heating values are reported. A breakdown of the components of these peak loads is also calculated via the EnergyPlus Sizing Manager. For full information on the EnergyPlus sizing methods used by loadmodleing.tool refer to this Engineering Reference.

How can I assign safety factors?

Sizing criteria or safety factors can be assigned on the General Settings page. These default to 1.25 for heating and 1.15 for cooling.

How can I assign diversity to internal loads for room sizing?

When sizing room level equipment it is standard practice not to apply diversity, but rather to 'saturate' internal loads such as lighting or equipment to generate the peak cooling load of an individual room. For peak heating load, the opposite is standard where the internal loads are turned off to produced the highest heating load. This is handled via the Summer Design Day and Winter Design Day assigned in each project schedule.

How can I check the load sizing methodology?

The best way to check any engineering calculation is to compare against rules-of-thumb or other basic hand calculation. For example checking the cooling load per area against know standard values is a great way of confirming results make sense. Room checks are included on the Room Results page to make this important step easy.

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