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Heating load calculation and results

 Go to the Simulation tab

 Open heating load calculation setup to define key parameters to be applied in the calculation

 Turn off mechanical ventilation to consider worst case heating load (neglect air-borne heating from the AHU)

👉  Define percentage of internal gains (percentage of all gains as defined in the zone form) that should be active during the heat load calculation (normally zero)

 Select synthetic weather and constant ambient temperature -26 °C

Note: With synthetic weather, the date of the simulation as well as the clearness number influences solar radiation: Set clearness number to 0 % to calculate without any solar radiation or to 100 % to calculate with clear sky conditions. (The sky is often clear on cold days.).

Note: You can leave fixed ambient temperature empty to calculate ambient temperature from the winter design day minimum and maximum. Once a fixed ambient temperature has been given, the minimum and maximum dry bulb temperatures from the Location object are no longer used. Together with clearness number of 0 % and no internal gains, this means that we will do a steady state calculation with fixed ambient temperature and no solar radiation.

Note: Selection of ‘Design period using climate file’ requires hourly climate data for the period to be calculated.

 Run the heating load calculation. For the Standard edition, the Heating Load Report is automatically displayed after the simulation. For the Expert edition, the Summary tab is displayed first. If you run the Expert edition, revert back to the Simulation tab and open the relevant Report link.

Heating load results:

For each zone:

• Heat supplied: This is – during the heating load calculation period – the maximum heat supplied to the zones by all air flows and room units.

Note: Values shown are not instantaneous values, but 15 minute sliding averages. This is to avoid showing results for very brief extreme peaks that may occur, .e.g., just when the fans start in the morning. The sliding average length can be changed in the System parameters form, available from the General tab.

• Time: Time of day when the peak in supplied heat occurs
• Room unit heat: This is the maximum heat supplied by all room units to the zone and you should select equipment that are able to deliver this heat. Often, ‘Room unit heat’ is greater than ‘Heat supplied’, since the ventilation air cools the room.
   

Note: The peak in ‘Room unit heat’ may occur at a different time than that of ‘Heat supplied’. This time is not shown in the report.

• Vent. heat loss: This is, for information, the heat lost at the time of maximum heat supply by infiltration and ventilation.
• Temp.: This is the dry bulb air temperature at the time of maximum heat supply. Make sure that the setpoint has been reached (otherwise the available heating capacity in the zone was too small.)
• Sup airflow: This is the mechanical supply air flow rate at the time of maximum heat supply.

For each air handling unit:

• Heating: This is the maximum heat added to the supply air stream by the heating coil(s)
• Time: Time of the maximum
• AHU heat recovery: The heat added to the supply air stream from the return air stream

For the building:

• Zone heating: Maximum heating power delivered by the plant to room units.
• AHU heating: Maximum heating power delivered by the plant to the air handling units.
• Total: Maximum heating power to both zones and AHUs.
• Time: Time when the total building heating power peaks.

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