Heating Loads

Heating Loads implements CIBSE procedures for the calculation of room heating requirements and the sizing of heating plant.

Steady-state room heat losses are calculated in the absence of casual and solar heat gains. The calculation optionally includes conduction heat gains from adjacent rooms and the effects of mechanical and natural ventilation air exchanges.

Results are presented in Vista as tables or graphs of room or zone heat loss, broken down by heat loss mechanism. Losses can be expressed on a floor area or room volume basis. Room temperatures are also displayed. The data may be exported to other applications such as spreadsheets and word processors.

Results from Heating Loads also appear in Space Data and Apache Systems, where they can be used for equipment and air flow sizing.

For a description of the calculation methods used in Heating Loads see CIBSE Heat Loss & Heat Gain Calculation Methods.

 

Tick this box to include a Heating Loads calculation when you click on Calculate.

Air exchanges specified in Space Data are divided into three categories: infiltration, auxiliary ventilation and natural ventilation. Any infiltration air exchanges are included unconditionally, but auxiliary and natural ventilation air exchanges may be switched on or off at calculation time.

Tick this box if you wish to include Space Data auxiliary ventilation air exchanges in the Heating Loads calculation.

Air exchanges are specified in Space Data in terms of a Maximum Value and a Variation Profile. In Heating Loads the Variation Profile requires interpretation because the calculation does not involve the time variable. The assumption is that the exchange rate takes the value at the time indicated under ‘Time settings for profiles’ unless the profile is a formula profile (which is not supported by Heating Loads). In this case it takes the value zero.

Tick this box if you wish to include Space Data natural ventilation air exchanges in the Heating Loads calculation.

Variation Profiles for natural ventilation are interpreted as for mechanical ventilation.

If you tick this box the calculation will include the effects of heat gains from neighbouring rooms, leading to reduced figures for net heat loss. The gains may be from conduction or air movement. A strict application of CIBSE recommendations requires this box to be un-ticked. However, by including heat gains from adjacent rooms a more realistic calculation of heat loss is obtained.

For rooms where the Heating Profile is off at the time indicated under ‘Time settings for profiles’, or a formula profile (which Heating Loads does not support), no heat is supplied and the room temperature free-floats. For such rooms, which typically represent buffer spaces such as roof voids, heat gains from neighbouring rooms are always included in order to provide correct boundary conditions for the heated rooms.

If you tick this box the calculated heating loads will be adjusted for intermittent heating according to the procedure described below. The adjustment applied to steady state heating loads for intermittent operation follows the treatment described in CIBSE Guide A, where it is calculated as a function of the fraction of the day for which the plant operates. This fraction is derived from the ‘Time settings for profiles’ described below.

If you tick this box the heating loads calculated for Apache Systems will include the Domestic Hot Water demand for each room.

Select ‘Use peak values’ to set DHW demand to the peak value in the room, or ‘Use time settings below’ to set it according to the demand at the indicated time of day and year.

The profile settings determine whether heating is available in each room, and, where appropriate, the adjustment for intermittent heating. If the heating profile is off at the specified hour, week day and month there is assumed to be no heating. In the case of annual profiles the profile is evaluated for the indicated weekday in the central week of the month. The thermal response characteristic of the room (‘response factor’) also plays a part in the calculation. In the CIBSE Loads interface the number of hours of operation is derived (if you tick the box ‘Adjust for intermittent heating using profiles?’) from the heating profile for a particular month and week day. You specify these in the box labelled ‘Time settings for profiles’.

Click on this button to start the Heating and Cooling Load calculations.

Click on this button to leave the CIBSE Loads dialog and save the data.

Click on this button to leave the CIBSE Loads interface.