System Parameters

 

Parameters on this tab are displayed for rooms and plenums. They specify system-related infomation including room-plenum associations.

System tab data for a room wth ApSys methodology

 

System tab data for a room wth ApHVAC methodology

 

 

System tab data for a Return Air Plenum

 

Parameters in this frame relate to HVAC system modelling for rooms.

This parameter is displayed for rooms and plenums.

The HVAC methodology specifies the framework for modelling HVAC systems. The ApSys methodology uses a parametric approach based on Apache Systems. The ApHVAC methodology uses component-based ApacheHVAC system models, and is integrated with a set of additional capabilities relating to HVAC zones, plenum spaces and advanced report formats. HVAC Methodology is defined in the space template and may not be edited in Space Data. This setting affects the display of certain methodology-dependent fields in the template data and the associated Space Data. For plenums HVAC Methodology is forced to ApHVAC, and for voids it is not relevant.

This parameter is displayed for ApHVAC methodology rooms. The setting specifies the type of conditioning applied to the room:

Yes. Room is conditioned.

No (free-floating for Room Loads). Room is not conditioned, and free-floats during Room Loads analyses.

No (tempered for Room Loads). Room is not conditioned, but is tempered during Room Loads analyses (as specified on the Room Conditions tab) to emulate its expected behaviour under normal operation.

Parameters in this frame specify systems serving a room. They relate mainly to the ApSys methodology.

In ApacheSim, the system parameters entered here will be overridden (with one exception) in any spaces that feature in an attached ApacheHVAC system. The exception is the setting ‘Auxiliary mech. vent. system’ (which applies to the ApSys methodology). A space served by an ApacheHVAC system may also have one or more auxiliary ventilation air supplies defined on the Air Exchange tab, and for ApSys methodology rooms these are always associated with an Apache System.

Parameters labelled in blue are autosized parameters calculated by the loads analysis program. Buttons in the ASHRAE Loads and CIBSE Loads (ApacheCalc) dialogs allow these parameters to be re-zeroed or set back to the values they had before the last loads analysis.

This parameter is displayed for ApSys methodology rooms.

The Apache System serving the room. Select a system from a list of those defined in the Apache Systems utility, or use the option ‘None’ to indicate an unconditioned room. The system will initially be set by the room thermal template. The template specifies a type of system (currently there is only one type – Generic heating & cooling), which is then instantiated by the following procedure. For each type of system a specific system is nominated in Apache Systems as the default system of that type. It is this system that is assigned to the room. System assignments, like other Space Data parameters, can be overridden by un-ticking the Template check box and editing the setting.

This parameter is displayed for ApSys methodology rooms.

If there are air exchanges of the ‘Auxiliary ventilation’ type defined on the Air Exchange tab these will be supplied by an Apache System. By default they will be handled by the main system serving the room, but you can source them from another system by un-ticking this check box and specifying a second system for this purpose.

This parameter is displayed for ApSys methodology rooms.

The Apache System handling auxiliary ventilation air exchanges defined on the Air Exchange tab. The auxiliary ventilation system will calculate the heating, cooling and dehumidification required to process outside air to the specified supply condition.

This parameter is displayed for ApSys methodology rooms.

If hot water use is included in the Space Conditions tab the energy use associated with this will be calculated by an Apache System. By default they will be handled by the main system serving the room, but you can source them from another system by un-ticking this check box and specifying a second system for this purpose.

This parameter is displayed for all rooms (ApSys or ApHVAC methodology).

The Apache System that handles Domestic Hot Water. The DHW system will calculate the energy required, using a model which assumes a temperature rise of 50K between the mains water supply temperature and the hot water temperature.

 

Parameters in this frame are displayed for rooms, and are used for room and system load calculations. For rooms with ApSys methodology they are also used for simulations.

During ASHRAE Loads and CIBSE Loads runs the value of this parameter is automatically updated (autosized) to record the maximum heating unit demand encountered during the loads analysis.

This parameter only applies to simulation runs (not ASHRAE Loads or CIBSE Loads) for ApSys methodology rooms. It allows you to specify a maximum capacity available from the heating units in the room.

The fraction of the heating plant’s output that is in the form of radiant, rather than convected, heat. A value of 0.0 is appropriate for warm air heating and a value of 0.9 for high-temperature radiant heaters.  See Table 13 for further guidance.

 

Parameters in this frame are displayed for rooms, and are used for room and system load calculations. For rooms with ApSys methodology they are also used for simulations.

During ASHRAE Loads and CIBSE Loads (ApacheCalc) runs the value of this parameter is automatically updated (autosized) to record the maximum cooling unit demand encountered during the loads analysis.

This parameter only applies to simulation runs, not to ASHRAE Loads or CIBSE Loads. It allows you to specify a maximum capacity available from the cooling units in the room.

The fraction of the cooling plant’s output that is in the form of radiant, rather than convected, heat. A value of 0.0 is appropriate for air conditioning. See Table 13 for further guidance.

 

Parameters in this frame are displayed for rooms. For rooms with ApHVAC methodology they are applied conditionally (subject to options in the ASHRAE Loads dialog) to room loads analyses. For rooms with ApSys methodology they are applied to room loads analyses and simulations.

The maximum flow rate of air supplied to the room from the system at the condition specified in the Apache System settings. This can be entered in four forms: air changes per hour, volume flow rate, volume flow rate per unit floor area or volume flow rate per person (based on number of people defined in Occupancy internal gains for the room). Whichever form is chosen (as indicated by the asterisk) the value expressed in that form will be preserved if the room geometry subsequently changes. The air is assumed to be drawn from outside. Mechanical ventilation can alternatively be specified using air exchanges of type ‘Auxiliary ventilation’.

A modulating profile specifying the time variation of the system supply air flow.

For rooms with ApSys methodology this parameter sets the maximum intake of outside air that is available for free cooling in simulations. Free cooling is under the control of the cooling variation profile. It will be supplied when the room temperature exceeds the cooling set point, provided that it is advantageous in terms of reducing room temperature or cooling demand. If mechanical cooling is also available, this will be provided in addition if free cooling is unable to maintain the room temperature at the cooling set point. If free cooling is not required the free cooling flow capacity should be set to zero. A value of 5 ach would be typical to model ventilation by window opening. In the case of an air conditioned room, where the outside air is brought in via the system, it would be usual to express the value in l/(s·m²) and a value of 0.5 in l/(s·m²) would be typical.

 

The parameters in this frame are displayed for rooms with ApSys methodology when the Apache System serving the room has Cooling/ventilation mechanism set to ‘Mechanical ventilation’. They do not feature in the space template.

Tick the box if the room is served by a mechanical ventilation air supply. This invokes auxiliary energy calculations applied at room level when the auxiliary energy method is set appropriately. The flow rate used in the calculation is the value specified as auxiliary ventilation or Apache System air supply.

The specific fan power to be used for the calculation of auxiliary energy associated with room-level ventilation supply.

Tick the box if the room has mechanical ventilation extract. This invokes auxiliary energy calculations applied at room level when the auxiliary energy method is set appropriately.

Tick the box if the extract fan is remote from the room. This invokes auxiliary energy calculations applied at room level when the auxiliary energy method is set appropriately.

The exhaust flow rate, can be entered as air changes per hour, flow rate, flow rate per unit floor area or flow rate per person (defined by Occupancy internal gains).

The specific fan power to be used for the calculation of auxiliary energy associated with room-level ventilation extract.