Apache Systems

Apache Systems allow you to describe the characteristics of systems supplying heating, domestic hot water, ventilation and air conditioning to rooms. The system specifications entered here are used for sizing central plant and calculating fuel consumption and carbon emissions.

Each room is assigned an Apache System on the Space Data System tab. (In the case of an unconditioned room, the system is set to ‘None’.). The system handles the room’s heating, cooling and air conditioning needs in the modules ApacheSim, ASHRAE Loads and CIBSE Loads.

An exception to this rule applies in ApacheSim when the room features in an ApacheHVAC system included in the simulation. In this case the ApacheHVAC system replaces the Apache System for the room in question.

The Apache Systems dialog allows you to create systems and set their properties. They can then be assigned to rooms, either in Space Data or indirectly via the assignment of room templates.

Currently all Apache Systems are of type ‘Generic heating & cooling’. This provides a generic approach to modelling a variety of systems. In future, other specific types of system will be offered. The ‘Generic heating & cooling’ system provides, under the control of set points specified in Space Data, room units supplying heating, cooling, and optionally humidification and dehumidification to the room. In addition it allows a system air supply to be specified, characterised by a supply condition (‘adjacent condition’ setting) and a flow rate, which may be variable, specified in Space Data. Generic heating & cooling systems also handle any auxiliary ventilation air supplies set for rooms on the Space Data Air Exchange tab.

The Apache System generic heating and cooling model has three key parameters, which can be defined in summary as follows:

SCoP – the efficiency of the heating system

SSEER – the efficiency of the cooling system (if present)

Auxiliary Energy Value – energy required for fans, pumps and controls

These are the most important parameters featuring in the calculation of the energy consumed by the space heating and cooling systems. Taken together with the fuels specified for heating and cooling, they encapsulate most of the important data about system performance in relation to carbon emissions.

On the Apache System dialog there are other parameters that are linked with the heating and cooling system efficiencies and do not represent independently editable settings. For example, the heating system’s Generator seasonal efficiency and Heating delivery efficiency are linked to the SCoP by the relation

SCoP = HEFF * HDE

where the symbols have the following meanings:

HEFF – the heat generator seasonal efficiency

HDE – the heating delivery efficiency

so that in terms of carbon emissions HEFF and HDE can be viewed as secondary to SCoP.

On the cooling side an analogous relationship exists between SSEER and the following parameters:

SEER – the cooling system generator seasonal energy efficiency ratio

CDE – the cooling delivery efficiency, and

HRP – the heat rejection pump and fan power fraction

namely

SSEER = SEER * CDE / (1 + (SEER + 1)*HRP)

In terms of carbon emissions SEER, CDE and HRP can thus be viewed as secondary to the SSEER.

Auxiliary energy value is a concept that has been developed in connection with the UK NCM methodology. This parameter indicates the power consumption of fans, pumps and controls associated with the space heating and cooling systems. It is expressed in terms of Watts per square metre of floor area served, and is incurred when the heating, cooling or ventilation systems are running. For certain types of system, the calculation of auxiliary energy also involves terms directly related to fan power associated with mechanical ventilation air supplies.

Parameters labelled in blue are autosized parameters calculated by the loads analysis program. The values of autosized parameters do not affect simulation performance or compliance/certification results. 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.

A system data wizard that applies the UK National Calculation Methodology system information but is relevant worldwide can be used to select pre-built Apache Systems. Choices made in the wizard are interpreted into the variables required in the Apache Systems dialog. The SBEM route will show a reduced data set in the Apache Systems dialog.

The dialog can be accessed by clicking on the icon “Apache Systems” or choosing from the “Edit”-menu when using the Apache or the <VE>Compliance module.

The Apache System approach to domestic hot water (DHW) systems is slightly different from that adopted in iSBEM, but allows essentially the same flexibility. By default DHW is assumed to be the supplied by the same Apache System as the space heating system. If the building has a separate DHW system this can be created as an Apache System and connected to the rooms it supplies by means of the DHW System selector on the Space Data System tab. The efficiency of the DHW system must be expressed in terms of a generator (eg boiler) efficiency and a DHW delivery efficiency, the overall efficiency of the system being the product of these two efficiencies.

Apache Systems are shown for the currently selected building - Actual, Notional or Reference.  For the benchmark buildings (Notional and Reference) the systems are created automatically and may not be edited.

A list at the side of the dialog displays the Apache Systems in the model. You can add further systems using the ‘Add’ button and remove them (if they are not in use) using the ‘Remove’ button. The properties of the currently selected system are displayed in the main dialog area.

A tick in the ‘Default?’ column indicates that the system will be assigned by default to imported room templates. You can change the default system by double clicking in the ‘Default?’ column. The system assignment may be overridden, like other template assignments, in Space Data.

The name of the system.

The type of system chosen in the UK NCM system data wizard (if used).

This button launches the NCM system data wizard, a utility which provides help with setting parameters on the Apache System dialog and an interface for additional parameters required for ratings analyses.

The NCM System Wizard is used to define initial data based on the system type and these values can be further edited on return to the Apache systems dialog. However, any changes made that conflict with the UK NCM Type will result in a warning.

The NCM System Wizard forms an essential part of ratings analysis, since it is the mechanism for setting certain parameters which affect system performance as measured by the ratings systems but which are not reflected in the main Apache System dialog.

More details on the system Wizard are provided in section 6 of this user guide.

The main dialog area displays the properties of the currently selected system and allows them to be edited. Boxes labelled in blue represent autosized parameters calculated by the loads analysis programs. The values of autosized parameters do not affect simulation performance or ratings results. They may not be edited in this dialog. They may, however, be reset to zero or wound back to the values applying before the last loads analysis using options on the ASHRAE and CIBSE Loads dialogs.

When used in the VE Compliance View, you should invoke the NCM System Wizard to assign an initial set of values to the parameters on the main Apache Systems dialog before any editing is done on that dialog.

The main of the dialog is spread over seven tabs, as follows.