Apache Systems allows you to describe the characteristics of systems supplying the heating, ventilating and air conditioning requirements of spaces. The system specifications entered here are used for sizing central plant and calculating fuel consumption and carbon emissions.
Viewing and editing Apache Systems
Each room using the ApSys system methodology is assigned an Apache System on the Space Data System tab for room conditioning and a second Apache System for the conditioning of auxiliary ventilation ari. (In cases where there is no conditioning the system is set to ‘None’.). These systems handle the room’s heating, cooling and air conditioning needs in the modules ApacheSim ASHRAE Loads and CIBSE Loads.
When the room features in an ApacheHVAC system the roles of these Apache Systems are taken by the ApacheHVAC system.
Rooms using either system methodology are assigned an Apache System for the supply of domestic hot water (DHW). 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. The Apache Systems dialog also displays the values of parameters such as boiler size and maximum flow rate that have been set by autosizing in ASHRAE Loads or CIBSE Loads.
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:
EER – the cooling system generator energy efficiency ratio or COP
CDE – the cooling delivery efficiency, and
HRP – the heat rejection pump and fan power fraction
namely
SSEER = EER * CDE / (1 + (EER + 1)*HRP)
In terms of carbon emissions EER, 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. Plant profile (auxiliary energy) is a modulating profile specifying the times when auxiliary energy will be included. Several profiles are given as options to choose from in a drop-down menu including one independent option to choose any available profile.
Parameters labelled in blue are autosized parameters calculated by the loads analysis programs. 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 can be used to set Apache System data. Choices made in the wizard are interpreted into the parameters required by the Apache Systems dialog.
