Location & Site Data

 

ApLocate utilises site data that contains values for latitude, longitude and height above sea level of a wide range of sites throughout the world drawn from standard tables published by CIBSE and ASHRAE. Non-ASHRAE locations are marked in ApLocate with an asterisk (*).

 

 

 

 

The Selection Wizard… button launches a series of dialogs which help the user select the location, the design weather data and the simulation weather data. The Set Location Only button allows the location alone to be set without using the wizard.

 

The information in this section is not editable by the user. Whenever a new location is selected by either of the two buttons above, this section is automatically updated.

 

The Latitude within ApLocate is expressed as decimal degrees North or South. In other words, 20º 30” N appears as 20.50 with the drop-down box beside the number set to N.

 

The height above sea level of the building. For locations below sea level, negative values are appropriate. The data is used in the calculation of solar gains and atmospheric pressure in Heat Gain. In System Simulation the solar gains and atmospheric pressure are read in directly from the weather file and so this data is not used.

 

The Longitude within ApLocate is expressed as decimal degrees East or West. In other words, 20º 30” E appears as 20.50 with the drop-down box beside the number set to E. The longitude is regarded as increasing westwards from Greenwich, so 20º East of Greenwich is rendered as 340º.

 

The local time correction applicable for Daylight saving time during the months From to Through inclusive. The value is approximated to the nearest hour. Positive is in advance of sun time.

 

These are the two months within which the local time correction firstly starts to apply, and secondly no longer applies.

Note that in Northern latitudes, the Through month will normally be later than the From month and in Southern latitudes it will be earlier.

 

 ‘Other Months’ are those months not included in the From - Through period. For example, if the From month were April and the Through month October (the default condition), then this time correction would apply to November to March inclusive.

 

The information in this section is editable by the user.

 

This is a measure of the ground albedo (Kr). Typical values are listed below, or in CIBSE Guide A2, Table A2.31. It is used in APcalc and ApacheSim for the calculation of ground reflected radiation on building facades.

There is some built-in assistance with setting the reflectance level. Select the more info button and a table with sample values will appear.

 

 

·       Country

·       Suburbs

·       City

This data is used in both ApacheSim and in external CFD assessments in MicroFlo. The terrain types define how the wind speed will vary with height, dependant upon the local terrain. These definitions are based on ASHRAE 2001 wind speed profiles. This data affects the natural ventilation air exchange rates when MacroFlo is run in conjunction with ApacheSim and the external convective losses in ApacheSim. In MicroFlo the velocity profile changes with height in relation to the choice of terrain type.

 

·       Sheltered:          Sheltered sites (e.g. city centres)

·       Normal:              Normal exposure sites

·       Severe:              Sites with severe exposure (e.g. coastal)

 

The appropriate value will be entered into the weather file when a selection is made from the drop-down box.

The wind exposure index is used to calculate the external surface resistance of walls, windows, roofs etc. when a value is not explicitly entered in APcdb. In most cases, the peak summertime conditions will occur for a sheltered site. This is because the higher surface resistance levels give rise to higher sol-air temperatures on external surfaces. Higher surface resistance levels also reduce the conduction of heat out of the building at night.

 

For winter heat loss design calculations, the peak conditions occur when the exposure index is set to 3, i.e. severe (but only if your constructions are defined without typing in surface resistance levels). This index is only used for the CIBSE Heating Loads calculation.

 

This is the value for concentration of carbon dioxide in the atmosphere. The default is 400ppm which is considered to be the global current daily average. It is used in ApacheSim for the calculation of room CO2 concentration. The calculation assumes volumetric carbon dioxide concentration of 400ppm unless updated by the user.

 

The modelling of room carbon dioxide concentration is detailed within ApacheSim Calculation Methods User Guide, Section 11.3 Carbon Dioxide Balance.

 

 

Reference Air Density is used to convert user-specified air flow parameters conventionally expressed as volume flow rates to mass flow rates for use in load calculations and simulations. It is also used to convert calculated and simulated HVAC system and ventilation mass flow rates to volume flow rates for display in ApacheHVAC and VistaPro. This includes volume flow rates for the MacroFlo external vent and internal vent room variables. Flow rates expressed as volume flows in VE are converted to mass flows in Apache for the purpose of thermal simulation, and subsequently converted back to volume flow in results data. Thus, a larger reference air density will typically yield larger heating and cooling loads since the volumetric heat capacity of a substance at a given temperature is directly proportional to its density.

 

Because mass flow is used to determine MacroFlo vent gain, thermal gains resulting from MacroFlo ventilation are unaffected. Adjustment of Reference Air Density also does not influence the actual weather file data or the presentation of that data on the psychrometric chart in VistaPro.

 

The opening-level variables 'Volume flow in' and 'Volume flow out' are actual volume flows calculated by MacroFlo for the air entering or leaving using variable density. However,the room-level results variables 'MacroFlo external vent' and 'MacroFlo internal vent' are MacroFlo mass flows converted to volume flows using the Reference Air Density. This convention ensures consistency with other room-level volume flow rates, so that when summed over all sources, reported net volume flow into the room (being here a proxy for net mass flow) should be zero.

 

The value is conventionally set to 1.2 kg m^-3 via the Standard option. However, the user has the freedom to override this value and specify their own value.

This can be set explicitly by using the Custom control, wherein the user may enter any value between 0.12 kg m^-3 and 2.05 kg m^-3 (values outside this range are unrealistic from the perspective of building physics).

Alternatively, the value can be calculated via the Derived control. This allows the user to enter an elevation (between 0 m and 9000 m), a reference temperature (between -100 °C and 60 °C) and a relative humidity. The reference air density will then be calculated via a standard atmospheric model to be equal to that of air at the specified elevation above sea level, at the specified temperature and the specified relative humidity.

 

Note that the elevation, temperature and relative humidity specified here are not used outside of this calculation; the only value that is used elsewhere is the reference air density.

The reference air density specified in this section is, however, not used for NCM simulations; for such cases, Apache will disregard the user-specified value and instead use the standard value of 1.2 kg m^-3.

It should also be noted that, when using ApacheHVAC, any auto-sizing calculations should be carried out with respect to the reference air density that will be used for the final Apache simulation.