Models of Room Control
The simulation of heating, cooling and humidity control systems may be achieved in ApacheSim by two alternative means:
· Idealised room control
· Detailed system simulation using ApacheHVAC
The capabilities available within ApacheHVAC are described in a separate section. Here we deal with the idealised temperature and humidity control that can be modelled by ApacheSim operating in standalone mode.
Idealised Control of Room Temperature
The idealised plant model provided within ApacheSim is illustrated in Figure 1 , which shows a graph of sensible heat (Q sens ) supplied to a room as a function of room temperature (T room ). The shape of the plant characteristic is defined by four parameters:
Simulation Heating Set-point (ºC )
Simulation Cooling Set-point (ºC )
Simulation Heating Capacity (kW )
Simulation Cooling Capacity (kW )
Figure 1 : Idealised room temperature control
Figure 2 Idealised room temperature control without capacity limits
With no limit on heating or cooling capacity (Q hmax and Q cmax effectively infinite), the characteristic is as shown in Figure 2 . In this case the plant has the effect of constraining to be in one of the following three states:
T room = T h , with heating being supplied as required, or
T room = T c , with cooling being supplied as required, or
T h < Tr oom < T c (in the dead-band), with no heating or cooling supplied.
When a limit is imposed on either Q hmax or Q cmax ( Figure 1 ), two further possibilities exist:
T room < T h , with heating at maximum, or
T room > T c , with cooling at maximum.
To provide additional flexibility, the Simulation Heating and Cooling Set-points may vary with time. This is done using absolute profiles. If this option is chosen it is important to ensure that the condition
is satisfied at all times.
The model is further elaborated by the additional parameters:
· Control Temperature Radiant Fraction
· Heating Device Radiant Fraction
· Cooling Device Radiant Fraction
· Heating Profile
· Cooling Profile
Control Temperature Radiant Fraction specifies the characteristic of the room thermostat, a value of 0 (the most common setting) denoting an air temperature sensor. The radiant fractions for heating and cooling specify the fraction of the output of the heating and cooling devices that is in the form of thermal radiation. Heating and cooling profiles allow the periods of plant operation to be specified.
Idealised Control of Room Humidity
An idealised model of room humidity control is provided by the parameters:
· Minimum Percentage Saturation
· Maximum Percentage Saturation
During periods of cooling plant operation (as dictated by the Cooling Profile), the room percentage saturation will be held between these limits by the addition or removal of water vapour. Setting Minimum Percentage Saturation to 0% disables humidification control and setting Maximum Percentage Saturation to 100% disables dehumidification control.
