This tab controls the temperature and humidity. It contains a gains table with the following parameters:
Upper Limit
The upper limit of the cooling control band. If no cooling is required then the Upper Limit should be set to a very high value e.g. 150 deg. C. This will simulate the room being cooled from a temperature greater than 150 deg. C down to 150 deg. C. Given that a room will never realistically reach these sort of temperatures, the cooling will never be 'on', giving a room load of 0W.
Lower Limit
The lower limit of the heating control band. If no heating is required then the Lower Limit should be set to a very low value e.g. -50 deg. C. This will simulate the room being heated from a temperature below -50 deg. C up to -50 deg. C. Given that a room will never realistically reach these sort of temperatures, the heating will never be 'on', giving a room load of 0W.
Humidity Upper Limit
This sets the maximum acceptable zone humidity. This limit will be maintained by the operation of de-humidification plant. If no upper limit on humidity control is required the Humidity Upper Limit should be set to 100.
If, when the Humidity Upper Limit is set to 100, moisture build-up occurs in the zone and causes the humidity to reach 100%, the program will always calculate the de-humidification load required to prevent condensation in the zone. If there is no plant available for de-humidification, this load gives an indication that condensation is occurring.
Humidity Lower Limit
This sets the minimum acceptable zone humidity. This limit will be maintained by the operation of humidification plant. If no lower limit is required the Humidity Lower Limit should be set to zero.
No control band is specified for humidity control.
The user can also set up Proportional or On/Off control.
Proportional Control
To select proportional control enter a non-zero value for the control range and check the Proportional Control check box. If a zero is entered in the Control Range box, the effect will be a tight control characteristic such as might be achieved in practice using a proportional/integral/derivative controller.
The quality of control imposed upon internal air temperature may be specified by means of a proportional control band. The operation of the proportional controller is best described by means of an example. With a temperature upper limit of 26 degrees, a temperature lower limit of 20 degrees, and a proportional control band of 2 degrees, the control system will operate in the following way.
Heating is supplied when the air temperature lies between 20 degrees (Temperature Lower Limit) and 22 degrees (Temperature Lower Limit plus Control Range). Heating is at maximum at or below 20 degrees, and reduces proportionally to zero as the air temperature rises from 20 to 22 degrees.
Cooling is supplied when the air temperature lies between 26 degrees (Temperature Upper Limit) and 24 degrees (Temperature Upper Limit minus Control Range). Cooling is at maximum at or above 26 degrees, and reduces proportionally to zero as the air temperature falls from 26 to 24 degrees.
In the dead band between 22 and 24 degrees no heating or cooling is supplied.
Warning - When the heating or cooling capacity is set to 'SIZING' the proportional control band is automatically set to 0, so that at the sizing condition the temperature is held at the Temperature Lower Limit or Temperature Upper Limit.
On/Off control
To select On/Off control enter a non-zero value for the control range and untick the Proportional Control check box. If a zero is entered in the Control Range box, the effect will be a tight control characteristic such as might be achieved in practice using a proportional/integral/derivative controller.
An On/Off control regime can be specified as an alternative to proportional control. The principle is illustrated by the following example, in which we assume an On/ Off control band of 2 degrees and temperature upper and lower limits as above. For air temperatures below 20 degrees (temperature lower limit) maximum heating is supplied. For air temperatures above 26 degrees (temperature upper limit) maximum cooling is supplied. For air temperatures in the dead band (22 to 24 degrees) no heating or cooling is supplied.
When the air temperature lies in either of the control bands (20 to 22 degrees or 24 to 26 degrees) the amount of heating or cooling supplied depends on the direction from which the band was entered. If the air temperature enters the heating control band from below, the system will continue to supply maximum heating until the temperature passes through the top of the band (22 degrees in our example), at which point the heating will be switched off. If subsequently the air temperature falls back into the heating band (entering this time from above) the heating will remain off until the temperature passes through the lower limit of the band (20 degrees), at which point the heating is again switched on to maximum. The same principle governs behaviour in the cooling band: if the band is entered from above, maximum cooling will continue to be supplied; if entered from below, the cooling remains off. In normal operation the system will typically be cycling within the cooling band or the heating band.
Warning - When the heating or cooling capacity is set to 'SIZING' the On/Off control band is automatically set to 0, so that at the sizing condition the temperature is held at the Temperature Lower Limit or Temperature Upper Limit.
