Specifications

DT90 DIGITAL ROOM THERMOSTAT
EN0H 8578 UK07 R1 12/08
6
INSTALLER MODE – APPLICATIONS SETTINGS
The DT90 has a special Installer Mode where some features can be adjusted to suit the application and the needs or
lifestyle of the user. Each adjustable feature is called a Parameter. These are described below.
Specific Applications
Setting
What requires to be changed?
Cycles
/ hour
Minimum
on/off time
Heating
Gas boilers
(<30kW)
6
1
No changes required
Oil boiler
3
4
1. Set minimum ON/OFF time to 4 minutes
2. Set cycle rate to 3 cycles/hour
Thermal actuator
12
1
Set cycle rate to 12 cycles/hour
Zone valve
6
1
No changes required
Air
conditioning
1. Configure the thermostat to allow switching between
heating and cooling modes (set parameter HC = 1)
2. Set the thermostat to the required mode of operation
(heating or cooling) by pressing the ▲ and ▼ buttons
together for 3 seconds when in normal run mode
(does not work in off/standby mode).
Heatpump / Air
conditioner
3
4
1. Set minimum ON/OFF time to 4 minutes
2. Set cycle rate to 3 cycles/hour
Fan-coil unit
6
1
No changes required
Parameter
Description and typical use
Minimum ON/OFF time
DT90 is able to set a minimum limit for the on and off times of the controlled device or
appliance, to prevent damage or excessive wear. This minimum time can be set to 1,
2, 3, 4, or 5 minutes, and is particularly important for heating applications with oil
boilers, or air conditioning applications with compressors. Recommended settings are
shown in the next table.
Cycle rate
Within the control proportional band, the output will be cycled several times per hour,
to give precise temperature control. This can be set to 3, 6, 9, or 12 cycles, depending
on the application. Recommended settings are shown in the next table.
Proportional band width
The proportional band is the temperature band, adjacent to the set temperature point,
within which the thermostat will cycle the controlled output (to control the boiler, for
example). Above or below this band the output will either be fully on or fully off.
The band can be adjusted up to 3°C (default 1.5°C) to provide improved temperature
control. This is useful for (a) well-insulated homes with over-sized heating systems or
(b) air systems with a fast response
Temperature
measurement offset
If the thermostat is located in a particularly hot/cold location and cannot be moved
because of the wiring, then the measured/displayed temperature can be adjusted by
+/- 3°C. This is useful if the homeowner wants the reading to match the temperature
display on another appliance.
Upper / Lower
temperature limits
The normal upper temperature limit of 35°C can be reduced as low as 21°C to save
energy. The normal lower limit of 5°C can be raised as high as 21°C to protect
inhabitants from the cold.
Energy saving ECO
temperature
On the DT90E ECO model, pressing the ECO button immediately puts the thermostat
into energy saving mode, where it will control at this predefined temperature for as
long as the user wishes. This temperature can be set from 5°C to 35°C.
Heating or Cooling
operation
DT90 can be used for heating or cooling applications. If heating/cooling changeover is
selected, the thermostat can be manually switched from heating to cooling (and back
again) by pressing and holding the ▲ and ▼ buttons together for 3 seconds.
Off/standby setpoint
When the off/standby button is activated, the DT90 will control to a special off/standby
setpoint. By default this is set to 5°C to provide frost protection, but it can be set up to
16°C if required. It can also be set off, by setting the parameter value to -- to provide
a positive off function. In cooling mode the default setting is off.
Electric heat operation
If a direct electric heating application > 3A switching current is required, DT90 will use
more energy to operate its relay and so ensure the higher current is switched reliably.
Reset parameters
This provides a means of resetting all the parameters to the factory supplied values.
Some parameters require to be set to match specific applications. Recommended settings are shown in the table
below.