Rehau PD1 Instructions Manual page 5

When operating with only a slab sensor, the on times for the Heat 1 and Heat 2 relays are
calculated to satisfy the requirements of the slab sensor. The thermostat operates to maintain the
slab at the minimum slab temperature setting
Note: Operating with only a slab sensor can lead to either overheating or underheating of the
space
.
Air and Slab Sensor Operation
When operating with both air and slab sensors, the thermostat calculates an on time for the Heat 1
relay to satisfy the slab sensor's requirements and on times for the Heat 1 and Heat 2 relays to
satisfy the air sensor's requirements. The thermostat operates the Heat 1 relay for the longer of
these two on times.
While the minimum slab temperature is satisfied, the on times of the Heat 1 and Heat 2 relays are
calculated to satisfy the air temperature requirements
During heavy loads, the maximum slab temperature setting limits the on time of the Heat 1 relay. In
this situation, the Heat 2 relay may be on while the Heat 1 relay is off.
Note: During light heating loads, overheating can occur due to the minimum slab temperature
requirements
.
Mode
Heat In the heat mode, the Heat 1 and Heat 2 relays are operated to satisfy the temperature
requirement of the zone
Note: If an air or slab sensor is active in the Off mode, a freeze protection is enabled that allows
the relays to be operated to keep the zone above 35° F (2° C).
PD2 (Heat / Cool)
The Heat / Cool mode of operation is selected using the DIP switch located on the circuit board inside the
thermostat
.
Air Sensor(s) Only Operation
When operating with only an air sensor, the on times of the Heat 1 relay and the Cool relay are calculated to
satisfy the requirements of the air sensor
Slab Sensor Only Operation
When operating with only a slab sensor, the on time of the Heat 1 relay is calculated to satisfy the
requirements of the slab sensor. The thermostat operates to maintain the slab at the minimum slab
temperature setting
.
Note: When operating with only a slab sensor, the Cool relay does not operate. Operating with only a slab
sensor can lead to either overheating or underheating of the space
Air and Slab Sensor Operation
When operating with both air and slab sensors, the thermostat calculates an on time for the Heat 1 relay to
satisfy the slab sensor's requirements and an on time to satisfy the air sensor's requirements. The Heat 1
relay operates for the longer of these two on times. The thermostat also calculates an on time for the Cool
relay to satisfy the air sensor's requirements. In this situation,
heating and cooling can happen at the same time to prevent the space from overheating. This is most likely
to occur when the slab is operating at the slab minimum temperature
While the minimum slab temperature is satisfied, the Heat 1 relay on time is calculated to satisfy the air
temperature setting However, the maximum slab temperature setting limits the Heat 1 relay on time when
.
the slab temperature becomes too warm. In this situation, under heating can occur in the space
Mode
.
Off In the Off mode, the Heat 1 and Heat 2 relays are not operate
.
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