EH-105
HRU
Operating mode
EH-105
A pressure difference switch that gives a defrost command to the controller ( HRU defrost ) is
connected above the HRU. When the pressure difference exceeds the pressure difference switch
set value the defrost function starts lowering the HRU output toward the ”DefrostOutp” set value
at a speed depending on the post defrost time. When the pressure difference drops below the
pressure difference switch set value, HRU control remains at its attained state for the post defrost
period. After that the HRU is driven to the state it is in during normal control (100%). If only a 1/1
output pressure difference switch is used, defrost control also operates according to it at ½
output. Pressure difference switch connection and taking into use is outlined in On/Off inputs, see
p. 44.
The controller measures the temperature of the exhaust air channel which is after the HRU. The
controller decreases the HRU output so that the exhaust air temperature after the HRU does not
drop below the ”Fr.Protect” set value which is set in the maintenance mode. This prevents the
HRU unit from frosting over.
The AH unit speed is determined here, when the defrost command has come from
the pressure switch or the pressure difference transmitter.
During HRU defrost the AH unit runs at minimum speed.
During HRU defrost the AH unit running time remains constant.
The supply air unit runs at minimum speed during HRU defrost. The exhaust air unit running
speed remains constant. An AC freq. converter controlled supply air unit must be in use for the
function to be activated.
Operating mode
Not in use
Normal funct->
Rev.Summer F->
During defrost:
AHU at minimum
AHU constant
SF AC f.conv
Frost info
Temperature
PressureSwitch
PressSw1/1-1/2
PressureTransm
Not in use:
Normal funct:
Rev. Summer F:
The HRU has not been taken into use.
A plate HRU, glycol HRU or a rotating HRU is used in the HRU which is driven to
a higher output when the temperature needs to be increased.
HRU has a reverse summer function. When it is warmer outside than inside and
when half of the hysteresis between heating and cooling has been realised, the HRU is driven on.
The normal HRU function is on during heating.
The heat recovery unit may frost over (freeze), if the temperature of the
exhaust air after the LTO drops too low. The controller automatically
switches on the defrost function (drops the HRU output) if frosting over has
occurred. Select the mode for giving frost information and select the frost
protection function.
The controller activates the defrost function on the basis of the measurement information from the
pressure difference transmitter connected above the HRU. Needed settings are set in the
controller's maintenance mode settings (”Defr.Limit Pr”, see p. 36). A pressure difference
transmitter can be connected to measurement channels 7-11 and can be taken into use in
measurement 7-11 settings, where the emitter's range is determined. If the AH unit output is
controlled steplessly (min max), the pressure difference limit for defrost also changes steplessly
between ”AHU min Pa” and ”AHU max Pa” (see page 36). The defrost function is the same as
”PressureSwitch” (above).
The HRU is taken into use here and the operating modes are defined. EH-105 can
control different types (rotating, plate and glycol) of heat recovery units (HRU's).
Temperature:
PressureSwitch:
PressSw 1/1 -1/2
PressureTransm:
AHU at minimum:
AHU constant:
SF AC f.conv:
DURING DEFROST
+/-
Select
Mainten.mode
HRU
HRU
Operation mode
Settings
Tuning values
Actuator
FROST INFO:
35
+
The defrost function functions the same as in ”PressureSwitch”, but 2 pressure difference switches
are connected over the HRU: This makes it possible to get correct settings for both AH outputs
(1/1 and 1/2 output) when the defrost function begins.
Instr.
p.23
Heat recovery function requires that frost protection function
measurement has been connected to the controller and the
connection point has been entered in the measurements menu.
