The logic is as follows:
The indoor air temperature setpoints of the air conditioning
system in winter and summer are defined in order to
maintain conditions of comfort
:
theating
tcooling
normally theating = 20°C
normally tcooling = 26°C
(temperatures can be modified by the installer according to
the actual settings of the plant)
The following are also defined:
ti = indoor air temperature (return air)
EAT = External Air Temperature
FREE-COOLING CONDITION
EAT > theating and simultaneously ti>EAT
FREE-HEATING CONDITION
EAT < tcooling and simultaneously ti<EAT
35
30
25
20
15
10
15
10
25
20
35
30
T1 [C°]
T3 [C°]
26
There can be climatic conditions during the year that
make it impractical to recover heat from extracted
air for treating fresh air from outside.
For example, in mid-season, the outdoor air temperature
can be lower than the indoor air temperature due to solar
and internal factors, and this tends to occur when the
indoor temperature is between 22 and 26°C so there is
more of a need for cooling than for heating. In this case it
is advisable to use free-cooling, i.e. fresh air from outdoors
to cool for free, bypassing the heat recovery unit.
Conversely, it is possible to use fresh air for heating
during a change in season, in which case the process is
known as free-heating.
The units are equipped with a bypass damper system
that totally disables use of the recovery heat exchanger
to permit free-cooling (or free-heating).
The system is controlled on the basis of a logic subject to
the feedback of the integrated temperature probes.
SUMMER
RECO
V
ERY
t
heating
F
REE-HEATING
MODE
F
REE-C
OOL
ING
MODE
t
cooling
WINTER
RECO
V
ERY
Lindab reserves the right to make changes without prior notice
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RHR-CF
lindab | we simplify construction
Installation instructions
17.4 Free cooling function
Fig. 69 Free cooling graph
4
2
