26
ENG
“optiMist” +0300065EN- rel. 1.1 - 29/01/2013
7. CONTROL
7.1 Humidifi cation
lgorithms, which can be selected from the installer menu.
• HH control:
modulates the capacity (water fl ow-rate) using two humidity probes, one
control probe normally installed in the AHU in the return air, and one limit
probe, usually installed downstream of the droplet separator.
• HT control:
modulates the capacity (water fl ow-rate) with two probes, one humidity
control probe and one limit temperature probe. This confi guration is
recommended for systems in which a certainly humidity level is required
without however excessively cooling the air.
• H control:
like the HH algorithm but without the limit humidity probe;
Below is the diagram of operation using humidity control probes
100%
Set point
1
3
4
2
6
5
Fig. 7.a
Key:
1.
production
2.
humidity control probe
3.
maximum production
4.
minimum production
5.
proportional band
6.
hysteresis (10% of “5”)
• PH/PT control:
capacity is modulated proportionally to an external control signal and is
limited based on the value measured by the limit temperature or humidity
probe. This is the typical confi guration used in optiMist installations
connected to a Building Management System that generates a control
signal;
• P control:
like the PH/PT algorithm but without the limit humidity probe;
Below is the diagram of operation with proportional control.
100%
max
1
2
3
4
5
%
5
%
Fig. 7.b
Key:
1.
production
2.
external request
3.
maximum production
4.
minimum production
• CH/CT control:
operation in on/off mode, based on a voltage-free external contact (for
example, a humidistat). The capacity will thus be either the maximum
set or nothing, depending on the status of the external contact, and is
limited based on the value measured by the limit probe.
• C control:
like the CH/CT algorithm but without the limit probe;
The HH and TH algorithms are the most commonly-used, and
recommended for optiMist installations.
The limit humidity probe described above is usually set to high values, e.g.
80% rH, so as to limit the maximum moisture in the air introduced into the
duct and into the room. This is especially recommended in installations
where air fl ow-rate and operating, temperature and humidity conditions,
may change over time and, consequently an additional safety system is
required to prevent the humidifi er from over-humidifying the air and, in
the worse case scenario, condensing in the ducts downstream.
Below are the two diagrams of operation with humidity or temperature
probes
100%
Set point
1
3
4
2
6
5
Fig. 7.c
Key:
1.
production
2.
limit probe
3.
maximum production
4.
minimum production
5.
proportional band
6.
hysteresis (10% of the set point)
N.B.:
for convenience, the diagrams show continuous modulation of
the fl ow-rate while, depending on the model, control may be continuous
or in steps.
