  In the framework of the Global Architecture of Planetary Systems (GAPS)
project we collected more than 300 spectra with HARPS-N at the TNG for the
bright G9V star HD164922. This target is known to host one gas giant planet in
a wide orbit (Pb~1200 days, semi-major axis ~2 au) and a Neptune-mass planet
with a period Pc ~76 days. We searched for additional low-mass companions in
the inner region of the system. We compared the radial velocities (RV) and the
activity indices derived from the HARPS-N time series to measure the rotation
period of the star and used a Gaussian process regression to describe the
behaviour of the stellar activity. We exploited this information in a combined
model of planetary and stellar activity signals in an RV time-series composed
of almost 700 high-precision RVs, both from HARPS-N and literature data. We
performed a dynamical analysis to evaluate the stability of the system and the
allowed regions for additional potential companions. Thanks to the high
sensitivity of the HARPS-N dataset, we detect an additional inner super-Earth
with an RV semi-amplitude of 1.3+/-0.2 m/s, a minimum mass of ~4+/-1 M_E and a
period of 12.458+/-0.003 days. We disentangle the planetary signal from
activity and measure a stellar rotation period of ~42 days. The dynamical
analysis shows the long term stability of the orbits of the three-planet system
and allows us to identify the permitted regions for additional planets in the
semi-major axis ranges 0.18-0.21 au and 0.6-1.4 au. The latter partially
includes the habitable zone of the system. We did not detect any planet in
these regions, down to minimum detectable masses of 5 and 18 M_E, respectively.
A larger region of allowed planets is expected beyond the orbit of planet b,
where our sampling rules-out bodies with minimum mass > 50 M_E.
