Heatrae Sadia HI-MAX INSTANT ID 5-60 Installation, Operation And Maintenance Manual page 21

4.2.3 Apartment Heating Operation
The PID controller works with the room thermostat
to control the apartment heating system. In simple
terms the room thermostat is set to the desired
room temperature and the PID controller in the HIU
controls the temperature of water going out to the
heating system. In AUTO mode the PID controller
can compensate the heating system temperatures
depending on the system demand to maintain low
district heating return temperatures.
Within the unit there is a self-regulating pump which
can regulate the fl ow rates within the heating system to
match the demand, thus keeping energy consumption
to a minimum.
There are four heating programmes:
1) Manual heating - the HIU runs to achieve the heating
set point at the heating fl ow sensor.
2) Optimised heating - the HIU runs to achieve the
optimised heating return temperature measured by
the heating return sensor by calculating the optimum
target fl ow temperature.
3) Weather compensated heating - the HIU runs to
achieve the heating set point at the heating fl ow sensor
to maintain a desired ambient room temperature
calculated by the algorithms. See separate instructions
for more details.
4) Weather compensated and Optimised heating
- The HIU runs to achieve the optimised heating
return temperature measured by the heating return
temperature sensor taking into consideration the
input from the outdoor sensor used for the weather
compensated heating set point calculation.
See separate instructions for more details.
4.2.4 Anti-scale function
During times when there is no hot water demand the
controller switches the district heating fl ow to heating
plate heat exchanger, this takes heat away from the
domestic hot water plate heat exchanger, thus lowering
the risk of scale formation within the DHW plate heat
exchanger.
4.2.5 Zero demand pulsed fl ow function
The Heatrae Sadia HI-MAX INSTANT HIU has a built-
in pulsed fl ow function, which if activated, periodically
opens the district heating PICV to allow a low fl ow of
primary water (circa 100 litres per hour) through the unit
during periods when there is no demand. This feature
is designed to maintain the heat within the district
heating fl ow pipe, thus ensuring the HIU responds as
quickly as possible to a hot water demand. The start-up
time, the pulse duration and the dwell time between
each pulse can be adjusted in the installer parameter
set-up menu (see Page 54 for details). The start-up time
and the dwell time periods are determined by the rate
of heat loss in the district fl ow pipe. The pulse duration
time is determined by the distance the HIU is away
from the riser and the size of the district fl ow pipework
away from the riser.
4.2.6 Pulsed fl ow bypass function
This function combines both the anti-scale function
and the zero demand pulsed fl ow function to keep
heat in the district fl ow pipes without continuously
heating the domestic hot water through the DHW
plate heat exchanger. The function diverts district
fl ow water away from the DHW plate heat exchanger
through the heating plate heat exchanger. The heating
plate heat exchanger is protected from scale formation
by inhibitors. At the same time the district fl ow rate is
reduced to keep energy consumption within the district
system to a minimum.
4.2.7 DHW Outlet tempering feature
The unit is fi tted with a safety tempering valve (Stv)
which is set at 60 O C +/-2
high temperature hot water going to the taps during a
malfunction or power cut.
4.2.8 Anti-seizure function
The heating pump is equipped with an anti-seizure
function. This function rocks the impeller backwards
and forwards at different torque settings to help free
up the pump should it become clogged with debris.
4.2.9 Anti-gravitation feature
The unit and its components have been designed so
as not to promote natural circulation when the pump
is not in operation. An anti-thermal dip pipe on the
primary fl ow to the DHW plate heat exchanger helps
prevent the DHW plate heat exchanger from being
heated when not in use.
4.2.10 Sleep mode
The Heatrae Sadia HI-MAX INSTANT has a sleep
mode function. Simply press the ON/OFF button for
3 seconds and the unit goes into sleep mode. In sleep
mode the unit is still powered ON, but the PICV is fully
closed and all functions and features are disabled.
If the unit is in sleep mode, simply press the ON/OFF
button again and the unit will go back into standby
mode where all activated functions are then available.
Sleep mode enables the unit to come back on line
without the need to go through the start up cycle. This
is ideal for when you are away from your apartment on
holiday or a business trip.
4.3 Heat Meters
Provision is made in the Heatrae Sadia HI-MAX
INSTANT HIU for a heat meter comprising:
1. A removable stool piece (3/4"bsp x 110mm centres)
in the district return pipe to house the volumetric fl ow
measuring part of the heat meter.
2. A 1/4"bsp boss in the district fl ow pipe to house a
district fl ow temperature sensor.

The heat meter district return temperature
sensor is usually incorporated in the body of the
heat meter volumetric fl ow measuring device and as
such an additional pocket is not provided. However,
there is a 1/4"bsp boss in the district return pipe
intended for a P/T test point which could be utilised if
necessary. Threaded adaptors (bsp to metric thread)
are available on request.

Care must be taken not to under or oversize
the heat meter. Undersizing the heat meter can lead
to excessive resistance in the district heating system,
which will affect the performance of the unit and
potentially the whole system. Oversizing can result
in energy usage not being detected in low output
conditions. Contact Heatrae Sadia for advice.
O C to prevent excessively
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