H E A T I N T E R F A C E U N I T
P R O D U C T D E S C R I P T I O N
Page 8
H E A T I N T E R F A C E U N I T
P R O D U C T D E S C R I P T I O N
Page 9
4. PRODUCT DESCRIPTION
4.1 General Function
The design of the HIU is for parallel production of
DHW and HTG.
4.1.1 Keep Warm Bypass
The keep warm function of the HIU is required to
maintain heat to the HIU, this function assists a
fast DHW response time to the DHW outlets.
A bypass is installed across the primary flow and
return pipework to allow a small flow of water
through the HIU without warming the plates. The
flow of water through the bypass is controlled by
a PICV, the PICV is controlled by a thermostatic
actuator with the probe measuring the
temperature at the entry point of the DHW plate.
4.1.2 Domestic Hot Water
The DHW is controlled by two control valves,
which control the flow of primary water through
the plate to generate instantaneous DHW.
1.
Taco valve: When a DHW outlet is opened the
valve detects MCW flow, the valve then opens to
allow the primary flow through the plate.
2.
Thermostatically controlled PICV. The actuators
thermostat is installed in the DHW flow out of
the plate, the actuator then controls the PICV
and the required primary flow rate through the
plate to maintain the DHW temperature.
The recommended setting is for 55 deg C
domestic hot water. Lower temperatures can
increase the risk of bacteria growth and higher
temperatures can cause scalding and damage
the HIU by increasing limescale formation. It is the
recommendation of CIBSE CP1 and NHBC section
8 that the temperature is set at this level.
4.1.3 Central Heating
The Central Heating Room Thermostat /
Programmer is connected directly to the HIU.
When there is a HTG demand, the primary side
HTG on/off control valve opens to allow primary
water to circulate through the HTG plate, the
heating pump is enabled to circulate water
through the radiators. The thermostatic actuator
controls the flow of primary water through the
PICV and heat exchanger to maintain the heating
flow temperature, which is measured by the
actuators thermostat installed in the outlet of the
HTG plate.
A manometer and thermometer are installed on
the heating flow pipework within the HIU. This
is visible through the front cover of the HIU. This
gauge displays the heating flow temperature and
heating system pressure.
The HIU has an expansion vessel installed on the
heating circuit to accommodate water expansion
as the system heats up. The heating system is
filled through the filling loop with MCW. A suitable
inhibitor should be used to protect the HIU and HTG
system.
4.1.4 Metering
There is a flow meter installed on the primary return
connection which monitors the flow of water to
the HIU. This combined with temperature sensors
allows the energy usage to be calculated. The meter
calculator is positioned on the front of the HIU in
an accessible location to allow usage to be checked
regularly.
4.1.5 Safety Devices
The central HTG system has a safety relief valve
installed, rated at 3bar. This valve has been installed
to protect the HIU and HTG system from over
pressurisation. The valve will require a connection
to drain, refer to approval document G typical
discharge safety valve arrangement.
It is recommended that a high temperature cut
off switch is installed to protect floor construction
when serving UFH. This should be installed on the
flow pipe leaving the HIU serving the UFH manifold.
Note: High temperature thermostat must be
installed on pipework by HIU installer, it is not
installed during manufacture.
The switch should be set 5 deg C higher than
the flow temperature of the UFH, but not higher
than the floor material maximum temperature
specification.
REF
COMPONENT
1
Backplate
2
Bracket (Expansion Vessel)
3
Bracket (Pipes)
4
EPP Cabinet
5
DHW Heat Exchanger
6
DHW Actuator
7
DHW Control Valve
8
Heating Heat Exchanger
9
Heating Actuator
10
Heating Control Valve
11
Heat Meter (Flow Sensor)
12
Pump
13
Junction Box
14
Check Valve
15
Mini Expansion Vessel
16
Expansion Vessel
17
Thermomanometer
18
Safety Relief Valve (SRV)
19
Test Point (Blue)
20
Test Point (Red)
21
Strainer
22
Ball Valve
23
Filling Loop Connections
24
Drain Valve
25
Spool Piece For Prepay
Valve
26
Heating On/Off Valve
27
Heat Meter Calculator
28
Keep Warm Actuator
29
Keep Warm Control Valve
30
MCW Strainer
31
Proportional Flow Controller
HIU Components
Fig. 2
