Hiper II Heat Interface Unit 2021



Hiper II is a twin plate, priority hot water (DHWS) electronically controlled heat interface unit.

The electronics provide automatic fault diagnostics and also error warnings when the supply to the HIU is not suitable for efficient operation. These can be read on the screen, or when linked with the iPulse monitor be read externally. Multiple parameters are adjustable to enable the commissioning engineers to adapt the operation of the HIU to suit the operating conditions of the heat network it is installed in. A temperature controlled keep warm function can be used or turned off if the installation does not require. To protect the pump during long summer periods where heating is not required can be programmed to run the pump for minutes to prevent sticking and formation of chemical residue on moving parts.

Electronic Control

Variable system conditions present challenges that the Hiper HIU PID control system meet by providing stability and rapid reaction to changes in supply and demand. The PICV (control valve) regulation delivers the design flow rate without affecting the modulating travel of the valve, so full authority is available throughout the full scope of the modulation. It is controlled by the electronic PID controller with constant monitoring from temperature and flow sensors at all critical flow and return paths. Key is control of the DHW demand, even at low flow, and still maintaining low return temperatures.

A proportional–integral–derivative controller (PID) continuously calculates an error value as the difference between a set point and a measured process variable and applies a correction based on the ‘proportional, integral and derivative’ values. In practical terms it automatically applies accurate and responsive correction to a control function, much like cruise control on a car. The PID algorithm maintains the set point without delay or overshoot, by controlling the stepper motor of the PICV actuator.

Control of Pressure Differential

Having one modulating valve with control of pressure differential means that it must adapt to the different demands of either hot water or central heating which is not possible with a thermostatic valve. The Hiper HIU electronically maintains the temperature set points and limits the flowrates to presets within the controller.

In the Hiper HIU pressure drop is created by the primary control valve and not the heat exchanger itself. For a low secondary flow, the primary valve is only going to open a small amount (10-15%). This will create a very high pressure drop from the valve itself. The pressure drops over the heat exchanger will be low. When the flow rate is high, this causes the primary valve to open wider or fully, and then decreasing the pressure drop over this valve significantly. In Hiper II the total pressure drop decreases as the primary flow increases. The maximum pressure differential across the PICV is 400 kPa giving a good scope for consultants to size pipes according even for the closest connections to the pump.

Keep Warm and Instant Heat

Delivering DHW at the taps without long waiting times is down to the response time of the HIU and the plumbing design of the pipework in the home. The response time set in the BESA test regime for HIU’s sets the standard as the DHW temperature leaving the HIU must reach 45oC in 15 seconds or less.

The Hiper HIU in enters its Keep Warm mode after a preset time, which the installer sets on commissioning, which can be on or off. Factory set on.

The time range for initiating this function is between 5 minutes and 24 hours, factory set to 24 hours.

The primary return temperature limit is set at 39oC

In some circumstances end users will not want or need this function, but the choice is there.

When the Hiper HIU then enters Keep Warm mode, after it’s elected time to activate, it maintains heat in the PHE by temperature control of the plate and limiting the temperature of the primary return. It is important in any HIU manual bypasses are not used, and the HIU should have a means of controlling the return temperature through any ‘Keep Warm’ functions to prevent excessive temperatures back to the Boiler Plant Room.

Lowest possible return temperature in the heat network.

These have been measured and calculated in the BESA test regime. This is the VWART (Volume Weighted Average Return Temperature) calculation and is a good guide to the HIU characteristics. VWART calculations are provided for DHW, Space Heating and Standby operational modes. Then an overall average figure is stated for each tested HIU.

Heating takes up most of the operational mode, either by radiators or by underfloor heating, and returns the highest temperatures to the network and plant. It is very important therefore that the circuit is balanced and uses the most effective means of control, and no circuits left ‘open’. Underfloor heating by nature of its lower operating temperatures is particularly suited to HIUs.

Hiper HIU by nature of being electronically controlled has an ‘optimised heating’ feature. Temperature on both flow and return are monitored by the controller, and as the room temperature gets close to the comfort level of the room, the controller then reduces the temperature to the space heating circuit, preventing overshoot of room temperature and maintaining lowest return temperatures to the network and plant.

So the important trade off against the Space Heating VWART is the DHW and Standby modes.

Standby, or ‘Keep warm’ is temperature controlled and controls and limits the return temperature to 40C (a programmable function).

Low DHW return temperature is provided by the PHE. Hiper II uses a ‘asymmetric’ design gives the highest thermal performance with low pressure drop.





Standby VWART


Space Heating VWART


Overall Result






Standby VWART


Space Heating VWART


Overall Result


Metering Pre-payment ‘out of credit shutdown’

For installations where the landlord of the properties has fitted a metering system that enables a scheme where the tenant pays for heat by pre-payment, the HIU has the capability to shut down the supply of heat when payment agreements have not been met. The HIU Controller has an auxiliary connection terminal that facilitates this option.

To connect to a prepayment billing system simply go into the installer setting and turn ‘ON’ Prepayment function, and connect the billing system cable to the connection in the controller.

The controller shuts down the PICV completely and also cancels out keep warm function to prevent ‘credit minus’ on billing.

The HIU needs no other valves to shut down when the billing is out of credit, saving cost on purchase of a motorised valve capable of closing against pressure differentials in the system and installation time.

The billing system working in conjunction with the heat meter selected by the consultant or energy provider, is usually volt free, but if is 230 volt signal then an accessory relay box is available. Consult the billing provider for this information.

Heat Loss and Insulation

Insulation Properties –

  • FT7 724 FR NP Low Density Open Cell Polyether Polyurethane
  • Flexible low density open cell polyether polyurethane foam
  • Containing a flame retardant additive to reduce ease of ignition.
  • Black Dual-Melt 25- 30 micron Polyurethane film on one surface.
  • Thermal conductivity 0.033W/mk
  • Density BS EN 845:1995: 24±3 Kgs/m3

Optimised heating is a function which manages the lowest return temperatures by monitoring the rise in the temperature on the secondary return temperature sensor. As the room temperature starts to near the room thermostat set point, then the temperature in the return pipework will also start to rise. To optimise the efficiency of the heating function, the HIU controller will compensate this rise by modulating down the PICV to reduce the flow of heat into the heating PHE. This then stops the secondary return temperature continuing to rise. This is particularly effective with under floor heating, where temperature overshoot can be a problem. Less heat is wasted, and comfort levels improved.

Product Range

Product Code
Hiper II Twin Plate HIU SZ 80kW DHW, 3 - 30 HTG HIPER2TP1580
Hiper II Twin Plate HIU 15-80kW DHW, 3 - 30 HTG HEAT METER HIPER2TP1580ZE