FAQ
Frequently Asked Questions for HIU's
DHW control
How does your HIU control DHW temperature at appliances and whatever the means of control, Mechanical or electrical, can it ensure stable DHW temperature should there be fluctuations in the district network primary temperature. Please provide details.
DHW control is achieved by modulation of the primary stepper valve, based on detected DHW flow, primary supply temperature, and delivery temperature. Changes in flow are immediately detected by the cold water turbine sensor, and translate to immediate movement of the primary valve, providing rapid response and accurate temperature control. Likewise, changes in primary temperature are fed into the control loop. Stable hot water delivery is demonstrated in the BESA test results.
All our electronic HIU's come as standard with a function to learn the differential pressure of the primary system during operation, adjusting performance characteristics to suit. This self learning feature works by examining the effect of a valve movement compared to known characteristics, and hence determining what the differential pressure actually is. The self learning feature takes three seconds to perform, and is done every time a tap is opened and temperatures stabilise.
Compliance
WRAS approval
Does your HIU have WRAS approval? If so please provide certificate.
The DATA HIU has full WRAS approvals. All other HIU's use the same components and control philosophy.
Test against established HIU standard
CIBSE’s Heat Networks: Code of Practice for the UK (2015) states: “Best practice could include the testing of the HIU performance against established standards”. Please provide, technical data for your unit under dynamic load conditions, such as BESA’s UK test standard for heat interface units.
Our DATA HIU has had the best performance of any HIU that has gone through BESA testing, since records began in 2016.
Our latest results are as follows:
The DATA SPLIT HIU has exactly the same components and control philosophy as the DATA HIU, we have simply rearranged the layout. It therefore operates to the exact same level of performance.
System return temperatures
Please provide confirmation of Primary LTHW Return temperature when your HIU is under full Domestic Hot water load conditions, confirm if your unit complies with industry guidance such as; CIBSE Heat Networks: Code of Practice (2015); CIBSE AM12:2013; BRE - A technical guide to district heating, 2014; GLA - London Heat Network Manual, 2014, etc.
Under full load DHW, the return temperature with vary between 15 and 25°C dependent on primary supply temperature. We use SWEP L-AS Plate Heat Exchangers, offering the best performance in the industry. Plate heat exchanger performance calculations are generated on a contract by contract basis to specific loads and temperatures.
The DATA HIU complies with industry guidance, including the latest CP1.2 requirements.
HIU Insulation
Is your unit fully insulated.
All HIU's have an EPP (Expanded Polypropylene) fully insulating casing as standard. A metal wrap is available with the DATA HIU, and a full metal casing is available for the SLIM range of HIU's.
Differential Pressure Control
Please confirm if your DHW & LTHW is independently controlled via DPCV or if 1 x DPCV controls both circuits, please confirm how the configuration impacts on Primary LTHW return temperatures
The control valves on both the heating and hot water primary circuits are pressure independent, and a DPCV is an option, only required where differential pressure in service exceeds 2.5 bar. If fitted, the DPCV locates on the common return in the HIU. If not fitted, all flow control on the primary is controlled to target temperatures using available sensor data. The BESA test results show a system without a DPCV fitted.
A DPCV has no impact on return temperatures.
Pressure Absorber
Does your unit have a pressure absorber or surge arrestor to safe guard against water hammer etc.
A water hammer arrestor is a standard option to fit within the DATA HIU. All other HIU's can be supplied with the water hammer arrestor for fitting external to the casing.
Flushing Bypass and Binder points
Does your unit come with a primary LTHW flushing bypass valve ? If so does it have integral binder points for flow rate verification and strainer
The DATA has a flushing bypass as a standard option. The bypass is fitted with binder test points on both flow and return.
The design of the flushing bypass does not allow the installer / commissioning engineer or end user to leave the bypass open whilst the HIU is in use. This means that the performance of the district heating network cannot be inadvertently compromised by a flushing bypass being left open for a prolonged period of time, without the resident complaining about lack of heat or hot water.
All other HIU's can be supplied with a basic flushing bypass, or where a flushing bypass is not supplied, primary isolating valves are fitted with Schrader valve binder test points.
System bypasses and DHW reaction times
What provision is there within your unit that safeguards against slow reaction for Hot water generation at appliances in times of Low demand on primary LTHW circuits ? A device such as a Danfoss FJV Valve or equal to. Please confirm.
The HIU's provide three modes of keep warm operation:
- No keep-warm. This is the default setting, with system relying on thermal bypasses on the network to maintain heat near by.
- Constant keep warm. The HIU will maintain primary temperatures to a setpoint between 25°C and 55°C.
- Timed keep warm. The HIU will maintain primaries to setpoint for a set period following use. Then turn off.
In addition to the keep warm setting, the HIU flushes primary pipework at an increased flow rate until heat arrives. This boost flow is adjustable between 5 and 20 litres per minute, with 16 l/m being the standard. This function typically allows keep warm to be turned off where there is a thermal bypass on risers, as recommended by guidance.
This method of operation has been demonstrated in the BESA testing to result in significantly lower return temperatures, with an official VWART as low as 15.8°C with no keep warm, or 28°C with keep warm (15 seconds delay) turned on.
No additional control valves are required for keep warm functionality and the keep warm temperature setting is independent to the DHW setpoint.
Position of strainer
Please confirm location of strainer & orientation with regards to water flow direction
The primary strainer is fitted within the casing on the primary flow pipe, in a horizontal position to assist in function, and to enable easy maintenance.
The secondary strainer is also fitted within the casing on the return pipe of the central heating system. Again it is mounted horizontally and in an accessible location.
Prepayment valve
Does your unit have a pre-payment facility – i.e.: 2 port pre-payment valve
The HIU provides three pre-payment options:
- A pre-payment valve can be fitted in the HIU. This option cannot be taken together with a fitted DPCV valve.
- A pre-payment relay can be fitted in the HIU to shut-down the system using the existing control valves. The HIU's LED will change to a red blink to indicate mode to user. This is the most economical option.
- The HIU can be connected over 2 wires to a riser located communications bridge, enabling remote control over pre-payment functions via Ethernet, WiFi, GSM, MQTT or Modbus networks.
Heat meter
Please confirm Manufacturer & model of proposed energy meter and protocols
The standard heat meter offered would be a Zenner C5 Heat Meter, providing M-Bus and three axillary pulsed inputs/outputs. All other makes and models available on request, based on 110mm spool size, allowing any protocol to be met.
Manufacturer’s maintenance requirements
Please confirm all maintenance tasks & frequencies for your unit.
The HIU itself has no maintenance requirements. There are however requirements to maintain water quality, as follows:
- Primary strainers on a small number of random HIU's, as well as in plantroom, should be checked at regular intervals. Any signs of debris would require planned maintenance on all HIU's to clear primary strainers.
- Any chemicals used in the central heating system should be maintained as per manufacturers instructions. The HIU is fitted with a strainer on the central heating return that should be checked at the time of service.
- A post installation check should be performed on all HIU's after a few weeks operation, to check all strainers, as well as connections for leaks.
For more information about water quality, please see Requirements on water quality
Where HIU systems are connected to a communication infrastructure, remote fault diagnosis is provided, along with the routing of alarms to personnel. See Node-HIU_Switch
