HIU Specification Text

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This article is our attempt to define specification that ensures efficiency, and manufacturers can aim at to help ensure competition. Every one of the points has been included for a specific reason, having either a significant impact on efficiency, or reliability.

We have limited the figures to what we feel is a minimum requirement. Our own products go beyond these figures and options, but to specify such would serve to prevent competition, and could only be justified in certain circumstances rather than a general specification.

Note that exactly the same wording can be applied to direct heating HIUs, as well as twin plate HIUs. (Although no direct HIUs have yet been BRSA approved).

Each HIU shall include the following features:

  • HIU settings should be applied my the manufacturer as per site requirements, and be tamper-proof to ensure only approved engineers can alter settings.
  • The DHW functions must include the facility to have both a keep-warm mode to a pre-determined temperature, as well as the ability to turn off the keep warm completely where pipework allows.
  • Where keep-warm is to be turned off, the HIU must be capable of clearing X litres of cold water from primary pipework in under Y seconds. Actual figures will be specific to contract pipework layout and sizing, with volume calculated from volume of water in index runs to HIUs, and the time been the maximum delay for DHW production from a cold start.
  • Where a keep-warm mode is to be deployed with temperatures below 50C, an Anti-legionella cycle should be available. Where there is no keep-warm, or keep warm is over 50C, this function should be disabled (or not present).
  • Where HIUs are fitted within properties, there should be a means to interrogate the HIU and change settings without gaining entry to the property. This would normally be provided by a communication cable from the HIU to the riser or plantroom.
  • The HIU must have been tested to the BESA independent testing standard at an approved test centre (RISE/Enertek/BSRIA), and must have passed all tests without failing on any. This is to ensure the HIU performs to minimum standards and meets safety requirements.
  • The published VWART figure from BESA testing (as per the high/low keep warm on/off) to be a maximum of [enter figure]°C. The actual temperature will depend on the fuel mix to be used and how return temperatures effect generation efficiency. For waste heat this may, for example, be 20C, and for heat pumps 30C.
  • The HIU should be WRAS approved, preferably as a complete system.
  • To satisfy a peak DHW load of 50kW.
  • To satisfy a peak central heating load of 10kW.
  • To operate (to specification) with a minimum primary differential pressure of 50kPa (0.5 bar).
  • Commissioning settings should include as a minimum:
    • DHW Set-point between 45C and 60C.
    • Keep warm on/off.
    • Keep warm temperature adjustable between 30C and 50C.
    • Adjustable and optional return temperature limitation.
    • Central heating setpoint adjustable between 35C and 55C for underfloor heating systems, and between 45C and 75C for radiator systems.
  • Where heat network supply temperatures drop below setpoint heating temperatures, the return temperature should be protected from rising as a result.
  • Central heating pumps should be activated (exercised) at intervals when not in use to prevent seizing.
  • The facility to accept a heat meter within casing.
  • The facility to include a pre-pay isolation valve within casing.
  • Suitable for a maximum network differential pressure of 2 bar.
  • Suitable for a maximum network static pressure of 10 bar.
  • Option for a first fix bracket(s) with isolation valves.
  • The HIU must include an insulating casing with the facility for tamper-proof access.
  • Any EPP insulation should be self-extinguishing when ignited.
  • All components should include a minimum 2 year warranty.
  • A minimum one year on-site cover to be provided by the manufacturer.
  • System settings to be commissioned and made tamper-proof by manufacturer, either on-site (post-installation), or off-site (pre-installation), with certificate issued.
  • All components (including plate heat exchangers, control valves, pumps and expansion vessels) should be serviceable without removal of the HIU.
  • Running costs (including heat losses from service pipework, and generation efficiency) over a five year period will be evaluated based on the declared VWART results from independent testing and added to the tender price.
  • Maximum dimensions of...