The DATA HIU

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The article forms the basis of the literature on the DATA and DATA PLUS HIU's.

Contents

Introduction

Official VWART Comparison from Independent Testing
Official VWART Comparison from Independent Testing
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The DATA is our standard twin plate Heat Interface Unit.

It is one of six HIUs now tested independently to the new UK HIU standards, and has demonstrated beyond doubt to offer greater efficiencies than any other system.

Click here to learn more about the new UK standards.

It is built using tried and tested electronic controls with over 10,000 in the field.

The system is immune to installation error (within reason) and required no site commissioning, with units are supplied pre-set to consultants requirements. Only approved engineers can adjust settings, and the system will protect itself against unbalanced radiators. Commissioning software is provided to third party commissioning engineers.

It has the ability to connect through billing and BMS systems to provide functions such as remote commissioning and fault reporting, ensuring heat networks can be maintained at peak efficiency throughout their life.

We are a UK manufacturer, with 25 years experience building HIUs, some of the most advanced training facilities in the UK, as well as nationwide servicing capabilities. We take pride in our products and service levels, and have never left a customer with a complaint - be they a local authority, or a private individual.

BESA Results

Our latest results are as follows:



Documents

Installation Instructions

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Installation Instructions for the Data HIU
Comprehensive installation manual for the twin plate DATA HIU.

Datasheet

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DATA Datasheet

Approvals

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WRAS Approval Certificate

Click Here to find out more about The DATA WRAS Approval

3D Model

Data External by heatweb on Sketchfab


The DATA by heatweb on Sketchfab

Please click HERE to go to the BIM / CAD File downloads page.

Previous Versions of Literature

File:DATA Brochure 020715.pdf

HIUs from Thermal Integration

Introduction

The DATA is our flagship twin plate HIU, it has WRAS approval and has been tested to the latest BESA Standard. The DATA represents the new standard in twin plate HIU's, combining all the latest technologies into a solid, compact unit that outperforms anything in its class.

Features & Benefits

  • Compact design with no need for clearance either side for servicing. Allowance made for extra options, yet small enough to fit into a standard kitchen cupboard
  • Instantaneous hot water up to 65kW (Standard Model) 75kW (PLUS Model) - at 37 & 48kPa (respectively) Primary Differential Pressure. Temperature adjustable from 45-60°C
  • Indirect central heating up to 24.7kW (@ 30° Delta T) Temperature adjustable from 50-80°C (To suit radiators or underfloor heating applications)
  • Primary return temperature limitation, settable at commissioning
  • Heat-up boost, enabling the DATA to get up to temperature with maximum power before ramping down to maintain a steady output
  • Option for Inter-networking of all DATA units within a development to enable site wide adjustments to match loads to primary circuit heat availability
  • Option for browser based interface and online dashboard for remote commissioning, monitoring, control adjustments, performance visualisation, fault detection and diagnosis using pc, tablet or phone
  • Sensors for temperature, pressure and flow rate allow the system to monitor performance and detect fault conditions locally, or on the district heat network
  • The latest stepper motor valve technology allows the system to react rapidly, thereby maintaining accurate control over domestic hot water temperatures
  • Pre-install plumbing jig complete with isolation valves to allow pipework on site to be completed prior to HIU installation
  • Primary circuit trickle flow can be set during commissioning to maintain heat within the unit. When in Economy Mode it allows the unit to go cold following one hour of inactivity, preventing unnecessary use of metered energy
  • Insulated removable EPP casing with less than 50 Watts standing heat loss; ensures the unit can be maintained at temperature with little impact of metered energy use
  • Sterilisation programme raises the Domestic Hot Water temperature periodically; preventing the development of Legionella bacteria
  • Casing and Heat Meter anti-taper fixings
  • Option for Built-in security valve feature for landlord isolation
  • Pump exercise function
  • Option for integral hammer arrestor
  • Option for integral Domestic Hot Water re-circulation pump
  • Site specific factory calibration of controls to predefined settings
  • Customised connections top/bottom (standard connections:-TOP - Primary flow & return and Mains Cold Water / BOTTOM - Central heating flow & return and Domestic Hot Water)
  • WRAS approved DATA WRAS Certificate

Technical Data

Description Units Value
Height (excl. mounting bracket) mm 640
Width mm 490
Depth mm 271
Weight (excl. mounting bracket) kg <30
Connections
Position Primaries top. All else bottom.
Primary Connections 3/4” BSP Female
Distribution Net Return 3/4” BSP Female
Cold Water Inlet 15mm Compression Female
Hot Water Outlet 15mm Compression Male
CH supply 3/4” BSP Female
CH Return 3/4” BSP Female
Safety Relief Valve 15mm Copper Pipe
Primary Circuit
Maximum Supply Temperature ˚C 85
Minimum Supply Temperature ˚C 65
Nominal Supply Temperature ˚C 80
Maximum Return Temperature ˚C 40
Pressure Class PN 16
Maximal Permissible Differential Pressure* kPa 250 Standard - 450 With dp Regulator
Minimal Permissible Differential Pressure kPa 50
Max.flow l/h 1400
Primary Circuit (after dP/security)
Pressure Loss kPa 20-60
Secondary Circuit CH
Max. output kW 25
Pump (Energy Class A) 15-6; 130
Expansion Vessel ltr 8
Pressure Relief Valve bar 3
Maximum Flow Rate l/h 720
Secondary Circuit DHW - DATA
Output (@10-55 ˚C) l/min 20.5
Output (@10-55 ˚C) kW 65
Secondary Circuit DHW - DATA PLUS
Output (@10-55 ˚C) l/min 24
Output (@10-55 ˚C) kW 75
Pressure Class PN10
Minimum Pressure kPa 50
Design Temperature (Cold Water) ˚C 10
Nominal DHW Temperature ˚C 55
DHW Temperature Setpoint ˚C 35-60
Additional Features
Casing Material EPP (Expanded Polypropylene)
Maximum Heat Losses W 50 (1.2 kWh/day)
Typical Heat Losses (DHW Only, Keep Warm) W 25
Keep Warm Modes Economy & Comfort
Max. Return Temperature During Keep Warm Mode DHW Setpoint -2˚C
Electrical Information
Electrical Supply Info 230V 50Hz
Fuse Ratings 3 Amp
Sensor DHW NTC 10kOhm @ 25 Degrees

The DATA and DATA PLUS Specification Text

The following specification text can be used as guidance when writing a District heating design specification.

DATA

All apartments should be fitted with a Heat Interface Unit (HIU). Each HIU should take its primary heat source from a district heating system, and must be capable of indirectly exchanging heat to the apartment heating system and Domestic Hot Water.

The HIU should be fitted with plate heat exchangers capable of the heating and hot water loads of the property. It should be possible for the heating plate heat exchanger to effectively operate at 3.4kW output at 80 deg C Primary flow & 65-35 deg C across the heating circuit whilst maintaining a turbulent flow on the primary circuit. It should also be possible for both the heating and hot water temperatures to be pre-set on the unit during commissioning, the heating temperature should be settable for radiator or underfloor heating systems, however all temperature controls should be inaccessible to the occupant.

The DHW mode should be activated by a flow turbine at 0.6 l/min, and the HIU should have a primary boost function to accelerate the primary flow to the plate heat exchanger, enabling the HIU to achieve DHW setpoint stability within 60 seconds from cold.

Each HIU should be fitted with an EPP casing to reduce heat loss. The casing should be fitted with tamper-proof security screws to restrict access to internal components. Overall dimensions of the HIU must not exceed 640mm High x 490mm Wide x 271mm Deep.

Each HIU should be fitted with an ultrasonic energy meter. The energy meter should enable wired connection to an M-Bus network but also have 3 pulse inputs to make possible the connection of additional hot and cold water meters and an electricity meter. The energy meter must be accessible to the occupant without the need to remove the HIU casing. The heat meter must also be powered by the M-Bus network with battery back-up should the M-Bus network fail.

Each HIU shall include the following features:-

  • Commissioning settings accessible locally via a laptop or handheld device.
  • Self learning and adjusting to fluctuations in primary system pressure.
  • Option for remote connectivity for data logging, fault finding, and adjustment of operating parameters.
  • Stepper Motor control over both the heating and hot water circuits with full primary closure within 5 seconds of tap closure.
  • DHW Set-point between 45C and 60C.
  • Return temperature limitation.
  • Anti-legionella cycle if there has been no hot water draw-off for 24 hours.
  • Intelligent Domestic Hot Water pre-heat function with the ability to turn the pre-heat off after a defined period of inactivity and the ability to set the pre-heat temperature independently of the DHW temperature.
  • Landlord Security valve fitted within the casing. Valve must be full bore and close on loss of power.
  • Pre-plumbing bracket with isolation valves and flushing bypass.
  • 8 Ltr Heating Expansion Vessel.
  • Optional Secondary return pump on DHW circuit.
  • Optional Low flow Heating plate heat exchanger to achieve 3.5kW Output.
  • Qp1.5 Heat Meter with M-Bus output and 3 Pulse Inputs

Heating Performance

  • Maximum - 24.7kW - @ 30°C ΔT across Secondary Flow/Return (based on 75°C Primary flow temperature)

Hot Water Performance

  • Minimum - 1 ltr / Min
  • Maximum - 65kW - 20.5 ltr / Min @ 55°C (based on 80°C Primary flow temperature)

DATA PLUS

All apartments should be fitted with a Heat Interface Unit (HIU). Each HIU should take its primary heat source from a district heating system, and must be capable of indirectly exchanging heat to the apartment heating system and Domestic Hot Water.

The HIU should be fitted with plate heat exchangers matched to the heating and hot water loads of the property. It should be possible for the heating plate heat exchanger to effectively operate at 3.4kW output at 80 deg C Primary flow & 65-35 deg C across the heating circuit whilst maintaining a turbulent flow on the primary circuit. It should also be possible for both the heating and hot water temperatures to be pre-set on the unit during commissioning, the heating temperature should be settable for radiator or underfloor heating systems, however all temperature controls should be inaccessible to the occupant.

The DHW mode should be activated by a flow turbine at 0.6 l/min, and the HIU should have a primary boost function to accelerate the primary flow to the plate heat exchanger, enabling the HIU to achieve DHW setpoint stability within 60 seconds from cold.

Each HIU should be fitted with an EPP casing to reduce heat loss. The casing should be fitted with tamper-proof security screws to restrict access to internal components. Overall dimensions of the HIU must not exceed 640mm High x 490mm Wide x 271mm Deep.

Each HIU should be fitted with an ultrasonic energy meter. The energy meter should enable wired connection to an M-Bus network but also have 3 pulse inputs to make possible the connection of additional hot and cold water meters and an electricity meter. The energy meter must be accessible to the occupant without the need to remove the HIU casing. The heat meter must also be powered by the M-Bus network with battery back-up should the M-Bus network fail.

Each HIU shall include the following features:-

  • Commissioning settings accessible locally via a laptop or handheld device.
  • Self learning and adjusting to fluctuations in primary system pressure.
  • Option for remote connectivity for data logging, fault finding, and adjustment of operating parameters.
  • Stepper Motor control over both the heating and hot water circuits with full primary closure within 5 seconds of tap closure.
  • DHW Setpoint between 45C and 60C.
  • Return temperature limitation.
  • Anti-legionella cycle if there has been no hot water draw-off for 24 hours.
  • Intelligent Domestic Hot Water pre-heat function with the ability to turn the pre-heat off after a defined period of inactivity and the ability to set the pre-heat temperature independently of the DHW temperature.
  • Landlord Security valve fitted within the casing. Valve must be full bore and close on loss of power.
  • Pre-plumbing bracket with isolation valves and flushing bypass.
  • 8 Ltr Heating Expansion Vessel.
  • Optional Secondary return pump on DHW circuit.
  • Optional Low flow Heating plate heat exchanger to achieve 3.5kW Output.
  • Qp2.5 Heat Meter with M-Bus output and 3 Pulse Inputs

Heating Performance

  • Maximum - 24.7kW - @ 30°C ΔT across Secondary Flow/Return (based on 80°C Primary flow temperature)

Hot Water Performance

  • Minimum - 1 ltr / Min
  • Maximum - 75kW - 24 ltr / Min @ 55°C (based on 80°C Primary flow temperature

Schematic

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As Standard

Electronic Control

Rather than purely mechanical controls, the DATA uses an electronic controller to read sensors and control outputs such as valves and pumps. The big advantage of this approach is it enables every control function desired to be implemented through lines of software code, where a mechanical system requires a separate device to perform each function. This is best demonstrated by the list of functions the DATA can perform using just one valve for each heat exchanger, including temperature control, differential pressure compensation, domestic hot water preheat, heat boost, and security shut-off. A mechanical system to achieve this requires a multitude of valves, and becomes complicated, large, and heavy. The DATA's electronics also enable such functions as smartphone control, network load management, and remote commissioning and fault reporting, by exposing data and receiving commands via a serial port to the optional IHIU Ethernet/WiFi control system.

Stepper Motor Technology

The DATA makes use of the latest stepper motor technology for both the hot water and central heating control valves. This provides a number of advantages over more traditional thermostatic or motorised valves, allowing significantly faster and more accurate control of flow rate and temperature. More significantly the DATA can operate the valves to perform a range of functions, rather than simple fixed temperature control. These include return temperature limitation, flow limitation, and sterilisation cycles.

Economy / Comfort Mode

It is common for HIU's to include a thermostatic bypass to maintain heat across the domestic hot water plate heat exchanger at all times, this helps minimise delays in hot water supply when a tap is opened.

The DATA, DIGI and SLIM HIU's all perform a similar function with the Economy or Comfort mode, by momentarily opening the domestic hot water stepper motor to allow small quantities of primary water to creep into the unit at regular intervals. The primary pipework leading to and from the HIU usually loses heat faster than the HIU itself, hence the unit will typically settle trickling in heat fast enough to keep the primary return at or just below domestic hot water temperature. The DATA, DIGI and SLIM HIU's are the only HIU's capable of this level of control with electronics to ensure that primary return temperatures remain below the domestic hot water setpoint at all times.

Each HIU has two domestic hot water keep hot modes, Economy or Comfort. These can only be selected during commissioning or by a trained engineer.

The default setting is Eco mode, and this can be specified to run for 0 minutes (which turns the feature off all together), 15, 30, 60 or 120 minutes after the last hot water draw off. In Eco mode the heat exchanger is kept to a specified temperature (between 25 and 60 Deg C) for the selected period of time and after this period of inactivity has elapsed the stepper motor closes completely and the temperature in the domestic hot water circuit is allowed to drop through natural dissipation to minimize energy consumption. If a hot water draw off is made any time throughout the Eco mode function the unit will deliver hot water as usual and the Eco mode function will begin counting down for the selected time once again.

In Comfort mode the heat exchanger is continuously supplied with a trickle of primary water for quicker hot water delivery, however energy consumption will be slightly higher than if the unit was set in Eco mode.

Anti Legionella Function

After 24 hours of inactivity, the HIU will bring the domestic hot water plate heat exchanger up to temperature to prevent legionella from growing. The heat exchanger is heated to 57°C for a period of at least 60 minutes.

It is not possible to specify the time at which this occurs, however it will stop immediately upon a hot water draw off.

Moulded EPP Insulated Casing

The best way to reduce heat losses is typically to insulate. In an HIU this is especially important as there is very little water content and so even a small heat loss results in temperatures dropping and the controls cycling the primary supplies to reheat. To significantly reduce this, the DATA, DIGI and SLIM HIU's makes use of engineered EPP (Expanded Polypropylene) moulded enclosures that encase individual components preventing any heat bridging to the environment, or to other components within the unit. The resulting heat losses are under 50 Watts, helping to ensure that cupboard temperatures do not rise significantly, and although the finished moulded casing looks good in itself, there is also an option for an outer metal cladding.

Advanced Heat Exchanger Technology

District heating pipework should generally be sized for temperatures as high as the plant can typically generate, to satisfy those days when it is -5°C outside. Most of the time however, there is considerable space to run the network at lower temperatures during periods of reduced demand. In addition, modern heating loads are becoming very small indeed, making it difficult to maintain turbulence (and efficiency) within heat exchangers. The DATA makes use of Asymetric plate heat exchangers to best match the characteristics of modern dwellings, while maintaining efficiency.

Pump Exercise Function

During prolonged periods when the heating is not in use, it is important to ensure the heating pump does not seize up. This is often a problem with Mechanical HIU's and can require costly service visits or replacement of the pump. Therefore the DATA is programmed to perform an automatic pump ‘exercise’ function which takes place every 24 hours and lasts for 60 seconds. The function will take place regardless of whether the room thermostat or programmer are calling for heating. This ensures there are no nasty surprises when the heating season begins.

Metering & Security

The DATA has been designed with pre-pay billing systems taken into consideration, where HIUs need to be fitted with a security shut-off valve, and designed with tampering in mind. The DATA includes pipework allowance for both a heat meter and security valve internally. To simplify the process of securing bolts and access points on HIUs, we make use of unique moulded security clips and caps that once assembled, makes it impossible to access a bolt head or connection nut without breaking the cap. To secure casings, and any bolted on components that one would like secured, we use a Bolt Security Cap. Bolts are inserted through the lower part of the security cap assembly, and screwed into position. The upper part is then pushed into the lower part until it locks, at which point the cap cannot be removed, and the screw head cannot be accessed.

Reliability and Confidence

Ask yourself, is it possible for installers or users to modify any settings in an HIU that could affect performance? Then ask yourself, of all the problems you have ever had with HIUs, were any related to inconsistent settings or tinkering?

The performance settings on the DATA can only be altered by an approved engineer with the right kit and software, and is typically setup both in the factory, and again confirmed at commissioning. These settings are locked in software, with a report confirming all settings generated at commissioning. Following setup, no-one can change the settings, override DHW settings, open bypasses, or set the central heating temperatures too high. The whole system actually performs in reality as it does on paper.

Options

Heat Meter

A selection of heat meters are available to be factory fitted. Heat meters can be protected with a patented security clip to provide a permanent security fixing that prevents access to connections without breaking the tamperproof seal. The heat meter display is mounted on a metal panel recessed into the front of the unit, providing access to buttons, but preventing removal.

Security Valve

Where HIUs are intended to be used in conjunction with pre-pay systems where it is required for utility providers to have the facility to shutdown heat supply, the Data can be factory fitted with a security valve that can close against very high pressures, has a low pressure loss, and closes on loss of power.

As an alternative it is possible to fit the DATA with electronic isolation control, which communicates directly with the HIU controller to shutdown the unit with immediate effect, or gradually over a period of time, so that the end user does not get a nasty surprise mid shower.

Flushing Bypass

The DATA HIU can be fitted with a flushing bypass to allow flushing and cleaning of the primary circuit without contaminating the plate heat exchangers within the HIU.

We have sourced a flushing bypass that 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.

Our flushing bypass is also fitted with binder points as standard, to allow differential pressure measurement across the primary flow and return connections. This can aid fault finding on the district heating system.

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Flushing Bypass Instruction Sheet

Matched Heat Exchangers

It is not the case that bigger is always better, and oversizing a heat exchanger can cause as many problems as undersizing.

The reason is that efficient heat exchange requires turbulence within the water flow, however below a point the flow becomes laminar, and the hotter water tends to pass right through the heat exchanger resulting in elevated return temperatures that can destroy the efficiency of a district heating network.

To ensure optimum efficiency we can supply heat exchangers designed to match your heat loads to perfection. Typically we will issue heat exchanger calculations at the customers proposed operating parameters.

Network Control and User Interfaces

Home screen provides operating data, and user controls
Site Dashboards

As an optional extra, the Data can be supplied with an IHIU controller, providing the system with web server capabilities, and a host of options.

  • System will generate a local WiFi hotspot that can be used to access the Data controls.
  • The system can be logged onto an existing WiFi network to connect it to the internet and other devices.
  • Alternatively, a wired Ethernet connection is provided.
  • Provides end users with pc, smartphone or tablet interface, either locally or remotely.
  • Enables remote commissioning and fault response.
  • Connects system to Google calendar services for control over hot water and central heating.
  • Enables sensor and performance data to be logged to remote web servers for analysis, at up to one second resolution.
  • Enables data logging to the Energy Saving Trust's EMBED database
  • USB port enables connection to other devices via serial, RS232/485, mesh networking, Modbus, and more.

Secondary Return Pump

The domestic hot water circulation pump is an available option within the unit. The pump is added to minimize delay in the delivery of domestic hot water at the draw off point in a closed DHW circulation circuit. It is generally used in systems where the domestic hot water needs to travel greater distances to its draw off point.

Adjustments to the pump settings should be done by recognized personnel only.

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Data recirc pump.jpg

Status indicator LED

LED on (continuously): Normal operation (pump is running)
LED blinking short, long: Error due to low voltage
LED blinking short (4x), long: Error due to pump speed feedback
LED blinking short (3x), long: Error due to high temperature
LED blinking short (5x), long: Pump rotor is blocked
LED On 200 msec., Off 200 msec., On 200 msec. Air venting
LED On 50 msec., Off 50 msec., On 50 msec. Stand-by

Operation errors

Problem Cause Solution
Pump not running Not connected or connected correctly Connect correctly
  Pump too hot, dry operation or overheating protection active Allow pump to cool down, pump restarts automatically
  Pump is blocked Contact your supplier
Pump is noisy Not thoroughly air vented Air vent the pump
  Foreign objects in pump Contact your supplier
  Worn bearing Replace pump

 

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Air venting the pump The pump has an air venting function that can be activated by turning the knob to position 7 for 5 seconds. Afterwards the desired position can be chosen. The procedure will take about 10 minutes. The procedure can be canceled by switching to position 3 and then back to position 7. Audible flow noises indicate that there is still air in the pump. Should this be the case the air venting procedure needs to be repeated.
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Pump settings The circulation pump has 7 settings to choose from to accommodate different situations, position 1 being the lowest and 7 the highest setting.

Water Hammer Arrester

Water hammer can occur in the HIU and connected pipes when water is accelerated or decelerated very quickly. This can be caused by certain types of valve or tap connected to the DHW system, but can also occur when the Secondary DHW recirculation pump stops.

The phenomenon can, in extreme circumstances, result in noise and damage to the whole system, and the Water Hammer Arrester prevents such damage.

Depending on other options we can fit two different models, the flow through or single inlet option. Both are WRAS approved and function in the same way.

Caleffi Water Hammer Arrestor

Differential Pressure Control Valve

A Differential Pressure Control Valve (DPCV) is only required where differential pressures across the primary flow and return are likely to exceed 2.5 bar.

The DIGI, DATA and SLIM electronic HIUs, all come as standard with a function to learn the differential pressure of the primary system during operation, and adjust their characteristics to suit.

Differential pressures (DP) can vary significantly across a network. The properties nearest to the plant room will see the maximum pressures generated at the plant, where as the index flat, furthest from the plant, will see much lower pressures - enough to work at full network load. The typical range of pressures is from 0.5 bar up to 1.5 bar, but can be higher on some networks.

The traditional approach is to fit a DP valve, that knocks out excess pressure so the HIU only sees a constant DP. A perfectly adequate solution, however has three disadvantages compared to using an electronic self-learning system:

  • They add cost, taking up more space and hence increasing HIU size and heat loss.
  • They introduce pressure loss of their own, so that the index flat will in fact need a higher DP to achieve maximum load.
  • One more component to go wrong.

The self learning feature works by examining the effect of a valve movement compared to known characteristics, and hence determining what the DP actually is. The self learning feature takes three seconds to perform, and is done every time a tap is opened and temperatures stabilise.

The following graph shows how the self learning feature works during an independent test. The test shows the commissioning process where the unit is turned on for the first time. The preset DP value is 0.6 bar. The actual DP of the system is 2.5 bar. The first test draw-off shows how the system would react without self-learning in place. The hot water temperature overshoots the target on first draw-off, and a spike in DH flow (red dotted line) can clearly be seen. The second draw off starts with heat in the system, allowing advanced functionality to start and enables the system to learn the new DP value. From there on you see no spikes in DH flow or significant overshoot of temperatures when taps are opened.

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DP values will vary with load for any one property, so once the initial commissioning has been performed (by running hot taps a few times) then the system is setup to go, and will continue to fine tune itself every draw off.

Metal Casing Wrap

Return Temperature Performance

Return Temperature Performance

Low primary return temperatures are important on district heating systems for three main reasons.


  • Efficiency of heat generation - CHP, condensing boilers and heat pumps all benefit greatly from lower return temperatures.
  • Heat losses - colder return pipework results in lower network heat losses.
  • Pipe and pump sizing - sending hot water back to plant is a waste of available pipework capacity, and greater loads can be transmitted through a network if the overall temperature drop is greater.

The task of achieving low return temperatures is made difficult by the need to maintain high enough temperatures in pipework to respond to immediate DHW demand. This function, referred to as a keep-warm or trickle flow, needs to also satisfy a Legionella duty of care, ensuring water does not remain at low temperatures for lengthy periods.

Mechanical Technology

HIU technology using mechanical controls relies on valves being manually setup (and ideally locked) at settings that meet both load requirements, while maintaining low return temperatures. The least efficient (and hence most costly to the user in terms of energy costs) is to use a by-pass that passes a low flow rate of hot water from the flow to the return. The fixed flow must as a minimum cover HIU and pipework losses and results in return temperatures similar to flow temperatures. Across a whole site, where 95% of units are not running taps at the same time, the majority of return water to plant will be bypass flow, destroying return temperatures.

A thermal bypass, or use of a mechanical temperature control valve on the DHW, relies on the sensor loosing temperature to open the valve and allow a small flow of water through. As with nearly all mechanical control loops however, the valve characteristics and rate of sensor response to changes in primary flow and temperature makes a massive difference, and it is normal to see cyclic reheating rather than a steady very low flow equal losses. As soon as the smallest cycle is introduced into a mechanical system, the control valve will close in response to higher temperatures. Given heat losses of pipework are greater than the plate heat exchanger (a solid insulated thermal mass), by the time the DHW sensor (mounted into the PHE) has cooled enough to open, the pipework is considerably cooler. As this colder water then enters the PHE, the valve opens further. Flow increases until heated primary water reaches the PHE, and continues (now with very hot water flowing fairly rapidly from flow to return) until the sensor react - up to 30 seconds later. The system overshoots until the sensor again closes the primary valve in response to the elevated temperatures and the cycle continues. The vast majority of flow through the system is at temperatures far higher than is required to maintain losses, and the rapid fluctuations in flow and return temperatures can influence heat meter readings.

Electronic Technology

Electronics make advanced control simple, and very reliable.

An electronic control system has the ability to work out the average losses from the pipework and combine this information with the system temperatures to accurately control average flow through the PHE to perfectly match heat losses. Electronic systems are also much simpler - with only one control valve (that can be exercised) to perform all functions, where a decent mechanical system would require temperature control valve, differential pressure control valve, return temperature limitation valve, and possibly a separate thermal by-pass valve to achieve arguably comparable performance. Each valve different, requiring space, cost, spares, and introducing extra possibilities of a wrong setting that inadvertently destroys return temperature performance.

The graph below best highlights the benefits of an electronic system over any other when it comes to return temperature performance. As you will see, the return temperatures to the heat network remain as low as possible at all times. Even in keep warm mode, between draw offs, the system manages primary flow to ensure the return temperature does not fluctuate, and stays below the DHW setpoint.


Return Sample 19-10-13.jpg

A key point to notice is the primary flow temperature in red during keep warm periods between draw-offs. It remains below the DHW setpoint, very close to the return temperature. This is because the heat losses from the HIU will always be lower than local primary pipework losses, so the unit regulates to a primary flow that just maintains DHW readiness. Lower HIU (and local pipework) temperatures results in even lower heat losses, as well as improved meter accuracy.

DHW Performance - DATA

DHW Performance Table

DHW Power Chart for 10-55°C

Primary Return Temperatures for 10-55°C

Primary Flow Rates for 10-55°C

Primary Pressure Drop for 10-55°C

Domestic Hot Water Pressure Drop for 10-55°C

DHW Performance - DATA PLUS

DHW Performance Table

DHW Power Chart for 10-55°C

Primary Return Temperatures for 10-55°C

Primary Flow Rates for 10-55°C

Primary Pressure Drop for 10-55°C

Domestic Hot Water Pressure Drop for 10-55°C

Central Heating Temperature Curves

Central Heating Temperature Curves for 80-50°C

Central Heating Temperature Curves for 70-40°C

Central Heating Temperature Curves for 60-40°C

Central Heating Temperature Curves for UFH 45-35°C

Images



Components

DATA Components.png DATA Components Key.png

Comfort and Economy Modes

It is common for HIU's to include a thermostatic bypass to maintain heat across the domestic hot water plate heat exchanger at all times, this helps minimise delays in hot water supply when a tap is opened.

The DATA, DIGI and SLIM HIU's all perform a similar function with the Economy or Comfort mode, by momentarily opening the domestic hot water stepper motor to allow small quantities of primary water to creep into the unit at regular intervals. The primary pipework leading to and from the HIU usually loses heat faster than the HIU itself, hence the unit will typically settle trickling in heat fast enough to keep the primary return at or just below domestic hot water temperature. The DATA, DIGI and SLIM HIU's are the only HIU's capable of this level of control with electronics to ensure that primary return temperatures remain below the domestic hot water setpoint at all times.

Note that the units perform a Legionella protection cycle every 24 hours overnight, for 60 minutes over 57°C, enabling the safe use of lower keep warm temperatures.

Each HIU has two domestic hot water keep hot modes, Economy or Comfort. These can only be selected during commissioning or by a trained engineer.

The default setting is Eco mode, and this can be specified to run for 0 minutes (which turns the feature off all together), 15, 30, 60 or 120 minutes after the last hot water draw off. In Eco mode the heat exchanger is kept to a specified temperature (between 25 and 60 Deg C) for the selected period of time and after this period of inactivity has elapsed the stepper motor closes completely and the temperature in the domestic hot water circuit is allowed to drop through natural dissipation to minimize energy consumption. If a hot water draw off is made any time throughout the Eco mode function the unit will deliver hot water as usual and the Eco mode function will begin counting down for the selected time once again.

In Comfort mode the heat exchanger is continuously supplied with a trickle of primary water for quicker hot water delivery, however energy consumption will be slightly higher than if the unit was set in Eco mode.

Commissioning Options

The DIGI, DATA and SLIM HIUs all offer a choice between two modes of keep warm function:

  • Comfort Mode maintains heat up to the HIU at all times
  • Eco Mode maintains heat up to the unit for a set period of time following hot water use, then goes cold for up to 23 hours. The period of time is selectable.
  • Keep Warm Temperature determines the temperature maintained in the HIU.

Comfort Mode

In Comfort Mode, the HIU maintains temperature into the HIU by pulsing in a calculated volume of primary flow water every few minutes. The amount of water let in is very small, and not enough to pass through the plate heat exchanger. The heat then dissipates throughout the plate.

Kw1.png

Reduced Comfort Temperature

The latest firmware provides for a separate temperature setpoint for the keep warm mode, that can be set lower than the hot water temperature setpoint. This is to allow the system to be setup to maintain heat in main distribution pipework, but let branch pipework drop significantly in temperature.

The Comfort temperature setting must be high enough to maintain enough overall flow to maintain heat in the primary flow pipe.

Kw2.png

The following shows how the use of reduced comfort mode at 26°C settles to a state where heat is maintained in the main pipework in readiness for a draw-off, however the branches see considerably lower temperatures and lower heat losses. Return temperatures are just above room temperature at all times (outside of heating season and Legionella cycles).

Riser 20 26C keep warm.png

Economy Mode

Economy mode allows HIUs to turn off during periods of inactivity, only coming up to heat once per day as part of the sterilisation cycle.

The following diagram shows how the network can go completely cold, however there is significant risk that one system may call for hot water overnight, and experience a significant delay before heat can arrive from the plant, as the entire volume of cold primary flow pipework will need to be expelled.

Kw4.png

To overcome this, a thermal bypass can be fitted on the end of the primary pipework. Given the main primary branches are well insulated, the heat losses in maintaining them at temperature this way is far lower than if HIUs are kept warm also. The primary return will reflect the setting of the thermal bypass.

Kw3.png

District Heating Networks

Types of Network

District heating, otherwise known as communal heating, makes use of centralised boiler plants to generate heat for distribution to properties for the provision of hot water and central heating. Heated water is pumped from the plant along a distribution (flow) pipe, branching off to feed properties along the way. Once the heat has been extracted from the water, it returns along a return pipe, laid alongside the flow.

Central Heating is provided within properties by either passing the flow of heated water from the plant directly to radiators (or underfloor heating), or by using a plate heat exchanger to transfer heat from the plant supply to the properties internal central heating system, keeping them separated form each other. The former method is more common on the Continent, and allows for more efficient and simpler systems. The second, indirect method, is more common in the UK as if provides a demarcation between plant supplies and landlords own systems, protects the main network from leaks within properties, and does not potentially expose end users to very high pressure boiler water (such as when bleeding a radiator on the ground floor of a high rise).

Domestic hot water is typically generated within properties, by using the heated plant supply to in turn heat domestic water, using either a hot water storage cylinder, or by generating the hot water to demand using a plate heat exchanger. In some networks however, the domestic hot water is generated at the plant also, and piped to properties. To keep the domestic water from going cold in the supply pipe and causing both delays to taps, and risks of Legionella growth, it is usually re-circulated, with some returning back to the plant along domestic return pipes, maintaining flow, and hence temperature throughout the network.

The big advantage of district heating is it allows the implementation of large scale heat generation, reclamation, and renewables, without the need for any heat generation in properties. The end result should be cheaper, more efficient, and far easier to maintain than generating heat within each property. If designed and implemented properly that is.

Calculating Diversity

Diversity, or coincidence factor, is a description of the probability of taps running at the same time, and as such is used to size the peak demand on a system. There are a number of standards describing the diversity that should be used for various numbers of properties, and more recently there is an increase in the number on monitored systems contributing data to a public data set upon which to base diversities.

Diversity decreases as the number of properties increases. With only a couple of properties there is a high likelihood that most taps,will be run at the same time at some point, so a diversity near 100% would be used. By the time you get to ten properties, the diversity drops to around 30%, as the probability is lower. Its a bit synonymous to working out how many heads you may throw in a row when tossing a coin. Its quite likely to get two or three in a row, but ten is far less likely. Data from sites can show diversities over larger sites in the region of 3%. It is important to look, however, at the type of occupancy. If the properties are attached to conferencing facilities where there is a good chance all the occupants will be setting their alarm clocks at the same time, diversity may be significantly higher.

The approach of designing with a diversity higher than reality, to be safe, leads to oversized pipework and plant, increases heat losses, and increases running costs. It has more of a negative impact on user satisfaction than if the system was sized more to the limits, and ran more efficiently.

If diversity is worked out lower than it really is, then at times of peak demand, there is more chance of those extra few outlets running that take the system beyond its capabilities, and outputs will under-perform.

Requirements on Water Quality

Thermal Integration partner with HSF B.V. in the Netherlands who manufacture a full range of HIU's for Thermal Integration but also for the European market. Their expertise and experience is second to none, and they have carried out a significant study on water quality in district heating systems.

We place as much emphasis on water quality as we do system design and we have therefore adopted their document D53261A - Requirements on water quality for Heat Interface Units for District Heating systems, a copy of which can be downloaded here

Guarantees and After Sales Backup for HIU's

Heat Interface Units (HIUs) carry the following guarantees as standard:

FACTORY WARRANTY

1. The warranty begins on the date of delivery. A dated delivery note will be issued to the customer and a copy will be stored by Thermal integration.

2. 12 Months Parts and labour - Parts or labour proven to be defective will be replaced / repaired free of charge for a period of 12 months from date of delivery, provided the HIU is installed by a qualified engineer within 6 months of date of delivery.

24 Months Parts Only - Parts proven to be defective will be supplied free of charge (for fitting by others) for a period of 24 months from date of delivery.

3. Replacement of parts under warranty does not extend the duration of the warranty.

4. Any other costs are not covered by this warranty. All other damages of any nature whatsoever and howsoever arising, are expressly excluded from this guarantee.

5. The warranty conditions above only apply:

a. In the UK only on items provided exclusively by Thermal Integration.
b. If the product is installed by a Thermal Integration approved engineer in compliance with the installation instructions.
c. The installer must complete the commissioning checklist in full at the time the HIU is installed. This checklist must be returned to Thermal Integration within 30 days of commissioning. Checklists are enclosed in the HIU installation instructions.
d. If the installation complies with all current and relevant building regulations and codes of practice. (including the requirement to clean the primary and secondary heating systems and add corrosion inhibitor in line with BS7593:2006)
e. If the product is used and maintained exclusively according to the manufacturer's instructions and proof of periodic inspection / maintenance by a Thermal Integration approved engineer is available.
f. If the returned item is accompanied by a fully completed Thermal Integration Warranty Return Form.

6. Excluded are defects caused by:

a. Failure to maintain in accordance with manufacturer’s instructions.
b. Improper use.
c. Any attempt at repairs / maintenance by un-qualified persons.
d. where parts other than Thermal Integration Genuine Parts have been used in any service or repair.
e. Lightning, fire or natural disasters.
f. Deterioration and / or pollution from the district heating system or water network, either domestic hot water or heating side.
g. PH values of the primary medium being less than 7.5 or greater than 9.0.
h. Harmful additives to the heating water.
i. Consumables as specified by us, including but not limited to: hoses, gaskets and batteries.

7. Report any faults to your installer, service engineer or Thermal Integration directly. Faulty parts must be accompanied by a fully completed Thermal Integration Warranty Return form, to be returned to Thermal Integration. Returned items remain the property of Thermal Integration Ltd.

The Thermal Integration Warranty Return Form can be requested by phone or email. Returns are not accepted unless expressly agreed in writing.
Transport risk of returned items lies with the sender. The shipping of replacement parts are the responsibility of the supplier.

8. If the HIU breaks down, we may ask you to pay us a deposit before we visit you to repair it. We will return the deposit in full if we find a fault that is covered by this warranty. We may keep the deposit if we cannot access your property at the time we had arranged with you to visit or we find other conditions of this warranty have not been met. A responsible adult must be at the property to give our engineer this access to the HIU.

9. COMMISSIONING
Thermal Integration offer commissioning services across the UK. The service includes:

a. The fulfilment of the defined commissioning instructions.
b. Completion and return of site wide commissioning paperwork.
c. Rectification of any HIU problems.
d. Confirmation of HIU performance to contract specifications.
e. Engineer travel and subsistence.

Commissioning rates are charged on a whole day basis, and it is the responsibility of the client to ensure:

a. Safe access to properties and HIUs
b. Correct operation of central plant with delivery of heat to HIUs at specified temperatures, flow and pressures.
c. All pipework has been correctly tested and flushed.
d. Credit on billing system to enable security valve.

A minimum 2 weeks notice is required in writing to Thermal Integration before the requested commissioning date.

SERVICE
Technical assistance and engineer backup can be obtained by calling our offices:

  • Commercial Sales and Operations: 0845 2411441
  • Specflue Sales: 0333 9997974
  • Email: newenquiries@heatweb.com

FURTHER INFORMATION

The Heatweb Wiki website at www.heatweb.com/wiki contains information on all aspects of HIU design, function, and servicing, and is always the best place to visit for additional documentation or how to guides.

Other Products in our range

On this page you will find technical datasheets for many of the products in the Thermal Integration range.

The DATA HIU

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DATA Datasheet

The DATA Amazon


The DIGI HIU

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DIGI Datasheet

The SLIM HIU

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SLIM Datasheet

The Amazon HX SLIM

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Amazon HX SLIM

The SLIM Extra HIU

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SLIM Extra Datasheet