sav-systems.comDanfoss FlatStations (Heat Interface Units / HIUs)

Features and Benefits

Supply chain

Tried. Tested. TrustedDanfoss is a global leader within district heating and based on decades of experience and continuous optimisation, Danfoss FlatStations have proven performance under demanding/dynamic conditions.

SAV as the solo supplier of Danfoss FlatStations in the UK offers project specific support whether during design, installation or operation stage, transferring this way, its knowledge and experience on optimum indoor climate with minimum use of energy.

Danfoss was founded in 1933 by Mads Clausen and began with the manufacture of thermostatic valves. Company growth was steady and sustained, with expansion into other areas of technology, including compressors, pressure switches and motor controls.

A key area of expertise by Danfoss is the design, development and supply of control valves. The expansion of the district heating market in Denmark provided the springboard for control valve development, especially in the area of differential pressure control valves (DPCV). Such technology remains a key differentiator in the HIU units as currently supplied by its Termix subsidiary.

Termix entered the field of heat exchange equipment in 1986, with the launch of the Termix 20 hot water system. With a firm commitment to heat exchanger development, growth of turnover and product range continued steadily. It was success with heat interface units that led to interest by Danfoss and in 2004 Gemina Termix became part of the Danfoss Heating Division. This brought together the Termix expertise with heat exchangers and the advanced control valve technology from Danfoss.

Development continues to this day, with the design of plate heat exchangers providing a good example. Up till 2015, plate heat exchangers were based on a herringbone pattern. From that date, a dimple design has been used, providing a gain in thermal efficiency of around 10%. The factory makes use of advanced automation and robotics, for operations such as pipe bending and heat exchanger manufacture.

From modest beginnings in 1994, SAV has since championed the efficient use of energy. Early on, SAV focused on the supply of valves with integral filters and commissioning modules. Familiarity with DPCV technology, led to a productive association with Danfoss.

In 2006 SAV introduced Danfoss HIUs to M & E Consultants in the UK. The first significant HIU orders arrived in 2008, reaching 11,000 per annum in 2015. As of 2019, total orders received passed 90,000 units, with SAV/Danfoss currently the HIU market leader in the UK.

Together, SAV and Danfoss have developed the HIU product range, based on decades of Scandinavian experience combined with the specific UK market demands. This ongoing product development reflects the needs identified.

Danfoss FlatStations (Heat Interface Units / HIUs)

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Danfoss FlatStations - Features and Benefits

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Plate heat exchanger design and efficiencyThe Micro PlateTM heat exchangers include a patented “dimple” plate design (as opposed to the traditional “fish-bone” pattern).

Due to an optimised flow velocity, this design ensures a better heat transfer across the plate heat exchanger.

The result is reduced pressure losses, lower system return temperatures and increased system efficiency.

Instantaneous responsivenessDanfoss FlatStations are “primed” for DHW production. By allowing a small trickle of primary water through the DHW plate heat exchanger Danfoss FlatStations ensure that system branches do not “turn cold” after a period of no demand.

As the DHW plate heat exchanger is kept warm this ensures that DHW is always available instantaneously and that the user will not have to wait for the plate heat exchanger and pipework to heat up and stabilise at the right temperature. A further benefit is that no system branch by-passes are needed which could otherwise potentially compromise the system efficiencies by increasing system return temperatures.

Example test result of DHW control valve responsivenessThe rapid responsiveness of the thermostatic control valves (within seconds) ensure that no energy is wasted.

Furthermore, it prevents primary water from flooding the plate heat exchanger, preventing scaling and prolonging the lifetime of the heat exchangers without reducing its heat exchange capacity.

Traditional fish-bone pattern

Optimised Micro PlateTM heat exchangers

IHPT DHW control valve

• Self acting pressure independent thermostatic control valve

700

Flow [l/h]

Time [sec]

600

500

400

300

200

100

0

0 1

DHW DH

2 3 4 5 6

Primary supply = 70°C ΔP = 1.0 bar

* Closing of primary flow as a consequence

of closing of DHW outlet

Closing time of DHW control valve (IHPT)*

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System Efficiency

• Hydraulic balancing of the district heating network

• Reduced system flow rates

• Reduced heat losses

• Improved variable speed system pump performance

• Lower system return temperatures

System reliability

• Constant differential pressure (ΔP) across the control valve

• Enabling accurate heating circuit temperature control

• Ensuring the control equipment will still work when differential pressures rise

• Prolonged life-time of control equipment

Danfoss FlatStations include temperature controls enabling the setting of a consistent, fixed flow temperature whether for DHW or space heating – irrespective of changes in system temperature or pressure. Each sensor is filled with gas which is chosen according to the force that each particular valve requires to operate.

Temperature control

Correctly sized and positioned DPCVs are essential to achieve the following goals:

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Danfoss FlatStations - Features and Benefits

Compliance and best practice

Danfoss FlatStations do not only provide an accurate and stable DHW flow temperature. System return temperatures are also minimised in line with recommendations for the industry.

Based on this “Best practice could include the testing of the HIU performance against established standards such as the Swedish Standard F:103-7e: Certification of District Heating Substations (Svensk Fjärrwärme, 2009)”. Danfoss FlatStations are among the few HIUs that have been certified under the stringent Swedish requirements (certificate available upon request).

More importantly, this performance is also maintained at part load and dynamic load conditions.

The Heat Networks Code of Practice specifically defines this as one of the main themes of the Code (p. 5), based, among other reasons, on the fact that “maintaining low return temperatures under part- load conditions is important to keep heat losses and pumping energy low (…) If the design return temperatures are not maintained in operation then the heat network capacity will be reduced”.

“To provide a high quality hydraulic interface unit (HIU) and building connection construction to provide good customer service levels” is an independent objective in The Heat Networks Code of Practice (p. 52) as “The hydraulic interface unit (HIU) is a key component of the heat network system as it provides user control, ensures hydraulic balance within the heat network and may also include a domestic hot water heat exchanger.

It should also be designed to have low maintenance requirements and perform reliably over a long period of time.

The required customer service levels of the heat supply will only be achieved from a high quality HIU and building connections to non- domestic buildings”.

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BESA testThe below performance diagram is part of the Danfoss FlatStation BESA DHW test (carried out in 2017). The test method is described in the UK HIU Test Regime Technical Specification, Rev-007, issued by the Building Engineering Services Association (BESA).

Pressure controlDanfoss FlatStations are always pressure controlled. A differential pressure control valve (DPCV) is dedicated to the primary supply to the space heating plate heat exchanger. This optimises valve sizing, as capacity requirements are often 10 times higher for DHW than heating (particularly for new build), which means the DPCV is oversized when only the space heating is on (DHW is required less than 1% of the day).

An oversized DPCV compromises control and system efficiencies.

Tem

per

atur

e (t

) [˚

C]

Time [s]

Flow

(q

) [l

/s]

80

70

60

50

40

30

20

10

00 20 40 60 80 100 120 140 160 180 200

0.00

0.05

0.10

0.15

0.20

0.25

0.30

t - DHW supply ˚C

t - CW supply ˚C

t - District Heating return ˚C

q - District Heating l/s

q - DHW l/s

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Danfoss FlatStations - Features and Benefits

IHPT controller for DHW• Integral DPCV, Valve Authority = 1 (Excellent)

DPCV for space heating circuit• Maintains the valve authority of the HTG thermostatic

controller at not less than 0.5 (Good)

Pt40 Pressure Independent Thermostatic Radiator Valve (PITRV)• Integral DPCV, Valve Authority = 1 (Excellent)

Rt40 Pressure Independent Return Temperature Limiter (PIRTL)• Integral DPCV, Valve Authority = 1 (Excellent)

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www.sav-systems.com – www.linkedin.com/company/sav-systems Rev 1 2019

For further information please contact

Head Office: SAV Systems

Scandia House, Boundary Road

Woking, Surrey GU21 5BX

+44 (0)1483 771910