Flat stations - EvoFlat 4.0

The Danfoss flat station concept "EvoFlat 4.0" comprises an installation, for which flat stations that are supplied from a central energy source, are built into each flat. These units normally incorporate a compact plate heat exchanger, which delivers instantaneous hot water on demand and a differential pressure control valve to control the heating flow to the tenants’ radiators.

The main difference between traditional heating systems and decentralized ones with flat station is that in decentralized systems the process of domestic hot water preparation is moved from central heat source (traditional systems) to flat station units in each apartment. In traditional systems 5 main ascending pipes are using instead of 3 in decentralized heating systems.

There are two typical applications which depend on the type of heating installation in the apartment – Radiator heating and Floor heating.

The heat source to the decentralized system can be oil, gas or wood-fired boiler, district heating, heat pumps or a combination of these. Furthermore, the system can also be supported by solar energy. It is important that the energy source(s) is/are capable of generating a sufficient minimum supply temperature with the object of producing acceptable domestic hot water temperatures in the heat exchanger, placed in each apartment. Furthermore, the installation includes a buffer tank.

The buffer tank avoids frequent starts and stops of the burner in Or the compressor in a heat pump installation and is thereby contributing to increasing the service life of the heat pump and reducing its harmful emissions. The buffer tank also stores an adequate volume of energy that allows an instant supply of sufficient flow to the water heaters in each flat during peak load intervals. The buffer tank is then loaded to the desired supply temperature for the distribution system. In principle, the buffer tank is not required for a large number of flats as the entire piping system and the larger boilers will provide a sufficient buffer volume to accommodate the large load changes in domestic hot water use. The actual limit will depend on the volume in pipes and boiler as stated previously, but it does also relate to the boiler load.

In the EvoFlat 4.0 concept for decentralized system the heat exchangers are used mainly for producing domestic hot water. The operating principle of instantaneous water heating/the flow principle can be described as follows:

• Heating water circulates on one side of the plate heat exchanger transferring heat to cold water passing through on the other side. The heated water is then fed straight to local hot water taps
• To control the domestic hot water capacity of the unit a self-acting control valve, especially developed for this purpose, is used to regulate the flow across both sides of the plate heat exchanger
• For instantaneous water heaters various DHW control valves with control principles, which each incorporate advantages and disadvantages, can be implemented
  These are typically grouped accordingly: temperature-controlled, pressure-controlled, temperature and pressure controlled.

Danfoss offers a comprehensive product range, which includes flat station variants with ALL control principles.

The advantages of the instantaneous DHW preparation are:

• Minimized risk of legionella bacteria
• Added comfort due to a continuously high output
• Very little space required for installation
• Low return temperatures, which increase the overall efficiency in systems including condensing boilers, solar energy etc.
• Operates at as low supply temperatures as e.g. 50 - 55 °C

Alternatively, a domestic hot water cylinder, placed in each flat, could be implemented. This solution, however, does not offer the same advantages as the flow system. The cylinder solution cannot be excluded on account of not being operational and can be incorporated in the concept at the request of the client.

In the EvoFlat concept for the decentralized system the heating circuit of a flat station can be configured in 3 ways:

• Directly – controlled only by a differential pressure controller and optionally by a zone valve controlled by a programmable room thermostat. This principle is applicable mainly for radiator heating in supply systems with maximum PN10.
• Directly with mixing circuit – controlled by a differential pressure controller and a mixing circuit. This principle is applicable mainly for floor heating and systems with maximum PN10.
• Indirectly - a plate heat exchanger is controlled by a 2-way thermostatic valve and optionally by a zone valve, controlled by a programmable room thermostat. This principle is applicable mainly for floor heating and systems with maximum PN16.

An estimation of the domestic hot water requirement is part of the total evaluation, which is the reason why the term coincidence factor is relevant in this context. Briefly stated, only a part of all tap points is used in actual practice, based on a 99.9 % confidence interval in a statistic probability distribution.

In the Danish standard for domestic hot water installations DS439 and the specifications from TU-Dresden the consumption pattern of a “standard flat”, which by definition includes 3.5 persons, constitutes the basis for the factors. Deviations may occur if the dwelling for example is inhabited by residents for which an atypical consumption pattern can be expected. Therefore, the application of these factors must be supported by an estimation of the composition of the residents of the building. In the EvoFlat Selector the following factors can be selected: Danish Norm DS439, Danfoss-Redan, Swedish and German factor.

The total flow is formed by the heating loop flow rate and the primary supply flow rate for the water heaters, reduced by the relevant coincidence factor and a flow rate to compensate for other heat losses.

The size of pipes is determined by maximum flow rates in each partials section. Criteria are normally a certain velocity and a certain pressure loss per running meter. For visible pipes typically v≤1m/s and <100 Pa/m has been recommended, but for other sections and pipes covered in shafts other criteria can be used for dimensioning.

Yes, Danfoss offers a software for dimensioning flat stations. It is called "EvoFlat Selector" and can be found from EvoFlat Selector

This dimensioning has to be viewed in a context, as the buffer tank and the boiler/HEX size can be adapted according to each other to cover the energy requirement for domestic hot water and heating. A major quality of the buffer tank is to cover domestic hot water peak loads and to reduce the number of boiler starts and stops and thereby ensure a more economical operation. Finally, a buffer tank is the automatic choice, if solar heating supports the other heat sources. In such situations the size of the solar collector area will often be dimensioning, and it is recommended that separate calculations are made.

Following advantages compared to traditional system installation designs can be listed:

• The flat station concept can be implemented in both new buildings as well as by refurbishments.
• The system is independent of the energy supply – gas, oil, district heating, heat pump, biomass or solar.
• Individual, fair energy bills for each flat or tenancy are possible.
• The system enables remote monitoring of the energy consumption of each flat with the proper energy meter.
• Only three ascending pipes are required in the building – cold water, supply and return heating.
• Minimum space requirements for fitting the unit in the flat - comprising possible integration in wall construction.
• Individual adjustment of room temperature over time and independent domestic water production is possible.
• Bacteria-free domestic water production with the flow principle – minimized risk of the legionella bacteria.
• Added hot domestic water comfort compared with traditional gas-fired water heaters (35 – 80 kW against 22 kW).
• Increased energy efficiency through improved boiler or district heating installation operation and through possibly low operational temperatures.
• Reduced heat loss in the distribution network compared to the classic solution as the hot water and domestic water circulation line is not required.
• A minimum of maintenance in each flat thanks to the simple technique.
• Relatively safe system as electrical short circuits and gas leakages are not possible.
• Suitable for operation with condensing boilers and solar energy owing to the low return temperatures of the system.

Electronically controlled flat stations have automatic domestic hot water priority.

In mechanical stations, if the DHW control valve turns off mechanically the supply of heat for the radiators/floor heating, the existence of 100% DHW priority may be assumed. In case control valves for DHW without mechanical changeover function are used, it must be calculated, whether DHW priority may be assumed (Hydraulic priority).

• when ΔpDHW < Δp Heating DHW priority in the unit can be assumed

• when ΔpDHW ≥ ΔpHeating DHW priority cannot be assumed

Summer bypass is applicable with NC DHW controllers – PM2+P, PTC2+P and TPC+M. When the units are mounted more than 2-3 meters away from the main risers, a thermostatic bypass (FJVR) is recommended. During the summer the bypass keeps supply pipes warm and enables tapping of hot water without any delay – ensuring the best possible efficiency and economy during summer when the heating system is in reduced operation. The bypass can be mounted before or after a heat meter.

When the unit is mounted far from hot water taps, a DHW re-circulation is recommended to increase customer comfort by shortening the waiting period during hot water tapping. DHW re-circulation sets are available as accessories for flat stations.

To guarantee customer comfort according to design parameters, mounting a flow limiter on the DHW outlet pipe is recommended.

There are 2 ways to install Danfoss flat stations:

The unit is mounted directly on the wall (on-wall mounting concept).
The unit is mounted in the wall, using recess boxes (in-wall mounting concept).
Stations can be mounted in shafts, but one of above-mentioned concepts is always used. Please ask your local Danfoss sales office for more information.

No, it is not always possible. Follow the mounting instructions exactly - or ask your local Danfoss sales office for support.

Yes, it is possible. Ask your local Danfoss sales office for more information and support.

Product naming of the EvoFlat 4.0 series is as follows:

EvoFlat F1/2/3/4 – a compact and simple to operate flat station for direct radiator heating and instantaneous domestic hot water with an innovative self-acting TPC – M controller for control of heating and DHW temperature. Digit behind the name shows the type of HEX:

• type 1 for XB05H 36 (up to 45kW)
• type 2 for XB05H 46 (up to 53kW)
• type 3 for XB05H 54 (up to 60kW)
• type 4 for XB05H 70 (up to 80kW)

EvoFlat M1/2/3/4 – a compact and simple to operate flat station for direct heating with mixing loop and instantaneous domestic hot water with an innovative self-acting TPC – M controller for control of heating and DHW temperature. Digit behind the name shows the type of HEX:

• type 1 for XB05H 36 (up to 45kW)
• type 2 for XB05H 46 (up to 53kW)
• type 3 for XB05H 54 (up to 60kW)
• type 4 for XB05H 70 (up to 80kW)

Both product types cover up to 17,5 kW for heating

• Two differential pressure controllers for heating and domestic hot water

• EPP insulation box

• Composite body

• Danfoss XB05H Heat exchanger

• Valves and sensors for heating and DHW control

• Summer by-pass

• Zone valve

• Air vent

The main parts are:

• Room thermostat

• Safety valve

• Ball valves (60mm)

• Ball valves with connection for pressure gauge ¾”(120mm)

• Energy and water meters (3/4” x 110mm)

• Mounting rail for mount-on-wall variant

• Recess box for build-in variant incl. mounting rail

• High-temperature connection set

• Circulation set

• SG, SGC and SGCI distribution units

• Reduced heat loss due to insulation cover, insulated back-plate and less radiating surfaces inside the station.
• No need of re-tightening after transportation or other vibrations due to the improved Click-fit connections
• Two separate ΔP controllers for DHW and HE bring best-in-class hydronic balancing for stable hot water temperatures and energy efficient heating operation
• New HEX and hot water controller for up to 70 kW hot water capacity at high tapping rate
• Prepared for low supply temperature
• Easy access during installation and maintenance, for example for heat exchanger
• Lightweight PPS composite body

Build-in or wall-mounted variant