The Danfoss flat station concept "EvoFlat" 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 a boiler installation and is thereby contributing to increasing the service life of the boiler 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 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:
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.
View the flat stations range
The advantages of the instantaneous DHW preparation are:
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 can not 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:
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 dimensioning tool 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 dimensioning tool". Contact your local Danfoss sales office for more information.
Learn more about the EvoFlat dimensioning tool here
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:
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 shortning 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.
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 series is as follows:
Both product types cover up to 15 kW for heating.
The main parts are:
The following accessories for EvoFlat units are available:
The main benefits of EvoFlat stations are:
The patented sensor accelerator accelerates the closing of the Danfoss AVTB valve and protects the heat exchanger against overheating and lime scale formation. The heat exchanger cools the DH water very efficiently, thereby creating a very good operating economy. The sensor accelerator and AVTB valve also works as a bypass keeping the house supply line warm. This shortens the waiting periods during summer when the heating system is in reduced operation. The sensor accelerator helps to ensure a stable hot water temperature regardless of varying loads, flow temperatures and differential pressure without the need for readjusting the valve.
Flat stations for Direct Heating & DHW
Flat stations for Direct Heating with Mixing Loop & DHW
Distribution Systems (FH) for Flat stations
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