FlatStation HIUs (Heat Interface Units) are located at the interfaces between a communal heating system and each individual user. Hot water is generated in a centralized plant room using high efficiency heat generators such as combined heat and power (CHP), and is then circulated through flow and return mains. At each dwelling interface, an HIU draws only as much heat as the user requires from the circulating hot water. The interface circuits are kept hydraulically separate by a compact plate heat exchanger. 

FlatStation HIUs are highly efficient, easy to install and come in 2 main types: Direct and Indirect. In both of these, a Domestic Hot Water (DHW) plate heat exchanger is heated by primary water circulating from the central plant room. Space heating is often arranged by Direct FlatStations, where the primary circuit connects directly to apartment space heating circuits. This arrangement can be adapted to either underfloor heating (UFH) or to radiators. 

Alternatively, Indirect FlatStations enable the primary circuit to be kept hydraulically separate from the apartment space heating by using a second heat exchanger. In this situation, provision needs to be made for a circulator, strainer and expansion vessel. 

DHW provided by a plate heat exchanger is available just as rapidly as if it were supplied from an adjacent hot water storage cylinder. Accurate control of DHW temperature and pressure at the tap ensure that user comfort is never compromised. FlatStations have no DHW storage requirement. This enables considerable savings to be made in terms of cylinder cost, standing heat losses and installation space. 

Plate heat exchangers are excellent in maintaining a high Δt across the primary connections, thereby helping to secure low return temperatures. This is a valuable benefit when it comes to reducing heat losses from all return pipe work. It leads to lower requirements for pumped volume round the primary system and provides good operating conditions for high-efficiency condensing boilers. 

Most FlatStation installations are specified with in-built metering. Energy meters can easily be incorporated at works, with output made available by either MBus wiring or radio signal. Individual usage data can be made available for easy download or for individual billing. Where specified, water meters can be installed at works within each FlatStation. 

Applications for FlatStation HIUs vary from 1-bedroom flats to large houses. Unit specification can be adapted to take account of the exact user needs: Direct or Indirect, with / without energy metering, rating between 35 and 90kW, connecting piping to be either from above or below. To assist with site construction, bespoke first-fix rails with isolators can provide the hydraulic boundary where pipework fill is required before HIUs are required on site.