The control solutions chosen for underfloor heating has a big impact on their efficiency, says Laurence Chownsmith.
Long presented as the ideal partner for the low flow and return temperatures generated by ground and air source heat systems, underfloor heating has been given a welcome boost by the confirmation of the new RHI tariffs in the commercial sector.
However, if users are to maximise the return on their investment by optimising the efficiency and CoPs of the associated heat pumps, then one of the overriding considerations will be the control solutions chosen for the underfloor heating.

Over the years, control options for underfloor heating have evolved from simple, fixed water temperature systems to variable water temperature systems. Simple mechanical bi metallic room thermostats have been replaced first with electronic stats or sensors and now with optimising sensors which limit the under or over shoot against the set point temperature, and the main wiring centre has become much more sophisticated in terms of how it monitors and optimises the water temperature flowing into the floor.

There is typically now less energy going into the building because the control is better matched both in terms of weather compensation and in meeting changing daily or zoned heat demands.

This has of course translated into reduced running costs, improved comfort levels and faster response times and has helped underfloor heating make the transition from a niche to a mainstream heating solution.

However, in the commercial sector where the RHI tariffs will essentially be trialled for the rest of this year before being extended to the domestic sector in 2012, much of the potential for controlling underfloor heating systems is still too often being compromised because of the difficulties some contractors face in integrating the separate software systems which control underfloor heating with a building management system.

Standard underfloor heating controls simply do not communicate properly with BMS systems, with only an on or off signal translating to the daytime temperature and set back temperature set points.

It is possible to program complex algorithms into bespoke BMS software for each separate underfloor heating installation but it is only since the launch last year of controls in MODBUS based open protocol that full plug and play compatibility with BMS systems has been an option.

New level of monitoring

By switching to the MODBUS protocol, manufacturers have given clients and contractors a new level of monitoring and usability for their underfloor heating, which we believe meets the demands of clients more effectively than any of the previous options.

It is now possible for the operator or administrator of the BMS system to look at the remote room temperature anywhere within the building and remotely change the set points on screen as required. They can have full control of actuator and valves throughout the underfloor heating or cooling system and can adjust flow temperature to ensure optimal performance of the heating or cooling source, whether it is a boiler, chiller, heat pump or biomass unit.

It is even possible to monitor the systems online using TCP/IP connectivity and to carry out diagnostic checks via the internet.

Where clients are looking to maximise efficiencies, the ability to reduce set point temperatures in rooms where there is no occupation or usage for certain periods is obviously very useful but previously it would have been necessary for someone to physically walk around the building and make the adjustments manually.
From a contractor's perspective, installation is the same as it is for conventional controls but the BMS systems company needs to be involved with the set up because they are the ones who need to write the software and protocol to give the system the necessary functionality required by the client.

Obviously, close liaison between the underfloor heating supplier, the installer and the BMS company is essential to ensure that full compatibility is achieved but this can be factored into the installation schedule.

In terms of cost, a BMS compatible underfloor heating system probably costs around 5 per cent more than one with conventional controls, but if the BMS interface is definitely required, then this is more than outweighed by the savings available in terms of being able to replace BMS nodes with sensors run on a BUS loop (daisy chain) system.

We have calculated savings of between 25 and 40 per cent on side by side installations, before taking into account the additional energy savings which the improved controllability can offer.

• Laurence Chownsmith is sales manager of Rehau Underfloor Heating