Boosting the efficiency of underfloor heating with good controls

Rehau
Underfloor heating operates very successfully with all types of heat pumps and with the condensing boilers which are now routinely specified.
Graham Richardson explains the importance of controls in enabling underfloor heating to enable the heat generators that deliver hot water to operate at maximum efficiency.Consultants and contractors are under constant pressure to deliver ever more efficient heating solutions. Quite legitimately, governments and consumers are demanding a response from the construction sector to help the UK meet its commitments under the Kyoto protocol, and there is a new urgency in the pressure to reduce whole-life building costs as the future price of energy looks increasingly uncertain. From the viewpoint of an underfloor heating manufacturer, all this is very good news. By definition, underfloor heating operates most successfully with all types of heat pumps and with the condensing boilers which are now routinely specified. This is because the low return-water temperatures in the pipework systems allow these boilers to operate at their optimum efficiency for more of the time. Huge potential In a market which already understands and appreciates the benefits of underfloor heating in terms of aesthetics and comfort levels, there is huge potential for consultants and contractors to combine underfloor heating with low-energy heat sources to maximise the energy efficiency of any domestic or commercial/industrial installation; most the underfloor heating manufacturers are looking to exploit this. Rehau is working hard alongside the most forward-thinking specifiers to communicate to clients the inherent energy efficiency of the underfloor heating concept when used with weather compensation. This is a differentiator for our most environmentally astute customers and so far is helping to prevent the leverage of specification from one system to another. Control However, it is in the control of underfloor heating systems where the opportunity for real system differentiation exists. Rehau, for example, has developed an intelligent control system for its underfloor heating which can improve its energy efficiency performance still further. These types of control system rely on a variable temperature rather than a constant temperature within the underfloor heating circuit. This requires more control equipment but has the twin advantages of greater energy efficiency (and thus a faster payback) and increased comfort levels. A variable-temperature system can adjust the temperature of the warm water circulating within the piped circuits. When used with a building-management system or a computerised controller linked to an external temperature system, it will always choose the optimal flow temperature in relation to the actual heat demand, based on the current external temperature rather than a fixed, pre-selected level. Our intelligent zone control system, for example, uses the weather-compensation option and has a sophisticated electronic control system specifically designed to give optimum and accurate control to floor-heating (FH) systems. In operation, the underfloor heating circuits are connected to a central manifold or manifolds. Each FH circuit has a thermo-electric actuator on the manifold operating the return valve. The heat output in each room is controlled by a room sensor which continuously compares the required room temperature with the actual room temperature. If the room temperature is too low, the return valve of that circuit is opened to that warm water can flow through it. Weather compensation The flow temperature of the warm water in the heating circuits is automatically controlled and adjusted by the intelligent master controller linked to a weather-compensation module outside the building. Once the master controller is programmed, which has to be done just once at initial set up, the temperature of water flowing to the underfloor heating system is controlled automatically. We call our system intelligent control because it uses well proven PI (proportional-integral) logic to optimise energy distribution throughout the system. This compares the actual room temperature with the set temperature and delivers regular pulses of heat into the floor to maintain a constant temperature. The length and frequency of the pulses are optimised to ensure constant room temperatures and minimum boiler firing, thus delivering a more stable temperature and ultimately greater comfort levels. Sensors are connected to the master controller in a daisy chain series for quicker installation. The system relies on a simple 2-wire 5 V bus communication system, which is very easy to install — with very little scope for mistakes or, indeed, resulting call backs. The controller also has in-built fault-detection logic which tells the installer if all connections have been made correctly and if all sensors are correctly functioning. The Rehau system is not unique, but as the market focuses more and more on reducing carbon emissions from buildings, such products which promise much more than just incremental improvements in efficiency are the ones which will make an impact. Graham Richardson is application engineer with Rehau Underfloor Heating.
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