Need to limit flow temperature
With the growing popularity of "alternative" heat sources such as heat pumps, underfloor heating companies are increasingly supplying systems without the traditional set-up of using a mixer or injector valve. This is because the "alternative" heat sources, in normal operation, provide water at a compatible flow temperature for underfloor heating (UFH), for example 35°C design dependent.
A similar scenario has also developed with the increasing popularity of modulating condensing boilers, where a dedicated flow from the boiler can be used and the output temperature can be limited to no greater than 55°C to suit the UFH system.
Doing away with the mixer or injector valve reduces cost for the end-buyer, simplifies the installation for the inexperienced installer, and can lead to an increase in efficiency: three very good reasons for not fitting such devices.
With UFH there is a very real need to limit the flow temperature to below 55°C. This limit, enforced in the European Standard for UFH (BS EN 1264), provides a safe level above which damage can start to occur to screed floors, potentially resulting in screed failure. A higher temperature can also lead to excessive floor surface temperatures, which in turn can lead to damage to expensive floor coverings.
Condensing boilers, despite sophisticated controls, can go wrong and exceed temperatures of 55°C. Similarly the new generation of heat pumps can also potentially give outputs over 55°C if component failure occurs. However, the most likely cause of excessive temperatures is because the end-user has played with the settings on the heat source after it has been commissioned.
Simple measures can prevent these issues occurring in the first place, for example fitting floor temperature sensors to cut out the flow if it exceeds a set temperature. The preferred method is to fit pipe stats on the flow side and prior to the underfloor heating system. These pipe stats are linked to either the circulation pump or a two port valve so that if an over temperature situation occurs water will be prevented from flowing to the UFH system. All Continental systems supplied without mixers or injectors now incorporate the latter method because we believe that prevention is better than cure.
Concern has been reported with some types of pipe, especially those made from Santoprene (typically sold as a three-tube system) where no plate-heat exchanger is fitted, and also with pipes imported from China that have testing and approval credentials which are hard to verify by the installer.
At Continental we have been asked on several occasions to suggest remedial works to overcome the problems associated with systems that have not been supplied with mixers/injectors, don't include temperature limiters, or use low quality pipe. Invariably the simplest solution is to get it right first time.
The pipes Continental supply (AluPex and 5 layer PEX) all have verifiable testing and approvals - in common with all members of the Underfloor Heating Manufacturers Association (UHMA). This is a key reason why installers should only purchase from companies which are UHMA members.
In summary, there are good reasons to not fit mixers or injectors when your heat source delivers water below 50°C, but care needs to be taken to ensure that there are adequate control safeguards built in to the emitter system to overcome either component failure at the heat source, or end-users fiddling with the controls.
Explaining mixers and injectors
A mixer valve blends a high temperature flow from an energy source eg a boiler typically operating at 75°C, with the lower temperature return water from the heat emitter, eg a UFH system which typically returns at 35°C, in order to provide a flow to the heat emitter at a lower level than the output from the boiler - up to 50°C for UFH.
An injector valve basically injects bursts of hot water generated by the boiler - typically at 75°C - into the return water from the UFH. The mixed water is then recirculated into the flow side of the UFH.
Both methods enable the installer to set the desired flow temperature, the main difference being that a system which uses a mixer valve returns water to the boiler at the same temperature as the return from the heat emitter ie. 35°C, whereas an injector system returns water to the boiler at the same temperature as the flow to the heat emitter ie. 45°C.
Continental Underfloor Heating offers the most comprehensive range of warm water UFH in the UK and has an expert technical team on hand to answer any questions. For more information log onto www.continental-ufh.com or call 0845 108 7001.
