An introduction to the principles and benefits of this increasingly popular method of heating.
Reliance’s thermostatic technology offers expert control solutions for our OEM partners to build into their underfloor systems.
Reliance Water Controls became involved in underfloor heating systems in the 1980s, when underfloor heating installers started to use Reliance products such as thermostatic control valves and manifolds. Over ten years later, it became apparent that the use of thermostatic valves to control the circulation temperature in underfloor heating systems in the UK was increasing at a dramatic rate. By this time a variation of Reliance’s highest selling thermostatic mixing valve, the Heatguard® Highflow, was being sold to a specialist distributor in Canada to control circulation temperatures in heating systems – a very similar application. It was then that Reliance Water Controls decided to look at what was happening and to devote the experiences it had gained worldwide as a leader in thermostatic valve technology to develop control solutions for this rapidly growing market.
History
Underfloor heating is not a new idea; over 2000 years ago the Romans had developed warm air underfloor heating to such an extent that original examples (not still working) can be found all over the former Roman empire even today.
In the early 1980’s there were still examples of the modern warm air systems in use but these were going out of fashion and were being replaced with wet radiator systems. At the same time electric underfloor systems, installed in the 1960’s, were also going out of favour because of running cost and practical control problems. The running cost problems often arose as a result of the way they were run and the generally poor levels of home insulation. The availability of more sophisticated types of control and improved levels of insulation have helped to encourage the current growth in underfloor heating systems.
The basic idea
The ground floor in many houses is made up of a large slab of concrete or is constructed with wooden joists and plywood floors. The basic idea is to use this floor area as a radiator. The surface temperature required to produce a comfortable temperature in this application is much lower than in a conventional wet radiator system, and the heat is produced where it is most needed. Time control is also important, because one of the shortcomings of the 1960’s electric systems was that, to use cheap electricity, the floor area was heated between midnight and early morning. This produced floors that were too hot first thing in the morning and too cold in the evening when people wanted to sit down and relax. To overcome this problem the system could be switched on again to give an early evening boost, and whilst this solved in part the comfort problem, it did not do a great deal for the economy of the system.
How the system works in comparison to a wet radiator system
A conventional radiator system uses one or more heat surfaces within a room. These heat the air in their immediate vicinity by radiation and convection air currents around the room then distribute this air. Doorways and windows, which create their own airflows, will also affect the heat distribution. This results in the colder air being at the floor level and much warmer air at ceiling level. Some products advertised as ‘saving wasted heat’ or even ‘using free heat’ use this effect. These consist of a de-stratification fan that takes the warmer air at ceiling level and discharges it at floor level. Even with extra air circulation the room will have hot and cold spots within it. A further disadvantage of air circulation is that it will distribute dust as well as the heat. A modern underfloor heating system works almost completely by radiating heat. Furniture will reflect and absorb this radiated heat. By absorbing heat they also become secondary heat emitters.
This results in a much more even heat distribution, and the air at floor level being warmer than that near the ceiling. This type of heat distribution is also more comfortable for the people using the room. People often say that if their feet are comfortable then they are more likely to be comfortable in themselves. However it is important that one’s feet do not get too hot.
Health & safety implications
If an underfloor heating system is run so that the floor surface temperature goes above 29°C then there is a greater chance of thrombosis, but there is no danger of being burnt on a high temperature surface. With wet radiator systems the radiator surface temperature is the same as the circulating heated water. This can be as high as 80-85°c, but lower surface temperature radiators are available which protect the room users from contact with high temperature surfaces. The fact that there is much lower air movement with underfloor heating systems has already been mentioned, as well as the resultant effect on dust distribution. This can be very important for people who have some of the more common dust allergies. Underfloor heating also has the major advantage of depriving the common house dust mite of the one thing it needs to survive and reproduce - “moisture”. Without moisture the house dust mite will simply die. Underfloor heating maintains
a much higher relative temperature in carpets and consequently reduces the amount of moisture available.
The control system
All underfloor heating systems work on a lower temperature than a radiator system. Normally a radiator system will have 82°C hot water for the flow, the underfloor heating will run at much lower temperatures in the region of 35 to 60°C, depending on the floor construction and the building. The tempering or blending valve is the heart of an underfloor heating system. It blends colder water from the underfloor heating system return with hot water from the heat source to supply the correct temperature of water to the underfloor pipework. The required temperature will vary depending on the type of flooring and the sub-floor structure but as these valves are adjustable the correct temperature can be easily obtained. Reliance has been supplying a version of the Heatguard® TMV2, called Heatguard® UFH, for use in underfloor heating systems for some time. As the floor area served in domestic applications has increased so the required flow rate has also increased. To keep the physical size of the control assembly within reason, Reliance has developed a new valve with a shorter fitting dimension yet 50% more flow. The new 28mm Heatguard® UFH is able to supply a 250m2 system against a 150m2 system with the basic 22mm valve.
Reliance has an active interest in the fitting dimensions of these valves as they are now supplied in pre-plumbed kits. Reliance currently supplies to the underfloor heating industry several different underfloor heating packs. In addition Reliance has developed for many years a range of bespoke valves for specific OEM customers to sell on as part of their own product range.
