Wall radiators and underfloor heating in one combined central heating system.
Is underfloor heating a modern heating system? It is fashionable heating and that is not the same thing… Modern heating systems must meet the ever increasing demands for thermal comfort.
In the intelligent house of the future, underfloor heating alone will not work because of its far too long reaction time. Only a small amount of heat energy is needed to heat modern houses, so for most of the day and the heating season in a warm, well-stocked house, the system need not heat at all. To reduce the heating costs, all heat gains should be used. This can be done, but not if you only have underfloor heating.
When the set indoor temperature is reached, the central heating system should completely stop heating.
Due to significantly higher temperature of the base floor than the temperature of the heating surface of the floor and its gigantic weight (150-350 kg/m2), stopping heating is completely unfeasible for the owners of underfloor heating systems.
The base temperature of a warm, well-stored house is unshakeable in the short term. It is true that a short-term increase in air temperature is sometimes very desirable, but soon after the short heating period is over, the indoor air temperature returns to the base temperature. This is the so-called self-regulation of the interior temperature in houses with high heat accumulation (all partitions participate in self-regulation). For those with only underfloor heating, a quick, short-term increase in air temperature is not feasible. To achieve this goal, which is important for complete thermal comfort, it is necessary to have additional radiators, wall or trench heaters, with the lowest possible thermal inertia.
Underfloor heating and wall radiators in one heat distribution system.
There is an opinion circulating that mixed heating containing wall radiators and underfloor heating is a bad choice. It is assumed in advance that the radiator and wall installation must work at different supply temperatures. WRONG!!! In warm houses built according to modern standards, there is nothing to prevent both radiators and underfloor heating from being supplied from a common manifold with water of the same supply temperature Tz.
How to configure such installation? Underfloor heating, as poorly controllable due to huge thermal inertia, is installed only on the exposed part of floors, in passageways, bathrooms etc., securing with it about 20-40% of needed heating power resulting from the general heat demand.
Such a location of underfloor heating will guarantee warm (summer) floors for warmer people. The price of underfloor heating, built only on a part of the floor, will be inevitably much lower than the price of underfloor heating built under the whole floor.
The rest of the required heating power, i.e. 60-80%, will be provided by appropriately smaller wall radiators placed in the same room, or by duct heaters placed in the floor, working just as dynamically. Radiators will fulfil their task mainly in transition periods, which constitute about 70% of the entire heating season. In the period of a full winter and long-lasting considerable temperature drops, both systems work in solidarity with the heating power appropriate for the needs. We gain enormous room for manoeuvre. We gain much greater influence on the work of the installation which translates into much greater thermal comfort.
Without our will, the interior temperature will not rise above the set point. We are the ones who control the heating.
Contemporary radiators can have a decorative design, vary in size, can be matched in color to the interior decor. In this configuration, the amount of emitted heat will always correspond to the current heating needs of the household, taking into account all, even the most changeable and unexpected weather situations, both now and in the future. Whether one route of heat distribution is used or both at the same time depends on the choice of household members and the current heating needs of the house.
Optimally operating central heating
Central heating consists of: factory, i.e. heat source, distribution system, i.e. radiators and “market”, i.e. our house. Heat has to be optimally produced, optimally stored (when needed) and finally optimally dosed. There cannot be too little heat on the “market” and too much… Each of the mentioned stages should be considered separately, because it is possible to optimally produce heat, but not to optimally store or dose it. Unjustified losses can occur at any stage.
Most users focus on the optimization of the heat source and lose sight of the optimization of heat utilization. Too little heat bad, too much heat bad, at the wrong time bad. The factory (heat source) does not have the right to decide how much heat is needed, when it is needed, but the “market”, i.e. the household and house.
Optimal heat production means that the heat source operates at maximum efficiency. A buffer is therefore sometimes needed between heat production and heat distribution. Optimal distribution means satisfying even the most sophisticated heating needs of household members, which are constantly evolving. The all-season isotherm offered by underfloor heating is now no longer sufficient. Wall radiators are back, although not as we know them today
When is a heat buffer?
If the heat source produces heat despite having no heating needs, or if the heat production is relatively uncontrollable (solid fuel boilers), or if we deliberately produce it at a certain time due to a lower carrier price (electricity on the second tariff), we need to store this heat optimally.
Also, whenever the heat consumption is turned off (thermostats), if it is still produced, the surplus should be redirected to a buffer tank, to the heat tank and not “up the chimney”… The buffer tank should be large enough and should have enough accumulated heat to be able to heat the house for several hours without starting the heat source.
If you have a buffer tank, the calorific value of the fuel and the heat generated will be used to the maximum possible extent. Having a buffer tank the user is able to significantly reduce the number of days in the heating season during which the solid-fuel boiler works. The benefits are obvious. The amount of fuel burned in an optimal way will be reduced, the service life of the optimally used boiler and chimney system will increase. There will also be benefits for the environment – lower emissions of exhaust gases and soot.
No sensible manufacturer would launch a product when the market does not need it! Heat source + buffer + floor is also a wrong configuration. We should stick to the “one buffer principle”. Why do we need two large heat stores, one larger than the other? Will it improve the maneuverability of the installation? Nothing of the sort. For the “sales market” it is a bad solution.
Boiler + large buffer will enable any technique of burning, with any fuel, while only a low-inertia heating system will enable precise heat dosage. For heat-lovers, the effect of warm floor with the temperature minimally higher than the air temperature will complete the thermal comfort.
Underfloor heating allows you to maintain a lower interior temperature? Myth.
Why would you think that? Is it because it warms your feet? After all, the perceptible temperature is mainly affected by the temperature of the other five partitions – four walls and the ceiling… Why 20oC with an underfloor heating system should be better than 22oC with radiators?
It is only important that the floor is not colder than the room temperature, i.e. that it has the current room temperature. The floor should be lukewarm or pleasantly neutral in terms of temperature, while we should have an influence on a relatively quick change of the interior temperature within the range of a few tenths of a degree, and if necessary even within the range of two or three degrees…
Why is that? At different times of our activity the temperature may be slightly different, when we work, when we rest, when we sleep, when we are not at home. It can be done! Modern controllers can really do a lot, the progress in control technology is extremely fast. The number of available applications for remote control is growing rapidly. Owners of underfloor heating alone can only look on with envy…
Over the entire heating season, a 1°C reduction in the average indoor temperature means a reduction in heat loss of around 6%, i.e. a reduction in heating costs and exhaust emissions of the same amount. Lowering the average by 2°C is already 12%…
No economical heating system can replace proper thermal insulation of the building. First of all, insulate and eliminate thermal bridges. Only with small heating needs it makes sense to think about precision heating.