Note: The Floor Heating app for iPhone and iPod touch was recently updated to a new version. The new version is easier to use as it gets rid of the max. loop length input value. The (max.) loop length is now calculated automatically to provide pressure drop that is inside some predefined, reasonable, range.
Floor Heating app for iPhone and iPod touch is suitable for calculation of different characteristics of a floor heating system as shown on the scheme, i.e. with pipes installed in a screed layer below the floor covering. The output characteristics include, most notably, the required flow and return temperatures of water, but also floor surface temperature, heat losses downwards, number of pipe loops, pipe length required to cover a room, water volume flow and pressure losses.
The application can be used by engineers, designers and homeowners. Basic floor heating characteristics can be quickly determined. It is interesting to observe how different floor coverings, insulation thickness and specific heat losses of a room affect the required water temperature in order to keep the room warm.
Modern low-energy and passive houses require lower water temperatures than houses with poor thermal insulation. But how much lower? This application will give the answer to that question.
The Floor Heating application will also provide information on whether the building’s individual rooms will need additional heating or not. If either the required floor surface temperature or water flow temperature is too high, additional heat source will be needed for that particular room.
Floor Heating for iPhone availability
How to use Floor Heating for iPhone
The scheme posted above can be brought up at any time by tapping the View Scheme link at the top of the main application view. The scheme outlines the underfloor heating layout, which contains the following layers, from top to bottom:
- air, present in the room and heated to the desired temperature;
- floor covering. This is the top layer of the floor and has a significant impact on the required water temperature;
- screed. The screed should preferably have as high a thermal conductivity as possible;
- floor heating pipes. These are the water-carrying pipes and it is assumed in the application that they are made of plastic material (PEX or PEX-Al-PEX), though this doesn’t have a significant impact on the results;
- thermal insulation. Under the floor heating pipes there should be some thermal insulation. The more, the better, as this has a very big impact on the heat losses caused by heat conduction in the downwards direction;
- slab. This is the (load-carrying) slab of the floor structure.
- underneath the floor structure there can be (cold) outside air, a heated space (warm air) or ground (soil).
The first section, named Basic room characteristics, requires input of the following values:
- Treated floor area: this is the inner floor area of the heated space, which can be a single room or a group of rooms with the same characteristics, i.e. the same floor covering, specific heat losses, location (a room located above outside air has larger specific heat losses than a room located above a heated space) and so on.
- Room air temperature is the desired air temperature to be maintained in the room. Generally, this parameter will be in 20-22 degrees Celsius for living rooms, 24 degrees Celsius in bathrooms, 18-20 degrees Celsius in bedrooms. But any value can be entered, if so desired.
- Specific heat losses are heat losses of the room per square meter of the living space, excluding the heat losses downwards (through the slab), which are calculated in this application. This value needs to be determined separately, but for a rough approximation these values will be good:
- old buildings with no insulation: 100-120 W/m2;
- old buildings with poor insulation: 80-100 W/m2;
- buildings with minimal insulation: 65-75 W/m2;
- newer buildings with modest insulation: 65-75 W/m2;
- newer buildings with good insulation: 55-65 W/m2;
- newer buildings with very good insulation: 45-55 W/m2;
- low energy buildings: 20-30 W/m2;
- passive houses: 10 W/m2.
Don’t forget, thermal insulation is the single most important aspect of low energy use for heating a building, especially in connection with floor heating and a heat pump.
- Tap Room location and select where the room is located: on the ground, above outside air or above a heated space. The application will select the correct thermal resistance below the slab.
- Then select the temperature of the air or the ground below the room. For a heated space, this will probably be close to 20 ºC, for example. For outside air underneath the slab, this should be the design outside air temperature, e.g. -10 ºC. With ground (soil) beneath the slab, this should be the design soil temperature, e.g. 0 ºC.
The next section requires input of values relative to the floor structure of the room.
- Tap Floor covering (top layer) to select the floor covering, which is the top layer of the finished floor structure. The app allows to choose between three categories:
- Ceramic tiles, stone
- Wood
- Carpet, textile.
The application will choose the correct thermal resistance of the selected covering. This selection has quite a large impact on the required water temperature, so it is important to calculate rooms with different coverings separately.
- Screed thickness is the thickness of the screed above the floor heating pipes.
- Screed conductivity is the thermal conductivity of the screed. If the value is not known, the default value of 1.2 W/(m*K) can be used for the classic wet cement screed. For a wooden screed, this should be considerably lower, about 0.15 W/(m*K).
- Insulation thickness is the thickness of the insulation material beneath the floor heating pipes. This value has a very big impact on the heat losses downwards as the heat from warm water will spread in all directions around the pipes. The better the insulation, the less heat will be lost.
- Insulation conductivity: the standard value of insulation thermal conductivity is 0.04 W/(m*K), but if another type of insulation is used, the value should be changed accordingly.
- Slab thickness is the thickness of the (load carrying) slab.
- Slab conductivity is the thermal conductivity of the (load carrying) slab underneath the floor heating pipes. For a standard concrete slab, the value is 1.2 W/(m*K), while for a wooden slab, this value should be much lower, about 0.15 W/(m*K).
The Pipe / water data section of the application requires the input of a few parameters regarding the heating medium (water) and floor heating pipes.
- Water temperature difference is the temperature difference between the water entering a floor heating loop and leaving that same loop. This temperature difference should be 5 ºC, but if desired, other values can be entered. The larger the temperature difference, the lower the required water volume flow, but the worse the energy performance, as this leads to higher flow temperatures, resulting in larger heat losses and, when used with a heat pump, a lower heat pump COP.
- Pipe inside diameter is the inside diameter of the pipes used for floor heating.
- Distance between pipes is self-explanatory.
- Max. loop length is the maximum desired length of a single pipe loop. While tempted to use the largest value possible, resulting in a manifold with a minimum number of pipe connections, this value should not be too large in order to keep the pressure loss of water low enough (usually it should be lower than 1 m of water column). Larger pressure losses require a larger, less efficient circulation pump which results in larger electricity use in order to run the pump.
- Lead pipe length is the length of the pipe before entering the room and after leaving it to connect to the manifold.
The calculation process should be repeated for every room connected to the same manifold. The room with the most unfavourable conditions (most heat-resistant floor covering, poorest insulation, highest specific heat losses) will result in the maximum needed water temperature. The same water temperature will be distributed to all the floor-heating loops connected to the same manifold, and maybe also to all other manifolds. Loops covering other, more favourable rooms, will need to be throttled in order to lower the return water temperature. This will ensure lower water volume flow, lower mean surface temperature and consequently lower heat output of those loops, otherwise the rooms covered by those loops would be too warm.
Always be sure to check that the required flow temperature isn’t too high, as this could lead to damaging the floor covering and possibly other parts of the floor structure! The developer of this application will not be responsible for the damage that could originate from improper installation of floor heating systems. The application will show a note at the bottom of the screen if too high temperatures are required in order to heat a room. In this case, additional heating source such as radiators or fan-coils are needed to keep the room warm.
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