ECOFILM heating films are becoming increasingly well-known amongst an ever-growing number of potential users and businesses. This growing trend in interest in electric underfloor heating is confirmed not only by the number of enquiries about heating films, but also by the actual increase in sales of the heating films themselves. Unfortunately, however, this trend also brings with it certain risks. Businesses are also getting involved in the design and installation of heating films; whilst they may be meticulous and technically competent – after all, laying ECOFILM foils is very straightforward and, provided the instructions in the manual are followed, almost anyone can do it – but they lack the necessary theoretical knowledge from other fields – specifically in the area of heating. If ECOFILM foils are used solely for comfortable underfloor heating, in principle you really do only need the installation instructions. However, if the films are also to serve as the main source of heating, you simply cannot do without a certain level of experience and a professional assessment of the building itself.
In March 2009, the FENIX Group received a complaint regarding underfloor heating using ECOFILM heating foils. The complaint letter stated that, at an outdoor temperature of -15°C, the heating films did not heat the room to more than +18°C, and the floor temperature was only 21–22°C. Given that our documentation states that ECOFILM foils are also designed for heating and can heat the floor to around 30°C, the foils are apparently faulty and the customer is requesting a visit from a FENIX representative.
Following a brief email exchange, a visit was arranged during which the heating system would be inspected by a technician from the FENIX Group. The following facts were established on site:
- The property was a flat on the raised ground floor of a block of flats in the Vysočina region. Below the flat in question were unheated cellars, and above it was another flat. The external walls were brick, approximately 50 cm thick, with no additional thermal insulation. The floor above the unheated cellars lacked the necessary thermal insulation; the windows were new and made of plastic.
- The foil was laid by a firm specialising in the installation of floor coverings. The foil was laid in two rooms – the children’s room and the bedroom – where it was intended to fully replace the original direct-heating convectors. The installation company informed the occupants that if they used more powerful heating films – 80 W/m² – the convectors could be removed from the rooms and the films would heat them.
- In the installation company’s defence, it must be noted that the installation itself was carried out flawlessly, all information was provided in good faith as being accurate, and the main motivation was to recommend a comfortable system to the customer with which they would be completely satisfied. Unfortunately, this is precisely where a failure to consider the broader context came to light. The FENIX Group’s website does indeed state that 80 W/m² heating films are also suitable for heating; however, it is, of course, always necessary to assess the building’s heat loss. To heat an uninsulated flat, you will naturally need a significantly higher output than when heating, for example, a low-energy house.
The inspection of the heating foils itself was carried out in three steps:
- The current flow and resistance of the heating films were checked – this was arranged by the flat’s occupant through a specialist electrical installation firm
- A simplified calculation of heat loss for a single room (the children’s bedroom) was carried out and compared with the power consumption of the heating films
- The system’s start-up dynamics were measured, and the layout of the foils and their functionality were checked using an infrared camera
Re 1) The values measured by the electrical installation firm were correct and corresponded to the data in the tables
Re 2) The children’s room measures 3.7 x 3.5 m, with a height of 2.57 m. Two walls are outdoor; two walls and the ceiling adjoin living (heated) rooms. There is an unheated cellar beneath the floor. One of the outdoor walls has a window and balcony doors.
Desired room temperature ti = 21°C
Design outdoor temperature te = -15°C
Temperature in the unheated cellar +5°C
Heat transfer coefficients:
- external wall U = 1.2 W/m²K
- window, balcony doors U = 1.5 W/m²K
- floor U = 0.8 W/m²K
In this indicative calculation, heat loss through internal walls, the ceiling and air infiltration is not taken into account. The heat transfer coefficients have been estimated – they have not been determined by calculation.
Q = S x U x (ti-te)
Qwalls = 15.7 m² × 1.2 W/m²K × 36 °C = 678 W
Qwindows = 2.84 m² × 1.5 W/m²K × 36 °C = 154 W
Qfloor = 12.9 m² × 0.8 W/m²K × 16 °C = 165 W
Qtotal = 997 W
For heating, 6 ECOFILM Set 80 W/m² films were used, each with a heating width of 0.55 m, a length of 3 m and an output of 132 W. The total output of the films is therefore 6 × 132 W = 792 W. As part of the area is covered by furniture, only approximately 8.3 m² × 80 W/m² = 664 W remains effective for heating purposes.
There is no thermal insulation in the floor. The installation company correctly used a 6 mm Extrupor underlay (which had a positive effect on the heat-up dynamics – see point 3); however, this underlay has the same thermal resistance as approximately 1.5 cm of polystyrene, which is insufficient as thermal insulation above an unheated cellar. We are therefore considering reducing the actual output of the heating foil by approximately 10% to account for heat loss into the subfloor.
- Underfloor heating power consumption = 664 W – 10% = 598 W
- Calculated total heat loss = 997 W
It can be seen from the above calculation that the power input of the heating foils is insufficient and that it covers approximately half of the heat loss.
Re 3) The user had doubts about the functionality of the heating foil, so a measurement of the rise time was carried out using a Cometer measuring device, and images of the floor were also taken using an infrared camera. The floor temperature was measured at two points, whilst the room air temperature was also measured simultaneously. The device recorded the temperature every minute.
As the measurements were taken at an outdoor temperature of approximately +15°C, which significantly reduced heat loss (to only around 200 W), the underfloor heating output is, of course, now entirely sufficient; the graph below shows that the floor warmed from 21°C to 27°C in just 38 minutes! In the same time, after switching on the heating films, the room temperature rose from 21°C to 23°C. Using an infrared camera, it was then possible to see that all the heating films were heating the entire surface. The images taken clearly show the effect of the cold wall, window and balcony door – the floor is cooler near this wall than in the centre of the room. The effect of sunlight is also evident, with sunlight streaming through the balcony doors into the corner behind the cupboard – the temperature there is 29°C.
Conclusion
Underfloor heating using ECOFILM heating foils can, of course, be used as the main and sole source of heating; however, it is always necessary to assess the thermal properties of the building. This system is ideal, above all, for well-insulated buildings with low heat loss – which is essentially the case for every new build today. The trend in construction is clearly moving towards ‘Low-Energy House’ (NED) buildings, where heat loss is approximately 35–40 W/m² (15–18 W/m³), which can be covered without any difficulty even in the most severe frosts using ECOFILM films with an output of 80 W/m² or even 60 W/m².
In this specific case, unfortunately, it will be necessary either to install an additional heat source or to insulate the building. As things stand, the films are capable of heating a room to an outdoor temperature of approximately +5°C. As the outdoor temperature drops, the room temperature will also begin to fall; insufficient insulation will also have a negative impact on running costs.
