Question QUESTION: In Scandinavia a lot of new and refurnished houses are heated with an underfloor water distibution system (in pipes). The system are (normally) fed via a heat-pump combined with electrics. My question is: Do you have to feed the system with more energy the thicker the floor is above the pipes? Many systems incorporate the pipes in the the underfloor (chip floors) and then put parquet or whole-plank wooden floors on top (ca 14-20mm). Other systems attach heat-conductive sheets with the pipes incorporated UNDER the chip-floor, i.e. you get a layer of 22mm + 14-20mm floor before you hit the air you want to heat. Will such a system require more energy - i.e. you need higher water-temperatur to get the desired air-temperature? In my world energy can't be created or disapperat, i.e. the thicker floor only delays the heat (from you turn it on), but it doesn't require higher temperature. The heat resistance formula does not take into account that energy "disappear", only the rate of which heat flows through the material (as far as I understand).
ANSWER: Hi Thomas,
You are thinking entirely along the right lines. A thicker floor only delays the heat from getting to the air in the room. Under steady state conditions, provided losses to the ground are at a minimum, there will be no difference. On start up the thick floors will take longer to reach steady state this will be recovered on shut down when the thicker floors will stay hotter for longer.
I hope this helps
Best wishes
Kevin
---------- FOLLOW-UP ----------
QUESTION: Hi Kevin,
Thanks for this - I'm relieved that you confirm my line of thinking being correct.
To follow up - is it not at all possible that the thicker floors (i.e. higher thermal resistance) require a bit more energi - due to e.g. the floor expanding and exercising work on the surrounding materials? Maybe other things? You see - many people claim that thicker floors require higher water temperature (they are possibly claiming that the difference between out (the water emitted) and return water (the temperature of the water when a full loop is completed) is higher, i.e. more energy is needed to re-heat the water to the desired round-trip temperature).
It is strange that even professionals in the industry claim this - are they just plain wrong, or are there other forces in play that I'm not thinking about here? In other words are you absolute positive that thicker insulation between the pipes and the air we want to heat has no impact on energy-consumption?
Answer Hi Thomas,
It will also depend on heat losses from the home. These arise from the following areas.
Ground
Roof
Walls
Windows
Water out flow
Air changes.
If these add up to a significant proportion of the input heat then in order to meet these losses higher temperatures will be needed for more insulated floors.
What is needed in the calculation in this case is the Wattage required to keep the home at say 23°C when it is, say, 1°C outside.
I think at Scandinavian latitudes very prolonged and very cold periods are possible thus the loss rate (Watts) will be high and compensation in terms of heat input will be needed.
This is the rate of heat loss with a temperature difference of 22°C.
This must be matched by a heat input in Watts from the heating system. As the increasing insulating properties of the floor slow heat transfer and thus reduce heat flow a higher water temperature will be needed to supply more wattage.
