How good is underfloor heating in a large room

[Simon47]

... for design purposes, you can consider the oversite concrete to be a constant 5 degrees.

Which is (I assume) a true statement, but does not actually support your blanket statement. "For design purposes" really means "if you want to avoid calculating actual figures, then this will be near enough for common situations". U (or R) values for soil varies significantly, but it DOES have thermal resistance, and it is not "negligible".
And as I said, part of the reason it will appear to have exceedingly poor insulating qualities is the thermal mass that will suck heat away until equilibrium is reached. Put another way, if you did rely on a couple of meters of soil as insulation - you'd find yourself putting lots of heat in initially and might conclude that the soil has no insulating quality, but that heat isn't "gone", that thermal mass is now holding much of it.
And "I've designed and installed ..." is not automatically a qualification to be taken at face value*. If you've always assumed that soil is not an insulator, and you've always assumed that the oversite is a constant 5˚C, then you have probably never even considered the design of an earth insulated system. And if you've never looked at the numbers, then your experience is not relevant to the specific case in point.
Not that I plan on relying on soil for thermal insulation - it won't be necessary.

* Apologies, this really isn't aimed at yourself, but I've met a few "heating engineers" who I wouldn't trust to plug in a fan heater. And often the reason for "disagreement" is them relying on stuff they take for granted - like "it's illegal for a homeowner to touch anything to do with gas" (it isn't) and "the boiler must be connected with a fused spur, it's in the instructions" (I made them put the socket back when doing mum's boiler, and it wasn't). And my favourite was the guy who was 101% adamant that Grundfoss, DAB, Wilo (and I assume others) don't make these modern modulating pumps.

 

[Peter Earthmother]

In China, we recommend Dry UFH system(water pipe), save one third of the gas cost compared with the traditional wet method, also fast heat up, while the initial installation cost is slightly higher.
We also provide electric system, however the result is low market acceptance in China, for example Shanghai, due to the cost.

 

[Peter Earthmother]

A resident of a residential area with pre installed floor heating by a developer found us and installed floor heating, and then compared it with other residents in the same residential area.
The result is that the cost is saved.

 

[Simon47]

In China, we recommend Dry UFH system(water pipe), save one third of the gas cost compared with the traditional wet method, also fast heat up, while the initial installation cost is slightly higher.

"Dry UFH system(water pipe)" - so that's pipes carrying hot water embedded in (e.g.) a concrete slab ? We call that a wet UFH system because the heat carrying medium is water. If you say dry, then to most of us (or at least to me) that implies no water, so probably electric.

We also provide electric system, however the result is low market acceptance in China, for example Shanghai, due to the cost.

Ah, so same problem as here then - lecky costs a lot more per unit of energy than gas does.

A resident of a residential area with pre installed floor heating by a developer found us and installed floor heating, and then compared it with other residents in the same residential area.

I don't quite follow that. I read it as the property was built with UFH by the developer - but the resident came to you to install UFH ? Or was it electric originally installed, and you replaced it with a wet (water) system ? Or something else ?

 

[Peter Earthmother]

"Dry UFH system(water pipe)" - so that's pipes carrying hot water embedded in (e.g.) a concrete slab ? We call that a wet UFH system because the heat carrying medium is water. If you say dry, then to most of us (or at least to me) that implies no water, so probably electric.

Ah, so same problem as here then - lecky costs a lot more per unit of energy than gas does.

I don't quite follow that. I read it as the property was built with UFH by the developer - but the resident came to you to install UFH ? Or was it electric originally installed, and you replaced it with a wet (water) system ? Or something else ?

Dear Simon,
Hello! Nice to meet you!
First of all, in China, we identify the heating system as WET or DRY by whether there is cement backfill in the end of UFH process.
I will list some common construction systems in China's floor heating market as below ——
XPS foam board + manual clips + water pipe + cement + tile = WET
EPS foam slotted board + aluminum layer + water pipe + wood floor = DRY
EPS foam slotted board + aluminum layer + water pipe + cement + tile = WET
XPS foam board + aluminum layer + electric cable + wood floor = DRY
These are basically the above types.
Of course, the product types are not involved, e.g. XPS itself has many specifications to adapt to different needs.
In addition, as a result of home renovation, the resident chose our DRY system products.
Meanwhile, we need to conduct actual research on the product, we reached a cooperation with him and collected the gas cost.
Hope you can understand, and thank you for asking questions, cuz most people don't know about China's floor heating market.

 

[Mike Johnson]

In the UK, all of Europe and the USA any underfloor heating that contains water pipes is called WET, any electric UFH is called DRY, the type of construction is not taken into account. China's floor heating market is only of academic interest to most on here.

 

[Peter Earthmother]

In the UK, all of Europe and the USA any underfloor heating that contains water pipes is called WET, any electric UFH is called DRY, the type of construction is not taken into account. China's floor heating market is only of academic interest to most on here.

Good afternoon, Mike,
The development of China's floor heating market is relatively slow, and industry standard documents related to floor heating were established in 2004.
Some technical terms are different from those in Europe.
Fortunately, we can understand each other.
Thank you for your correction.

 

[pc1966]

Ah, so same problem as here then - lecky costs a lot more per unit of energy than gas does.

Very much so, and why water UFH makes more sense as it can be fed from a heat pump.

Not up to date on prices, but until recently electricity was about 4 times the price of gas per unit energy, so even with a heat pump with a COP of around 3 (i.e. 3kW heat out for 1kW electricity in) gas is/was still a bit cheaper. However in the long-term that is going to change and so UFH is likely to work out cheaper.

Also a warm floor is really comfortable in winter!