Newbie UFH questions

[LordLyon]

Hi,

I had a mid life crisis and decided to rip out the central heating system and install underfloor heating ? The project isn't finished yet, but most of the rooms now have heating. This is a retrofit system using overboards with pipes laid in them at 150mm centres.

I have a couple of questions that I'd like to get a better understanding of (bit late, I know!).

Q1 - Efficient UFH temperature

I don't know much about thermal dynamics, so hypothetically, if I have a system that loses 1 degree per hour when the heating is off, and it takes 1 hour to increase the temperature by 1 degree when it is on, would it be more efficient to let the heating go from 21 to 18 over 3 hours and then from 18 to 21 over another 3 hours, or would it be better to go from 21 to 20 and then back to 21 every two hours, or doesn't it make a difference?

The reason for this question is that I'm thinking of leaving it polling constantly between 20 and 21 degrees.

Q2 - UFH max floor temperature dilemma

I currently have the manifold set to 42 degrees. This is taking a lot of time to get up to room temperature (5-8  hours, and it's not even winter yet!). The problem is, if I set the temperature any higher then the floor gets above 27 degrees (tested with an infrared thermometer, although this may be inaccurate?), and as most of the house is laminate, I believe this is not a good idea. I did think about installing floor probes, but I figured that once the floor got above 27 degrees, the heating would cut off until the floor temperature dropped below 27, which may protect the floor, but would defeat the object of trying to heat the house, albeit heat would still be coming from the floor?
I also assume that once the temperature drops outside in the winter, the floor won't reach 27 unless I increase the output temperature from the manifold, so it will be a juggling act through the seasons?

As you can see, I didn't think this through first ? and I hope I haven't left out any vital information in these questions.

Still glad I did it though!

 

Regards

Edited November 23, 2020 by LordLyon

[ProDave]

The No 1 question is how much insulation did you put under the floor before laying the UFH?

 

It sounds like it is an old house with little insulation so whatever you do will have to work with that.  Have you tried running it 24/7 at a lower water temperature?  Then you can play with the water temperature to find the optimum temperature to keep the heating running most of the time, i.e. the minimum temperature it can get away with and still get enough heat into the house.

 

What is heating the UFH?

[SteamyTea]

As Dave said.

 

But as a general rule, heat loss and heat gain have different 'curves'.  So the energy needed to heat something up is greater than the energy lost during cooling, this is because during the heating stage, energy is also being lost.  The greater the temperature differences, the greater the losses (look up Newton's Law of Cooling).

So with all things being equal (which they won't be), limiting the temperature rise to the minimum acceptable (your 20°C to 21°C) is the better option.

The unequal things are: efficiency of heat source, external inputs and outputs (solar gain and opening doors), changes is external temperature, Internal inputs and outputs (cooking, bathing, ventilation).

 

[LordLyon]

Thanks for your quick responses.

 

ProDave, The house is 24 yours old, and does have wall and floor insulation, but not much? I believe the wall insulation is about 12mm, or at least this is what I can see in the integral garage wall, and the floor insulation is only about 50mm. I do plan to try and run at a lower temperature 24/7, that way, if I get the temperature right, the floor will always be warm, as opposed to currently, where it switches off for periods when the rooms are warm enough, but I'm not sure what effect, if any, this will have on the condensing combi boiler if it is working most of the time?
The UFH is wet with 16mm pert-al-pert pipe, using a 7 port manifold, 3 zones downstairs, and 4 zones upstairs...I know I should have had a manifold on each floor, but I had no where to put one upstairs. All controlled by wireless thermostats.

 

SteamyTea, thank you for the info. The house doesn't usually get that cold, but it has always been heated in the past by traditional radiators. The only room that is not currently heating that well is the kitchen, but I guess this is down to the lack of floor space containing UFH, but having said that, it does contain an oven, so not too worried. Draught wise, it is not a draughty house, so I'm actually hoping for a cold winter, so I can properly test the system ?

Edited November 24, 2020 by LordLyon

[SteamyTea]

1 hour ago, LordLyon said:

and the floor insulation is only about 50mm

Not much.  Fitting UFH may cost you more to run.

Still, loosing the radiators is a good move.

[LordLyon]

SteamyTea,

Yeah I realised it wasn't much when I took up the chipboard flooring and saw the concrete slabs with only 50mm wooden framework on top, and I couldn't raise it any more because of the external doors.