Balancing UFH

[vala]

We've now had our polished concrete floor installed and the required time has passed so we can now slowly introduce heat into it.

Thought I'd use this time to try and get the upstairs UFH working better, and try and mimic the way we hope to run an ASHP - all open loop, at one temp. Granted with the heat pump and WC the flow temp will vary but I haven't got that option with my oil combi.

What info do I need to have in order to balance the manifold and set the flow rates?

Wunda say just divide the loop length by 40 to get the flow rate. Tried this when the first floor UFH was installed and didn't really get anywhere.

I've come across another method which is to do with mass flow rate.

Has anyone here used this method and if so what info did you require from your own system to starting calculating the flow rate required.

FWIW - ground floor is 125mm concrete on top of 200mm PIR with 100mm pipe spacings. First floor is predominately carpet (1.9TOG for carpet and underlay combined) on top of 25/30mm pug mix on 100mm PIR with 135mm spacings.

Current flow temp is 25º and this is ok to increase at 1º a day as advised by the concrete installers.

[JohnMo]

At those spacing and if well insulated 25 to 28 will be all you need to flow at.

 

So do have mixer and pump as you are running an oil boiler?

 

1 hour ago, vala said:

Tried this when the first floor UFH was installed and didn't really get anywhere.

Not sure what you mean?

80m loop divided by 40 is 2L/min. You set the flow meter for that loop at 2 etc.

 

Start with the loops at the calculated flow rate. If all open loop you then have to tune the system. If rooms are to warm decrease the loop flow rate, if to cool increase flow rate.

[vala]

1 hour ago, JohnMo said:

At those spacing and if well insulated 25 to 28 will be all you need to flow at.

 

So do have mixer and pump as you are running an oil boiler?

 

Not sure what you mean?

80m loop divided by 40 is 2L/min. You set the flow meter for that loop at 2 etc.

 

Start with the loops at the calculated flow rate. If all open loop you then have to tune the system. If rooms are to warm decrease the loop flow rate, if to cool increase flow rate.

 

I have a mixer and pump as supplied by Wunda at present on both floors.

 

Initially when the first floor was installed all loops were set as per the guidelines by Wunda, so loop length divided by 40. All that I got was the same flow and return temp on the manifold and cold rooms.

Hence when I started looking into flow rates more I became aware of a different method using mass flow rate to determine the L/min required.

[JohnMo]

8 hours ago, vala said:

Initially when the first floor was installed all loops were set as per the guidelines by Wunda, so loop length divided by 40. All that I got was the same flow and return temp on the manifold and cold rooms.

What temperature were you flowing at and how long did you run the system? The divide by 40 is just a simplified version of the mass flow calculation.

 

What do you mean by "got was the same flow and return temp on the manifold" were both the flow and return exactly the same going in and coming out i.e. 25 in and 25 out?

[vala]

7 hours ago, JohnMo said:

What temperature were you flowing at and how long did you run the system? The divide by 40 is just a simplified version of the mass flow calculation.

 

What do you mean by "got was the same flow and return temp on the manifold" were both the flow and return exactly the same going in and coming out i.e. 25 in and 25 out?

The flow temp started around 15-16° on a couple of weeks ago. After 3 days or so at that, it's been increased by a degree a day.

Today it's up to 26°.

 

Yes, for example yesterday the manifolds said 25° flow temp and 25° return temp.

[JohnMo]

At 15 to 16 your floor is certainly not giving heat off, so no surprise you dT is zero. So you are getting heat added to the system as you have gone from 15 to 25 degs flow temp.  But it could be your boiler has so little to do it just puts a blast of heat in to get the general water temp to 25.

 

To demonstrate what I mean, this is my heat pump, when running its flowing about 30 degs, and has a dT of about 4-5.  However when the heat pump or boiler is not actively heating, there is being little or no work done or energy added to the system, so the flow return temps dT drops to zero.

 

This could be what you are seeing, so the yellow section is the kW being added to system, the red and green the flow and return.  See how they converge once the heat pump stops adding heat.  At time of screen shot the water temp had decreased to mid 20s.  The heat is still being added to house as floor is warmer that the air.

 

How is your boiler connected to the heating system? And how are you mixing the flow from boiler to UFH?

 

With carpets you may need to go a little hotter yet to get any meaningful heat from the floor.

 

[vala]

@JohnMo

From the combi the flow and return go to a buffer vessel.

This has a temp probe about 1/4 and 3/4 up, measuring a min and max temp.

When there is a call for heat (24/7) at present, the UFH pumps activate and the flow and return goes to and from this.

When the temp in the buffer reaches a min set point and there's a call for heat the boiler fires up to get the buffer up to the max temp it's been set at.

 

Looking at your screen grab, I do notice that when the boiler fires up, the flow temp at the manifolds increase but the return doesn't go up as much creating around 5° dT. However this always overshoots the temp set on the mixing valve.

Once the buffer is satisfied and the boiler is off, the flow temp comes back down to the figure it's set at.

[vala]

Little update from the weekend.

 

so I've used the information from this video to determine and set the flow rates

 

however one thing I've noticed is it doesn't take into account the floor covering.

 

does anyone know how I can add the TOG or thermal conductivity value to get a more accurate flow rate?

 

Edited yesterday at 11:02 by vala

[JohnMo]

11 minutes ago, vala said:

 

however one thing I've noticed is it doesn't take into account the floor covering.

 

does anyone know how I can add the TOG or thermal conductivity value to get a more accurate flow rate?

 

Tog values affect flow temp, you really need to get the system up to temperature. Leave for 24hrs and then assess if rooms are not getting hot enough. I would wind the thermostat(s) up to a little warmer than normally set, so it doesn't affect results too much.

 

If all room are getting to temperature job done.

If all room are not warm enough trim flow temperature up.

If you get to temp really quickly and it overshoots trim temps down a little at a time.

If the odd room is too warm decrease flow temperature of loops in that room - opposite in cool rooms.