7° delta t

[vala]

My first floor UFH system is now up and running and I'm struggling to get the 7° delta t between flow and return temps on the.manifold.

Been speaking to Wunda to try and resolve this however the suggestions from thwm are getting better results but not quite there.

When the system first went properly on I was getting a 1° (at best) difference.

Wunda suggested manually turning the flow rate to 2.5, then recalibrating which has now achieved a 3°-4° difference.

Manifold temp is 40°.

They have suggested that this should now be fine, and to increase the manifold temp to 45° however I'm not sure how this will get me towards that 7° differential.

 

I've had a read through many topics on here and have yet to come across a simile case and possible solution.

 

Tomorrow I'll get some temps of the floor now I have my thermal camera back.

 

Hoping I can get some suggestions from here as to what may be the cause.

[jayc89]

Try reducing the flow rate and see if the return temp lowers, it should.

 

FWIW, I've always gone on a delta-t of 11c for flow temps > 35c and a delta-t of 7c for flow temps 35 and below.

[JohnMo]

What are you recalibrating?

 

Are you using Salus self actuating actuators?

 

 

[vala]

@jayc89

I'll give that a try. It did seem to help after I reduced it from fully open and recalibrated it.

@JohnMo

yes, I've got salus auto balancing actuators.

[JohnMo]

If that's the case not really understanding why Wunda would ask to set the flow rate at 2.5 before calibration, that makes no sense.  As flow meter are to be fully opened at all times.

 

I found if there a delay to the pump starting (which is pretty standard in UFH control centres), from powering up the actuator then calibration never seems to be right.  You may have to frig the the pump temporarily to be running prior to doing a recalibration.

 

I also found it a pain to get them running right.

 

 

[dpmiller]

as wonderful as the Salus jobbies are, perhaps they struggle at the small openings required if there are no other flow restrictions, the stepper will only have a certain resolution. Doing a "rough" balance with the flow meters (and maybe turning the pump down a bit?) should let the actuator work over more of it's span.

[SteamyTea]

Small point:

t is time 

T is temperature

 

[vala]

@JohnMo

originally the flow rates were fully opened however I was then achieving a delta T of 0.5-1°.

it's got slightly better since reducing the flow rates and recalibrating however today noticed we're back to between 1-2° delta T.

 

@dpmiller

do you think maybe manually setting the flow rates to what they should be based on the loop lengths whilst still using the salus actuators be worth a try?

 

@SteamyTea

Noted.

[dpmiller]

@vala  yes. But what is the pump set to/ can you turn it down a speed?

[Adsibob]

Wouldn’t Delta T of the in and out flows also depend on what floor finishes you have and what the temperature of the floor is. For example, if you have thick 24mm oak plank as your floor finish, and the room is 23C to start with, then surely the pipes would lose less heat than if you had 6mm porcelain laid in a room that was 12C to start with.

[JohnMo]

but the actuator is supposed to modulate the flow to maintain the 7 deg differential between flow and return

[vala]

@dpmiller

This is the pump and settings,

set to speed 3??? Is this possible to slow down, I've not changed anything, it's all as it came from Wunda.

 

@Adsibob

Floor build up is 22mm T&G ply, underlay and carpet (underlay and carpet come to 2.1tog) in all areas upstairs except the bathroom which is, 18mm T&G ply, 6mm hardie, ditra, then tiles.

[dpmiller]

try it on 2...

[vala]

@dpmiller

So set the pump speed to 2 on Saturday. Went passed the house and checked today and with one zone active the delta T is 2°.

Is the 7° difference supposed to be when all zones are active or can if differ depending on how many zones are active.

2 of the rooms get a lot of solar gain during the day, so much they increase to around 24° according to the graphs on the Wunda app.

Out of the 2 rooms at the back of the house, 1 is the bathroom which is where the manifold is located, the other is the main bedroom and the temp seems to hover within a degree of the set temp (19°).

Is it worth dropping down to speed 1? Or maybe now set the flow rates as per if I was to use manual actuators, and then recalibrate the salus ones?

[dpmiller]

@vala you might try doing both tbh.

[jayc89]

1 hour ago, vala said:

@dpmiller

So set the pump speed to 2 on Saturday. Went passed the house and checked today and with one zone active the delta T is 2°.

Is the 7° difference supposed to be when all zones are active or can if differ depending on how many zones are active.

2 of the rooms get a lot of solar gain during the day, so much they increase to around 24° according to the graphs on the Wunda app.

Out of the 2 rooms at the back of the house, 1 is the bathroom which is where the manifold is located, the other is the main bedroom and the temp seems to hover within a degree of the set temp (19°).

Is it worth dropping down to speed 1? Or maybe now set the flow rates as per if I was to use manual actuators, and then recalibrate the salus ones?

The idea is they always maintain the desired delta-T, regardless. Do you have a standard actuator you can stick on one of the loops to test with?

[vala]

Just bringing this thread back up as we're now back to using the UFH and still struggle to get this 7° delta T.

After much purging I'm confident now that all air is expelled.

And following @Nickfromwales suggestion of opening up the manifold pump I did indeed find a tiny piece of metal.

Wunda sent me out some manual actuators and have suggested to use these to achieve the correct delta T before sending me out new Salus ABA's.

I'm going to set 1 loop at a time and the system was cold, as had been off for a few days, prior to restarting.

The loop length I'm working on is 80m and flow rate should be 2 l/min, however I'm currently at 0.6 l/min and achieving delta T of 7°.

Strange this is flow temp was set at 45°, and has been constant since I started this yesterday morning however now it's suddenly creeping up to 47°. Will see if that settles in the next hour or so.

Temp of the room in question is gaining heat but extremely slowly, up from 14.5° to 18.5° since 1300hrs yesterday.

Am I wrong in expecting the temp in the room to be up higher by now?

[JohnMo]

Heat up time is a combination of kW of heat input, and then how much concrete/screed you have to heat up, plus heat loss downwards.  Not sure I would get to hung up on the DT until the floor is up to temp, even then not bother that much. 

 

The basic of floor heating system are

 

The greater the mean flow temperature, the higher the heat output of the floor.  The mean temp is set with a combination of flow temp and delta T.  For a given flow temperature the lower the DT the higher the kW rate the floor will give out.  As you have realised lowering the flow rate increases the DT.  

 

Your issue at the moment is the energy transfer from the water is too low to heat the room at an acceptable rate (its too slow).  Increase flow rate, ignore the delta T.  Get the room up to temp, your balancing act should be not overshooting room temp too much (flow temp not to high and/or DT to low) and not taking a couple of days to reheat (flow temp to low and/or DT to high).

 

How much insulation do you have under the floor?

[vala]

8 minutes ago, JohnMo said:

Heat up time is a combination of kW of heat input, and then how much concrete/screed you have to heat up, plus heat loss downwards.  Not sure I would get to hung up on the DT until the floor is up to temp, even then not bother that much. 

 

The basic of floor heating system are

 

The greater the mean flow temperature, the higher the heat output of the floor.  The mean temp is set with a combination of flow temp and delta T.  For a given flow temperature the lower the DT the higher the kW rate the floor will give out.  As you have realised lowering the flow rate increases the DT.  

 

Your issue at the moment is the energy transfer from the water is too low to heat the room at an acceptable rate (its too slow).  Increase flow rate, ignore the delta T.  Get the room up to temp, your balancing act should be not overshooting room temp too much (flow temp not to high and/or DT to low) and not taking a couple of days to reheat (flow temp to low and/or DT to high).

 

How much insulation do you have under the floor?

 Hi @JohnMo, thanks for the reply.

Would you suggest upping the flow rate to what it should be based on loop length or just going in 0.5 l/min increments?

Insulation under the floor is 100mm PIR between the joists.

[JohnMo]

I would up to about 1.5, see what happens 

[vala]

Thanks for the repliy. Have got it currently set to 45° flow and 1.5 l/min. In the last 4hrs we’re still in the low 18’s.

Would upping to pump speed 2 be a sensible option? At present although I’m not focusing on it, the delta T is circa 4-5°.

[JohnMo]

Pump speed will change anything other than you will use slightly more electric drive the pump.  You flow rate is set on the manifold, as long you meet the flow rate you want the pump setting is fine.

 

Just open the flow meter some more, up to 2.

 

Are you still running just one loop?  If so make sure all the room doors are closed, otherwise the heat will be lost to the other rooms.

 

What is the floor coverings, we have carpet in the bedrooms and the UFH is useless.

[vala]

No problem. I'll leave it then pump set to 1 then.

Opened up to 2l/min. This looks like the maximum for this pump speed. Any higher and I'll need to go to speed 2.

Yes just the 1 room running at the moment, and door is kept closed.

Floor covering is indeed carpets (tog for carpet and underlay comes to 2), in the bedrooms and landing. Tiled in the bathroom.

[Adsibob]

@vala did you resolve this issue?

 

[vala]

On 24/01/2023 at 11:34, Adsibob said:

@vala did you resolve this issue?

 

Apologies for the delay I’m replying. No still not sorted. Have resorted to just using the manual actuators for now. Tbh when we had that cold snap in December it highlighted the CWI that apparently has been fitted (says so on the last 2 EPC reports) is not very good. This has resorted in one room in particular that struggles to get up to temp when the cold weather is present (1-2° and colder temps).

So looking into getting that sorted along with the ground floor works which will include wet UFH throughout.

Then we’ll get back onto trying to use the ABA’s.