UFH Return Temp Problems

[swisscheese]

Hi All,

 

My UFH return temp is currently way too low coming back to the downstairs manifold.

 

It's from an ASHP, temp currently around 38degress, so I'm mixing down to around 30-32 degrees at the manifold for the UFH heating.

The return is pipe is cold, I'm thinknig there will be cold spots on the floor also, not tested.  I upped the flow rates to see if that helped,  to push something round, but the return pipe at the manifold stayed cold, all it did was make the ASHP work stupidly hard.

 

Any tips is troubleshooting return temps?

 

Thanks

[ProDave]

Has it worked before or is this the first time you have turned it on?

[swisscheese]

It's been "working" for a while though I have never been super happy with the temp difference between flow and return.

This prolonged cold weather has made the issue more noticeable as it becomes more obvious as set back temps take longer to get back and on closer inspection there are cold spots on the floor and the ASHP works harder than it needs to.

[andy]

I have been on a "journey" with my ASHP UFH which has just been turned on.  Right now I am running mine at 42C from ASHP with a target 5C delta and a flow rate of about 22l/min to the loft on pump #1 (to low loss header).  From there there's pump #2 to circulate towards the manifolds and a pump at each manifold too.  I've got the pump #3 and #4 by each manifold to drive that local flow but I feel it's only just enough to get flow on the larger 10 port manifold with that local pump on highest constant pressure mode.

 

I only have a limited amount of senosrs in place so far but I get circa 2.5C loss from ASHP to loft with it leaving ASHP about 40C (Samsung reading), gets to loft about 37C (1-Wire sensor) and gets to manifolds at (rubbish dial, 1-Wire soon!) about 32C.  But my house shape's terrible from that perspecitve - strung-out bungalow...

 

Crucial thing for me was to run the ASHP for longer than the completely unfounded preconceived ideas in my head said I needed to

[Temp]

3 hours ago, swisscheese said:

The return is pipe is cold,

 

Define cold? What actual temperature? 

 

[Rich123]

3 hours ago, swisscheese said:

Hi All,

 

My UFH return temp is currently way too low coming back to the downstairs manifold.

 

It's from an ASHP, temp currently around 38degress, so I'm mixing down to around 30-32 degrees at the manifold for the UFH heating.

The return is pipe is cold, I'm thinknig there will be cold spots on the floor also, not tested.  I upped the flow rates to see if that helped,  to push something round, but the return pipe at the manifold stayed cold, all it did was make the ASHP work stupidly hard.

 

Any tips is troubleshooting return temps?

 

Thanks

The standard design temperature drop of underfloor heating is 10 degrees, so a supply of 32 c would mean a return of 22 c.

If it’s a new system in a new floor then it also depends on the type of floor and any moisture which will add a load to the system.

My thought is that a supply temperature of 32 C is low and I would raise that to 40 C at least .

if you have flow balancing indicators , then ensure that these are correctly balanced. Also check that the pump is set up correctly with proportional flow selected .

[swisscheese]

14 hours ago, Temp said:

 

Define cold? What actual temperature? 

 

16-18

 

15 hours ago, andy said:

I have been on a "journey" with my ASHP UFH which has just been turned on.  Right now I am running mine at 42C from ASHP with a target 5C delta and a flow rate of about 22l/min to the loft on pump #1 (to low loss header).  From there there's pump #2 to circulate towards the manifolds and a pump at each manifold too.  I've got the pump #3 and #4 by each manifold to drive that local flow but I feel it's only just enough to get flow on the larger 10 port manifold with that local pump on highest constant pressure mode.

 

I only have a limited amount of senosrs in place so far but I get circa 2.5C loss from ASHP to loft with it leaving ASHP about 40C (Samsung reading), gets to loft about 37C (1-Wire sensor) and gets to manifolds at (rubbish dial, 1-Wire soon!) about 32C.  But my house shape's terrible from that perspecitve - strung-out bungalow...

 

Crucial thing for me was to run the ASHP for longer than the completely unfounded preconceived ideas in my head said I needed to

Hi Andy, also on a Samsung and also with a strung out L shaped design.  How do you get on with the Samsung?  Any wild config tips!

[andy]

On 09/01/2021 at 10:55, swisscheese said:

16-18

 

Hi Andy, also on a Samsung and also with a strung out L shaped design.  How do you get on with the Samsung?  Any wild config tips!

 

I will look at screen shotting my settings for reference tonight and will post but nothing radical.  Heating and DHW are working though!  When it's cold (zero or below) I was underestimating the amount of time required to run the heating to get sufficient temperature in the slab, once it is warm then it stays warm for ages though, so it's pre-empting of immenent cold weather that helps (will look to automate this with leveraging weather input into Loxone).

 

Not sure what settings I can change to influence it's defrost frequency though, I need to start capturing the data but it is defrosting at least every hour which seems too often but as I say I don't see how I can influence that behaviour, could it be the fin desgin on the unit, for example?  Beginning to regret Samsung as a choice now but hey ho, too late for all that

[Rich123]

I’m amazed it’s working at all at the low temp settings you have if it’s a slab.

The recommended max floor temperature is 28 C , so I’d up the temperature to get to that on the surface 

Also the warm up depends on differential temperature between the pipe and the slab, so the heat transfer rate is a lot less at reduced temperature. This is known as exergy https://en.wikipedia.org/wiki/Exergy

[swisscheese]

1 hour ago, Rich123 said:

I’m amazed it’s working at all at the low temp settings you have if it’s a slab.

The recommended max floor temperature is 28 C , so I’d up the temperature to get to that on the surface 

Also the warm up depends on differential temperature between the pipe and the slab, so the heat transfer rate is a lot less at reduced temperature. This is known as exergy https://en.wikipedia.org/wiki/Exergy

 

That's the return temperature 16-18

 

ASHP, out temp currently around 38 degrees, I have switched over to the "heat Curve" , so I'm now mixing down to around 35 at the manifold, the return pipe is still currently around 16

 

The question is really about balancing.

[Rich123]

39 minutes ago, swisscheese said:

 

That's the return temperature 16-18

 

ASHP, out temp currently around 38 degrees, I have switched over to the "heat Curve" , so I'm now mixing down to around 35 at the manifold, the return pipe is still currently around 16

 

The question is really about balancing.

If this is a new slab then it will take weeks to dry and therefore the return temp will be low As far as flow rates are concerned unless you have the indicators on the manifold then it’s pretty difficult unless you have an ultra sonic flow measuring device.

I have recently installed under floor in an anhydride screed and it has taken 4 weeks to stabilise with a flow of 55 C .

As you say increasing the flow made the heat pump work hard it suggests that the system is under excessive load which is an indication of the load on the slab evaporating moisture. It’s pretty normal on a new system . 

[joe90]

On 08/01/2021 at 20:19, Rich123 said:

The standard design temperature drop of underfloor heating is 10 degrees,

Not heard that before, I run mine at 25’ and return at 21’, yes slow to react but keeps house a constant temp.

[Rich123]

49 minutes ago, joe90 said:

Not heard that before, I run mine at 25’ and return at 21’, yes slow to react but keeps house a constant temp.

 

Hi actually it can vary 10 is max nominally around 7 but it varies with the underfloor design. Usually this is a specialist supplier so it may vary depending who is selected.

25 seems low however if it works that’s great , you must have a well insulated house.

The problem as a designer is that the output can be radically affected by the occupier, so furniture, carpets , rugs etc need to be considered. I see here that most people are self build so you know what the end game is and it’s very interesting and informative.

 

[Pete]

48 minutes ago, joe90 said:

Not heard that before, I run mine at 25’ and return at 21’, yes slow to react but keeps house a constant temp.

@jackruns his at a low temp and I think I need to try this. I am starting to understand my new house but because you do not get instant feed back from any changes you make and no two days are the same weather wise then you a few variables to contend with can confuse matters. My heat pump does seem to defrost quite regularly so not sure how to combat this or whether my heat pump is prone to this? Have you always run your temp so low or have you had them higher and then reduced them once you got used to the house? With you saying the house is slow to react because you have such low temps does this mean the heat pump is running longer to maintain a constant internal temp? 

Edited January 11, 2021 by Pete
To add more information

[joe90]

9 minutes ago, Pete said:

Have you always run your temp so low or have you had them higher and then reduced them once you got used to the house? With you saying the house is slow to react because you have such low temps does this mean the heat pump is running longer to maintain a constant internal temp? 

Before the heat pump was installed I ran the UFH on immersion within the buffer tank (£££££) just to get the house up to temp. It runs rarely, my problem is my room stat has a high hysteresis (3’) so I tend to manually turn it on/off now and again, but saying that the house stays a constant 20/21 degrees, we tend to use the wood burner on cold winter nights mainly because it makes us feel better, lounge gets up to 24’ ? (which er indoors loves) and it’s still noticeably warmer in the morning as well. 

[PeterW]

1 hour ago, Rich123 said:

have recently installed under floor in an anhydride screed and it has taken 4 weeks to stabilise with a flow of 55 C

That is a significant flow temperature and not needed in a decently insulated properly. It is also above the maximum flow temperature of a couple of thin screws products. 35-37°C is fine and you will get a return of around 28-30°c when balanced which on a heat pump will be pretty close to max CoP. 
 

I’ve seen a couple of your posts that refer to commercial standards and residential is usually slightly cooler as the overshoot can be more pronounced. 

[Pete]

2 minutes ago, joe90 said:

Before the heat pump was installed I ran the UFH on immersion within the buffer tank (£££££) just to get the house up to temp. It runs rarely, my problem is my room stat has a high hysteresis (3’) so I tend to manually turn it on/off now and again, but saying that the house stays a constant 20/21 degrees, we tend to use the wood burner on cold winter nights mainly because it makes us feel better, lounge gets up to 24’ ? (which er indoors loves) and it’s still noticeably warmer in the morning as well. 

I think this is the problem with your house and @ProDavein that you have log burners and this will add considerably to your heat input and thus reducing your heat pump usage compared to my house which has no log burner. My stat has a .5 degree increment but the temp of the house goes nearly a degree over the set temp if I do not turn it off manually. I have not introduced any heat into the house for over 24 hours and the temp inside has not dropped at all in this time 

[joe90]

4 minutes ago, Pete said:

I think this is the problem with your house and @ProDavei

oh it’s not a problem!!!. If we did not use the woodburner the UFH will cope, but the wood comes free, electricity does not and we love looking at a fire (cave man instinct ?).

 

7 minutes ago, Pete said:

My stat has a .5 degree increment but the temp of the house goes nearly a degree over the set temp if I do not turn it off manually.

then I suggest your hysteresis is not 0.5 degrees  

[Pete]

13 minutes ago, joe90 said:

oh it’s not a problem!!!. If we did not use the woodburner the UFH will cope, but the wood comes free, electricity does not and we love looking at a fire (cave man instinct ?).

 

then I suggest your hysteresis is not 0.5 degrees  

We had a log burner in our previous home and it was lovely but I had insulated the old cottage that much when we lit the fire (5KW) it used to send me to sleep!

Every day is a learning day! I had the number of the tech guy who stat I was using and after a call just now he is sending me an updated sender unit that is more suited to my house with a greater degree of hysteresis and a degree of self learning so what a great service that is. 

[joe90]

8 minutes ago, Pete said:

it used to send me to sleep!

? yup ?

[Pete]

1 minute ago, joe90 said:

? yup ?

How do you do that partial quoting of what people have said instead of their whole reply please? (Top Luddite here!!)

[joe90]

10 minutes ago, Pete said:

Top Luddite here!!)

Oh no your not, join the queue. I use an iPad. Touch the beginning of what you want to quote, drag to include text and a “quote’ thingy comes up. (No idea with any other devise).

[ProDave]

20 minutes ago, joe90 said:

Oh no your not, join the queue. I use an iPad. Touch the beginning of what you want to quote, drag to include text and a “quote’ thingy comes up. (No idea with any other devise).

OOOh I never knew that.

 

I had always quoted the whole message then deleted the bits of it I did not want to include.

[Gone West]

32 minutes ago, Pete said:

How do you do that partial quoting

Just highlight the bit of text you want to quote and a 'Quote Selection' box comes up.

[jack]

1 hour ago, joe90 said:

Oh no your not, join the queue. I use an iPad. Touch the beginning of what you want to quote, drag to include text and a “quote’ thingy comes up. (No idea with any other devise).

 

Works like that on PC too (as I just learned!)