Nibe ASHP and radiators

[Jde00]

Hi

 

I have a NIBE F2040 ASHP in a new build. The house is very well insulated and air tight. The ASHP finally works really well.

We do have issues with inconsistent heating.

 

The current set up is as follows: the 3-storey house is set up as a single heating circuit. Each room has a low-temperature radiator sized according to the BTUs needed for that room. Most radiators are sized correctly except three (see below). The radiators are connected to a multibore plumbing system whereby a manifold distributes the heating medium to all radiators (i.e. as I understand this, they aren't connected in a serial circuit like most heating systems I know). These radiators don't have TRV and instead of two lockshield valves, one in and one out. All radiators were set up with these valves fully open. The only temperature sensor in the house is located in the hall downstairs, between the kitchen and the front door. Arguably this is the coldest corner in the house, even in the summer.

 

Now, the issue we have:

 

* Downstairs is consistently colder than upstairs, while upstairs is almost always way hotter than it needs to be. Our compromise is to have the ASHP climate set at 19°C which means downstairs is roughly 20°C and upstairs is roughly 22°C.

 

* The problem though is that 3 rooms in the house are consistently extreme

- Entrance hall and living room are consistently colder. I don't think it's an issue with the radiator size as the temperature, taken with an infrared thermometer, is a couple of degrees colder than the other radiators

- Small studio room is always consistently way way hotter than it needs to be. Sometimes if I'm inside the temperature gets to 25°C.

 

 

this doesn't seem a balancing issue as my understanding is that all radiators should get the same flow rate independently of each other.

Thoughts? 

 

cheers!!

[ragg987]

It sounds like a balancing issue. You could try to reduce the flow to upstairs radiators, this should increase relative flow downstairs. To prove this throttle back the upstairs radiators to very low flow, give it a few hours or a day and check the room and radiator temperatures. Once proven case of trial and error to get the right balance.

 

My understanding of radiator balancing is to aim for a constant temperature drop between in and out flows. This would assume the radiators are sized correctly for each room. This does not factor in external events e.g. sunny room or personal preferences. So a degree of adjustment from the ideal would still be required.

[Jde00]

thanks - my understanding was that balancing only really applies to radiators connected on a circuit... by balancing the first one in the series you allow more or less flow rate into the second one and so on. With these radiators all connected to a manifold, each radiator effectively acts like its own circuit so whether one is fully open or close should have no effect on every other radiator.

 

My that's my understanding, I'm quite possibly wrong as my background is in human circulation, rather than home central heating systems

[ProDave]

Ballancing is to get the rate of temperature rise the same in all rooms.  So even if the radiators have been "sized" correctly there will be differences as nothing is ever like the theory exactly.

 

So the rooms that are getting too hot, you need to turn down one of the lockkshield valves a bit to reduce the flow to that radiator which should reduce it's temperature a bit.  It will be a long process of make an adjustment and wait a day or more to see the change.

 

Reducing the flow in the hot rooms should increase the flow in the rest and eventually you will get to a point where the cold rooms have more flow and heat up better.

 

Alternatively just fit TRV's to every radiator and let them regulate the room temperature but probably not fit a TRV to the living room being the coldest room.

[Jde00]

Thanks - I'm going to try this out. I'll go one room a day. Funnily enough, I completely closed down the radiator in the study and the temperature is still 22-23°C. The room is right next door to the water tank and I believe is surrounded by all pipes (the ones going to the ASHP outside) and the manifold that distributes the water to all radiators. I'll follow this but it could be I don't need a radiator here at all! 

 

I can't really mess anything up as I can just return to the way it was before by opening up all valves.

 

I assume installing TRVs require me calling a plumber?

[ragg987]

Ensure the dhw tank and pipes are well insulated to reduce over heating the study. You could also box in the manifold.

 

Don't forget this process is iterative, if you reduce the flow in one rad it will increase the flow in the others so you may have to go round the rooms a couple of times to get it right.

 

One other factor would be to check the speed of the circulator pump(s) on the heating circuit. If you have more than one pump then you can fiddle with the speed setting to control flow from one manifold to another.

 

Trv is for a plumber if you are not skilled. Bit like open heart surgery ?. Might require draining the rad.

[Jde00]

9 hours ago, ragg987 said:

Ensure the dhw tank and pipes are well insulated to reduce over heating the study. You could also box in the manifold.

 

Don't forget this process is iterative, if you reduce the flow in one rad it will increase the flow in the others so you may have to go round the rooms a couple of times to get it right.

 

One other factor would be to check the speed of the circulator pump(s) on the heating circuit. If you have more than one pump then you can fiddle with the speed setting to control flow from one manifold to another.

 

Trv is for a plumber if you are not skilled. Bit like open heart surgery ?. Might require draining the rad.

 

To be absolutely honest I have no freaking idea where the maniford is. I would guess that it is either under the studio floor or by the cupboard where the SMO and water tank are. I've asked the builders and plumbers and no one could tell me. 

[Jde00]

Hi all,

 

Reporting back from testing for a couple of days.

I seem to have no margin of action with these radiators. I begin by closing the lockshield valve entirely, let the radiator cool down.

Then I open in 1/4 increments, and the first two quarter turns I hear a hissing noise which I assume is the heating medium flowing through. I can continue to 3 quarters and the hissing noise stops, let the radiator stabilise but it gets hot, almost as hot as if the lockshield valve was fully open. I can't find a sweet spot where the radiator is functional but slightly colder without making a loud hissing noise.

 

I'm really puzzled with all of this. I'm thinking of calling a ASHP installer to seek advice on the whole ASHP+radiator central heating system.

 

Could it be that the rooms that are cold have undersized radiators and that's why they are cooler to the touch to begin with, rather than a problem with balancing?  I suppose I could take temperature readings of the water coming in rather than of the radiator top.

[Ferdinand]

The rads are bled, aren't they?

 

(Tops will be cold if not)

[Gone West]

7 hours ago, Jde00 said:

Then I open in 1/4 increments, and the first two quarter turns I hear a hissing noise which I assume is the heating medium flowing through. I can continue to 3 quarters and the hissing noise stops, let the radiator stabilise but it gets hot, almost as hot as if the lockshield valve was fully open. I can't find a sweet spot where the radiator is functional but slightly colder without making a loud hissing noise.

Let the radiator try to get hot on the first 1/4 turn and see if the hissing stops when it's hot. There are additives that can be added to CH systems to stop noise.

[Jde00]

8 hours ago, Ferdinand said:

The rads are bled, aren't they?

 

(Tops will be cold if not)

 

53 minutes ago, PeterStarck said:

Let the radiator try to get hot on the first 1/4 turn and see if the hissing stops when it's hot. There are additives that can be added to CH systems to stop noise.

 

Thanks

Yes, the radiators are bled and have no trapped air.

I will try if letting the hiss stops when the radiator is hot.  

[Jde00]

I think I got it !!!

Changed the heating curve to a -1 degree offset. Shut off the studio radiator off completely and restricted the guest bedroom and the landing radiators to as low as I could get it without the rads making the hissing noice. Set the heating temperature aim in the ASHP to 21 degrees. 

 

Voila! downstairs is 21 degrees, floors aren't stone cold anymore, upstairs is decently warm 21-22 degrees, office is slightly colder to 20 when unoccupied but as soon as I close the work and get to work it goes up to 22-23 which I can deal with by opening the window a tiny bit.

 

I realise the temperature right now is not as cold as previous days but it feels as though the heating has stabilised somewhat and I'm not loosing heat by reducing the temperature aim to silly low levels. I've also looked at the degree minute graph and it looks much more stable in the last 2 days or so.

 

Let's see how long it lasts!!

[Oldsteel]

On 15/01/2021 at 00:56, Jde00 said:

Hi all,

 

Reporting back from testing for a couple of days.

I seem to have no margin of action with these radiators. I begin by closing the lockshield valve entirely, let the radiator cool down.

Then I open in 1/4 increments, and the first two quarter turns I hear a hissing noise which I assume is the heating medium flowing through. I can continue to 3 quarters and the hissing noise stops, let the radiator stabilise but it gets hot, almost as hot as if the lockshield valve was fully open. I can't find a sweet spot where the radiator is functional but slightly colder without making a loud hissing noise.

 

I'm really puzzled with all of this. I'm thinking of calling a ASHP installer to seek advice on the whole ASHP+radiator central heating system.

 

Could it be that the rooms that are cold have undersized radiators and that's why they are cooler to the touch to begin with, rather than a problem with balancing?  I suppose I could take temperature readings of the water coming in rather than of the radiator top.

Glad you have fixed it - looked like a balancing issue. I have a traditional system - but had the same issue with upstairs taking the lions share of heat. Went through a balancing exercise as described earlier and now its fine. Although downstairs rads are closer to the boiler, I suspect I may have microbore pipes downstairs (through a manifold) and copper 15mm upstairs but I am not ripping up floors just to find out. To comment on your earlier experience, those lockshield valves don't regulate flow in a linear fashion, they are designed to be on or off. My experience is that the first full turn is the difference between full on and full off. So the 1/4 turn (the hissing noise is the valve restricting the flow) would be about 25% open. This may vary dending on the type of valve of course.

[Jde00]

7 minutes ago, Oldsteel said:

Glad you have fixed it - looked like a balancing issue. I have a traditional system - but had the same issue with upstairs taking the lions share of heat. Went through a balancing exercise as described earlier and now its fine. Although downstairs rads are closer to the boiler, I suspect I may have microbore pipes downstairs (through a manifold) and copper 15mm upstairs but I am not ripping up floors just to find out. To comment on your earlier experience, those lockshield valves don't regulate flow in a linear fashion, they are designed to be on or off. My experience is that the first full turn is the difference between full on and full off. So the 1/4 turn (the hissing noise is the valve restricting the flow) would be about 25% open. This may vary dending on the type of valve of course.

 

 

Very good point, I'd agree with that observation on the lockshielf valve based on the temperature achieved. As I said my sweet spot was very very small. Probably worth installing TRVs even though the heat pump manufacturer doesn't recommend them.