Bin the Buffer?

[Mr Blobby]

Our heating system is currently designed for ground floor UFH and ASHP.  So far so good.  It has always been in the plan to fit a buffer tank.  I'm now beginning to re-think the buffer tank and remove zoning.

 

To give some context, we have a block house on insulated slab and <3kW peak heating load.  Floor temperature will change very slowly hence individual zone control seems to make little sense, even with solar gain moving around the house.  We have about 600 metres of UFH pipe in the floor at 200 centres.

 

I see from discussion here that there is a school of thought that questions the conventional wisdom of installing a buffer tank to stop short cycling because there is already sufficient volume in system. And so it may be more efficient to remove the buffer tank all together and connect the ASHP diretly to the UFH manifold.  Is this a contentious area, or is this well established?

 

If we delete the buffer tank, are we then limited to a maximum of one UFH manifold?  I am toying with the idea of another manifold on the First floor, but only for some additional cooling, or maybe heating under bathrooms.

 

What about hydraulic separation?  I would need a pump at the manifold of course, so what if this manifold pump runs at different flow rate than the ASHP pump? How does that work without seperation?

 

If I did decide to add another manifolfd for some UFH upstairs, would that mean a buffer tank must be included?

 

Our plumber will be horified at the suggestion of dropping the buffer tank, so I need to be certain of this before I give him his next heart attack.

 

[JohnMo]

Single zoned heating system is fine, multiple manifolds fine. You need to check the volume flow and head loss for the circulation pump.

 

But we are on 300mm centres and have 7 loops in the floor plus a further loop for a fan coil. We actually have our floor loops turned up pretty high. So the heat is churning around 1m³ per hour.

 

Once you have checked flow rates against pressure drop, if all is fine no buffer is needed and no additional pumps or mixers. Fan coils should run.fine a UFH flow temperature.

21 minutes ago, Mr Blobby said:

buffer tank to stop short cycling because there is already sufficient volume in system

Buffer is generally needed if you zone to the house to keep minimum engaged water volume and minimum flow rate for the heat pump.

22 minutes ago, Mr Blobby said:

I would need a pump at the manifold of course

No you wouldn't 

23 minutes ago, Mr Blobby said:

decide to add another manifolfd for some UFH upstairs, would that mean a buffer tank must be included?

Possibly less need for a buffer. But bedrooms and UFH is a waste of time. We have it wish I had just installed fan coils.

 

You need to start with heating design then decide on a need for primary and secondary loops. Not the other way around.

 

Start with you heat losses, then emitters, the then pipe to the heat pump, do you pressure loss and flow calcs, then you know where you are. If and I may - bad idea you will end up in a muddle.

[Mr Blobby]

26 minutes ago, JohnMo said:

No you wouldn't [need a pump at the manifold]

 

So the water pump in a panasonic heat pump can push water all the way round the ufh loops?  That would be good.  For some reason I just imagined it would be too feeble. 

 

26 minutes ago, JohnMo said:

You need to start with heating design then decide on a need for primary and secondary loops. Not the other way around.

 

We know our heat loss calcs and 95% ruled out UFH upstairs except possibly to add a bit of cooling.  Just in case.

Agree that fan coils better, maybe need to think about this some more.  Maybe one or two upstairs above dew point at UFH temps to avoid condensate drain.  External blinds will hopefully control the worst of any overheating but we only have this one chance to put the pipes in now for extra cooling, just in case.

 

26 minutes ago, JohnMo said:

We actually have our floor loops turned up pretty high. So the heat is churning around 1m³ per hour.

 

So your ashp water pump controls flow rate through the UFH loops?

 

 

... Its funny how the decision to install a buffer tank was cast in stone two years ago but is now, like so mamy other decisons, going to change.  Keeping it simple and running a single zone without any actuators or additional pumps is very appealing.  Apart from the cost, it just seems like a better way to do it. 

Edited September 8 by Mr Blobby

[JohnMo]

26 minutes ago, Mr Blobby said:

So the water pump in a panasonic heat pump can push water all the way round the ufh loops?  That would be good.  For some reason I just imagined it would be too feeble

You cannot assume you need to get pump curves from the manual. Calculate the head loss (system pressure drop) at yourq flow rate required. But generally they are not feeble.

 

Keeping it simple pays off. At 9 to 12 degs outside, when the heat pump is running, the CoP is mid 6s. That includes everything electrical in the system. So way cheaper than gas or anything else.

[MikeGrahamT21]

Have a look at this guys blog, he did a similar thing and has lots of data both with and without buffer: https://protonsforbreakfast.wordpress.com/

[JackofAll]

On 08/09/2024 at 17:37, Mr Blobby said:

 

So the water pump in a panasonic heat pump can push water all the way round the ufh loops?  That would be good.  For some reason I just imagined it would be too feeble. 

 

 

We know our heat loss calcs and 95% ruled out UFH upstairs except possibly to add a bit of cooling.  Just in case.

Agree that fan coils better, maybe need to think about this some more.  Maybe one or two upstairs above dew point at UFH temps to avoid condensate drain.  External blinds will hopefully control the worst of any overheating but we only have this one chance to put the pipes in now for extra cooling, just in case.

 

 

So your ashp water pump controls flow rate through the UFH loops?

 

 

... Its funny how the decision to install a buffer tank was cast in stone two years ago but is now, like so mamy other decisons, going to change.  Keeping it simple and running a single zone without any actuators or additional pumps is very appealing.  Apart from the cost, it just seems like a better way to do it. 

Take it you didn't opt for the pre plumbed panasonic tank with built in buffer.

[Mr Blobby]

On 12/09/2024 at 14:43, JackofAll said:

Take it you didn't opt for the pre plumbed panasonic tank with built in buffer.

 

No.  I remember our M and E consultants tried to persuade to install a combined buffer/DHW tank some time ago.  I didn't like the idea then and still don't.  Call me old fashoined but I like to keep these things seperate.  And also at 285L DHW maximum capacity is perhaps a little smaller than we would like. 

 

And now it looks like we will bin the buffer all together and go for a single zone UFH.  

 

[Mr Blobby]

Our builder keeps telling me I should put some UFH loops under first floor bathrooms to have a warm floor.  Should I?  And if so, then how is that connected when running an otherwise very simple single-zone system with no additional pumps?  A second manifold in series?

[AppleDown]

5 minutes ago, Mr Blobby said:

Our builder keeps telling me I should put some UFH loops under first floor bathrooms to have a warm floor.  Should I?  And if so, then how is that connected when running an otherwise very simple single-zone system with no additional pumps?  A second manifold in series?

We're going electric in the first floor ensuite. Easier to control - especially when the other half wants warm floor to wake up to!

[JohnMo]

11 minutes ago, AppleDown said:

We're going electric in the first floor ensuite. Easier to control - especially when the other half wants warm floor to wake up to!

If was doing it again I would do water UFH at 100mm centres in bathrooms AND electric.  Water supplies the bulk of the heating in winter, the electric makes the floor feel warm if you want

[Super_Paulie]

I have my bathroom towel rad as the bypass radiator for my UFH. I loop the return from this rad up and down in an UFH fashion before it leaves the room and back to the boiler. I'm looking to get a radiator that also heats up with electric for the months I don't use the underfloor, best of both worlds. 

[JohnMo]

58 minutes ago, Super_Paulie said:

I'm looking to get a radiator that also heats up with electric

Convert to dual fuel with Termo One thermostatic heat element 

[Super_Paulie]

3 hours ago, JohnMo said:

Convert to dual fuel with Termo One thermostatic heat element 

 

That's what I was looking at for when I get round to replacing the rad for a nice one, just bring it on with a timer or something. What's your experience with it John, effective?

[JohnMo]

Mine are only 200W elements so ok for towels, but not really heating the room, just adding a little heat. But bigger wattage are available. They come with a tee piece to dual fuel. But mine are just electric.

 

I use a Termo TTIR, thermostat and timer.

[Dave Jones]

14 hours ago, JohnMo said:

If was doing it again I would do water UFH at 100mm centres in bathrooms AND electric.  Water supplies the bulk of the heating in winter, the electric makes the floor feel warm if you want

 

i did think the same but its massively more costly and hassle to do underfloor for 1st floor. In the end its not needed, if anything upstairs is too warm at night even with heating on fallback after 6pm.

 

Bathrooms we have electric wet rads all controlled by home assistant as somewhere to dump spare solar/free sessions and ride the cheap rate sessions. Karndean floor is not cold once ambient air temp is 21 anyway.

[Mr Blobby]

On 19/09/2024 at 07:24, Dave Jones said:

its massively more costly and hassle to do underfloor for 1st floor. In the end its not needed, if anything upstairs is too warm at night even with heating on fallback after 6pm.

 

For us we have screed going on top of hollowcore slabs so easy to lay the UFH pipe.  I just don't know how we'd plumb in a second manifold without adding another pump.

 

In our passive house I agree that first floor UFH is probaply unecessary.  Our builder struggles to understand this however, and keeps telling me we should put the UFH pipes in the bathroom floor so the tiles aren't cold in the morning.  Is he right?  Will the floor be cold? 

[SteamyTea]

8 hours ago, Mr Blobby said:

Is he right?  Will the floor be cold

They will be close the the mean air temperature, which is about 18K lower than body temperature.

The problem is that tiles conduct heat well, so they may feel cold.

Will also help water evaporate away quickly, though this can cause discolouration of the grout (ask other about the best stain resistance grout).

[JackofAll]

On 23/09/2024 at 12:06, Mr Blobby said:

 

For us we have screed going on top of hollowcore slabs so easy to lay the UFH pipe.  I just don't know how we'd plumb in a second manifold without adding another pump.

 

In our passive house I agree that first floor UFH is probaply unecessary.  Our builder struggles to understand this however, and keeps telling me we should put the UFH pipes in the bathroom floor so the tiles aren't cold in the morning.  Is he right?  Will the floor be cold? 

Currently living in house, no electric and no water connected, we're a solid 19 degrees first thing every morning, If you built a passive house probably wouldn't be too concerned about UFH on either floor. just use slippers 🙂

Edited September 24 by JackofAll

[Dave Jones]

On 23/09/2024 at 12:06, Mr Blobby said:

 

For us we have screed going on top of hollowcore slabs so easy to lay the UFH pipe.  I just don't know how we'd plumb in a second manifold without adding another pump.

 

In our passive house I agree that first floor UFH is probaply unecessary.  Our builder struggles to understand this however, and keeps telling me we should put the UFH pipes in the bathroom floor so the tiles aren't cold in the morning.  Is he right?  Will the floor be cold? 

 

if you have budget, id go for electric  underfloor in bathrooms so you can use it in the summer when you dont want the rest of the heating on. As i mentioned earlier with karndean its not cold anyway, ceramic tiles are different of course.