UFH manifold problem

[PeterW]

Tempest should be ok - you could re-plumb it quickly to see if removing the coil helps. 
 

Add a tee to the inlet and outlet and then connect the flow from the ASHP to the top connection then on to the manifold, plumb the return from the manifold to the bottom inlet on the buffer then on to the ASHP return. The coil becomes redundant at this point, but it means the pumps need to be running roughly the same speed. 

[Nickfromwales]

@joe90 are you heating the 'buffer tank' via the coil, or are you using the coil to extract heat? The whole idea of a buffer is to add volume to the primary side so going via a coil will not achieve that. In honesty, I do remember sorting the deal out on price, but I'm pretty sure I did not spec the cylinder you bought to use as a buffer..... IIRC you followed @PeterW's install that he was on at the time where he used the same UVC as a buffer? Been a while of course.

Agree that it's a simple fix to reconfigure, but with the caveat that the system volume will increase, thus, requiring an additional volume of antifreeze when you mix ( combine ) the 2 bodies of water. You have 2 filling loops atm? One for the ASHP primary and a second for the internal heating system? Internal UFH on inhibitor only and antifreeze in just the external primary's?

 

Run the ASHP flow through to the buffer coil inlet, and come out of the coil output and feed that into the bottom ( cold in ). Then take the flow from the 'hot out' back to the ASHP as the buffer return. You then need a tee immediately off the top connection of the buffer ( the 'hot out' ) where you will pick up the flow to the manifold, and then a tee  lower down the same pipe run to pick up a return for the manifold.

Edited January 8, 2022 by Nickfromwales

[Nickfromwales]

[dpmiller]

8 hours ago, Nickfromwales said:

The whole idea of a buffer is to add volume to the primary side so going via a coil will not achieve tha

 

Doesn't the surrounding volume of water act as the additional volume? The ASHP isn't measuring any volumes, it just wants a manageable DeltaT to stop short-cycling...

[JohnMo]

If its noisy it could be pump cavitation, due to limited water pressure upstream of pump.  It will wear the impeller in the pump quite quickly.

 

To fix either increase elevation of tank upstream or install a pump.  Or a small hole in blocked bypass may fix, but would reduce temp at manifold.  Tweek temp up at cylinder to compensate.

 

Or small high efficiency CH pump set to min speed, let it run 24/7 during heat season?

[joe90]

Well done @Nickfromwales, yes it’s been a long while and so much has been going on since. I do remember the buffer was to separate both water volumes so antifreeze was only required in the ASHP loop. I always (assumed) the buffer worked like the DHW tank I.e. heat input via the coil ?. Yes I have two filling loops.

27 minutes ago, JohnMo said:

If its noisy it could be pump cavitation

It was only noisy till it was bled completely.

[joe90]

Just been to see a neighbour who is a plumber and fits ASHPs, I explained my problem and  he says most don’t have buffer tanks nowadays and work very well. So who out there has UFH without a buffer tank? I am tempted to remove the tank and see how it works,. The only problem I have is I have no wire between the room stat and the ASHP to call for heat, is there a wireless option (kinetic?). This also means I can re instal the TRV on the manifold and remove the blanking on the bypass/NRV that I installed. Opinions please.

[Nickfromwales]

4 hours ago, dpmiller said:

 

Doesn't the surrounding volume of water act as the additional volume? The ASHP isn't measuring any volumes, it just wants a manageable DeltaT to stop short-cycling...

If you feed the ASHP into a coil there is bugger all primary volume, and a far reduced medium for transferring heat energy from one ‘side’ to the other. This is being demonstrated here. 
Buffers can he volumetric or energy devices, so can be plumbed in in 2 different ways to do 2 different things.

[Nickfromwales]

53 minutes ago, joe90 said:

Just been to see a neighbour who is a plumber and fits ASHPs, I explained my problem and  he says most don’t have buffer tanks nowadays and work very well. So who out there has UFH without a buffer tank? I am tempted to remove the tank and see how it works,. The only problem I have is I have no wire between the room stat and the ASHP to call for heat, is there a wireless option (kinetic?). This also means I can re instal the TRV on the manifold and remove the blanking on the bypass/NRV that I installed. Opinions please.

I would not do this. Conversely I am in regular contact with Trevor of Cylinders2go and he has had to petition Telford to start producing small buffer tanks ( sub 100L ) as there are lots

of enquiries for these to be retrospectively installed in ASHP installs where they should have gone on on day 1.

You already have it, it’s bought and paid for, so my advice would be to plumb it in as I show above and keep the ASHP as happy as possible. 
No 2 instances are really the same, so this is general advice, but I’ll put money on it that removing it would be a bad choice. Measuring its success as is is not a fair representation of how it ‘could’ perform, so as it’s there anyway, plumb it as above and see how you get on. 
Around £150 of antifreeze will need introducing to keep the concentration levels as required. 

Edited January 8, 2022 by Nickfromwales

[dpmiller]

No discrete buffer tank here, but all heating flow passes through the 35kW coil in the bottom of the thermal store.

[PeterW]

@joe90 I’d start by replumbing the buffer and leaving everything else as is. The buffer - either plumbed how @Nickfromwales or I said will then just become part of the system  and you’ll have a lot more system content to be flowing around but first off it will either prove or disprove you have an issue. 
 

 

[joe90]

2 minutes ago, PeterW said:

@joe90 I’d start by replumbing the buffer and leaving everything else as is. The buffer - either plumbed how @Nickfromwales or I said will then just become part of the system  and you’ll have a lot more system content to be flowing around but first off it will either prove or disprove you have an issue. 
 

 

Thanks mate, I am giving it some thought before I dive in but I like your idea (might be easier for my plumbing). My only issue is letting the room stat call for heat from the ASHP rather than just starting the manifold pump as I have no direct wiring (hence my new thread about remote switching. ) I am ploughing through my old wiring diagram to get my head around what I did ?.

 

i was wondering if I did this below, my worry is when heating is required if I have to heat the buffer tank before the manifold gets the heat then heating is delayed, the diagram below allows the buffer to add the volume and act as a bypass and the heat from the ASHP will get to the manifold quicker. Am I mad (don’t answer that).

 

 

[Nickfromwales]

If it’s a stainless coil then fine, but copper coils should never be left open to atmosphere as the insides get condensation and corrode badly over time, hence my seemingly unnecessary inclusion of it in my drawing. Fwiw, I would still include the coil in the pathway, even if it’s just teed in one side ( highest connection ) and capped off at the lower so it stays ‘wet’. 
The way it’s drawn by you @joe90 is an energy buffer arrangement, and will do as you suggest eg allow heat to the path of least resistance, so when hearing from ‘cold’ the lions share of heat energy will go almost directly to the UFH ( with any residual head diverting / bypassing through the buffer and back to the HP ). Only pitfall is heat has to creep all the way down the buffer to the very bottom to escape as return to the HP.

Have the expansion vessel teed into the return down low so it’s on the coolest pipework possible ( or you get a wasteful heat bomb ). 

[ProDave]

5 hours ago, joe90 said:

Just been to see a neighbour who is a plumber and fits ASHPs, I explained my problem and  he says most don’t have buffer tanks nowadays and work very well. So who out there has UFH without a buffer tank?

Mine has no buffer, because when I plumbed it I didn't know I should.  Last house had UFH from an oil boiler without a buffer as well.

 

Present house has ASHP "leaving water temperature" regulating the UFH temperature mostly.  The blending valves on the manifolds protect the UFH pipes from the slug of hotter water left in the ASHP when it switches from DHW mode to heating mode.

[joe90]

19 minutes ago, Nickfromwales said:

If it’s a stainless coil then fine, but copper coils should never be left open to atmosphere as the insides get condensation and corrode badly over time, hence my seemingly unnecessary inclusion of it in my drawing. Fwiw, I would still include the coil in the pathway, even if it’s just teed in one side ( highest connection ) and capped off at the lower so it stays ‘wet’. 
The way it’s drawn by you @joe90 is an energy buffer arrangement, and will do as you suggest eg allow heat to the path of least resistance, so when hearing from ‘cold’ the lions share of heat energy will go almost directly to the UFH ( with any residual head diverting / bypassing through the buffer and back to the HP ). Only pitfall is heat has to creep all the way down the buffer to the very bottom to escape as return to the HP.

Have the expansion vessel teed into the return down low so it’s on the coolest pipework possible ( or you get a wasteful heat bomb ). 

That makes perfect sense (and I understood it ?) just need to sort my wiring out (and buy shed loads of antifreeze). 

[JohnMo]

Bit confused by this thread, the issue is not short cycling of the ASHP, which seems to what everyone is trying to fix.  Instead the issue seems to be hot water not being drawn into the pump suction.

 

Nick's drawing would allow the pump in the ASHP to push hot water the the UFH manifold pump, but needs the whole system with anti freeze, £150 mentioned.

 

A small pump would fix issue, without a major replumb, or am I missing something?

[joe90]

32 minutes ago, JohnMo said:

the issue is not short cycling of the ASHP,

Correct, it’s hot water not reaching the UFH manifold.

33 minutes ago, JohnMo said:

A small pump would fix issue, without a major replumb,

No, there is a pump from the ASHP and another at the UFH manifold already.

 

shame about spending £150 on antifreeze ? but hey I don’t have to pay a plumber to do the work ?‍♂️

[JohnMo]

But the pump at the ASHP is pumping around the coil in the cylinder and cannot affect what's happening at the UFH pump manifold.  The pump at the manifold is trying to suck hot water from the cylinder and and around the UFH loops, but cannot as the required suction head is not adequate.

 

My system is exactly the same as you're got, with the cylinder 3m above the the UFH manifold, have no issues, as I am giving the pump at manifold the required suction head.

 

So all you need to do is increase the suction head.  Either raise the cylinder to increase suction head available at the UFH pump or install pump.

[PeterW]

4 minutes ago, JohnMo said:

My system is exactly the same as you're got, with the cylinder 3m above the the UFH manifold, have no issues, as I am giving the pump at manifold the required suction head.

 

So all you need to do is increase the suction head.  Either raise the cylinder to increase suction head available at the UFH pump or install pump.

No such thing as suction head in this system as it’s all ground floor, plus the pump should be more than adequate and in any case these are all 5 or 6m head pumps. 

[joe90]

1 hour ago, JohnMo said:

without a major replumb,

Less than 1 metre of 22mm pipe and a few bends and joints, hardly major, just a re jig.

[JohnMo]

17 minutes ago, PeterW said:

No such thing as suction head in this system as it’s all ground floor, plus the pump should be more than adequate and in any case these are all 5 or 6m head pumps. 

All centrifugal pumps require a positive suction head, if they don't have it they cavitate and do not push flow forward..  the 5 or 6m head is the discharge head.

[joe90]

3 minutes ago, JohnMo said:

All centrifugal pumps require a positive suction head,

I am not an expert but mine is pressurised to 1 or 2 bar, this surely stops cavitation (as long as enough water is available) I do know of cavitation with outboard motor propellers!

[PeterW]

8 minutes ago, JohnMo said:

All centrifugal pumps require a positive suction head, if they don't have it they cavitate and do not push flow forward..  the 5 or 6m head is the discharge head.

Need to probably clarify what you mean here as a circulation pump in a sealed system can be mounted half way up a wall or on the first floor of a house and still drive the flow of the system. If not, they would need to be mounted at the lowest point of the system to actually work. 

[JohnMo]

30 minutes ago, PeterW said:

Need to probably clarify what you mean here as a circulation pump in a sealed system can be mounted half way up a wall or on the first floor of a house and still drive the flow of the system. If not, they would need to be mounted at the lowest point of the system to actually work. 

In a sealed system the pressure within the system gives the suction head.  An open vented system, the suction head comes the loft mounted cold tank, so as you say the pump can be mounted anywhere in the system.

 

The suction head required increases with flow and generally in the range of just over 1 to 2m.

 

 

[Nickfromwales]

5 hours ago, JohnMo said:

or am I missing something?

Hi. 
Yes, I re read this a couple of times before dipping my toe here.   The transfer rate of heated water from the coil ( note : 5kw ASHP ) to the surrounding body of water in the vessel is insufficient in linear ( attempts to be linear ) output. Therefore we are advising here that the buffer ( a small UVC in this instance ) becomes part of the whole single system. 
In my pic there will be both hydraulic separation, initially, and then energy buffering second eg when the house comes up to temp.