Buffer tank connections

[IanR]

33 minutes ago, JohnMo said:

Your inlet outlet temp for flow and return?  Your flow in-out should be the same temperature, if working as you describe if no mixing is occurring.

 

So your temps are?

 

Equal, within a degree, at the times they should be. Unfortunately the thermocouples I have are +/-0.5° accuracy. But that's close enough for me.

 

How about yours? I hadn't appreciated you had a 4P buffer installed. Is it designed for stratification? What's the model number? what ASHP have you got attached to it? and how are you controlling it? 

Edited March 12, 2023 by IanR

[dpmiller]

12 hours ago, IanR said:

and the diagrams of the internal porting that came in the paperwork

 can we see these please?

[IanR]

10 minutes ago, dpmiller said:

 can we see these please?

 

To hand, I have the labelling on the tank itself, which this is a photo of:

 

 

In the paper work, somewhere, there is the same image but with a little more detail. It's only used in a schematic showing the plumbing options, so isn't intended to be a set of engineering drawings of the internal details, but if I find it I will post it.

[Dave Jones]

excuse my ignorance, can a buffer tank also have an immersion to blast it up to say 70c when cheap/free electric is available ? 

 

Do they come with a a mixer to drop the temp of delivered hot water to whatever the ufh is set at ?

[JohnMo]

That's a good cylinder design, you have, that possibly explains why there is always stratification in your buffer. 

 

It's a pity they are not all designed that way.  Most are designed with a compression fitting swaged or brazed to the cylinder shell and nothing to actively promote stratification, just an empty cylinder full off water swirling and sloshing about.

 

Cannot measure my temps as I am away for a few days.  But I have a 2 port design with oversized tees to give hydraulic sepereration. Mine is on a low flow temp gas boiler at present.  When the heat pump is installed there will be no buffer.

[sharpener]

 

19 hours ago, sharpener said:

From what I remember of undergraduate fluid dynamics it would seem very unlikely that with radial inlet ports you would get streamline flow in the tank. Then with a low aspect ratio tank the turbulence would ensure pretty thorough mixing. @IanR does mention and post some diagrams that show internal design features which would help, I would be surprised if these are fitted at the bottom of the market but Advance and Trident might, do we know? (I would go for a fish-tail nozzle tangential to the side of the tank and one or more perforated separator plates.)

 

 

 

2 hours ago, IanR said:

 

To hand, I have the labelling on the tank itself, which this is a photo of:

 

 

In the paper work, somewhere, there is the same image but with a little more detail. It's only used in a schematic showing the plumbing options, so isn't intended to be a set of engineering drawings of the internal details, but if I find it I will post it.

 

 

42 minutes ago, JohnMo said:

That's a good cylinder design, you have, that possibly explains why there is always stratification in your buffer. 

 

It's a pity they are not all designed that way.  Most are designed with a compression fitting swaged or brazed to the cylinder shell and nothing to actively promote stratification, just an empty cylinder full off water swirling and sloshing about.

 

 

Thanks @IanR that clearly represents some effort on the part of Nibe. AFAIR I have seen this pic before, might have been posted by you in another thread as I searched the Nibe web site yesterday for the internals but couldn't find it.

 

I assume the swept bends are the inlets but for clarity can you confirm which way round the connections are? You can direct flow over quite a long distance - it's an old fallacy that you can direct "suck" to any useful extent but I have often seen pipework details that attempt to achieve it.

 

Agree with @JohnMo less likely to find anything similar at the low end. I will ask CoolEnergy what they have when I talk to them next week, though their 60l tank is very squat to look at.

Edited March 12, 2023 by sharpener

[IanR]

4 hours ago, Dave Jones said:

excuse my ignorance, can a buffer tank also have an immersion to blast it up to say 70c when cheap/free electric is available ? 

 

Yes, there are buffers that make provision for an immersion and I believe that was an option on the Nibe. Standing losses will increase significantly if you hold the buffer at 70°, rather than flow temp, circa 35°C, only when it's running and you'll need to supply the extra plumbing to blend it down before going into your UFH. The Cool Energy buffer in the first post of this thread shows a tapping for an immersion.

 

3 hours ago, sharpener said:

I searched the Nibe web site yesterday for the internals but couldn't find it.

 

Nibe sell through an Approved dealer Network and appear to actively discourage others from using their products. It seemed their Approved dealers can only install the Nibe products in an agreed configuration. When I asked to do something slightly different it needed a discussion with the Nibe UK service manager to get approval. The backup support to the dealers was first class and they were very open to doing things differently, as long as they felt it wouldn't impact the core performance of their systems.

 

My buffer is a Nibe UKV 200, and does not match the buffer on their website, under that name. There's at least 20 different configurations available for 2, 3 and 4 port versions, with different temp sensor and immersion pockets etc. None of this is advertised to the public as it's only available to the Approved installers.

 

3 hours ago, sharpener said:

I assume the swept bends are the inlets but for clarity can you confirm which way round the connections are?

 

The left hand ports are the feed and return from the ASHP and the right hand ports are the feed and return to the emitters.

 

3 hours ago, sharpener said:

I will ask CoolEnergy what they have when I talk to them next week, though their 60l tank is very squat to look at.

 

I know nothing about the CoolEnergy product, but it struck me how low the external hot ports appear, but perhaps the cylinder doesn't go all the way to the top of the enclosure or they have some trick porting to speed up the time it takes to get hot water to the emitters.

 

4 hours ago, JohnMo said:

But I have a 2 port design with oversized tees to give hydraulic sepereration. Mine is on a low flow temp gas boiler at present. 

 

With respect, I won't be taking that as evidence of correctly designed and matched 4P buffers having no stratification.

Edited March 12, 2023 by IanR

[sharpener]

1 hour ago, IanR said:

 

Yes, there are buffers that make provision for an immersion and I believe that was an option on the Nibe. Standing losses will increase significantly if you hold the buffer at 70°, rather than flow temp, circa 35°C, only when it's running and you'll need to supply the extra plumbing to blend it down before going into your UFH. The Cool Energy buffer in the first post of this thread shows a tapping for an immersion.

 

 

Hence the traditional siting of the HW tank in the airing cupboard. My grandparents had a completely unlagged galvanised tank with the immersion htr on a peak rate supply. It much have cost a fortune to run but they always said it kept the landing warm(!)

 

But I am not sure that is the intention behind an immersion htr boss on a buffer, it may be more as an auxiliary heater for severely cold weather, some HPs have them integral but some don't.

 

1 hour ago, IanR said:

I know nothing about the CoolEnergy product, but it struck me how low the external hot ports appear, but perhaps the cylinder doesn't go all the way to the top of the enclosure or they have some trick porting to speed up the time it takes to get hot water to the emitters.

 

Elsewhere CoolEnergy say you can use it also as the expansion tank, this reduces the capacity to 45l, maybe this explains it.

Edited March 12, 2023 by sharpener

[ReedRichards]

My buffer tank has an immersion heater fitted, although it has never been connected.  It's also integrated with (underneath) the hot water cylinder which makes it short and squat and probably the opposite of the optimal configuration.  I wonder if I could add a tall thin buffer, bypass two ports on my existing buffer and just use it as a volumiser?

[sharpener]

What does your present setup not achieve, and do you need a buffer at all?

 

@IanR's list posted 1750 last Friday seems a good checklist for this.

 

If not then yes, connecting the existing tank as a volumiser in the return line might give an improvement.

[ReedRichards]

One thing that my present setup does not achieve is circulation through the heating system when the heat pump is off.  There is a short period of a few minutes when both the water pumps are on whilst the heat pump is not active.  But as soon as the heat pump stops pumping heat then the water pump for the central heating goes off.

 

I would have to strip off some insulation to measure the pipe temperatures to and from the buffer; I haven't got around to doing that so I don't know if I get mixing inside the buffer or not.  Even then, I have only the one thermometer and measuring a temperature differential is quite difficult because temperatures very rarely hold constant.    

 

Also, I could not use the existing tank alone as a volumiser because the water pump inside the ASHP would have to pump water through the stopped central heating water pump in order to defrost.     

[sharpener]

9 minutes ago, ReedRichards said:

One thing that my present setup does not achieve is circulation through the heating system when the heat pump is off.  There is a short period of a few minutes when both the water pumps are on whilst the heat pump is not active.  But as soon as the heat pump stops pumping heat then the water pump for the central heating goes off.

No quick fix for this. How is the ch pump controlled, is it from the HP itself or from the system call for heat and can you change it somehow?

 

Is there a programmable run-on setting? Can you wire the ch pump to be on all the relevant time and if necessary put an NRV in parallel with the HP?

 

12 minutes ago, ReedRichards said:

Also, I could not use the existing tank alone as a volumiser because the water pump inside the ASHP would have to pump water through the stopped central heating water pump in order to defrost.     

 

That's easier, you can put an auto bypass valve across F and R, after the volumiser but before the ch pump. It may be necessary anyway if your rads all have TRVs. That is the layout I am contemplating.

 

[ReedRichards]

The first thing my heat pump did, about a day after it was installed, was to come to a complete stop with an error message.  It turned out this was due to a "blocked" filter causing insufficient flow and was easily rectified by the installer.  But given the sensitivity to flow, I worry that an auto-bypass valve might cause the flow rate error before it was able to operate.  Also, does the flow reverse for defrosting, or is that just my fanciful imagination?

 

The central heating pump causes enough pipe and radiator noise that I would not want it running when it was not necessary to do so.  I'm not aware that I can program a run-on but I'll look into that.  But is it desirable?  My heat pump is limited to 20 minute cycles and if it goes off after 15 minutes, as it often does, do I really benefit from circulating water round the heating system rather than leaving it to stand?

[JamesPa]

23 minutes ago, ReedRichards said:

Also, does the flow reverse for defrosting, or is that just my fanciful imagination?

The refrigerant flow reverses for defrosting but not the water flow.

[IanR]

36 minutes ago, JamesPa said:

The refrigerant flow reverses for defrosting but not the water flow.

 

Now I'd assumed the water flow reverses, pulling heat out the emitter circuit or buffer (or UVC when on DHW heating cycle)

 

I can't see there'd be sufficient energy in the "water" in the condenser, to defrost the ASHP, without pulling warm water back out of the house.

[JamesPa]

Just now, IanR said:

Now I'd assumed the water flow reverses, pulling heat out the emitter circuit or buffer (or UVC when on DHW heating cycle)

 

I can't see there'd be sufficient energy in the "water" in the condenser, to defrost the ASHP, without pulling warm water back out of the house.

The water flow doesn't need to reverse for this to happen.  The water can keep circulating in the same direction through the heat exchanger in the hp and, provided the refrigerant is colder than the water, heat will transfer to the refrigerant.   Same as when the unit is in cooling mode.

[IanR]

15 minutes ago, JamesPa said:

The water flow doesn't need to reverse for this to happen.  The water can keep circulating in the same direction through the heat exchanger in the hp and, provided the refrigerant is colder than the water, heat will transfer to the refrigerant.   Same as when the unit is in cooling mode.

 

Ah, ok, you're not saying the water flow is stopped, just that it continues in the same direction. But that still puts water that's at least 5°C below what was the retuned temp, back into the emitters, or top of a 4P buffer. Hopefully mine doesn't do that, I had assumed not, and haven't seen/noticed that sort of temp drop off. Something for me to investigate, since it if does, I need some additional control to stop the emitter circuit circulating when the ASHP is defrosting.

Edited March 13, 2023 by IanR

[DanDee]

24 minutes ago, IanR said:

 

Now I'd assumed the water flow reverses, pulling heat out the emitter circuit or buffer (or UVC when on DHW heating cycle)

 

I can't see there'd be sufficient energy in the "water" in the condenser, to defrost the ASHP, without pulling warm water back out of the house.

Water doesn't reverse the flow as it's taking the heat from the return side, and the flow becomes colder.

 

https://emoncms.org/heatgeek

Edited March 13, 2023 by DanDee
https://emoncms.org/heatgeek

[JamesPa]

9 minutes ago, IanR said:

Ah, ok, you're not saying the water flow is stopped, just that it continues in the same direction. But that still puts water that's at least 5°C below what was the retuned temp, back into the emitters, or top of a 4P buffer. Hopefully mine doesn't do that,

I don't know that it does, simply that it can. I imagine a hp that knows there is a buffer _and_ which has control of both pumps might switch off the ch circulation pump and switch on the buffer pump, so that the energy is taken from the buffer.  Once defrost is finished it might then heat the buffer up before switching on the ch circulation pump back on. 

 

Having said this provided the temperature of the water circulating in the ch is above the room temperature, it will still give up heat to the room so letting it continue to circulate is likely OK.

 

I really have no idea how heat pumps in practice manage this, particularly if they don't have control of both pumps.

 

Edited March 13, 2023 by JamesPa

[HughF]

1 minute ago, JamesPa said:

I don't know that it does, simply that it can. I imagine a hp that knows there is a buffer _and_ which has control of both pumps might switch off the ch circulation pump and switch on the buffer pump, so that the energy is taken from the buffer.  Once defrost is finished it might then heat the buffer up before switching on the ch circulation pump back on.  I really have no idea how heat pumps in practice manage this, particular they don't have control of both pumps.

 

They don't.... defrost just sucks some heat out of the water circuit by reversing the F-Gas valve. Be that a buffer, or a direct connection to the heating circuit.

[JamesPa]

2 minutes ago, HughF said:

They don't.... defrost just sucks some heat out of the water circuit by reversing the F-Gas valve. Be that a buffer, or a direct connection to the heating circuit.

Thanks, ... and provided the temperature of the water circulating in the ch is above the room temperature, it will still give up heat to the room, so letting it continue to circulate is  OK.

 

 

[sharpener]

11 hours ago, ReedRichards said:

One thing that my present setup does not achieve is circulation through the heating system when the heat pump is off. 

 

 

Well you imply yourself this is undesirable but see below.

 

3 hours ago, ReedRichards said:

But given the sensitivity to flow, I worry that an auto-bypass valve might cause the flow rate error before it was able to operate.  Also, does the flow reverse for defrosting, or is that just my fanciful imagination?

 

The central heating pump causes enough pipe and radiator noise that I would not want it running when it was not necessary to do so.  I'm not aware that I can program a run-on but I'll look into that.  But is it desirable?  My heat pump is limited to 20 minute cycles and if it goes off after 15 minutes, as it often does, do I really benefit from circulating water round the heating system rather than leaving it to stand?

 

If you have a buffer then it is theoretically desirable to maintain the circulation when the HP stops heating to benefit from the stored heat therein. Ditto a volumiser. But if the HP is running for 15 mins in every 20 anyway there is probably not much benefit to be had.

 

Boiler systems almost always have the circulating pump running all the time and manage to be more or less silent. Mine are, apart from 1 rad which gurgles a bit because (I think) it is where the air collects. If yours is unacceptably noisy perhaps it is worth tracking down the cause, air in the system or something partially closed or blocked may be needing attention. Or maybe the pump is turned up too high or knackered or the wrong type for the duty, there are constant-pressure pumps designed to automatically handle widely varying flow volumes which might be better.

 

Bypass valves are adjustable, you would need to set it just a bit higher than the pressure drop required when all the emitters are in circuit, then when the pump stops or other valves close the pressure will only rise slightly and I would expect the HP to handle this OK.

 

Having the volumiser in the return means the losses are lower and there is a good heat reservoir for the defrost cycle. The downside is that this will push cold water into the ch loop - unless of course it is arranged that the ch pump is off during defrost, that is when/why the bypass valve will help.

 

Can you tell us how the ch pump is controlled? Also you have not said if your rads are also controlled by zone valves or TRVs, that would be helpful.

 

Edited March 13, 2023 by sharpener

[JamesPa]

46 minutes ago, sharpener said:

Having the volumiser in the return means the losses are lower and there is a good heat reservoir for the defrost cycle. The downside is that this will push cold water into the ch loop - unless of course it is arranged that the ch pump is off during defrost, that is when/why the bypass valve will help.

Does the water cool below room temperature during the defrost cycle.  I would have expected hps to stop this happening, to avoid the risk of condensation.  If water stays above room temperature then no harm is done if it continues to circulate.

[Wil]

On 13/03/2023 at 11:49, JamesPa said:

Does the water cool below room temperature during the defrost cycle.  I would have expected hps to stop this happening, to avoid the risk of condensation.  If water stays above room temperature then no harm is done if it continues to circulate.

I've never seen it happen, but not sure that it CAN'T.

 

I have the CoolEnergy 120l buffer and it definitely has an immersion which I use for dumping excess heat after the HW tank has had it's fill. The 120l immersion gets turned over bloody quickly by my system though:

 

 

my heating is still just Rads, and no 3Pv on the cold return to ASHP 1 but otherwise it's pretty much ready for me to do the renovation and change the emitters.

 

ASHP1 is HW led but primary heating and ASHP2 only comes in if ASHP1 isn't coping with the heat loss. They have  two thermostat pockets at different height in the buffer tank, so I can confirm a small degree of stratification going on, it's what I use to ensure HP2 cuts off and leaves HP1 running (Hp1 stat lower in the tank). Sadly Immersion 1 doesn't exist either for a part-tank top up.

[JohnMo]

Why do you need the circulation pump on the return going ASHP 2, the heating manifold pumps will do just fine, pulling from the buffer and returning it.  You have 4 pumps, without hydraulic seperation, so you could/will end up with pumps chasing there tails.

 

ASHP 1 and 2 seem huge.   If No 2 is just back filling if No 1 doesn't cope.