Buffer tank connections

[Wil]

 

14 hours ago, JohnMo said:

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.

 

 

 

The heating manifolds don't (yet) exist- I'm still direct to rads so the return pump is doing the internal heating circuit.

 

I've tried a few different running configs- ASHP1 doing HW, with ASHP2 leading heating etc, but always seems more efficient to have the smaller one lead. Sadly the heat loss calcs say I need the capacity of these two to cope. I'm hoping that once I've done my renovations I can cope with just one of the ASHPs, then I'll move the other to a class Q conversion I'm planning.

[MikeJH]

On 11/03/2023 at 15:52, JamesPa said:

@IanRis absolutely adamant that is not the case, if you follow the thread.  So far nobody has posted measurements to confirm either way.,

I have followed the discussion between @JohnMo and @IanR with great interest. I suspect Ian is right if buffer tanks are suitably designed and sized. However, I believe that most are similar to my own 50L buffer tank (see attached photo), installed by a company that claims to install more ASHPs than anyone else. There is a 4-5 deg C temperature drop between the flow from the 12kW Samsung ASHP into the buffer and the flow out of the buffer to the radiator circuit as seen in the attached diagram. This adds around 10-12% to the energy costs of heating for no apparent benefit. When the ASHP cycles in warmer ambient temperatures it cycles every 8-9 minutes, despite the buffer. In fact I believe that the lower heat delivery from the radiators due to their lower temperature means that cycling becomes more likely, not less.

 

When I reduced the setting on the primary water pump from 3 to 1 and increased the setting on the secondary water pump (to the radiators) from 1 to 3, the difference between buffer in and buffer out rose to around 10 deg C and the ASHP started cycling 5-6 mins on and 3-4 mins off. This cycling stopped once the pump settings were restored.

 

I am hoping to have my buffer tank removed and bypass valves installed. Together with the removal of glycol, this might reduce energy costs by 25%. The expected SCOP of 3.68, based on Samsung's datasheet at 50 deg C flow temperature is a complete joke. I can only surmise that Samsung's 'Seasonal' was from June to August, possibly in the Bahamas!

[IanR]

28 minutes ago, MikeJH said:

However, I believe that most are similar to my own 50L buffer tank 

 

I'm not sure how any of us would know. I was told my installation was typical of a Nibe install at the time, accept for the cooling.

 

It does look as though your flow Temp is around 5°C higher than your emitters require to meet the heat demand.

 

Are all the temps taken at the buffer?

 

From the temp trace there doesn't appear to be any of the cycling you mention, was the temp trace during a particularly cold period?

 

Are your tanks installed within the thermal envelope? I can see what looks like an external wall, and, is that buffer insulated? Neither would account for the delta between buffer in and out temps, it's just out of interest.

 

Visually, it does look as though the port positions on the buffer are unlikely to stop the buffer mixing.

[JohnMo]

I would look to dump the buffer, but would not install bypass valves, I would ensure a proportion of the rads stay open, so take any trv's off a couple of the bigger rads, so you have good size of system always open to the heat pump, if room get to hot fine tune the lock shield valves to balance. Or better still modify the WC curve downwards, so it reduces overall flow temp.

 

Are you running weather compensation? This would help the overall SCoP, if you are not.

[MikeJH]

14 minutes ago, IanR said:

Are all the temps taken at the buffer?

Yes, they are all taken from the pipes leading into or from the buffer. I also recorded the flow and return temperatures recorded by the Sontex heat meter and these were virtually identical to the buffer in and buffer return values (the lines on the graph with all values overlap almost completely).

 

18 minutes ago, IanR said:

From the temp trace there doesn't appear to be any of the cycling you mention, was the temp trace during a particularly cold period?

There was no cycling during this period. Ambient was around 7 deg C

 

19 minutes ago, IanR said:

Are your tanks installed within the thermal envelope? I can see what looks like an external wall, and, is that buffer insulated? Neither would account for the delta between buffer in and out temps, it's just out of interest.

The tanks are installed in an unheated porch. The buffer has internal insulation presumably as it it is not warm to touch on the outside, similar to the DHW cylinder.

[MikeJH]

6 minutes ago, JohnMo said:

I would look to dump the buffer, but would not install bypass valves, I would ensure a proportion of the rads stay open, so take any trv's off a couple of the bigger rads, so you have good size of system always open to the heat pump, if room get to hot fine tune the lock shield valves to balance. Or better still modify the WC curve downwards, so it reduces overall flow temp.

Thanks. The advice to install bypass valves came from Brendon Uys, plus remove TRVs and the Honeywell valves and anything else that will reduce flow. My pipework to the radiators is 22mm to 2 kitchen radiators and the upstairs bathroom radiator and then 15mm to 5 other radiators, so I won't be able to get a flow rate much above 20L/min. According to the Samsung wired controller the maximum flow rate is 23L/min in the primary circuit, but the Sontex heat meter gives a value of 15L/min, so this may not be an issue.

 

According to Freedom Heat Pumps, a buffer tank with flow separation is required by the Samsung warranty. This despite its previous owner now saying that buffer tanks should rarely be used.

 

15 minutes ago, JohnMo said:

Are you running weather compensation? This would help the overall SCoP, if you are not.

Yes I am, but obviously I have to run 4-5 deg C higher than I would if I had a direct system.

[JamesPa]

1 hour ago, MikeJH said:

I have followed the discussion between @JohnMo and @IanR with great interest. I suspect Ian is right if buffer tanks are suitably designed and sized. However, I believe that most are similar to my own 50L buffer tank (see attached photo), installed by a company that claims to install more ASHPs than anyone else. There is a 4-5 deg C temperature drop between the flow from the 12kW Samsung ASHP into the buffer and the flow out of the buffer to the radiator circuit as seen in the attached diagram. This adds around 10-12% to the energy costs of heating for no apparent benefit. When the ASHP cycles in warmer ambient temperatures it cycles every 8-9 minutes, despite the buffer. In fact I believe that the lower heat delivery from the radiators due to their lower temperature means that cycling becomes more likely, not less.

 

When I reduced the setting on the primary water pump from 3 to 1 and increased the setting on the secondary water pump (to the radiators) from 1 to 3, the difference between buffer in and buffer out rose to around 10 deg C and the ASHP started cycling 5-6 mins on and 3-4 mins off. This cycling stopped once the pump settings were restored.

 

I am hoping to have my buffer tank removed and bypass valves installed. Together with the removal of glycol, this might reduce energy costs by 25%. The expected SCOP of 3.68, based on Samsung's datasheet at 50 deg C flow temperature is a complete joke. I can only surmise that Samsung's 'Seasonal' was from June to August, possibly in the Bahamas!

@IanRs argument (which, ultimately, was fairly convincing) depended on stratification, which in turn depends on (all of) a well designed tank, the thermostat controlling the hp being located correctly, the pumps being more or less well adjusted, and a good height to diameter ratio. Yours doesn't have the last of these, your measurements confirm 100% mixing in the tank and, as you correctly say, this will be a 10%+ efficiency hit solely because of the mixing and hence elevated flow temperature.  Losses from the tank will add to this and if WC is not correctly adjusted (which seems unlikely given that your installer clearly has not prioritised efficiency), will add further.  

 

If the buffer tank is essential for the warranty (which I doubt), plumb it as 2 or 3 port but definitely not 4.  If it's plumbed as 2 port, you will need to lose a pump.

 

Unless there is a good reason that you have not stated, this is a poor installation.  However that's nothing special to heat pumps, since condensing gas boilers were introduced (and widely touted to be a good thing) most installations seem to have been poor, ie with a flow and return temp adjusted to exceed the maximum figure at which condensation occurs this sacrificing 10% or so in efficiency.  Installers, it seems, frequently prioritise avoiding support calls over efficiency, and there is no reason on earth why new technology will change that behaviour.

[sharpener]

Have seen the  Samsung warranty stuff before e.g. here. From what I have read elsewhere you might as @JamesPa says do better with it as a 3-port buffer, as a compromise between too much mixing and not enought engagement. Ideally with the 1 port teed off the flow and the 2 ports on the return.

 

If you can then tune the pump settings so there is least flow through the tank when the demand is greatest I think you will have better efficiency. Fortunately you seem to have better instrumentation than the installer!

[MikeJH]

19 hours ago, JamesPa said:

Unless there is a good reason that you have not stated, this is a poor installation.

To be fair to Greener Living, this is likely to be a fairly standard Samsung install. Even if Freedom HP is wrong about the warranty, a buffer appears to be recommended as part of installing a Samsung. This was confirmed by another company that serviced it this year. GL has also returned to fit the missing strainer and fix the MMSP monitoring when requested, but there was no real commissioning or attempt to make the system more efficient. The engineers were called to another job before the electrician had even finished! It is only through forums like this, that I have begun to understand how to get the best out of it.

[JamesPa]

1 hour ago, MikeJH said:

To be fair to Greener Living, this is likely to be a fairly standard Samsung install. Even if Freedom HP is wrong about the warranty, a buffer appears to be recommended as part of installing a Samsung. This was confirmed by another company that serviced it this year. GL has also returned to fit the missing strainer and fix the MMSP monitoring when requested, but there was no real commissioning or attempt to make the system more efficient. The engineers were called to another job before the electrician had even finished! It is only through forums like this, that I have begun to understand how to get the best out of it.

Fair enough.  To some extent it's 'of our own creation'. If the majority of customers expect a heating system just to work and magically be the correct temperature whatever happens, then the industry will deliver just that. 

 

There is, of course, a price to be paid for this luxury, either in efficiency or system cost or both.  Who knew until recently that turning down the flow temp on your gas boiler was _necessary_ to make it achieve the designed-in and much touted efficiency?

 

It's just sad that we don't get to make an informed choice, instead the industry does what it thinks is right (and for the majority of customers probably is right) rather than presenting customers with options.  I suspect those in the industry will say, doubtless with some justification, that giving customers choice with trade-offs to evaluate is too complex for most customers.  We are victims of our wealth (and perhaps our laziness?)

Edited April 18, 2023 by JamesPa

[sharpener]

5 hours ago, JamesPa said:

 Who knew until recently that turning down the flow temp on your gas boiler was _necessary_ to make it achieve the designed-in and much touted efficiency?

 

Well I guess we all did. But it's scandalous that even now it's not part of official advice on fuel economy. If you don't have condensing operation anyway you might as well have the Ideal Mexico which was simple, robustly built, and easy to service.

 

<It's just sad that we don't get to make an informed choice, instead the industry does what it thinks is right (and for the majority of customers probably is right) rather than presenting customers with options.  I suspect those in the industry will say, doubtless with some justification, that giving customers choice with trade-offs to evaluate is too complex for most customers.  We are victims of our wealth (and perhaps our laziness?)>

 

If "The industry" means the manufacturers then (having consulted for them) I think they are mostly OK but there is a total gulf between them and installers, be they one-man bands or national networks.* Ultimately I fear this is a lack of numeracy and basic scientific understanding on the part of the latter, which leads to over-simplification and playing safe in installation guidance. This is a far-reaching problem, underlying UK plc's poor productivity growth over the last decade and more.

 

*According to a major manufacturer, condensate drain installation problems account for a large proportion of warranty callouts. I had to ask the plumbers who installed my gas boiler to re-do the drain as the pipe had a dip in it. When they had finished, it had a slightly smaller dip in it so in the end I sorted it out myself.

 

[JamesPa]

1 hour ago, sharpener said:

 

Well I guess we all did. But it's scandalous that even now it's not part of official advice on fuel economy. If you don't have condensing operation anyway you might as well have the Ideal Mexico which was simple, robustly built, and easy to service.

 

<It's just sad that we don't get to make an informed choice, instead the industry does what it thinks is right (and for the majority of customers probably is right) rather than presenting customers with options.  I suspect those in the industry will say, doubtless with some justification, that giving customers choice with trade-offs to evaluate is too complex for most customers.  We are victims of our wealth (and perhaps our laziness?)>

 

If "The industry" means the manufacturers then (having consulted for them) I think they are mostly OK but there is a total gulf between them and installers, be they one-man bands or national networks.* Ultimately I fear this is a lack of numeracy and basic scientific understanding on the part of the latter, which leads to over-simplification and playing safe in installation guidance. This is a far-reaching problem, underlying UK plc's poor productivity growth over the last decade and more.

 

*According to a major manufacturer, condensate drain installation problems account for a large proportion of warranty callouts. I had to ask the plumbers who installed my gas boiler to re-do the drain as the pipe had a dip in it. When they had finished, it had a slightly smaller dip in it so in the end I sorted it out myself.

 

For the avoidance of doubt my reference to 'the industry' was meant as a reference to installers (in the UK) not manufacturers (who by and large seem to be doing a good job).

 

Like you I fear that lack of training, basic numeracy and basic scientific understanding drags the UK down.  We were all told by our politicians, not so long ago, that we don't need experts, and this plays straight into a culture which values celebrity more than engineering.  In fairness to our current pm, he has highlighted that aversion to maths is a drag on the economy, I look forward to him implementing a coherent strategy to fix this (but won't be holding my breath).