Low loss header feed and returns

[nippyjock]

Hi, I would welcome some advice, I have a Daikin HT ASHP installed and for some months now it has been struggling to get my house up to temperature, despite the flow temperature from the ASHP being set to 55C, and the feed pipe being hot to touch. On investigation it seems to me that the installer has swapped the feed and returns to my low loss header, it is the opposite to connections shown on the image below i.e. the flow from the ASHP is at the bottom of the low loss header, (next to the returns from the heating circuits), and the return to the low loss header being at the top, (next to the flows to the heating circuits).

low loss header.jpg

The installer is of the opinion that this will make little difference to the system performance, however, I fail to see how this can be true.

[Mods edit: Additional text from poster]
In the illustration above starting at the top right hand side and working down our connections to the low loss header for our heating circuits are radiator feed, UFH feed, radiator return, UFH return.

Any advice would be welcome.

[frank]

As you have the HT Altherma, have you tried increasing the flow temperature up to 80C?

Are you radiators sized for a flow temperature of 55C?

[nippyjock]

Hi, thanks for your reply. Yes, the radiators are sized for a flow temperature of 55C. The Daikin engineer set the flow temperature to 55C when we complained about how much it was costing us to run, (our electicity bill was 3K last year!). Am I missing something, to me it seems the problem is that the the low loss header never gets hot because the feed is to the bottom, not the top, and the return is at the top, not the bottom. If you put your hand onto the feed pipe on the bottom of the low loss header, from the ASHP, it is really hot, when you put your hand on the secondary flows at the top, or the low loss header itself, it is luke warm. It only becomes hot if it has been running pretty much all day. In the photo attached to the original thread it shows the boiler primary flow going to the top of the low loss header, which seems to make sense, our ASHP is connected in reverse, our secondary flow and returns are as shown on the photo.

[martinw58]

has the system ever worked corectly

[frank]

What heating system did you replace when you had the ashp installed.

Did you change the radiators?

[martinw58]

is there a pump on the secondary circuit

[nippyjock]

The system worked correctly in the sense that it heated the house, the temperature was steady, minimum 17C during night, typically 21C during the day.

[nippyjock]

Hi, there are pumps on the UFH manifolds, (there are two of these), and a pump on the return of the central heating circuit. Does nobody think the crossing of the feed and return to the low low header from the ASHP has an impact then? To me the hot water feed will be getting cooled from the UFH and radiator returns, it feels like this is happening, the secondary feeds take an eternity to warm, almost the whole day, despite the feed from the ASHP feeling very hot. Looking at the photo in the original post it would seem the feed should be at the top for hot water stratification illustrated.

[Brian_UK]

As long as the secondary circuit pumps are drawing water from the hottest end of the LLH then it shouldn't make any real difference. If the pumps are in the supposed flow pipes then lower performance would be expected.

You might encounter problems if you have one way thermostatic valves fitted as the water flow will be in the wrong direction and the valves may chatter as they begin to close down.

[nippyjock]

Hi Brian, thanks for your comments, that was my point, the secondary circuits are drawing water from the top of the LLH, as the shown on the photo on the right hand side. However, the top of the LLH does not get warm for ages as the feed from the ASHP is fed into the bottom of the LLH, not the top as shown in the photo, due to stratification the bottom should be the coldest point of the LLH, the 55C hot feed coming in from the ASHP is not being used to heat the house, it is effectively immediately being cooled immediately by the secondary circuits returns also coming in to the bottom of the LLH on the right hand side of the photo. The net result is my secondary circuit feeds are at something like 32C rather than closer to 55C as they should be if the feed from ASHP was fed into the top of the LLH, so it takes ages to heat the house, and I am wasting energy. Does this make more sense?

[monkey spanners]

I have no experience of these things so bare that in mind. It seems to me you want all your flows at one end of the manifold and all the returns ato the other end.

You want all you rads and floor drawing off the warmest water from the altherma, and all the retuns going back to the coldest water. To my mind this will give the warmest water for heating and send the coolest water to the althema for reheating.

If now say you have 55c flow and 35c return you the altherma can only put in 20c, but if you return drops to 25c with different pipe layout then you'll be getting 30c worth of energy in the water.

But like i said i work on dairy refrigeration so this is not my area...

[The Viking]

As you seem to have a crossflow if I understand it correctly you do not in practice have a low loss header, by swapping the primary flow and return the installer has created a cross flow heat exchanger.

If correctly designed there will be little or no temperature differential between the flow from the boiler [primary flow] and the flow to the system [secondary flow] when the heating is called for.

A low loss header should by definition have very little flow between the "hot" and the "cold" ends when the system is operating flat out. As the demands fall and reduce the secondary flow there will be some flow from the hot end to the cold end thus reducing the duty required of the boiler.

A cross flow in the header will not only create a colder secondary flow temperature, it is also likely to create unnecessary short run/standby cycles for the boiler. If the boiler were an old fashioned cast iron gas fired thing this might not matter so much but for a heatpump this is a killer. A heatpump pulls much more energy when it starts than when it actually is running and compressors lives much longer the fewer starts they have to cope with.



.

[al]

Does the primary and secondary physically mix in the header or is a shell and tube type design? If they mix then you have a problem with flow, if not then the loss "should" be minimal.

Are all pumps running, all rads clear of air, header clear of air and sufficient water in circuit?

alec

[MikeHolm]

OK, This setup is OK but the two feeds out to the load need to be quite close together and they need non return valves on them. ALSO, very important is that the flow from the two pumps should each match their respective heat loads and together needs to roughly match the total max heat load which, theoretically, should be less than the flow rate on the primary side. If you can slow down those secondary loops pumps, you will fix most of the problem. Your LLH may also be too small for the load as well. What size is it?

[nippyjock]

Hi, thank you all for your comments.

Al, To be frank I do not know if the LLH is of shell and tube design or not, it was manufactured by the ASHP installors and it is not an off the shelf product, I did request this information from them earlier but as yet they have failed to provide it.

My feeling based on instinct and system behaviour is that they do mix.

All pumps are running, are radiators are bled.

MikeHolm, the feeds are very close together, a few inches apart at worst, they have no non return valves fitted.

When you ask what size is it, are you asking physically or are they rated on kW or something, as I said to Al the installors had this manufactured and I had no information on it at all.

I can adjust the speed of the secondary loop pumps.

[nippyjock]

I just received the information from the installer for the LLH, see marked up drawing.

header.jpg

[The Viking]

OK,
Regardless of theories of how it might work, or not as the case might be, the proof of the pudding is in the (h)eating.

Correctly designed and installed there should be no temperature differential between the primary and secondary flows.

[MikeHolm]

I just received the information from the installer for the LLH, see marked up drawing.

Judging from the markings on the paper you sent, the flow and return are in the wrong locations. Flow FROM the heatpump should enter in the top. Everything on the right is correct. The pump speeds are the other big issue but the piping should be switched first. I did mean the LLH dimensions which are fine. It is oversized for the job anyway. If the two pumps will be on and off at different times, than the NRV is important as one can draw through the other in reverse, potentially, and the same is true if one pump has a much higher flow rate than the other one for conditions. Lots of things will get messed up.

[nippyjock]

Thank you all for you comments, it was as I suspected, however, I valued the opinion of people with more experience than myself, namely all those who took the time to respond, all your comments will be useful for improving the performance of my system. The thing that worried me the most was the installer had been called out a number of times to look at the performance and running costs, as is often the case numerous people come out to look, but nobody really looks, all they all just tweak settings. They had got it to work by cranking up the flow temperature, then when it cost a lot to run and I complained they cranked it down again, to typical settings for similar installations, at which point it all got a bit chilly. It was through frustration that I finally had a look at the installation myself, (I am a control systems engineer, but Oil & Gas applications), and thought to myself this makes no sense at all. The rest is history, once again appreciate everyones input.

[nippyjock]

See what you did there, I am a lover of puns myself, not so keen on non-specialised specialists, (aka my installers).

[nippyjock]

Header.jpg

Attached is a photograph of the offending low loss header installed in my home, complete with primary feed/return cross over.

I would be grateful if anyone can help me with the purpose of the clouded section in the photograph of the low loss header, it appears to be some kind of pressure relief line.
The installer has been ambiguous about its purpose and indeed its requirement, he stated within 10 minutes that it was needed, then he then said it could be taken out if I want as the header was there anyway.

The "if I want" statement appears to be their way of trying to say nothing is wrong but they will change it to my preference. Obviously my preference is fairly straightforward, that it is installed as it should have been in the first instance.

When I suggested the primary flows and returns may indeed be crossed over during their last visit, (prior to me posting this thread), they offered to swap over the primary flow and returns too "if I want".

This was just before they beat a hasty retreat from my property when I raised the issue of a contribution towards my 3000GBP electricity bill for last years heating.

The profanities uttered by the managing director of the company in question prior to their departure are not allowed to be posted on this forum. They related to me having more chance of performing a bodily function in a member of the royal families handbag than getting any money, a further reference to wishing my house burned down, (presumably not from over-heating), plus a few more run of the mill obscenities.

They stated however in a subsequent email that they accepted no responsibilities for any installation errors at this point.

As always any comments are appreciated.

[nippyjock]

MikeHolm, You stated "the two feeds out to the load need to be quite close together and they need non return valves on them. ALSO, very important is that the flow from the two pumps should each match their respective heat loads and together needs to roughly match the total max heat load which, theoretically, should be less than the flow rate on the primary side. If you can slow down those secondary loops pumps, you will fix most of the problem."
I agree these are crucial to system optimum performance and efficiency, however, would you consider that these issues are secondary, i.e. not the root cause of the problem, and the biggest impact on performance and efficiency is the primary flow and return being crossed over?
To me this appears to be the case, my 55C flow temperature is getting nowhere near my secondary heating circuits, it is being cooled immediately by the secondary returns, in reality my secondary feed circuits are typically 32C when the heating is first switched on.

[MikeHolm]

They are all important but to what degree is hard to tell. If the combined flow of the two pumps greatly overpowers the HP flow (and there is a place for the heat to go) it will draw down the HP temp too much which you don't want. The first thing is getting the piping rearranged then look at the pump speeds. Nothing will be solved until this is done.

On the HP side of the LLH, the clouded portion is a pressure bypass but I'm not sure why it is needed. I also see a couple of temps sensors but you guys use some components that are not used here much so I am not sure what/why there are there. If there is a flow sensor, it is not visible. The flow to/from the HP should be as open as possible and the only thing there should be a throttling valve to set the flow to the HP properly.

Also, my preference is to pump OUT of the LLH at the top and to the load and it appears that the the one pump I see is pumping into the return but it is hard to be certain of that.

[nippyjock]

Hi Mike, I share your view about the first thing that needs to be done is having the piping re-arranged.

I am sure the greater part of the problem is the cross in the primary flow and returns, I have felt the heat in the pipework leaving the ASHP, and the lack of heat at the top of the LLH, unless it has literally been running all day, more than 12 hours, then it gets hot.

There are a number of measurement components shown in the photo installed by a third party to monitor the performance of the ASHP, required by the Microgeneration Certification Scheme, in order to qualify for an interim grant.

The pump on the return you have correctly identified is the return from the secondary radiator circuits, I intend to have that transferred to pump out of the LLH, that was installed by my installers plumber again.

[hyperion]

My understanding is that the flow from the heat source and the flow to the heating circuit should always go to the top of the LLH. The flow rate through the primary side will need to be set up first, to give the optimum flow rate through the ASHP. If this flow rate is too high, the the ASHP will not achieve optimum performance. Then set up the various heating circuit flow rates. Too high a flow rate will not give the emitters a chance to make the most use of the heat energy in the water. See this link http://www.vaheating.co.uk/header%20basics.html for a better explanation. Hope that this helps.
You mentioned the MCS scheme, if your original installer certificated and registered the system, you may be able to get some backing from the MCS Scheme as the installer should have taken out REAL Assurance. Might be worth enquiring into this once you have the system working properly.

[nippyjock]

Hi Hyperion, thanks for your comments, yes they do help.
That's a great link, I had seen a similar photograph but your link with the additional animation and supporting wording is exactly what I had thought.
I have been forced to initiate a MCS complaint against the installer I am afraid.
He is indeed MCS registered, however, his reaction to me suggesting the primary flow and primary feeds was referenced in my earlier comments today, took me a little by surprise to say the least i.e. he could swap them "if I want" then the caveat of stating they accepted no responsibility for any installation errors.
It was slightly worrying that I was explaining to him how the system was actually piped up when he visited me last week and we were both standing in front of the installation.
I have not lodged the complaint as yet, I am just putting my case together, it will be done this weekend at the latest.
I have spoken to MCS and they have been very helpful to date.
All the illustrations I have found online for LLH's show the primary flow going to the top, as does the link you provided, it makes sense, hot at the top, cold at the bottom.

[hyperion]

The important part after correcting the pipework is getting the correct flow rate set up for the ASHP. Once this is correct, which will be confirmed by checking the delta T across the ASHP, then you can start up the other pumps individually and set the correct flow rates through the UFH and the radiators. It does not matter what order the secondaries are set up. Make sure that you have not got any air trapped in the UFH, this can sometimes be a little tricky to get out.
Take plenty of further photos of the as installed and the revised version to add to your case with MCS. Hopefully you have kept all of the original and subsequent correspondence.
The caveat of not accepting any installation errors, is no form of defence. As long as no other party has attempted to modify the pipework since the original installation, then the system is "as installed" and from your observations, blatantly not working correctly. Whilst the original installing company may have used an "authorised" sub contractor to carry out the work, the MCS Accredited company who commissioned and signed the system off takes ultimate responsibility for the design, specification and effecient functioning of the complete system. MCS is very clear cut, there are no "part" responsibilities, it either passes and is registered or it does not pass.
If for reasons of economy you choose to leave your flow temperature at 55 and the temperature is satifactory in the house, then you should end up with a relatively economical system.

[frank]

The part highlighted in the 'cloud' looks like the normal run of the mill bypass valve.

These are a requirement to ensure that your pump does not burn out while all heat emitters on the circuit are satisfied and their respective valves are closed (TRV's)

In this case, your LLH will never 'close' so flow through the pump is always assured. In my opinion, this valve arrangement should never have been installed.

If this valve is incorrectly set, or has dirt stuck in the seat allowing bypass to happen, the symptoms you are experiencing can be attributed to this.

Taking pipe temperature measurements close to the valve should indicate if bypass is happening, but I would have it removed as a first step.

From your comments, the installer has stated that he will do this. Measure the flow temperatures around you LLH before he removes it and then again after, to see if there is any improvement. The price of a decent digital thermometer and a couple of pipe sensors is small change compared to the legal future you are looking at. Data readings are cast iron proof of performance should it reach court.
http://thermometer.co.uk/841-dial-pi...rmometers.html

[nippyjock]

LLH Installation.jpg

Hi, once again thanks for the comments, all very useful.

Frank, thanks for your link for the thermometers, exactly what I need, in fact I have already purchased 10 of them this morning and will get them fitted to assist in collecting data to support my claim, and to monitor system performance in the future.

Hyperion, I will make sure we have plenty of photos.
I have not made any changes to the pipework I am glad to say, it is all exactly as installed, I am not having the installer back into my property again after his outburst and profanities etc. on his last visit.
I have notified MCS of this fact and they have conceded under the circumstance I do not need to allow him an opportunity to address the issue due to his unacceptable behaviour.
I will raise the MCS complaint and they will appoint someone to review the installation and carry out any remedial work required, in addition they stated they would carry out calculations to estimate what the heating costs should have been, and initiate a refund of any excess charges, which all sounds very comforting.

I have all my emails, I even sent emails after phone calls detailing the conversation that had taken place, as a record.

When I stated earlier "it looks like the primary feeds and returns have been crossed", you can clearly see from the attached photograph that they have been crossed.

[hyperion]

Keep us updated with the results after the pipework reconfiguration.
As a further aside, it is my opinion that in order to receive MCS approval, all of the primary heating pipework should have been insulated, this would also include the LLH as that is part of the primary circuit. Perhaps you have removed this to carry out the recent checks.
Whilst this would not solve your current operational problems, it should be considered to assist in reducing potential areas for loss of heating effect. All means to minimise heat loss should be actively persued, particularly if you are utilising lower flow temperatures.

[nippyjock]

I will keep you updated, I have appreciated everyone's input.

I am looking forward to being able to see actual temperatures, rather than hot, not so hot, and pretty cold.

I am not sure how quickly I will get it swapped over, I want to have some before data before I allow anyone to change things over so will hold a few days before initiating the official complaint.

I will take some photos of thermometer readings on primary and secondary pipework before the heating is switched on, then periodically after, along with photos of the ASHP flow and return readings on the control unit display.

Is there a specific digital thermometer type or even model you would recommend?

To be fair, there was some insulation on the LLH, not much, bandage stuff, I removed it to see if I could find any manufacturers information to allow me to check plumbing arrangements online, none existed, but the installer provided me with the construction drawing.