@derek-m interesting video on low loss headers for people

That has certainly improved my knowledge of low loss headers, which it would appear are like 'small buffer tanks'.

It has now made clear some of the points that Brendon has been making about buffer tanks, and how they can possibly affect the efficiency of ASHP systems.

Let's first of all consider what I feel would be the ideal system, as pointed out by Brendon, and some of the possible limitations. Please feel free to correct me if any of you feel I am wrong.

An ideal system would consists of the following:-

Only one water pump located within the ASHP.

One adequately sized diverter valve for central heating or DHW.

As many fully open heat emitters as possible, with limited use of TRV's  and only used if absolutely necessary.

No buffer tanks or low loss headers to be installed.

Control using weather compensation and preferably an indoor temperature sensor, or a thermostat as a second option.

That there is adequate water capacity in the system to meet the minimum requirements specified for the ASHP.

The vast majority of the heat energy supplied by the ASHP would be going to the heat emitters, hence lower flow temperature.

What are the possible limitations:-

If the system is large, the water pump (primary) in the ASHP may not be capable of pushing the water around the system. This would mean that a second water pump (secondary) would be required, which would, as I understand, require the installation of a low loss header or buffer tank. If my understanding is correct, this would not be a major problem provided that the water flow rate from the primary pump is the same or slightly higher than the secondary pump. In this case, the warm water flowing from the ASHP, would pass through the low loss header or buffer tank and be pushed around the system by the secondary pump at near full temperature.

If however, the flow rate of the secondary pump is greater than the primary pump, then some of the return water from the heat emitters, will mix with the supplied water from the ASHP within the header or buffer, so that the water going to the heat emitters will not be at full temperature. Lower water temperature to the heat emitters would mean less heat output, so the control system would need to increase the water flow temperature to compensate. Less efficient heat pump.

Opening and closing of valves within the central heating system, would vary the flow rate through the secondary pump, which could conceivably affect the system performance and efficiency.

So in the first instance, anyone with a secondary pump with low loss header or buffer tank, should if possible check the flow in and flow out temperatures of the header or buffer, to try to ensure that under all operating conditions, the water coming out is as warm as the water going in. If not then you may wish to consider some of Brendon's suggestions to get your system working correctly.

Before making any modifications you should try to get some before and after data so that any improvements can be quantified.

I think that is enough for consideration at the moment, but please feel free to join the discussion.

Hi Everyone,

I suppose the question now, is how many people have one or more secondary pumps along with a low loss header or buffer tank? The next question would then be, is this arrangement affecting the operation of their ASHP system.

@derek-m I have a secondary pump after the low loss header. However I very much doubt this was paired with the system to maintain flow rates...

@derek-m A couple of things to clarify but you have the concept.

As many fully open heat emitters as possible, with limited use of TRV's and only used if absolutely necessary. We only control the temperature in bedrooms independently through modulating systems, trv's or modulating thermostats. On-Off thermostats have no place what soever in low-temperature systems.

Control using weather compensation and preferably an indoor temperature sensor, or a thermostat as a second option. Whether compensation is more suited to high thermal mass applications (thick under floor screed and old solid stone buildings) , it struggles to maintain a constant temperature in the transition periods (spring and autumn) in low thermal mass applications and most radiator systems (except in solid stone buildings with big stone internal walls) where load compensation (or internal temperature control) should be used as it reacts quickly to the thermal gains. High-end units, have a combination of both that can be tuned to suit the actual installation.

If the system is large, the water pump (primary) in the ASHP may not be capable of pushing the water around the system. It is not if the system is large, it if the system is incorrectly designed with the wrong valves, pipe sizes etc. The designer should be aware of the available pressure and required flow for the system to perform correctly and should design the system accordingly. This is not always possible on a retrofit, where another pump can be installed in series to help the pump in the unit. Most good heat pumps will control this second pump.

So in the first instance, anyone with a secondary pump with low loss header or buffer tank, should if possible check the flow in and flow out temperatures of the header or buffer, to try to ensure that under all operating conditions, the water coming out is as warm as the water going in. This is a good suggestion in theory but is not possible in real life. Buffers and system separation should not be used in any circumstances in low-temperature applications where performance is required.

Before making any modifications you should try to get some before and after data so that any improvements can be quantified. Get somebody who knows what they are doing, and has experience installing high performing installations. There are too many variables to generalize but in general if you follow my guidance, you will significantly improve your performance and comfort level, evidenced by the guys on here who have tried it.

Otherwise, you are spot on. If these rules are followed, you will get a reasonably performing system with low running costs and high comfort levels. Good luck and thanks to those that took my advice and validated my design. (by the way, it works for condensing boilers as well)

Unfortunately my direct approach does not seam to please the moderator of this forum and my advice does not follow his native which he deems to be indisputably correct as it is preached by most in the industry. I have been warned about my direct approach and upsetting people by telling them the truth (I do not think the person was upset as he threw it right back at me which I respect) and he has questioned and attempted to ridicule me on other social media platforms which I do not appreciate. I have given my advice here in good faith and free of charge (I usually do charge to fix systems) and people who have listed and tried it have found that I am correct.

I am clearly not wanted here by the moderator and have better things to do with my time, so this will be my last post. If anyone wants more advice, you can contact me on 07883064216 or info@heacol.co.uk and I will do what I can do.

Just for your interest, I am putting my money where my mouth is, and I am developing a new heat pump which will be a direct replacement for a combi boiler, produces instantaneous hot water, no requirement for a cylinder and is completely self commissioning and adapting its operation to match the distribution system and property to supply the use with the lowest possible running costs and comfort levels, it logs all the data at 30 second intervals. It is about 8 months away from production. Do not watch this space, I will not be here.

@heacol shame to see you go. However you do have somewhat a direct approach which personally I feel doesn't come across well online in text form. Speaking with someone in person and communication with written medium are different in how they come across - the nuance is lost when someone reads from a screen and they add their own connotation and tone to a persons message. 

I've noticed with many people on here that they tend to say things as fact, when they are opinions (informed or not). Often they also sign off with something along the lines of "its your system, you don't have to listen to me, your the one who is going to XYZ" etc etc. 

You're clearly knowledgeable about heating systems and heat pumps - but its your choice if you choose to share that and engage with others. I see much of myself in the way you speak (not on heating systems, obviously). And I suspect you've been told before your direct style rubs people up the wrong way. Ultimately this is an online forum for a small group of people to discuss heat pumps, your engagement (or not) is your own choice.

Cheers for the help anyway - all the best

@heacol 

Hi Brendon,

I will be sorry to see you leave the forum. Whilst I have not agreed with everything that you have stated in the past, and have questioned some of your more extravagant claims, I have also learned a great deal from your posts and it has led me to question and research more deeply the wonderful world of central heating.

As an Engineer I deal in facts and figures, so will question unsubstantiated claims and look deeply into the design and operation of systems that do not appear to be operating and performing adequately.

Having dealt with numerous clients over the years, I think that I have learned some of the best methods of 'getting the message over'. With a less knowledgeable audience, it is often necessary to explain, in very basic terms, why modifications or alternations may be necessary, rather than the do this then do that and everything will be fine approach. When someone has just paid some 'experts' thousands of pounds to design and install a system, that as far as they are aware is working correctly, they don't often appreciate someone coming along who tells them that they have wasted a load of money on a substandard system. When working on many projects I would often describe myself as a 'Guide Engineer', rather than a Consultant, since I would often have to guide the client, until they arrived at the correct conclusion.

For those of you on the forum with additional pumps, low loss headers or buffer tanks, do not despair, there may be fairly simple adjustments that can be made to ensure that your present system can provide optimum performance without extensive modification.

Likewise @heacol, sorry to see you leave.  I was never offended by anything you said to me and I have listened to your advice and views and implemented some of it.

I can only reiterate and agree that it’s a shame you feel the need to leave.  Personally I would prefer that you stayed but, to use your own oft used expression,  it’s your choice.

Good luck fella.

Brendon, like others have said I’m sorry to hear you’re leaving and good luck with your heat pump design and production.

Interesting article with direct comparison on several different setups, not withstanding the reference building is in Estonia and they’re using radiators it proves the point regarding buffer tanks, optimum is no buffer tank or bypass valve. SPF 4.21 vs 3.72

RESEARCHGATE.NET "https://www.researchgate.net/profile/Jarek-Kurnitski/publication/273525301_Heating_system_return_temperature_effect_on_heat_pump_performance/links/589dec5caca272046aa9345c/Heating-system-return-temperature-effect-on-heat-pump-performance.pdf?origin=publication_detail"

@mattengineer always interesting to read a paper covering something. Of course thinking about it, it does make sense - there is less "stuff" in the way of the heat and the return. Buffers are just stores of heat you need to make and must have some kind of losses associated with them

@mattengineer 

Thanks Matt, looks like excellent bedtime reading.