Posted by: @jancold

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@editor Am I cynical in wondering why the two large energy providers design systems eg, BG with a buffer and Octopus with a high flow rate? Both of these are likely (proven?) to increase fuel use and hence costs. The installation cost may be lower which encourages the buyer but what about higher long term costs which benefits energy suppliers. Why can't we have the option of designs say max efficiency and lowest cost/upheaval  based on acceptable efficiency? Of course that is ridiculous as what we are offered is the best as they see it? Cynical thoughts off I'll bake some sourdough. 😊

Your question touches on a significant concern. It's not cynical at all to wonder why large energy providers like British Gas and Octopus design systems that may increase fuel use and costs.

I can’t speak for Octopus, but things at British Gas are changing since @heacol took over their heat pump installations a month or two ago.

Generally speaking, most installers prioritise solutions that are easier and cheaper to install to attract more customers. However, this approach can result in higher running costs. It's a valid concern that these designs might not always align with the consumer's best interest in terms of long-term efficiency and cost savings.

What would be ideal is offering customers a choice between maximum efficiency designs and lower cost/upheaval options, with transparent information about the long-term implications of each. Unfortunately, such tailored options are rarely presented, as providers often push what they consider best, which might not always align with the consumer's long-term best interest.

Enjoy baking that sourdough!

When I queried Octopus on the buffer I was told it was installed as a volumiser on the return line. They specifically mentioned to help with defrosts. A positive in that they aren't pushing hydraulic separation!

@gunboatdiplomat the industry's flippant use of terms causes countless unnecessary issues. For clarity: a tank with 2 ports is a volumisor, while one with 3 or more ports is a buffer. So, if they're calling it a buffer, it’s a buffer. To my limited knowledge, because I’ve only seen a handful of installation posts, Octopus still default to buffer tank installations. 

From what I've heard from competent installers, a volumisor is only necessary if there's insufficient volume in an open zone system. However, with modern open zone systems using modulating compressors, this is a rare requirement.

It's frustrating that these distinctions are often overlooked, leading to avoidable complications.

@gunboatdiplomat

From my limited knowledge an actual buffer tank can have quite a number of possible pipe connections with unused ones simply being plugged. Whether it functions as a buffer tank or a volumiser is simply how it is piped into the system.

I also believe that some buffer tanks can be directional, in that they only function correctly if the flow is in the correct direction.

@roel I also have a 12kW Samsung with the same 50L volumiser, although my volumiser is fitted to the primary return rather than on the primary flow.

Have a look at this discussion relating to the placement of volumisers (the discussion in the comments is useful also):

https://www.linkedin.com/pulse/how-your-heat-pump-system-designer-can-cost-save-you-money-hendra/

Ideally it should be in the heating circuit only, but if installed in the primary side, it's definitely beneficial to have it on the return.

As others have said, the two main justifications you will hear for this setup is (a) Samsung cite a minimum 50L volume requirement for the 12kW model so it saves any quibbling there if there are any issues, and (b) it will help with the defrost cycle and short cycling. I got the sense that installers do not really care about efficiency, rather just want an off the peg recipe for an installation that will work in 99.9% of cases. By "work", I mean they will not be receiving call outs at 6am on a cold winter's morning because the heat pump will not defrost, or that the manufacturer will not honour a warranty call because they cannot guarantee there is 50L of volume available to the heat pump.

Get it moved to the return side if you can, for the reasons cited in the article linked above.

@old_scientist Thanks. We came to this conclusion earlier, but good to see it confirms our thoughts.
Note, placing the tank as suggested in the article we tend to call a buffer and not a volumiser, but that's just wording.

I'm due to speak with the heating engineer from Joule who designed our system, so let's see how this develops.

@roel please keep us updated. I’d really like to hear what they do next.

sure, he's currently on holiday...

Spoke to a representative of Joule today.

He confirmed the volumiser was designed in to allow more volume for the defrost cycle. He said that the controller will open the necessary valves in the control unit on the Kodiak tank to allow for the flow so this should not be restricted by any closed manifold actuators. He kinda 'dismissed' the loss during a DHW cycle, and as this is currently done by my PV/battery system, and doesn't cost me a penny, it's hard for me to argue differently. As expected the argument "there's no issue so all is fine" did get used as well.

As I can't assess the performance on the heating side yet, we agreed to wait for colder times and see how I get on and if I'm not happy I can (and will) contact him again at which point he will get me in contact with a technical engineer.

So for now it's still a 'wait and see...'