@jamespa

I want to clarify that my hybrid example was posted specifically in response to Johnmo’s system description. I would not recommend it universally, nor do I believe every home needs a complex or hybrid setup.

But I would suggest that even in smaller, modest homes — like the 100 m² properties you mention — the foundational issues that limit efficiency or comfort are rarely about the appliances themselves. They’re nearly always tied to system structure: how water is moved, how returns are blended, how zones are defined, and how appliances "see" system demand.

NRG Structural Zoning came about not to make things more complex, but to make proper system behaviour more reliable, by solving these recurring design flaws in a repeatable way. It's not about upselling controls or adding gadgets. Most systems we support are simple in principle and often use single appliances. The main difference is that their layouts are hydraulically correct, with pressure-stable, independently circulated zones, and clean return paths that let the appliance do its job correctly.

When we design for this, even in a basic two-zone retrofit, we remove much of the guesswork around balancing, modulation, and control feedback. Oversizing, short cycling, mixing, and loss of condensing are all symptoms of structural shortcuts we’ve seen for decades, regardless of the fuel source.

I also understand the view that every few years there’s a "new best thing" in heating. But what hasn’t changed is thermodynamics. Water still behaves the same way. Return temperatures still matter. Pressure still governs flow. That’s why we developed a fuel-agnostic layout method that is future-proof for whatever heating technology comes next. What we call NRG Structural Zoning™ is the most straightforward way to structure a system so the appliance doesn’t need to be ‘tricked’ into working well.

It’s a principle, not a product. But we’ve backed it up with products — because that’s the only way to make it easy to install at scale.

Ok so I think you consider it (structural zoning, not hybrids) mainstream.  Fair enough. Let's consider a couple of fairly mainstream examples. 

a) A 100sq m new build by a volume builder built to building regs, IE the sort of property that is being thrown up at the rate of 100000 per year with a target of 300000.  Probably 3kW or less at design temp

b) A 200 sq m retrofit to a two storey property with radiators, primaries split upstairs/downstairs.  Let's say 7kW at design temperature.

c) A 100 sq m retrofit like (b) but with single primaries.  Let's say 5kW at design temperature.

In all cases ASHP / ASHP replacing gas boiler.

How does your structural zoning apply to these cases, how much will it reduce fuel consumption/increase comfort and why?

Also I note that the product description says 'Also, the fully open bypass between each chamber neutralises the various pump’s activity from each other,'.  Doesn't that mean that it it, in essence, a llh with the possibility of mixing between flow and return, compromising COP?

That’s a great question, James, and it goes right to the heart of what sets structural zoning apart from conventional approaches like LLHs or buffer tanks.

Let’s begin by clarifying the premise. We're assuming (reasonably) that the heat pump is adequately sized, the pipework is correct, emitters are correctly selected, and the system has been commissioned to deliver a suitable ∆T at the design flow rate. If those conditions are met, then the heat pump will deliver enough energy to meet the load, and the system’s structure should allow it to do that without interference or artificial restriction.

Now, regarding your specific question: Does the open bypass between chambers in the NRG Zone act like a low-loss header and risk flow/return mixing that compromises COP?

No — and here’s why:

In a traditional LLH or buffer arrangement, water is mixed from various circuits before it's distributed to the zones — or blended upon return, distorting the return signal the heat pump sees. This often leads to artificially elevated return temperatures, triggering early modulation or shutdown, especially in low-load conditions — i.e., exactly when the system should be coasting.

The NRG Zone is different. Each circuit draws from its own dedicated outlet first — flow is established independently, at the correct rate, using each zone’s circulator. There is no blending before circuit delivery. Any residual flow passes through the open bypass only once those circuits are satisfied. In effect, the system satisfies the load first and only then provides a clean, undistorted return path.

This design ensures that:

Each zone receives its required volume independently.

The heat pump sees a return temperature that genuinely reflects what the system is doing — not an average distorted by bypass bleed.

There is no hydraulic interference between zones.

The system does not suffer from reverse flows, artificial blending, or unpredictable ∆T behaviour.

In low-load conditions, if zone demand is low, the open bypass allows the excess flow to return — cleanly — giving the heat pump accurate feedback so it can modulate down. The bypass may carry nothing in high-load conditions because all available flow is directed to the zones.

So, to summarise, the bypass is a safety release — not a dilution point. That’s a crucial distinction.

I'll follow up with a breakdown for your three property scenarios (100 m² new build, 200 m² retrofit with upstairs/downstairs primaries, and 100 m² single primary). But the short version is this: NRG Structural Zoning works in all of them, and it doesn’t require complex extras. For a modest two-zone system, it adds stability, balancing, serviceability, and future upgrade potential—with little more effort than a conventional manifold setup.

I am happy to expand further if helpful.

@jamespa, following on from your examples — here's how I’d approach each:
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a) 100 m² New Build (3kW @ -2°C, typical spec):

In this case, structural zoning might not seem necessary — but even a simple two-zone layout (living + bedroom split or living + DHW) can benefit:

Improved temperature control between day/evening spaces and sleeping zones without relying on high-override TRVs.

Cleaner appliance behaviour, especially if using low-temperature emitters like underfloor or large radiators.

Straightforward install: an NRG Zone 2-port manifold simplifies wiring and commissioning rather than mixing valves and manual balancing.

Impact: Marginal energy savings in mild weather, but noticeable comfort improvements and lower support burden — particularly as tenants or owners adjust their use habits.
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b) 200 m² Retrofit, Two Primaries (Up/Downstairs Radiators, 7kW load):

This is an ideal candidate for NRG Structural Zoning.

Split the system into 2 or 3 pumped zones (up/down/DHW), each independently balanced.

Remove the need for restrictive motorised valves, which often fail or create reverse flow paths.

Return temperature control becomes stable, and modulation is more effective — especially in partial load conditions.

Impact: Reduced short cycling, improved boiler or ASHP modulation, and future-proofing (e.g., easier to add another source or update emitters later).
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c) 100 m² Retrofit, Single Primary, 5kW load:

Even in this more constrained setup, structurally separating space heating from DHW provides a benefit, if not more.

The manifold provides a clean way to connect both, avoiding interaction.

It adds minimal cost or effort compared to a standard replacement, and the payback is in stability and serviceability.

Impact: This layout reduces temperature overshoot, simplifies heat pump response to mixed demand, and allows for basic expansion later (e.g., adding a towel rail or small loop).
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The system doesn’t need to be complex in all three cases—it just needs to be well structured.

@johnmo, I can see what you mean by the heat pump switching over and back between cooling and DHW, but I was referring to the heating season when you might need a simultaneous operation if you have two appliances where each could do separate jobs while working together.

Posted by: @harryrea

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@johnmo, I can see what you mean by the heat pump switching over and back between cooling and DHW, but I was referring to the heating season when you might need a simultaneous operation if you have two appliances where each could do separate jobs while working together.

Have configured the hybrid based on cost of running mostly.

Tried a few different configurations and every time I found the heat pump and boiler could run happily together, but when a defrost came along the heat pump would see an elevated return temp and see it had nothing to do. So I use that to my advantage, if it's defrosting the CoP can drop like a stone. So I let the gas boiler take over and it runs on a +0, -0.1 hysterisis thermostat. The gas boiler will not run unless outside is 5 degs or below for 6 hrs and room sensor is below target.

@johnmo That’s a clever use of defrost behaviour to guide handover — and it sounds like you’ve fine-tuned it well for your setup. Just for reference, the Lex v3 controller allows similar logic but builds it into the system structure. It can call the secondary boiler in three ways:

 

 

Posted by: @harryrea

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@johnmo, I can see what you mean by the heat pump switching over and back between cooling and DHW, but I was referring to the heating season when you might need a simultaneous operation if you have two appliances where each could do separate jobs while working together.

@harryrea In a heat pump only system you are never heating space and DHW simultaneously because they require different flow temperatures.  For the same reason in a hybrid system, if you do bith simultaneously you won't be feeding both through the same manifold.  Your responses to my practical examples seem to envisage the dhw heating as just another zone connected to the manifold, I do grant its just another zone but isnt going to be energised simultaneously so can equally well be separate.

Posted by: @harryrea

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100 m² New Build (3kW @ -2°C, typical spec):

Straightforward install: an NRG Zone 2-port manifold simplifies wiring and commissioning rather than mixing valves and manual balancing.

Impact: Marginal energy savings in mild weather, but noticeable comfort improvements and lower support burden — particularly as tenants or owners adjust their use 

Why would you have mixing valves which are always detrimental.  In a retrofit there may be no choice but they can be designed out in a new build.

How is your system balanced?  You still have to ensure each zone gets about the right amount of energy.

In 100sq m new build, well insulated on the outside but with minimal internal insulation,  how much difference in temp do you think you can support between rooms in reality?

If there are no savings why is a mass market builder going to bother when plumbing it as a single zone directly connected to the heat pump is simpler and cheaper and very likely works as well?

Posted by: @harryrea

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b) 200 m² Retrofit, Two Primaries (Up/Downstairs Radiators, 7kW load):

This is an ideal candidate for NRG Structural Zoning.

Split the system into 2 or 3 pumped zones (up/down/DHW), each independently balanced.

Remove the need for restrictive motorised valves, which often fail or create reverse flow paths.

Return temperature control becomes stable, and modulation is more effective — especially in partial load conditions.

Impact: Reduced short cycling, improved boiler or ASHP modulation, and future-proofing (e.g., easier to add another source or update emitters later).
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With an ashp ( or indeed a boiler with weather compensation) DHW is separate and not run at same time as space heating, see above.  So 2 zones in reality.

If it were one zone no need for 'restrictive motorised valves' except to switch between dhw and space heating which is unavoidable.

Why is return temp more stable, surely that depends on load unless your system modulates the speed of the secondary pumps?

Why us there reduced short cycling, that depends on heat pump min output and load neither of which is affected by your system.

Posted by: @harryrea

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c) 100 m² Retrofit, Single Primary, 5kW load:

Even in this more constrained setup, structurally separating space heating from DHW provides a benefit, if not more.

The manifold provides a clean way to connect both, avoiding interaction.

As above space heating and dhw will never occur simultaneously and are structurally separated in any conventional ashp install with a diverter valve.  Why add an unnecessary manifold and additional pump?

Posted by: @harryrea

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There is no blending before circuit delivery. Any residual flow passes through the open bypass only once those circuits are satisfied.

Presumably this assumes that the volumetric rate of the primary pump exceeds the sum of the volumetric rates of the secondary.  In this circumstance there would be no blending before delivery with a buffer or llh either, (nor of course with a direct connection between heat pump and emitters which still appears to be the best solution)

Hi James,

Thanks again for your detailed thoughts. I appreciate how precisely you're interrogating the claims and looking for practical value — so here’s a more complete breakdown in reply to your six points:

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1. DHW and Space Heating — Why Use the Same Manifold?
You’re absolutely right that most ASHPs don’t support simultaneous DHW and heating at different temperatures. However, the NRG Zone allows something different:

During heating mode, the DHW zone can preheat the cylinder (e.g., up to 35–40°C) while the heating zones are active.

When DHW priority is needed, the NRG Lex interrupts the space zones and raises the DHW zone to full temperature.

This staged approach reduces the time the heat pump spends operating at inefficient high flow temperatures — and in hybrid systems, it can optionally shift final heating to the boiler (e.g., for legionella).

That ability to use zone isolation and staged heating gives much better control, especially in systems where DHW demand varies or when occupants want the shortest DHW recovery times.

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2. Why Use Structural Zoning in Simple Systems?
The typical response is, “Isn’t that overkill for a small house?” — but the reality is that even basic systems can suffer from:

Oversized emitters drawing more flow than needed

Return temps rising too early, reducing COP or condensing

Rooms heating unevenly due to poor balancing or shared pipe losses

NRG Structural Zoning™ eliminates these common faults with minimal added cost.

You still only use two or three circuits.

Each one is isolated correctly hydraulically.

You avoid cross-flow, blending, and backfeeding — even in compact builds.

Yes, it's more structured than a single loop with TRVs, but the payoff is less modulation error, easier diagnostics, and better comfort stability.

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3. Do TRVs or Mixers Still Have a Place?
Absolutely. NRG doesn’t oppose them — they serve different purposes:

TRVs/mixers control temperature per room or circuit.

Structural zoning manages flow clarity and pressure separation.

If you use TRVs within a zone, you still benefit from balanced delivery to that zone and stable return signals from it. The two approaches are compatible and often complementary.

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4. Return Temp Stability and Modulation — Does Zoning Help?
Yes — and this is the heart of the method.

In conventional shared-pipe systems, when one small zone calls, the appliance still sees the full loop — which distorts flow and return data.

Structural zoning meets each call with the correct volume via its own pump and flow control.

That means the heat pump sees a clean delta-T that is reflective of the actual load, not phantom demand or unintended recirculation.

So, modulation works as intended. Systems short-cycle less, and heat pumps stay longer in their high-COP range.

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5. Isn’t DHW Already Separated with a 3-Port Valve?
Yes — but using a 3-port means relying on mechanical diverters, motorised logic, and sequencing. That works, but it’s not always flexible.
NRG Zone integrates DHW into the same manifold as a hydraulic peer, meaning:

You can add solar preheat, hybrid boosting, or future DHW load changes easily

The return path remains separate, clean, and correctly sensed

You don’t need an external diverter valve — the control module handles the logic
It’s simpler long-term and easier to upgrade — especially in homes with future electrification plans.

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6. Isn’t the Bypass Just a LLH in Disguise?
This is a great question — but there’s a critical distinction:

In an LLH or buffer, blending happens before zones are satisfied, masking load and compromising control.

In NRG Structural Zoning™, the bypass is downstream of all zones.

If zones are calling, the flow goes directly to them.

If there’s excess, it’s returned cleanly through the bypass, maintaining accurate ∆T for the appliance.

If no zones call, the bypass acts like a pressure equaliser, not a mixer.

This setup avoids false return temperatures, meets demand before any bypass flow is triggered, and preserves system modulation behaviour.

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Final Thoughts:
None of this is about adding unnecessary components. It is about eliminating inefficiencies that controls can’t fix while making the job simpler to commission, diagnose, and upgrade.

NRG Structural Zoning is already widely used in modest homes, often with single appliances. It becomes even more beneficial when heat pumps, mixed loads, or low ∆T demands are involved. And perhaps most importantly — it helps the heat source work with the system, not against it.

I am happy to continue this discussion — I genuinely appreciate how well you’re drilling into the principles

Thanks for the detailed reply and I apologise if I can sometimes be pedantic and determined to 'get to the bottom' of product claims. My aim is simply to bring clarity.

Unfortunately your reply, whilst detailed, does not appear to respond directly to my questions and instead introduces new arguments.  As a result some key concepts remain unclear, at least to me.

To simplify things at this early stage I will therefore respond to three of your sections above only, concentrating on those key concepts.

Posted by: @harryrea

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1. DHW and Space Heating — Why Use the Same Manifold?
You’re absolutely right that most ASHPs don’t support simultaneous DHW and heating at different temperatures. However, the NRG Zone allows something different:

During heating mode, the DHW zone can preheat the cylinder (e.g., up to 35–40°C) while the heating zones are active.

When DHW priority is needed, the NRG Lex interrupts the space zones and raises the DHW zone to full temperature.

Well that depends on your flow temperature (as modified by the WC curve - which might take it as low as 25C) and your tank temperature, furthermore you also need to take into account stratification of the tank. Without proper control and several thermistors on the tank so the controller can determine the state of stratification this simply isn't going to work, in fact you will end up cooling the tank instead!

Unless you offer all the components and a controller to do this I cannot see it's practical.  Furthermore the claimed performance advantage doesn't exist with any heat pump (such as my Vaillant) that adjusts the flow temp as the dhw tank heats up.

Posted by: @harryrea

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5. Isn’t DHW Already Separated with a 3-Port Valve?
Yes — but using a 3-port means relying on mechanical diverters, motorised logic, and sequencing. That works, but it’s not always flexible.

Sorry but even with a manifold you are still going to need either a motorised valve, or an additional pump somewhere, whether it is in your unit or separate because somehow you need to stop the high temperature water destined for dhw going to the emitters circuit.  What's the essential difference/advantage that makes your system more 'flexible' and how does it interact with the dhw control function of the ashp?

Posted by: @harryrea

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6. Isn’t the Bypass Just a LLH in Disguise?
This is a great question — but there’s a critical distinction:

In an LLH or buffer, blending happens before zones are satisfied, masking load and compromising control.

In NRG Structural Zoning™, the bypass is downstream of all zones.

If zones are calling, the flow goes directly to them.

If there’s excess, it’s returned cleanly through the bypass, maintaining accurate ∆T for the sppliance

i completely agree llhs and buffers are bad news in almost all domestic cases.   My point is that I can't see how your solution differs materially in this respect and so far your explanations haven't clarified this, at least for me. Here are my comments on the arguments (as I understand them) that you have made to date:

(a) I commented above that your assertion that there is no flow water blending is surely dependent on the sum of the secondary flow rates being less than the primary flow rate.  Can you confirm that this is the case.  If it is the case how is that guaranteed and if it is not the case how do the flows work?

(b) Perhaps the reason is contained in the statement "In NRG Structural Zoning, the bypass is downstream of all zones". Could you explain this and how it ensures no reduction in flow temperature occurs?

(c). So far as I can see youur final statement above ( If there’s excess, it’s returned cleanly through the bypass, maintaining accurate ∆T for the sppliance) can't possibly be true.  If say 50percent of the emitter capacity is engaged and supplied with water, the remaining being bypassed, then the delta T seen by the appliance will be half what it would be if 100pc of the emitter capacity is engaged (all other conditions remaining the same), for the simple reason that only half as much energy is being extracted from the water by the house.

I won't respond to the other comments you have made at this stage, I would prefer if you are willing first to 'run to ground'

a)  if your argument that NRG structural zoning offers benefits for dhw is true (see my comments above)

b) how exactly your system avoids the possibility that flow temperature is diluted in a similar way to an llh, unless similar care is taken setting it up (again see my comments above)

c) how your system does what you appear to claim in respect of deltaT as seen by the appliance (again see my comments above)

James, thanks again for your thoughtful and persistent questioning — this kind of interrogation helps clarify the strengths and limits of any approach. I’ll reply here in the same order as your points for clarity:
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1. DHW Preheat via Manifold — Is it Practical or Effective?

You're absolutely right that successful DHW preheating depends on stratification, accurate control, and appropriate flow temperature. We don’t claim that the NRG Zone alone manages this — what it does is provide the structural means to allow DHW preheat if the controls support it and the conditions are favourable (e.g. cold tank, flow temp in the 35–40°C range).

This preheat typically happens during space heating before full DHW priority is called. For example, if the heat pump is heating rooms at 35°C and the cylinder is at 20°C, raising the cylinder’s base temperature before triggering a full 50–55°C DHW cycle makes sense. That reduces the time the system spends operating inefficiently at higher flow temperatures.

Of course, this is optional—not required. The NRG Lex control can isolate space heating pumps during priority demand and resume them automatically, just like 3-port valves do. However, the NRG approach simplifies wiring and preserves zone separation, so the switch-over is hydraulically clean.
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2. 3-Port Valves vs Structural Zoning — What’s the Difference?

You’re right again — both approaches need some mechanism to isolate high-temp DHW from space heating circuits.

In our system, this isolation is achieved electrically rather than hydraulically. The NRG Lex uses the DHW call signal (from the heat pump or third-party control) to interrupt power to the space heating pumps during DHW operation. This means:

No diverter valve is needed

Fewer moving parts (no valve motors)

Priority can be flexibly reassigned (e.g. DHW vs second zone) by reconfiguring wiring or dip switches

This is particularly useful in hybrid systems, where the heat pump and boiler might heat different zones concurrently. The NRG Zone structure keeps them separated and avoids conflicts.
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3. Is the Bypass Just a LLH in Disguise?

This is a vital point — and it’s where structure matters.

Yes, every heat pump system needs an open path to ensure flow. But here’s the difference:

In an LLH or buffer, flow and return meet before zone delivery — so blending is inherent.

In NRG Structural Zoning, zones draw their flow directly primarily before any return path or bypass. The bypass sits after the zones and carries only surplus, if present.

Let me answer your specific sub-points:

(a) Is blending avoided only if primary > sum of secondaries?
Yes—and that is always the design intention. The NRG system is sized to ensure the primary pump delivers slightly more flow than the combined zone demand. But even if that margin is small, zone flow is protected because of how the manifold is built: the supply chamber is separate and ahead of any mixing point. There's no shared body of blended water, as in an LLH.

(b) What does "bypass is downstream of all zones" mean?
It means water only enters the bypass once all zones have taken their required volume. Structurally, the zone flows are prioritised, and only leftover volume flows back to the appliance through the bypass. So, there is no chance of flow water being diluted before it reaches a zone — which is what compromises COP in LLHs.

(c) Doesn’t delta-T reduce if only some zones are calling?
Not necessarily. Delta-T at the appliance reflects energy actually being used, which should drop when only a partial load exists. What matters is that this feedback is accurate, and NRG Structural Zoning provides just that. It doesn’t hide unused volume in a buffer or blend return temps; it delivers only what’s needed and lets the appliance respond correctly.
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Closing Thought

No system can override the laws of thermodynamics, and we don’t claim to. However, structural clarity, pressure separation, and accurate feedback allow the appliance to work with the system, not against it.

Importantly, the NRG Zone isn’t a magic box—it’s a method. It simplifies repeatable installation, avoids return temperature distortion, and makes multi-appliance layouts (hybrid or otherwise) easier to wire, balance, and service.

I hope this clears up the key points. I'm happy to dig into any part you'd like more detail on.

Some further info that might help:

NRGAWARENESS.COM "https://www.nrgawareness.com/images/PDFs/NRG_Zone_Brochure_Split_for_digital_use.pdf"

https://www.nrgawareness.com/images/PDFs/NRG_Lex_v3.1_Manual_.pdf