Happy that A2W will prove less effective, although @bobflux comments about cooling with just AC and with slab then AC are interesting. 

Not looking for American style freeze yourself, just avoid the overheat. 

With regards to recirculation for DHW, instant hot water is something I am going to strive for, having been in properties with and without. My thinking is properly(read overly) lagged pipework, on a zoned system based on occupancy/motion gives a good trade off in terms of functionality and standing losses. 

The POU idea is interesting, and like I mentioned I have been circling around this for a while. My issue is the house will be long so tank near bathrooms isnt achievable. I did briefly look at dual tanks at either end. 

My issue is making sure I have enough power output available from the batteries, I can easily get 60kW, which is just shy of 2 full DHE27s, which would allow 2 simultaneous showers at either end of the house. Taking from cold water mains up to shower temp, at shower rate full flow.

But anything more than that at the same time and start being limited. To go to the next size of gateway, and with enough power costs considerably more. More than would be ever lost to heat loss (or extra cooling in the summer due to that)

Whereabouts in the country are you based, @chastity_outward053simplelogi? It feels to me like you're now at the stage where it's worth sounding a few installers out to pick one you're happy to work with, then providing your plans to them so they can suggest based on actual details. This thread has quickly got into a surprising amount of detail and making design decisions before involving an installer feels like the tail might be starting to wag the dog.

@majordennisbloodnok 

No that is just me trying to design and understand as much as possible myself. 

I am actually working in the middle east at the moment, but we have just put an offer in on a plot of land in Hampshire. It will be a few years before we break ground. 

But I have been going through everything with as finer tooth comb as I can mange to work out what is within my capability to do myself and what I cant. 

And also get a realistic total project cost

Posted by: @chastity_outward053simplelogi

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@majordennisbloodnok 

 

No that is just me trying to design and understand as much as possible myself. 

I am actually working in the middle east at the moment, but we have just put an offer in on a plot of land in Hampshire. It will be a few years before we break ground. 

But I have been going through everything with as finer tooth comb as I can mange to work out what is within my capability to do myself and what I cant. 

And also get a realistic total project cost

 

That makes far more sense, and is, of course, an ideal way of using the forum. Chewing over multiple alternatives can certainly give surprising results and there's no shortage of people here who know their stuff and can think laterally.

Do bear in mind, of course, that if you're thinking several years ahead you're also potentially planning for solutions that haven't been brought to market yet. One criticism of hot water heat pumps (DHW cylinders with small dedicated ASHPs on top) is that they're not the quickest to reheat the water after the tank has been emptied, but if A2A gains more traction in the UK then the whole issue of how to provide DHW may well get some inventive attention in ways that might affect your outlook one way or another.

Interesting times...

Posted by: @chastity_outward053simplelogi

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My issue is making sure I have enough power output available from the batteries, I can easily get 60kW, which is just shy of 2 full DHE27s, which would allow 2 simultaneous showers at either end of the house. Taking from cold water mains up to shower temp, at shower rate full flow.

You could consider putting the DHE27 on the hot water pipe near the shower.  Then you get instant hot water at a COP of 1, whilst the water from the tank (at a COP of 3) works its way to the outlet.  

In my previous apartment I put a 10 liter water heater right below the kitchen sink. Instant hot water to the tap, but only 2kW power consumption, much more manageable than tankless. This small tank was fed from the big tank that was a bit further away, far enough to create an annoying delay.

Or, if you use recirculation and home automation, here's an idea. I put a Zigbee button in the bathroom. One click means a shower is imminent, so it turns on the towel warmer and also switches the ventilation to high for a set amount of time. It could also switch on the recirculation pump. Then once showered you also get a warm towel, which is nice.

You could also combine recirculation with a small unpowered insulated tank. In the morning, simply circulate the hot water to bring the tank to temperature, then it's not an issue if water in the pipes is cold, it'll mix with the hot water inside the tank. The idea here is that it's much easier to insulate a small tank than a long pipe.

Posted by: @chastity_outward053simplelogi

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that is just me trying to design and understand as much as possible myself. 

[...]

And also get a realistic total project cost

One of the issues I'm finding difficult here is that you aren't worried about choosing some very expensive bits of kit.

When I design something for the house I'm usually constrained financially, whilst also wanting to produce something that's functionally appropriate.

Thus, when you would consider buying a Stiebel Eltron DHE27 (£850+) for each shower room at opposite ends of the house, my starting point is a nominal 10kW inline heater like the Redring Powerstream, which costs 20% of your solution!

Here's a similar unit to the Redring which I built into a Guest-room en suite by placing it within a double-thickness wall:

May I still make suggestions which cost very little?

Your aspiration for a state-of-the-art Passiv House allows you to easily trump my proposals by simply spending more!  🤔 

@transparent 

You are right, I am not too concerned about choosing expensive kit, if the function justifies it! But likewise I do not want to spend money for the sake of spending money. 

By all means please do suggest any and all ideas, even if they get discarded they may get me thinking about something from an angle I hadn't even imagined. 

In your example of the DHE27s vs RedRing - my concern would be heating up the water to achieve a sufficient flow rate at an appropriate temperature, and if I was running a tank already to pre heat the water, I could achieve instant hot water via other means. It is certainly an option I have explored! 

I would also ad for example my auto balance valves (that i have discounted) my perception was incorrect and I now know they werent doing what I assumed they were, so happy not to spend money there!

I wouls sacrifice COP for functionality up to a certain point. But if I could spend a little more to get both, I wouldn't discount it either. 

I am so early in the journey that anything is fair game for consideration 

Another option for instant hot water at shower volumes distant from a tank:

Calculate the time it takes for the dhw to get from tank to outlet (say 1 min).  Install a recirculating system and a small (say 15l) local tank (15 l because it avoids the need for the D1 d2 arrangement).  When the outlet is switched on activate the recirculation but feed the outlet from the local tank until hot water arrives.  You get most of the dhw at a cop of 3 without 24*7 losses and without the need to press a button.

Posted by: @bobflux

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Currently, I send water above the dew point (17°C) into the slabs. The effect is... subtle. In fact I can't really tell whether it's doing anything. Yeeeah it is that effective lmao.

On the other hand, my second hand 3kW mobile AC unit has no trouble bringing the living room down to 19°C with an outdoors temperature of 33°C...

However, at night, I turn the mobile AC unit off, because it is noisy as hell. Then, normally, when I turn it off, room temperature rises quickly because it cools the air but it doesn't cool the masonry much. However, when I cooled the slab earlier in the day, even after turning off the AC, temperature remains at civilized levels until the next morning.

Therefore, cooling the slab is not very useful on its own, but it is a good complement to cooling the air with fan coils.

Now this has got me thinking quite a bit - I know this is not the best advice for perfect COP... but bare with me:

I would like slab cooling
I would like FCU cooling. I would value FCU cooling working better - ie as we discussed earlier, I need the flow temp to be low, for argument sake lets say 5.

But can I have my cake and eat it (at a cost - more later)? Could I set the flow temp to 5 - run the FCUs at 5, but at the same time run the UFH with a mixing valve such as the ESBE VRG130 series, the accompanying actuator and a flow temp gauge. Controlled via KNX to never allow the UFH temp to be < dew point plus 2. 

Now the cost is complexity, as soon I put the mixing valve in - I have to have a dedicated UFH circulating pump - as it is possible for the valve to be 100% using UFH return, 0% ASHP. And with the same logic I then have to have hydraulic separation from this and the ASHP, as if I am using minimal ASHP flow, and then FCU's turn off that is not a good situation for the ASHP. 
The other cost is COP, which comes from mixing the water (increase in temp in this case) but that means I am cooling to then heat up again.
And I would either need a buffer, or a LLH and a volumiser. which would also increase the loss of COP from distortion.

Is there a way to quantify how much this negatively effects the system?
And then I can do a fairer comparison on benefit (cooled slab as well as effective FCUs) vs complexity and worse COP (another circulating pump, LLH/volumiser or buffer)

Yes you can do that, you can also send the water first through the FCUs then through the slabs.

In both cases the return temperature to the heat pump will increase due to the slabs return being hotter than the FCUs' return. So, suppose you run the FCUs at 7/13°C, if you mix in a bit of warmer return from the slabs, but you still want the flow temperature to be low enough for the FCUs to cool well, maybe you'll have to run at 7/19°C. That's a pretty large flow-return deltaT. Since the product of flow, deltaT, and heat capacity is power in Watts, and the heat pump maximum cooling power sets a limit on how many watts it can remove from the water. Thus running at higher deltaT either means flow remains the same but power increases, or power remains the same (ie, maxed out) and flow has to decrease. Otherwise you won't get the higher deltaT.

Therefore... maybe, you'd have to run the math.

Even with a 16kW heat pump, I don't plan to do it, because there's a much simpler way: during the night, there is little need for air cooling because outside temperature is low, the sun is not shining through the windows, therefore heat gain is low. So why not simply do air cooling during the day, and slab cooling at night?

Okay, you have me convinced. KISS. 

No buffer, no LLH, no mixing VRG130, FCUs and cold temp by day, slab post solar gain window at dew point + 2.

So in the mentality of removing unnecessary components, if I am doing a UFH manifold of Tees (28mm to 3/4" M) for my 22mm Ridgeline eco Max, like we spoke about earlier, if I have isolating valves on each leg, do i need manual balancing valves at all? 

Given this will be UFH in a slab, open loop, no zoning and running with weather compensation. If the loops are all +/-10% of the same length, do I care particularly if the flow rates are subtly different. My thinking is that the slab is a huge thermal store, so any subtle discrepancies will even out as long as the length is within a reasonable tolerance. Especially as it will be Passivhaus standard, so low loads and flow temps anyway?