Posted by: @chastity_outward053simplelogi

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Okay good to hear about fan coil cooling with water temp above  dew point - I had toyed with being below but thought I may save myself potential condensation issues, but if it is not worth the time I can go back to no slab cooling, and just fan coils at low temp with vapour sealing on all cold pipework.

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.

I have not installed the fan coils yet, they're sitting in a pile while I finish that damn ceiling. I am sure the vapor insulation will be a challenge, we'll see. But I'm going to do it, because I absolutely want quiet AC.

Posted by: @chastity_outward053simplelogi

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Please can you expand on why PICVs are useless? My intent was to use a 0-10v actuator on them as well as the FCUs ESC fan, controlled by a Zennio KNX product (MiniBox 0-10V x2) that modulates both - and has a dedicated module that is designed for modulating both.
In my head the PICV is just a slightly more fancy individual zone valve, that caps it at a set max flow rate, but allows me to modulate below that? So I could still open it up (via KNX) and pass water through without turning the fan on etc to avoid minimum flow rate issues.

Looking at Caleffi 145 Flowmatic PICV datasheet I see it needs a minimum pressure drop of 30kPa in order to open and do its job. 30kPa is 3 mH2O or 0.3 bar which is already more than half of what the circulator in your heat pump can provide, so... problem. It would be more rational to use the circulator's pressure budget to push water through pipes and emitters rather than waste it on a valve. These valves are designed for big buildings with powerful circulators. They don't make sense in a residential setting.

If you want to modulate flow through your fan coil it is simpler to use something like a radiator valve with an actuator on top. I tried it and fitted a Siemens SUE 21P on a radiator TRV in place of the knob. It works absolutely fine. Control is by two wires (open/close), if you power the motor for longer it will open and close more. These also fit on UFH manifolds but they're too wide, and the manifold valve they fit on is only good for on/off so it won't modulate your UFH loops. Honeywell also makes valves for this but I couldn't find them, apparently only available in the US and Asia. I also tried Honeywell M6410C-7410C actuator on a radiator TRV: the adapter broke on the first use so nope. You can also use a small motorized ball valve, reduced bore 1/2", that should work fine, and it doubles as a zone valve. They're simple, cheap and easy to use, so that's what I'm going to use. None of these options have the minimum pressure drop requirement from the PICV so they are a much better fit for a single circulator heat pump system.

So in order to keep it simple, since I was going to put ball valves on the FCUs to isolate them in case of maintenance, I simply went with motorized ball valves instead. I might use them as flow control, but most likely not.

Posted by: @chastity_outward053simplelogi

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I was under the impression that FCUs can require quite a high flow rate? Will the ASHP pump be able to cope with them at full tilt if required?

FCUs are a bit counter intuitive: in cooling mode, if you increase the fan speed, the output temperature will increase, that's because its maximum power is determined by the water (flow * deltaT). So increasing the fan speed will blow more air, but it will be less cool. If you want more airflow AND cooler output air then you need more water flow. In cooling mode, your 5kW heat pump should have enough power to max out 2-3 fan coil units, you plan to install more so if they're all on, the heat pump won't be able to cool the water enough to max them all out. This isn't about flow, it's about power. This isn't necessarily a problem: if they are balanced and one doesn't hog all the flow it will work fine.  All that matters is that the FCUs and heat pump have enough power to suck the heat that gets into the house. But do you really need this many?

FCUs only have a flow requirement in so far as to get the cooling power you need the flow, but if the flow is not high enough then you just get reduced power. The issue is more the other way around: you have to make sure the heat pump gets enough flow so it runs at low deltaT and doesn't trigger an error. Low deltaT is important, because water freezes at 0°C, so you can't get below 5°C to avoid cold spots in the heat exchanger... but you also want the water to be as cold as possible so the FCUs work efficiently. So if you work with 7°C/10°C flow/return (deltaT 3°C) the FCU heat exchanger will be 1-2°C cooler than at 7°C/13°C (deltaT 5°C), so it will boost performance a bit.

I'm about to run the risk of oversimplifying and asking a dumb question. However.....

This is a new build we're talking about, and one where insulation and airflow are capable of being kept to PassivHaus standards. MVHR has already been mentioned as a desirable inclusion, and that means ducting. Cooling is getting a lot of discussion, and heating capacity required is expected to be low. Given all this, is there any reason why an air to air system isn't being considered? The only thing it wouldn't be able to do is DHW and there are several options for that besides an A2W heat pump.

Seems to me that going from the start with A2A would simplify the design significantly as well as removing the need for radiators entirely and having the summer cooling inherently included. Am I missing something and talking spherical objects?

@bobflux Perfect - thank you. Okay the PICVs I were looking at were 16kPa, but even with that 7 of those robs me of too much, and I achieve the same goal with actuated ball valves. I had been looking at he belimo ones, so I may have another look.

@majordennisbloodnok Now this is a completely new train of thought for me - and no there is no reason other than I have very (even less) working knowledge of A2A. Lets say I got a ducted unit, would that sit alongside MVHR? Or can you combine the two? Is that advisable, or a fallacy? 

Would give me the question about DHW - which, and I haven't broached this here, I have had some interesting thought cycles about. I like the idea of POU instantaneous boilers, I know they only achieve a COP of 1. But, if I have a large bank of batteries (3 phase) and a suitably large inverter, it saves me me all standing losses. Significant pipework, a secondary recirculating loop, the pump, valves, a tank etc. So it may be a case that actually it is worth it in the long run.
I did toy around with very low tank temps, and then DHE27's to ensure it maintained a nice temp (because they modulate the power, costing very little) and gave instant hot water.
I had binned off the idea after doing a fair amount of research, as I came to conclusion with the A2W heat pump it worked out easier to have just a larger UVC and a secondary loop to get instant hot water.
But with just an A2A, I could do one POU boiler (something like the DHE27) for each bathroom group (so bath/shower/sink), a smaller unit for the kitchen and another one for the garage. I reckon the cost is probably similar to tank+ancillaries and pipework. Without even including the recirculating loop.
Plus saved cost on UFH etc.

The batteries and invertor required were part of my plan anyway - so that is neither here nor there in terms of cost. 

What about comfort factor? Anyone with thoughts/opinions on A2A heating vs UFH for example?

Posted by: @chastity_outward053simplelogi

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Lets say I got a ducted unit, would that sit alongside MVHR? Or can you combine the two? Is that advisable, or a fallacy?

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That's the big question. I've seen lots of bits of that conversation going on around t'Interweb but I don't know the answer and haven't seen a complete answer in one place. It's likely to need someone knowledgeable on the subject (like @ashp-bobba) to give a considered opinion.

If it is possible, though, everything you said afterwards is valid. I must admit I wasn't envisaging a DHE 27 (I was thinking more along the lines of a Vaillant aroSTOR hot water heat pump) but if POU hot water works for you then as I said there are plenty of alternative approaches. 

Posted by: @majordennisbloodnok

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Posted by: @chastity_outward053simplelogi

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Lets say I got a ducted unit, would that sit alongside MVHR? Or can you combine the two? Is that advisable, or a fallacy?

...

That's the big question. I've seen lots of bits of that conversation going on around t'Interweb but I don't know the answer and haven't seen a complete answer in one place. It's likely to need someone knowledgeable on the subject (like @ashp-bobba) to give a considered opinion.

If it is possible, though, everything you said afterwards is valid. I must admit I wasn't envisaging a DHE 27 (I was thinking more along the lines of a Vaillant aroSTOR hot water heat pump) but if POU hot water works for you then as I said there are plenty of alternative approaches. 

 

Mitsubishi and I think another manufacturer used to make a Guffy unit which was a combined split type AC system with a HR ventilation unit, also commercially we do often inject fresh air on to the back of cassettes and ducted units but this must be no more than 20% of the FCU flow rate not to effect the operation. 

@chastity_outward053simplelogi Hello, TBH, I think you could afford an AC units or 2 on top of the ASHP if you strip out most of the over complicated valves, pumps and FCU's these will all cost quite a bit. 

If you have a passiv house, unless its a castle, your heat losses, especially with HVHR should be very low. at 10w/m2 standard a 300m2 home would only need 3kW at peak heating, having a 5 or 7kW unit with all those controls will cause you problems in mild seasons.

I would install the following:

1No 3kW good brand ASHP

1No XXXltr HP compliant hot water cylinder 

1No Adia Thermal intelligent control unit, gives you room by room control, managed open loop, TOU tariff control and brilliant hot water control (this makes up for all the valves and complex control you were looking at as it does the same but is actually interfaced with the ASHP control.

1No small split in your favourite room 

1No small split in your favourite bedroom 

You can combine the splits to a multi split so only 1 units outside. 

All of the above give you exactly what you were trying to do and hopefully at a lower price, also the AC will actually battle the solar gain or over heating which is likely your biggest issues for 6 months a year if you have beautiful glass everywhere, an ASHP will not so much even with the FCU's as you can only run the system at 16/17 deg C. Split will run at 5-8 Deg C.

Please keep in mind I dont' know your whole design, the above is based on my experience of passiv house design.

I hope it helps a bit.  

Posted by: @ashp-bobba

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@chastity_outward053simplelogi Hello, TBH, I think you could afford an AC units or 2 on top of the ASHP if you strip out most of the over complicated valves, pumps and FCU's these will all cost quite a bit. 

If you have a passiv house, unless its a castle, your heat losses, especially with HVHR should be very low. at 10w/m2 standard a 300m2 home would only need 3kW at peak heating, having a 5 or 7kW unit with all those controls will cause you problems in mild seasons.

I would install the following:

1No 3kW good brand ASHP

1No XXXltr HP compliant hot water cylinder 

1No Adia Thermal intelligent control unit, gives you room by room control, managed open loop, TOU tariff control and brilliant hot water control (this makes up for all the valves and complex control you were looking at as it does the same but is actually interfaced with the ASHP control.

1No small split in your favourite room 

1No small split in your favourite bedroom 

You can combine the splits to a multi split so only 1 units outside. 

 

All of the above give you exactly what you were trying to do and hopefully at a lower price, also the AC will actually battle the solar gain or over heating which is likely your biggest issues for 6 months a year if you have beautiful glass everywhere, an ASHP will not so much even with the FCU's as you can only run the system at 16/17 deg C. Split will run at 5-8 Deg C.

Please keep in mind I dont' know your whole design, the above is based on my experience of passiv house design.

I hope it helps a bit.  

 

I should add, the 3kW ASHP in the list is just an example, I don't know your heat loss, please don't order on my say so 🙂

Posted by: @ashp-bobba

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1No small split in your favourite room 

1No small split in your favourite bedroom 

Could you please say that in a less technical way?

As these rooms will all have UFH manifolds, just what does a 'small split' entail?
Is heating and ventilation interlinked in any way?

This topic is very likely to be followed by others in future; so a photo/diagram would be great if you could manage that. Thanks.

@chastity_outward053simplelogi - I have experience of assembling my own MVHC system, using an off-the-shelf heat exchanger from Baxi.
That model is no longer available, but there's plenty of similar ones.

I added a small radiator to the port which feeds warmed air into living spaces, and built my own controller.

That controller runs the axial fans slightly faster if a bathroom is used, for example.
And it shuts down if the (linked) smoke alarms go off, to avoid feeding oxygen into rooms which are on fire.

The controller was built 20yrs ago, and uses a few relays.
I'd like to replace it with one based on an Arduino when I have enough time.

If I'd wanted to, I can think of ways to incorporate A/C into the same ducting systems, but it isn't an issue for this particular house.

I'm only mentioning this here in case you'd like to further discuss a combined A/C & MVHR approach.

But there's now likely to be several commercially available units which can offer all you'd want...
... albeit at a price.

My starting point would be to visit one of the larger Homebuilding and Renovating Exhibitions (London or NEC) and talk to the manufacturers rather than installers.

Okay, thank you for the replies. 

I think at the moment (having spoken to the good lady) we are leaning towards preferring A2W over A2A in terms of prefer the UFH aspect than blown warm air. 

Now that clearly may change over time before I commit to this. But lets work on that assumption

I think from the various bits of information, I am leaning towards:

No UFH pump, no FCU pump.  Do away with the PICVs, replace with 0-10v modulating ball valves. I am still tempted to use those in conjunction with the Zennio MiniBox 0-10v x2 to modulate that and the fan together. 

Do a DIY UFH manifold of 28mm tees to 3/4 BSP M, for 22mm ridgeline pipework. Yet to settle on what manual balancing valves I want, but something as mentioned that is not limiting at full open, but has good authority.

I will take a look at the pressure drop excel tonight, hopefully, and work out some more realistic numbers based on my hypotheticals.

But I think the game plan of heating: open loop UFH, WC, with FCUs as trim heating, if required. 

Cooling: close the UFH zone off, drop temp to ~5, and use FCUs, maybe have an enforced minium number of FCUs cycling water (even if fans are off) to ensure that i meet minimum flow/volume requirements.

What would be interesting is to have the ability to have above dew point water through the UFH loops at the same time as the FCU water colder. But I don't see an easy way if achieving that. 

Keep the MVHR purely as ventilation. 

In response to the why not do some AC units in a room or 2, we have planned a FCU in each bedroom, and the main living areas. Cooling is important to us.

I am also keen to minimise how many times I have to penetrate the external wall, to keep the air tightness requirements as simple as possible. 

This plan also has me back into a standard tank and recirculation loop for the DHW. Something that I planned on making a little more over engineered again, with zoned recirculation based on occupancy (ie movement in bedroom/bedroom bathroom - turn on that zone until movement stops +15 mins. All controlled via KNX) but DHW is probably worthy of another topic rather than let this grow too many arms and legs 

A2A is better at cooling, and has no risk of condensation because the heat is transported as latent not sensible. Condensation only occurs on the heat exchanger inside the indoor unit (it requires a condensate evacuation pipe).

A2A introduces legal uncertainty: if you put refrigerant piping everywhere, what will happen when R32 is outlawed?

A2W with UFH provides more comfortable heating, but A2W is much mroe complicated for cooling.

Due to low heat capacity of air, air emitters (splits and FCUs) need quite high airflow, much more than MVHR, so if ducted, they need much wider ducts than MVHR.

Ducts carrying cool air from ducted AC may cause condensation on the outside so must be insulated.

For cooling the single most important thing is to not let the heat get inside, ie provide shade on windows to block sun.

Slabs have huge inertia, you don't need to run FCUs and cool the slab at the same time. You can run FCUs during the day and cool the slab at night for example, which solves the "two incompatible temperatures issues".

DHW recirculation: if the pipes are not well insulated it can waste a ton of energy and heat the house during summer.

Tankless heaters have insane power requirements so watch out.

Posted by: @chastity_outward053simplelogi

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In response to the why not do some AC units in a room or 2, we have planned a FCU in each bedroom, and the main living areas. Cooling is important to us.

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Several other posts have already touched on this but it bears being singled out and underlined. An A2W system will not do what you want for cooling.

Even with fan coils, the effect of sending cool water through the system is subtle to the extent of not being able to call it "cooling" per se; it's more temperature moderation. That doesn't mean it isn't worth doing for some people in some situations, but if cooling is important to you, do not rely on an A2W system to provide it.

chastity_outward053simplelogi

@majordennisbloodnok and @bobflux and @ashp-bobba are all making very sound points. 

I would personally not even consider recirculating hot water, its inevitably going to lose lots of heat in winter (not so bad because at least its lost to the house, albeit at a poor COP) and heat the house in summer (very bad particularly as you house is going to be well insulated).  Instead locate bathrooms close to the tank (or tanks) and/or use point of use heaters for everything except showers and baths, where the flow rate requirements aren't so demanding.  Note however that 3kW is only 1.5l/min if you are heating from 10V to say 40C, which is a pretty slow flow rate.  Its fine for washing your hands but a pain for washing the dishes!

Likewise A2W will do mild cooling and several report that with UFH/fancoils it makes a material difference.  So if thats good enough then go for the simple approach and add A2A if it proves necessary.  But if you want to guarantee American style freeze-yourself aircon, it simply wont cut it. 

Either way concentrate first and principally on excluding the heat by shading and natural (or even forced) ventilation at night to cool the fabric.