Ducted A2A and floor level vents

[JohnMo]

 

  On 12/10/2023 at 00:12, Crofter said:

Do you remember what specific unit it was, and was it running at full speed most of the time?

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These were in cooling mode, usually a low (ish) output speed, the high speed settings bugged us even more. No idea of models, sorry. One may have been a Mitsubishi the other a Toshiba.

 

Efficiency is great, coming home to a nice cool space is good, when it's mid 30s outside, we only really noticed the annoying drafts when we we sat watching the TV and in bed. We ended up getting used to sleeping with the unit off in the bedroom.

[Beelbeebub]

  On 11/10/2023 at 19:07, JohnMo said:

Having lived with one (a few) for a couple years, I found them annoying and the wife hated them. As much as the blurb says they don't blow at you, they always seemed to be aimed at someone. A2W gets my vote (radiators or better UFH), A2A doesn't get my vote.

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That's fair enough and a good point. Different people ha e different preferences and tolerances. My mate can't stand UFH. Even when he was putting a new slab floor in his place and could have chucked in some ufh popes for let tile extra he was adamant he didn't want it. The floor in their house is bloody freezing and they all wear slippers, which they like. <shrugs>

 

A2A emitters are far from perfect, especially as they are primarily designed for cooling, hence their high wall location and aggressive blowing. Maybe with hearing being the focus more low wall "radiator" type units with a gentle waft will become availible. 

  On 11/10/2023 at 19:07, JohnMo said:

If you want a hybrid system, have a hybrid system, keep the old boiler, most if not all A2W, can be run in hybrid mode, boiler just gets used when it's really cold. Especially useful for a combi.

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The key point is hybrid systems *integrate* with the existing wet heating system. There is still a considerable amount of replumbing needed (low loss headers, control systems etc) and if you don't update the radiators for the lower temps your HP will be less effective. 

 

The only system that looks like it might plug in is the Alpha, where the unit piggybacks onto any primary return, but I'm  not sure if you need to have their boiler anyway. 

 

Sticking an A2W system in leaves the wet heating system totally untouched. Indeed many people have already done this when they fitted air con after last year's heatwave. Admittedly this might be slightly less true if you were looking to put in low wall units as they would be competing with radiators for wall space.

 

If sutible designed for heating emitters could be made readily available it would make sense (from a national perspective) to push these units on a par with a2w eg same treatment for grants, planning etc.

 

My understanding is there is a reluctance to promote them as they are seen as cooling and therefore an additional "luxury" drain on the grid

[JamesPa]

  On 11/10/2023 at 19:07, JohnMo said:

Having lived with one (a few) for a couple years, I found them annoying and the wife hated them. As much as the blurb says they don't blow at you, they always seemed to be aimed at someone. A2W gets my vote (radiators or better UFH), A2A doesn't get my vote.

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That's interesting.  I wonder if it's a function of where on the body they hit you.  A2W units tend to be at ceiling height thus aimed at head and upper arms, even if you are sitting down.  I would guess these are where most people would be most sensitive to light wind.  I would also guess that air hitting the torso (when clothed) would be less annoying to many. 

 

It's entirely understandable why they are normally mounted near the ceiling, but is this form over function?

[JohnMo]

  On 12/10/2023 at 07:31, Beelbeebub said:

There is still a considerable amount of replumbing needed (low loss headers, control systems etc) and if you don't update the radiators for the lower temps your HP will be less effective. 

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Not always true, for example Daikin hybrid, the heat pump just ties into the existing boiler.

 

The Alpha one is just copying what Daikin have been offering for a decade. 

 

My ASHP (Maxa/Viessmann) has all the controls built in, with full control if how the circulation pump responds, so hydraulic sepereration isn't needed.

 

It's all run weather compensated, so smaller, original radiators are fine, the really cold weather the original boiler takes over.

 

However if you go hybrid no grants are available, which puts most off.

[Beelbeebub]

  On 12/10/2023 at 07:55, JohnMo said:

Not always true, for example Daikin hybrid, the heat pump just ties into the existing boiler.

 

The Alpha one is just copying what Daikin have been offering for a decade. 

 

My ASHP (Maxa/Viessmann) has all the controls built in, with full control if how the circulation pump responds, so hydraulic sepereration isn't needed.

 

It's all run weather compensated, so smaller, original radiators are fine, the really cold weather the original boiler takes over.

 

However if you go hybrid no grants are available, which puts most off.

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Yes, if you have a HP that can easily integrate then it's an option. 

 

As for not getting a grant, I was discussing with some installers. There is nothing in the regulations that say you have to physically remove the existing boiler, only that it cannot be part of the system if you want the grant. Equally there is nothing to stop the customer contracting a heating engineer to integrate a boiler with the existing HP, say a month after installation and after the grant process is complete.....

[JamesPa]

  On 12/10/2023 at 09:19, Beelbeebub said:

As for not getting a grant, I was discussing with some installers. There is nothing in the regulations that say you have to physically remove the existing boiler, only that it cannot be part of the system if you want the grant. Equally there is nothing to stop the customer contracting a heating engineer to integrate a boiler with the existing HP, say a month after installation and after the grant process is complete.....

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That's sailing a bit close to the wind IMHO.  See regulations 17 - 24 for extensive inspection and enforcement powers and note that regulation 2 says that the heat pump is eligible if 'it replaces the heat generating components of the original heating system installed in that property (where applicable).  I do grant that this does not require removal, but equally Im not sure a heat pump could be said to 'replace' existing kit if the existing kit is still used and one might even argue that replace includes physical replacement as well as functional replacement.

 

I'm normally happy to sail close to the wind when interpreting legislation, but if I were an installer (which I'm not, I hasten to add) I would absolutely refuse to get involved in anything where I could reasonably be assumed to know that there is a likelihood of reversion.

 

 

Edited October 12, 2023 by JamesPa

[Crofter]

  On 12/10/2023 at 07:31, Beelbeebub said:

A2A emitters are far from perfect, especially as they are primarily designed for cooling, hence their high wall location and aggressive blowing. Maybe with hearing being the focus more low wall "radiator" type units with a gentle waft will become availible. 

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This is one reason why I'm hoping to use a ducted system.

It just seems to make sense to have big ducts emitting through grilles at floor level. I'm looking at a maximum airspeed of less than 4mph which hopefully will be barely noticeable.

[Beelbeebub]

  On 12/10/2023 at 09:34, JamesPa said:

That's sailing a bit close to the wind IMHO.  See regulations 17 - 24 for extensive inspection and enforcement powers and note that regulation 2 says that the heat pump is eligible if 'it replaces the heat generating components of the original heating system installed in that property (where applicable).  I do grant that this does not require removal, but equally Im not sure a heat pump could be said to 'replace' existing kit if the existing kit is still used and one might even argue that replace includes physical replacement as well as functional replacement.

 

I'm normally happy to sail close to the wind when interpreting legislation, but if I were an installer (which I'm not, I hasten to add) I would absolutely refuse to get involved in anything where I could reasonably be assumed to know that there is a likelihood of reversion.

 

 

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Sensible. 

 

It woukd be extremely close to the wind if the same installer reconnected the old boiler. 

 

Wouldn't be on the installer if the customer got a different heating engineer to reconnect the boiler. 

 

Of course the customer might be in hot water (ha), but there isn't a requirement that once a HP is fitted and a grant issued that property can never again have a boiler fitted. HP installs go wrong, fail, customers decide they don't like the noise etc. 

[DanDee]

  On 12/10/2023 at 17:40, Beelbeebub said:

Sensible. 

 

It woukd be extremely close to the wind if the same installer reconnected the old boiler. 

 

Wouldn't be on the installer if the customer got a different heating engineer to reconnect the boiler. 

 

Of course the customer might be in hot water (ha), but there isn't a requirement that once a HP is fitted and a grant issued that property can never again have a boiler fitted. HP installs go wrong, fail, customers decide they don't like the noise etc. 

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https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1133079/Approved_Document_L__Conservation_of_fuel_and_power__Volume_1_Dwellings__2021_edition_incorporating_2023_amendments.pdf

 

 

[Archer]

  On 07/10/2023 at 13:12, Crofter said:

 

I see in the US people use floor gratings. It must work, otherwise they wouldn't be doing it. But it feels a bit wrong to me, for some reason. Can imagine it working in rooms with hard flooring, I suppose, but not so much with carpet.

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Our (70's) house has a combination of floor and wall gratings. Apart from looking a bit dated they are mostly fine in the floor if you know your room layouts. We've noticed that all sorts of stuff falls down the grates, but it's easy to lift out and vacuum clean. This is one of the advantage of the lift out grates, albeit they don't look as good as flush linear slot diffusers. 

 

I'll send some pictures of ours in carpet later if that helps. We're actually doing the opposite to you and moving some floor ones to the ceiling on the first floor where we have a loft above. This isn't for aesthetic reasons though, they look fine in bedrooms - for us it's technical, around our heat pump installation. 

 

[Archer]

  On 10/10/2023 at 17:55, Crofter said:

I've been crunching some numbers.

I don't think I need a 10kw unit.

Heatgeek's rules of thumb suggest around 5.5kw, and an onlinev radiator sizing tool returns a range of 4.5-6.5kw, depending on how exactly I answer it.

So I think a 7.1kw unit ought to be ample?

At full chat this is delivering 780m³/hr, or 216l/s. Which seems proportionally far less airflow than the bigger unit, and much easier to handle.

This flow rate tallies with the numbers from engineering toolbox.

Splitting it through four 200mm diameter ducts results in a max flow speed of 1.7m/s (3.8mph).

 

I think I messed up earlier when calculating cross sectional area of the ducting, so despite the much lower flow rate the 7.1kw still works out to have about the same airspeed.

 

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I don't know if this is helpful or not because our A2A system hasn't been installed yet (gas warm air currently...)

 

But... We've specced a Mitsubishi unit, and gone for one considerably larger than the expected heat loss. For a few reasons. 

 

1. All the AC engineers seem to recommend it based on experience (but this may just be natural caution)

2. A2A units have reasonably good modulation ratio's so short cycling should be less of an issue. Ours is around 6;1 (so 1.4kw to 9.5kw

3. You get lower output in extreme temperatures, as much as a 25% drop @ -10 degrees on our unit

4. There seem to be some efficiency advantages to HP's running in the middle/ lower end of their capacity so long as they don't excessively cycle. This is also true for unit noise

5. On the Mitsubishi range, the COP increases quite a lot for the larger units over some of the the smaller ones. 

 

On the positioning of the outlet grille and return duct - there are some brilliant resources from the US online. I'll try and post one I found later on

[Archer]

  On 10/10/2023 at 18:45, SteamyTea said:

@Crofter

 

There are problems with air handling, main ones I see are the size of ductwork, flowrates and limited temperature, and then the big one, sound transmission between spaces.

When I was a kid, our neighbours has a hot air system, and it was almost as good as an intercom system for attracting attention.  I can imagine a drunken conversation where one half hears everything from another room.  Would probably end badly.

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I was worried about this when we moved in March but honestly hasn't been an issue at all. We get noise from footsteps through the ceilings but no conversation audible from the ducts. That was a nice surprise, it might just be the way our system was designed though

[SteamyTea]

  On 13/10/2023 at 03:28, Archer said:

 

I was worried about this when we moved in March but honestly hasn't been an issue at all. We get noise from footsteps through the ceilings but no conversation audible from the ducts. That was a nice surprise, it might just be the way our system was designed though

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That is good, you can type away, with the World Service on the radio, at 4:30 AM, without waking up the rest of the house.

I know why I am up, trip up country, no one else should be though.

[Archer]

  On 13/10/2023 at 03:34, SteamyTea said:

That is good, you can type away, with the World Service on the radio, at 4:30 AM, without waking up the rest of the house.

I know why I am up, trip up country, no one else should be though.

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Hahaha The worst part is that it's usually our young girls walking me up bit this time I don't even have an excuse... Just insomnia muscle memory! I'll go to sleep I think, enjoy the trip! 

[RichardL]

  On 13/10/2023 at 03:21, Archer said:

Mitsubishi range

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Word to the wise - there is Mitsubishi Heavy and Mitsubishi Electric,

Completely separate companies, very similar product lines - from what I originally researched very similar +ve reliability longevity reputation.
 

[Crofter]

I've just learned about the existence of intelligent duct controls. I hadn't really considered this before. I had kind of assumed that I would just set the system up with adjustable vents and/or baffles to deliver the required amount of heat to each room and just leave it alone after that.

But maybe that's a bit naive.