Putting in Air Conditioning Ducting - Just In Case

[puntloos]

I'm sure most "properly done" passivhauses will never ever need air conditioning, but since we are building a house from scratch, and you know, maybe climate change will give us particularly nasty firestorms in 2040, we are planning to at least install some basic air conditioning ducting rather than regret not doing it, and buy an AC if we find we need it because perhaps our PHPP calcs were off, and the ASHP doesn't cool (enough) either etc etc.. You get the idea.

 

As such, assuming indeed a slightly-out-of-spec passivhaus of 300sqm, how big does an aircon and the associated ducting need to be?

 

I'm in particular looking to understand how large the ducts are that have to go into the walls,. so an answer such as "You minimum need a 1-ton cooling system, with 15cm duct diameter" would be helpful

 

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[ProDave]

As long as the ASHP can do cooling, then it will cool "enough"

 

But the heat delivery system, typically UFH may not deliver that cooling to the building very well.

 

From my brief experiments, it is upstairs that needs cooling when it gets hot (and the cool air will find it's way down) which is the exact opposite of where the heating is.

 

So I would provision for taking flow and return pipes from the ASHP to the upstairs ceilings where you can install a couple of fan coil units to deliver cooling.  And provision for ducting to take cabling and power feeds for them.

[PeterW]

I would go for point use AC with A2A units in strategic places like vaulted hallways with high ceilings and master bedrooms. You can’t hide a big AC duct set and you’ll be ripping walls apart to put gas pipework in anyway as that can’t be installed and left as it may be in the wrong places for your fan coil units. You’ll also need condensate pipework and a whole host of other connections - one or two A2A units and cooled UFH will resolve this. 

[puntloos]

6 minutes ago, PeterW said:

I would go for point use AC with A2A units in strategic places like vaulted hallways with high ceilings and master bedrooms. You can’t hide a big AC duct set and you’ll be ripping walls apart to put gas pipework in anyway as that can’t be installed and left as it may be in the wrong places for your fan coil units. You’ll also need condensate pipework and a whole host of other connections - one or two A2A units and cooled UFH will resolve this. 

 

In my case though I still am designing a house from scratch, so dimensioning in a few ducts is fairly light on cost, no? I have the impression "10cm" pipes might be sufficient for a low-ish flow of cooling?

 

56 minutes ago, ProDave said:

As long as the ASHP can do cooling, then it will cool "enough"

 

But the heat delivery system, typically UFH may not deliver that cooling to the building very well.

 

From my brief experiments, it is upstairs that needs cooling when it gets hot (and the cool air will find it's way down) which is the exact opposite of where the heating is.

 

So I would provision for taking flow and return pipes from the ASHP to the upstairs ceilings where you can install a couple of fan coil units to deliver cooling.  And provision for ducting to take cabling and power feeds for them.

 

"enough"....

 

to be clear I do indeed intend to go for an ASHP that indeed is reversible, but well, as we all know the #1 sad story here on buildhub seems to be 'my super well designed passivhaus is too hot". Presumably most of these people do still have a cooling ASHP, so unless the cost of some piping ('cost' can include sacrificing house space by increasing void width) really is unreasonable I'm thinking of creating this 'Plan B'

[TonyT]

I would go with the traditional air to air unit,  with 2 copper pipes, condensate and control cable between 

diy Kit’s are available, or just the pipework 

[puntloos]

11 minutes ago, TonyT said:

I would go with the traditional air to air unit,  with 2 copper pipes, condensate and control cable between 

diy Kit’s are available, or just the pipework 

 

To be clear I fully intend to also provision for the "inside-to-outside" link for a classic A2A. Indeed something like copper pipes etc. Not thinking of a "dual (air) hose" device And you're right they also should be put in during construction.

But currently I'm primarly thinking about how to get cooled air from the device (in the loft) to the actual rooms. 

[PeterW]

You need more than 10cm duct - you’ll need to work out the fan coil unit first (some only use rectangular for example) and then the flow rates, plenums and then insulate the whole lot with nitrile or rigid fibre insulation. That’s not a few quid while you’re pulling an extra cable or two in, and is a specialist design job that usually gets contracted out. 

[gc100]

I lived in the south of France for 20 years so know what living in a hot climate is like. For me you get used to the hot weather in and around the house and typically you just have all the doors window open for airflow. The only issue is sleeping - a cooler room makes for a much better nights sleep. For my build I’ve installed a cassette type AC above the en-en-suite and pipped the in/out duct (15cm) into the bedroom. The larger the pipe the less noisy it will be. It will be very expensive cool the whole house over the course of a summer (and not great for the environment). If you can generate enough solar energy to cover the AC you’re not adding to the problem (we are doing this). of course if you don’t really care about either (running cost and environment) go for it. I hate the split type systems personally and would always got for inbuilt AC vent setups but they are a lot more expensive to buy/install.

 

I looked into using the MVHR ducts for the AC in the summer and I’m 100% sure this can be done . However I could not find anyone with enough expertise to help. AC knowledge here is thin on the ground outside large commercial projects.

 

I suspect you could even reuse the ASHP compressor as well but alas I could not find a solution.

 

 

 

[TonyT]

17 minutes ago, puntloos said:

 

To be clear I fully intend to also provision for the "inside-to-outside" link for a classic A2A. Indeed something like copper pipes etc. Not thinking of a "dual (air) hose" device And you're right they also should be put in during construction.

But currently I'm primarly thinking about how to get cooled air from the device (in the loft) to the actual rooms. 

I wouldn’t be putting the outside unit in a loft.. insufficient air flow

Edited January 18, 2021 by TonyT

[dnb]

1 hour ago, gc100 said:

 

I looked into using the MVHR ducts for the AC in the summer and I’m 100% sure this can be done . However I could not find anyone with enough expertise to help. AC knowledge here is thin on the ground outside large commercial projects.

This is my conclusion to the problem too. Then I spoke to a few of the mech eng people at my work and I am going to have a go anyway...

[SteamyTea]

I assume you are putting in MVHR.

Why not oversize the pipework.  Double the diameter and you can quadruple the mass airflow for any give slow speed.

You can initially hide the larger pipework behind smaller vents, but why bother.

Then, you you need AC, just pipe it in later.

Just a case of doing some sums for different climate scenarios i.e. prolonged temperatures above 28°C.

The marginal cost of larger pipework should be very small, and you will get a quieter MVHR system when it is on boost.

[puntloos]

1 hour ago, TonyT said:

I wouldn’t be putting the outside unit in a loft.. insufficient air flow

Oh absolutely not, I was just thinking to put most of my 'plant' in the loft, and put outside units "close to it", for example I have a flat-ish roof so perhaps I can just put it there? I suspect, 

 

 

36 minutes ago, dnb said:

This is my conclusion to the problem too. Then I spoke to a few of the mech eng people at my work and I am going to have a go anyway...

 

I would love to hear about anyone who thinks they can do this ? Clearly dual-purposing "air pipes" for both trickle-mode as well as power-mode seems like an amazing solution, but indeed if most people don't know how to do this properly I could imagine it being a can of worms... 

7 minutes ago, SteamyTea said:

I assume you are putting in MVHR.

Why not oversize the pipework.  Double the diameter and you can quadruple the mass airflow for any give slow speed.

You can initially hide the larger pipework behind smaller vents, but why bother.

Then, you you need AC, just pipe it in later.

Just a case of doing some sums for different climate scenarios i.e. prolonged temperatures above 28°C.

The marginal cost of larger pipework should be very small, and you will get a quieter MVHR system when it is on boost.

 

Yes absolutely planning to use MVHR but as people above said it seems the expertise might not exist in UK? Suggestions? ?

[SteamyTea]

3 minutes ago, puntloos said:

Suggestions

 

12 minutes ago, SteamyTea said:

Just a case of doing some sums for different climate scenarios

https://www.engineeringtoolbox.com/cooling-heating-equations-d_747.html

 

https://www.engineeringtoolbox.com/air-ducts-sizing-d_1736.html

[puntloos]

12 minutes ago, SteamyTea said:

 

https://www.engineeringtoolbox.com/cooling-heating-equations-d_747.html

 

https://www.engineeringtoolbox.com/air-ducts-sizing-d_1736.html

 

Ha thanks, I'm not too concerned about the calculations, I'm more thinking about the expertise needed to use dual-purpose ducts. Or are people overselling the difficulty for a decently skilled heating team to do this?

[PeterW]

42 minutes ago, puntloos said:

Or are people overselling the difficulty for a decently skilled heating team to do this?

Good luck .... 

 

AC designers that a client of mine uses won’t go near any job that is less than 6,000sqft - there is no money in it and it is a specialist industry. I can find plenty of FGas certified refrigeration engineers, try finding one who can design the AHU and ductwork is a different issue entirely. 
 

1 hour ago, puntloos said:

outside units "close to it", for example I have a flat-ish roof so perhaps I can just put it there?

Nope - may require PP if it was plant on a roof and it would be horrendously noisy as the roof will act like a drum. 
 

This is why this stuff needs professional design. 

[puntloos]

7 minutes ago, PeterW said:

Good luck .... 

 

AC designers that a client of mine uses won’t go near any job that is less than 6,000sqft - there is no money in it and it is a specialist industry. I can find plenty of FGas certified refrigeration engineers, try finding one who can design the AHU and ductwork is a different issue entirely. 
 

Nope - may require PP if it was plant on a roof and it would be horrendously noisy as the roof will act like a drum. 
 

This is why this stuff needs professional design. 

 

Absolutely.   I'm not going with my suspicions here, I'm trying to somewhat wrap my head around the challenges and figure out how to find specialists that understand the same.