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Ducting an air source heat pump for the purpose of potentially fitting it the cellar

 
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Air Source Heat Pumps (ASHPs)
Last Post by Gild 2 years ago
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 5 years ago
Posts: 4519
14/09/2024 9:34 pm  

@gild yeah, that’s a tricky one. I just don’t think the cellar is going to work. I’ve had hypothetical conversations with installers about air source heat pumps in garages, sheds, outbuildings, etc. and it always comes back to movement and replacement of air. I’ll put this question to some knowledgable installers this week. I’m recording my next episode of Homeowners’ Q&A and this could be a great question.


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 Anonymous 5011
(@Anonymous 5011)
Joined: 3 years ago
Posts: 562
14/09/2024 9:47 pm  

No idea how big a heat pump you need, but this would easy to do, or even cascade 2x.

https://trianco.co.uk/activair-indoor-9111-9111



   
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 Gild
(@gild)
Active Member Member
Joined: 2 years ago
Posts: 7
Topic starter 14/09/2024 10:08 pm  

@editor Thanks! Fwiw I can open enough intake area for the basement that would be roughly twice the fan's apartue area. Maybe even more.

The alternative would be to install an oil boiler which would be a sad thing to do in 2024...

@johnmo Thanks! That's interesting as it's actually small enough that I can put it in different sides of the house (maybe in the other basement too) I think I'll need 3.

Are.these inverter units? I'll start reading more. Edit: I see a buffer in the installation doc so probably no inverter:/

 

Cheers.



   
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 Anonymous 5011
(@Anonymous 5011)
Joined: 3 years ago
Posts: 562
14/09/2024 10:22 pm  

Posted by: @gild
↑

Are.these inverter units?

Would doubt it. But my 6kW inverter ASHP is running at around 4 to 5kW are the moment no less. So cascade them you should be able to 3x 3kW when really cold and 3 kW when just cold enough to need heat. 30 min on off cycle your down to 1.5kW etc.

From reading the manual (many months ago) I recall the ability to drive an external heat source, this could drive a second unit easily enough then a third I would think.



   
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 AllyFish
(@allyfish)
Prominent Member Contributor
Joined: 3 years ago
Posts: 518
16/09/2024 8:48 am  

The problem with ducting or enclosing a ASHP is adding external static pressure (ESP) to the fan. The fan impeller is designed to move large volumes of air with no ESP other than the unit evaporator coil and inlet and outlet grilles. As soon as you add anything else into the airflow; a grille, louvre, a duct, a deflector or hit'n'miss fence, etc., you add ESP to the fan & reduce the volume flow through the unit. That will impair the capacity and performance of the ASHP, with risk of the ASHP starting to recycle air that it has already processed, or the fan going into a stall, which is where the airflow through the fan impeller collapses and drastically reduces.

You could include a second in-duct fan in series with and interlocked and controlled by the in-built ASHP fan, and this is sometimes done with split A2A systems or ducted cooling systems in basements or cellars, but it needs specialist design, and the second fan generates noise and consumes additional power. System efficiency is always lost.

I've read acoustic reports where an acoustic engineer's suggestion is to acoustically enclose an air-cooled machine or air source heat pump unit. Well, it fixes the noise problem, but so reduces the capacity of the unit that you might as well switch it off, which is a cheaper and simpler solution!



   
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 Gild
(@gild)
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Joined: 2 years ago
Posts: 7
Topic starter 17/09/2024 6:04 pm  

Thanks @allyfish . Yes, I mentioned static pressure as the main issue here. That's why I specifically wondered about the exaust as this will be the real ducted part.

The inflow will be nearly resistant free I think, as I can create a large opening for the cellar. (depending on how I'll do it, but can be twice or 4 times the surface area of the fan) so it should be pretty free for the air supply.

I am not worried about acoustics there to be honest, there is a thick concrete ceiling between where I want to place it to the house.

Thanks again for taking the time for your detailed answer!

 



   
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